Molecular Biology - The Scripps Research Institute
Molecular Biology - The Scripps Research Institute
Molecular Biology - The Scripps Research Institute
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
<strong>Molecular</strong> <strong>Biology</strong>
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Yun Yung, Graduate Student, and Jerold Chun, M.D., Ph.D., Professor,<br />
Department of <strong>Molecular</strong> <strong>Biology</strong>
DEPARTMENT OF<br />
MOLECULAR BIOLOGY<br />
STAFF<br />
Peter E. Wright, Ph.D.*<br />
Professor and Chairman<br />
Cecil H. and Ida M. Green<br />
Investigator in Medical<br />
<strong>Research</strong><br />
Ruben Abagyan, Ph.D.<br />
Professor<br />
Carlos F. Barbas III, Ph.D.*<br />
Professor<br />
Janet and W. Keith Kellogg II<br />
Chair, <strong>Molecular</strong> <strong>Biology</strong><br />
Michael N. Boddy, Ph.D.<br />
Assistant Professor<br />
Charles L. Brooks III, Ph.D.<br />
Professor<br />
Monica J. Carson, Ph.D.**<br />
Associate Professor<br />
University of California<br />
Riverside, California<br />
David A. Case, Ph.D.<br />
Professor<br />
Geoffrey Chang, Ph.D.*<br />
Associate Professor<br />
Jerold Chun, M.D., Ph.D.<br />
Professor<br />
Lisa Craig, Ph.D.**<br />
Assistant Professor<br />
Simon Fraser University<br />
Burnaby, British Columbia<br />
Valerie De Crecy Lagard,<br />
Ph.D.**<br />
Assistant Professor<br />
University of Florida<br />
Gainesville, Florida<br />
Luis De Lecea, Ph.D.<br />
Associate Professor<br />
Lluis Ribas De Pouplana,<br />
Ph.D.<br />
Adjunct Assistant Professor<br />
Ashok Deniz, Ph.D.<br />
Assistant Professor<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
H. Jane Dyson, Ph.D.<br />
Professor<br />
John H. Elder, Ph.D.<br />
Professor<br />
Martha J. Fedor, Ph.D.*<br />
Associate Professor<br />
James Arthur Fee, Ph.D.<br />
Professor of <strong>Research</strong><br />
Elizabeth D. Getzoff,<br />
Ph.D.****<br />
Professor<br />
David B. Goodin, Ph.D.<br />
Associate Professor<br />
David S. Goodsell Jr., Ph.D.<br />
Associate Professor<br />
Joel M. Gottesfeld, Ph.D.<br />
Professor<br />
Robert Hallewell, D.Phil.<br />
Adjunct Associate Professor<br />
Jennifer Harris, Ph.D.<br />
Assistant Professor of<br />
Biochemistry<br />
Christian A. Hassig, Ph.D.<br />
Adjunct Assistant Professor<br />
Mirko Hennig, Ph.D.<br />
Assistant Professor<br />
John E. Johnson, Ph.D.<br />
Professor<br />
Gerald F. Joyce, M.D.,<br />
Ph.D.*****<br />
Professor<br />
Ehud Keinan, Ph.D.<br />
Adjunct Professor<br />
Richard A. Lerner, M.D.,<br />
Ph.D.*****<br />
President, <strong>Scripps</strong> <strong>Research</strong><br />
Lita Annenberg Hazen Professor<br />
of Immunochemistry<br />
Cecil H. and Ida M. Green<br />
Chair in Chemistry<br />
Scott Lesley, Ph.D.<br />
Assistant Professor of<br />
Biochemistry<br />
Tianwei Lin, Ph.D.<br />
Assistant Professor<br />
Clare McGowan, Ph.D. †<br />
Associate Professor<br />
Duncan E. McRee, Ph.D.<br />
Adjunct Associate Professor<br />
David P. Millar, Ph.D.<br />
Associate Professor<br />
Louis Noodleman, Ph.D.<br />
Associate Professor<br />
Arthur J. Olson, Ph.D.<br />
Professor<br />
James C. Paulson, Ph.D. ††<br />
Professor<br />
Vijay Reddy, Ph.D.<br />
Assistant Professor<br />
Steven I. Reed, Ph.D. †<br />
Professor<br />
Victoria A. Roberts, Ph.D.**<br />
Associate Professor<br />
University of California<br />
San Diego, California<br />
Paul Russell, Ph.D.<br />
Professor<br />
MOLECULAR BIOLOGY 2005 155<br />
Michel Sanner, Ph.D.<br />
Associate Professor<br />
Harold Scheraga, Ph.D.<br />
Adjunct Professor<br />
Paul R. Schimmel, Ph.D.*****<br />
Ernest and Jean Hahn<br />
Professor of <strong>Molecular</strong><br />
<strong>Biology</strong> and Chemistry<br />
Anette Schneemann, Ph.D.<br />
Associate Professor<br />
Subhash C. Sinha, Ph.D.*<br />
Associate Professor<br />
Gary Siuzdak, Ph.D.<br />
Adjunct Associate Professor<br />
Robyn L. Stanfield, Ph.D.<br />
Assistant Professor<br />
James Steven, Ph.D.<br />
Assistant Professor<br />
Raymond C. Stevens, Ph.D. †††<br />
Professor<br />
Charles D. Stout, Ph.D.<br />
Associate Professor<br />
Peiqing Sun, Ph.D.<br />
Assistant Professor<br />
J. Gregor Sutcliffe, Ph.D.<br />
Professor<br />
John A. Tainer, Ph.D.*<br />
Professor<br />
Fujie Tanaka, Ph.D.<br />
Assistant Professor<br />
Elizabeth Anne Thomas, Ph.D.<br />
Assistant Professor<br />
SECTION COVER FOR THE DEPARTMENT OF MOLECULAR BIOLOGY: Toll-like<br />
receptors (TLRs) recognize various pathogen-associated molecules and play an important role in<br />
innate immune responses. <strong>The</strong> human TLR3 recognizes double-stranded RNA from viruses and initiates<br />
an intracellular signaling pathway through the interaction of TIR domains of TLR3 and the<br />
adaptor molecule TRIF. <strong>The</strong> proposed dimer of the TLR3 ectodomain is displayed on the membrane<br />
surface with double-stranded RNA from viruses. <strong>The</strong> crystal structure was determined by Jungwoo<br />
Choe, Ph.D., in the laboratory of Ian A. Wilson, D.Phil.
156 MOLECULAR BIOLOGY 2005<br />
James R. Williamson,<br />
Ph.D.*****<br />
Professor<br />
Associate Dean, Kellogg<br />
School of Science and<br />
Technology<br />
Ian A. Wilson, D.Phil.*<br />
Professor<br />
Curt Wittenberg, Ph.D. †<br />
Professor<br />
Kurt Wüthrich, Ph.D.<br />
Cecil H. and Ida M. Green<br />
Professor of Structural<br />
<strong>Biology</strong><br />
Todd O. Yeates, Ph.D.<br />
Adjunct Professor<br />
Qinghai Zhang, Ph.D.<br />
Assistant Professor<br />
Guo Fu Zhong, Ph.D.**<br />
Fudan University<br />
Shanghai, China<br />
SERVICE FACILITIES<br />
Ola Blixt, Ph.D.<br />
Core Manager, Consortium<br />
for Functional Glycomics<br />
John Chung, Ph.D.<br />
Manager, Nuclear Magnetic<br />
Resonance Facilities<br />
Gerard Kroon<br />
Assistant Manager, Nuclear<br />
Magnetic Resonance Facilities<br />
Michael E. Pique<br />
Director, Graphics Development<br />
Nahid Razi, Ph.D.<br />
Assistant Core Manager,<br />
Consortium for Functional<br />
Glycomics<br />
Peter Sobieszcsuk, Ph.D.<br />
Core Manager, Consortium<br />
for Functional Glycomics<br />
SENIOR STAFF SCIENTIST<br />
Wayne A. Fenton, Ph.D.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
STAFF SCIENTISTS<br />
Aymeric Pierre De Parseval,<br />
Ph.D.<br />
Karla Ewalt, Ph.D.**<br />
Princeton University<br />
Princeton, New Jersey<br />
Brian M. Lee, Ph.D.<br />
Maria Martinez-Yamout, Ph.D.<br />
Garrett M. Morris, Ph.D.<br />
Chiaki Nishimura, Ph.D.<br />
Jeffrey Speir, Ph.D.<br />
Manal Swairjo, Ph.D.<br />
Mutsuo Yamaguchi, Ph.D.<br />
Xueyong Zhu, Ph.D.<br />
SENIOR RESEARCH<br />
ASSOCIATES<br />
David Barondeau, Ph.D.<br />
Kirk Beebe, Ph.D.<br />
Ryan Burnett, Ph.D.<br />
Brian Collins, Ph.D.<br />
Adrienne Elizabeth Dubin,<br />
Ph.D.<br />
Maria Alejandra Gamez-<br />
Abascal, Ph.D.<br />
Peter B. Hedlund, M.D., Ph.D.<br />
Ying Chuan Lin, Ph.D.<br />
Rebecca Page, Ph.D.**<br />
Brown University<br />
Providence, Rhode Island<br />
Mikhail Popkov, Ph.D.<br />
Richard R. Rivera, Ph.D.<br />
Lincoln Scott, Ph.D.<br />
Koji Tamura, Ph.D.<br />
Liang Tang, Ph.D.**<br />
Burnham <strong>Institute</strong><br />
La Jolla, California<br />
Ellie Tzima, Ph.D.**<br />
University of North Carolina<br />
Chapel Hill, North Carolina<br />
Xiang-Lei Yang, Ph.D.<br />
Dirk M. Zajonc, Ph.D.<br />
RESEARCH ASSOCIATES<br />
Sunny Abraham, Ph.D.<br />
Fabio Agnelli, Ph.D.<br />
Moballigh Ahmad, Ph.D.<br />
Alexander Ivanov Alexandrov,<br />
Ph.D.<br />
Marcius Da Silva Almeida,<br />
Ph.D.<br />
Beatriz Gonzalez Alonso, Ph.D.<br />
David Alvarez-Carbonell, Ph.D.<br />
Jianghong An, Ph.D.**<br />
British Columbia Cancer<br />
Agency<br />
Vancouver, British Columbia<br />
Yu An, Ph.D.<br />
Crystal Stacy Anglen, Ph.D.**<br />
Neurome, Inc.<br />
La Jolla, California<br />
Brigitte Anliker, Ph.D.<br />
Roger Armen, Ph.D.<br />
Joseph W. Arndt, Ph.D.<br />
Mabelle Ashe, Ph.D.<br />
Jamie Mitchell Bacher, Ph.D.<br />
Michael F. Bailey, Ph.D.**<br />
Bio21 <strong>Institute</strong><br />
Parkville, Victoria, Australia<br />
Manidipa Banerjee, Ph.D.<br />
Christopher Baskerville, Ph.D.<br />
Lipika Basummalick, Ph.D.<br />
Konstantinos Beis, Ph.D.<br />
Per Bengston, Ph.D.<br />
Svitlana Berezhna, Ph.D.<br />
William Henry Bisson, Ph.D.<br />
Pilar Blancafort, Ph.D.**<br />
University of North Carolina<br />
Chapel Hill, North Carolina<br />
David Boehr, Ph.D.<br />
David Bostick, Ph.D.<br />
Ronald M. Brudler, Ph.D.<br />
Lintao Bu, Ph.D.<br />
Rosa Maria Cardoso, Ph.D.<br />
Justin E. Carlson, Ph.D.<br />
Andrew Barry Carmel, Ph.D.<br />
Qing Chai, M.D., Ph.D.<br />
Brian Chapados, Ph.D.<br />
Eli Chapman, Ph.D.<br />
Anju Chatterji, Ph.D.<br />
Anton Vladislavovich<br />
Cheltsov, Ph.D.<br />
Jianhan Chen, Ph.D.<br />
Yen-Ju Chen, Ph.D.<br />
Zhiyong Chen, Ph.D.<br />
Jaeyoung Cho, Ph.D.**<br />
Hallym University<br />
Kangwon, South Korea<br />
Jungwoo Choe, Ph.D.<br />
Chung Jen Chou, Ph.D.<br />
Li-Chiou Chuang, Ph.D.<br />
Jean-Pierre Clamme, Ph.D.
Linda Maria Columbus, Ph.D.<br />
Adam Corper, Ph.D.<br />
Qizhi Cui, Ph.D.<br />
Carla P. Da Costa, Ph.D.<br />
Douglas Daniels, Ph.D.**<br />
Yale University<br />
New Haven, Connecticut<br />
Sanjib Das, Ph.D.<br />
Paramita Dasgupta, Ph.D.**<br />
Mayo Clinic<br />
Rochester, Minnesota<br />
Robert De Bruin, Ph.D.<br />
Roberto N. De Guzman,<br />
Ph.D.**<br />
University of Kansas<br />
Lawrence, Kansas<br />
Sohela De Rozieres, Ph.D.<br />
Qingdong Deng, Ph.D.<br />
Paula Desplats, Ph.D.<br />
Buchi Ramachary<br />
Dhevalapally, Ph.D.**<br />
University of Hyderabad<br />
Hyderabad, India<br />
Claire Louise Dovey, Ph.D.<br />
Zhanna Druzina, Ph.D.<br />
Li-Lin Du, Ph.D.<br />
<strong>The</strong>resia Dunzendorfer-Matt,<br />
Ph.D.**<br />
Leopold Franzens Universität<br />
Innsbruck, Austria<br />
Scott Eberhardy, Ph.D.<br />
Marc-Olivier Ebert, Ph.D.**<br />
Leopold Franzens Universität<br />
Innsbruck, Austria<br />
Stephen Edgcomb, Ph.D.<br />
Susanna V. Ekholm-Reed,<br />
Ph.D.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Reza Mobini Farahani, Ph.D.**<br />
Sahlgrenska University<br />
Hospital<br />
Göteborg, Sweden<br />
Daniel Felitsky, Ph.D.<br />
Allan Chris Merrera Ferreon,<br />
Ph.D.<br />
Josephine Chu Ferreon, Ph.D.<br />
Pierre Henri Gaillard, Ph.D.<br />
Hui Gao, Ph.D.<br />
Elsa D. Garcin, Ph.D.<br />
Shannon E. Gardell, Ph.D.<br />
Edith Caroline Glazer, Ph.D.<br />
Bettina Groschel, Ph.D.<br />
Björn Grünenfelder, Ph.D.**<br />
Novartis <strong>Institute</strong>s for<br />
BioMedical <strong>Research</strong><br />
Cambridge, Massachusetts<br />
Fang Guo, Ph.D.<br />
Gye Won Han, Ph.D.<br />
Hongna Han, Ph.D.**<br />
American BioScience, Inc.<br />
Santa Monica, California<br />
Shoufa Han, Ph.D.<br />
Wenge Han, Ph.D.<br />
Jason W. Harger, Ph.D.<br />
Brian Henriksen, Ph.D.**<br />
Eurogentec North America, Inc.<br />
San Diego, California<br />
David M. Herman, Ph.D.<br />
Deron Herr, Ph.D.<br />
Kenichi Hitomi, Ph.D.<br />
Reto Horst, Ph.D.<br />
Yunfeng Hu, Ph.D.<br />
Joy Huffman, Ph.D.**<br />
McKinsey & Company<br />
Los Angeles, California<br />
Laura M. Hunsicker, Ph.D.**<br />
Trinity University<br />
San Antonio, Texas<br />
Kwan Hoon Hyun, Ph.D.<br />
Wonpil Im, Ph.D.<br />
Tasneem Islam, Ph.D.**<br />
University of Melbourne<br />
Melbourne, Australia<br />
Shuichiro Ito, Ph.D.**<br />
Sankyo Co., Ltd.<br />
Tokyo, Japan<br />
Kai Jenssen, Ph.D.<br />
Glenn C. Johns, Ph.D.<br />
Eric C. Johnson, Ph.D.<br />
Margaret Alice Johnson, Ph.D.<br />
Hamid Reza Kalhor, Ph.D. ††††<br />
Christian Kannemeier, Ph.D.<br />
Mili Kapoor, Ph.D.<br />
Andrey Aleksandrovich<br />
Karyakin, Ph.D.<br />
Yang Khandogin, Ph.D.<br />
Ilja V. Khavrutskii, Ph.D.<br />
Reza Khayat, Ph.D.<br />
Dae Hee Kim, Ph.D.<br />
Min Ju Kim, Ph.D.**<br />
Genomics <strong>Institute</strong> of the<br />
Novartis <strong>Research</strong> Foundation<br />
San Diego, California<br />
Eda Koculi, Ph.D.<br />
Milka Kostic, Ph.D.<br />
Julio Kovacs, Ph.D.<br />
Irina Kufareva, Ph.D.<br />
MOLECULAR BIOLOGY 2005 157<br />
Shantanu Kumar, Ph.D.<br />
Iaroslav Kuzmin, Ph.D. ††††<br />
Hugo Alfredo Lago-Zarrilli,<br />
Ph.D. ††††<br />
Bianca Lam, Ph.D.<br />
Polo Chun Hung Lam, Ph.D.<br />
Emma Langley, Ph.D.<br />
Jason Lanman, Ph.D.<br />
Jonathan C. Lansing, Ph.D.**<br />
Momenta Pharmaceuticals<br />
Cambridge, Massachusetts<br />
Chang-Wook Lee, Ph.D.<br />
Chul Won Lee, Ph.D.<br />
Jinhyuk Lee, Ph.D.<br />
June Hyung Lee, Ph.D.<br />
Kelly Lee, Ph.D.<br />
Katrina Lehmann, Ph.D. ††††<br />
Chenglong Li, Ph.D.<br />
Vasco Liberal, Ph.D.<br />
William M. Lindstrom, Ph.D.<br />
Hui-Yue Christine Lo, Ph.D.<br />
Kunheng Luo, Ph.D.<br />
John Gately Luz, Ph.D.**<br />
Harvard University<br />
Boston, Massachusetts<br />
Che Ma, Ph.D.**<br />
Academia Sinica<br />
Taipei, Taiwan<br />
Ann MacLaren, Ph.D.<br />
Laurent Magnenat, Ph.D.**<br />
Serono Pharmaceutical<br />
<strong>Research</strong> <strong>Institute</strong> SA<br />
Geneva, Switzerland<br />
Darly Joseph Manayani, Ph.D.
158 MOLECULAR BIOLOGY 2005<br />
Jeff Mandell, Ph.D.<br />
Maria Victoria Martin-<br />
Sanchez, Ph.D.<br />
Tsutomu Matsui, Ph.D.<br />
Daniel McElheny, Ph.D.**<br />
University of Chicago<br />
Chicago, Illinois<br />
Benoit Melchior, Ph.D.**<br />
University of California<br />
Riverside, California<br />
David Metzgar, Ph.D.**<br />
Naval Health <strong>Research</strong> Center<br />
San Diego, California<br />
Jonathan Mikolosko, Ph.D.<br />
Susumu Mitsumori, Ph.D.<br />
Heiko Michael Moeller,<br />
Ph.D.**<br />
Universität Konstanz<br />
Konstanz, Germany<br />
Seongho Moon, Ph.D.<br />
Bettina Moser, Ph.D.**<br />
University of Illinois at Chicago<br />
Chicago, Illinois<br />
Samrat Mukhopadhyay, Ph.D.<br />
Christopher Myers, Ph.D.**<br />
Naval Health <strong>Research</strong> Center<br />
San Diego, California<br />
Sreenivasa Chowdari Naidu,<br />
Ph.D.**<br />
MediVas, L.L.C.<br />
San Diego, California<br />
Toru M. Nakamura, Ph.D.**<br />
University of Illinois at Chicago<br />
Chicago, Illinois<br />
Sujatha Narayan, Ph.D.<br />
Hung Nguyen, Ph.D.<br />
Tadateru Nishikawa, Ph.D.<br />
Eishi Noguchi, Ph.D.**<br />
Drexel University<br />
Philadelphia, Pennsylvania<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Wataru Nomura, Ph.D.<br />
Brian Nordin, Ph.D.**<br />
ActivX Biosciences, Inc.<br />
La Jolla, California<br />
Karin E. Norgard-Sumnicht,<br />
Ph.D.**<br />
San Diego State University<br />
San Diego, California<br />
Brian V. Norledge, Ph.D.<br />
Michael Oberhuber, Ph.D.**<br />
Leopold Franzens Universität<br />
Innsbruck, Austria<br />
Wendy Fernandez Ochoa,<br />
Ph.D.<br />
Amy Odegard, Ph.D.<br />
Yoshiaki Zenmei Ohkubo,<br />
Ph.D.**<br />
Rutgers University<br />
Piscataway, New Jersey<br />
Brian L. Olson, Ph.D.<br />
Brian Paegel, Ph.D.<br />
Covadonga Paneda, Ph.D.**<br />
<strong>Molecular</strong> and Integrative<br />
Neurosciences Department,<br />
<strong>Scripps</strong> <strong>Research</strong><br />
Sandeep Patel, Ph.D.<br />
Natasha Paul, Ph.D.**<br />
Stratagene, Inc.<br />
La Jolla, California<br />
Stephanie Pebernard, Ph.D.<br />
Suzanne Peterson, Ph.D.**<br />
University of California<br />
San Diego, California<br />
Wolfgang Stefan Peti, Ph.D.**<br />
Brown University<br />
Providence, Rhode Island<br />
Goran Pljevaljcic, Ph.D.<br />
Corinne Chantal Ploix, Ph.D.**<br />
Novartis International AG<br />
Basel, Switzerland<br />
Stephanie Pond, Ph.D.<br />
Owen Pornillos, Ph.D.<br />
Daniel Joseph Price, Ph.D.<br />
Plachikkat Krishnan Radha,<br />
Ph.D. ††††<br />
Grazia Daniela Raffa, Ph.D.<br />
John Reader, Ph.D.**<br />
University of North Carolina<br />
Chapel Hill, North Carolina<br />
Stevens Kastrup Rehen,<br />
Ph.D.**<br />
Universidade Federal do Rio<br />
de Janeiro<br />
Rio de Janeiro, Brazil<br />
Jean-Baptiste Reiser, Ph.D.**<br />
European Synchrotron<br />
Radiation Facility<br />
Grenoble, France<br />
Miguel A. Rodriguez-<br />
Gabriel, Ph.D.**<br />
Universidad Complutense de<br />
Madrid<br />
Madrid, Spain<br />
Stanislav Rudyak, Ph.D.<br />
Sean Ryder, Ph.D.<br />
Sanjay Adrian Saldanha, Ph.D.<br />
Sanjita Sasmal, Ph.D. ††††<br />
Mika Aoyagi Scharber, Ph.D.**<br />
Burnham <strong>Institute</strong><br />
La Jolla, California<br />
Jennifer S. Scorah, Ph.D.<br />
Pedro Serrano-Navarro, Ph.D.<br />
Craig McLean Shepherd, Ph.D.<br />
William Shih, Ph.D**<br />
Dana Farber Cancer <strong>Institute</strong><br />
Boston, Massachusetts<br />
David S. Shin, Ph.D.<br />
Develeena Shivakumar, Ph.D.<br />
Holly Heaslet Soutter, Ph.D.<br />
Natalie Spielewoy, Ph.D.**<br />
Weatherall <strong>Institute</strong> of<br />
<strong>Molecular</strong> Medicine<br />
Oxford, England<br />
Greg Springsteen, Ph.D.<br />
Deborah J. Stauber, Ph.D.**<br />
Novartis <strong>Institute</strong>s for<br />
BioMedical <strong>Research</strong><br />
Cambridge, Massachusetts<br />
Derek Steiner, Ph.D.**<br />
Johnson & Johnson<br />
San Diego, California<br />
Gudrun Stengel, Ph.D.<br />
Daniel Stoffler, Ph.D.**<br />
Universität Basel<br />
Basel, Switzerland<br />
Kenji Sugase, Ph.D.<br />
Vidyasankar Sundaresan,<br />
Ph.D.**<br />
GE Infrastructure<br />
Trevose, Pennsylvania<br />
Magnus Sundstrom, Ph.D.<br />
Jeff Suri, Ph.D.**<br />
GluMetrics, Inc.<br />
Long Beach, California<br />
Blair R. Szymczyna, Ph.D.<br />
Florence Muriel Tama, Ph.D.<br />
Jinghua Tang, Ph.D.**<br />
University of California<br />
San Diego, California<br />
Nardos Tassew, Ph.D.<br />
Hiroaki Tateno, Ph.D.<br />
Michela Taufer, Ph.D.**<br />
University of Texas<br />
El Paso, Texas<br />
Ewan Richardson Taylor, Ph.D.<br />
Donato Tedesco, Ph.D.**<br />
Berlex Biosciences<br />
Richmond, California
Hua Tian, Ph.D.<br />
Rhonda Torres, Ph.D.**<br />
Merck & Co.<br />
Rahway, New jersey<br />
Megan Wright Trevathan,<br />
Ph.D.**<br />
Harvard Medical School<br />
Boston, Massachusetts<br />
Ulrich Ignaz Tschulena, Ph.D.<br />
Julie L. Tubbs, Ph.D.<br />
Naoto Utsumi, Ph.D.<br />
Frank van Drogen, Ph.D.<br />
Philip Arno Venter, Ph.D.<br />
Petra Verdino, Ph.D.<br />
Stefan Vetter, Ph.D.**<br />
Florida Atlantic University<br />
Boca Raton, Florida<br />
William Frederick Waas,<br />
Ph.D.<br />
Shun-ichi Wada, Ph.D.<br />
Ross Walker, Ph.D.<br />
Robert Scott Williams, Ph.D.<br />
Raphaelle Winsky-<br />
Sommerer, Ph.D.**<br />
Universität Zürich<br />
Zürich, Switzerland<br />
Eric L. Wise, Ph.D.<br />
Jonathan Wojciak, Ph.D.<br />
Dennis Wolan, Ph.D.**<br />
Sunesis Pharmaceuticals,<br />
Inc.<br />
South San Francisco,<br />
California<br />
Hyung Sik Won, Ph.D.**<br />
Konkuk University<br />
Chungju, Korea<br />
Timothy I. Wood, Ph.D.<br />
Eugene Wu, Ph.D.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Lan Xu, Ph.D.<br />
Yoshiki Yamada, Ph.D.<br />
Atsushi Yamagata, Ph.D.<br />
Qi Yan, Ph.D.<br />
Yong Yao, Ph.D.<br />
Xiaoqin Ye, M.D., Ph.D.<br />
Yongjun Ye, Ph.D.<br />
Yong Yin, Ph.D.<br />
Veronica Yu, Ph.D.<br />
Yuan Yuan, Ph.D.<br />
Markus Zeeb, Ph.D.<br />
Ying Zeng, Ph.D.<br />
Haile Zhang, Ph.D.<br />
Yong Zhao, Ph.D.<br />
Peizhi Zhu, Ph.D.<br />
SCIENTIFIC ASSOCIATES<br />
Enrique Abola, Ph.D.<br />
Andrew S. Arvai, M.S.<br />
Eric Birgbauer, Ph.D.<br />
Ognian V. Bohorov, Ph.D.<br />
Dennis Carlton, B.S.<br />
Ellen Yu-Lin Tsai Chien,<br />
Ph.D.<br />
Xiaoping Dai, Ph.D.<br />
Liliane Dickinson, Ph.D. ††††<br />
Michael Allen Hanson,<br />
Ph.D.<br />
Diane Marie Kubitz, B.A.<br />
Marcy A. Kingsbury, Ph.D.<br />
Rolf Mueller, Ph.D.<br />
Padmaja Natarajan, Ph.D.<br />
Marianne Patch, Ph.D.<br />
Gabriela Perez-Alvarado,<br />
Ph.D.<br />
Nicholas Preece, Ph.D.<br />
Lin Wang, Ph.D.<br />
VISITING<br />
INVESTIGATORS<br />
Stephen J. Benkovic, Ph.D.<br />
Pennsylvania State University<br />
University Park, Pennsylvania<br />
Astrid Graslund, Ph.D.<br />
Stockholm University<br />
Stockholm, Sweden<br />
Arne Holmgren, M.D., Ph.D.<br />
Karolinska <strong>Institute</strong>t<br />
Stockholm, Sweden<br />
Barry Honig, Ph.D.<br />
Columbia University<br />
New York, New York<br />
Arthur Horwich, M.D.<br />
Yale University<br />
New Haven, Connecticut<br />
Tai-huang Huang, Ph.D.<br />
Academica Sinica<br />
Taipei, Taiwan<br />
Robert D. Rosenstein, Ph.D.<br />
Lawrence Berkeley National<br />
Laboratory<br />
Berkeley, California<br />
MOLECULAR BIOLOGY 2005 159<br />
* Joint appointment in <strong>The</strong> Skaggs<br />
<strong>Institute</strong> for Chemical <strong>Biology</strong><br />
** Appointment completed; new<br />
location shown<br />
*** Joint appointment in the<br />
<strong>Molecular</strong> and Integrative<br />
Neurosciences Department<br />
**** Joint appointments in the<br />
Department of Immunology and<br />
<strong>The</strong> Skaggs <strong>Institute</strong> for<br />
Chemical <strong>Biology</strong><br />
***** Joint appointments in the<br />
Department of Chemistry and<br />
<strong>The</strong> Skaggs <strong>Institute</strong> for<br />
Chemical <strong>Biology</strong><br />
† Joint appointment in the<br />
Department of Cell <strong>Biology</strong><br />
†† Joint appointment in the<br />
Department of <strong>Molecular</strong> and<br />
Experimental Medicine<br />
††† Joint appointment in the<br />
Department of Chemistry<br />
†††† Appointment completed
160 MOLECULAR BIOLOGY 2005<br />
Chairman’s Overview<br />
<strong>Research</strong> in the Department of <strong>Molecular</strong> <strong>Biology</strong><br />
encompasses a broad range of disciplines, extending<br />
from structural and computational biology at<br />
one extreme to molecular genetics at the other. During<br />
the past year, our scientists continued to make rapid<br />
progress toward understanding the fundamental molecular<br />
events that underlie the processes of life. Major<br />
advances have been made in elucidating the structural<br />
biology of signal transduction and viral assembly, in<br />
understanding mechanisms of viral infectivity, in determining<br />
the structure of membrane proteins, in understanding<br />
the molecular basis of nucleic acid recognition<br />
and DNA repair, and in determining the mechanism of<br />
ribosome assembly. Progress was made in elucidating<br />
the molecular events involved in regulation of the cell<br />
cycle, in tumor development, in induction of sleep, in<br />
the molecular origins of neuronal development and of<br />
CNS disorders, in the regulation of transcription, and in<br />
the decoding of genetic information in translation. Finally,<br />
new advances were made in the design of novel low<br />
molecular weight compounds that can specifically regulate<br />
genes and in the area of biomolecular engineering,<br />
building novel functions into viruses, antibodies, zinc<br />
finger proteins, RNA, and DNA. Progress in these and<br />
other areas is described in detail on the following pages,<br />
and only a few highlights are mentioned here.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Peter E. Wright, Ph.D.<br />
Structural biology continues to be a major activity<br />
in the department, and many new x-ray and nuclear<br />
magnetic resonance structures of major biomedical<br />
importance were completed during the past year. Among<br />
the highlights was the determination, in Ian Wilson’s laboratory,<br />
of the first structure of a human Toll-like receptor,<br />
a protein that plays a key role in the innate immune<br />
system as a sensor of molecules associated with the cell<br />
wall and genetic material of pathogenic bacteria. Dr. Wilson<br />
and his coworkers also reported structures of the<br />
protein CD1a, another key receptor in the innate immune<br />
response, and of an antibody that neutralizes most strains<br />
of HIV. Other advances came in the area of membrane<br />
protein crystallography: Geoffrey Chang and colleagues<br />
determined the structures of 2 proteins (MsbA and EmrE)<br />
involved in drug transport and the development of drug<br />
resistance in bacteria and cancer cells, and David Stout<br />
and James Fee determined the structure of a cytochrome<br />
ba 3 oxidase. Finally, the Joint Center for Structural<br />
Genomics, directed by Ian Wilson, was selected by the<br />
National <strong>Institute</strong>s of Health as 1 of 4 large-scale centers<br />
for high-throughput determination of protein structures.<br />
Several research groups are working in areas directly<br />
related to drug discovery and protein therapeutics. Joel<br />
Gottesfeld and colleagues have developed a small DNAbinding<br />
molecule that turns off the gene for histone H4<br />
and blocks replication in a wide variety of cancer cells.<br />
<strong>The</strong> compound is active in vivo and blocks the growth<br />
of tumors in mice. <strong>Research</strong> in the laboratory of Carlos<br />
Barbas is directed toward genetic reprogramming of<br />
tumor cells via engineered zinc finger transcription factors.<br />
<strong>The</strong>se artificial transcription factors are powerful<br />
tools for determining the function of genes in tumor<br />
growth and progression and have potential applications<br />
in cancer therapy. John Elder and colleagues are studying<br />
development of resistance to drugs that target the<br />
HIV protease. A complementary approach to the same<br />
problem is being taken by Arthur Olson and researchers<br />
in his laboratory in their FightAIDS@Home program.<br />
This program is a large-scale computational effort in<br />
which a grid of personal computers distributed around<br />
the world is used to design effective therapeutic agents<br />
that target the HIV protease. Raymond Stevens and<br />
coworkers have engineered a phenylalanine ammonia<br />
lyase enzyme as a potential injectable therapeutic agent<br />
for treating phenylketonuria. Finally, Paul Schimmel and<br />
colleagues have identified a naturally occurring fragment<br />
of tryptophanyl-tRNA synthetase that is highly potent in<br />
arresting angiogenesis and is being introduced in a clinical<br />
setting for treatment of macular degeneration.
Many of the research groups in the department are<br />
applying the tools of molecular genetics to understand<br />
the molecular basis of human disease. Jerold Chun and<br />
his colleagues recently established a relationship between<br />
lysophospholipid signaling and neuropathic pain. In addition,<br />
they made the surprising discovery that lysophosphatidic<br />
acid receptors play an important role in embryonic<br />
implantation and thereby influence female fertility.<br />
<strong>Research</strong> in the laboratory of Luis de Lecea has indicated<br />
that a newly discovered neuropeptide, neuropeptide S,<br />
plays a functional role in modulation of sleep and suppression<br />
of anxiety. Work in the laboratory of James<br />
Paulson has led to the development of novel microarray<br />
technology for profiling glycoproteins, a technology that<br />
could eventually be developed into a powerful diagnostic<br />
screen for various infections and diseases.<br />
On the more fundamental side, major advances have<br />
been made in understanding mechanisms of protein and<br />
RNA folding, both in vitro and in a cellular environment.<br />
<strong>Research</strong> in the laboratory of Martha Fedor has resulted<br />
in new insights into mechanisms by which RNA folds<br />
into its specific functional structures and has provided<br />
evidence that RNA chaperones mediate folding pathways<br />
in the cell. Work by James Williamson and colleagues<br />
has led to a detailed map of the assembly landscape of<br />
the 30S ribosome, providing new understanding of the<br />
mechanism by which assembly proceeds through a succession<br />
of RNA conformational changes and protein<br />
binding events. Arthur Horwich and coworkers have<br />
made major progress in elucidating the mechanism by<br />
which the chaperone ClpA mediates unfolding and translocation<br />
of proteins.<br />
<strong>Molecular</strong> biology remains a field of enormous opportunity<br />
and excitement. <strong>The</strong> scientists in the department<br />
are taking full advantage of powerful new technologies<br />
to advance our understanding of fundamental biological<br />
processes at the molecular level. <strong>The</strong>ir discoveries will<br />
ultimately be translated into new advances in biotechnology<br />
and in medicine.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 161
162 MOLECULAR BIOLOGY 2005<br />
INVESTIGATORS’ REPORTS<br />
Structural <strong>Biology</strong> of<br />
Immune Recognition,<br />
<strong>Molecular</strong> Assemblies,<br />
and Anticancer Targets<br />
I.A. Wilson, R.L. Stanfield, J. Stevens, X. Zhu, Y. An,<br />
K. Beis, T.A. Bowden, D.A. Calarese, R.M.F. Cardoso,<br />
P.J. Carney, J.-W. Choe, A.L. Corper, M.D.M. Crispin,<br />
T.A. Cross, X. Dai, W.L. Densley, E.W. Debler, M.-A. Elsliger,<br />
S. Ferguson, G.W. Han, P.A. Horton, S. Ito, M.J. Jimenez-<br />
Dalmaroni, M.S. Kelker, J.G. Luz, J.B. Reiser,<br />
E.B. Shillington, D.A. Shore, D.J. Stauber, R.S. Stefanko,<br />
J.A. Vanhnasy, P. Verdino, E. Wise, D.W. Wolan, L. Xu,<br />
M. Yu, D.M. Zajonc, Y. Zhang<br />
Our main research focus is concerned with macromolecules<br />
and molecular complexes related to<br />
the innate and adaptive immune responses, viral<br />
pathogenesis, protein trafficking, purine biosynthesis, and<br />
reproductive biology. We use x-ray crystallography to<br />
determine atomic structures of key proteins in these systems<br />
in order to interpret functional data to probe mechanisms<br />
and modes of interaction and to aid in the design<br />
of therapeutic agents as potential drugs or vaccines.<br />
THE INNATE IMMUNE SYSTEM<br />
Toll-like receptors (TLRs) are important mammalian<br />
glycoproteins involved in innate immunity that recognize<br />
conserved structures in pathogens called pattern recognition<br />
motifs. We recently determined the 2.1-Å crystal<br />
structure of the extracellular domain of human TLR3,<br />
which is activated by double-stranded viral RNA. TLR3<br />
forms a large horseshoelike structure with an outer diameter<br />
of 80 Å. Key features include a hydrophobic core<br />
formed by the conserved leucine-rich repeats and a<br />
continuous β-sheet that spans 270° of arc. We are also<br />
investigating other TLRs and their ligands to understand<br />
how microorganisms are initially sensed by the innate<br />
immune system. Our goal is to use the data to design<br />
novel selective agonists and antagonists of TLR signaling<br />
pathways. This research is being done in collaboration<br />
with R.J. Ulevitch and B. Beutler, Department<br />
of Immunology.<br />
Another family of pattern recognition molecules called<br />
peptidoglycan recognition proteins (PGRPs) interacts<br />
with peptidoglycans. We have determined the crystal<br />
structure of the “recognition” PGRP-SA at 1.56 Å. Com-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
parison of PGRP-SA with a “catalytic” PGRP-LB indicates<br />
overall structural conservation and a hydrophilic<br />
groove that most likely corresponds to the peptidoglycan<br />
core binding site.<br />
Approximately 22,500 intensive care patients across<br />
the United States die of septic shock syndrome every<br />
year. Recently, researchers found that a newly discovered<br />
receptor termed triggering receptor expressed on myeloid<br />
cells 1 (TREM-1) mediates septic shock. We determined<br />
structures of human and mouse TREM-1 immunoglobulin-type<br />
domains to 1.47 Å and 1.76 Å, respectively.<br />
<strong>The</strong>se structural results provided insights into the nature<br />
of ligand recognition by the TREM family in innate immunity.<br />
<strong>The</strong> studies on TREMs and PGRPs are being done in<br />
collaboration with L. Teyton, Department of Immunology.<br />
CLASSICAL AND NONCLASSICAL MHC AND T-CELL<br />
RECEPTOR SIGNALING<br />
In cellular immunity, T-cell receptors (TCRs) sense<br />
invading pathogens by recognizing pathogen-derived peptide<br />
fragments presented by MHC molecules. <strong>The</strong> TCRs<br />
then act in concert with CD8 and CD3, which assist in<br />
transducing the antigen recognition signal. Aberrant signaling<br />
can result in numerous disease states. <strong>The</strong> αβ TCR<br />
coreceptor CD8 is an essential factor in the TCR-mediated<br />
activation of cytotoxic T lymphocytes. We are doing structural<br />
studies of the CD8αβ and the CD8αα isoforms and<br />
of other constituents of the TCR signaling complex.<br />
<strong>The</strong> CD1 family of nonclassical MHC molecules presents<br />
lipid antigens to CD1-restricted TCRs. Our recent<br />
crystal structure of mouse CD1d at 2.2 Å in complex<br />
with the exceptionally potent short-chain sphingolipid<br />
α-galactosyl ceramide (Fig. 1) reveals a precise hydro-<br />
Fig. 1. <strong>The</strong> short-chain sphingolipid α-galactosyl ceramide bound<br />
to mouse CD1d. This sphingolipid is a strong agonist of natural killer<br />
T cells. Both alkyl chains of the ligand are buried deep inside the<br />
binding groove, whereas the galactose headgroup is optimally positioned<br />
on top of the binding groove to directly interact with the TCR.
gen-bonding network that positions the galactose moiety.<br />
Other CD1 structures determined include those of<br />
CD1a with a bound sulfatide and with a lipopeptide<br />
that have revealed how dual- and single-chain lipids<br />
interact with the same CD1 molecule. Collaborators in<br />
this research include D.B. Moody and M.B. Brenner,<br />
Harvard Medical School, Boston, Massachusetts; C.-H.<br />
Wong, Department of Chemistry; L. Teyton, Department<br />
of Immunology; M. Kronenberg, La Jolla <strong>Institute</strong> for<br />
Allergy and Immunology, San Diego, California; V. Kumar,<br />
Torrey Pines <strong>Institute</strong> for <strong>Molecular</strong> Studies, San Diego,<br />
California; and Wayne Severn, Ag<strong>Research</strong>, Upper Hut,<br />
New Zealand.<br />
1918 INFLUENZA VIRUS<br />
Flu is a contagious respiratory disease caused by<br />
influenza viruses. Of all the known pandemics in the<br />
history of humans, the 1918 influenza outbreak was<br />
the most destructive; according to estimates, 40 million<br />
persons died. As a member of the “flu consortium”<br />
funded by the National <strong>Institute</strong>s of Health, we are<br />
working toward a molecular understanding of why this<br />
particular influenza virus was so pathogenic and how<br />
it managed to evade the immune system so effectively.<br />
We have determined the structure of the hemagglutinin<br />
of the 1918 virus, and now we are investigating<br />
the other viral proteins. We recently analyzed the receptor<br />
specificity of the 1918 hemagglutinin by comparing<br />
its binding to a panel of carbohydrates with the binding<br />
of more modern human and avian viruses (Fig. 2). For<br />
these studies, we are using novel glycan array technology<br />
developed by O. Blixt and J. Paulson, Consortium<br />
for Functional Glycomics, La Jolla, California.<br />
HIV TYPE 1 NEUTRALIZING ANTIBODIES<br />
A vaccine effective against the HIV type 1 must<br />
elicit antibodies that neutralize all circulating strains of<br />
the virus. However, antibodies with such properties are<br />
extremely rare; to date, only a handful have been isolated.<br />
Crystal structures for 4 of these rare, potent,<br />
broadly neutralizing antibodies (b12, 2G12, 4E10,<br />
447-52D) in complex with their viral antigens have<br />
revealed the structural basis for the effectiveness of the<br />
antibodies (Fig. 3). Our goal is to design compounds on<br />
the basis of this structural information (retrovaccinology)<br />
for testing as potential vaccines. <strong>The</strong> research on HIV<br />
is being done in collaboration with D. Burton, Department<br />
of Immunology; P. Dawson, Department of Cell<br />
<strong>Biology</strong>; C.-H. Wong, Department of Chemistry; S. Danishefsky,<br />
Sloan-Kettering <strong>Institute</strong>, New York, New York;<br />
J.K. Scott, Simon Fraser University, Burnaby, British<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 163<br />
Fig. 2. Results for carbohydrate array binding of the 2 natural<br />
hemagglutinins from the influenza virus that circulated during the<br />
1918 pandemic. Human-adapted viruses preferentially bind to receptors<br />
with a terminal sialic acid linked by an α2,6 linkage to a vicinal<br />
galactose, whereas avian-adapted viruses recognize an α2,3 linkage.<br />
Glycan array results are shown for 18SC (A/South Carolina/1/18; A),<br />
and 18NY (A/New York/1/18; B). <strong>The</strong>se 2 hemagglutinins differ by<br />
a single point mutation that is sufficient to alter the carbohydrate specificity<br />
from exclusively α2,6 to mixed α2,6/α2,3. AGP indicates α1- acid glycoprotein.<br />
Fig. 3. Antigen binding site of the Fab fragment of 4E10, an<br />
antibody to gp41. 4E10 cross-reacts with more viral isolates (clades)<br />
than any other known HIV type 1 neutralizing antibody. <strong>The</strong> crystal<br />
structure of Fab 4E10 is shown in complex with a synthetic peptide<br />
that encompasses the highly conserved 4E10 epitope. <strong>The</strong> peptide<br />
(ball and stick) binds to the surface of Fab 4E10 (solid surface) in<br />
a shallow hydrophobic cavity in a helical conformation. <strong>The</strong> structure<br />
also suggests that the complementarity-determining region H3<br />
loop of 4E10 may contact the cell membrane, because the loop is<br />
adjacent to the membrane-proximal epitope.
164 MOLECULAR BIOLOGY 2005<br />
Columbia; S. Zolla-Pazner, New York University School<br />
of Medicine, New York, New York; J. Moore, Cornell<br />
University, Ithaca, New York; Repligen Corporation,<br />
Waltham, Massachusetts; H. Katinger, R. Kunert, and<br />
G. Stiegler, University für Bodenkultur, Vienna, Austria;<br />
and R. Wyatt and P. Kwong, Vaccine <strong>Research</strong> Center,<br />
National <strong>Institute</strong>s of Health, Bethesda, Maryland.<br />
PRIMITIVE IMMUNOGLOBULINS<br />
Cartilaginous fish are the phylogenetically oldest<br />
living organisms known to have components of the<br />
vertebrate adaptive immune system, such as antibodies,<br />
MHC molecules, and TCRs. Key to their immune<br />
response are heavy-chain, homodimeric immunoglobulins<br />
(“new antigen receptors” or IgNARs) in which the<br />
antigen-recognizing variable domains consist of only a<br />
single immunoglobulin domain. In collaboration with<br />
M. Flajnik, University of Maryland Medical School, Baltimore,<br />
Maryland, we determined the crystal structure for<br />
an IgNAR variable domain in complex with its lysozyme<br />
antigen (Fig. 4). <strong>The</strong> results revealed that 2 complementarity-determining<br />
regions are sufficient for antigen<br />
recognition. <strong>The</strong>se and ongoing studies will determine<br />
whether the IgNAR variable domains are an evolutionary<br />
precursor to mammalian TCR and antibody<br />
immunoglobulin domains.<br />
CATALYTIC ANTIBODIES<br />
Catalytic antibodies can be generated to carry out<br />
many difficult and novel chemical reactions, including<br />
Fig. 4. Nurse shark IgNAR type I variable domain (tubes) bound<br />
to its lysozyme antigen (solid surface). <strong>The</strong> IgNAR variable domains<br />
have an unusual antigen-binding site that contains only 2 of the 3<br />
conventional complementarity-determining regions (CDRs), but it still<br />
binds antigen with nanomolar affinity via an interface comparable<br />
in size to conventional antibodies. Two other regions, HV2 and HV4,<br />
are also somatically mutated, suggesting that they may also be<br />
involved in antigen recognition for other IgNAR-antigen complexes.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
reactions not catalyzed by naturally occurring enzymes.<br />
Examples currently under study include several cocainehydrolyzing<br />
antibodies that could act as possible therapeutic<br />
agents to counter cocaine overdose or addiction,<br />
highly efficient but widely acting aldolase antibodies,<br />
and antibodies that carry out proton abstraction from<br />
carbon (Fig. 5). <strong>The</strong> studies on catalytic antibodies<br />
are being done in collaboration with R.A. Lerner, C.F.<br />
Barbas, K.D. Janda, P.G. Schultz, F. Tanaka, P. Wentworth,<br />
and P. Wirsching, Department of Chemistry;<br />
D.W. Landry, Columbia University, New York, New York;<br />
and D. Hilvert, ETH Zürich, Zürich, Switzerland.<br />
Fig. 5. Antibody-combining site of 34E4 bound to hapten. Catalytic<br />
antibody 34E4 catalyzes the conversion of benzisoxazoles to<br />
salicylonitriles with high rates and multiple turnovers. This reaction<br />
is a widely used model system for studies of proton abstraction from<br />
carbon. <strong>The</strong> structure of 34E4 in complex with its hapten has revealed<br />
many similarities to biological counterparts that promote proton transfers.<br />
Nevertheless, the reliance of 34E4 on a single catalytic residue<br />
(GluH50 ) probably prevents it from achieving the rates of the<br />
most efficient enzymes. Two of the active-site water molecules are<br />
designated S1 and S21. <strong>The</strong> 3Fo-2Fc σA-weighted electron density<br />
map around the hapten and key active-site residues is contoured at<br />
1.3 σ. Hydrogen bonds are shown as broken lines. TrpL91 forms a<br />
cation-π interaction with the guanidinium moiety of the hapten.<br />
EVOLUTION OF LIGAND RECOGNITION AND<br />
SPECIFICITY<br />
<strong>The</strong> antibodies 1E9 and DB3 share a human germline<br />
precursor but recognize different ligands. Residues<br />
in the Diels-Alderase antibody 1E9 active site have<br />
been sequentially mutated by D. Hilvert to change the<br />
specificity of 1E9 to that of the steroid-binding DB3.
Only 2 key residues in 1E9 are required to switch<br />
between the catalytic antibody activity and steroid binding<br />
that is 14,000-fold higher than in the original 1E9<br />
antibody. Crystal structures of these steroid-bound 1E9<br />
mutants show that although 1E9 and DB3 share similar<br />
steroid-binding properties, they surprisingly accomplish<br />
binding and specificity in a structurally distinct manner.<br />
BLUE AND PURPLE FLUORESCENT ANTIBODIES<br />
Antibodies generated against trans-stilbene have<br />
an interesting, unexpected photochemistry when bound<br />
to that hapten. Several of these antibodies bind stilbene<br />
with high affinity, yet have significantly different<br />
spectroscopic properties. Crystal structures have now<br />
been determined to probe the antibodies’ mechanism<br />
of action, and further biophysical and biochemical<br />
studies are being performed in the laboratories of our<br />
collaborators, R.A. Lerner, Department of <strong>Molecular</strong><br />
<strong>Biology</strong>; K.D. Janda and F.E. Romesberg, Department<br />
of Chemistry; and H.G. Gray, California <strong>Institute</strong> of Technology,<br />
Pasadena, California.<br />
PROTEIN TRAFFICKING<br />
<strong>The</strong> Rab family GTPases are ubiquitously involved<br />
in regulation of membrane docking and fusion in endocytic<br />
and exocytic pathways. <strong>The</strong> tethering factor p115<br />
is recruited by Rab1 to vesicles of coat protein complex<br />
II during budding from the endoplasmic reticulum<br />
and subsequently interacts with a set of SNARE proteins<br />
associated with the vesicles to promote targeting<br />
to the Golgi complex. In collaboration with W.E. Balch,<br />
Department of Cell <strong>Biology</strong>, we determined the crystal<br />
structure of p115 at 2.0 Å and localized the binding<br />
site on p115 for Rab1 by mutational analysis.<br />
ENZYMATIC CANCER TARGETS<br />
<strong>The</strong> de novo purine biosynthesis pathway is the primary<br />
provider of purine nucleotides, which are converted<br />
to DNA building blocks. This biosynthesis pathway is<br />
a validated target for the development of anticancer<br />
drugs because of heavy dependence on it by fast-growing<br />
cells, such as tumor cells. We have focused on 2<br />
folate-dependent enzymes in the pathway: glycinamide<br />
ribonucleotide transformylase and the bifunctional aminoimidazole<br />
carboxamide ribonucleotide transformylase<br />
inosine monophosphate cyclohydrolase (ATIC, Fig. 6).<br />
Crystal structures of these 2 enzymes in complex with<br />
many different classes of inhibitors have provided a valuable<br />
platform for development of antineoplastic agents.<br />
<strong>The</strong>se investigations are being done in collaboration with<br />
D.L. Boger, Department of Chemistry; A.J. Olson, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>; G.P. Beardsley, Yale Univer-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 165<br />
Fig. 6. <strong>The</strong> active site of ATIC in complex with a novel nonfolate<br />
inhibitor identified by virtual ligand screening. <strong>The</strong> inhibitor is depicted<br />
in ball-and-stick representation and is surrounded by 2Fo-Fc electron<br />
density contoured at 1σ.<br />
sity, New Haven, Connecticut; and S.J. Benkovic, Pennsylvania<br />
State University, University Park, Pennsylvania.<br />
GHMP KINASES IN REPRODUCTIVE BIOLOGY<br />
XOL-1 is the primary sex-determining signal from<br />
Caenorhabditis elegans. <strong>The</strong> crystal structure of XOL-1<br />
revealed that the protein belongs to the GHMP kinase<br />
family of small-molecule kinases, establishing an unanticipated<br />
role for this protein family in differentiation and<br />
development. In collaboration with B.J. Meyer, University<br />
of California, Berkeley, California, we identified<br />
XOL-1 homologs in the genomes of Caenorhabditis<br />
briggsae and Caenorhabditis remanei and are examining<br />
their function by using suppression of gene expression<br />
mediated by RNA interference. Although XOL-1 is<br />
structurally similar to its GHMP kinase neighbors, its<br />
endogenous ligand is unknown. Using the crystal structure<br />
of XOL-1 as a template for virtual screening, we<br />
identified several potential synthetic XOL-1 ligands, and<br />
in collaboration with J.R. Williamson, Department of<br />
<strong>Molecular</strong> <strong>Biology</strong>, we confirmed their binding by using<br />
nuclear magnetic resonance.<br />
JOINT CENTER FOR STRUCTURAL GENOMICS<br />
<strong>The</strong> Joint Center for Structural Genomics is a large<br />
consortium of scientists from <strong>Scripps</strong> <strong>Research</strong>, the<br />
Stanford Synchrotron Radiation Laboratory, the University<br />
of California, San Diego, the Burnham <strong>Institute</strong>, and<br />
the Genomics <strong>Institute</strong> of the Novartis <strong>Research</strong> Foundation.<br />
<strong>The</strong> center is funded by the Protein Structure
166 MOLECULAR BIOLOGY 2005<br />
Initiative of the National <strong>Institute</strong> of General Medical<br />
Sciences. Its purpose is the high-throughput structure<br />
determination of the complete proteomes of a procaryote,<br />
<strong>The</strong>rmotoga maritima, and a eukaryote, the mouse.<br />
To date, members of the consortium have pioneered<br />
the development of many novel high-throughput methods,<br />
constructed a high-throughput pipeline, and determined<br />
more than 200 nonredundant structures, including<br />
100 in the past year.<br />
PUBLICATIONS<br />
Arndt, J.W., Schwarzenbacher, R., Page, R., et al. Crystal structure of an / serine<br />
hydrolase (YDR428C) from Saccharomyces cerevisiae at 1.85 Å resolution. Proteins<br />
58:755, 2005.<br />
Bakolitsa, C., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of an<br />
orphan protein (TM0875) from <strong>The</strong>rmotoga maritima at 2.00-Å resolution reveals<br />
a new fold. Proteins 56:607, 2004.<br />
Blixt, O., Head, S., Mondala, T., Scanlan, C., Huflejt, M.E., Alvarez, R., Bryan,<br />
M.C., Fazio, F., Calarese, D., Stevens, J., Razi, N., Stevens, D.J., Skehel, J.J.,<br />
van Die, I., Burton, D.R., Wilson, I.A., Cummings, R., Bovin, N., Wong, C.H.,<br />
Paulson, J.C. Printed covalent glycan array for ligand profiling of diverse glycan<br />
binding proteins. Proc. Natl. Acad. Sci. U. S. A. 101:17033, 2004.<br />
Bryan, M.C., Fazio, F., Lee, H.K., Huang, C.Y., Chang, A., Best, M.D., Calarese,<br />
D.A., Blixt, O., Paulson, J.C., Burton, D., Wilson, I.A., Wong, C.-H. Covalent display<br />
of oligosaccharide arrays in microtiter plates. J. Am. Chem. Soc. 126:8640, 2004.<br />
Canaves, J.M., Page, R., Wilson, I.A., Stevens, R.C. Protein biophysical properties<br />
that correlate with crystallization success in <strong>The</strong>rmotoga maritima: maximum clustering<br />
strategy for structural genomics. J. Mol. Biol. 344:977, 2004.<br />
Cardoso, R.M., Zwick, M.B., Stanfield, R.L., Kunert, R., Binley, J.M., Katinger, H.,<br />
Burton, D.R., Wilson, I.A. Broadly neutralizing anti-HIV antibody 4E10 recognizes<br />
a helical conformation of a highly conserved fusion-associated motif in gp41.<br />
Immunity 22:163, 2005.<br />
Crispin, M.D., Ritchie, G.E., Critchley, A.J., Morgan, B.P., Wilson, I.A., Dwek, R.A., Sim,<br />
R.B., Rudd, P.M. Monoglucosylated glycans in the secreted human complement component<br />
C3: implications for protein biosynthesis and structure. FEBS Lett. 566:270, 2004.<br />
Debler, E.W., Ito, S., Seebeck, F.P., Heine, A., Hilvert, D., Wilson, I.A. Structural<br />
origins of efficient proton abstraction from carbon by a catalytic antibody. Proc.<br />
Natl. Acad. Sci. U. S. A. 102:4984, 2005.<br />
Foss, T.R., Kelker, M.S., Wiseman, R.L., Wilson, I.A., Kelly, J.W. Kinetic stabilization<br />
of the native state by protein engineering: implications for inhibition of transthyretin<br />
amyloidogenesis. J. Mol. Biol. 347:841, 2005.<br />
Han, G.W., Schwarzenbacher, R., Page, R., et al. Crystal structure of an alanineglyoxylate<br />
aminotransferase from Anabaena sp at 1.70 Å resolution reveals a noncovalently<br />
linked PLP cofactor. Proteins 58:971, 2005.<br />
Hava, D.L., Brigl, M., van den Elzen, P., Zajonc, D.M., Wilson, I.A., Brenner,<br />
M.B. CD1 assembly and the formation of CD1-antigen complexes. Curr. Opin.<br />
Immunol. 17:88, 2005.<br />
Heine, A., Canaves, J.M., von Delft, F., et al. Crystal structure of O-acetylserine<br />
sulfhydrylase (TM0665) from <strong>The</strong>rmotoga maritima at 1.8 Å resolution. Proteins<br />
56:387, 2004.<br />
Heine, A., Luz, J.G., Wong, C.H., Wilson, I.A. Analysis of the class I aldolase<br />
binding site architecture based on the crystal structure of 2-deoxyribose-5-phosphate<br />
aldolase at 0.99 Å resolution. J. Mol. Biol. 343:1019, 2004.<br />
Jaroszewski, L., Schwarzenbacher, R., von Delft, F., et al. Crystal structure of a<br />
novel manganese-containing cupin (TM1459) from <strong>The</strong>rmotoga maritima at 1.65 Å<br />
resolution. Proteins 56:611, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Kelker, M.S., Debler, E.W., Wilson, I.A. Crystal structure of mouse triggering<br />
receptor expressed on myeloid cells 1 (TREM-1) at 1.76 Å. J. Mol. Biol.<br />
344:1175, 2004.<br />
Kelker, M.S., Foss, T.R., Peti, W., Teyton, L., Kelly, J.W., Wüthrich, K., Wilson,<br />
I.A. Crystal structure of human triggering receptor expressed on myeloid cells 1<br />
(TREM-1) at 1.47 Å. J. Mol. Biol. 342:1237, 2004.<br />
Larsen, N.A., de Prada, P., Deng, S.X., Mittal, A., Braskett, M., Zhu, X., Wilson,<br />
I.A., Landry, D.W. Crystallographic and biochemical analysis of cocaine-degrading<br />
antibody 15A10. Biochemistry 43:8067, 2004.<br />
Levin, I., Miller, M.D., Schwarzenbacher, R., et al. Crystal structure of an indigoidine<br />
synthase A (IndA)-like protein (TM1464) from <strong>The</strong>rmotoga maritima at 1.90 Å<br />
resolution reveals a new fold. Proteins 59:864, 2005.<br />
Levin, I., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of a putative<br />
NADPH-dependent oxidoreductase (GI: 18204011) from mouse at 2.10 Å resolution.<br />
Proteins 56:629, 2004.<br />
Levin, I., Schwarzenbacher, R., Page, R., et al. Crystal structure of a PIN (PilT<br />
N-terminus) domain (AF0591) from Archaeoglobus fulgidus at 1.90 Å resolution.<br />
Proteins 56:404, 2004.<br />
Li, C., Xu, L., Wolan, D.W., Wilson, I.A., Olson, A.J. Virtual screening of human<br />
5-aminoimidazole-4-carboxamide ribonucleotide transformylase against the NCI<br />
diversity set by use of AutoDock to identify novel nonfolate inhibitors. J. Med.<br />
Chem. 47:6681, 2004.<br />
Mathews, I., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of<br />
S-adenosylmethionine:tRNA ribosyltransferase-isomerase (QueA) from <strong>The</strong>rmotoga<br />
maritima at 2.0 Å resolution reveals a new fold. Proteins 59:869, 2005.<br />
McMullan, D., Schwarzenbacher, R., Hodgson, K.O., et al. Crystal structure of a<br />
novel <strong>The</strong>rmotoga maritima enzyme (TM1112) from the cupin family at 1.83 Å<br />
resolution. Proteins 56:615, 2004.<br />
Miller, M.D., Schwarzenbacher, R., von Delft, F., et al. Crystal structure of a tandem<br />
cystathionine-β-synthase (CBS) domain protein (TM0935) from <strong>The</strong>rmotoga<br />
maritima at 1.87 Å resolution. Proteins 57:213, 2004.<br />
Page, R., Peti, W., Wilson, I.A., Stevens, R.C., Wüthrich, K. NMR screening and<br />
crystal quality of bacterially expressed prokaryotic and eukaryotic proteins in a<br />
structural genomics pipeline. Proc. Natl. Acad. Sci. U. S. A. 102:1901, 2005.<br />
Pantophlet, R., Wilson, I.A., Burton, D.R. Improved design of an antigen with<br />
enhanced specificity for the broadly HIV-neutralizing antibody b12. Protein Eng.<br />
Des. Sel. 17:749, 2004.<br />
Reiser, J.B., Teyton, L., Wilson, I.A. Crystal structure of the Drosophila peptidoglycan<br />
recognition protein (PGRP)-SA at 1.56 Å resolution. J. Mol. Biol. 340:909, 2004.<br />
Santelli, E., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of a glycerophosphodiester<br />
phosphodiesterase (GDPD) from <strong>The</strong>rmotoga maritima (TM1621)<br />
at 1.60 Å resolution. Proteins 56:167, 2004.<br />
Schwarzenbacher, R., Jaroszewski, L., von Delft, F., et al. Crystal structure of an<br />
aspartate aminotransferase (TM1255) from <strong>The</strong>rmotoga maritima at 1.90 Å resolution.<br />
Proteins 55:759, 2004.<br />
Schwarzenbacher, R., Jaroszewski, L., von Delft, F., et al. Crystal structure of a<br />
type II quinolic acid phosphoribosyltransferase (TM1645) from <strong>The</strong>rmotoga maritima<br />
at 2.50 Å resolution. Proteins 55:768, 2004.<br />
Schwarzenbacher, R., von Delft, F., Jaroszewski, L., et al. Crystal structure of a<br />
putative oxalate decarboxylase (TM1287) from <strong>The</strong>rmotoga maritima at 1.95 Å<br />
resolution. Proteins 56:392, 2004.<br />
Spraggon, G., Pantazatos, D., Klock, H.E., Wilson, I.A., Woods, V.L., Jr., Lesley,<br />
S.A. On the use of DXMS to produce more crystallizable proteins: structures of the<br />
T maritima proteins TM0160 and TM1171 [published correction appears in Protein<br />
Sci. 14:1688, 2005]. Protein Sci. 13:3187, 2004.<br />
Spraggon, G., Schwarzenbacher, R., Kreusch, A., et al. Crystal structure of a methionine<br />
aminopeptidase (TM1478) from <strong>The</strong>rmotoga maritima at 1.9 Å resolution.<br />
Proteins 56:396, 2004.
Spraggon, G., Schwarzenbacher, R., Kreusch, A., et al. Crystal structure of a Udpn-acetylmuramate-alanine<br />
ligase MurC (TM0231) from <strong>The</strong>rmotoga maritima at<br />
2.3 Å resolution. Proteins 55:1078, 2004.<br />
Stanfield, R.L., Dooley, H., Flajnik, M.F., Wilson, I.A. Crystal structure of a shark single-domain<br />
antibody V region in complex with lysozyme. Science 305:1770, 2004.<br />
Wang, X., Matteson, J., An, Y., Moyer, B., Yoo, J.S., Bannykh, S., Wilson, I.A., Riordan,<br />
J.R., Balch, W.E. COPII-dependent export of cystic fibrosis transmembrane conductance<br />
regulator from the ER uses a di-acidic exit code. J. Cell Biol. 167:65, 2004.<br />
Xu, L., Li, C., Olson, A.J., Wilson, I.A. Crystal structure of avian aminoimidazole-<br />
4-carboxamide ribonucleotide transformylase in complex with a novel non-folate<br />
inhibitor identified by virtual ligand screening. J. Biol. Chem. 279:50555, 2004.<br />
Xu, Q., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of a formiminotetrahydrofolate<br />
cyclodeaminase (TM1560) from <strong>The</strong>rmotoga maritima at 2.80 Å<br />
resolution reveals a new fold. Proteins 58:976, 2005.<br />
Xu, Q., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of a ribose-5phosphate<br />
isomerase RpiB (TM1080) from <strong>The</strong>rmotoga maritima at 1.90 Å resolution.<br />
Proteins 56:171, 2004.<br />
Xu, Q., Schwarzenbacher, R., Page, R., et al. Crystal structure of an allantoicase<br />
(YIR029W) from Saccharomyces cerevisiae at 2.4 Å resolution. Proteins 56:619, 2004.<br />
Zajonc, D.M., Crispin, M.D., Bowden, T.A., Young, D.C., Cheng, T.Y., Hu, J., Costello,<br />
C.E., Rudd, P.M., Dwek, R.A., Miller, M.J., Brenner, M.B., Moody, D.B., Wilson, I.A.<br />
<strong>Molecular</strong> mechanism of lipopeptide presentation by CD1a. Immunity 22:209, 2005.<br />
Zhu, X., Tanaka, F., Hu, Y., Heine, A., Fuller, R., Zhong, G., Olson, A.J., Lerner,<br />
R.A., Barbas, C.F. III, Wilson, I.A. <strong>The</strong> origin of enantioselectivity in aldolase antibodies:<br />
crystal structure, site-directed mutagenesis, and computational analysis. J.<br />
Mol. Biol. 343:1269, 2004.<br />
Structure and Function of<br />
Proteins as <strong>Molecular</strong> Machines<br />
E.D. Getzoff, M. Aoyagi, A.S. Arvai, D.P. Barondeau,<br />
R.M. Brudler, T. Cross, E.D. Garcin, C. Hitomi, K. Hitomi,<br />
L. Holden, C.J. Kassmann, I. Li, M.E. Pique, M.E. Stroupe,<br />
J.L. Tubbs, T.I. Wood<br />
Our goals are to understand how proteins function<br />
as molecular machines. We use structural,<br />
molecular, and computational biology to study<br />
proteins of biological and biomedical interest, especially<br />
proteins that work synergistically with coupled<br />
chromophores, metal ions, or other cofactors.<br />
PHOTOACTIVE PROTEINS AND CIRCADIAN CLOCKS<br />
To understand in atomic detail how proteins translate<br />
sunlight into defined conformational changes for<br />
biological functions, we are exploring the reaction mechanisms<br />
of the blue-light receptors photoactive yellow<br />
protein (PYP), photolyase, and cryptochrome. PYP is<br />
the prototype for the Per-Arnt-Sim domain proteins of<br />
circadian clocks, whereas proteins of the photolyase<br />
and cryptochrome family catalyze DNA repair or act in<br />
circadian clocks. To understand the protein photocycle<br />
(Fig. 1), we combined our ultra-high-resolution and<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 167<br />
Fig. 1. Changes in the flexibility and mobility of PYP during its<br />
light cycle revealed by mapping the results of hydrogen-deuterium<br />
exchange mass spectrometry analyses (gray-scale shading) onto the<br />
x-ray crystallographic structure (ribbon showing overall protein fold).<br />
In the signaling state, regions of the protein including the N terminus<br />
are released for protein-protein interactions.<br />
time-resolved crystallographic structures of the dark<br />
state and 2 photocycle intermediates of PYP with sitedirected<br />
mutagenesis; ultraviolet-visible spectroscopy;<br />
time-resolved Fourier transform infrared spectroscopy;<br />
deuterium hydrogen exchange mass spectrometry, in<br />
collaboration with V. Woods, University of California,<br />
San Diego; and quantum mechanical and electrostatic<br />
computational methods, in collaboration with L. Noodleman,<br />
Department of <strong>Molecular</strong> <strong>Biology</strong>.<br />
Cryptochrome flavoproteins are homologs of lightdependent<br />
DNA repair photolyases that function as<br />
blue-light receptors in plants and as components of<br />
circadian clocks in animals. We determined the first<br />
crystallographic structure of a cryptochrome, which<br />
revealed commonalities with photolyases in DNA binding<br />
and redox-dependent function but showed differences<br />
in active-site and interaction surface features. New<br />
structures of photolyases from 2 other branches of the<br />
photolyase/cryptochrome family that repair cyclobutane<br />
pyrimidine dimers and photoproducts helped us decipher<br />
the cryptic structure, function, and evolutionary<br />
relationships of these fascinating redox-active proteins.<br />
A simple, but functional, circadian clock can be<br />
reconstituted in vitro from the 3 cyanobacterial proteins<br />
KaiA, KaiB, and KaiC alone. Yet, the structure<br />
and dynamics of the functional assembly of these proteins<br />
are not understood. Our crystallographic, dynamical<br />
light scattering and small-angle x-ray scattering<br />
studies revealed that KaiB self-assembles into a tetramer<br />
(Fig. 2). We are also studying clock proteins with<br />
PYP-like and Per-Arnt-Sim domains that bind to mammalian<br />
cryptochromes. Our goal is to determine the<br />
detailed chemistry and atomic structure of these pro-
168 MOLECULAR BIOLOGY 2005<br />
Fig. 2. <strong>The</strong> tetrameric assembly of the cyanobacterial circadian<br />
clock protein KaiB revealed by small-angle x-ray scattering (experimentally<br />
determined shape) and x-ray crystallography (ribbon showing<br />
protein fold).<br />
teins, define their mechanisms of action and interaction,<br />
and use our results to understand and regulate<br />
biological function.<br />
METALLOENZYME STRUCTURE AND FUNCTION<br />
Superoxide dismutases (SODs) act as master regulators<br />
of intracellular free radicals and reactive oxygen<br />
species by transforming superoxide to oxygen and<br />
hydrogen peroxide. Novel nickel SODs assemble into<br />
hollow spheres composed of six 4-helix bundle subunits.<br />
<strong>The</strong> 9 N-terminal residues fold into a unique<br />
nickel hook motif that shows promise as a detectable<br />
metal ion–binding tag in protein purification and structure<br />
determination.<br />
Our crystallographic structures of classic copper-zinc<br />
SODs from mammals, bacterial symbionts, and pathogens<br />
revealed striking differences in the enzyme assembly<br />
and in the loops flanking the active-site channel,<br />
despite the shared β-barrel subunit fold, catalytic<br />
metal center, and electrostatic enhancement of activity.<br />
With J. Tainer, Department of <strong>Molecular</strong> <strong>Biology</strong>,<br />
we determined structures of mutant human SODs<br />
found in patients with the disease amyotrophic lateral<br />
sclerosis (Lou Gehrig disease), and proposed a hypothesis<br />
for how single-site mutations cause this fatal neurodegenerative<br />
disease.<br />
To synthesize nitric oxide, a cellular signal and defensive<br />
cytotoxin, nitric oxide synthases (NOSs) require calmodulin-orchestrated<br />
interactions between their catalytic,<br />
heme-containing oxygenase module and their electronsupplying<br />
reductase module. Crystallographic structures<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
of wild-type and mutant NOS oxygenase dimers with<br />
substrate, intermediate, inhibitors, cofactors, and cofactor<br />
analogs, determined in collaboration with D. Stuehr,<br />
the Cleveland Clinic, Cleveland, Ohio, and J. Tainer,<br />
provided insights into the catalytic mechanism and<br />
dimer stability.<br />
Our structure-based drug design projects are aimed<br />
at selectively inhibiting inducible NOS, to prevent inflammatory<br />
disorders, or neuronal NOS, to prevent migraines,<br />
while maintaining blood pressure regulation by endothelial<br />
NOS. We integrated biochemical data with our<br />
structures of NOS oxygenase, NOS reductase, and calmodulin<br />
in complex with peptides derived from NOS<br />
to propose a model for the assembled holoenzyme that<br />
provides a moving-domain mechanism for electron flow<br />
from NADPH through 2 flavin cofactors to the heme.<br />
Our structure of the NOS reductase provides new<br />
insights into the complex regulatory mechanisms of<br />
this enzyme family.<br />
METALLOPROTEIN DESIGN<br />
An ultimate goal for protein engineers is to design<br />
and construct new protein variants with desirable catalytic<br />
or physical properties. As members of the <strong>Scripps</strong><br />
<strong>Research</strong> Metalloprotein Structure and Design Group,<br />
we are testing our understanding of the affinity, selectivity,<br />
and activity of metal ions by transplanting metal<br />
sites from structurally characterized metalloproteins into<br />
new protein scaffolds. To aid our design efforts, we have<br />
organized quantitative information and interactive viewing<br />
of protein metal sites at the Metalloprotein Database<br />
and Browser (available at http://metallo.scripps.edu).<br />
For green fluorescent protein and the homologous<br />
red fluorescent protein, we designed, constructed, and<br />
characterized metal-ion biosensors in which binding of<br />
metal ions is signaled by changes in the spectroscopic<br />
properties of the naturally occurring fluorophores. <strong>The</strong><br />
green fluorescent protein scaffold provides advantages<br />
over existing probes by allowing optimization with random<br />
mutagenesis, noninvasive expression in living cells,<br />
and targeting to specific cellular locations. By completing<br />
the metalloprotein design cycle from prediction to<br />
highly accurate structures, we can rigorously evaluate<br />
and improve our algorithms for the design of metal sites.<br />
Our related structural studies of green and red fluorescent<br />
protein intermediates in chromophore cyclization<br />
and oxidation provide a novel mechanism for the spontaneous<br />
synthesis of these tripeptide fluorophores within<br />
the protein scaffold.
PUBLICATIONS<br />
Barondeau, D.P., Getzoff, E.D. Structural insights into protein-metal ion partnerships.<br />
Curr. Opin. Struct. Biol. 14:765, 2004.<br />
Barondeau, D.P., Kassmann, C.J., Tainer, J.A., Getzoff, E.D. Understanding GFP<br />
chromophore biosynthesis: controlling backbone cyclization and modifying posttranslational<br />
chemistry. Biochemistry 44:1960, 2005.<br />
Dunn, A.R., Belliston-Bittner, W., Winkler, J.R., Getzoff, E.D., Stuehr, D.J., Gray,<br />
H.B. Luminescent ruthenium(II)- and rhenium(I)-diimine wires bind nitric oxide<br />
synthase. J. Am. Chem. Soc. 127:5169, 2005.<br />
Hitomi, K., Oyama, T., Han, S., Arvai, A.S., Getzoff, E.D. Tetrameric architecture<br />
of the circadian clock protein KaiB: a novel interface for intermolecular interactions<br />
and its impact on the circadian rhythm. J. Biol. Chem. 280:19127, 2005.<br />
Stroupe, M.E., Getzoff, E.D. <strong>The</strong> role of siroheme in sulfite and nitrite reductases.<br />
In: Tetrapyrroles: <strong>The</strong>ir Birth, Life and Death. Warren, M.J., Smith, A. (Eds.). Landes<br />
Bioscience, Georgetown, Tex, in press.<br />
Stuehr, D.J., Wei, C.C., Santolini, J., Wang, Z., Aoyagi, M., Getzoff, E.D. Radical<br />
reactions of nitric oxide synthases. In: Free Radicals: Enzymology, Signaling, and<br />
Disease. Cooper, C.E., Wilson, M.T., Darley-Usmar, V.H. (Eds.). Portland Press,<br />
London, 2004, p. 39. Biochemical Society Symposia, Vol. 71.<br />
Tiso, M., Konas, D.W., Panda, K., Garcin, E.D., Sharma, M., Getzoff, E.D., Stuehr, D.J.<br />
C-terminal tail residue ARG1400 enables NADPH to regulate electron transfer in<br />
neuronal nitric oxide synthase. J. Biol. Chem., in press.<br />
Tubbs, J.L., Tainer, J.A., Getzoff, E.D. Crystallographic structures of Discosoma<br />
red fluorescent protein with immature and mature chromophores: linking peptide<br />
bond trans-cis isomerization and acylimine formation in chromophore maturation.<br />
Biochemistry 44:9833, 2005.<br />
Vevodova, J., Graham, R.M., Raux, E., Schubert, H.L., Roper, D.I., Brindley,<br />
A.A., Scott, A.I., Roessner, C.A., Stamford, N.P., Stroupe, M.E., Getzoff, E.D.,<br />
Warren, M.J., Wilson, K.S. Structure/function studies on an S-adenosyl-L-methionine-dependent<br />
uroporphyrinogen III C methyltransferase (SUMT), a key regulatory<br />
enzyme of tetrapyrrole biosynthesis. J. Mol. Biol. 344:419, 2004.<br />
Wei, C.C., Wang, Z.Q., Durra, D., Hemann, C., Hille, R., Garcin, E.D., Getzoff,<br />
E.D., Stuehr, D.J. <strong>The</strong> three nitric-oxide synthases differ in their kinetics of tetrahydrobiopterin<br />
radical formation, heme-dioxy reduction, and arginine hydroxylation. J.<br />
Biol. Chem. 280:8929, 2005.<br />
Structural <strong>Molecular</strong> <strong>Biology</strong> of<br />
Interactions and Protein Design<br />
J.A. Tainer, A.S. Arvai, D.P. Barondeau, M. Bjoras,<br />
B.R. Chapados, L. Craig, T.H. Cross, D.S. Daniels, G. DiVita,<br />
L. Fan, C. Hitomi, K. Hitomi, J.L. Huffman, C.J. Kassmann,<br />
I. Li, G. Moncalian, M.E. Pique, D.S. Shin, O. Sundheim,<br />
R.S. Williams, T.I. Wood, A. Yamagata<br />
Our goals are to bridge the gap between the vastly<br />
improved tools and insights for structural cell<br />
biology at the molecular level and the applications<br />
of these advances for the molecular-based understanding<br />
of and eventual intervention in human diseases.<br />
Thus, our primary concern is the application of structural<br />
biology to fundamental questions of molecular and<br />
cellular biology relevant to human disease. Currently,<br />
we are investigating fundamental processes and principles<br />
of DNA repair, control of reactive oxygen species,<br />
control of the cell cycle, and pathogenesis. We think<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 169<br />
these processes have networked connections and common<br />
themes in terms of structural mechanisms and<br />
controls and medical implications. In general, our<br />
structural determination and design work involves<br />
hypothesis-driven studies; we focus on high-resolution<br />
structural analyses, functionally important conformational<br />
changes, and macromolecular interactions,<br />
including design of inhibitors and dynamic assemblies<br />
that act as macromolecular machines to control the<br />
fundamental processes of cell biology.<br />
To accomplish our basic research, we use protein<br />
crystallography, solution x-ray scattering, fluorescence,<br />
biochemistry, mutagenesis, and protein expression. Our<br />
experimental work is complemented by efforts to develop<br />
new methods, particularly in structural analysis, protein<br />
and drug design, and the merging of crystal structures<br />
with x-ray solution structures and electron microscopy.<br />
<strong>The</strong>se new experimental integrations involve the use of<br />
synchrotron radiation to bridge the size and resolution<br />
gap between high-resolution macromolecular structures<br />
and the multiprotein macromolecular machines and<br />
reversible interactions in the cell. For protein design,<br />
we have an active collaboration with E. Getzoff, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>, to understand and control<br />
the formation of self-synthesizing chromophores in green<br />
fluorescent protein and its homologs. We are increasingly<br />
interested in structure-based design of inhibitors<br />
that are relevant to the development of novel therapeutic<br />
agents and inhibitors that chemically knock out or block<br />
gene function to complement genes that are knocked<br />
out by removing the DNA. <strong>The</strong> synergy between basic<br />
research and advances in techniques is allowing us to<br />
contribute to the basic understanding and treatment of<br />
degenerative and infectious diseases and cancer.<br />
SUPEROXIDE DISMUTASES<br />
Superoxide dismutases (SODs) are master regulators<br />
for reactive oxygen species involved in injury, pathogenesis,<br />
aging, and degenerative diseases. In basic<br />
research on these enzymes, we are characterizing the<br />
activity of the mitochondrial SODs. We discovered a<br />
novel nickel ion SOD and characterized its hexameric<br />
assembly. For the human cytoplasmic copper, zinc SOD,<br />
we examined how single-site mutations cause the neurodegenerative<br />
Lou Gehrig disease or familial amyotrophic<br />
lateral sclerosis (FALS). We found that point mutations<br />
destabilize the copper, zinc SOD dimer and dramatically<br />
increase its propensity to aggregate and form filaments<br />
that resemble those seen in motor neurons of<br />
patients with FALS. <strong>The</strong>se findings provide a molecu-
170 MOLECULAR BIOLOGY 2005<br />
lar basis for the notion that a single FALS disease phenotype<br />
arises from diverse point mutations throughout<br />
the protein that reduce the structural integrity of<br />
copper, zinc SOD and lower the energy barrier for fibrous<br />
aggregation. Additionally, our new high-resolution structures<br />
of a related thermophilic copper, zinc SOD showed<br />
a trapped product complex. This novel finding helps<br />
define the enzyme’s mechanism of action and its susceptibility<br />
to inactivation by hydrogen peroxide.<br />
DNA REPAIR<br />
All life requires constant repair of DNA. Structural<br />
and mutational analyses of DNA repair enzymes provide<br />
a framework for understanding the molecular basis<br />
of genetic integrity and the loss of this integrity in cancer<br />
and degenerative diseases. We are interested in how specific<br />
types of damage are detected, how repair enzymes<br />
are coordinated within different pathways, and the<br />
nature and role of conformational change in proteins<br />
and DNA in repair pathways. We use electron microscopy,<br />
x-ray crystallography, small-angle x-ray scattering,<br />
and complementary in vitro and in vivo mutational<br />
analysis to go from enzyme structures to repair pathways<br />
and the coordination of repair with replication<br />
and transcription.<br />
We focus on pathways for DNA base repair, DNA<br />
nick translation in repair and replication (Fig. 1), and<br />
repair of double-stranded breaks. Understanding the<br />
structural chemistry and cell biology of DNA repair is<br />
critical for designing specific inhibitors to increase the<br />
effectiveness of chemotherapy and also for assessing<br />
how DNA repair enzyme polymorphisms may affect<br />
diseases in humans. Currently, we are designing inhibitors<br />
of enzymes that repair alkylated and oxidized guanines.<br />
<strong>The</strong>se enzymes are one of the body’s natural<br />
defenses against DNA damage, but they can also inadvertently<br />
protect cancer cells from chemotherapeutic<br />
agents. For example, the human repair protein O 6 -alkylguanine-DNA<br />
alkyltransferase, which acts in the repair<br />
of alkylated guanines, repairs damaged DNA inside<br />
human cells, and cancer cells can use it to repair DNA<br />
that has been damaged in the course of chemotherapy,<br />
thus making the chemotherapy ineffective.<br />
BACTERIAL PILI<br />
Type IV pili are essential virulence factors for many<br />
gram-negative bacteria, playing key roles in surface<br />
motility, adhesion, formation of microcolonies and biofilms,<br />
natural transformation, and signaling. We have<br />
determined structures for the type IV pilin subunits and<br />
for the assembled pilus fiber. Currently, we are investigating<br />
the type IV pilus assembly system, including the<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 1. Interactions between the complex consisting of flap endonuclease<br />
1 (FEN-1), DNA, and proliferating cell nuclear antigen<br />
(PCNA) and the interface of DNA repair and replication. A, Nicked<br />
DNA is protected and repaired by the sequential activities of DNA<br />
polymerase δ (pol δ) and FEN-1 held to DNA by the "sliding clamp"<br />
PCNA. In the absence of FEN-1, a complex of pol δ and PCNA binds<br />
to and protects the nick (top). FEN-1 initiates nick translation by<br />
binding to PCNA (bottom), recognizing the 3′ DNA flap and cleaving<br />
the 5′ flap, generating a nick translated by 1 nucleotide. B. Structures<br />
of FEN-1 bound to DNA show that FEN-1 recognizes the 3′ flap<br />
in a sequence-independent manner. C, A composite model of the<br />
FEN-1–DNA–PCNA complex suggests how a kinked DNA intermediate<br />
might facilitate sequential activities of FEN-1 and pol δ.<br />
assembly ATPase, the membrane anchor protein interactions,<br />
and the assembled pilus fiber (Fig. 2). Our electron<br />
Fig. 2. A schematic view of the assembly machinery of type IV<br />
pili: the electron cryomicroscopy structure of the pilus of Neisseria<br />
gonorrhoeae (GC); crystal structures of full-length Pseudomonas<br />
aeruginosa (P.a) pilin; BfpC, the binding partner protein to ATPase<br />
from enteropathogenic Escherichia coli; and GspE2, the hexameric<br />
assembly ATPase from Archaeoglobus fulgidus.
microscopy and x-ray structures of protein components<br />
and complexes are helping us understand the architecture<br />
and assembly mechanism as a basis for the design<br />
of antibacterial vaccines and therapeutic agents.<br />
PUBLICATIONS<br />
Ayala, I., Perry, J.P., Szczepanski, J., Tainer, J.A., Vala, M.T., Nick, H.S., Silverman,<br />
D.N. Hydrogen bonding in human manganese superoxide dismutase containing<br />
3-fluorotyrosine. Biophys. J., in press.<br />
Barondeau, D.P., Kassmann, C.J., Tainer, J.A., Getzoff, E.D. Understanding GFP<br />
chromophore biosynthesis: controlling backbone cyclization and modifying posttranslational<br />
chemistry. Biochemistry 44:1960, 2005.<br />
Crowther, L.J., Yamagata, A., Craig, L., Tainer, J.A., Donnenberg, M.S. <strong>The</strong> ATPase<br />
activity of BfpD is greatly enhanced by zinc and allosteric interactions with other<br />
Bfp proteins. J. Biol. Chem. 280:24839, 2005.<br />
de Jager, M., Trujillo, K.M., Sung, P., Hopfner, K.P., Carney, J.P., Tainer, J.A.,<br />
Connelly, J.C., Leach, D.R., Kanaar, R., Wyman, C. Differential arrangements of<br />
conserved building blocks among homologs of the Rad50/Mre11 DNA repair protein<br />
complex. J. Mol. Biol. 339:937, 2004.<br />
Garcin, E.D., Bruns, C.M., Lloyd, S.J., Hosfield, D.J., Tiso, M., Gachhui, R.,<br />
Stuehr, D.J., Tainer, J.A., Getzoff, E.D. Structural basis for isozyme-specific regulation<br />
of electron transfer in nitric-oxide synthase. J. Biol. Chem. 279:37918, 2004.<br />
Hendrickson, E.A., Huffman, J.L., Tainer, J.A. Structural aspects of Ku and the<br />
DNA-dependent protein kinase complex. In: DNA Damage Recognition. Seide, W.,<br />
Kow, Y.W., Doetsch, P.W. (Eds.). Taylor & Francis, New York, 2005, p. 629.<br />
Huffman, J.L., Sundheim, O., Tainer, J.A. DNA base damage recognition and<br />
removal: new twists and grooves. Mutat. Res. 577:55, 2005.<br />
Huffman, J.L., Sundheim, O., Tainer, J.A. Structural features of DNA glycosylases<br />
and AP endonucleases. In: DNA Damage Recognition. Seide, W., Kow, Y.W.,<br />
Doetsch, P.W. (Eds.). Taylor & Francis, New York, 2005, p. 299.<br />
Manuel, R.C., Hitomi, K., Arvai, A.S., House, P.G., Kurtz, A.J., Dodson, M.L., McCullough,<br />
A.K., Tainer, J.A., Lloyd, R.S. Reaction intermediates in the catalytic mechanism<br />
of Escherichia coli MutY DNA glycosylase. J. Biol. Chem. 279:46930, 2004.<br />
Putnam, C.D.. Tainer, J.A. Protein mimicry of DNA and pathway regulation. DNA<br />
Repair (Amst.), in press.<br />
Sarker, A.H., Tsutakawa, S.E., Kostek, S., Ng, C., Shin, D.S., Peris, M., Campeau, E.,<br />
Tainer, J.A., Nogales, E., Cooper, P.K. Recognition of RNA polymerase II and transcription<br />
bubbles by XPG, CSB, and TFIIH: insights for transcription-coupled repair<br />
and Cockayne syndrome. Mol. Cell 20:187, 2005.<br />
Simeoni, F., Arvai, A., Bello, P., Gondeau, C., Hopfner, K.P., Neyroz, P., Heitz, F.,<br />
Tainer, J., Divita, G. Biochemical characterization and crystal structure of a Dim1<br />
family associated protein: Dim2. Biochemistry 44:11997, 2005.<br />
Tubbs, J.L., Tainer, J.A., Getzoff, E.D. Crystallographic structures of Discosoma<br />
red fluorescent protein with immature and mature chromophores: linking peptide<br />
bond trans-cis isomerization and acylimine formation in chromophore maturation.<br />
Biochemistry 44:9833, 2005.<br />
Williams, R.S., Tainer, J.A. A nanomachine for making ends meet: MRN is a flexing<br />
scaffold for the repair of DNA double-strand breaks. Mol. Cell 19:724, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 171<br />
Structural <strong>Biology</strong> of Integral<br />
Membrane Proteins<br />
G. Chang, A. Chen, Y. Chen, X. He, O. Pornillos, C.R. Reyes,<br />
P. Szewczk, A. Ward, S. Wada, Y. Yin<br />
X-ray crystallography of integral membrane proteins<br />
is an exciting and rapidly growing frontier in<br />
molecular structural biology. We are interested in<br />
5 areas: (1) the molecular structural basis for lipid and<br />
drug transport across the cell membrane by multidrugresistance<br />
(MDR) transporters, (2) the high-resolution<br />
structure of yeast and mammalian MDR transporters,<br />
(3) signal transduction by receptors, (4) discovery and<br />
the structurally based design of potent MDR reversal<br />
agents, and (5) the development of an in vitro cell-free<br />
system capable of overproducing integral membrane proteins<br />
suitable for biophysical study. We use several experimental<br />
methods, including detergent/lipid protein<br />
biochemistry, 3-dimensional crystallization of integral<br />
membrane proteins, and x-ray crystallography. We are<br />
developing and using an efficient cell-free membrane protein<br />
expression system in collaboration with T. Kudlicki,<br />
Invitrogen Corporation, Carlsbad, California, for the overexpression<br />
integral membrane proteins for both x-ray<br />
crystallography and nuclear magnetic resonance studies.<br />
We are addressing the molecular basis of MDR, a<br />
significant challenge in the treatment of infectious disease<br />
and cancer. A major cause of MDR in both of these<br />
situations is a battery of drug efflux pumps imbedded<br />
in the cell membrane. Through our structural studies<br />
on MDR transporters, we hope to gain insights into<br />
the mechanics of translocating amphipathic substrates<br />
across the cell membrane and also the rational design<br />
of potent MDR reversal agents.<br />
We are combining chemistry and biology with structure<br />
for the discovery and design of potent MDR reversal<br />
agents for cancer chemotherapy in collaboration with<br />
M.G. Finn, Department of Chemistry; I. Urbatsch, Texas<br />
Tech University Health Sciences Center, Lubbock Texas;<br />
and S. Reutz, Novartis International AG, Basel, Switzerland.<br />
In collaboration with M. Saier, University of California,<br />
San Diego, and Q. Zhang, Department of <strong>Molecular</strong><br />
<strong>Biology</strong>, we are determining the x-ray structures and<br />
mapping the detailed functional components of 3 families<br />
of bacterial MDR transporters that are dominant<br />
in gram-positive pathogens. In another collaboration,<br />
with R.A. Milligan, Department of Cell <strong>Biology</strong>, we are<br />
using electron cryomicroscopy to visualize the low-res-
172 MOLECULAR BIOLOGY 2005<br />
olution structures of our transporters. Through these<br />
united efforts, we will gain a broader understanding of<br />
the structure and function of drug transporters that<br />
cause MDR in cancer and bacterial infection.<br />
Recently, we determined a new structure of the MDR<br />
ATP-binding cassette transporter homolog MsbA in complex<br />
with magnesium, adenosine diphosphate, inorganic<br />
vanadate, and rough-chemotype lipopolysaccharide.<br />
This structure supports a model involving a rigid-body<br />
torque of the 2 transmembrane domains during ATP<br />
hydrolysis and suggests a mechanism by which the<br />
nucleotide-binding domain communicates with the transmembrane<br />
domain. We propose a lipid “flip-flop” mechanism<br />
in which the sugar groups are sequestered in<br />
the chamber while the hydrophobic tails are dragged<br />
through the lipid bilayer (Fig. 1). This posthydrolysis<br />
Fig. 1. Proposed model for sequestering the polar sugar headgroup<br />
of lipopolysaccharide (LPS) in the internal chamber of MsbA (for<br />
clarity, only 1 LPS is shown). A, LPS initially binds to the elbow<br />
helix as modeled onto the closed apo structure. B, Lipid headgroups<br />
modeled to insert into the chamber of the apo closed structure.<br />
C, As the transporter undergoes conformational changes related<br />
to binding and hydrolysis of ATP, the headgroup is “flipped” within<br />
the polar chamber while the LPS hydrocarbon chains are freely exposed<br />
and dragged through the lipid bilayer. Both LPS and MsbA conformations<br />
are modeled. D, LPS is presented to the outer leaflet of the<br />
membrane as observed in this structure. Reprinted with permission<br />
from Reyes, C.L., Chang, G. Science 308:1028, 2005.<br />
structure of MsbA also gives insight into the possible<br />
drug-binding sites for a number of cancer compounds.<br />
We are continuing our x-ray structural studies of the<br />
small MDR transporter EmrE and of other families of<br />
bacterial MDR transporters to better understand the<br />
molecular basis of the drug-proton antiport. <strong>The</strong> x-ray<br />
structures of MsbA and EmrE are excellent models for<br />
drug efflux systems that confer MDR to cancer cells and<br />
infectious microorganisms.<br />
PUBLICATIONS<br />
Ma, C., Chang, G. Crystallography of the integral membrane protein EmrE from<br />
Escherichia coli. Acta Crystallogr. D Biol. Crystallogr. 60:2399, 2004.<br />
Reyes, C.L., Chang, G. Structure of the ABC transporter MsbA in complex with<br />
ADP•vanadate and lipopolysaccharide. Science 308:1028, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Structure and Function of<br />
Membrane-Bound Enzymes<br />
C.D. Stout, H. Heaslet, M. Yamaguchi, V. Sundaresan,<br />
L. Hunsicker-Wang, J. Chartron<br />
One focus of our research is the structure and<br />
function of transhydrogenase, an essential<br />
enzyme of respiration in mitochondria and bacteria.<br />
Transhydrogenase couples proton translocation<br />
across the membrane with hydride transfer between<br />
cofactors bound to soluble domains. We are determining<br />
the structure of the enzyme in its membrane-bound<br />
conformation and are studying the structures of the<br />
soluble domains. For studies of enzyme function, we<br />
are using biochemical methods and mutagenesis. Structural<br />
studies entail x-ray crystallography, electron microscopy<br />
studies done in collaboration with M. Yeager and<br />
B. Carragher, Department of Cell <strong>Biology</strong>, and nuclear<br />
magnetic resonance experiments done in collaboration<br />
with J. Dyson, Department of <strong>Molecular</strong> <strong>Biology</strong>.<br />
In collaboration with E.F. Johnson, Department of<br />
<strong>Molecular</strong> <strong>Biology</strong>, and J.R. Halpert, University of Texas<br />
Medical Branch, Galveston, Texas, we are studying highresolution<br />
crystal structures of mammalian cytochrome<br />
P450s. <strong>The</strong> P450s are monooxygenases involved in<br />
the biosynthesis and oxidation of lipophilic molecules,<br />
and they specifically metabolize a wide range of exogenous<br />
compounds and drugs. More than 60 genes for<br />
P450s occur in the human genome. We are studying<br />
high-resolution structures and drug-bound complexes<br />
of the human P450s 2C8, 2C9, 2A6, 3A4, and 1A2<br />
and the rabbit P450s 2B4 and 2C5.<br />
In collaboration with J.A. Fee, Department of <strong>Molecular</strong><br />
<strong>Biology</strong>, we are studying the structure and mechanism<br />
of cytochrome ba 3 oxidase, the terminal enzyme<br />
of respiration responsible for the reduction of molecular<br />
oxygen to water. <strong>The</strong> high-resolution crystal structure<br />
of the enzyme from a thermophilic bacterium has<br />
been determined (Fig. 1). Crystallographic experiments,<br />
in combination with mutagenesis and spectroscopy, are<br />
being used to capture intermediates in the reaction<br />
cycle and to define the pathways of proton translocation<br />
to and from the active site within the membrane.<br />
In parallel with these studies, we are developing<br />
the application of nanodiscs for biophysical studies of<br />
integral membrane proteins. <strong>The</strong>se experiments are<br />
being done in collaboration with S.G. Sligar, University<br />
of Illinois, Urbana, Illinois, and M. Yeager, Department
Fig. 1. Crystal structure of the integral membrane protein cytochrome<br />
ba3 oxidase from the thermophilic bacterium <strong>The</strong>rmus<br />
thermophilus. Cytochrome oxidase is responsible for the reduction<br />
of oxygen to water during respiration in all higher organisms.<br />
of Cell <strong>Biology</strong>. Nanodiscs are water-soluble particles<br />
that consist of 2 copies of an engineered construct of<br />
human apolipoprotein A-I (~200 amino acids) encircling<br />
a patch of bilayer containing the approximately 160<br />
molecules of dimyristoyl-sn-glycero-3-phosphocholine<br />
or other phospholipids. Integral membrane proteins<br />
can be inserted into these particles by spontaneous<br />
self-assembly, and to date we have incorporated both<br />
cytochrome ba 3 oxidase and transhydrogenase.<br />
Additional research projects involve collaboration<br />
with other faculty members at <strong>Scripps</strong> <strong>Research</strong>. <strong>The</strong>se<br />
projects include studies of iron-sulfur and electron transfer<br />
proteins, in collaboration with J.A. Fee and L. Noodleman,<br />
Department of <strong>Molecular</strong> <strong>Biology</strong>; RNA-protein<br />
complexes, with J.R. Williamson, Department of <strong>Molecular</strong><br />
<strong>Biology</strong>; synthetic, self-assembling peptides, with<br />
M.R. Ghadiri, Department of Chemistry; and HIV protease<br />
inhibitor complexes, with A. Olson, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>, and B.E. Torbett, Department of<br />
<strong>Molecular</strong> and Experimental Medicine.<br />
PUBLICATIONS<br />
Carroll, K.S., Gao, H., Chen, H., Stout, C.D., Leary, J.A., Bertozzi, C.R. A conserved<br />
mechanism for sulfonucleotide reduction. PloS Biol. 3:e250, 2005.<br />
Fee, J.A., Todaro, T.R., Luna, E., Sanders, D., Hunsicker-Wang, L.M., Patel, K.M.,<br />
Bren, K.L., Gomez-Moran, E., Hill, M.G., Ai, J., Loehr, T.M., Oertling, W.A.,<br />
Williams, P.A., Stout, C.D., McRee, D., Pastuszyn, A. Cytochrome rC 552 , formed<br />
during expression of the truncated, <strong>The</strong>rmus thermophilus cytochrome c 552 gene<br />
in the cytoplasm of Escherichia coli, reacts spontaneously to form protein-bound,<br />
2-formyl-4-vinyl (Spirographis) heme. Biochemistry 43:12162, 2004.<br />
Hays, A.-M., Dunn, A.R., Chiu, R., Gray, H.B., Stout, C.D., Goodin, D.B. Conformational<br />
states of cytochrome P450cam revealed by trapping of synthetic wires. J.<br />
Mol. Biol. 344:455, 2004.<br />
Horne, W.S., Yadav, M.K., Stout, C.D., Ghadiri, M.R. Heterocyclic peptide backbone<br />
modifications in an α-helical coiled coil. J. Am. Chem. Soc. 126:15366, 2004.<br />
Hunsicker-Wang, L.M., Pacoma, R.L., Chen, Y., Fee, J.A., Stout, C.D. A novel<br />
cryoprotection scheme for enhancing diffraction of crystals of recombinant cytochrome<br />
ba 3 oxidase from <strong>The</strong>rmus thermophilus. Acta Crystallogr. D Biol. Crystallogr.<br />
61:340, 2005.<br />
Stout, C.D. Cytochrome P450 conformational diversity. Structure (Camb.)<br />
12:1921, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Sundaresan, V., Chartron, J., Yamaguchi, M., Stout, C.D. Conformational diversity<br />
in NAD(H) and interacting transhydrogenase nicotinamide nucleotide binding<br />
domains. J. Mol. Biol. 346:617, 2005.<br />
Wester, M.R., Yano, J.K., Schoch, G.A., Yang, C., Griffin, K.J., Stout, C.D., Johnson,<br />
E.F. <strong>The</strong> structure of human cytochrome P450 2C9 complexed with flurbiprofen<br />
at 2.0-Å resolution. J. Biol. Chem. 279:35630, 2004.<br />
Yadav, M.K., Redman, J.E., Leman, L.J., Alvarez-Gutierrez, J.M., Zhang, Y.,<br />
Stout, C.D., Ghadiri, M.R. Structure-based engineering of internal cavities in<br />
coiled-coil peptides. Biochemistry 44:9723, 2005.<br />
Yano, J.K., Hsu, M.H., Griffin, K.J., Stout, C.D., Johnson, E.F. Structures of<br />
human microsomal cytochrome P450 2A6 complexed with coumarin and<br />
methoxsalen. Nat. Struct. Mol. Biol. 12:822, 2005.<br />
Yano, J.K., Wester, M.R., Schoch, G.A., Griffin, K.J., Stout, C.D., Johnson, E.F.<br />
<strong>The</strong> structure of human microsomal cytochrome P450 3A4 determined by x-ray<br />
crystallography to 2.05-Å resolution. J. Biol. Chem. 279:38091, 2004.<br />
Lipid Chemistry for Studies of<br />
Integral Membrane Proteins<br />
Q. Zhang, M.G. Finn,* X. Ma<br />
* Department of Chemistry, <strong>Scripps</strong> <strong>Research</strong><br />
MOLECULAR BIOLOGY 2005 173<br />
Integral membrane proteins float in the lipid bilayer<br />
with their hydrophobic domains threaded through the<br />
membrane and their hydrophilic domains extended<br />
into the aqueous solution. <strong>The</strong>se proteins are extremely<br />
unstable outside the hydrophobic membrane bilayer, a<br />
situation that makes their in vitro biophysical and structural<br />
characterization difficult. An artificial environment<br />
is therefore needed to stabilize the proteins in their<br />
native state. We are attempting to synthesize new<br />
amphiphilic molecules that can extract integral membrane<br />
proteins from membranes and stabilize the proteins<br />
for structural characterization.<br />
Relatively few investigators have actually addressed<br />
questions about the design of appropriate amphiphilic<br />
molecules despite the extensive use of such molecules<br />
in studies of membrane proteins. <strong>The</strong> criteria that we<br />
apply to generate such amphiphilic molecules are based<br />
on the physical properties of the molecules and on their<br />
interactions with membrane proteins. Detergents that<br />
self-assemble into micellar structures are universally<br />
used to dissolve integral membrane proteins as single<br />
particles to facilitate protein crystallization. We intend<br />
to incorporate more hydrophobicity in the interior of<br />
detergent micelles to improve the stability of the micelles<br />
and consequently their ability to stabilize integral membrane<br />
proteins. We accomplish this incorporation by<br />
appending branches along the alkyl chains of detergents<br />
and, most interestingly, by adding a short branch at the<br />
interface between the hydrophobic tail and the hydro-
174 MOLECULAR BIOLOGY 2005<br />
philic head. <strong>The</strong>se branches may behave in 2 distinct<br />
ways like small amphiphile additives successfully used<br />
in crystallization of integral membrane proteins, thereby<br />
decreasing the micellar radius and extruding water<br />
from the hydrophobic core of the micelles.<br />
<strong>The</strong> effect of these modifications on detergent micelle<br />
properties and on the stabilization and crystallization of<br />
integral membrane proteins is being investigated in collaboration<br />
with members of the Center for Innovative<br />
Membrane Protein Technologies of the Joint Center for<br />
Structural Genomics at <strong>Scripps</strong> <strong>Research</strong>. We are also<br />
interested in synthesizing additional novel amphiphilic<br />
molecules, including peptides, fluorinated lipids, and polymers<br />
that have special properties to facilitate the structural<br />
and functional study of integral membrane proteins.<br />
High-Throughput Structure-<br />
Based Drug Discovery and<br />
Structural Neurobiology<br />
R.C. Stevens, E.E. Abola, A. Alexandrov, J.W. Arndt,<br />
G. Asmar-Rovira, R. Benoit, F. Bi, M.H. Bracey, D. Carlton,<br />
Q. Chai, J.C. Chappie, E. Chien, T. Clayton, B. Collins,<br />
A. Gámez, M. Griffith, C. Grittini, M.A. Hanson, A. Houle,<br />
J. Joseph, K. Masuda, B. McManus, K. Moy, M. Nelson,<br />
R. Page, M.G. Patch, C. Roth, K. Saikatendu, V. Sridhar,<br />
M. Straub, V. Subramanian, J. Velasquez, L. Wang, M. Yadav<br />
HIGH-THROUGHPUT STRUCTURAL BIOLOGY<br />
For the past several years, we have focused on<br />
developing tools to change the field of structural<br />
biology by accelerating the rate of determination<br />
of protein structures, an endeavor that includes pioneering<br />
microliter expression/purification for structural studies,<br />
nanovolume crystallization, and automated image<br />
collection. Applications of these technologies were initially<br />
tested at the Joint Center for Structural Genomics<br />
(http://www.jcsg.org), where we showed the power of the<br />
new tools. In addition to the recent funding of the JCSG-2<br />
as a second-phase production center of the National <strong>Institute</strong><br />
of General Medical Sciences, 2 new centers funded<br />
by the National <strong>Institute</strong>s of Health have been spun off for<br />
technologic innovations in structural biology. <strong>The</strong> first center<br />
is called the Joint Center for Innovative Membrane<br />
Protein Technologies (http://jcimpt.scripps.edu). Here, in<br />
collaboration with G. Chang, S. Lesley, K. Wüthrich,<br />
and Q. Zhang, Department of <strong>Molecular</strong> <strong>Biology</strong>; P. Kuhn<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
and M. Yeager, Department of Cell <strong>Biology</strong>; and M.G.<br />
Finn, Department of Chemistry, we do research exclusively<br />
on membrane proteins, including G protein–coupled<br />
receptors. <strong>The</strong> second center is the Accelerated Technologies<br />
Center for Gene to 3D Structure (http://www<br />
.atcg3d.org). Here we are doing collaborative studies with<br />
P. Kuhn, Department of Cell <strong>Biology</strong>, and researchers<br />
from deCODE biostructures, Bainbridge Island, Washington;<br />
Lyncean Technologies, Palo Alto, California; and<br />
the University of Chicago, Chicago, Illinois. In the near<br />
future, this center will build a synchrotron resource at<br />
<strong>Scripps</strong> <strong>Research</strong>.<br />
STRUCTURAL NEUROBIOLOGY<br />
Although we have developed high-throughput methods<br />
to accelerate the determination of protein structures,<br />
our primary interest is using these tools to study the<br />
chemistry and biology of neurotransmission and of diseases<br />
that affect neurons. Our goals are to understand<br />
how neuronal cells function on a molecular level and,<br />
on the basis of that understanding, create new molecules<br />
and materials that mimic neuronal signal transduction<br />
and recognition. We use high-throughput protein crystallography<br />
and biochemical methods to probe the structure<br />
and function of molecules involved in neurotransmission<br />
and neurochemistry.<br />
F A TTY ACID AMIDE HYDROLASE<br />
In collaboration with B.F. Cravatt, Department of<br />
Cell <strong>Biology</strong>, we solved the structure of fatty acid amide<br />
hydrolase (FAAH), a degradative integral membrane<br />
enzyme responsible for setting intracellular levels of<br />
endocannabinoids, to 2.8 Å. FAAH is intimately associated<br />
with CNS signaling processes such as retrograde<br />
synaptic transmission, a process that is also modulated<br />
by the illicit substance δ 9 -tetrahydrocannabinol. FAAH is<br />
a dimer capable of monotopic membrane insertion; it<br />
has an active-site structure consistent with the capacity<br />
for hydrolysis of hydrophobic fatty acid amides and<br />
structural features amenable to structure-based drug<br />
design. With our knowledge of the 3-dimensional structure,<br />
we are trying to understand how the enzyme works<br />
at a basic level and how it might be the basis for potential<br />
drug discovery.<br />
BIOSYNTHESIS OF NEUROTRANSMITTERS<br />
For neuronal signal transduction, the presynaptic<br />
cell synthesizes neurotransmitters that then traverse<br />
the synaptic cleft. We are using the high-throughput<br />
methods to determine the inclusive structures of complete<br />
biochemical pathways. Specifically, we are interested<br />
in determining the structures of all the enzymes
in the biosynthesis pathways of neurotransmitters in<br />
order to understand the mechanistic details of each<br />
individual enzymatic reaction at the atomic level. This<br />
approach also allows us to determine the best path of<br />
drug discovery in the areas of neurotransmitter biosynthesis<br />
and catabolism.<br />
Phenylalanine hydroxylase and tyrosine hydroxylase<br />
initiate the first committed step in the biosynthesis of<br />
the neurotransmitters dopamine, adrenaline, and noradrenaline,<br />
and tryptophan hydroxylase catalyzes the<br />
rate-determining step in the biosynthesis of serotonin.<br />
Because of the importance of these neurotransmitters<br />
in the proper functioning of the CNS, understanding<br />
the molecular details involved in the catalysis and regulation<br />
of these biosynthetic enzymes is crucial. We<br />
determined the 3-dimensional structures for tyrosine<br />
hydroxylase, tryptophan hydroxylase, and phenylalanine<br />
hydroxylase, and we are uncovering specific mechanistic<br />
details for these enzymes.<br />
THERAPEUTIC AGENTS FOR TREATMENT OF<br />
PHENYLKETONURIA<br />
In addition to the basic hydroxylase enzymology<br />
questions under investigation, recent clinical studies<br />
suggest that some patients with the metabolic disease<br />
phenylketonuria are responsive to (6R)-L-erythro-5,6,7,<br />
8-tetrahydrobiopterin, the natural cofactor of phenylalanine<br />
hydroxylase. We are doing studies to correlate<br />
how structure can be used to predict which patients<br />
with phenylketonuria most likely will respond to treatment<br />
with this cofactor. Currently, the proprietary form<br />
of the cofactor, Phenoptin, is entering phase 3 clinical<br />
trials for the treatment of mild phenylketonuria. For<br />
classical phenylketonuria, we are developing an enzyme<br />
replacement therapeutic agent that is being tested in<br />
animal models. <strong>The</strong> therapy is based on administration<br />
of a modified form of phenylalanine ammonia lyase<br />
discovered in our structural studies (Fig. 1). Last, we<br />
are determining the structural basis of diseases caused<br />
by several other enzymes involved in the biosynthesis of<br />
neurotransmitters. Many of these disorders are rare or<br />
occur during childhood.<br />
NEUROTOXINS<br />
<strong>The</strong> clostridial neurotoxins include tetanus toxin and<br />
the 7 serotypes of botulinum toxin (Fig. 2). We are<br />
determining the molecular events involved in the binding,<br />
pore formation, translocation, and catalysis of botulinum<br />
neurotoxin. Although botulinum toxin is most<br />
known for its deadly effects, it is now being used<br />
therapeutically to treat involuntary muscle disorders.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 175<br />
Fig. 1. A, Crystal structure of phenylalanine ammonia lyase (PAL)<br />
determined at 1.6-Å resolution. This protein structure was engineered<br />
and chemically modified as a potential once-a-week injectable therapeutic<br />
agent for treatment of phenylketonuria. B, ENU2 mice are<br />
used as a model for phenylketonuria in preclinical studies. C and<br />
D, Reduction in phenylalanine and immune response levels in ENU2<br />
mice after the injection of PAL that has been chemically modified<br />
(pegylated). <strong>The</strong>se PEG-PAL formulations show promise as therapeutic<br />
agents for treatment of phenylketonuria.<br />
Fig. 2. Serotype structures of botulinum neurotoxin (BoNT), its<br />
light chain (LC), and the closely related tetanus neurotoxin (TeNT).
176 MOLECULAR BIOLOGY 2005<br />
Recently, we determined the structure of the 900-kD<br />
complex form of the toxin, the 150-kD holotoxin form,<br />
the catalytic domain, and the catalytic domain bound<br />
to substrates and inhibitors. <strong>The</strong>se structures are being<br />
used to understand and redesign the toxin’s mechanism<br />
of action and to determine additional therapeutic applications<br />
of the toxin.<br />
PUBLICATIONS<br />
Arndt, J.W., Gu, J., Jaroszewski, L., Schwarzenbacher, R., Hanson, M.A.,<br />
Lebeda, F.J., Stevens, R.C. <strong>The</strong> structure of the neurotoxin-associated protein<br />
HA33/A from Clostridium botulinum suggests a reoccurring β-trefoil fold in the<br />
progenitor toxin complex. J. Mol. Biol. 346:1083, 2005.<br />
Arndt, J.W., Schwarzenbacher, R., Page, R., et al. Crystal structure of an α/β serine<br />
hydrolase (YDR428C) from Saccharomyces cerevisiae at 1.85 Å resolution.<br />
Proteins 58:755, 2005.<br />
Arndt, J.W., Yu, W., Bi, F., Stevens, R.C. Crystal structure of botulinum neurotoxin<br />
type G light chain: serotype divergence in substrate recognition. Biochemistry<br />
44:9574, 2005.<br />
Cànaves, J.M., Page, R., Stevens, R.C. Protein biophysical properties that correlate<br />
with crystallization success in <strong>The</strong>rmotoga maritima: maximum clustering<br />
strategy for structural genomics. J. Mol. Biol. 344:977, 2004.<br />
Carter, D.C., Rhodes, P., McRee, D.E., Tari, L.W., Dougan, D.R., Snell, G., Abola, E.,<br />
Stevens, R.C. Reduction in diffuso-convective disturbances in nanovolume protein<br />
crystallization experiments. J. Appl. Crystrallogr. 38:87, 2005.<br />
Chappie, J.S., Cànaves, J.M., Han, G.W., Rife, C.L., Xu, Q., Stevens, R.C. <strong>The</strong><br />
structure of a eukaryotic nicotinic acid phosphoribosyltransferase reveals structural<br />
heterogeneity among type II PRTases. Structure (Camb.) 13:1385, 2005.<br />
Erlandsen, H., Pey, A.L., Gámez, A., Pérez, B., Desviat, L.R., Aguado, C., Koch,<br />
R., Surendran, S., Tyring, T., Matalon, R., Scriver, C.R., Ugarte, M., Martínez, A.,<br />
Stevens, R.C. Correction of kinetic and stability defects by the cofactor tetrahydrobiopterin<br />
in phenylketonuria patients with certain phenylalanine hydroxylase mutations.<br />
Proc. Natl. Acad. Sci. U. S. A. 101:16903, 2004.<br />
Gámez, A., Sarkissian, C.N., Wang, L., Kim, W., Straub, M., Patch, M.G., Chen,<br />
L., Striepeke, S., Fitzpatrick, P., Lemontt, J.F., O’Neill, C., Scriver, C.R., Stevens,<br />
R.C. Development of pegylated forms of recombinant Rhodosporidium toruloides<br />
phenylalanine ammonia-lyase for the treatment of classical phenylketonuria. Mol.<br />
<strong>The</strong>r. 11:986, 2005.<br />
Han, G.W., Schwarzenbacher, R., Page, R., et al. Crystal structure of an alanineglyoxylate<br />
aminotransferase from Anabena sp at 1.70 Å resolution reveals a noncovalently<br />
linked PLP cofactor. Proteins 58:971, 2005.<br />
Levin, I., Miller, M.D., Schwarzenbacher, R., et al. Crystal structure of an indigoidine<br />
synthase A (IndA)-like protein (TM1464) from <strong>The</strong>rmotoga maritima at 1.90 Å<br />
resolution reveals a new fold. Proteins 59:864, 2005.<br />
Matalon, R., Michals-Matalon, K., Koch, R., Grady, J., Tyring, S., Stevens, R.C.<br />
Response of patients with phenylketonuria in the US to tetrahydrobiopterin. Mol.<br />
Genet. Metab., in press.<br />
Mathews, I., Schwarzenbacher, R., McMullan, D., et al. Crystal structure of<br />
S-adenosylmethionine:tRNA ribosyltransferase-isomerase (QueA) from <strong>The</strong>rmotoga<br />
maritima at 2.0 Å resolution reveals a new fold. Proteins 59:869, 2005.<br />
Page, R., Deacon, A.M., Lesley, S., Stevens, R.C. Shotgun crystallization strategy<br />
for structural genomics, II: crystallization and conditions that produce high resolution<br />
structures for T maritima proteins. J. Funct. Struct. Genomics 6:209, 2005.<br />
Page, R., Peti, W., Wilson, I.A., Stevens, R.C., Wüthrich, K. NMR screening and<br />
crystal quality of bacterially expressed prokaryotic and eukaryotic proteins in a<br />
structural genomics pipeline. Proc. Natl. Acad. Sci. U. S. A. 102:1901, 2005.<br />
Pérez, B., Desviat, L.R., Gomez-Puertas, P., Martinez, A., Stevens, R.C., Ugarte, M.<br />
Kinetic and stability analysis of PKU mutations identified in BH4-responsive patients.<br />
Mol .Genet. Metab., in press.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Peti, W., Johnson, M.A., Hermann, T., Newman, B.W., Buchmeier, M.J., Nelson, M.,<br />
Joseph, J., Page, R., Stevens, R.C., Kuhn, P., Wüthrich, K. Structural genomics of<br />
the severe acute respiratory syndrome coronavirus: nuclear magnetic resonance<br />
structure of the protein nsP7. J. Virol . 79:12905, 2005.<br />
Peti, W., Page, R., Wilson, I., Stevens, R., Wüthrich, K. Structural proteomics<br />
pipeline miniaturized using micro expression and microcoil NMR. J. Struct. Funct.<br />
Genomics, in press.<br />
Pey, A.L., Pérez, B., Desviat, L.R., Martinez, M.A., Aguado, C., Erlandsen, H.,<br />
Gámez, A., Stevens, R.C., Thorolfsson, M., Ugarte, M., Martinez, A. Mechanisms<br />
underlying responsiveness to tetrahydrobiopterin in mild phenylketonuria mutations.<br />
Hum. Mutat. 24:388, 2004.<br />
Ricci, J.S., Stevens, R.C., McMullan, R.K., Klooster, W.T. <strong>The</strong> crystal structure of<br />
strontium hydroxide octahydrate, Sr(OH)2.8H 2 O at 20, 100, and 200 K from neutron<br />
diffraction. Acta Crystrallogr. B 61:381. 2005.<br />
Rife, C., Schwarzenbacher, R., McMullen, D., et al. Crystal structure of a putative<br />
modulator of DNA gyrase (pmbA) from <strong>The</strong>rmotoga maritima at 1.95 Å resolution<br />
reveals a new fold. Proteins 61:444, 2005.<br />
Rife, C., Schwarzenbacher, R., McMullen, D., et al. Crystal structure of a global<br />
regulatory protein CsrA from Pseudomonas putida at 2.05 Å resolution reveals a<br />
new fold. Proteins 61:449, 2005.<br />
Saikatendu, K.S., Joseph, J.S., Subramanian, V., Clayton, T., Griffith, M., Moy,<br />
K., Velasquez, J., Neuman, B.W., Buchmeier, M.J., Stevens, R.C., Kuhn, P.<br />
Structural basis of severe acute respiratory syndrome coronavirus (SARS-CoV) ADPribose-1′′-phosphate<br />
(Appr-1′′-p) dephosphorylation by a conserved domain of<br />
nsP3. Structure, in press.<br />
Scriver, C.R., Hurtubise, M., Prevost, L., Phommarinh, M., Konecki, D., Erlandsen,<br />
H., Stevens, R.C., Waters, P.J., Ryan, S., McDonald, D., Sarkissan C. A PAH<br />
gene knowledge base: content, informatics, utilization. In: PKU and BH 4 : Advances<br />
in Phenylketonuria and Tetrahydrobiopterin <strong>Research</strong>. Blaue, N. (Ed.), SPS Publications,<br />
Heilbrun, Germany, in press.<br />
Swaminathan, S., Stevens, R.C. Three-dimensional protein structures of botulinum<br />
neurotoxin light chains serotypes A, B, and E. In: Treatments from Toxins: <strong>The</strong><br />
<strong>The</strong>rapeutic Potential of Clostridial Neurotoxins. Foster, K., Hambleton, P., Shone,<br />
C. (Eds.). CRC Press, Boca Raton, FL, in press.<br />
Wang, L., Gámez, A., Sarkissian, C.N., Straub, M., Patch, M.G., Han, G.W.,<br />
Striepeke, S., Fitzpatrick, P., Scriver, C.R., Stevens, R.C. Structure-based chemical<br />
modification strategy for enzyme replacement treatment of phenylketonuria.<br />
Mol. Genet. Metab. 86:134, 2005.<br />
Xu, Q., Schwarzenbacher, R., McMullen, D., et al. Crystal structure of a formiminotetrahydrofolate<br />
cyclodeaminase (TM1560) from <strong>The</strong>rmotoga maritima at 2.80 Å<br />
resolution reveals a new fold. Proteins 58:976, 2005.<br />
Yadav, M.K., Gerdts, C.J., Sanishvili, R., Smith, W., Roach, L.S., Ismagilov, R.F.,<br />
Kuhn, P., Stevens, R.C. In situ data collection and structure refinement from<br />
microcapillary protein crystallization. J. Appl. Crystallogr., in press.<br />
Nuclear Magnetic Resonance<br />
in Structural <strong>Biology</strong> and<br />
Structural Genomics<br />
K. Wüthrich, M. Almeida, L. Columbus, T. Etezady,<br />
M. Geralt, S. Hiller, R. Horst, M. Johnson, W.J. Placzek,<br />
W. Peti, P. Serrano<br />
Members of our laboratory participate in the<br />
Joint Center for Structural Genomics (JCSG),<br />
the JCSG Center for Innovative Membrane
Protein Technologies, and the Functional and Structural<br />
Proteomics Analysis of SARS-CoV–Related Proteins<br />
Consortium. As part of these studies on protein structure,<br />
we develop and use nuclear magnetic resonance<br />
(NMR) methods to screen recombinant protein preparations<br />
for folded proteins. We are also exploring the<br />
use of microcoil NMR equipment combined with microexpression<br />
of proteins. We also use NMR spectroscopy to<br />
determine the structure of selected proteins from the<br />
proteomes under study in the structural genomics programs.<br />
Some of our research is described in the following<br />
sections.<br />
NMR SCREENING OF THERMOTOGA MARITIMA<br />
MEMBRANE PROTEINS<br />
A total of 45 predicted α-helical membrane proteins<br />
from <strong>The</strong>rmotoga maritima were selected as potential<br />
targets for solution NMR structural studies. <strong>The</strong>se<br />
proteins have between 1 and 4 predicted helical transmembrane<br />
segments and have molecular weights less<br />
than 16 kD. Of the 45 targets, 10 were overexpressed<br />
in Escherichia coli, and 8 of these 10 localized to<br />
the bacterial membrane. <strong>The</strong>se 8 protein targets were<br />
purified and screened to determine efficient detergents<br />
for solubilization.<br />
To evaluate the fold and the aggregation state of<br />
the proteins in the best conditions thus identified, we<br />
used 1-dimensional 1 H NMR spectroscopy to screen<br />
the targets. For 3 of the 8 proteins, the NMR spectra<br />
indicated soluble protein-detergent complexes. <strong>The</strong><br />
transverse relaxation optimized spectroscopy correlation<br />
spectra of these 3 targets provided evidence that<br />
these 3 proteins are folded helical proteins. Experiments<br />
are under way for NMR assignment and structure determination<br />
of these α-helical membrane proteins in mixed<br />
micelles with detergents.<br />
STRUCTURE DETERMINATIONS OF CONSERVED<br />
HYPOTHETICAL PROTEINS FROM T MARITIMA<br />
<strong>The</strong> NMR structure of the conserved hypothetical<br />
protein TM1816 from T maritima has an α/β topology<br />
with 3 α-helices and a 5-stranded β-sheet. <strong>The</strong> molecular<br />
architecture of TM1816 is similar to that of 2 other<br />
conserved hypothetical proteins, TM1290 from T maritima<br />
(33% sequence identity) and MTH1175 from<br />
Methanobacterium thermoautotrophicum (30% sequence<br />
identity). <strong>The</strong>se 3 proteins belong to the cluster of<br />
orthologous groups 1433 and are structurally similar<br />
to the Azobacter vinelandii iron, molybdenum cofactor-binding<br />
protein NafY. TM1816 is unique among<br />
the 3 homologs because it contains a histidine residue<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 177<br />
corresponding to the one that is crucial for cofactor<br />
binding in NafY.<br />
TM0487 is a 104-residue protein from T maritima<br />
that was identified via NMR screening as a potential<br />
target for NMR structure determination. <strong>The</strong> 3-dimensional<br />
structure of TM0487 provides a foundation for<br />
functional studies of an entire class of proteins, because<br />
TM0487 has a large number of homologs on the amino<br />
acid sequence level, including 216 nonredundant<br />
sequences that contain a type 59 domain of unknown<br />
function. So far, a 3-dimensional structure has not been<br />
determined for any of these homologous proteins. <strong>The</strong><br />
conserved residues among the aforementioned 216<br />
sequences are clustered in the hydrophobic core of the<br />
TM0487 fold and in a putative active site exposed to<br />
the solvent. Overall, strong evidence indicates that the<br />
TM0487 fold is preserved in all of this class of domains<br />
of unknown function, so that this structure determination<br />
provides a foundation for focused functional studies<br />
of a wide variety of otherwise so far only minimally<br />
characterized proteins.<br />
NMR STUDIES OF AN ACYL CARRIER PROTEIN<br />
FROM THE CYANOBACTERIUM ANABAENA<br />
Asl1650, a protein obtained from the cyanobacterium<br />
Anabaena, was identified as an ortholog of a<br />
mouse protein domain as part of a JCSG bioinformatics<br />
strategy to extend information on the protein folding<br />
space of eukaryotic proteins. <strong>The</strong> protein was<br />
selected for NMR structure determination on the basis<br />
of an NMR screen of recombinant mouse protein homologs<br />
expressed in E coli.<br />
Acyl carrier proteins (ACPs) are central components<br />
of complex multienzyme systems that function in the<br />
metabolism of all living organisms. <strong>The</strong>se systems catalyze<br />
the biosynthesis of fatty acids, signaling molecules,<br />
and bioactive natural products. <strong>The</strong> polyketide<br />
synthases and nonribosomal peptide synthetases of<br />
microorganisms produce compounds with antibiotic<br />
and anticancer activities. An understanding of structure-function<br />
relationships in these widely distributed<br />
enzyme systems is thus of obvious interest for the design<br />
of new therapeutic compounds.<br />
<strong>The</strong> protein Asl1650 is only distantly related to<br />
previously characterized ACPs. It was derived from<br />
Anabaena sp PCC 7120, a filamentous cyanobacterium.<br />
Members of this genus of cyanobacteria produce<br />
a variety of bioactive compounds, which are as<br />
yet only poorly characterized. We determined the solution<br />
structure of Asl1650 by using high-resolution NMR
178 MOLECULAR BIOLOGY 2005<br />
spectroscopy. <strong>The</strong> structure had a surprising similarity<br />
to the structures of peptidyl carrier protein domains,<br />
which usually occur as single domains of giant, multifunctional<br />
proteins. A variant active-site sequence,<br />
asparagine–serine–serine, occurs in similar orientation<br />
to the aspartic acid–serine–leucine sequence of known<br />
ACPs. <strong>The</strong>se structural similarities suggest that Asl1650<br />
may function as a discrete peptidyl carrier protein<br />
domain in a nonribosomal peptide synthetase pathway<br />
or a hybrid polyketide synthase–nonribosomal peptide<br />
synthetase pathway.<br />
PUBLICATIONS<br />
Almeida, M.S., Peti, W., Wüthrich, K. 1 H-, 13 C- and 15 N-NMR assignment of the<br />
conserved hypothetical protein TM0487 from <strong>The</strong>rmotoga maritima. J. Biomol.<br />
NMR 29:453, 2004.<br />
Etezady-Esfarjani, T., Herrmann, T., Peti, W., Klock, H.E., Lesley, S.A., Wüthrich, K.<br />
NMR structure determination of the hypothetical protein TM1290 from <strong>The</strong>rmotoga<br />
maritima using automated NOESY analysis. J. Biomol. NMR 29:403, 2004.<br />
Page, R., Peti, W., Wilson, I.A., Stevens, R.C., Wüthrich, K. NMR screening and<br />
crystal quality of bacterially expressed prokaryotic and eukaryotic proteins in a<br />
structural genomics pipeline. Proc. Natl. Acad. Sci. U. S. A. 102:1901, 2005.<br />
Peti, W., Etezady-Esfarjani, T., Herrmann, T., Klock, H.E., Lesley, S.A., Wüthrich, K.<br />
NMR for structural proteomics of <strong>The</strong>rmotoga maritima: screening and structure<br />
determination. J. Struct. Funct. Genomics 5:205, 2004.<br />
Peti, W., Norcross, J., Eldridge, G., O’Neil-Johnson, M. Biomolecular NMR using<br />
a microcoil NMR probe: new technique for the chemical shift assignment of aromatic<br />
side chains in proteins. J. Am. Chem. Soc. 126:5873, 2004.<br />
Nuclear Magnetic Resonance of<br />
3-Dimensional Structure and<br />
Dynamics of Proteins in Solution<br />
P.E. Wright, H.J. Dyson, R. Burge, R. De Guzman,<br />
T. Dunzendorfer-Matt, J. Ferreon, N. Greenman,<br />
T.-H. Huang, M. Kostic, J. Lansing, B. Lee, M. Landes,<br />
M. Martinez-Yamout, T. Nishikawa, J. Wojciak, M. Zeeb,<br />
E. Manlapaz, L.L. Tennant, J. Chung, D.A. Case,<br />
J. Gottesfeld, R. Evans,* M. Montminy*<br />
* Salk <strong>Institute</strong>, La Jolla, California<br />
We use multidimensional nuclear magnetic<br />
resonance (NMR) spectroscopy to investigate<br />
the structures, dynamics, and interactions<br />
of proteins in solution. Such studies are essential<br />
for understanding the mechanisms of action of these<br />
proteins and for elucidating structure-function relationships.<br />
<strong>The</strong> focus of our current research is protein-protein<br />
and protein–nucleic acid interactions involved in<br />
the regulation of gene expression.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
TRANSCRIPTION FACTOR–NUCLEIC ACID COMPLEXES<br />
NMR methods are being used to determine the<br />
3-dimensional structures and intramolecular dynamics<br />
of zinc finger motifs from several eukaryotic transcriptional<br />
regulatory proteins, both free and complexed with<br />
target nucleic acid. Zinc fingers are among the most<br />
abundant domains in eukaryotic genomes. <strong>The</strong>y play a<br />
central role in the regulation of gene expression at both<br />
the transcriptional and the posttranscriptional levels,<br />
mediated through their interactions with DNA, RNA,<br />
or protein components of the transcriptional machinery.<br />
<strong>The</strong> C 2 H 2 zinc finger, first identified in transcription<br />
factor IIIA (TFIIIA), is used by numerous transcription<br />
factors to achieve sequence-specific recognition of DNA.<br />
<strong>The</strong>re is growing evidence, however, that some C 2 H 2<br />
zinc finger proteins control gene expression both through<br />
their interactions with DNA regulatory elements and,<br />
at the posttranscriptional level, by binding to RNA.<br />
<strong>The</strong> best-characterized example of a C 2 H 2 zinc<br />
finger protein that binds specifically to both DNA and<br />
to RNA is TFIIIA, which contains 9 zinc fingers. We<br />
showed previously that different subsets of zinc fingers<br />
are responsible for high-affinity binding of TFIIIA to DNA<br />
(fingers 1–3) and to 5S RNA (fingers 4–6). To obtain<br />
insights into the mechanism by which the TFIIIA zinc<br />
fingers recognize both DNA and RNA, we are using NMR<br />
methods to determine the structures of the complex<br />
formed by zf1-3 (a protein containing fingers 1–3) with<br />
DNA and by zf4-6 (a protein consisting of fingers 4–6)<br />
with a fragment of 5S RNA.<br />
Three-dimensional structures were determined previously<br />
for the complex of zf1-3 with the cognate 15-bp<br />
oligonucleotide duplex. <strong>The</strong> structures contain several<br />
novel features and reveal that prevailing models of DNA<br />
recognition, which assume that zinc fingers are independent<br />
modules that contact bases through a limited<br />
set of amino acids, are outmoded.<br />
In addition to its role in binding to and regulating<br />
the 5S RNA gene, TFIIIA also forms a complex with the<br />
5S RNA transcript. We recently determined the NMR<br />
structure of the complex formed by zinc fingers 4–6 with<br />
a truncated form of 5S RNA (Fig. 1). <strong>The</strong> structure has<br />
provided important insights into the structural basis for<br />
5S RNA recognition. Finger 4 of the protein recognizes<br />
both the structure of the RNA backbone and the specific<br />
bases in the loop E motif of the RNA, in a classic lockand-key<br />
interaction. Fingers 5 and 6, with a single residue<br />
between them, undergo mutual induced-fit folding<br />
with the loop A region of the RNA, which is highly flexible<br />
in the absence of the protein.
Fig. 1. Structure of zinc fingers 4–6 of TFIIIA bound to 5S RNA.<br />
<strong>The</strong> protein backbone is shown as a ribbon, and the phosphate<br />
backbone and bases of the RNA are displayed as gray tubes.<br />
NMR studies of 2 alternate splice variants of the<br />
Wilms tumor zinc finger protein are in progress. <strong>The</strong>se<br />
proteins differ only through insertion of 3 additional<br />
amino acids (the tripeptide lysine-threonine-serine) in<br />
the linker between fingers 3 and 4, yet have marked<br />
differences in their DNA-binding properties and subcellular<br />
localization. 15 N relaxation measurements indicate<br />
that the insertion increases the flexibility of the<br />
linker between fingers 3 and 4 and abrogates binding<br />
of the fourth zinc finger to its cognate site in the DNA<br />
major groove, thereby modulating DNA-binding activity.<br />
<strong>The</strong> x-ray structure of the DNA complex has now been<br />
determined, and NMR studies of RNA binding are in<br />
progress. We have also determined the structure of the<br />
first member of a novel class of C 2 H 2 zinc finger proteins<br />
that bind specifically to double-stranded RNA.<br />
Several novel zinc binding motifs have recently<br />
been identified that mediate gene expression at the<br />
posttranscriptional level by regulating mRNA processing<br />
and metabolism. Regulatory proteins of the TIS11<br />
family bind specifically, through a pair of novel CCCH<br />
zinc fingers, to the adenosine-uridine–rich element in<br />
the 3′ untranslated region of short-lived cytokine, growth<br />
factor, and protooncogene mRNAs and control expression<br />
by promoting rapid degradation of the message. We<br />
recently determined the NMR structure of the complex<br />
formed between the tandem zinc finger domain of TIS11d<br />
and its binding site on the adenosine-uridine–rich ele-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 179<br />
ment. This structure showed sequence-specific recognition<br />
of single-stranded RNA through formation of a<br />
network of hydrogen bonds between the polypeptide<br />
backbone and the Watson-Crick edges of the bases.<br />
PROTEIN-PROTEIN INTERACTIONS IN<br />
TRANSCRIPTIONAL REGULATION<br />
Transcriptional regulation in eukaryotes relies on<br />
protein-protein interactions between DNA-bound factors<br />
and coactivators that, in turn, interact with the basal<br />
transcription machinery. <strong>The</strong> transcriptional coactivator<br />
CREB-binding protein (CBP) and its homolog p300 play<br />
an essential role in cell growth, differentiation, and<br />
development. Understanding the molecular mechanisms<br />
by which CBP and p300 recognize their various target<br />
proteins is of fundamental biomedical importance. CBP<br />
and p300 have been implicated in diseases such as<br />
leukemia, cancer, and mental retardation and are novel<br />
targets for therapeutic intervention.<br />
We previously determined the structure of the kinaseinducible<br />
activation domain of the transcription factor<br />
CREB bound to its target domain (the KIX domain) in<br />
CBP. Ongoing work is directed toward mapping the interactions<br />
between KIX and the transcriptional activation<br />
domains of the proto-oncogene c-Myb and of the mixedlineage<br />
leukemia protein. <strong>The</strong> solution structure of the<br />
ternary complex composed of KIX, c-Myb, and the mixedlineage<br />
leukemia protein has been completed (Fig. 2)<br />
and provides insights into the structural basis for the<br />
ability of the KIX domain to interact simultaneously and<br />
allosterically with 2 different effectors. Our work has also<br />
provided new understanding of the thermodynamics of<br />
the coupled folding and binding processes involved in<br />
interaction of KIX with transcriptional activation domains.<br />
Fig. 2. Structure of the ternary complex between the KIX domain<br />
of CBP (pale gray) and the transcriptional activation domains of<br />
c-Myb and the mixed-lineage leukemia protein (MLL).
180 MOLECULAR BIOLOGY 2005<br />
Recently, we determined the structure of the complex<br />
between the hypoxia-inducible factor Hif-1α and<br />
the CH1 domain of CBP. <strong>The</strong> interaction between Hif-1α<br />
and CBP/p300 is of major therapeutic interest because<br />
of the central role Hif-1α plays in tumor progression and<br />
metastasis; disruption of this interaction leads to attenuation<br />
of tumor growth. A protein named CITED2 functions<br />
as a negative feedback regulator of the hypoxic<br />
response by competing with Hif-1α for binding to the<br />
CH1 domain of CBP. We determined the structure of<br />
the complex formed between CITED2 and the CH1<br />
domain and were able to show that the CH1 domain<br />
is folded into a stable 3-dimensional structure even in<br />
the absence of binding partners. <strong>The</strong> intrinsically unstructured<br />
Hif-1α and CITED2 domains use partly overlapping<br />
surfaces of the CH1 motif to achieve high-affinity<br />
binding and compete effectively with each other for<br />
CBP/p300. <strong>The</strong> structure of another zinc-binding module<br />
of CBP, the ZZ domain, has a novel fold (Fig. 3),<br />
but its function is not yet understood. We are continuing<br />
to map the multiplicity of interactions between CBP/p300<br />
domains and their numerous biological targets to understand<br />
the complex interplay of interactions that mediate<br />
key biological processes in health and disease.<br />
Fig. 3. Structure of the ZZ zinc finger domain of CBP.<br />
PUBLICATIONS<br />
De Guzman, R.N., Goto, N.K., Dyson, H.J., Wright, P.E. Structural basis for cooperative<br />
transcription factor binding to the CBP coactivator. J. Mol. Biol., in press.<br />
De Guzman, R.N., Wojciak, J.M., Martinez-Yamout, M.A., Dyson, H.J., Wright,<br />
P.E. CBP/p300 TAZ1 domain forms a structural scaffold for ligand binding. Biochemistry<br />
44:490, 2005.<br />
Dyson, H.J., Wright, P.E. Intrinsically unstructured proteins and their function. Nat.<br />
Rev. Mol. Cell Biol. 6:197, 2005.<br />
Gearhart, M.D., Dickinson, L., Ehley, J., Melander, C., Dervan, P.B., Wright, P.E., Gottesfeld,<br />
J.M. Inhibition of DNA binding by human estrogen related receptor-2 and estrogen<br />
receptor α with minor groove binding polyamides. Biochemistry 44:4196, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Legge, G.B., Martinez-Yamout, M.A., Hambly, D.M., Trinh, T., Lee, B.M., Dyson,<br />
H.J., Wright, P.E. ZZ domain of CBP: an unusual zinc finger fold in a protein interaction<br />
module. J. Mol. Biol. 343:1081, 2004.<br />
Möller, H.M., Martinez-Yamout, M.A., Dyson, H.J. Wright, P.E. Solution structure<br />
of the N-terminal zinc fingers of the Xenopus laevis double-stranded RNA-binding<br />
protein ZFa. J. Mol. Biol. 351:718, 2005.<br />
Folding of Proteins and<br />
Protein Fragments<br />
P.E. Wright, H.J. Dyson, C. Nishimura, D. Felitsky, Y. Yao,<br />
J. Chung, L.L. Tennant, V. Bychkova*<br />
* <strong>Institute</strong> of Protein <strong>Research</strong>, Puschino, Russia<br />
<strong>The</strong> molecular mechanism by which proteins fold<br />
into their 3-dimensional structures remains one<br />
of the most important unsolved problems in structural<br />
biology. Nuclear magnetic resonance (NMR) spectroscopy<br />
is uniquely suited to provide information on<br />
the structure of transient intermediates formed during<br />
protein folding. Previously, we used NMR methods to<br />
show that many peptide fragments of proteins have a<br />
tendency to adopt folded conformations in water solution.<br />
<strong>The</strong> presence of transiently populated folded structures,<br />
including reverse turns, helices, nascent helices,<br />
and hydrophobic clusters, in water solutions of short<br />
peptides has important implications for initiation of protein<br />
folding. Formation of elements of secondary structure<br />
probably plays an important role in the initiation<br />
of protein folding by reducing the number of conformations<br />
that must be explored by the polypeptide chain and<br />
by directing subsequent folding pathways.<br />
APOMYOGLOBIN FOLDING PATHWAY<br />
A major program in our laboratory is directed<br />
toward a structural and mechanistic description of the<br />
apomyoglobin folding pathway. Previously, we used<br />
quenched-flow pulse labeling methods in conjunction<br />
with 2-dimensional NMR spectroscopy to map the<br />
kinetic folding pathway of the wild-type protein. With<br />
these methods, we showed that an intermediate in<br />
which the A, G, and H helices adopt hydrogen-bonded<br />
secondary structure is formed within 6 ms of the initiation<br />
of refolding. Folding then proceeds by stabilization<br />
of structure in the B helix and then in the C and<br />
E helices. We are using carefully selected myoglobin<br />
mutants and both optical stopped-flow spectroscopy<br />
and NMR methods to further probe the kinetic folding<br />
pathway. For some of the mutants studied, the changes<br />
in amino acid sequence resulted in changes in the fold-
ing pathway of the protein. <strong>The</strong>se experiments are providing<br />
novel insights into both the local and the longrange<br />
interactions that stabilize the kinetic folding<br />
intermediate. Of particular importance, long-range<br />
interactions have been observed that indicate nativelike<br />
packing of some of the helices in the kinetic molten<br />
globule intermediate.<br />
Apomyoglobin provides a unique opportunity for<br />
detailed characterization of the structure and dynamics<br />
of a protein-folding intermediate. Conditions were previously<br />
identified under which the apomyoglobin molten<br />
globule intermediate is sufficiently stable for acquisition<br />
of multidimensional heteronuclear NMR spectra.<br />
Analysis of 13 C and other chemical shifts and measurements<br />
of polypeptide dynamics provided unprecedented<br />
insights into the structure of this state.<br />
<strong>The</strong> A, G, and H helices and part of the B helix are<br />
folded and form the core of the molten globule. This<br />
core is stabilized by relatively nonspecific hydrophobic<br />
interactions that restrict the motions of the polypeptide<br />
chain. Fluctuating helical structure is formed in regions<br />
outside the core, although the population of helix is low<br />
and the chain retains considerable flexibility. <strong>The</strong> F helix<br />
acts as a gate for heme binding and only adopts stable<br />
structure in the fully folded holoprotein.<br />
<strong>The</strong> acid-denatured (unfolded) state of apomyoglobin<br />
is an excellent model for the fluctuating local interactions<br />
that lead to the transient formation of unstable<br />
elements of secondary structure and local hydrophobic<br />
clusters during the earliest stages of folding. NMR data<br />
indicated substantial formation of helical secondary<br />
structure in the acid-denatured state in regions that form<br />
the A and H helices in the folded protein and also<br />
revealed nonnative structure in the D and E helix region.<br />
Because the A and H regions adopt stabilized helical<br />
structure in the earliest detectable folding intermediate,<br />
these results lend strong support to folding models<br />
in which spontaneous formation of local elements of<br />
secondary structure plays a role in initiating formation<br />
of the A-[B]-G-H molten globule folding intermediate.<br />
In addition to formation of transient helical structure,<br />
formation of local hydrophobic clusters has been detected<br />
by using 15 N relaxation measurements. Significantly,<br />
these clusters are formed in regions where the average<br />
surface area buried upon folding is large. In contrast<br />
to acid-denatured unfolded apomyoglobin, the ureadenatured<br />
state is largely devoid of structure, although<br />
residual hydrophobic interactions have been detected<br />
by using relaxation measurements.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 181<br />
We measured residual dipolar couplings for unfolded<br />
states of apomyoglobin by using partial alignment in<br />
strained polyacrylamide gels. <strong>The</strong>se data provide novel<br />
insights into the structure and dynamics of the unfolded<br />
polypeptide chain. We have shown that the residual<br />
dipolar couplings arise from the well-known statistical<br />
properties of flexible polypeptide chains. Residual dipolar<br />
couplings provide valuable insights into the dynamic<br />
and conformational propensities of unfolded and partly<br />
folded states of proteins and hold great promise for<br />
charting the upper reaches of protein-folding landscapes.<br />
To probe long-range interactions in unfolded and<br />
partially folded states of apomyoglobin, we introduced<br />
spin-label probes at several sites throughout the polypeptide<br />
chain. <strong>The</strong>se experiments led to the surprising<br />
discovery that structures with nativelike topology exist<br />
within the ensemble of conformations formed by the<br />
acid-denatured state of apomyoglobin. <strong>The</strong>y also indicated<br />
that the packing of helices in the molten globule<br />
state is similar to that in the native folded protein.<br />
<strong>The</strong> view of protein folding that results from our<br />
work on apomyoglobin is one in which collapse of the<br />
polypeptide chain to form increasingly compact states<br />
leads to progressive accumulation of secondary structure<br />
and increasing restriction of fluctuations in the<br />
polypeptide backbone. Chain flexibility is greatest at<br />
the earliest stages of folding, in which transient elements<br />
of secondary structure and local hydrophobic<br />
clusters are formed. As the folding protein becomes<br />
increasingly compact, backbone motions become more<br />
restricted, the hydrophobic core is formed and extended,<br />
and nascent elements of secondary structure are progressively<br />
stabilized. <strong>The</strong> ordered tertiary structure<br />
characteristic of the native protein, with well-packed<br />
side chains and relatively low-amplitude local dynamics,<br />
appears to form rather late in folding.<br />
We recently introduced a variation on the classic<br />
quench-flow technique, which makes use of the capabilities<br />
of modern NMR spectrometers and heteronuclear<br />
NMR experiments, to study the proteins labeled<br />
along the folding pathway in an unfolded state in an<br />
aprotic organic solvent. This method allows detection<br />
of many more amide proton probes than in the classic<br />
method, which required formation of the fully folded<br />
protein and the measurement of the protein’s NMR<br />
spectrum in water solutions (Fig. 1). This method is<br />
particularly useful in documenting changes in the folding<br />
pathway that result in the destabilization of parts of the<br />
protein in the molten globule intermediate. We recently
182 MOLECULAR BIOLOGY 2005<br />
Fig. 1. High-resolution view of the backbone structure of the<br />
6.4-ms burst-phase kinetic folding intermediate of apomyoglobin.<br />
<strong>The</strong> tube thickness and darkness indicate the extent of folding into<br />
helical structure. Helices that are fully folded are indicated by thick,<br />
dark tubes. Regions that are partly folded are intermediate in thickness<br />
and shade, and regions of the protein that remain fully unstructured<br />
in the kinetic intermediate are represented by thin lines.<br />
introduced self-compensating mutations designed to<br />
change the amino acid sequence such that the average<br />
area buried upon folding in the A and E helix regions is<br />
significantly changed, while the 3-dimensional structure<br />
of the final folded state remains the same. <strong>The</strong>se studies<br />
indicated that the average area buried upon folding is an<br />
accurate predictor of those parts of the apomyoglobin<br />
molecule that will fold first and participate in the molten<br />
globule intermediate (Fig. 2).<br />
FOLDING-UNFOLDING TRANSITIONS IN CELLULAR<br />
METABOLISM<br />
Many species of bacteria sense and respond to their<br />
own population density by an intricate autoregulatory<br />
mechanism known as quorum sensing; the bacteria<br />
release extracellular signal molecules, called autoinducers,<br />
for cell-cell communication within and between<br />
bacterial species. A number of bacteria appear to use<br />
quorum sensing for regulation of gene expression in<br />
response to fluctuations in cell population density. Processes<br />
regulated in this way include symbiosis, virulence,<br />
competence, conjugation, production of antibiotics, motility,<br />
sporulation, and formation of biofilms.<br />
We determined the 3-dimensional solution structure<br />
of a complex composed of the N-terminal 171 residues<br />
of the quorum-sensing protein SdiA of Escherichia coli<br />
and an autoinducer molecule, N-octanoyl-1-homoserine<br />
lactone (HSL). <strong>The</strong> SdiA-HSL system shows the<br />
“folding switch” behavior associated with quorum-sensing<br />
factors produced by other bacterial species. In the<br />
presence of HSL, the SdiA protein is stable and folded<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 2. Correlation between average surface area buried upon<br />
folding (AABUF, gray line) and regions of apomyoglobin that are<br />
folded in the kinetic burst-phase intermediate. Folded regions are<br />
indicated by high values of the proton occupancy (A0, black circles).<br />
Data are shown for the wild-type protein (A) and for a mutant protein<br />
(B) in which hydrophobic residues are moved from the A helix<br />
into the E helix region, thereby changing the folding pathway in a<br />
predictable manner.<br />
and can be produced in good yields from an E coli<br />
expression system. In the absence of the autoinducer,<br />
the protein is expressed into inclusion bodies. Samples<br />
of the SdiA-HSL complex can be denatured but<br />
cannot be refolded in aqueous buffers. <strong>The</strong> solution<br />
structure of the complex provides a likely explanation<br />
for this behavior. <strong>The</strong> autoinducer molecule is tightly<br />
bound in a deep pocket in the hydrophobic core and<br />
is bounded by specific hydrogen bonds to the side<br />
chains of conserved residues. <strong>The</strong> autoinducer thus<br />
forms an integral part of the hydrophobic core of the<br />
folded SdiA.<br />
PUBLICATIONS<br />
Dyson, H.J., Wright, P.E. Elucidation of the protein folding landscape by NMR.<br />
Methods Enzymol. 394:299, 2005.<br />
Dyson, H.J., Wright, P.E. Intrinsically unstructured proteins and their functions.<br />
Nat. Rev. Mol. Cell Biol. 6:197, 2005.<br />
Nishimura, C., Dyson, H.J., Wright, P.E. Enhanced picture of protein-folding intermediates<br />
using organic solvents in H/D exchange and quench-flow experiments.<br />
Proc. Natl Acad. Sci. U. S. A. 102:4765, 2005.<br />
Nishimura, C., Dyson, H.J. Wright, P.E. Identification of native and nonnative<br />
structure in kinetic folding intermediates of apomyoglobin. J. Mol. Biol., in press.<br />
Nishimura, C., Lietzow, M.A., Dyson H.J., Wright, P.E. Sequence determinants of<br />
a protein folding pathway. J. Mol. Biol. 351:383, 2005.
Nuclear Magnetic Resonance<br />
Studies of the Structure and<br />
Dynamics of Enzymes<br />
H.J. Dyson, P.E. Wright, D. Boehr, M.O. Ebert, G. Kroon,<br />
J. Lansing, C.W. Lee, M. Martinez-Yamout, D. McElheny,<br />
N.E. Preece, K. Sugase, H.S. Won, Y. Yao, L.L. Tennant,<br />
J. Chung, C.L. Brooks, S.J. Benkovic,* A. Holmgren**<br />
* Pennsylvania State University, University Park, Pennsylvania<br />
** Karolinska <strong>Institute</strong>t, Stockholm, Sweden<br />
We use site-specific information from nuclear<br />
magnetic resonance (NMR) to further the<br />
understanding of enzyme function through<br />
study of enzyme structure and dynamics. We focus on<br />
the mechanisms of enzymes and the relationship<br />
between dynamics and function in cellular control by<br />
thiol-disulfide chemistry.<br />
DYNAMICS IN ENZYME ACTION<br />
Dynamic processes are implicit in the catalytic function<br />
of all enzymes. We use state-of-the-art NMR methods<br />
to elucidate the dynamic properties of several enzymes.<br />
New methods have been developed for analysis of NMR<br />
relaxation data for proteins that tumble anisotropically<br />
and for analysis of slow time scale motions.<br />
Dihydrofolate reductase plays a central role in folate<br />
metabolism and is the target enzyme for a number of<br />
anticancer agents. 15 N relaxation experiments on dihydrofolate<br />
reductase from Escherichia coli revealed a<br />
rich diversity of backbone dynamics for a broad range<br />
of time scales (picoseconds to milliseconds). <strong>The</strong>se studies<br />
were extended to additional intermediates in the<br />
reaction cycle and to forms of the enzyme with mutations<br />
at various motional “hot spots.”<br />
In addition, we are using 2 H relaxation measurements<br />
in triple-labeled dihydrofolate reductase to elucidate<br />
the dynamics of critical active-site side chains.<br />
So far, we have identified functionally important motions<br />
in loops that control access to the active site of the<br />
reductase on the same time scale as the hydride transfer<br />
chemistry. <strong>The</strong>se motions become attenuated once the<br />
NADPH cofactor is bound in the active site, locking the<br />
nicotinamide ring in a geometry conducive to hydride<br />
transfer to substrate. We also found evidence of motion<br />
of active-site side chains that are implicated in the<br />
catalytic process.<br />
Most recently, we used relaxation dispersion measurements<br />
to obtain direct information on microsecond-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 183<br />
millisecond time scale motions in dihydrofolate reductase,<br />
allowing us to characterize the structures of the<br />
excited states involved in some of these catalysis-relevant<br />
processes. Fluctuations between these states, which<br />
involve motions of the nicotinamide ring of the cofactor<br />
into and out of the active site, occur on a time scale<br />
that is directly relevant to the structural transitions<br />
involved in progression through the catalytic cycle.<br />
Dihydrofolate reductase is also the test system for<br />
a series of experiments to address the question, If all<br />
of the chemistry goes on at the active site, what is the<br />
purpose of the rest of the enzyme? We will use a series<br />
of chimeric mutants, synthesized by our collaborator<br />
S.J. Benkovic, Pennsylvania State University, by using<br />
a library approach. <strong>The</strong> purpose of these experiments<br />
is to test the hypothesis that local variations in amino<br />
acid sequence, 3-dimensional structure, and polypeptide<br />
chain dynamics strongly influence the local interactions<br />
that mediate enzyme catalysis and may constitute the<br />
essential circumstance that allows enzymes to achieve<br />
high turnover rates as well as exquisite specificity in<br />
their reactions. A combination of NMR structure and<br />
dynamics measurements, single-molecule fluorescence<br />
measurements, and analysis of the catalytic steps in<br />
these mutant proteins will provide new insights into<br />
the role of the protein in enzyme catalysis.<br />
REDOX CONTROL BY THIOL-DISULFIDE CHEMISTRY<br />
Many cellular functions are regulated by thiol-disulfide<br />
chemistry. <strong>The</strong> importance of redox chemistry, particularly<br />
disulfide-dithiol equilibria, in cellular control<br />
mechanisms has only recently been recognized. For<br />
example, the chaperone heat-shock protein 33 (Hsp33)<br />
is regulated by a redox switch; the C-terminal domain<br />
of Hsp33 contains cysteines that are reduced and bound<br />
to zinc under normoxic conditions, but upon oxidation,<br />
the zinc is lost and disulfide bonds form. Interestingly,<br />
the zinc-bound form of the C-terminal domain is well<br />
structured, with a distinctive fold. NMR studies revealed<br />
that upon oxidation, the C-terminal domain becomes<br />
unstructured. We think that this loss of local structure<br />
exposes a dimerization site. Thus, under oxidative stress<br />
conditions, the chaperone dimerizes to the active form.<br />
We did an extensive study of the structural basis<br />
for the activity of several thiol-disulfide enzymes. Thioredoxin,<br />
a small, 108-residue thiol-disulfide oxidoreductase,<br />
has many functions in the cell, including reduction<br />
of ribonucleotides to form deoxyribonucleotides for DNA<br />
synthesis. A primary function of thioredoxin in the cell<br />
is as a protein disulfide reductase, a function vital for
184 MOLECULAR BIOLOGY 2005<br />
the prevention of misfolded proteins in vivo. <strong>The</strong> E coli<br />
thioredoxin system has been fully characterized by using<br />
NMR, including the calculation of high-resolution structures<br />
for both the oxidized (disulfide) and the reduced<br />
(dithiol) forms of the protein.<br />
Using backbone dynamics and amide proton hydrogen<br />
exchange, we found that functional differences in<br />
phage systems between oxidized and reduced thioredoxin<br />
were due to differences in the flexibility of the molecules<br />
rather than to structural differences. We also delineated<br />
the mechanism of E coli thioredoxin. We found that the<br />
reduction reaction of thioredoxin depends critically on<br />
the movement of protons, during the 2-electron–2-proton<br />
transfer reaction, as a substrate disulfide is reduced.<br />
We are investigating a variant E coli thioredoxin with<br />
an N-terminal extension that binds zinc. This exciting<br />
new molecule may be another example of a redox-active,<br />
zinc-binding protein, previously exemplified by the redoxswitch<br />
domain of the chaperone Hsp33.<br />
Glutaredoxins are another major class of thiol-disulfide<br />
regulatory proteins. We recently determined the<br />
structure of glutaredoxin-2 from E coli. This protein<br />
appears to be a link between the glutaredoxin-thioredoxin<br />
class of small thiol-active proteins and the extensive<br />
glutathione-S-transferase class of detoxification enzymes.<br />
Glutaredoxins are thought to be involved in the processes<br />
that result in the attachment and removal of glutathione<br />
and nitrosyl groups from redox-active proteins.<br />
<strong>The</strong>se processes, together with the formation of disulfide<br />
bonds, regulate the activity of redox-active proteins<br />
such as the transcription factor OxyR, which we<br />
also study.<br />
PUBLICATIONS<br />
Chen, J., Won, H.-S., Im, W., Dyson, H.J., Brooks, C.L. III. Generation of nativelike<br />
protein structures from limited NMR data, modern force fields and advanced<br />
conformational sampling. J. Biomol. NMR 31:59, 2005.<br />
McElheny, D., Schnell, J.R., Lansing, J.C., Dyson, H.J., Wright, P.E. Defining the<br />
role of active-site loop fluctuations in dihydrofolate reductase catalysis. Proc. Natl.<br />
Acad. Sci. U. S. A. 102:5032, 2005.<br />
Venkitakrishnan, R.P., Zaborowski, E., McElheny, D., Benkovic, S.J., Dyson, H.J.,<br />
Wright, P.E. Conformational changes in the active site loops of dihydrofolate reductase<br />
during the catalytic cycle. Biochemistry 43:16046, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Ring Assemblies Mediating<br />
ATP-Dependent Protein Folding<br />
and Unfolding<br />
A.L. Horwich, W.A. Fenton, E. Chapman, E. Koculi<br />
Large ring assemblies function in many cellular<br />
contexts as compartments within a compartment,<br />
where actions can be carried out on a substrate<br />
bound in the central space inside an oligomeric ring<br />
by a high local concentration of surrounding active sites.<br />
Both protein folding and unfolding are carried out in<br />
an ATP-dependent fashion by such assemblies. We are<br />
studying the essential double-ring components, chaperonins,<br />
that assist protein folding to the native state.<br />
We are focusing on the bacterial chaperonin GroEL<br />
and more recently have been examining an opposite<br />
number, an “unfoldase,” the bacterial heat-shock protein<br />
100 ring assembly known as ClpA. In the past<br />
year, we focused on polypeptide binding and ATPmediated<br />
action by both machines, showing quite different<br />
mechanisms.<br />
GROEL-MEDIATED FOLDING<br />
We are investigating polypeptide binding by an open<br />
ring of GroEL that is mediated through contacts between<br />
the exposed hydrophobic surface of nonnative polypeptide<br />
and a hydrophobic lining of the open ring. This step<br />
is one that potentially mediates unfolding of kinetically<br />
trapped states. In collaboration with K. Wüthrich, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>, using solution nuclear magnetic<br />
resonance and transverse relaxation optimized<br />
spectroscopy, we examined the structure of isotopelabeled<br />
human dihydrofolate reductase bound to GroEL.<br />
<strong>The</strong> resonances detected indicate that the reductase<br />
does not occupy a stable tertiary structure while bound<br />
to an open GroEL ring and also suggest that the enzyme<br />
is undergoing conformational exchange. This unfolded<br />
state was, however, productive; upon addition of ATP<br />
and the cochaperonin GroES, a nativelike pattern of<br />
resonances was recovered.<br />
<strong>The</strong> binding of ATP and GroES triggers productive<br />
GroEL-GroES–mediated folding in the encapsulated<br />
now-hydrophilic cavity of the GroES-bound ring (Fig. 1).<br />
By contrast, addition of ADP and GroES does not trigger<br />
folding. Surprisingly, however, x-ray and solution<br />
electron cryomicroscopy structures of GroEL-GroES-<br />
ADP and GroEL–GroES–ADP–aluminum fluoride, which<br />
is a folding-active state, are isomorphous. We noted
Fig. 1. Protein folding and unfolding by chaperone ring assemblies.<br />
In protein folding mediated by the chaperonin GroEL (left), the energy<br />
of binding ATP and the cochaperonin GroES are used to produce<br />
rigid body movements of a GroEL ring that eject a bound nonnative<br />
substrate polypeptide into a GroES-encapsulated central cavity,<br />
switched from hydrophobic (shaded) to hydrophilic wall character,<br />
where productive folding proceeds. <strong>The</strong> free energy provided by a<br />
set of hydrogen bonds formed between the γ-phosphate of ATP and<br />
the nucleotide pocket is critical to producing a power stroke of apical<br />
domain movement that can eject the substrate polypeptide into<br />
the folding chamber. In contrast, in ClpA-mediated unfolding (right),<br />
this chaperone seems to use ATP hydrolysis by its D2 ATPase domain<br />
to drive a forceful distalward movement of a loop facing its central<br />
channel, exerting mechanical force on a bound protein that is proposed<br />
to exert an unfolding action.<br />
that these structure determinations were all carried out<br />
in the absence of substrate polypeptide and that a<br />
bound substrate potentially represents a load on the<br />
ring to which it is bound, resisting nucleotide/GroESdriven<br />
elevation and twist of the apical domain that are<br />
associated with ejection of a bound polypeptide off<br />
the cavity wall into the GroES-encapsulated cavity where<br />
productive folding occurs. Thus, the γ-phosphate of ATP<br />
might be critical to exerting a power stroke of apical<br />
movement. Consistent with such an idea, we found that<br />
addition of aluminum fluoride to a GroEL-GroES-ADPpolypeptide<br />
complex triggered productive folding. Further,<br />
we found that a substantial amount of free energy<br />
was released upon binding of aluminum fluoride to<br />
GroEL-GroES-ADP.<br />
To directly monitor apical movement, we used fluorescence<br />
resonance energy transfer between a fluorophore<br />
placed on the stable equatorial base of a subunit<br />
and a fluorophore placed in the apical domain (at a<br />
position that moves ~30 Å during the transition of a<br />
ring from unbound to GroES bound). Indeed, when no<br />
substrate was present, the apical domains opened rapidly<br />
(40 seconds).<br />
Additional studies with fluorophores placed on GroEL<br />
and GroES indicated that GroES can associate rapidly<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
with GroEL-polypeptide complexes in ADP, evidently<br />
forming a collision complex, but subsequent apical<br />
movement is impaired. We are using electron microscopy<br />
to examine the putative collision state, because<br />
it most likely is a state that is transiently populated in<br />
the physiologic nucleotide ATP.<br />
CLPA-MEDIATED UNFOLDING<br />
MOLECULAR BIOLOGY 2005 185<br />
ClpA recognizes terminal peptide tags of proteins<br />
that are concordantly unfolded and translocated through<br />
its central channel. <strong>The</strong> polypeptide is generally directly<br />
translocated into a double-ring proteasome-like protease,<br />
ClpP, where it is degraded. During this past year,<br />
we used chemical cross-linkers placed on tag elements<br />
to identify channel-facing structures of ClpA that bind<br />
the tags and then did mutational analysis of the identified<br />
regions. For example, the C-terminal 11-residue<br />
ssrA peptide, which is added to proteins stalled at the<br />
ribosome to recruit these chains to ClpA, binds to 3<br />
loops in the central channel of ClpA, 2 at the level of<br />
the proximal D1 ATPase domain and 1 at the level of<br />
the distal D2 ATPase (Fig. 1). Interestingly, a mutation<br />
at the point of insertion of the D2 loop into the channel<br />
wall allows substrate binding but blocks unfolding/<br />
translocation, suggesting that this loop, connected to<br />
the more active D2 ATPase of ClpA, is a translocator<br />
that pulls on bound polypeptide in association with<br />
ATP hydrolysis, exerting a mechanical force that mediates<br />
unfolding. Consistently, x-ray studies of different<br />
nucleotide states have shown that 2 other such ring<br />
components that act on nucleic acids, the phi12 packaging<br />
motor and simian virus 40 T antigen, undergo<br />
such movements of channel-facing loops.<br />
PUBLICATIONS<br />
Hinnerwisch, J., Fenton, W.A., Furtak, K., Farr, G.W., Horwich, A.L. Loops in the<br />
central channel of ClpA chaperone mediate protein binding, unfolding, and translocation.<br />
Cell 121:1029, 2005.<br />
Horst, R., Bertelsen, E.B., Fiaux, J., Wider, G., Horwich, A.L., Wüthrich, K.<br />
Direct NMR observation of a substrate protein bound to the chaperonin GroEL.<br />
Proc. Natl. Acad. Sci. U. S. A. 102:000, 2005.<br />
Motojima, F., Chaudhry, C., Fenton, W.A., Farr, G.W., Horwich, A.L. Substrate<br />
polypeptide presents a load on the apical domains of the chaperonin GroEL. Proc.<br />
Natl. Acad. Sci. U. S. A. 101:15005, 2004.
186 MOLECULAR BIOLOGY 2005<br />
Chemical Regulation of<br />
Gene Expression<br />
J.M. Gottesfeld, D. Alvarez-Carbonell, R. Burnett, J. Chou,<br />
D. Herman, K. Jennsen, S. Ku, P.B. Dervan*, K. Luger**<br />
* California <strong>Institute</strong> of Technology, Pasadena, California<br />
** Colorado State University, Fort Collins, Colorado<br />
TRANSCRIPTION REGULATION WITH SMALL<br />
MOLECULES<br />
Pyrrole-imidazole polyamides are the only available<br />
class of synthetic small molecules that can be<br />
designed to bind predetermined DNA sequences<br />
with affinities comparable to those of cellular gene regulatory<br />
proteins. In collaboration with P.B. Dervan and<br />
colleagues at the California <strong>Institute</strong> of Technology, we<br />
showed that polyamides inhibit the DNA-binding activities<br />
of various transcriptional regulatory proteins and<br />
can be used to inhibit transcription in cell culture experiments.<br />
Previous studies established that transcription<br />
can be inhibited with polyamides by targeting the binding<br />
sites for essential transcription regulatory proteins in<br />
gene promoters in the cell nucleus. We also found that<br />
site-specific DNA alkylation by polyamide-chlorambucil<br />
conjugates within a coding region of a gene strongly<br />
blocks transcription elongation by mammalian RNA<br />
polymerase II, both in vitro and in reporter gene transfection<br />
experiments in cell culture.<br />
We screened a series of polyamide-chlorambucil<br />
conjugates with different DNA sequence specificities<br />
for effects on morphology and growth characteristics<br />
of human colon carcinoma cell lines. We identified a<br />
compound that causes cells to arrest in the G 2 /M stage<br />
of the cell cycle, without any apparent cytotoxic effects.<br />
This change in growth properties required both the DNAbinding<br />
specificity of the polyamide and the alkylator<br />
moiety, suggesting that growth arrest is due to the silencing<br />
of a set of specific genes by site-specific alkylation.<br />
Surprisingly, DNA microarray analysis indicated that<br />
only a few genes of about 18,000 genes probed were<br />
significantly downregulated by this polyamide, and<br />
reverse transcriptase–polymerase chain reaction and<br />
Western blotting experiments confirmed that among<br />
these genes, a member of the human gene family that<br />
encodes histone H4, an essential component of chromatin,<br />
is significantly downregulated. This particular<br />
gene, the gene for histone H4c, is actively transcribed<br />
in various cancer cell lines but is only moderately<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
transcribed in normal cells and tissues. Downregulation<br />
of H4c mRNA by small interfering RNA yielded the<br />
same cellular response, providing target validation.<br />
<strong>The</strong> gene for histone H4c contains binding sites for<br />
the active polyamide, and DNA alkylation within the<br />
coding region of the gene was confirmed in cell culture<br />
by using ligation-mediated polymerase chain reaction.<br />
Cells treated with this polyamide-chlorambucil conjugate<br />
did not grow in soft agar and did not form tumors<br />
in nude mice, indicating that polyamide-treated cells<br />
are no longer tumorigenic. <strong>The</strong> compound is active in<br />
vivo, blocking tumor growth in mice, without any obvious<br />
toxic effects. We extended these studies to various<br />
cell lines representing various types of human cancers,<br />
including solid tumors of the breast, cervix, lung, pancreas,<br />
prostate, and bone and blood cancers, such as<br />
leukemias. Our results suggest that polyamide-DNA<br />
alkylators may lead to a new class of cancer chemotherapeutic<br />
agents.<br />
POLYAMIDES AS ACTIVATORS OF GENE EXPRESSION<br />
In several human diseases, activation of a repressed<br />
gene might be useful as a therapeutic approach. One<br />
example is the neurodegenerative disease Friedreich’s<br />
ataxia, in which gene silencing caused by an unusual<br />
DNA structure is the primary cause of the disease. <strong>The</strong><br />
DNA abnormality found in 98% of patients with Friedreich’s<br />
ataxia is the unstable hyperexpansion of a GAA<br />
triplet repeat in the first intron of the frataxin gene,<br />
which adopts a triplex DNA structure, resulting in<br />
decreased transcription and reduced levels of frataxin<br />
protein. Frataxin is a mitochondrial protein that functions<br />
in iron homeostasis, and decreased levels of frataxin lead<br />
to neurodegeneration and cardiomyopathies.<br />
We designed pyrrole-imidazole polyamides to target<br />
GAA repeats in DNA with high affinity, and we found<br />
that these molecules relieved transcription inhibition<br />
of the frataxin gene in cell lines and in primary lymphocytes<br />
derived from patients with Friedreich’s ataxia.<br />
<strong>The</strong>se molecules localize in the cell nucleus, as determined<br />
by fluorescence deconvolution microscopy with<br />
polyamide-dye conjugates, and most likely reverse repression<br />
of the frataxin gene by stabilizing canonical Watson-<br />
Crick B-type DNA. Changing the sequence specificities<br />
of the molecules abolished their ability to induce frataxin<br />
expression. <strong>The</strong>se molecules are a first step toward<br />
therapeutic agents for treatment of Friedreich’s ataxia.<br />
DNA RECOGNITION WITHIN CHROMATIN<br />
Biochemical and x-ray crystallography studies indicate<br />
that nucleosomal DNA is largely available for molec-
ular recognition by pyrrole-imidazole polyamides. Polyamide<br />
binding sites that are located 80 bp apart on<br />
linear DNA lie across the 2 gyres of the DNA superhelix<br />
in the nucleosome, forming a supergroove that is<br />
unique to the nucleosome. On the basis of this observation,<br />
we developed bivalent pyrrole-imidazole polyamide<br />
clamps that bind with high specificity across<br />
the nucleosomal supergroove. X-ray crystallography<br />
studies performed in the laboratory of our collaborator,<br />
K. Luger, Colorado State University, indicated that the<br />
clamps bind as designed and effectively cross-link the<br />
2 gyres of the DNA superhelix in the nucleosome and<br />
stabilize nucleosomal DNA from dissociation. <strong>The</strong>se<br />
molecules are useful probes of chromatin structure and<br />
dynamics and are tools for regulation of nucleosome<br />
mobility during transcription.<br />
PUBLICATIONS<br />
Beltran, A.C., Dawson, P.E., Gottesfeld, J.M. Role of DNA sequence in the binding<br />
specificity of synthetic basic-helix-loop-helix domains. Chembiochem 6:104, 2005.<br />
Dickinson, L.A., Burnett, R., Melander, C., Edelson, B.S., Arora, P.S., Dervan,<br />
P.B., Gottesfeld, J.M. Arresting cancer proliferation by small-molecule gene regulation.<br />
Chem. Biol. 11:1583, 2004.<br />
Edayathumangalam, R.S., Weyermann, P., Dervan, P.B., Gottesfeld, J.M., Luger, K.<br />
Nucleosomes in solution exist as a mixture of twist-defect states. J. Mol. Biol.<br />
345:103, 2005.<br />
Gearhart, M.D., Dickinson, L., Ehley, J., Melander, C., Dervan, P.B., Wright, P.E.,<br />
Gottesfeld, J.M. Inhibition of DNA binding by human estrogen-related receptor 2<br />
and estrogen receptor with minor groove binding polyamides. Biochemistry<br />
44:4196, 2005.<br />
Single-Molecule Conformational<br />
Dynamics of Nucleic Acid<br />
Enzymes<br />
D.P. Millar, M.F. Bailey, G. Pljevalj˘cić, S. Pond, G. Stengel,<br />
N. Tassew, E.J.C. Van der Schans<br />
<strong>The</strong> focus of our research is the assembly and conformational<br />
dynamics of nucleic acid–based<br />
macromolecular machines. We use single-molecule<br />
fluorescence methods to investigate a range of<br />
systems, including ribozymes, DNA polymerases, and<br />
topoisomerases. Our studies reveal the large structural<br />
rearrangements that occur as an integral component of<br />
the catalytic mechanism of these enzymes.<br />
RIBOZYMES<br />
RNA conformation plays a central role in the mechanism<br />
of ribozyme catalysis. <strong>The</strong> hairpin ribozyme is a<br />
small nucleolytic ribozyme that serves as a model sys-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
tem for detailed biophysical studies of RNA folding and<br />
catalysis. <strong>The</strong> hairpin ribozyme consists of 2 internal<br />
loops, 1 of which contains the scissile phosphodiester<br />
bond, displayed on 2 arms of a 4-way multihelix junction.<br />
To attain catalytic activity, the ribozyme must fold<br />
into a specific conformation in which the 2 loops are<br />
docked with each other, forming a network of tertiary<br />
hydrogen bonds. We monitor the formation of this<br />
docked structure by using fluorescence resonance energy<br />
transfer (FRET) and ribozyme constructs labeled with<br />
donor and acceptor dyes. By measuring FRET at the<br />
level of single ribozyme molecules, we reveal subpopulations<br />
of compact and extended conformers that are<br />
hidden in conventional experiments. Using this approach,<br />
we found that the ribozyme populates an intermediate<br />
state in which the 2 loops are in proximity but tertiary<br />
interactions have yet to form. This quasi-docked state<br />
forms rapidly (submillisecond time scale), but the subsequent<br />
formation of tertiary contacts between the<br />
loops occurs much more slowly. Surprisingly, the rate<br />
of formation of tertiary structure is essentially independent<br />
of temperature, indicating that the activation<br />
enthalpy is negligible. Hence, the slow tertiary folding<br />
is due to an unfavorable entropy change in reaching<br />
the transition state.<br />
<strong>The</strong>se observations reveal that the tertiary structure<br />
of the hairpin ribozyme is formed through a slow<br />
conformational search process. This fundamental mechanism<br />
of formation of RNA tertiary structure was<br />
obscured in most previous folding studies because of<br />
the strong propensity of RNA molecules to populate<br />
nonnative conformations that act as kinetic traps during<br />
the course of folding.<br />
DNA POLYMERASES<br />
MOLECULAR BIOLOGY 2005 187<br />
DNA polymerases are remarkable for their ability<br />
to synthesize DNA at rates approaching several hundred<br />
base pairs per second while maintaining an extremely<br />
low frequency of errors. To elucidate the origin of polymerase<br />
fidelity, we are using single-molecule fluorescence<br />
methods to examine the dynamic interactions<br />
that occur between a DNA polymerase and its DNA<br />
and nucleotide substrates. <strong>The</strong> FRET method is being<br />
used to observe conformational transitions of the<br />
enzyme-DNA complex that occur during selection and<br />
incorporation of an incoming nucleotide substrate. Our<br />
results reveal that binding of a correct nucleotide substrate<br />
induces a slow conformational change within the<br />
polymerase, altering the contacts between the enzyme<br />
and the DNA primer/template. This conformational
188 MOLECULAR BIOLOGY 2005<br />
change appears to primarily involve the finger and<br />
thumb subdomains of the enzyme. Our studies are providing<br />
new insights into the dynamic structural changes<br />
responsible for nucleotide recognition and selection by<br />
DNA polymerases. Single-pair FRET methods are also<br />
being used to monitor the movement of the DNA primer/<br />
template between the separate polymerizing and editing<br />
sites of the enzyme. This active-site switching of<br />
DNA plays a key role in the proofreading process used<br />
to remove misincorporated nucleotides from the newly<br />
synthesized DNA. <strong>The</strong> advantage of single-molecule<br />
observations is that they eliminate the need to synchronize<br />
a population of molecules, allowing these dynamic<br />
processes to be directly observed.<br />
TOPOISOMERASES<br />
Topoisomerases are enzymes that control the state<br />
of DNA supercoiling in the cell. Type I topoisomerases<br />
introduce a nick into a strand of DNA and become<br />
covalently joined to the cleaved strand. This process<br />
allows the other strand to freely swivel around the first,<br />
resulting in the relaxation of supercoils within the DNA.<br />
<strong>The</strong> enzyme-DNA connection is then reversed, and the<br />
broken strand is rejoined, completing the process of<br />
supercoil removal. We are using single-pair FRET methods<br />
to observe the DNA-unwinding activity of single<br />
type I topoisomerase enzymes in real time. <strong>The</strong> purpose<br />
of these studies is to directly observe DNA rotational<br />
motions during supercoil relaxation and to<br />
determine whether the same number of supercoils is<br />
removed during each enzyme-DNA encounter.<br />
PUBLICATIONS<br />
Millar, D., Traskelis, M.A., Benkovic, S.J. On the solution structure of the T4 sliding<br />
clamp (gp45). Biochemistry 43:12723, 2004.<br />
Pljevalj˘cić, G., Klostermeier, D., Millar, D.P. <strong>The</strong> tertiary structure of the hairpin ribozyme<br />
is formed through a slow conformational search. Biochemistry 44:4870, 2005.<br />
Single-Molecule Biophysics<br />
A.A. Deniz, S.Y. Berezhna, J.P. Clamme, A.C.M. Ferreon,<br />
E.A. Lemke, S. Mukhopadhyay, S. Stanford, P. Zhu<br />
We develop and use state-of-the-art singlemolecule<br />
fluorescence methods to address<br />
key biological questions. Single-molecule and<br />
small-ensemble methods offer key advantages over traditional<br />
measurements, allowing us to directly observe the<br />
behavior of individual subpopulations in mixtures of<br />
molecules and to measure kinetics of structural transi-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
tions of stochastic processes under equilibrium conditions.<br />
We use these methods to study multiple structural<br />
states or reaction pathways and stochastic dynamics<br />
during the folding and assembly of biomolecules.<br />
One major goal is to apply single-molecule methods<br />
to studies of protein and RNA folding. Using relatively<br />
simple model systems, we are addressing several fundamental<br />
questions about folding mechanisms. Partially<br />
folded or misfolded protein structures are also thought<br />
to play important cellular roles, and these states also<br />
can be studied by using single-molecule methods. In this<br />
context, we are examining the folding and aggregation of<br />
synuclein, a protein implicated in the pathogenesis of<br />
Parkinson’s disease and other neurodegenerative diseases.<br />
We also continue to use single-pair fluorescence<br />
resonance energy transfer (FRET) to study the folding<br />
of RNA hairpin ribozymes, in collaboration with D.A.<br />
Millar, Department of <strong>Molecular</strong> <strong>Biology</strong>. In addition,<br />
we are developing a single-molecule fluorescence<br />
quenching method that will be useful for measuring<br />
distance changes of less than 30 Å in proteins and<br />
RNA, a scale at which the resolution of single-pair<br />
FRET is low.<br />
To better study the folding, assembly, and activity of<br />
larger and multicomponent biological complexes, we are<br />
developing new multicolor single-molecule FRET methods.<br />
As a first step, we developed a diffusion 3-color singlemolecule<br />
FRET method by which 2 or more intramolecular<br />
or intermolecular distances can be measured<br />
simultaneously. In collaboration with J.R. Williamson,<br />
Department of <strong>Molecular</strong> <strong>Biology</strong>, we are using these<br />
novel methods to study the detailed mechanisms of<br />
assembly of the bacterial ribosome. <strong>The</strong> small 30S<br />
subunit of the ribosome assembles from a large RNA<br />
and 21 small proteins through a complex process that<br />
involves several steps of binding and conformational<br />
changes. Initially, we are focusing on the conformational<br />
properties of small RNA fragments from the 30S<br />
subunit and on the interactions of the fragments with<br />
their protein partners. <strong>The</strong>se studies are also being<br />
extended to the assembly of entire domains of the<br />
30S subunit.<br />
Finally, using a combination of high-sensitivity<br />
imaging and fluorescence correlation spectroscopy, we<br />
are beginning to study the lipid-mediated entry and<br />
intracellular delivery pathways of antisense oligodeoxynucleotides<br />
and small interfering RNA. An understanding<br />
of these mechanisms will be critical to improving<br />
the efficiencies of these important genetic tools.
PUBLICATIONS<br />
Berezhna, S., Schaefer, S., Heintzmann, R., Jahnz, M., Boese, G., Deniz, A.A.,<br />
Schwille, P. New effects in polynucleotide release from cationic lipid carriers<br />
revealed by confocal imaging, fluorescence cross-correlation spectroscopy and single<br />
particle tracking. Biochim. Biophys. Acta 1669:193, 2005.<br />
Clamme, J.-P., Deniz, A.A. Three-color single-molecule fluorescence resonance<br />
energy transfer. Chemphyschem 6:74, 2005.<br />
Zhu, P., Clamme, J.-P., Deniz, A.A. Fluorescence quenching by TEMPO: a sub-30 Å<br />
single molecule ruler. Biophys. J., in press.<br />
Computer Modeling of Proteins<br />
and Nucleic Acids<br />
D.A. Case, M. Crowley, Q. Cui, P. Dasgupta, F. Dupradeau,*<br />
N. Grivel,* R. Lelong,* S. Moon, D. Nguyen, D. Shivakumar,<br />
R. Torres, R.C. Walker, L., Yan,* J. Ziegler**<br />
* Université Jules Verne, Amiens, France<br />
** Universität Bayreuth, Bayreuth, Germany<br />
Computer simulations offer an exciting approach<br />
to the study of many aspects of biochemical<br />
interactions. We focus primarily on molecular<br />
dynamics simulations (in which Newton’s equations of<br />
motions are solved numerically) to model the solution<br />
behavior of biomacromolecules. Recent applications<br />
include detailed analyses of electrostatic interactions<br />
in short peptides (folded and unfolded), proteins, and<br />
oligonucleotides in solution.<br />
In addition, molecular dynamics methods are useful<br />
in refining solution structures of proteins by using<br />
constraints derived from nuclear magnetic resonance<br />
(NMR) spectroscopy, and we continue to explore new<br />
methods in this area. Our developments are incorporated<br />
into the Amber molecular modeling package, designed<br />
for large-scale biomolecular simulations, and into other<br />
software, including Nucleic Acid Builder, for developing<br />
3-dimensional models of unusual nucleic acid structures;<br />
SHIFTS, for analyzing chemical shifts in proteins and<br />
nucleic acids; and RNAmotif, for finding structural motifs<br />
in genomic sequence databases.<br />
Additional studies on active sites of nitrogenase<br />
and other metalloenzymes are described in the report<br />
of L. Noodleman, Department of <strong>Molecular</strong> <strong>Biology</strong>.<br />
NMR AND THE STRUCTURE AND DYNAMICS OF<br />
PROTEINS AND NUCLEIC ACIDS<br />
Our overall goal is to extract the maximum amount<br />
of information on biomolecular structure and dynamics<br />
from NMR experiments. To this end, we are studying<br />
the use of direct refinement methods for determining<br />
biomolecular structures in solution, going beyond dis-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
tance constraints to generate closer connections between<br />
calculated and observed spectra. We are also using<br />
quantum chemistry to study chemical shifts and spinspin<br />
coupling constants. Other types of data, such as<br />
chemical shift anisotropies, direct dipolar couplings in<br />
partially oriented samples, and analysis of cross-correlated<br />
relaxation, are also being used to guide structure<br />
refinement. In recent structural studies, we focused on<br />
minor groove–binding drugs in complex with DNA and<br />
on complexes of zinc finger proteins with RNA.<br />
NUCLEIC ACID MODELING<br />
MOLECULAR BIOLOGY 2005 189<br />
Another project centers on the development of novel<br />
computer methods to construct models of “unusual”<br />
nucleic acids that go beyond traditional helical motifs.<br />
We are using these methods to study circular DNA, small<br />
RNA fragments, and 3- and 4-stranded DNA complexes,<br />
including models for recombination sites. We continue<br />
to develop efficient computer implementations of continuum<br />
solvent methods to allow simplified simulations<br />
that do not require a detailed description of the<br />
solvent (water) molecules; this approach also provides<br />
a useful way to study salt effects.<br />
This research is part of a larger effort to develop<br />
low-resolution models for nucleic acids that can be<br />
extended to much larger structures such as circular DNA,<br />
viruses, or models of ribosomal particles. A computer<br />
language, NAB, was developed to make it easier to<br />
construct and simulate molecular models for complex<br />
and often low-resolution problems. <strong>The</strong> language is<br />
being used to study compact and swollen viruses, to<br />
analyze curved and circular DNA, and to simulate<br />
assembly of ribosomes.<br />
DYNAMICS AND ENERGETICS OF NATIVE AND<br />
NONNATIVE STATES OF PROTEINS<br />
Analysis methods similar to those described for<br />
nucleic acids are also being used to estimate thermodynamic<br />
properties of “molten globules” and unfolded<br />
states of proteins. <strong>The</strong>se studies are an extension of<br />
our earlier work on the folding of peptide fragments of<br />
proteins. A key feature is the development of computational<br />
methods that can be used to model pH and<br />
salt dependence of complex conformational transitions,<br />
such as unfolding events.<br />
A second aspect of this research is a detailed interpretation<br />
of NMR results for protein nonnative states<br />
through molecular dynamics simulations and the construction<br />
of models for molecular motion and disorder.<br />
In a parallel effort, we are studying correlated fluctuations<br />
about native conformations in a variety of pro-
190 MOLECULAR BIOLOGY 2005<br />
teins, including dihydrofolate reductase, metallo-β-lactamase,<br />
binase, and cyclic-dependent kinase, in an<br />
effort to make more secure connections between the<br />
motions of proteins and the activities of enzymes.<br />
All of these modeling activities are based on molecular<br />
mechanics force fields, which provide estimates of<br />
energies as a function of conformation. We continue to<br />
work on improvements in force fields; recently, we<br />
focused on adding aspects of electronic polarizability,<br />
going beyond the usual fixed-charge models, and on<br />
methods for handling arbitrary organic molecules that<br />
might be considered potential inhibitors in drug discovery<br />
efforts. Overall, the new models should provide<br />
a better picture of the noncovalent interactions between<br />
peptide groups and the groups’ surroundings, leading<br />
ultimately to more faithful simulations.<br />
BIOCHEMICAL SIMULATIONS AT CONSTANT pH<br />
Like temperature and pressure, the solution pH is<br />
an important intensive thermodynamic variable that is<br />
commonly varied in experiments and that is used by<br />
cells to influence biochemical function. It is now becoming<br />
feasible to carry out practical molecular dynamics<br />
simulations that mimic the thermodynamics of such<br />
experiments, by allowing proton transfer between the<br />
system of interest and a hypothetical bath of protons at<br />
a given pH. <strong>The</strong>se calculations are demanding, both<br />
because the changes in the energetics of charge that<br />
occur upon protonation or deprotonation must be accurately<br />
modeled and because such simulations must<br />
sample both molecular configurations and the large<br />
number of protonation states that are possible in a<br />
molecule with many acidic or basic sites.<br />
This problem is difficult, because almost all biomolecules<br />
have multiple sites that can bind or release<br />
protons, and these sites are coupled to one another in<br />
complex ways. In recent years, however, increases in<br />
computational power and new models for estimating<br />
the energetics of protonation and deprotonation events<br />
have led to serious attempts at simulations that allow<br />
the solution pH to be specified as an external variable<br />
in a manner that parallels the ways in which temperature<br />
or pressure are specified.<br />
We recently developed practical methods for estimating<br />
ionization probabilities and for allowing the<br />
solution pH to be entered as an input variable. Figure 1<br />
shows the results for an acidic group in the protein<br />
thioredoxin. <strong>The</strong> curves show the distribution of energy<br />
differences between the protonated and deprotonated<br />
forms of the acid or base residue. We can examine the<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 1. Probability profile for the energy gap (the energy difference<br />
between the protonated and deprotonated forms, in kcal/mol)<br />
for the side chain of aspartic acid at position 26 in thioredoxin.<br />
Values of λ (shown beside the curves) interpolate between the neutral<br />
form at λ = 0 and the ionized form at λ = 1. Simple behavior<br />
would appear as an inverted parabola; multiple conformations lead<br />
to the more complex behavior seen at λ = 0.11.<br />
behavior of this variable near the ionized form, corresponding<br />
to ordinary pH, or near the neutral, protonated<br />
form, at low pH. <strong>The</strong> results show complex<br />
behavior at low pH, which can be analyzed and related<br />
to the nature of the acid-base transition under those<br />
conditions. <strong>The</strong>se ideas can form the foundation of<br />
powerful methods to explore the response of proteins<br />
to changes in solvent pH.<br />
PUBLICATIONS<br />
Baker, N.A., Bashford, D., Case, D.A. Implicit solvent electrostatics in biomolecular<br />
simulation. Adv. Macromol. Simul., in press.<br />
Beveridge, D.L., Barreiro, G., Byun, K.S., Case, D.A., Cheatham, T.E. III, Dixit, S.B.,<br />
Giudice, E., Lankas, F., Lavery, R., Maddocks, J.H., Osman, R., Siebert, E., Sklenar,<br />
H., Stoll, G., Thayer, K.M., Varnai, P., Young, M.A. <strong>Molecular</strong> dynamics simulations of<br />
the 136 unique tetranucleotide sequences of DNA oligonucleotides, 1: research<br />
design, informatics, and results on d(CpG) steps. Biophys. J. 87:3799, 2004.<br />
Case, D.A., Cheatham, T.E., Darden, T., Gohlke, H., Luo, R., Merz, K.M., Onufriev, A.,<br />
Simmerling, C., Wang, B., Woods, R. <strong>The</strong> Amber biomolecular simulation programs.<br />
J. Comput. Chem., in press.<br />
Mongan, J., Case, D.A. Biomolecular simulations at constant pH. Curr. Opin.<br />
Struct. Biol. 15:157, 2005.<br />
Mongan, J., Case, D.A., McCammon, J.A. Constant pH molecular dynamics in<br />
generalized Born implicit solvent. J. Comput. Chem. 25:2038, 2004.<br />
Zhang., Q., Dwyer, T., Tsui, V., Case, D.A., Cho, J., Dervan, P.B., Wemmer, D.E. NMR<br />
structure of a cyclic polyamide-DNA complex. J. Am. Chem. Soc. 126:7958, 2004.
Quantum Chemistry for<br />
Intermediates, Reaction<br />
Pathways, and Spectroscopy<br />
L. Noodleman, D.A. Case, W.-G. Han, F. Himo,* T. Lovell,**<br />
T. Liu,*** M.J. Thompson,**** R.A. Torres<br />
* Royal <strong>Institute</strong> of Technology, Stockholm, Sweden<br />
** AstraZeneca R&D, Mölndal, Sweden<br />
*** University of Maryland, College Park, Maryland<br />
**** Boston University, Boston, Massachusetts<br />
We use a combination of modern quantum chemistry<br />
(density functional theory) and classical<br />
electrostatics to describe the energetics, reaction<br />
pathways, and spectroscopic properties of enzymes<br />
and to analyze systems with novel catalytic, photochemical,<br />
or photophysical properties.<br />
Critical biosynthetic and regulatory processes may<br />
involve catalytic transformations of fairly small molecules<br />
or groups by transition-metal centers. <strong>The</strong> ironmolybdenum<br />
cofactor center of nitrogenase catalyzes<br />
the multielectron reduction of molecular nitrogen to 2<br />
ammonia molecules plus molecular hydrogen. We are<br />
continuing our work on the catalytic cycle of this enzyme,<br />
following up on our earlier research on the structure of<br />
the MoFe 7 S 9 X prismane active site, where the central<br />
ligand X most likely is nitride.<br />
Class I ribonucleotide reductases are aerobic enzymes<br />
that catalyze the reduction of ribonucleotides to deoxyribonucleotides,<br />
providing the required building blocks<br />
for DNA replication and repair. <strong>The</strong>se ribonucleotideto-deoxyribonucleotide<br />
reactions occur via a long-range<br />
radical (or proton-coupled electron transfer) propagation<br />
mechanism initiated by a fairly stable tyrosine<br />
radical, “the pilot light.” When this pilot light goes<br />
out, the tyrosine radical is regenerated by a high-oxidation-state<br />
iron(III)-iron(IV)-oxo enzyme intermediate,<br />
called intermediate X. We are using density functional<br />
and electrostatics calculations in combination with<br />
analysis of Mössbauer, electron nuclear double resonance,<br />
and magnetic circular dichroism spectroscopic<br />
findings to search for a proper structural and electronic<br />
model for intermediate X. On the basis of these studies,<br />
we propose that intermediate X contains a di-oxo<br />
that bridges the iron(III)-iron(IV) in an asymmetric diamond<br />
structure (Fig. 1).<br />
In studies with E. Getzoff and M.J. Thompson,<br />
Department of <strong>Molecular</strong> <strong>Biology</strong>, and D. Bashford, St.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 191<br />
Fig. 1. Proposed model for the active site of class I ribonucleotide<br />
reductase intermediate X.<br />
Jude Children’s Hospital, Memphis, Tennessee, we are<br />
examining the basis for the spectral tuning of the<br />
chromophore at the active site of photoactive yellow<br />
protein as an example of a light-activated signal transducing<br />
protein.<br />
In collaborations with K. Hahn, A. Toutchkine, and<br />
D. Gremiachinsky, University of North Carolina, Chapel<br />
Hill, North Carolina; F. Himo, Royal <strong>Institute</strong> of Technology,<br />
Stockholm, Sweden; and M. Ullmann, University<br />
of Bayreuth, Bayreuth, Germany, we examined the<br />
optical properties of solvent-dependent fluorescent<br />
dyes as prototypes for fluorescent tags that could act<br />
as reporters of protein conformational change due to<br />
ligand binding. <strong>The</strong>se detailed calculations will be used<br />
to improve design strategies for stable and optically<br />
useful dyes.<br />
Also, with Dr. Bashford’s group, we are studying<br />
reaction pathways for the catalytic dephosphorylation<br />
of a tyrosine side chain by a low molecular weight<br />
protein tyrosine phosphatase. <strong>The</strong> reaction occurs in 2<br />
distinct steps: first, formation and then hydrolysis of a<br />
phosphocysteine intermediate.<br />
In a collaboration with K. Janda and T. Dickerson,<br />
Department of Chemistry, we used quantum chemical<br />
density functional theory methods to examine the mechanism<br />
of nornicotine-catalyzed aldol reactions in<br />
aqueous solution. Nornicotine is a long-lived nicotine<br />
metabolite generated under physiologic conditions in cigarette<br />
smokers. This reaction leads to abnormal protein<br />
glycation and to covalent modification of steroid drugs,<br />
including the prescription corticosteroid prednisone.<br />
We are continuing our collaboration with K.B.<br />
Sharpless, V.V. Fokin, R. Hilgraf, and V. Rostovtsev,<br />
Department of Chemistry, on the catalytic mechanisms<br />
used by transition-metal ions in click chemistry, in which<br />
metal centers catalyze ring formation from multiply
192 MOLECULAR BIOLOGY 2005<br />
bonded precursors. Our current focus is the mechanism<br />
of copper(I) reactions, because copper(I) in water shows<br />
great versatility in ligating organic azides and alkynes<br />
to form 5-membered heterocycles (triazoles) with wide<br />
molecular diversity. On the basis of density function<br />
theory calculations, we predict that an unusual 6-membered<br />
copper(III) metallocycle intermediate is formed,<br />
with only a low barrier to the triazole-copper(I) derivative,<br />
leading to the triazole product after proteolysis.<br />
PUBLICATIONS<br />
Asthagiri, D., Liu, T., Noodleman, L., Van Etten, R.L., Bashford, D. On the role of the<br />
conserved aspartate in the hydrolysis of the phosphocysteine intermediate of the low<br />
molecular weight tyrosine phosphatase. J. Am. Chem. Soc. 126:12677, 2004.<br />
Dickerson, T.J., Lovell, T., Meijler, M.M., Noodleman, L., Janda, K.D. Nornicotine<br />
aqueous aldol reactions: synthetic and theoretical investigations into the origins of<br />
catalysis. J. Org. Chem. 69:6603, 2004.<br />
Himo, F., Lovell, T., Hilgraf, R., Rostovtsev, V.V., Noodleman, L., Sharpless, K.B.,<br />
Fokin, V.V. Copper(I)-catalyzed synthesis of azoles: DFT study predicts unprecedented<br />
reactivity and intermediates. J. Am. Chem. Soc. 127:210, 2005.<br />
<strong>The</strong>oretical and Computational<br />
<strong>Molecular</strong> Biophysics<br />
C.L. Brooks III, C. An, R. Armen, I. Borelli, D. Bostick,<br />
S.R. Brozell, D. Braun, L. Bu, J. Chen, M.F. Crowley,<br />
O. Guvench, R. Hills, W. Im, J. Khandogin, I. Khavrutskii,<br />
J. Lee, R. Mannige, M. Michino, H.D. Nguyen, Y.Z. Ohkubo,<br />
M. Olson,* S. Patel, D.J. Price, V. Reddy, H.A. Scheraga,**<br />
C. Shepard, A. Stoycheva, F.M. Tama, M. Taufer,***<br />
K.A. Taylor,**** I.F. Thorpe, C. Wildman<br />
* U.S. Army Medical <strong>Research</strong> <strong>Institute</strong> of Infectious Diseases, Fort Detrick,<br />
Maryland<br />
** Cornell University, Ithaca, New York<br />
*** University of Texas, El Paso, Texas<br />
**** Florida State University, Tallahassee, Florida<br />
Understanding the forces that determine the<br />
structure of proteins, peptides, nucleic acids,<br />
and complexes containing these molecules and<br />
the processes by which the structures are adopted is<br />
essential to complete our knowledge of the molecular<br />
nature of structure and function. To address such questions,<br />
we use statistical mechanics, molecular simulation,<br />
statistical modeling, and quantum chemistry.<br />
Creating atomic-level models to simulate biophysical<br />
processes (e.g., folding of a protein or binding of a<br />
ligand to a biological receptor) requires (1) the development<br />
of potential energy functions that accurately<br />
represent the atomic interactions and (2) the use of<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
quantum chemistry to aid in determining the parameters<br />
for the models. Calculation of thermodynamic properties<br />
requires the development and implementation of<br />
new theoretical and computational approaches that connect<br />
averages over atomistic descriptions to experimentally<br />
measurable thermodynamic and kinetic properties.<br />
Interpreting experimental results at more microscopic<br />
levels is fueled by the development and investigation<br />
of theoretical models of the processes of interest.<br />
Massive computational resources are needed to realize<br />
these objectives, and this need motivates our efforts<br />
aimed at the efficient use of new computer architectures,<br />
including large supercomputers, Linux Beowulf<br />
clusters, and computational grids. Each of the objectives<br />
and techniques mentioned represents an ongoing<br />
area of development within our research program in<br />
computational biophysics. <strong>The</strong> following are highlights<br />
of a few specific projects.<br />
FOLDING, STRUCTURE, AND FUNCTION OF<br />
MEMBRANE-BOUND PROTEINS<br />
Folding, insertion, and stability of membrane proteins<br />
are directly governed by the unique hydrophilic<br />
and hydrophobic environment provided by biological<br />
membranes. Modeling this heterogeneous environment<br />
is both an obstacle and an essential requisite to experimental<br />
and computational studies of the structure and<br />
function of membrane proteins. Because of the biological<br />
importance and marked presence of membrane<br />
proteins in known genomes (i.e., they account for<br />
about 30% of all proteins), one aim of modern molecular<br />
biophysics should be the development of methods<br />
that can be used in experimental studies to understand<br />
the structure and function of these systems. We recently<br />
developed theoretical methods that enable the exploration<br />
of protein insertion and folding in membranes.<br />
<strong>The</strong>se methods combine the sampling methods of<br />
replica-exchange molecular dynamics with novel generalized<br />
Born implicit solvent/implicit membrane continuum<br />
electrostatic theories.<br />
We recently used de novo folding–membrane association–insertion<br />
simulations of a series of peptides<br />
(tryptophan-flanked α-helical peptides) designed to<br />
explore the concept of hydrophobic mismatch in modulating<br />
folding and membrane insertion. Using the simulations,<br />
we examined the detailed molecular mechanism<br />
of peptide insertion into biological membranes. Our<br />
results indicated a common mechanism for the insertion<br />
of transmembrane helices of relatively hydrophobic<br />
sequences. As illustrated in Figure 1, a peptide
ecomes associated with the membrane interface, transferring<br />
from the aqueous phase, and then helical structure<br />
begins to form. <strong>The</strong> fluctuating helical structure in<br />
the interfacial peptide grows until a critical helical length<br />
is achieved, and the peptide then inserts via its N-terminal<br />
end to form a transmembrane helix. <strong>The</strong>se findings<br />
suggest an emerging potential for the de novo investigation<br />
of integral membrane peptides and proteins and<br />
a mechanism to assist in experimental approaches to<br />
characterizing and determining the structure of these<br />
important systems.<br />
Fig. 1. Mechanism of membrane association, folding, and insertion<br />
of a designed membrane peptide. <strong>The</strong> headgroup regions of the<br />
membrane are schematically represented by the parallel plates; the<br />
lipid tail–group regions, by the intervening space. Peptides first move<br />
from an aqueous environment above the membrane to the interfacial<br />
region, where they begin to form helical structure. When the<br />
fluctuating helical structure reaches a critical value near 70%–80%<br />
helix, the peptide spontaneously inserts from its N-terminal end.<br />
LARGE-SCALE FUNCTIONAL DYNAMICS IN<br />
MOLECULAR ASSEMBLIES<br />
Many naturally occurring “machines,” such as<br />
ribosomes, myosin, and viruses, require large-scale<br />
dynamical motions as a component of their normal<br />
functioning. <strong>The</strong>se motions involve the “mechanical”<br />
reorganization of major parts of the structure of the<br />
machine in response to binding of effectors or to the<br />
addition of energy in the form of thermal fluctuations<br />
or provided by chemical catalysis. Exploring and understanding<br />
the character and nature of such large-scale<br />
reorganization of biological machines are ongoing goals<br />
in our laboratory. Using theoretical approaches derived<br />
from the treatment of mechanoelastic materials, we<br />
are constructing theoretical models for the motions of<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 193<br />
large molecular assemblies, including viral capsids,<br />
ribosomes, and myosin.<br />
In the life cycle of viruses, large-scale reorganization<br />
of the protein-protein interfaces of the viral capsid<br />
coat is necessary for the functioning of the virus. <strong>The</strong>se<br />
motions involve the overall swelling (or shrinking) of<br />
the capsid as it reveals (or sequesters) its genome.<br />
How such large conformational changes occur is key<br />
to understanding and potentially controlling aspects of<br />
viral infectivity. Using theoretical methods called elastic<br />
network normal mode analysis, we explored putative<br />
swelling and shrinking transitions for a number of<br />
icosahedral viral capsids of various complexity, from<br />
T-numbers of 1 to 13. We discovered a surprisingly<br />
similar mechanism for particle expansion and shrinking,<br />
despite the significant variation of individual capsid<br />
architectures. We examined the collective modes<br />
of motion that were energetically easiest to excite,<br />
while also directing the conformational change between<br />
a swollen (or contracted) icosahedrally symmetric conformation,<br />
as observed experimentally.<br />
Our calculations (Fig. 2) show that the lowest energy<br />
modes that lead to swollen (compressed) states, despite<br />
the complexity of the underlying capsid architecture as<br />
indicated by the T-number, involves one key mode that<br />
produces a uniform deformation of the entire capsid<br />
and another that predominately distorts the structures<br />
around the 5-fold symmetry axes. Because the mechanical<br />
properties, and the global level of deformations<br />
necessary for viral functioning, appear to depend solely<br />
on the shape of the viral particle, we can hypothesize<br />
general mechanisms for a number of viral functions,<br />
Fig. 2. Displacement directions for the swelling of the capsid of<br />
the bacteriophage HK97 during maturation from the prohead II state<br />
to the head II state as calculated by using elastic network normal<br />
mode analysis. <strong>The</strong> amplitude and direction of motion are indicated<br />
by the arrows. <strong>The</strong> first mode (A) accounts for nearly uniform displacement<br />
of all protein units in the capsid, whereas the next lowest<br />
energy mode (B) promotes “bulging” around the 5-fold axes of<br />
the capsid.
194 MOLECULAR BIOLOGY 2005<br />
from the transfer of genetic material to a host system<br />
to the encapsulation of this genetic material in the<br />
assembly and maturation of viruses.<br />
PUBLICATIONS<br />
Chen, J., Brooks, C.L. III, Wright, P.E. Model-free analysis of protein dynamics:<br />
assessment of accuracy and model selection protocols based on molecular dynamics<br />
simulation. J. Biomol. NMR 29:243, 2004.<br />
Chen, J., Im, W., Brooks, C.L. III. Refinement of NMR structures using implicit solvent<br />
and advanced sampling techniques. J. Am. Chem. Soc. 126:16038, 2004.<br />
Chen, J., Won, H.S., Im, W., Dyson, H.J., Brooks, C.L. III. Generation of nativelike<br />
protein structures from limited NMR data, modern force fields and advanced<br />
conformational sampling. J. Biomol. NMR 31:59, 2005.<br />
Dominy, B.N., Minoux, H., Brooks, C.L. III. An electrostatic basis for the stability<br />
of thermophilic proteins. Proteins 57:128, 2004.<br />
Falke, S., Tama, F., Brooks, C.L. III, Gogol, E.P., Fisher, M.T. <strong>The</strong> 13 Å structure<br />
of a chaperonin GroEL-protein substrate complex by cryo-electron microscopy. J.<br />
Mol. Biol. 348:219, 2005.<br />
Feig, M., Brooks, C.L. III. Recent advances in the development and application of<br />
implicit solvent models in biomolecule simulations. Curr. Opin. Struct. Biol.<br />
14:217, 2004.<br />
Feig, M., Im, W., Brooks, C.L. III. Implicit solvation based on generalized Born<br />
theory in different dielectric environments. J. Chem. Phys. 120:903, 2004.<br />
Feig, M., Onufriev, A., Lee, M.S., Im, W., Case, D.A., Brooks, C.L. III. Performance<br />
comparison of generalized Born and Poisson methods in the calculation of electrostatic<br />
solvation energies for protein structures. J. Comput. Chem. 25:265, 2004.<br />
Ferrara, P., Gohlke, H., Price, D.J., Klebe, G., Brooks, C.L. III. Assessing scoring<br />
functions for protein-ligand interactions. J. Med. Chem. 47:3032, 2004.<br />
Guvench, O., Brooks, C.L. III. Efficient approximate all-atom solvent accessible<br />
surface area method parameterized for folded and denatured protein conformations.<br />
J. Comput. Chem. 25:1005, 2004.<br />
Guvench, O., Brooks, C.L. III. Tryptophan side chain electrostatic interactions<br />
determine edge-to-face vs parallel-displaced tryptophan side chain geometries in<br />
the designed β-hairpin ”trpzip2.” J. Am. Chem. Soc. 127:4668, 2005.<br />
Guvench, O., Price, D.J., Brooks, C.L. III. Receptor rigidity and ligand mobility in<br />
trypsin-ligand complexes. Proteins 58:407, 2005.<br />
Im, W., Brooks, C.L. III. Interfacial folding and membrane insertion of designed<br />
peptides studied by molecular dynamics simulations. Proc. Natl. Acad. Sci. U. S. A.<br />
102:6771, 2005.<br />
Karanicolas, J., Brooks, C.L. III. An evolution of minimalist models for protein folding:<br />
from the behavior of protein-like polymers to protein function. Biosilico 2:127, 2004.<br />
Mackerell, A.D., Jr., Feig, M., Brooks, C.L. III. Extending the treatment of backbone<br />
energetics in protein force fields: limitations of gas-phase quantum mechanics<br />
in reproducing protein conformational distributions in molecular dynamics simulations.<br />
J. Comput. Chem. 25:1400, 2004.<br />
Natrajan, A., Crowley, M., Wilkins-Diehr, N., Humphrey, M.A., Fox, A.D., Grimshaw,<br />
A.S., Brooks, C.L. III. Studying protein folding on the Grid: experiences using CHARMM<br />
on NPACI resources under Legion. Concurr. Comput. Pract. Exp. 16:385-397, 2004.<br />
Patel, S., Brooks, C.L., III. A nonadditive methanol force field: bulk liquid and liquid-vapor<br />
interfacial properties via molecular dynamics simulations using a fluctuating<br />
charge model. J. Chem. Phys. 122:24508, 2005.<br />
Patel, S., Mackerell, A.D., Jr., Brooks, C.L. III. CHARMM fluctuating charge force<br />
field for proteins, 2: protein/solvent properties from molecular dynamics simulations<br />
using a nonadditive electrostatic model. J. Comput. Chem. 25:1504, 2004.<br />
Price, D.J., Brooks, C.L. III. A modified TIP3P water potential for simulation with<br />
Ewald summation. J. Chem. Phys. 121:10096, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Stoycheva, A.D., Brooks, C.L. III, Onuchic, J.N. Gatekeepers in the ribosomal protein<br />
S6: thermodynamics, kinetics, and folding pathways revealed by a minimalist<br />
protein model. J. Mol. Biol. 340:571, 2004.<br />
Tama, F., Brooks, C.L. III. Diversity and identity of mechanical properties of icosahedral<br />
viral capsids studied with elastic network normal mode analysis. J. Mol.<br />
Biol. 345:299, 2005.<br />
Tama, F., Feig, M., Liu, J., Brooks, C.L. III, Taylor, K.A. <strong>The</strong> requirement for<br />
mechanical coupling between head and S2 domains in smooth muscle myosin<br />
ATPase regulation and its implications for dimeric motor function. J. Mol. Biol.<br />
345:837, 2005.<br />
Tama, F., Miyashita, O., Brooks, C.L. III. Normal mode based flexible fitting of<br />
high-resolution structure into low-resolution experimental data from cryo-EM. J.<br />
Struct. Biol. 147:315, 2004.<br />
Taufer, M., Crowley, M., Price, D.J., Chien, A.A., Brooks, C.L. III. Study of a highly<br />
accurate and fast protein-ligand docking method based on molecular dynamics.<br />
Concurr. Comput. Pract. Exp., in press.<br />
Thorpe, I.F., Brooks, C.L. III. <strong>The</strong> coupling of structural fluctuations to hydride<br />
transfer in dihydrofolate reductase. Proteins 57:444, 2004.<br />
Computation and Visualization<br />
in Structural <strong>Biology</strong><br />
A.J. Olson, D.S. Goodsell, M.F. Sanner, A. Gillet, Y. Hu,<br />
R. Huey, C. Li, S. Karnati, W. Lindstrom, G.M. Morris,<br />
A. Omelchenko, M. Pique, B. Norledge, R. Rosenstein,<br />
D. Stoffler, Y. Zhao<br />
In the <strong>Molecular</strong> Graphics Laboratory, we develop<br />
novel computational methods to analyze, understand,<br />
and communicate the structure and interactions<br />
of complex biomolecular systems. This past year,<br />
we showed the effectiveness of 3-dimensional molecular<br />
models as a tangible human-computer interface in<br />
educational and research settings. Within our component-based<br />
visualization environment, we continue to<br />
develop methods for predicting biomolecular interactions,<br />
analyzing biomolecular structure and function,<br />
and presenting the biomolecular world in education<br />
and outreach.<br />
We have applied these methods to several important<br />
systems in human health and welfare. We continue<br />
the search for inhibitors of HIV protease to fight<br />
the growing problem of drug resistance in HIV disease.<br />
We used AutoDock, a suite of programs for predicting<br />
bound conformations and binding energies for biomolecular<br />
complexes, in the virtual screening of large databases<br />
of compounds and ultimately identified new compounds<br />
for use in the treatment of cancer. We used methods for<br />
predicting protein interactions to probe the mechanism<br />
of blood coagulation.
TANGIBLE INTERFACES FOR STRUCTURAL BIOLOGY<br />
We are using the evolving technology of computer<br />
autofabrication (“3-dimensional printing”) to produce<br />
physical models of complex molecular assemblies (Fig. 1).<br />
With this technology, a physical model based on a virtual<br />
computer model is built up layer by layer. <strong>The</strong> great<br />
advantage of autofabrication is that nearly any shape<br />
can be built; the shape is limited only by the imagination<br />
of the researcher and the structural integrity of the<br />
building material. We have used 2 technologies: 1 that<br />
is much like using a hot glue gun, in which the model is<br />
built from layers of molten plastic, and 1 in which gypsum<br />
powder and colored binders applied with an ink jet<br />
technology are used to create full-color models.<br />
Fig. 1. A sample of the molecular models built by using automated<br />
fabrication techniques shows a wide range of molecular representations,<br />
scales, and sizes.<br />
In collaboration with the Human Interfaces Technology<br />
Laboratory at the University of Washington, Seattle,<br />
Washington, we developed an augmented reality environment<br />
that embeds these 3-dimensional models within<br />
the virtual environment of the computer. <strong>The</strong> goal of this<br />
technology is to create a sense of user presence in a<br />
computational interaction, combining the intuitive tactile<br />
interaction of model manipulation with the rich bioinformatics<br />
and visualization tools that are available in<br />
the computer environment. As shown in Figure 2, the<br />
augmented reality environment tracks the position of the<br />
model, displaying a video image of the model and user<br />
and overlaying a computer-generated image that is spatially<br />
registered with the model as the user manipulates<br />
and explores the structure. In tests of the model, high<br />
school and college students reported that they experienced<br />
a compelling sense of realism of the virtual object<br />
and enhanced interaction with the subject matter.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 195<br />
Fig. 2. Top, <strong>The</strong> augmented reality environment. <strong>The</strong> user holds<br />
the model under a FireWire camera. Bottom, A video image of the<br />
model is displayed on the computer screen, with an overlaid computer-generated<br />
image. Here, the electrostatic potential and field of<br />
superoxide dismutase are shown with volume-rendered clouds and<br />
small animated arrows.<br />
We use the program Python Molecule Viewer to<br />
create a diverse range of different representations for<br />
both our virtual molecular objects and our tangible models,<br />
simplifying integration of the models with the virtual<br />
environment. Python Molecule Viewer allows us to<br />
combine backbone representation, atomic representations,<br />
and surfaces and to incorporate markers for spatial<br />
tracking. We are also using computer-aided design<br />
and manufacturing methods to design mechanical connectors<br />
and magnetic fittings that incorporate aspects<br />
of flexibility and interaction into the models. Vision,<br />
the visual programming interface, is used to integrate<br />
nonmolecular features and properties, such as electrostatics<br />
and hydrophobicity, into the virtual and physical<br />
environment.<br />
COMPONENT-BASED VISUALIZATION ENVIRONMENT<br />
To facilitate the integration and interoperation of<br />
computational models and techniques from a wide
196 MOLECULAR BIOLOGY 2005<br />
variety of scientific disciplines, we continue to expand<br />
our component-based software environment. <strong>The</strong> environment<br />
is centered on Python, a high-level, object-oriented,<br />
interpretive programming language. This approach<br />
allows the compartmentalization and reuse of software<br />
components. Python provides a powerful “glue” for<br />
assembling computational components and, at the same<br />
time, a flexible language for the interactive scripting of<br />
new applications.<br />
We recently added a visual programming environment,<br />
Vision, that supports the interactive and visual<br />
combination of computational nodes into networks that<br />
correspond to algorithms coded at a high level (Fig. 3).<br />
Vision provides nonprogrammers an intuitive interface<br />
for building networks that describe new computational<br />
pipelines and novel visualizations of data. <strong>The</strong> basic<br />
molecular visualization methods of Python Molecule<br />
Viewer, a molecular symmetry generator, and a volumerendering<br />
method are a few of the currently available<br />
nodes, and new nodes are easy to create in the Python<br />
language. <strong>The</strong> combination of the visual programming<br />
model and the ability to interactively inspect and edit<br />
nodes written in a high-level language creates an unprecedented<br />
number of levels at which users can interact<br />
with the program. <strong>The</strong> software tools developed by<br />
using our software components have been distributed<br />
to more than 10,600 users, with an average of 250<br />
downloads a month during the past year.<br />
We released a new version of our software tools in<br />
December 2004 that contains a large number of improve-<br />
Fig. 3. Vision, a visual programming environment, allows users<br />
to build networks of visualization software, creating new computational<br />
pipelines and novel visualizations of data. <strong>The</strong> canvas is shown<br />
at the center, where users interactively combine computational nodes.<br />
<strong>The</strong> network shown is a visualization of an electron micrograph<br />
reconstruction of a virus, colored by the radial depth and with a<br />
sector removed to show the interior structure.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
ments and additions. In particular, we streamlined our<br />
distribution mechanism and included concurrent versioning<br />
system entries that allow users to update the<br />
software once it has been installed. We fixed several<br />
bugs and added new packages, including mesh decimation<br />
algorithms and support for manipulating and<br />
visualizing volumetric data. In addition, we increased<br />
the number of tests that are run on a nightly basis to<br />
more than 2500.<br />
MODELING OF FLEXIBILITY<br />
In a project funded by the National <strong>Institute</strong>s of<br />
Health, we developed Flexibility Tree, a hierarchical and<br />
multiresolution representation of the flexibility of biological<br />
macromolecules that can be used in computational<br />
simulations. With this software, a user can encode a<br />
small subset of a protein’s conformational subspace.<br />
After implementing the core infrastructure of Flexibility<br />
Tree and integrating it with Python Molecule Viewer and<br />
Vision, we are building such trees for molecular systems,<br />
including HIV type 1 protease and protein kinases.<br />
A number of laboratories around the world have<br />
developed software tools for extracting the information<br />
that describes how the various parts of proteins move<br />
relative to each other. We are now using Flexibility Tree<br />
to assess the quality of the decomposition of the protein<br />
structure into rigid bodies provided by these tools<br />
as well as the accuracy of the motions calculated by<br />
using these methods. Early results indicate that when<br />
small local perturbations are allowed in addition to the<br />
motions predicted by these tools, the Flexibility Tree<br />
covers a conformational space that includes both open<br />
and closed conformations of our test systems with<br />
accuracy sufficient for docking experiments. Our next<br />
step will be to design prototype docking tools that can<br />
include protein flexibility based on the Flexibility Tree.<br />
VIRTUAL SCREENING WITH AUTODOCK<br />
We have developed new interactive tools to streamline<br />
the process of virtual screening in AutoDock. With<br />
these tools, users can perform docking experiments to<br />
evaluate the binding of a database of molecules with a<br />
particular macromolecule of interest. In collaboration<br />
with I.A. Wilson, Department of <strong>Molecular</strong> <strong>Biology</strong>, we<br />
used the method to discover new inhibitors for aminoimidazole<br />
carboxamide ribonucleotide transformylase, a<br />
target for new cancer chemotherapeutic agents. <strong>The</strong><br />
diversity set from the National Cancer <strong>Institute</strong> was<br />
screened, and 44 potential candidates were identified.<br />
In vitro inhibition assays indicated that 8 of the 44<br />
were soluble compounds, had chemical scaffolds that
differed from the general folate template, and caused<br />
inhibition when used in micromolar concentrations.<br />
Currently, we are optimizing the lead candidates; our<br />
goal is to obtain novel nonfolate inhibitors.<br />
AutoDock is currently used in more than 3200<br />
academic and commercial laboratories worldwide. We<br />
continued development of AutoDock by testing a new<br />
empirical free-energy force field. <strong>The</strong> force field incorporates<br />
a charge-based model for evaluation of hydrophobicity<br />
and an improved method for evaluating the<br />
geometry of hydrogen bonding. <strong>The</strong> force field was<br />
calibrated by using a set of 138 protein complexes of<br />
known structure taken from the Ligand Protein Database<br />
from the laboratory of C.L. Brooks, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>. We anticipate that the revised<br />
AutoDock, which incorporates this new force field and<br />
methods for selective flexibility in the protein target, will<br />
be released in 2005.<br />
We also used AutoDock to predict intermolecular<br />
interactions in several biological systems. In collaboration<br />
with C.F. Barbas, Department of <strong>Molecular</strong> <strong>Biology</strong>,<br />
we investigated the binding of peptides to the catalytic<br />
aldolase antibody 93F3. To explore the large conformational<br />
space available to these peptides, we used a<br />
divide-and-conquer approach that separates the search<br />
space into searchable blocks. In studies with G. Legge,<br />
University of Texas, Austin, Texas, we explored the<br />
interaction between the cytoplasmic tail of tissue factor<br />
and the WW domain of proline isomerase PIN1,<br />
focusing on the interaction of several key phosphoserine<br />
residues.<br />
FIGHTING DRUG RESISTANCE IN HIV DISEASE<br />
We are continuing our work on inhibitors to fight<br />
drug resistance in the treatment of AIDS (Fig. 4). In<br />
collaboration with K.B. Sharpless and C.-H. Wong,<br />
Department of Chemistry, we have focused on the<br />
design of inhibitors that assemble within the active<br />
Fig. 4. <strong>The</strong> predicted bound conformation of sanguinarine, a potential<br />
lead compound for the development of novel HIV protease<br />
inhibitors.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 197<br />
site of HIV protease. We showed that the triazole<br />
formed in the click chemistry reaction is an effective<br />
mimic for the peptide group in traditional inhibitors,<br />
forming similar hydrogen-bonding interactions.<br />
Currently, we are moving the FightAIDS@Home<br />
system from an outside provider to a new server strategy<br />
that will be implemented in the <strong>Molecular</strong> Graphics<br />
Laboratory. FightAIDS@Home enlists the worldwide<br />
community in a large computational effort to design<br />
effective therapeutic agents to fight AIDS. Personal<br />
computers are used in the program when the computers<br />
are not in use by their owners, providing an enormous,<br />
and largely untapped, computational resource.<br />
<strong>The</strong> current goal is to identify inhibitors that are effective<br />
against the wild-type virus and against common<br />
mutant forms of the virus. <strong>The</strong> large computational<br />
resources provided by FightAIDS@Home enables the<br />
screening of large databases of compounds and use<br />
of multiple mutant targets, allowing estimation of the<br />
potential of a compound to remain effective when viral<br />
mutations occur that cause resistance to drugs currently<br />
used to treat HIV disease.<br />
PREDICTING PROTEIN-PROTEIN INTERACTIONS<br />
With the goal of creating a comprehensive tool for<br />
predicting protein-protein interactions, we incorporated<br />
both SurfDock and AutoDock into the Python programming<br />
environment. SurfDock uses a variable-resolution<br />
spherical harmonics representation to find candidate<br />
orientations, and AutoDock is then used to explore local<br />
atomic rearrangements at the interface. We tested the<br />
method on a set of 59 protein-protein complexes of<br />
known structure and optimized the level of smoothing<br />
used in the spherical harmonics approximation of the<br />
molecular surfaces. <strong>The</strong> results of the docking test<br />
depended on the force field used to score possible orientations.<br />
<strong>The</strong> best results were obtained with a residue-based<br />
pair-wise potential of mean force.<br />
VISUAL METHODS FROM ATOMS TO CELLS<br />
Understanding structural molecular biology is essential<br />
to foster progress and critical decision making among<br />
students, policy makers, and the general public. In the<br />
past year, we continued our longstanding commitment<br />
to science education and outreach with a combination<br />
of presentations, popular and professional illustrations<br />
and animation, 3-dimensional tangible models, and a<br />
presence on the Worldwide Web. In these projects, we<br />
use the diverse visualization tools developed in the<br />
<strong>Molecular</strong> Graphics Laboratory to disseminate results<br />
that range from atomic structure to cellular function.
198 MOLECULAR BIOLOGY 2005<br />
We created a 3-dimensional model that demonstrates<br />
viral assembly. <strong>The</strong> model is composed of pentamers<br />
from the structure of poliovirus, with embedded magnets<br />
on the interacting faces. When 12 or more of<br />
these pentamer models are placed in a closed container<br />
and gently shaken, they self-assemble in a matter of<br />
seconds to form a spherical capsid.<br />
We also continued several regular features that<br />
informally present molecular structure and function.<br />
<strong>The</strong> “Molecule of the Month” at the Protein Data Bank<br />
(http://www.rcsb.org/pdb) provides an accessible introduction<br />
to this central database of biomolecular structure.<br />
Each month, a new molecule is presented with a<br />
description of its structure, function, and relevance to<br />
health and welfare (Fig. 5). Visitors are then given suggestions<br />
about how to begin their own exploration of<br />
the structures in the data bank. Currently, we are collaborating<br />
with T. Herman, Milwaukee School of Engineering,<br />
Milwaukee, Wisconsin, to combine material<br />
from the “Molecule of the Month” with 3-dimensional<br />
models and multimedia tutorials to create educational<br />
modules for use at high school and college levels. Other<br />
projects include “<strong>The</strong> <strong>Molecular</strong> Perspective,” articles<br />
in the journal <strong>The</strong> Oncologist that present structures<br />
of interest to clinical oncologists and provide a source<br />
of continuing education for physicians, and “Recognition<br />
in Action,” a new series in the Journal of <strong>Molecular</strong><br />
Recognition.<br />
Fig. 5. Three different types of catalase. Catalase was presented<br />
as a Molecule of the Month in 2004 after a request from a high<br />
school teacher.<br />
PUBLICATIONS<br />
Berman, H.M., Ten Eyck, L.F., Goodsell, D.S., Haste, N.M., Kornev, A. Taylor,<br />
S.S. <strong>The</strong> cAMP binding domain: an ancient signaling module. Proc. Natl. Acad.<br />
Sci. U. S. A. 102:45, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Brik, A., Alexandros, J., Lin, Y.-C., Elder, J.H., Olson, A.J., Wlodawer, A., Goodsell,<br />
D.S., Wong, C.-H. 1,2,3-Triazole as a peptide surrogate in the rapid synthesis<br />
of HIV protease inhibitors. Chembiochem 6:1167, 2005.<br />
Gillet, A., Sanner, M., Stoffler, D., Goodsell, D.S., Olson, A.J. Augmented reality<br />
with tangible auto-fabricated models for molecular biology applications. In: IEEE<br />
Visualization: Proceedings of the Conference on Visualization ’04. IEEE Computer<br />
Society, Washington, DC, 2004, p. 235.<br />
Gillet, A., Sanner, M., Stoffler, D., Olson, A. Tangible augmented interfaces for<br />
structural molecular biology. IEEE Comput. Graph. Appl. 25:13, 2005.<br />
Gillet, A., Sanner, M., Stoffler, D., Olson, A. Tangible interfaces for structural<br />
molecular biology. Structure (Camb.) 13:483, 2005.<br />
Goodsell, D.S. Computational docking of biomolecular complexes with AutoDock. In:<br />
Protein-Protein Interactions: A <strong>Molecular</strong> Cloning Manual, 2nd ed. Golemis, E., Adams,<br />
P. (Eds.). Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, in press.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: cyclins. Oncologist 9:592, 2004; Stem<br />
Cells 22:1121, 2004.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: cytochrome c and apoptosis. Oncologist<br />
9:226, 2004; Stem Cells 22:428, 2004.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: L-asparaginase. Oncologist 10:238,<br />
2005; Stem Cells 23:710, 2005.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: major histocompatibility complex.<br />
Oncologist 10:80, 2005; Stem Cells 23:454, 2005.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: morphine. Oncologist 9:717, 2004;<br />
Stem Cells 23:144, 2005.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: nicotine and nitrosamines. Oncologist<br />
9:353, 2004; Stem Cells 22:645, 2004.<br />
Goodsell, D.S. <strong>The</strong> molecular perspective: polycyclic aromatic hydrocarbons.<br />
Oncologist 9:469, 2004; Stem Cells 22:873, 2004.<br />
Goodsell, D.S. Recognition in action: flipping pyrimidine dimers. J. Mol. Recognit.<br />
18:193, 2005.<br />
Goodsell, D.S. Representing structural information. In: Current Protocols in Bioinformatics.<br />
Baxeranis, A.D., Davison, D.B. (Eds.). Wiley & Sons, Hoboken, NJ, in press.<br />
Goodsell, D.S. Visual methods from atoms to cells. Structure (Camb.) 13:347, 2005.<br />
Li, C., Xu, L., Wolan, D.W., Wilson, I.A., Olson, A.J. Virtual screening of human<br />
5-aminoimidazole-4-carboxamide ribonucleotide transformylase against the NCI<br />
diversity set by use of AutoDock to identify novel nonfolate inhibitors. J. Med.<br />
Chem. 47:6681, 2004.<br />
Sanner, M.F. A component-based software environment for visualizing large macromolecular<br />
assemblies. Structure (Camb.) 13:447, 2005.<br />
Sanner, M.F. Using the Python programming language for bioinformatics. In: Encyclopedia<br />
of Genetics, Genomics, Proteomics and Bioinformatics. Jorde, L.B., Little,<br />
P.F.R., Dunn, M.J., et al. (Eds.). Wiley & Sons, Hoboken, NJ, in press.<br />
Zhu, X., Tanaka, F., Hu, Y., Heine, A., Fuller, R., Zhong, G., Olson, A.J., Lerner,<br />
R.A., Barbas, C.F. III, Wilson, I.A. <strong>The</strong> origin of enantioselectivity in aldolase antibodies:<br />
crystal structure, site-directed mutagenesis, and computational analysis. J.<br />
Mol. Biol. 343:1269, 2004.
Computational Structural<br />
Proteomics and Ligand Discovery<br />
R. Abagyan, J. An, A. Cheltsov, A. Bordner,* C. Cavasotto,*<br />
J. Kovacs, J. Fernandez-Recio,** M. Totrov,* X. Zhang,***<br />
M. Dawson,*** A. McCluskey,**** B. Marsden*****<br />
* Molsoft L.L.C., La Jolla, California<br />
** Institut de Recerca Biomèdica, Barcelona, Spain<br />
*** Burnham <strong>Institute</strong>, La Jolla, California<br />
**** University of Newcastle, Callaghan, Australia<br />
***** Structural Genomics Consortium, Oxford, England<br />
Every day about 15 new crystal structures are<br />
deposited in the Protein Data Bank. <strong>The</strong> 30,000<br />
molecular structures in the bank contain rich information<br />
about protein function and provide a unique<br />
opportunity for rational search for or design of small<br />
molecules that can be used as therapeutic agents. We<br />
use computational structural proteomics, bioinformatics,<br />
molecular mechanics, and cheminformatics to<br />
characterize the function of proteins and to design<br />
molecular structures.<br />
Traditionally, we have focused on accurate docking<br />
and screening of small molecules and have used internal<br />
coordinate mechanics to predict protein association.<br />
In 2004, we focused on improving the information content<br />
of evolutionary sequence conservation; predicting<br />
and classifying ligand-binding pockets and protein-protein<br />
interfaces; improving sequence structure alignments<br />
for models by homology; and predicting effects of single-point<br />
mutations, loop conformations, and protein<br />
association geometry. We also improved protocols for<br />
predicting receptor flexibility in ligand docking and<br />
applied virtual screening to discover inhibitors of important<br />
biomedical targets.<br />
BIOINFORMATICS AND PREDICTION OF PROTEIN<br />
FUNCTION<br />
Functional characterization of tens of thousands of<br />
proteins is a key computational task. To build 3-dimensional<br />
models of structurally uncharacterized protein<br />
sequences, we developed a procedure to accurately<br />
align those sequences to their Protein Data Bank templates<br />
in the areas of weak alignment. <strong>The</strong> Structural<br />
Alignment Database of 1927 alignments was then used<br />
to develop improved alignment/threading parameters.<br />
Every molecular biologist is confronted with the<br />
tasks of discovering and annotating the functions of a<br />
protein of interest. A strong evolutionary conservation<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
measure in the context of a 3-dimensional model is a<br />
powerful source of functional information. However,<br />
the currently used measures have a strong dependence<br />
on the sequence composition biases of alignments. We<br />
developed mathematical formalism that gives a powerful<br />
measure of sequence conservation that does not<br />
depend on overrepresentation or underrepresentation of<br />
certain branches in the alignment. We also used this<br />
measure in an improved method to predict novel patches<br />
of protein-protein interactions on protein surfaces.<br />
Specific association of proteins is a key biological<br />
mechanism. However, accurate prediction of interfaces<br />
and residues involved in an interaction, often an interaction<br />
with an unknown protein partner, is a great<br />
challenge for most proteins or domains with known<br />
3-dimensional structure. <strong>The</strong> preference for any particular<br />
interface is subtle because the same surface is also<br />
happy to be exposed to water. We attempted to solve<br />
that problem by using more meaningful surface properties<br />
and more sophisticated numerical methods.<br />
Using the optimal docking area method, we showed<br />
that with optimized desolvation parameters and an<br />
adaptive algorithm of finding the optimal interaction<br />
patch, the desolvation signal itself without any other<br />
signals can be strong enough. In other studies, we<br />
combined a desolvation signal with the improved<br />
sequence conservation signal and used the method<br />
successfully with a benchmark of 1496 interfaces.<br />
PREDICTING PROTEIN STRUCTURE AND<br />
ASSOCIATION<br />
MOLECULAR BIOLOGY 2005 199<br />
Predicting partial protein structure or molecular<br />
association is a critical task in computational biology<br />
and chemistry. This past year we proposed a method<br />
to predict both geometry and stabilization energy for<br />
single mutations, improved protocols for predicting protein<br />
loops, and developed a method to predict largescale<br />
protein movements by using simplified protein<br />
models represented in internal coordinates.<br />
If both partners of a protein complex are known<br />
and their “uncomplexed” 3-dimensional models exist<br />
or can be built, attempts can be made to predict the<br />
association geometry (also called protein docking). In<br />
2004, we used the internal coordinate mechanics docking<br />
method successfully in the Critical Assessment of<br />
Prediction of Interactions competition, partially because<br />
of the improved docking energetics. Although in the<br />
first round we predicted only 3 of 7 complexes, in the<br />
second and the third rounds, we were correct in 8 of
200 MOLECULAR BIOLOGY 2005<br />
9 tasks. We are working on further improvements of<br />
the method.<br />
THE CELL POCKETOME<br />
Proteins also bind small molecules, the natural substrates<br />
or cofactors of the proteins, or specially designed<br />
therapeutic agents. Many orphan receptors and uncharacterized<br />
surfaces exist. This past year, we further<br />
optimized a pocket prediction algorithm and used it<br />
successfully on as many as 17,000 pockets from the<br />
Protein Data Bank. In this algorithm, a mathematical<br />
transformation of the Lennard-Jones potential is used<br />
to generate a potential that, contoured at a certain<br />
level, specifically locates the potential binding sites<br />
with a rather low level of false-positives and false-negatives<br />
(Fig. 1).<br />
Fig. 1. Several representatives of a predicted cell pocketome.<br />
Using this algorithm, we predicted as many as<br />
96.8% of experimental binding sites at an overlap level<br />
of better than 50%. Furthermore, 95% of the predicted<br />
sites from the apo receptors were predicted at the same<br />
level. We showed that conformational differences between<br />
the apo and bound pockets do not dramatically affect<br />
the prediction results. <strong>The</strong> algorithm can be used to predict<br />
ligand-binding pockets of uncharacterized protein<br />
structures, suggest new allosteric pockets, evaluate the<br />
feasibility of inhibition of protein-protein interactions,<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
and prioritize molecular targets. Finally, we collected<br />
and classified data for the human cell pocketome, a<br />
database of the known and the predicted binding pockets<br />
for the human proteome structures.<br />
<strong>The</strong> pocketome can be used for rapid evaluation of<br />
possible binding partners of a given chemical compound.<br />
We are using the predicted pockets to develop therapeutic<br />
molecules that target unexpected binding pockets.<br />
Our first result in using such a strategy was obtained in<br />
collaboration with D.A. Lomas, University of Cambridge,<br />
Cambridge, England; we identified the first small molecules<br />
that block the polymerization of the Z mutant<br />
of α 1 -antitrypsin.<br />
COMPOUND DOCKING AND VIRTUAL LIGAND<br />
SCREENING<br />
Small-molecule inhibitors or activators can be discovered<br />
rationally by carefully docking them to a target<br />
pocket and scoring the result according to the pose<br />
and interactions of the small molecule. <strong>The</strong> virtual<br />
screen can be performed against millions of available<br />
chemicals or against virtual chemically feasible molecules,<br />
and only several dozen computationally selected<br />
candidates need to be tested experimentally. We developed<br />
and improved different aspects of this strategy<br />
and applied it to different drug discovery projects. <strong>The</strong><br />
docking technology can also help in understanding the<br />
structural mechanisms of the actions of small molecules<br />
and can be used to rationally design better molecules.<br />
Recently, we used the technology to explain the antagonistic<br />
effect of an important class of retinoid X receptor<br />
antagonists.<br />
A major problem in small-molecule docking and<br />
screening is protein flexibility and conformational<br />
rearrangements of the binding pocket upon ligand binding.<br />
This past year we presented several scenarios for<br />
incorporating protein flexibility into docking calculations.<br />
In some instances, these protocols can be used<br />
to simultaneously predict the ligand-binding pose and<br />
the pocket rearrangements.<br />
PUBLICATIONS<br />
Abagyan, R. Problems in computational structural proteomics. In: Structural Proteomics.<br />
Sundstrom, M., Norin, M., Edwards, A. (Eds,). CRC Press, Boca Raton, FL,<br />
in press.<br />
An, J., Totrov, M., Abagyan, R. Comprehensive identification of “druggable” protein<br />
ligand binding sites. Genome Inform. Ser. Workshop Genome Inform. 15:31, 2004.<br />
An, J., Totrov, M., Abagyan, R. Pocketome via comprehensive identification and<br />
classification of ligand binding envelopes. Mol. Cell. Proteomics 4:752, 2005.<br />
Bordner, A.J., Abagyan, R. REVCOM: a robust Bayesian method for evolutionary<br />
rate estimation. Bioinformatics 21:2315, 2005.
Bordner, A.J., Abagyan, R. Statistical analysis and prediction of protein-protein<br />
interfaces. Proteins 60:353, 2005.<br />
Bordner, A.J., Abagyan, R.A. Large-scale prediction of protein geometry and stability<br />
changes for arbitrary single point mutations. Proteins 57:400, 2004.<br />
Cavasotto, C.N., Kovacs, J.A., Abagyan, R.A. Representing receptor flexibility in ligand<br />
docking through relevant normal modes. J. Am. Chem. Soc. 127:9632, 2005.<br />
Cavasotto, C.N., Liu, G., James, S.Y., Hobbs, P.D., Peterson, V.J., Bhattacharya,<br />
A.A., Kolluri, S.K., Zhang, X.K., Leid, M., Abagyan, R., Liddington, R.C., Dawson,<br />
M.I. Determinants of retinoid X receptor transcriptional antagonism. J. Med.<br />
Chem. 47:4360, 2004.<br />
Cavasotto, C.N., Orry, A.J.W., Abagyan, R.A. <strong>The</strong> challenge of considering receptor<br />
flexibility in ligand docking and virtual screening. Curr. Comput. Aided Drug<br />
Des., in press.<br />
Cavasotto, C.N., Orry, A.J.W., Abagyan, R. Receptor flexibility in ligand docking. In:<br />
Handbook of <strong>The</strong>oretical and Computational Nanotechnology. Reith, M., Schommers,<br />
W. (Eds.). American Scientific Publishers, Stevenson Ranch, Calif, in press.<br />
Fernandez-Recio, J., Abagyan, R., Totrov, M. Improving CAPRI predictions: optimized<br />
desolvation for rigid-body docking. Proteins 60:308, 2005.<br />
Fernandez-Recio, J., Totrov, M., Skorodumov, C., Abagyan, R. Optimal docking<br />
area: a new method for predicting protein-protein interaction sites. Proteins<br />
58:134, 2005.<br />
Hill, T.A., Odell, L.R., Quan, A., Abagyan, R., Ferguson, G., Robinson, P.J.,<br />
McCluskey, A. Long chain amines and long chain ammonium salts as novel inhibitors<br />
of dynamin GTPase activity. Bioorg. Med. Chem. Lett. 14:3275, 2004.<br />
Kovacs, J.A., Cavasotto, C.N., Abagyan, R.A. Conformational sampling of protein<br />
flexibility in generalized coordinates: application to ligand docking. J. Comput.<br />
<strong>The</strong>or. Nanosci., in press.<br />
Marsden, B., Abagyan, R. SAD—a normalized structural alignment database:<br />
improving sequence-structure alignments. Bioinformatics 20:2333, 2004.<br />
Mass Spectrometry<br />
G. Siuzdak, J. Apon, E. Go, K. Harris, R. Lowe, A. Meyers,<br />
A. Nordstrom, Z. Shen, C. Smith, G. Tong, S. Trauger,<br />
W. Uritboonthai, E. Want, W. Webb, C. Wranik<br />
METABOLITE PROFILING<br />
Small molecules ubiquitous in biofluids are now<br />
widely used to predict disease states. <strong>The</strong> inherent<br />
advantage of monitoring small molecules<br />
rather than proteins is the relative ease of quantitative<br />
analysis with mass spectrometry. We are implementing<br />
novel mass spectrometry and bioinformatics techniques<br />
(Fig. 1) to investigate the metabolite profiles of<br />
small molecules as diagnostic indicators of disease.<br />
<strong>The</strong> ultimate goal is to develop analytical and chemical<br />
technologies and a data management system to<br />
identify and structurally characterize metabolites of<br />
physiologic importance.<br />
VIRAL CHARACTERIZATION<br />
We have developed novel methods for characterizing<br />
viruses that have applications to whole viruses and<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
viral proteins. Our results enabled us to examine both<br />
local and global viral structure, gaining insight into the<br />
dynamic changes of proteins on the viral surface.<br />
MASS SPECTROMETRY IN SILICO<br />
MOLECULAR BIOLOGY 2005 201<br />
Fig. 1. A novel nonlinear approach to analyzing mass spectrometry<br />
data for identification of metabolites.<br />
We are also developing ultra-high-sensitivity<br />
approaches in mass spectrometry with a new strategy<br />
that involves pulsed laser desorption/ionization from a<br />
silylated silicon surface. In desorption/ionization on<br />
silicon, silicon is used to capture analytes, and laser<br />
radiation is used to vaporize and ionize these molecules.<br />
Using this technology, we can analyze a wide<br />
range of molecules with unprecedented sensitivity, in<br />
the yoctomole range (Fig. 2).<br />
Fig. 2. Laser desorption/ionization mass spectrometry on structured<br />
silylated silicon has sensitivity rivaling that of fluorescence.<br />
PUBLICATIONS<br />
Bothner, B., Taylor, D., Jun, B., Lee, K.K., Siuzdak, G., Schultz, C.P., Johnson,<br />
J.E. Maturation of a tetravirus capsid alters the dynamic properties and creates a<br />
metastable complex. Virology 334:17, 2005.
202 MOLECULAR BIOLOGY 2005<br />
Go, E.P., Apon, J.V., Luo, G., Saghatelian, A., Daniels, R.H., Sahi, V., Dubrow, R.,<br />
Cravatt, B.F., Vertes, A., Siuzdak, G. Desorption/ionization on silicon nanowires.<br />
Anal. Chem. 77:1641, 2005.<br />
Lacy, E.R., Wang, Y., Post, J., Nourse, A., Webb, W., Mapelli, M., Musacchio, A.,<br />
Siuzdak, G., Kriwacki, R.W. <strong>Molecular</strong> basis for the specificity of p27 toward<br />
cyclin-dependent kinases that regulate cell division. J. Mol. Biol. 349:764, 2005.<br />
Lowe, R., Go, E., Tong, G., Voelcker, N.H., Siuzdak, G. Monitoring EDTA and<br />
endogenous metabolite biomarkers from serum with mass spectrometry. Spectroscopy,<br />
in press.<br />
Saghatelian, A., Trauger, S.A., Want, E., Hawkins, E.G., Siuzdak, G., Cravatt,<br />
B.F. Assignment of endogenous substrates to enzymes by global metabolite profiling.<br />
Biochemistry 43:14332, 2004.<br />
Want, E., Cravatt, B.F., Siuzdak, G. <strong>The</strong> expanding role of mass spectrometry in<br />
metabolite profiling and characterization. Chembiochem, in press.<br />
Assembly Landscape of the<br />
30S Ribosome<br />
J.R. Williamson, F. Agnelli, A. Beck, A. Bunner, A. Carmel,<br />
J. Chao, S. Edgcomb, M. Hennig, E. Johnson, D. Kerkow,<br />
E. Kompfner, K. Lehmann, H. Reynolds, W. Ridgeway,<br />
S.P. Ryder, L.G. Scott, E. Sperling, B. Szymczyna,<br />
M. Trevathan<br />
<strong>The</strong> 30S ribosome is 1 of 2 subunits of the 70S<br />
ribosome, which is responsible for the synthesis<br />
of all proteins in bacterial cells. <strong>The</strong> 30S ribosome<br />
is responsible for decoding the mRNA for protein synthesis.<br />
It is composed of a large 16S RNA of approximately<br />
1500 nucleotides and 20 small proteins (S2–S21). <strong>The</strong><br />
biogenesis of ribosomes consumes approximately half<br />
of the energy of the cell in bacteria, and about 20% of<br />
the mass of a bacterium is composed of ribosomes. Thus,<br />
the assembly of ribosomes must be rapid and efficient.<br />
We are using a wide variety of biophysical techniques<br />
to study the mechanism of assembly of the 30S<br />
ribosome in vitro. We have used nuclear magnetic resonance,<br />
x-ray crystallography, isothermal titration calorimetry,<br />
single-molecule fluorescence, and transient electric<br />
birefringence to probe the details of the mechanism.<br />
Pioneering work by Nomura led to the in vitro assembly<br />
map for the 30S ribosome: some proteins bind independently<br />
to the 16S rRNA, and some require prior<br />
binding of other proteins. Using this map as a framework,<br />
we used 30S components from Escherichia coli,<br />
<strong>The</strong>rmus thermophilus, and Aquifex aeolicus to do<br />
detailed studies. We have constructed an updated and<br />
revised assembly map for the 30S subunit (Fig. 1) that<br />
contains all of the currently available information about<br />
the assembly pathway.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 2. <strong>The</strong> assembly landscape of the 30S subunit. <strong>The</strong> conformations<br />
of the 16S rRNA are represented in the horizontal plane,<br />
and the energy of the conformations is the height of the plane. Folding<br />
of parallel pathways is indicated by the arrows. <strong>The</strong> effects of protein<br />
binding are schematically illustrated by the 2 successive changes<br />
in the landscape. After protein binding (circles), new downhill folding<br />
directions are created. All parallel pathways converge on the<br />
native 30S conformation at the bottom corner of the landscape.<br />
<strong>The</strong> 30S unit has 3 structural domains, the 5′,<br />
central, and 3′, and each of these has one or more<br />
primary binding proteins that will bind independently<br />
to RNA. This binding is followed by a wave of secondary<br />
binding proteins for each domain and a third wave of<br />
tertiary binding proteins. Most of the proteins have<br />
dependencies solely within their domain; a few of the<br />
later binding proteins have interdomain dependencies.<br />
<strong>The</strong> assembly proceeds in a parallel manner, although<br />
each domain has a defined hierarchy of binding order.<br />
To probe the kinetics of the assembly of the 30S<br />
subunit, we developed a novel assay that allows binding<br />
of all 20 ribosomal proteins simultaneously. To<br />
achieve this simultaneous binding, we initiate assembly<br />
of the 30S subunit by combining 16S rRNA with a<br />
mixture of all 20 ribosomal proteins uniformly labeled<br />
with the stable isotope nitrogen 15. <strong>The</strong> isotopic label<br />
does not perturb the system, but it does result in a mass<br />
change of approximately 150 units for each protein.<br />
After assembly proceeds for a brief period, we add an<br />
excess of unlabeled ribosomal proteins that contain the<br />
natural stable isotope nitrogen 14. We can readily determine<br />
the amount of the 2 isotopes for each protein by<br />
using mass spectrometry. By measuring this fraction<br />
as a function of the assembly time, we can monitor the<br />
kinetics of all proteins; we term this assay isotope pulsechase<br />
kinetics.<br />
Using this approach, we did an extensive analysis<br />
of the assembly kinetics of the 30S ribosome under a<br />
variety of conditions. We systematically varied the concentration<br />
of the reaction, the temperature, and the<br />
magnesium ion concentration during assembly. Using<br />
the temperature dependence of the binding rates, we<br />
characterized the activation energy of binding for all of<br />
the proteins. We found that the rates of binding are<br />
not correlated to the activation energies, and we can
monitor many different assembly steps in this complex<br />
parallel process.<br />
To combine all of the mechanistic information,<br />
we have cast the assembly mechanism in terms of<br />
an assembly landscape, which has been recently developed<br />
in research on protein folding. <strong>The</strong> assembly<br />
landscape of the 30S subunit (Fig. 2) shows the many<br />
possible conformations of 16S rRNA in the horizontal<br />
plane, and the energy of those conformations is the<br />
height of the surface. <strong>The</strong> 30S final conformation is<br />
located at the lower corner of the landscape, but in<br />
the absence of ribosomal proteins, it is not the lowest<br />
energy conformation.<br />
Fig. 1. <strong>The</strong> revised assembly map of the 30S subunit. <strong>The</strong> 16S<br />
ribosomal RNA is shown at the top, oriented from 5′ to 3′ direction.<br />
Each of the arrows indicates an observed dependency of binding<br />
for each ribosomal protein. <strong>The</strong> primary binding proteins depend<br />
solely on interactions with 16S rRNA (top row); the secondary and<br />
tertiary binding proteins depend on prior binding of other proteins.<br />
<strong>The</strong> assembly proceeds in many parallel directions,<br />
heading downhill on the landscape, and the energy of<br />
the RNA is lowered by RNA-folding reactions that create<br />
more RNA structure. RNA folding creates the binding<br />
sites for the ribosomal proteins, which can then<br />
bind, and this binding has an important consequence:<br />
new downhill directions are created for more RNA folding.<br />
<strong>The</strong> assembly reaction proceeds by a series of<br />
alternating RNA conformational changes and proteinbinding<br />
events that eventually result in the complete<br />
assembly of the 30S subunit by the convergence of<br />
many parallel pathways.<br />
PUBLICATIONS<br />
Chao, J.A., Williamson, J.R. Joint x-ray and NMR refinement of the yeast L30emRNA<br />
complex. Structure (Camb.) 12:1165, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Klostermeier, D., Sears, P., Wong, C.-H., Millar, D.P., Williamson, J.R. A three-fluorophore<br />
FRET assay for high-throughput screening of small-molecule inhibitors of<br />
ribosome assembly. Nucleic Acids Res. 32:2707, 2004.<br />
Lehmann-Blount, K.A., Williamson, J.R. Shape-specific recognition of singlestranded<br />
RNA by the GLD-1 STAR domain. J. Mol. Biol. 346:91, 2005.<br />
Recht, M.I., Williamson, J.R. RNA tertiary structure and cooperative assembly of a<br />
large ribonucleoprotein complex. J. Mol. Biol. 344:395, 2004.<br />
Ryder, S.P., Williamson, J.R. Specificity of the STAR/GSG domain protein Qk1:<br />
implications for the regulation of myelination. RNA 10:1449, 2004.<br />
Scott, L.G., Geierstanger, B.H., Williamson, J.R., Hennig, M. Enzymatic synthesis<br />
and 19 F-NMR studies of 2-fluoroadenine substituted RNA. J. Am. Chem. Soc.<br />
26:11776, 2004.<br />
Torres, F.E., Kuhn, P., De Bruyker, D., Bell, A.G., Wolkin, M.V., Peeters, E.,<br />
Williamson, J.R., Anderson, G.B., Schmitz, G.P., Recht, M.I., Schweizer, S.,<br />
Scott, L.G., Ho, J.H., Elrod, S.A., Schultz, P.G., Lerner, R.A., Bruce, R.H.<br />
Enthalpy arrays. Proc. Natl. Acad. Sci. U. S. A. 101:9517, 2004.<br />
Nuclear Magnetic Resonance<br />
Studies of RNA and RNA-Ligand<br />
Complexes in Solution<br />
M. Hennig, N. Kirchner, G.C. Pérez-Alvarado, E.P. Plant,*<br />
J.D. Dinman*<br />
* University of Maryland, College Park, Maryland<br />
MOLECULAR BIOLOGY 2005 203<br />
Viruses constantly threaten human health. Not<br />
only are we unable to control infections caused<br />
by old enemies such as the influenza virus, but<br />
we are continually challenged by new enemies, such<br />
as severe acute respiratory syndrome–associated coronavirus<br />
(SARS-CoV). Viral mRNAs often contain signals<br />
that tell the ribosome to change reading frames during<br />
protein synthesis. This recoding event allows viruses<br />
to coordinate gene expression from overlapping reading<br />
frames such as open reading frames 1a and 1b, which<br />
are out-of-frame coding sequences within the SARS-<br />
CoV genome. Protein 1a is translated directly from open<br />
reading frame 1a; the fused polyprotein 1a-1b is produced<br />
by programmed –1 ribosomal frameshifting in<br />
which the ribosome slips back 1 nucleotide. Like other<br />
viral frameshift signals, the SARS-CoV signal contains<br />
2 cis-acting mRNA elements that make up a slippery<br />
heptanucleotide site, X XXY YYZ, followed by an adjacent<br />
downstream 3′ pseudoknot, a stable mRNA structure.<br />
Pseudoknots generally contain 2 stems of doublestranded<br />
RNA and 2 or 3 loops of unpaired nucleotides.<br />
Our biochemical and solution-state nuclear magnetic<br />
resonance studies revealed that the pseudoknot<br />
in the SARS-CoV frameshift signal contains 3 stems.<br />
Mutagenesis studies indicated that specific sequences
204 MOLECULAR BIOLOGY 2005<br />
and structures within the pseudoknot are needed for<br />
efficient frameshifting, but the exact role of the extra<br />
stem in the SARS-CoV frameshifting signal still remains<br />
to be determined. Our current results suggest that the<br />
3 stems form a complex globular RNA structure. <strong>The</strong><br />
elucidation of this structure via high-resolution nuclear<br />
magnetic resonance should facilitate the rational development<br />
of therapeutic agents designed to interfere with<br />
SARS-CoV programmed –1 ribosomal frameshifting and<br />
will increase our understanding of how pseudoknots<br />
stimulate frameshifting.<br />
We continue to develop nuclear magnetic resonance<br />
techniques to investigate the structural and functional<br />
diversity of RNA. Novel approaches were developed to<br />
identify and assign 2′-hydroxyl hydrogens that exchange<br />
rapidly with the solvent and thus are difficult to detect<br />
in aqueous buffers. <strong>The</strong> ribose 2′-hydroxyl group distinguishes<br />
RNA from DNA and is responsible for differences<br />
in conformation, hydration, and thermodynamic<br />
stability of RNA and DNA oligonucleotides. This important<br />
group lies in the shallow groove of RNA, where it<br />
is involved in a network of hydrogen bonds with water<br />
molecules stabilizing RNA A-form duplexes. Structural<br />
and dynamical information on 2′-hydroxyl protons is<br />
essential to understand their respective roles. We provide<br />
structural information on 2′-hydroxyl groups in the<br />
form of orientational preferences, contradicting the<br />
model that the 2′-hydroxyl typically points away from<br />
the ribose H-1′ proton.<br />
PUBLICATIONS<br />
Hennig, M., Fohrer, J., Carlomagno, T. Assignment and NOE analysis of 2′-hydroxyl<br />
protons in RNA: implications for stabilization of RNA A-form duplexes. J. Am. Chem.<br />
Soc. 127:2028, 2005.<br />
Plant, E.P., Pérez-Alvarado, G.C., Jacobs, J.L., Mukhopadhyay, B., Hennig, M.,<br />
Dinman J.D. A three-stemmed mRNA pseudoknot in the SARS coronavirus<br />
frameshift signal. PLoS Biol. 3:e172, 2005.<br />
Components of the Genetic<br />
Code in Translation, Cell<br />
<strong>Biology</strong>, and Medicine<br />
P. Schimmel, J. Bacher, K. Beebe, Z. Druzina, K. Ewalt,<br />
M. Kapoor, E. Merriman, C. Motta, L. Nangle, F. Otero,<br />
J. Reader, R. Reddy, M. Swairjo, K. Tamura, E. Tzima,<br />
W. Waas, X.-L. Yang<br />
<strong>The</strong> genetic code was established in the transition<br />
from the RNA world to the theater of proteins.<br />
<strong>The</strong> code is an algorithm, matching each<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
amino acid with a nucleotide triplet. <strong>The</strong> matching of<br />
triplets with amino acids occurs through aminoacylation<br />
reactions in which enzymes known as aminoacyltRNA<br />
synthetases catalyze attachment of each amino<br />
acid to its cognate tRNA. Each tRNA, in turn, has an<br />
anticodon nucleotide triplet that defines the amino<br />
acid–nucleotide triplet relationship of the code.<br />
Each amino acid has a single tRNA synthetase.<br />
<strong>The</strong> synthetases are thought to be among the earliest<br />
proteins and, as such, essential components of the<br />
translation apparatus that established the genetic code<br />
and that were present in the last common ancestor of<br />
the universal tree of life. As the tree developed and<br />
branched into the 3 great kingdoms—archaebacteria,<br />
bacteria, and eukaryotes—the enzymes were incorporated<br />
into every cell type of every organism. During<br />
this long evolutionary period and populating of every<br />
cell, the enzymes adopted novel functions while keeping<br />
their canonical role as determinates of the genetic<br />
code. Related to their central role, the enzymes acquired<br />
novel domains enabling them to correct errors of aminoacylation<br />
and thereby ensure the stringent accuracy of<br />
the code. Unrelated to their canonical activity in translation,<br />
their expanded functions include regulation of<br />
transcription and translation in bacteria, RNA splicing<br />
in fungal organisms, and cytokine signaling in mammalian<br />
cells. <strong>The</strong>se novel functions connect translation<br />
to other central pathways that control growth, development,<br />
and regulation of all cell types.<br />
Recently, we have focused on 2 of the expanded<br />
functions that have connections to disease and medicine.<br />
One function is the editing activity of the synthetases.<br />
Mutations in the editing domain of a specific<br />
tRNA synthetase cause ambiguity in the genetic code<br />
and result in subtle missense substitutions in proteins<br />
throughout the organism (Fig. 1). <strong>The</strong>se changes, in<br />
turn, cause global changes in protein function. Such<br />
changes can, in principle, lead to specific diseases, such<br />
as autoimmune disorders. Indeed, specific changes in<br />
the phenotypes of mammalian cells in culture occur<br />
when an editing-defective synthetase is present.<br />
In mammalian cells, tyrosyl- and tryptophanyl-tRNA<br />
synthetases are procytokines. When these synthetases<br />
are split by alterative splicing or natural proteolysis,<br />
specific fragments are released. <strong>The</strong>se fragments are<br />
active in signal transduction pathways. For example,<br />
T2-TrpRS, a fragment of tryptophanyl-tRNA synthetase,<br />
is a potent angiostatic agent. In collaborative experiments<br />
with M. Friedlander, Department of Cell <strong>Biology</strong>,
Fig. 1. Aminoacyl-tRNA synthetases catalyze the attachment of<br />
a noncognate amino acid onto tRNA. A distinct hydrolytic second<br />
site prevents these substrates from being released for use in protein<br />
synthesis. Mutations within the editing site result in the inability to<br />
clear noncognate amino acids from the tRNA. <strong>The</strong>se errors in proofreading<br />
ultimately lead to incorporation of wrong amino acids into<br />
a growing polypeptide. <strong>The</strong> final result of accumulation of proteins<br />
with errors in their primary sequences is cell death.<br />
we found that T2-TrpRS arrested angiogenesis in the<br />
retina in neonatal mice. <strong>The</strong> fragment is so effective in<br />
arresting angiogenesis that it is now being introduced<br />
into a clinical setting for the treatment of blindness<br />
caused by macular degeneration. In other research, we<br />
are focusing on the usefulness of T2-TrpRS for treatment<br />
of highly vascularized tumors.<br />
To understand the antiangiogenic activity of T2-TrpRS,<br />
we are identifying the cell signaling pathway involved.<br />
Recent experiments indicated that vascular endothelial<br />
cell cadherin (VE-cadherin), a calcium-dependent adhesion<br />
molecule specifically expressed in endothelial cells<br />
and essential for normal vascular development, binds<br />
directly to T2-TrpRS. This binding, in turn, blocks the<br />
proangiogenic activity of vascular endothelial cell growth<br />
factor (Fig. 2). Currently, we are examining the mechanism<br />
of signaling by T2-TrpRS after it is bound to VEcadherin<br />
and the mechanism of export of T2-TrpRS from<br />
the cytoplasm to the cell surface. In addition, on the<br />
basis of x-ray structures, we proposed a structure-based<br />
mechanism for cytokine activation: the structural changes<br />
that occur when tryptophanyl- and tyrosyl-tRNA synthetases<br />
are split into specific fragments that convert<br />
the synthetases to cytokines.<br />
In other research, we are investigating the critical<br />
steps in the transition from the RNA world to the theater<br />
of proteins. Recent findings established a plausible<br />
scenario for the selection of L- rather than D-amino<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 205<br />
Fig. 2. Schematic illustration of proposed model for how T2-TrpRS<br />
(T2) interacts with VE-cadherin and blocks signaling pathways for<br />
vascular endothelial cell growth vector (VEGF) and its receptor<br />
(VEGFR2).<br />
acids as the building blocks for proteins in all life forms.<br />
Using amino acids activated in a way similar to the way<br />
in which modern amino acids are activated, we showed<br />
chiral-selective aminoacylation of tRNA-like molecules.<br />
We are using x-ray analysis to understand the structural<br />
basis of the chiral selectivity.<br />
PUBLICATIONS<br />
Bacher, J.M., de Crécy-Lagard, V., Schimmel, P. Inhibited cell growth and protein<br />
functional changes from an editing-defective tRNA synthetase. Proc. Natl. Acad.<br />
Sci. U. S. A. 102:1697, 2005.<br />
Ewalt, K.L., Schimmel, P. Protein biosynthesis: tRNA synthetases. In: Encyclopedia<br />
of Biological Chemistry. Lennarz, W.J., Lane, M.D. (Eds.). Academic Press, San<br />
Diego, 2004, p. 263.<br />
Ewalt, K.L., Yang, X.-L., Otero, F.J., Liu, J., Slike, B., Schimmel, P. Variant of<br />
human enzyme sequesters reactive intermediate. Biochemistry 44:4216, 2005.<br />
Metzgar, D., Bacher, J.M., Pezo, V., Reader, J., Doring, V., Schimmel, P., Marlière,<br />
P., de Crécy-Lagard, V. Acinetobacter sp ADP1: an ideal model organism for<br />
genetic analysis and genome engineering. Nucleic Acid Res. 32:5780, 2004.<br />
Nordin, B.E., Schimmel, P. Isoleucyl-tRNA synthetases. In: Aminoacyl-tRNA Synthetases.<br />
Ibba, M., Francklyn, C., Cusack, S. (Eds.). Landes Bioscience/Eurekah.com,<br />
Georgetown, TX, 2005, p. 24.<br />
Ribas de Pouplana, L., Musier-Forsyth, K., Schimmel, P. Alanyl-tRNA synthetases.<br />
In: Aminoacyl-tRNA Synthetases. Ibba, M., Francklyn, C., Cusack, S. (Eds.). Landes<br />
Bioscience/Eurekah.com, Georgetown, TX, 2005, p. 241.<br />
Ribas de Pouplana, L., Schimmel, P. Aminoacylations of tRNAs: record-keepers for<br />
the genetic code. In: Protein Synthesis and Ribosome Structure: Translating the<br />
Genome. Nierhaus, K.H., Wilson, D.N. (Eds.), Wiley-VCH, New York, 2004, p. 169.<br />
Schimmel, P. Genetic code. In: McGraw-Hill Encyclopedia of Science and Technology,<br />
10th ed. McGraw-Hill, New York, in press.<br />
Schimmel, P., Beebe, K. From the RNA world to the theater of proteins. In: <strong>The</strong><br />
RNA World, 3rd ed. Gesteland, R.R., Cech, T.R., Atkins, J.F. (Eds.), Cold Spring<br />
Harbor Laboratory Press, Cold Spring Harbor, NY, in press.<br />
Schimmel, P., Ewalt, K. Translation silenced by fused pair of tRNA synthetases.<br />
Cell 119:147, 2004.
206 MOLECULAR BIOLOGY 2005<br />
Schimmel, P., Söll, D. <strong>The</strong> world of aminoacyl-tRNA synthetases. In: AminoacyltRNA<br />
Synthetases. Ibba, M., Francklyn, C., Cusack, S. (Eds.). Landes<br />
Bioscience/Eurekah.com, Georgetown, TX, 2005, p. 1.<br />
Swairjo, M.A., Schimmel, P. Breaking sieve for steric exclusion of a noncognate<br />
amino acid from active site of a tRNA synthetase. Proc. Natl. Acad. Sci. U. S. A.<br />
102:988, 2005.<br />
Tamura, K., Schimmel, P. Non-enzymatic aminoacylation of an RNA minihelix with<br />
an aminoacyl phosphate oligonucleotide. Nucleic Acids Symp. Ser. 48:269, 2004.<br />
Tang, H.-L., Yeh, L.-S., Chen, N.-K., Ripmaster, T.L., Schimmel, P., Wang, C.-C.<br />
Translation of a yeast mitochondrial tRNA synthetase initiated at redundant non-<br />
AUG codons. J. Biol. Chem. 279:49656, 2004.<br />
Tzima, E., Reader, J.S., Irani-Tehrani, M., Ewalt, K.L., Schwartz, M.A., Schimmel,<br />
P. VE-cadherin links tRNA synthetase cytokine to anti-angiogenic function. J.<br />
Biol. Chem. 280:2405, 2005.<br />
Mechanisms of RNA Assembly<br />
and Catalysis<br />
M.J. Fedor, E.M. Calderon, J.W. Cottrell, C.P. Da Costa,<br />
J.W. Harger, Y.I. Kuzmin, E.M. Mahen<br />
Recent evidence that RNA catalysis participates<br />
in regulation of gene expression as well as in<br />
RNA processing and protein synthesis underscores<br />
the importance of learning the molecular basis of<br />
ribozyme activity. <strong>The</strong> hairpin ribozyme is an especially<br />
good model for investigating RNA catalytic mechanisms<br />
because of its relative simplicity and the availability of<br />
high-resolution structures that provide a framework for<br />
evaluating structure-function relationships. This ribozyme<br />
catalyzes reversible phosphodiester cleavage<br />
through attack of a ribose 2′ oxygen nucleophile on an<br />
adjacent phosphorus (Fig. 1). Our goals have been to<br />
identify which parts of the ribozyme contribute to catalysis<br />
and to understand the chemical basis of this activity.<br />
Like all enzymes, hairpin ribozymes combine several<br />
strategies to enhance catalytic rate. One important<br />
Fig. 1. Chemical mechanism of RNA cleavage mediated by the<br />
family of small catalytic RNAs that includes the hairpin ribozyme.<br />
Cleavage proceeds through an SN2-type mechanism that involves<br />
in-line attack of the 2′ oxygen nucleophile on the adjacent phosphorus<br />
to form a trigonal bipyramidal transition state in which 5<br />
electronegative oxygen atoms form transient bonds with phosphorus.<br />
Breaking of the 5′ oxygen-phosphorus bond generates products<br />
with 5′ hydroxyl and 2′,3′-cyclic phosphate termini.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
strategy, which is apparent from crystal structures, is<br />
the alignment of nucleophilic and leaving-group oxygens<br />
in the optimal orientation for an SN 2 -type nucleophilic<br />
attack. Biochemical and structural studies also<br />
implicate 2 active-site nucleobases, guanine 8 and<br />
adenine 38, in catalytic chemistry; the N-1 ring nitrogen<br />
of guanine 8 is located near the 2′ oxygen that<br />
acts as the nucleophile during cleavage, and the N-1<br />
ring nitrogen of adenine 38 is located near the 5′ oxygen<br />
leaving group.<br />
Ribonuclease A is a protein enzyme that catalyzes<br />
the same chemical reaction as hairpin ribozyme cleavage<br />
and has 2 active-site histidines that occupy positions<br />
similar to those of guanine 8 and adenine 38.<br />
Ribonuclease A provides a textbook example of concerted<br />
general acid-base catalysis, and the similarity<br />
between hairpin ribozyme and ribonuclease A activesite<br />
structures led to the idea that guanine 8 and adenine<br />
38 might serve as general acid and base catalysts<br />
as the histidines of ribonuclease A do. <strong>The</strong> activity of<br />
the hairpin ribozyme increases with increasing pH,<br />
consistent with the notion that activity depends on the<br />
availability of guanine 8, in its unprotonated form, to<br />
accept a proton to activate the 2′ hydroxyl nucleophile<br />
as proposed in the general acid-base catalysis model.<br />
However, a ribozyme variant in which guanine 8 is<br />
replaced by an abasic residue has the same pH dependence<br />
as an unmodified ribozyme, suggesting that the<br />
pH transition in activity does not involve guanine 8.<br />
<strong>The</strong>se data support an alternative model in which the<br />
protonated form of guanine 8 donates hydrogen bonds<br />
that provide electrostatic stabilization as negative charge<br />
develops in the transition state (Fig. 2). Replacing<br />
adenine 38 with an abasic residue, on the other hand,<br />
does eliminate this pH-dependent transition, evidence<br />
that the protonation state of adenine 38 is important<br />
for activity.<br />
<strong>The</strong> activity that is lost when adenine 38 or guanine<br />
8 is replaced by abasic residues can be rescued<br />
by certain nucleobases provided in solution. <strong>The</strong> molecules<br />
that can rescue activity all have planar structures<br />
and an amidine group, that is, an amino group in α-position<br />
to a ring nitrogen. <strong>The</strong> same feature is shared with<br />
the Watson-Crick face of the missing adenine and guanine,<br />
suggesting that chemical rescue occurs through<br />
binding of exogenous nucleobases in the cavity left by<br />
an abasic substitution. Purines that lack an amidine<br />
group can inhibit chemical rescue, presumably by competing<br />
with rescuing nucleobases for binding in the cav-
Fig. 2. Results of mechanistic studies of the hairpin ribozyme<br />
are consistent with 2 models in which the functional form of adenine<br />
38 is either protonated or unprotonated. In the first model<br />
(A), protonated adenine 38 would act as a general acid by donating<br />
a proton to the 5′ oxygen, acting in concert with hydroxide ion<br />
that activates the 2′ oxygen nucleophile during cleavage, and unprotonated<br />
adenine 38 would act as a general base to activate the 5′<br />
oxygen nucleophile during ligation. In the second model (B), unprotonated<br />
adenine 38 accepts a hydrogen bond from the 5′ hydroxyl<br />
nucleophile during ligation and accepts a hydrogen bond from a<br />
protonated bridging 5′ oxygen during cleavage, providing electrostatic<br />
stabilization to developing negative charge. In both models, the<br />
amidine group of guanine 8, in its protonated form, donates hydrogen<br />
bonds to the 2′ and phosphoryl oxygens that stabilize the negative<br />
charge that develops in the transition state and that position<br />
reactive groups in the orientation appropriate for an SN2 in-line<br />
nucleophilic attack.<br />
ity left by the abasic substitution. Thus, rescue does not<br />
occur through binding alone, and amidine functional<br />
groups must form specific stabilizing interactions with<br />
the transition state. <strong>The</strong> pH dependence of chemical<br />
rescue of ribozymes lacking adenine 38 changes according<br />
to the intrinsic basicity of the rescuing nucleobase.<br />
<strong>The</strong>se and other results are consistent with 2 models<br />
of the hairpin ribozyme catalytic mechanism in which<br />
adenine 38 contributes either general acid-base catalysis<br />
(Fig. 2A) or electrostatic stabilization of negative charge<br />
that develops as 5 electronegative oxygen atoms form<br />
transient bonds with phosphorus in the transition state<br />
(Fig. 2B).<br />
PUBLICATIONS<br />
Fedor, M.J., Williamson, J.R. <strong>The</strong> catalytic diversity of RNAs. Nat. Rev. Mol. Cell<br />
Biol. 6:399, 2005.<br />
Kuzmin, Y.I, Da Costa, C.P., Cottrell, J.W., Fedor, M.J. Role of an active site adenine<br />
in hairpin ribozyme catalysis. J. Mol. Biol. 349:989, 2005.<br />
Mahen, E.M., Harger, J.W., Calderon, E.M., Fedor, M.J. Kinetics and thermodynamics<br />
make different contributions to RNA folding in vitro and in yeast. Mol. Cell<br />
19:27, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 207<br />
Directed Evolution of Nucleic<br />
Acid Enzymes<br />
G.F. Joyce, T.A. Jackson, G.C. Johns, H.R. Kalhor, C.-Y. Lai,<br />
M. Oberhuber, B.M. Paegel, G.G. Springsteen, S.B. Voytek<br />
All life known to exist on Earth today is based on<br />
DNA genomes and protein enzymes, but strong<br />
evidence indicates that it was preceded by a<br />
simpler form of life based on RNA. This earlier era is<br />
referred to as the “RNA world.” During that time, genetic<br />
information resided in the sequence of RNA molecules,<br />
and phenotype was derived from the catalytic behavior<br />
of RNA. By studying the properties of RNA in the laboratory,<br />
especially with regard to the evolution of catalytic<br />
function, we can gain insight into the RNA world.<br />
In addition, we can develop novel nucleic acid enzymes<br />
that have applications in biology and medicine.<br />
SYNTHESIS AND DERIVATIZATION OF RIBOSE<br />
Ribose, the sugar component of RNA, is a minor<br />
component among the many products of the condensation<br />
of formaldehyde. In addition, ribose is more<br />
reactive than most other sugars and degrades more<br />
rapidly than they do. Thus, it is difficult to understand<br />
why ribose is included in the genetic material.<br />
We exploited the greater reactivity of ribose by allowing<br />
it to react preferentially with cyanamide to form a<br />
stable product. This product crystallized spontaneously<br />
in aqueous solution under a broad range of conditions;<br />
the corresponding cyanamides derived from other sugars<br />
did not. Furthermore, the ribose-cyanamide crystals<br />
reacted with cyanoacetylene to form cytosine α-nucleoside<br />
in nearly quantitative yield.<br />
<strong>The</strong> RNA-catalyzed synthesis of ribose from simple<br />
starting materials would have been an essential reaction<br />
in the RNA world. We approached this problem<br />
by examining the ability of a nucleic acid template to<br />
direct the synthesis of ribose from 2 aldehyde-bearing<br />
oligonucleotides, one with glyceraldehyde at its 3′ end<br />
and the other with glycoaldehyde at its 5′ end. <strong>The</strong> 2<br />
oligonucleotides were allowed to bind at adjacent positions<br />
along a complementary template, resulting in an<br />
aldol reaction that gave rise to pentose sugars (Fig. 1).<br />
No reaction was detected in the absence of the template.<br />
Adding lysine to the mixture increased the reaction<br />
rate substantially. This reaction will be used as<br />
the basis for in vitro evolution experiments to obtain<br />
RNAs that catalyze the formation of ribose.
208 MOLECULAR BIOLOGY 2005<br />
Fig. 1. RNA-directed synthesis of pentose sugars via aldol condensation.<br />
Two oligonucleotides, one with glyceraldehyde at its 3′<br />
end (S1) and the other with glycoaldehyde at its 5′ end (S2), are<br />
joined in the presence of a complementary template to form a pentose-linked<br />
product.<br />
CROSS-REPLICATING RNA ENZYMES<br />
<strong>The</strong> central process of the RNA world was the RNAcatalyzed<br />
replication of RNA. We previously developed<br />
an RNA enzyme, termed the R3C ligase, that catalyzes<br />
the template-directed joining of 2 RNA molecules. This<br />
enzyme was converted to a format that allows it to<br />
produce additional copies of itself through the joining<br />
of 2 component subunits. <strong>The</strong> copies in turn give rise<br />
to additional copies, resulting in an exponential increase<br />
in the number of enzyme molecules over time. We further<br />
modified the reaction system so that it would operate<br />
cross-catalytically, whereby 2 RNA enzymes catalyze<br />
each other’s synthesis from a total of 4 substrates<br />
(Fig. 2). <strong>The</strong> newly formed copies of each enzyme give<br />
rise to additional copies of the cross-catalytic products,<br />
and the rate of formation of both enzymes increases<br />
during the course of the reaction. Currently, the crossreplicating<br />
system operates with a highly restricted set<br />
of RNA sequences, but it provides an opportunity for<br />
developing more efficient and more complex networks<br />
of replicating RNAs.<br />
CONTINUOUS EVOLUTION OF RNA ENZYMES<br />
Previously, we developed a powerful method for the<br />
in vitro evolution of RNA enzymes that catalyze the joining<br />
of RNA molecules. Rather than manipulating the<br />
RNAs through successive steps of reaction, selection,<br />
and amplification, we devised a way to have these steps<br />
occur continuously within a common reaction vessel.<br />
Evolution can be carried out indefinitely by a serial transfer<br />
procedure, whereby a small part of a completed<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 2. Cross-catalytic replication of RNA enzymes. <strong>The</strong> enzyme E<br />
binds the substrates S1′ and S2′ and catalyzes their joining to form<br />
the enzyme E′. Similarly, the enzyme E′ binds and joins the substrates<br />
S1 and S2 to form the enzyme E.<br />
reaction mixture is transferred to a new reaction vessel<br />
that contains a fresh supply of substrates and the other<br />
components necessary for selective amplification.<br />
During the past year, we began 3 new lines of investigation<br />
involving continuous in vitro evolution. First, we<br />
modified the system so that an increased frequency of<br />
random mutations would occur during amplification. This<br />
modification allows us to generate and exploit genetic<br />
diversity within the system, providing a more realistic<br />
model of biological evolution. Second, using either 2<br />
distinct variants of 1 enzyme or 2 different enzymes,<br />
we sought to evolve 2 different RNA enzymes within a<br />
common environment. <strong>The</strong>se evolved enzymes will be<br />
used to study competition and cooperation in the context<br />
of RNA-based evolution.<br />
Third, we implemented a novel microfluidic system<br />
for continuous in vitro evolution. In this system, the<br />
population of enzymes is confined to a microfluidic<br />
circuit within a fabricated glass wafer that contains a<br />
middle layer of an elastomeric material that functions<br />
as control valves. <strong>The</strong> concentration of RNA is monitored<br />
by using a confocal fluorescence microscope, and<br />
serial transfer is triggered automatically whenever the<br />
population size reaches a predetermined threshold. <strong>The</strong>
microfluidic system makes it possible to conduct thousands<br />
of generations of in vitro evolution in a highly precise<br />
manner with little intervention by the experimenter.<br />
PUBLICATIONS<br />
Johns, G.C., Joyce, G.F. <strong>The</strong> promise and peril of continuous in vitro evolution. J.<br />
Mol. Evol. 61:253, 2005.<br />
Joyce, G.F., Orgel, L.E. Progress toward understanding the origin of the RNA<br />
world. In: <strong>The</strong> RNA World, 3rd ed. Gesteland, R.F., Cech, T.R., Atkins, J.F. (Eds.).<br />
Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, in press.<br />
Kim, D.-E., Joyce, G.F. Cross-catalytic replication of an RNA ligase ribozyme.<br />
Chem. Biol. 11:1505, 2004.<br />
Paul, N., Joyce, G.F. Minimal self-replicating systems. Curr. Opin. Chem. Biol.<br />
8:634, 2004.<br />
Springsteen, G., Joyce, G.F. Selective derivatization and sequestration of ribose<br />
from a prebiotic mix. J. Am. Chem. Soc. 126:9578, 2004.<br />
Studies at the Interface of<br />
<strong>Molecular</strong> <strong>Biology</strong>, Chemistry,<br />
and Medicine<br />
C.F. Barbas III, B.A. Gonzalez, L. Asawapornmongkul,<br />
D.B. Ramachary, S. Eberhardy, R. Fuller, R. Gordley, J. Guo,<br />
B. Henriksen, C. Lund, J. Mandell, S. Mitsumori, R. Mobini,<br />
N.S. Chowdari, M. Popkov, D. Steiner, J. Suri, F. Tanaka,<br />
U. Tschulena, Y. Ye, Y. Yuan, G. Zhong<br />
We are concerned with problems in molecular<br />
biology, chemistry, and medicine. Many of<br />
our studies involve learning or improving on<br />
Nature’s strategies to prepare novel molecules that<br />
perform specific functional tasks, such as regulating a<br />
gene, destroying cancer, or catalyzing a reaction with<br />
enzymelike efficiency. We hope to apply these novel<br />
insights, technologies, methods, and products to provide<br />
solutions to human diseases, including cancer,<br />
HIV disease, and genetic diseases.<br />
DIRECTING THE EVOLUTION OF CATALYTIC FUNCTION<br />
Using our concept of reactive immunization, we<br />
have developed antibodies that catalyze aldol as well<br />
as retro-aldol reactions of a wide variety of molecules.<br />
<strong>The</strong> catalytic proficiency of the best of these antibodies<br />
is almost 10 14 , a value 1000 times that of the<br />
best catalytic antibodies reported to date and overall<br />
the best of any synthetic protein catalyst. We have<br />
shown the efficient asymmetric synthesis and resolution<br />
of a variety of molecules, including tertiary and<br />
fluorinated aldols, and have used these chiral synthons<br />
to synthesize natural products (Fig. 1). <strong>The</strong> results<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 209<br />
Fig. 1. A variety of compounds synthesized with the world’s first<br />
commercially available catalytic antibody, 38C2, produced at<br />
<strong>Scripps</strong> <strong>Research</strong>.<br />
highlight the potential synthetic usefulness of catalytic<br />
antibodies as artificial enzymes in addressing problems<br />
in organic chemistry that are not solved by using natural<br />
enzymes or more traditional synthetic methods.<br />
To further evolve these catalytic antibodies, we are<br />
developing genetic selection methods. Other advances<br />
in this area include the development of the first peptide<br />
aldolase enzymes. Using both design and selection, we<br />
created small peptide catalysts that recapitulate many<br />
of the kinetic features of large protein catalysts. With<br />
these smaller enzymes, we can address how the size<br />
of natural proteins is related to catalytic efficiency.<br />
ORGANOCATALYSIS: A BIOORGANIC APPROACH TO<br />
CATALYTIC ASYMMETRIC CARBON-CARBON<br />
BOND–FORMING REACTIONS<br />
To further explore the principles of catalysis, we<br />
are studying amine catalysis as a function of catalytic<br />
scaffold. Using insights garnered from our studies of<br />
aldolase antibodies, we determined the efficacy of simple<br />
chiral amines and amino acids for catalysis of aldol<br />
and related imine and enamine chemistries such as<br />
Michael, Mannich, Knoevenagel, and Diels-Alder reactions<br />
(Fig. 2). Although aldolase antibodies are superior<br />
in terms of the kinetic parameters, these more<br />
simple catalysts are enabling us to quantify the importance<br />
of pocket sequestration in catalysis.<br />
Furthermore, many of these catalysts are cheap,<br />
environmentally friendly, and practical for large-scale<br />
synthesis. With this approach, we showed the scope
210 MOLECULAR BIOLOGY 2005<br />
Fig. 2. L-Proline and other organocatalysts developed for a variety<br />
of catalytic asymmetric syntheses via aldol, Michael, Mannich,<br />
Diels-Alder, and Knoevenagel reactions provide access to important<br />
classes of compounds. <strong>The</strong>se catalysts make reactions that were<br />
once complex multistep reactions, simple 1-step reactions. A wide<br />
variety of medicinally important products can be assembled by<br />
using the Mannich reaction manifold alone.<br />
and usefulness of the first efficient amine catalysts of<br />
direct asymmetric aldol, Mannich, Diels-Alder, and<br />
Michael reactions. <strong>The</strong> organocatalyst approach is a<br />
direct outcome of our studies of catalytic antibodies<br />
and provides an effective alternative to organometallic<br />
reactions that use severe reaction conditions and oftentoxic<br />
catalysts.<br />
We think that our discovery that the simple naturally<br />
occurring amino acids such as L-proline and other<br />
amines can effectively catalyze a variety of enantioselective<br />
intermolecular reactions will change the way<br />
many reactions will be performed. Furthermore, these<br />
catalysts are functional in related ketone addition reactions<br />
such as Mannich- and Michael-type reactions. As<br />
a testament to the mild nature of this approach, we<br />
developed the first catalytic asymmetric aldol, Mannich,<br />
Michael, and fluorination reactions involving aldehydes<br />
as nucleophiles. Previously, such reactions were considered<br />
out of the reach of traditional synthetic methods.<br />
In an extension of these concepts, we invented a<br />
variety of novel multicomponent or asymmetric assembly<br />
reactions (Fig. 3). Our finding that a variety of optically<br />
active amino acids can be synthesized with proline<br />
catalysis in which an L-amino acid begets other L-amino<br />
acids suggests that this route may have been used in<br />
prebiotic syntheses of optically active amino acids. In<br />
addition, we showed that our strategy can be used to<br />
synthesize carbohydrates directly, thereby providing a<br />
provocative prebiotic route to the sugars essential for life.<br />
Unlike most catalysts obtained via traditional<br />
approaches, our catalysts are environmentally safe and<br />
are available in both enantiomeric forms. <strong>The</strong> reactions<br />
do not require inert conditions or heavy metals and<br />
can be performed at room temperature without preactivation<br />
of the donor substrates. Because amines can<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 3. A few recently developed catalytic asymmetric assembly<br />
reactions. In these reactions, designed small organic molecules are<br />
used to synthesize complex molecules.<br />
act as catalysts via both nucleophilic (enamine based)<br />
and electrophilic (iminium based) activation, they have<br />
great potential in catalytic asymmetric synthesis.<br />
THERAPEUTIC ANTIBODIES, IN AND OUT OF CELLS<br />
We developed the first human antibody phage display<br />
libraries and the first synthetic antibodies and<br />
methods for the in vitro evolution of antibody affinity.<br />
<strong>The</strong> ability to manipulate large libraries of human antibodies<br />
and to evolve such antibodies in the laboratory<br />
provides tremendous opportunities to develop new<br />
medicines. Laboratories and pharmaceutical companies<br />
around the world now apply the phage display<br />
technology that we developed for antibody Fab fragments.<br />
In our laboratory, we are targeting cancer and<br />
HIV disease. One of our antibodies, IgG1-b12, protects<br />
animals against primary challenge with HIV type 1<br />
(HIV-1) and has been further studied by many other<br />
researchers. We improved this antibody by developing<br />
in vitro evolution strategies that enhanced its neutralization<br />
activity. By coupling laboratory-evolved antibodies<br />
with potent toxins, we showed that immunotoxins<br />
can effectively kill infected cells.<br />
We are also developing genetic methods to halt<br />
HIV by using gene therapy. We created unique human
antibodies that can be expressed inside human cells<br />
to make the cells resistant to HIV infection. In the<br />
future, these antibodies might be delivered to the stem<br />
cells of patients infected with HIV-1, allowing the development<br />
of a disease-free immune system that would<br />
preclude the intense regimen of antiviral drugs now<br />
required to treat HIV disease.<br />
Using our increased understanding of antibody-antigen<br />
interactions, we extended our efforts in cancer therapy<br />
and developed rapid methods for creating human<br />
antibodies from antibodies derived from other species.<br />
We produced human antibodies that should enable us<br />
to selectively starve a variety of cancers by inhibiting<br />
angiogenesis and antibodies that will be used to deliver<br />
radionuclides to colon cancers to destroy the tumors.<br />
We hope that some of these antibodies will be used in<br />
clinical trials done by our collaborators at the Sloan-<br />
Kettering Cancer Center in New York City.<br />
On the basis of our studies on HIV-1, we used intracellular<br />
expression of antibodies directed against angiogenic<br />
receptors to create a new gene-based approach<br />
to cancer. We are determining if this new approach can<br />
be applied in vivo to halt tumor growth. Our preliminary<br />
results indicate that this type of gene therapy can<br />
be successfully applied to the treatment of cancer.<br />
THERAPEUTIC APPLICATIONS OF CATALYTIC<br />
ANTIBODIES<br />
<strong>The</strong> development of highly efficient catalytic antibodies<br />
opens the door to many practical applications.<br />
One of the most fascinating is the use of such antibodies<br />
in human therapy. We think that use of this strategy<br />
can improve chemotherapeutic approaches to diseases<br />
such as cancer and AIDS. Chemotherapeutic regimens<br />
are typically limited by nonspecific toxic effects. To<br />
address this problem, we developed a novel and broadly<br />
applicable drug-masking chemistry that operates in<br />
conjunction with our unique broad-scope catalytic antibodies.<br />
This masking chemistry is applicable to a wide<br />
range of drugs because it is compatible with virtually<br />
any heteroatom. We showed that generic drug-masking<br />
groups can be selectively removed by sequential<br />
retro-aldol–retro-Michael reactions catalyzed by antibody<br />
38C2 (Fig. 4). This reaction cascade is not catalyzed<br />
by any known natural enzyme.<br />
Application of this masking chemistry to the anticancer<br />
drugs doxorubicin, camptothecin, and etoposide<br />
produced prodrugs with substantially reduced toxicity.<br />
<strong>The</strong>se prodrugs are selectively unmasked by the<br />
catalytic antibody when the antibody is applied at thera-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
peutically relevant concentrations. <strong>The</strong> efficacy of this<br />
approach has been shown in in vivo models of cancer.<br />
Currently, we are developing more potent drugs and novel<br />
antibodies that will allow us to target breast, colon, and<br />
prostate cancer as well as cells infected with HIV-1. On<br />
the basis of our preliminary findings, we think that our<br />
approach can become a key tool in selective chemotherapeutic<br />
strategies. To see a movie illustrating this approach,<br />
visit http://www.scripps.edu/mb/barbas/index.html.<br />
ADAPTOR IMMUNOTHERAPY: THE ADVENT OF<br />
CHEMOBODIES<br />
We think that combining the chemical diversity of<br />
small synthetic molecules with the immunologic characteristics<br />
of antibody molecules will lead to therapeutic<br />
agents with superior properties. <strong>The</strong>refore, we developed<br />
a conceptually new device that equips small synthetic<br />
molecules with both the immunologic effector functions<br />
and the long serum half-life of a generic antibody molecule.<br />
For a prototype, we developed a targeting device<br />
based on the formation of a covalent bond of defined<br />
stoichiometry between (1) a 1,3-diketone derivative of<br />
an arginine–glycine–aspartic acid peptidomimetic that<br />
targets the integrins α v β 3 and α v β 5 and (2) the reactive<br />
lysine of aldolase antibody 38C2. <strong>The</strong> resulting<br />
complex spontaneously assembled in vitro and in vivo,<br />
selectively retargeted antibody 38C2 to the surface of<br />
cells expressing integrins α v β 3 and α v β 5 , dramatically<br />
increased the circulatory half-life of the peptidomimetic,<br />
and effectively reduced tumor growth in animal models<br />
of human Kaposi sarcoma and colon cancer (Fig. 5).<br />
<strong>The</strong>se studies have been extended to melanoma.<br />
ZINC FINGER GENE SWITCHES<br />
MOLECULAR BIOLOGY 2005 211<br />
Fig. 4. Targeting cancer and HIV with prodrugs activated by catalytic<br />
antibodies. A bifunctional antibody is shown targeting a cancer<br />
cell for destruction. A nontoxic analog of doxorubicin, prodoxorubicin,<br />
is being activated by an aldolase antibody to the toxic form<br />
of the drug.<br />
<strong>The</strong> solution to many diseases might be simply turning<br />
genes on or off in a selective way. In order to pro-
212 MOLECULAR BIOLOGY 2005<br />
Fig. 5. Adaptor Immunotherapy dramatically slows tumor growth.<br />
A variety of cancer xenografts have been effectively treated with<br />
chemobodies, a combination of small-molecule drugs and antibodies.<br />
Chemobodies have characteristics that can be superior to those<br />
of either the small molecule or the antibody alone.<br />
duce switches that can turn genes on or off, we are<br />
studying molecular recognition of DNA by zinc finger<br />
proteins and methods of creating novel zinc finger DNAbinding<br />
proteins (Fig. 6). Because of their modularity<br />
and well-defined structural features, zinc finger proteins<br />
are particularly well suited for use as DNA-binding proteins.<br />
Each finger forms an independently folded domain<br />
that typically recognizes 3 nucleotides of DNA. We<br />
showed that proteins can be selected or designed that<br />
contain zinc fingers that recognize novel DNA sequences.<br />
Fig. 6. A designed polydactyl zinc finger binds 18 bp of DNA. A<br />
single zinc finger domain is highlighted. With this direct approach,<br />
we can construct more than a billion gene switches and use the<br />
switches to specifically turn genes on or off in multiple organisms.<br />
With further elaboration of the approach, every gene in the genome<br />
can be either upregulated or downregulated, providing a new approach<br />
to probe gene function across the genome.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
<strong>The</strong>se studies are aiding the elucidation of rules for<br />
sequence-specific recognition within this family of proteins.<br />
We selected and designed specific zinc finger<br />
domains that will constitute an alphabet of 64 domains<br />
that will allow any DNA sequence to be bound selectively.<br />
<strong>The</strong> prospects for this “second genetic code” are<br />
fascinating and should have a major impact on basic<br />
and applied biology.<br />
We showed the potential of this approach in multiple<br />
mammalian and plant cell lines and in whole<br />
organisms. With the use of characterized modular zinc<br />
finger domains, polydactyl proteins capable of recognizing<br />
an 18-nucleotide site can be rapidly constructed.<br />
Our results suggest that zinc finger proteins might be<br />
useful as genetic regulators for a variety of human ailments<br />
and provide the basis for a new strategy in gene<br />
therapy. Our goal is to develop this class of therapeutic<br />
proteins to inhibit or enhance the synthesis of proteins,<br />
providing a direct strategy for fighting diseases<br />
of either somatic or viral origin.<br />
We are also developing proteins that will inhibit<br />
the growth of tumors and others that will inhibit the<br />
expression of a protein known as CCR5, which is a<br />
key to infection of human cells by HIV-1. We developed<br />
an HIV-1–targeting transcription factor that strongly<br />
suppresses HIV-1 replication. Genetic diseases such<br />
as sickle cell anemia are also being targeted. Using a<br />
library of transcription factors, we developed a strategy<br />
that effectively allows us to turn on and turn off every<br />
gene in the genome. With this powerful new strategy,<br />
we can quickly regulate a target gene or discover other<br />
genes that have a key role in disease. In the future,<br />
we hope to use novel DNA-modifying enzymes directed<br />
by zinc fingers to manipulate chromosomes themselves.<br />
PUBLICATIONS<br />
Amir, R.J., Popkov, M., Lerner, R.A., Barbas, C.F. III, Shabat, D. Prodrug activation<br />
gated by a molecular “OR” logic trigger. Angew. Chem. Int. Ed. 44:4378, 2005.<br />
Betancort, J.M., Sakthivel, K., Thayumanavan, R., Tanaka, F., Barbas, C.F. III. Catalytic<br />
direct asymmetric Michael reactions: addition of unmodified ketone and aldehyde<br />
donors to alkylidene malonates and nitro olefins. Synthesis 1509, 2004, Issue 9.<br />
Blancafort, P., Segal, D.J., Barbas, C.F. III. Designing transcription factor architectures<br />
for drug discovery. Mol. Pharmacol. Rev. 66:1361, 2004.<br />
Chen, E.I., Florens, L., Axelrod, F.T., Monosov, E., Barbas, C.F. III, Yates, J.R. III,<br />
Felding-Habermann, B., Smith, J.W. Maspin alters the carcinoma proteome.<br />
FASEB J. 19:1123, 2005.<br />
Chowdari, N.S., Barbas, C.F. III. Total synthesis of LFA-1 antagonist BIRT-377 via<br />
organocatalytic asymmetric construction of a quaternary stereocenter. Org. Lett.<br />
7:867, 2005.<br />
Chowdari, N.S., Suri, J.T., Barbas, C.F. III. Asymmetric synthesis of quaternary<br />
α- and β-amino acids and β-lactams via proline catalyzed Mannich reactions with<br />
branched aldehyde donors. Org. Lett. 6:2507, 2004.
Crotty, J.W., Etzkorn, C., Barbas, C.F. III, Segal, D.J., Horton, N.C. Crystallographic<br />
analysis of Aart, a designed six-finger zinc finger peptide, bound to DNA.<br />
Acta Crystallogr. F61:573, 2005.<br />
Gräslund, T., Li, X., Popkov, M., Barbas, C.F. III. Exploring strategies for the<br />
design of artificial transcription factors: targeting sites proximal to known regulatory<br />
regions for the induction of γ-globin expression and the treatment of sickle cell disease.<br />
J. Biol. Chem. 280:3707, 2005.<br />
Haba, K., Popkov, M., Shamis, M., Lerner, R.A., Barbas, C.F. III, Shabat, D. Single-triggered<br />
trimeric prodrugs, Angew. Chem. Int. Ed. 44:716, 2005.<br />
Jendreyko, N., Popkov, M., Rader, C., Barbas, C.F. III. Phenotypic knockout of<br />
VEGF-R2 and Tie-2 with an intradiabody reduces tumor growth and angiogenesis<br />
in vivo. Proc. Natl. Acad. Sci. U. S. A. 102:8293, 2005.<br />
Li, L.-S., Rader, C., Matsushita, M., Das, S., Barbas, C.F, III, Lerner, R.A., Sinha,<br />
S.C. Chemical adaptor immunotherapy: design, synthesis, and evaluation of novel<br />
integrin-targeting devices. J. Med. Chem. 47:5630, 2004.<br />
Magnenat, L., Blancafort, P., Barbas, C.F. III. In vivo selection of combinatorial libraries<br />
and designed affinity maturation of polydactyl zinc finger transcription factors for<br />
ICAM-1 provides new insights into gene regulation. J. Mol. Biol. 341:635, 2004.<br />
Mase, N., Thayumanavan, R., Tanaka, F., Barbas, C.F. III. Direct asymmetric organocatalytic<br />
Michael reactions of α,α-disubstituted aldehydes with β-nitrostyrenes for<br />
the synthesis of quaternary carbon-containing products. Org. Lett. 6:2527, 2004.<br />
Notz, W., Tanaka, F., Barbas, C.F. III. Enamine-based organocatalysis with proline<br />
and diamines: the development of direct catalytic asymmetric aldol, Mannich,<br />
Michael, and Diels-Alder reactions. Acc. Chem. Res. 37:580, 2004.<br />
Notz, W., Watanabe, S., Chowdari, N.S., Zhong, G., Betancort, J.M., Tanaka, F.,<br />
Barbas, C.F. III. <strong>The</strong> scope of the direct proline-catalyzed asymmetric addition of<br />
ketones to imines. Adv. Synth. Catal. 346:1131, 2004.<br />
Popkov, M., Jendreyko, N., McGavern, D.B., Rader, C., Barbas, C.F. III. Targeting<br />
tumor angiogenesis with adenovirus-delivered anti-Tie-2 intrabody. Cancer Res.<br />
65:972, 2005.<br />
Popkov, M., Rader, C., Barbas, C.F. III. Isolation of human prostate cancer cell reactive<br />
antibodies using phage display technology. J. Immunol. Methods 291:137, 2004.<br />
Ramachary, D.B., Barbas, C.F. III. Direct amino acid-catalyzed asymmetric desymmetrization<br />
of meso-compounds: tandem aminoxylation/O-N bond heterolysis reactions.<br />
Org. Lett. 7:1577, 2005.<br />
Ramachary, D.B., Barbas, C.F. III. Towards organo-click chemistry: development<br />
of organocatalytic multicomponent reactions through combinations of aldol, Wittig,<br />
Knoevenagel, Michael, Diels-Alder and Huisgen cycloaddition reactions. Chemistry<br />
10:5323, 2004.<br />
Sinha, S.C., Li, l.-S., Watanabe, S., Kaltgrad, E., Tanaka, F., Rader, C., Lerner,<br />
R.A., Barbas, C.F. III. Aldolase antibody activation of prodrugs of potent aldehydecontaining<br />
cytotoxics for selective chemotherapy. Chemistry 10:5467, 2004.<br />
Steiner, D.D., Mase, N., Barbas, C.F. III. Direct asymmetric α-fluorination of aldehydes.<br />
Angew. Chem. Int. Ed. 44:3706, 2005.<br />
Suri, J.T., Ramachary, D.B., Barbas, C.F. III. Mimicking dihydroxy acetone phosphate-utilizing<br />
aldolases through organocatalysis: a facile route to carbohydrates<br />
and aminosugars. Org. Lett. 7:1383, 2005.<br />
Tanaka, F., Barbas, C.F. III. Enamine-based reactions using organocatalysts: from<br />
aldolase antibodies to small amino acid and amine catalysts. J. Synth. Org. Chem.<br />
Jpn., in press.<br />
Tanaka, F., Barbas, C.F. III. Organocatalytic approaches to enantioenriched β-amino<br />
acids. In: Enantioselective Synthesis of β-Amino Acids, 2nd ed. Juaristi, E., Soloshonok,<br />
V. (Eds.). Wiley-VCH, New York, 2004, p. 195.<br />
Tanaka, F., Barbas, C.F. III. Reactive immunization: a unique approach to aldolase antibodies.<br />
In: Catalytic Antibodies. Keinan, E. (Ed.). Wiley-VCH, New York, 2004, p. 304.<br />
Tanaka, F., Flores, F., Kubitz, D., Lerner, R.A., Barbas, C.F. III. Antibody-catalyzed<br />
aminolysis of a chloropyrimidine derivative. Chem. Commun. (Camb.) 1242,<br />
2004, Issue 10.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Tanaka, F., Mase, N., Barbas, C.F. III. Determination of cysteine concentration by<br />
fluorescence increase: reaction of cysteine with a fluorogenic aldehyde. Chem.<br />
Commun. (Camb.) 1762, 2004, Issue 15.<br />
Thayumanavan, R., Tanaka, F., Barbas, C.F. III. Direct organocatalytic asymmetric<br />
aldol reactions of α-amino aldehydes: expedient synthesis of highly enantiomerically<br />
enriched anti-β-hydroxy-α-amino acids. Org. Lett. 6:3541, 2004.<br />
Zhong, G., Fan, J., Barbas, C.F. III. Amino alcohol catalyzed direct asymmetric<br />
aldol reactions: enantioselective synthesis of anti-α-fluoro-β-hydroxy ketones. Tetrahedron<br />
Lett. 45:5681, 2004.<br />
Zhu, X., Tanaka, F., Hu, Y., Heine, A., Fuller, R., Zhong, G., Olson, A.J., Lerner,<br />
R.A., Barbas, C.F. III, Wilson, I.A. <strong>The</strong> origin of enantioselectivity in aldolase antibodies:<br />
crystal structure, site-directed mutagenesis, and computational analysis. J.<br />
Mol. Biol. 343:1269, 2004.<br />
Synthetic Enzymes, Catalytic<br />
Antibodies, Ozone Scavengers,<br />
Organic Synthesis, and<br />
Biomolecular Computing<br />
E. Keinan, C.H. Lo, H. Han, S. Sasmal, S. Ledoux,<br />
N. Metanis, G. Sklute, E. Kossoy, M. Soreni, D. Vebenov,<br />
R. Piran, M. Sinha, A. Alt, I. Ben-Shir, R. Girshfeld, S. Yogev<br />
We focus on synthetically modified enzymes,<br />
antibody-catalyzed reactions, anticancer and<br />
antiasthma agents, and biomolecular computation,<br />
as illustrated in the following examples.<br />
SYNTHETIC ENZYMES<br />
MOLECULAR BIOLOGY 2005 213<br />
Efforts to generate new enzymatic activities from<br />
existing protein scaffolds may not only provide biotechnologically<br />
useful catalysts but also lead to better<br />
understanding of the natural process of evolution. We<br />
profoundly changed the catalytic activity and mechanism<br />
of the enzyme 4-oxalocrotonate tautomerase by<br />
means of rationally designed synthetic mutations. For<br />
example, a single amino acid substitution that corresponds<br />
to a mutation in a single base pair led to a<br />
dramatic change in the catalytic activity. Although the<br />
wild-type enzyme catalyzes only the tautomerization of<br />
4-oxalocrotonate, the mutant P1A catalyzes both the<br />
original tautomerization reaction via a general acid-base<br />
mechanism and the decarboxylation of oxaloacetate via<br />
a nucleophilic mechanism. <strong>The</strong> observation that a single<br />
catalytic group in an enzyme can catalyze 2 reactions<br />
by 2 different mechanisms supports the hypothesis<br />
that enzyme evolution is a continuum in which a new<br />
catalytic mechanism is gained while the parent activity<br />
declines gradually through small changes in the amino<br />
acid sequence of the primordial enzyme.
214 MOLECULAR BIOLOGY 2005<br />
We also showed that the electrostatic manipulation<br />
of an enzyme’s active site can alter the substrate specificity<br />
of the enzyme in a predictable way. We replaced<br />
1, 2, or all 3 active-site arginine residues with citrulline<br />
analogs to maintain the steric features of the active<br />
site of 4-oxalocrotonate tautomerase while changing<br />
its electronic properties. <strong>The</strong>se synthetic changes<br />
revealed that the wild-type enzyme binds the natural<br />
substrate predominantly through electrostatic interactions.<br />
This and other mechanistic insights led to the<br />
design of a modified enzyme that was specific for a<br />
new substrate that had different electrostatic properties<br />
and that bound the enzyme via hydrogen-bonding<br />
complementarity rather than electrostatic interactions.<br />
<strong>The</strong> synthetic analog of the natural 4-oxalocrotonate<br />
tautomerase was a poor catalyst of the natural 4-oxalocrotonate<br />
substrate but an efficient catalyst for a ketoamide<br />
substrate. This research on synthetic enzymes<br />
is being done in collaboration with P.E. Dawson, Department<br />
of Cell <strong>Biology</strong>.<br />
CATALYTIC ANTIBODIES<br />
Although the solution photochemical reaction of<br />
the ketone 1 (in Fig. 1) yields only the cleavage products<br />
2 and 3, in the presence of 20F10, an antibody<br />
to 5a and 5b, this Norrish type II reaction results in the<br />
selective formation of cis-cyclobutanol (compound 4<br />
in Fig. 1). Furthermore, the fact that compound 4,<br />
which consists of 2 asymmetric centers, is obtained<br />
as a single diastereomer makes this photoproduct a<br />
valuable building block for the synthesis of natural<br />
products. Another reaction that is exclusively catalyzed<br />
by 20F10 is the photochemical formation of cyclopropanol<br />
products.<br />
Fig. 1. <strong>The</strong> photochemical Norrish type II reaction of ketone 1<br />
produces in solution the cleavage products 2 and 3. Antibody<br />
20F10, which was elicited against a mixture of 5a and 5b, catalyzes<br />
enantioselective formation of cis-cyclobutanol (4).<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
An aldolase antibody, 24H6, obtained from immunization<br />
with large diketone haptens has an active-site<br />
lysine residue with a perturbed pK a of 7.0. This antibody<br />
catalyzes both the aldol addition and the retrograde<br />
aldol fragmentation with a broad range of substrates that<br />
differ structurally from the hapten. This observation<br />
suggests that in reactive immunization with 1,3-diketones,<br />
the hapten structure governs the chemistry but<br />
not the overall organization of the active site. Antibody<br />
24H6 also catalyzes the oxidation of α-hydroxyketones<br />
to α-diketones. <strong>The</strong> deuterium exchange at the α position<br />
of many ketones and aldehydes is also efficiently<br />
catalyzed by aldolase antibodies 38C2 and 24H6. All<br />
reactions were carried out in deuterium oxide under<br />
neutral conditions and showed regioselectivity, chemoselectivity,<br />
and high catalytic rates.<br />
OZONE SCAVENGERS AND ANTIASTHMA ACTIVITY<br />
A new hypothesis we proposed for the mechanism<br />
of asthmatic inflammation has led to an ozone-scavenging<br />
compound that prevents bronchial obstruction<br />
in rats with asthma. Previously, scientists at <strong>Scripps</strong><br />
<strong>Research</strong> discovered that ozone can be generated not<br />
only via the antibody-mediated water oxidation pathway<br />
but also by antibody-coated activated white blood<br />
cells during inflammatory processes. This finding led<br />
us to speculate that the pulmonary inflammation in<br />
asthma might be caused by ozone production by white<br />
blood cells in lungs and that inhalation of electron-rich<br />
olefins, which are known ozone scavengers, might have<br />
antiasthmatic effects. In experiments in rats, inhalation<br />
of such a compound, limonene, caused a significant<br />
improvement in asthmatic symptoms. <strong>The</strong>se<br />
results could have consequences in the management<br />
of asthma.<br />
ORGANIC SYNTHESIS<br />
Annonaceous acetogenins, particularly those with<br />
adjacent bis-tetrahydrofuran rings, have remarkable<br />
cytotoxic, antitumor, antimalarial, immunosuppressive,<br />
pesticidal, and antifeedant activities. More than 350<br />
different acetogenins have been isolated from only 35<br />
of 2300 plants of the family Annonaceae. We developed<br />
synthetic approaches that can be used to generate<br />
chemical libraries of stereoisomeric acetogenins.<br />
<strong>The</strong>se efforts resulted in the total synthesis of several<br />
naturally occurring acetogenins, including asimicin,<br />
bullatacin, trilobacin, rolliniastatin, solamin, reticulatacin,<br />
rollidecins C and D, goniocin, cyclogoniodenin,<br />
and mucocin, and many nonnatural stereoisomers. A<br />
substituted photoactive derivative of asimicin has been
prepared for photoaffinity labeling of the target protein<br />
subunit in the mitochondrial complex I. This research<br />
is being done in collaboration with S.C. Sinha, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>.<br />
BIOMOLECULAR COMPUTING DEVICES<br />
Four years ago we described the first nanoscale,<br />
programmable finite automaton with 2 symbols and 2<br />
states that computed autonomously. All of the components<br />
of the device, including hardware, software, input,<br />
and output, were biomolecules mixed together in solution.<br />
<strong>The</strong> hardware consisted of a restriction nuclease<br />
and a ligase; the software (transition rules) and the<br />
input were double-stranded DNA oligomers (Fig. 2).<br />
Fig. 2. A biomolecular computing machine made of molecules.<br />
<strong>The</strong> hardware consists of a restriction nuclease and a ligase; the<br />
input, transition molecules (software), and detection molecules are<br />
all made of double-stranded DNA.<br />
Computation was carried out by processing the input<br />
molecule via repetitive cycles of restriction, hybridization,<br />
and ligation reactions to produce a final-state output<br />
in the form of a double-stranded DNA molecule.<br />
Currently, we are taking the concept of molecular computing<br />
a step further and are constructing computing<br />
devices in which the computation output is a specific<br />
biological function rather than a specific molecule.<br />
Most recently, we markedly increased the levels of<br />
complexity and mathematical power of these automata<br />
by the design of a 3-state–3-symbol automaton, thus<br />
increasing the number of syntactically distinct programs<br />
from 765 to 1 billion. We have further amplified the<br />
applicability of this design by using surface-anchored<br />
input molecules and surface plasmon resonance technology<br />
to monitor the computation steps in real time.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
This technology allowed parallel computation and automatic,<br />
real-time detection with DNA chips that carry<br />
multiple input molecules and can be used as pixel arrays<br />
for image encryption.<br />
PUBLICATIONS<br />
Dubnikova, F., Kosloff, R., Almog, J., Zeiri, Y., Boese, R., Itzhaky, H., Alt, A.,<br />
Keinan, E. Decomposition of triacetone triperoxide is an entropic explosion. J. Am.<br />
Chem. Soc. 127:1146, 2005.<br />
Keinan, E., Alt, A., Amir, G., Bentur, L., Bibi, H., Shoseyov, D. Natural ozone<br />
scavenger prevents asthma in sensitized rats. Bioorg. Med. Chem. 13:557, 2005.<br />
Metanis, N., Keinan, E., Dawson, P.E. A designed synthetic analogue of 4-OT is<br />
specific for a non-natural substrate. J. Am. Chem. Soc. 127:5862, 2005.<br />
Saphier, S., Hu, Y., Sinha, S.C., Houk, K.N., Keinan, E. <strong>The</strong> origin of selectivity in the<br />
antibody 20F10-catalyzed Yang cyclization. J. Am. Chem. Soc. 127:132, 2005.<br />
Soreni, M., Yogev, S., Kossoy, E., Shoham, Y., Keinan, E. Parallel biomolecular<br />
computation on surfaces with advanced finite automata. J. Am. Chem. Soc.<br />
127:3935, 2005.<br />
Antibody Catalysis and<br />
Organic Synthesis<br />
S.C. Sinha, R.A. Lerner, S. Das, S. Abraham, F. Guo,<br />
Z. Chen<br />
MOLECULAR BIOLOGY 2005 215<br />
Our main research interests are antibody catalysis<br />
and the applications of antibody catalysts<br />
in organic synthesis, prodrug activation, and<br />
the development of cell-targeting antibody constructs.<br />
In addition, we also focus on synthetic and medicinal<br />
chemistry, including the total synthesis of biologically<br />
important natural products and synthetic compounds<br />
and their analogs and new methods of synthesis.<br />
ANTIBODY CATALYSIS AND ITS APPLICATIONS<br />
Aldolase antibodies 38C2, 84G3, and 93F3 produced<br />
by the reactive immunization technique are<br />
highly useful in synthetic organic chemistry, as indicated<br />
by their application in the syntheses of a number<br />
of natural products, including epothilones. <strong>The</strong>se<br />
antibodies catalyze both aldol and retro-aldol reactions<br />
and yield products with high enantioselectivities.<br />
<strong>The</strong> high catalytic rate of the retro-aldol reaction makes<br />
the antibodies useful in prodrug therapy.<br />
In prodrug therapy, an enzyme or a catalytic antibody<br />
is used to activate a nontoxic prodrug at a targeted<br />
site, thereby producing a cytotoxic drug. We are developing<br />
prodrugs of cytotoxic molecules, including paclitaxel,<br />
doxorubicin analogs, enediynes, CBI analogs, and<br />
epothilones, that can be activated efficiently by aldolase<br />
antibodies. In particular, we prepared and evaluated
216 MOLECULAR BIOLOGY 2005<br />
several prodrugs of the analogs of dynemicin B and doxorubicin.<br />
<strong>The</strong> prodrugs of dynemicin analogs are activated<br />
by using antibody 38C2; those of doxorubicin analogs,<br />
by 93F3 (Fig. 1). On the basis of these studies, we are<br />
developing new linkers for the prodrugs so that activation<br />
of the prodrugs can be selectively achieved at<br />
high catalytic rate.<br />
Fig. 1. Structure of the prodrugs of doxorubicin (DOX) analogs.<br />
Using antibody 38C2, we also developed antagonist-38C2<br />
conjugates. <strong>The</strong> conjugates bound efficiently<br />
to cells expressing the integrins α v β 3 and α v β 5 . <strong>The</strong><br />
conjugates have several advantages, including prolongation<br />
of half-life of the antagonist and in vivo assembly<br />
of the conjugate. On the basis of our initial studies,<br />
in collaboration with C.F. Barbas, Department of <strong>Molecular</strong><br />
<strong>Biology</strong>, we synthesized a series of antagonist-38C2<br />
conjugates and evaluated them by using breast cancer<br />
cell lines that express the integrins α v β 3 and α v β 5 . Several<br />
conjugates (Fig. 2) bound to these cell lines with<br />
high affinity. Our findings, which were supported by<br />
molecular docking studies, provided preliminary information<br />
on how the compounds should be derivatized.<br />
Fig. 2. Structure of the compounds that target the integrins α v β 3<br />
and α v β 5 for conjugation with 38C2.<br />
SYNTHESIS OF NATURAL PRODUCTS AND THEIR<br />
ANALOGS<br />
In the past year, we focused on the synthesis of<br />
naturally occurring macrocyclic molecules, sorangiolides<br />
A and B, and the library of bis-tetrahydrofuran annonaceous<br />
acetogenins. Sorangiolides (Fig. 3) are weakly<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 3. Structure of sorangiolides A and B (top) and a general<br />
structure of bis-tetrahydrofuran annonaceous acetogenins (bottom).<br />
active against gram-positive bacteria. Our goal is to<br />
synthesize analogs of sorangiolides that are highly active.<br />
<strong>The</strong> bis-tetrahydrofuran acetogenins are among the<br />
most active cancer agents and are toxic to a number of<br />
human cancer cell lines at much lower concentrations<br />
than doxorubicin is. In collaboration with E. Keinan,<br />
Department of <strong>Molecular</strong> <strong>Biology</strong>, we synthesized an<br />
analog of asimicin, an annonaceous acetogenin, for<br />
photoaffinity labeling of the corresponding receptor. In<br />
other studies, we developed a bidirectional approach for<br />
the synthesis of all 64 diastereomers of the adjacent<br />
bis-tetrahydrofuran acetogenins (Fig. 3). Starting with<br />
8 diene lactones, we synthesized 36 bifunctional adjacent<br />
bis-tetrahydrofuran lactones by using 5 key reactions:<br />
(1) monooxidative or bis-oxidative cyclization<br />
mediated by rhenium(VII) oxides, (2) Shi monoasymmetric<br />
or bis-asymmetric epoxidation, (3) Sharpless<br />
asymmetric dihydroxylation, (4) Williamson-type etherification,<br />
and (5) Mitsunobu inversion. Further studies<br />
are in progress.<br />
PUBLICATIONS<br />
Li, L.-S., Rader, C., Matsushita, M., Das, S., Barbas, C.F. III, Lerner, R.A., Sinha,<br />
S.C. Chemical-adaptor immunotherapy: design, synthesis and evaluation of novel<br />
integrin-targeting devices. J. Med. Chem. 47:5630, 2004.<br />
Saphier, S., Hu, Y., Sinha, S.C., Houk, K.N., Keinan, E. Origin of selectivity in the<br />
antibody 20F10-catalyzed Yang cyclization. J. Am. Chem. Soc. 127:132, 2005.<br />
Sinha, S.C., Li, L.-S., Watanabe, S.-I., Kaltgrad, E., Tanaka, F., Rader, C., Lerner,<br />
R.A., Barbas, C.F. III. Aldolase antibody activation of prodrugs of potent aldehydecontaining<br />
cytotoxics for selective chemotherapy. Chemistry 10:5467, 2004.
Structure, Function, and<br />
Applications of Virus Particles<br />
J.E. Johnson, L. Basumallic, A. Chatterji, W. Fernandez-<br />
Ochoa, L. Gan, I. Gertsman, R. Khayat, J. Lanman, K. Lee,<br />
T. Matsui, P. Natarajan, A. Odegard, J. Speir, L. Tang,<br />
H. Walukiewicz, E. Wu<br />
We investigate model virus systems that provide<br />
insights for understanding assembly, maturation,<br />
entry, localization, and replication of<br />
nonenveloped viruses. We also have developed viruses<br />
as reagents for applications in nanotechnology, chemistry,<br />
and biology. We investigate viruses that infect bacteria,<br />
insects, yeast, plants, and, recently, the extreme<br />
thermophile Sulfolobus. <strong>The</strong>se viruses have genomes<br />
of single-stranded RNA, double-stranded RNA, and double-stranded<br />
DNA. In many instances, we use viruslike<br />
particles that do not contain infectious genomes.<br />
We use a variety of physical methods to investigate<br />
structure-function relationships, including single-crystal<br />
and static and time-resolved solution x-ray diffraction,<br />
electron cryomicroscopy and image reconstruction, mass<br />
spectrometry, structure-based computational analyses,<br />
and methods associated with thermodynamic characterization<br />
of virus particles and their transitions. Biological<br />
methods we use include genetic engineering of viral<br />
genes and their expression in Escherichia coli, mammalian<br />
cells, insect cells, and yeast and the characterization<br />
of these gene products by the physical methods<br />
mentioned previously. For cytologic studies of viral<br />
entry and infection, we use fluorescence and electron<br />
microscopy and particles assembled in heterologous<br />
expression systems. Our studies depend on extensive<br />
consultations and collaborations with others at <strong>Scripps</strong><br />
<strong>Research</strong>, including groups led by C.L. Brooks, D.A.<br />
Case, B. Carragher, M.G. Finn, M.R. Ghadiri, T. Lin,<br />
M. Manchester, D.R. Millar, R.A. Milligan, C. Potter,<br />
V. Reddy, A. Schneemann, G. Siuzdak, K.F. Sullivan,<br />
J.R. Williamson, and M.J. Yeager, and a variety of groups<br />
outside of <strong>Scripps</strong>.<br />
DOUBLE-STRANDED DNA VIRUSES<br />
HK97 is a double-stranded DNA bacterial virus<br />
similar to phage λ. It undergoes a remarkable morphogenesis<br />
in its assembly and maturation, and this process<br />
can be recapitulated in vitro. We determined the<br />
atomic resolution structure of the 650-Å mature head<br />
II particle and discovered the mechanism used to concatenate<br />
the subunits of the particle into a chain-mail<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 217<br />
fabric similar to that seen in the armor of medieval<br />
knights. We created a model of the procapsid on the<br />
basis of the 5-Å electron cryomicroscopy structure in<br />
which the coordinates from the head II particle were<br />
readily fitted. Recently, we used single-value decomposition<br />
analysis of time-resolved solution x-ray scattering<br />
data and single-molecule fluorescence to show<br />
that the initial maturation of prohead II (~470 Å in<br />
diameter) to expansion intermediate I (546 Å in diameter)<br />
occurs as a highly cooperative, stochastic event<br />
with no significantly populated intermediates and takes<br />
less than 1 second for an individual particle.<br />
Bacteriophage P22 is the prototype of the Podoviridae,<br />
which are characterized by a T = 7 capsid with<br />
a short tail structure incorporated into a unique 5-fold<br />
vertex. We previously determined the icosahedrally averaged<br />
structure of the capsid at 20-Å resolution, the 10-Å<br />
structure of the connector protein, and the 20-Å structure<br />
of the tail machine. Recently, we did a reconstruction<br />
of the virus without imposing symmetry, enabling<br />
us to visualize the detailed relationship of all these<br />
components (Fig. 1).<br />
Fig. 1. Electron cryomicroscopy reconstruction of the bacteriophage<br />
P22. <strong>The</strong> reconstruction was done with 1800 particles and<br />
no applications of symmetry. <strong>The</strong> reconstructed density required<br />
first generating an icosahedrally averaged electron density that ignored<br />
the tail assembly and then inserting the tail assembly (determined<br />
as a separate reconstruction) into the icosahedral density to create<br />
a tailed phage model. <strong>The</strong> model was then back projected in all icosahedral<br />
orientations onto each individual particle, and the orientation<br />
that gave the highest correlation coefficient (i.e., aligned the<br />
tails) was used to reconstruct the final density. Note that without<br />
any application of symmetry, both the tail machine and the T = 7<br />
surface lattice are clearly defined in the reconstructed density.
218 MOLECULAR BIOLOGY 2005<br />
Sulfolobus turreted icosahedral virus is an archaeal<br />
virus isolated from Sulfolobus, which grows in the<br />
acidic hot sulfur springs (pH 2–4, 72°C–92°C) in Yellowstone<br />
National Park. An electron cryomicroscopy<br />
reconstruction of the virus showed that the capsid has<br />
pseudo T = 31 quasi symmetry and is 1000 Å in diameter,<br />
including the pentons. We solved the x-ray structure<br />
of the major capsid protein of the virus and revealed<br />
a fold nearly identical to the major capsid proteins of<br />
the eukaryotic adenoviruses; PBCV-1, a virus that infects<br />
fresh water algae; and PRD-1, a virus that infects bacteria.<br />
<strong>The</strong>se findings indicate a virus phylogeny that spans<br />
the 3 domains of life (Eucarya, Bacteria, and Archaea)<br />
and suggests that these viruses may be related to a<br />
virus that preceded the division of life into 3 domains<br />
more than 3 billion years ago.<br />
SINGLE-STRANDED RNA VIRUSES<br />
Flock House virus is a single-stranded RNA virus<br />
that infects Drosophila. We are studying viral entry<br />
and early expression and assembly of the capsid protein.<br />
Recently, studies on viral entry indicated the<br />
presence of an “eluted” particle early in infection that<br />
has initiated its disassembly program but is then eluted<br />
back into the medium. We did a phenotypic characterization<br />
of the particles, and we are using electron cryomicroscopy<br />
to study them. For studies on the expression<br />
and assembly of the capsid protein, we are using tags<br />
genetically inserted in the capsid protein that allow the<br />
freshly made proteins to be optically visualized with a<br />
fluorophore and in the electron microscope with photoconversion<br />
of the fluorophore.<br />
Tetraviruses are single-stranded RNA viruses that<br />
infect Lepidoptera. Expression of the capsid protein in<br />
the baculovirus system leads to spontaneous assembly<br />
of viruslike particles that we can investigate in vitro. <strong>The</strong><br />
particles exist as procapsids (480 Å) at pH 7 and as<br />
capsids (410 Å) at pH 5. We used limited proteolysis<br />
and mass spectrometry to investigate the driving force<br />
of the transition, the mechanism of an autocatalytic<br />
cleavage, and the dynamic features of both forms.<br />
Cowpea mosaic virus is a 30-nM reagent that we use<br />
for chemistry and nanotechnology. In collaboration with<br />
T. Lin, Department of <strong>Molecular</strong> <strong>Biology</strong>, we generated<br />
and produced a large variety of viable mutations of the<br />
virus in gram quantities for nanopatterning, molecular<br />
electronic scaffolds, and platforms for novel chemistry.<br />
PUBLICATIONS<br />
Blum, A.S., Soto, C.M. Wilson, C.D., Brower, T.L., Pollack, S.K., Schull, T.L.,<br />
Chatterji, A., Lin, T., Johnson, J.E., Amsinck, C., Franzon, P., Shashidhar, R.,<br />
Ratna, B.R. An engineered virus as a scaffold for three-dimensional self-assembly<br />
on the nanoscale. Small 1:702, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Blum, A.S., Soto, C.M., Wilson, C.D., Cole, J.D., Kim, M., Gnade, B., Chatterji, A.,<br />
Ochoa, W.F., Lin, T., Johnson, J., Ratna, B.R. Cowpea mosaic virus as a scaffold<br />
for 3-D patterning of gold nanoparticles. Nano Lett. 4:867, 2004.<br />
Bothner, B., Taylor, D., Jun, B., Lee, K.K., Siuzdak, G., Schultz, C.P., Johnson,<br />
J.E. Maturation of a tetravirus capsid alters the dynamic properties and creates a<br />
metastable complex. Virology 334:17, 2005.<br />
Chatterji, A., Ochoa, W.F., Paine, M., Ratna, B.R., Johnson, J.E., Lin, T. New<br />
addresses on an addressable virus nanoblock; uniquely reactive Lys residues on<br />
cowpea mosaic virus. Chem. Biol. 11:855, 2004.<br />
Chatterji, A., Ochoa, W.F., Ueno, T., Lin, T., Johnson, J.E. A virus-based nanoblock<br />
with tunable electrostatic properties. Nano Lett. 5:597, 2005.<br />
Falkner, J.C., Turner, M.E., Bosworth, J.K., Trentler, T.J., Johnson, J.E., Lin, T.,<br />
Colvin, V.L. Virus crystals as nanocomposite scaffolds. J. Am. Chem. Soc.<br />
127:5274, 2005.<br />
Girard, E., Kahn, R., Mezouar, M., Dhaussy, A.C., Lin, T., Johnson, J.E., Fourme, R.<br />
<strong>The</strong> first crystal structure of a complex macromolecular assembly under high pressure:<br />
CpMV at 330 MPa. Biophys. J. 88:3562, 2005.<br />
Johnson, K.N., Tang, L., Johnson, J.E., Ball, L.A. Heterologous RNA encapsidated<br />
in Pariacoto virus-like particles forms a dodecahedral cage similar to genomic RNA<br />
in wild-type virions. J. Virol. 78:11371, 2004.<br />
Lin, T., Lomonossoff, G.P., Johnson, J.E. Structure-based engineering of an icosahedral<br />
virus for nanomedicine and nanotechnology. In: Nanotechnology in <strong>Biology</strong><br />
and Medicine: Methods, Devices, and Applications. Vo-Dinh, T. (Ed.). CRC Press,<br />
Boca Raton, FL, in press.<br />
Lin, T., Schildkamp, W., Brister, K., Doerschuk, P.C., Somayazulu, M., Mao,<br />
H.K., Johnson, J.E. <strong>The</strong> mechanism of high pressure induced ordering in a macromolecular<br />
crystal. Acta Crystallogr. D Biol. Crystallogr. 61:737, 2005.<br />
Medintz, I., Mattoussi, H., Sapsford, K., Chatterji, A., Johnson, J.E. Decoration of<br />
discretely immobilized cowpea mosaic virus with luminescent quantum dots. Langmuir,<br />
in press.<br />
Natarajan, P., Lander, G., Shepherd, C., Reddy, V., Brooks, C.L. III, Johnson, J.E.<br />
Virus Particle Explorer (VIPER), a Web-based repository of virus structural data and<br />
derived information. Nat. Microbiol. Rev., in press.<br />
Reddy, V., Schneemann, A., Johnson, J.E. Nodavirus endopeptidase. In: Handbook<br />
of Proteolytic Enzymes, 2nd ed. Barret, A.J., Rawlings, N.D., Woessner, J.F.<br />
(Eds.). Academic Press, San Diego, 2004, Vol. 2, p. 198.<br />
Reddy, V.S., Natarajan, P., Lander, G., Qu, C., Brooks, C.L. III, Johnson, J.E.<br />
Virus Particle Explorer (VIPER): a repository of virus capsid structures. In: Conformational<br />
Proteomics of Macromolecular Architecture: Approaching the Structure of<br />
Large <strong>Molecular</strong> Assemblies and <strong>The</strong>ir Mechanisms of Action. Cheng, R.H., Hammar,<br />
L. (Eds.). World Scientific, River Edge, NJ, 2004, p. 403.<br />
Schwarcz, W.D., Barroso, S.P., Gomes, A.M., Johnson, J.E., Schneemann, A.,<br />
Oliveira, A.C., Silva, J.L. Virus stability and protein-nucleic acid interaction as<br />
studied by high-pressure effects on nodaviruses. Cell. Mol. Biol. (Noisy-le-grand)<br />
50:419, 2004.<br />
Strable, E., Johnson, J.E., Finn, M.G. Natural supramolecular building blocks:<br />
icosahedral virus particles organized by attached oligonucleotides. Nano Lett.<br />
4:1385, 2004.<br />
Tang, J., Naitow, H., Gardner, N.A., Kolesar, A., Tang, L., Wickner, R.B., Johnson,<br />
J.E. <strong>The</strong> structural basis of recognition and removal of cellular mRNA 7-methyl G<br />
“caps” by a viral capsid protein: a unique viral response to host defense. J. Mol.<br />
Recognit. 18:158, 2005.<br />
Tang, L., Marion, W.R., Cingolani, G., Prevelige, P.E., Johnson, J.E. <strong>The</strong> three-dimensional<br />
structure of the bacteriophage P22 tail machine. EMBO J. 24:2087, 2005.<br />
Taylor, D.J., Johnson, J.E. Folding and particle assembly are disrupted by singlepoint<br />
mutations near the autocatalytic cleavage site of nudaurelia capensis 4 virus<br />
capsid protein. Protein Sci. 14:401, 2005.<br />
Taylor, D.J., Speir, J., Reddy, V., Cingolani, G., Pringle, F., Ball, L.A., Johnson,<br />
J.E. Preliminary x-ray characterization of authentic providence virus and attempts<br />
to express its coat protein gene in recombinant baculovirus. Arch. Virol., in press.
An Icosahedral Scaffold for<br />
Biophysical Studies and<br />
Nanomanufacturing<br />
T. Lin, J.E. Johnson, A. Chatterji, W.F. Ochoa, A. Stone,<br />
T. Ueno<br />
Cowpea mosaic virus (CPMV) is an icosahedral<br />
plant virus with a diameter of 30 nm. Because<br />
of its exceptional stability, high yield, ease of<br />
production, structural information to the level of atomic<br />
definition, and accessible genetic programmability, the<br />
virus has been used as a model system for biophysical<br />
studies and has been engineered for applications in<br />
biotechnology and nanotechnology.<br />
ASSEMBLY OF NANOMATERIALS ON AN<br />
ICOSAHEDRAL SCAFFOLD<br />
A quintessential tenet of nanotechnology is the selfassembly<br />
of components at nanometer scale to form<br />
devices. Although small molecules with novel electronic<br />
properties can be synthesized, it is generally difficult<br />
to get functional connectivity among the different components<br />
in designed patterns. In contrast, because of<br />
their versatility, programmability through genetic engineering,<br />
and propensity to form arrays, biological macromolecules<br />
are more amenable for self-assembly either<br />
as devices for direct use or as scaffolds for patterning<br />
small molecules. We showed that CPMV can be used<br />
as a template for nanochemistry by introducing unique<br />
cysteine residues and exploiting the native lysine residues.<br />
In collaboration with B.R. Ratna, Naval <strong>Research</strong><br />
Laboratory, Washington, D.C., we used the viral capsid<br />
as a nano circuit board and the reactive groups as<br />
anchoring points for the assembly of electronic molecules,<br />
oligophenylene-vinylene and others. <strong>The</strong> establishment<br />
of the molecular network was demonstrated<br />
by measuring electronic conductance via scanning tunnel<br />
microscopy.<br />
HIGH-PRESSURE CRYSTALLOGRAPHY<br />
Using high pressure, we markedly improved the diffraction<br />
from the cubic crystals of CPMV from about 4-Å<br />
to 2.1-Å resolution. If this use of pressure is generally<br />
applicable, it can have a marked effect on structural biology.<br />
To this end, we carried out mechanistic studies of<br />
the pressure-induced rectification of crystal imperfection.<br />
Two types of cubic crystals were assigned to either<br />
an I23 or a P23 space group. <strong>The</strong> 2 types had the same<br />
rhombic dodecahedral morphology at atmospheric pres-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
sure. <strong>The</strong> crystals assigned to the I23 space group diffracted<br />
x-rays to higher resolution than did those<br />
assigned to the P23 space group. <strong>The</strong> assignment of<br />
the P23 space group was due to the presence of reflections<br />
with indices h + k + l = (2n + 1) (odd reflections),<br />
which are forbidden in the I23 space group.<br />
Analysis of the odd reflections from the P23 crystals<br />
at atmospheric pressure indicated that they originated<br />
from a rotational disorder in the the I23 crystals. <strong>The</strong><br />
odd reflections were eliminated by applying 3.5 kbar<br />
of pressure, which transformed the crystals from the<br />
apparently primitive cell to the body-centered I23 cell,<br />
with dramatic improvement in diffraction.<br />
PUBLICATIONS<br />
Blum, S.A., Soto, C.M., Wilson, C.D., Brower, T.L., Pollack, S.K., Schull, T.L.,<br />
Chatterji, A., Lin, T., Johnson, J.E., Amsinck, C., Franson, P., Shashidhar, R.,<br />
Ratna, B.R. An engineered virus as a scaffold for three-dimensional self-assembly<br />
on the nanoscale. Small 1:702, 2005.<br />
Chatterji, A., Ochoa, W., Shamieh, L., Salakian, S.P., Wong, S.M., Clinton, G.,<br />
Ghosh, P., Lin, T., Johnson, J.E. Chemical conjugation of heterologous proteins on<br />
the surface of cowpea mosaic virus. Bioconjug. Chem. 15:807, 2004.<br />
Chatterji, A., Ochoa, W.F., Paine, M., Ratna, B.R., Johnson, J.E., Lin, T. New<br />
addresses on an addressable virus nanoblock: uniquely reactive Lys residues on<br />
cowpea mosaic virus. Chem. Biol. 11:855, 2004.<br />
Chatterji, A., Ochoa, W.F., Ueno, T., Lin, T., Johnson, J.E. A virus-based<br />
nanoblock with tunable electrostatic properties. Nano Lett. 5:597, 2005.<br />
Falkner, J.C., Turner, M.E., Bosworth, J.K., Trentler, T.J., Johnson, J.E., Lin, T.,<br />
Colvin, V.L. Virus crystals as nanocomposite scaffolds. J. Am. Chem. Soc.<br />
127:5274, 2005.<br />
Girard, E., Kahn, R., Mezouar, M., Dhaussy, A.-C., Lin, T., Johnson J.E., Fourme, R.<br />
<strong>The</strong> first crystal structure of a complex macromolecular assembly under high pressure:<br />
CpMV at 330 MPa. Biophys. J. 88:3562, 2005.<br />
Lin, T., Schildkamp, W., Brister, K., Doerschuk, P.C., Somayazulu, M., Mao H.,<br />
Johnson, J.E. <strong>The</strong> mechanism of high-pressure-induced ordering in a macromolecular<br />
crystal. Acta Crystallogr. D Biol. Crystallogr. 61:737, 2005.<br />
Design and Informatics in<br />
Structural Virology<br />
V.S. Reddy, C.M. Shepherd, C. Hsu, S. Kumar, R. Mannige,<br />
I. Borelli, C.L. Brooks III, J.E. Johnson, M. Manchester,<br />
A. Schneemann<br />
MOLECULAR BIOLOGY 2005 219<br />
We are interested in understanding the structural<br />
underpinnings and requirements for<br />
formation of viral capsids and in designing<br />
novel protein shells that polyvalently display molecules<br />
of interest. To this end, we use structural, computational,<br />
informatics, and genetic methods.<br />
Viruses are highly evolved macromolecular machines<br />
that perform a variety of functions during their life cycle,
220 MOLECULAR BIOLOGY 2005<br />
including selective packaging of the genome, selfassembly,<br />
binding to host cells, and delivery of the<br />
genome to the targeted cells. Simple viruses, such as<br />
nonenveloped viruses, form closed protein shells or<br />
capsids of uniform size and character by the self-association<br />
of structural and functional components: proteins<br />
and the nucleic acid genome. Hence, these viruses are<br />
useful for structural and functional analyses.<br />
To understand the requirements for formation of<br />
the closed protein shell in viral capsids in terms of<br />
structure and interactions, we established a repository<br />
of structurally characterized viral capsids in a relational<br />
database format, namely the Viper Particle Explorer<br />
(http://viperdb.scripps.edu). At the database, we use<br />
computational methods to analyze these protein shells<br />
in terms of protein-protein interactions: contacting residue<br />
pairs, association energies, individual residue contributions,<br />
and surface characteristics. To facilitate these<br />
studies, we are developing structural tools for analysis<br />
of viral structures as part of the Multiscale Modeling<br />
Tools for Structural <strong>Biology</strong>, the National <strong>Institute</strong>s of<br />
Health research resource headed by C.L. Brooks, Department<br />
of <strong>Molecular</strong> <strong>Biology</strong>. <strong>The</strong> structural and taxonomic<br />
data and the derived results are stored in a MySQL<br />
database for ease of querying and comparing the properties<br />
of interest within and across families of viruses. Furthermore,<br />
using the structural similarity that occurs<br />
within a virus family, we are building homology models<br />
for the uncharacterized members of virus families. <strong>The</strong>se<br />
models will be useful for molecular virologists investigating<br />
structural and functional relationships in viruses.<br />
To generate novel reagents, such as vaccines and<br />
antitoxins against cytotoxins such as ricin and pathogens<br />
in general, we are expressing decoys of pathogenic<br />
molecules on the surfaces of viral capsids. Currently,<br />
tomato bushy stunt virus–like capsids are the display<br />
platform of choice; the platform consists of multiple<br />
copies of a 2-domain capsid protein subunit with the<br />
C-terminal P-domain exposed on the surface. Such a<br />
unique subunit structure is useful for attaching peptides<br />
or proteins of interest at the end of the C terminus of<br />
the capsid protein or for replacing the P-domain with the<br />
proteins of interest rather than inserting them in a loop.<br />
PUBLICATIONS<br />
Reddy, V.S., Johnson J.E. Structure-derived insights into virus assembly. Adv. Virus<br />
Res. 64C:45, 2005.<br />
Reddy, V.S., Schneemann, A., Johnson, J.E. Nodavirus endopeptidase. In: Handbook<br />
of Proteolytic Enzymes, 2nd ed. Barrett, A., Rawlings, N.D., Woessner, J.F.<br />
(Eds.). Academic Press, San Diego, 2004, p. 197.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Shepherd, C.M., Reddy, V.S. Extent of protein-protein interactions and quasi-equivalence<br />
in viral capsids. Proteins 58:472, 2005.<br />
<strong>Biology</strong> and Applications of<br />
Capsids of Icosahedral Viruses<br />
A. Schneemann, B. Groschel, J. Lee, D. Manayani,<br />
M. Siladi, P.A. Venter<br />
Coat proteins of nonenveloped, icosahedral viruses<br />
perform multiple functions during the course of<br />
viral infection, including capsid assembly, specific<br />
encapsidation of the viral genome, binding to a<br />
cellular receptor, and uncoating. In some viruses, a<br />
single type of protein is sufficient to carry out these<br />
functions; we are interested in the determinants that<br />
endow a polypeptide chain with such versatility. We<br />
seek to harness this versatility for novel applications<br />
of viruses in biotechnology and nanotechnology.<br />
We focus on a structurally and genetically wellcharacterized<br />
virus family, the T = 3 nodaviruses.<br />
Nodaviruses are composed of 180 copies of a single<br />
coat protein and 2 strands of positive-sense RNA. Currently,<br />
we are elucidating the mechanism by which the<br />
2 genomic RNAs are packaged into a single virion. Our<br />
long-term goal is to develop nodaviruses as RNA packaging<br />
and delivery vectors. Our data indicate that the<br />
2 viral RNAs are recognized separately, but it is not<br />
yet known whether packaging occurs sequentially and<br />
whether one or more coat protein subunits are involved<br />
in this process. Interestingly, we recently discovered<br />
that packaging of the RNA genome is directly coupled<br />
to replication of the genome, suggesting potential<br />
approaches for packaging of foreign RNAs.<br />
In other studies, we are investigating the mechanism<br />
by which nodaviral protein B2 suppresses RNA<br />
silencing in infected cells. Preliminary data indicate<br />
that protein B2 binds to double-stranded RNA and that<br />
it interferes with cleavage of double-stranded RNA<br />
substrates by the cellular protein Dicer.<br />
We are also collaborating with several investigators<br />
at <strong>Scripps</strong> <strong>Research</strong>, the Salk <strong>Institute</strong>, and Harvard<br />
University to develop nodaviruses as platforms for<br />
delivery of anthrax antitoxins. To this end, we are<br />
using particles to display the VWA domain of capillary<br />
morphogenesis protein 2, the cellular receptor for anthrax<br />
toxin, in a multivalent fashion on the surface of the<br />
virion. Two insertion sites yielding different patterns of
180 copies of the VWA domain were selected on the<br />
basis of computational modeling of the high-resolution<br />
crystal structure of the insect nodavirus Flock House<br />
virus. <strong>The</strong> resulting chimeric viruslike particles protect<br />
cultured cells from the toxic effects of protective antigen<br />
and lethal factor, 2 of the 3 proteins that make up<br />
anthrax toxin. Experiments in animals are currently under<br />
way to show that these particles also function as antitoxins<br />
in vivo. This research is important because it illustrates<br />
that protein domains containing more than 150<br />
amino acids can be displayed on Flock House virus in<br />
a biologically functional form, suggesting numerous additional<br />
applications.<br />
Flock House virus particles are also good candidates<br />
for novel materials in nanotechnology applications. <strong>The</strong><br />
particles are stable, easily manipulated, biocompatible,<br />
and nontoxic in vivo and can be produced easily and<br />
in high quantities. <strong>The</strong> high-resolution x-ray structure<br />
of the virus revealed the potential for using chemical<br />
approaches to attach ligands to the surface of the virus<br />
and for using genetic strategies to modify the capsid. In<br />
collaboration with M. Manchester, Department of Cell<br />
biology, and M. Ozkan, University of California, Riverside,<br />
California, we used conjugation chemistry to couple<br />
inorganic nanotubes and quantum dots to Flock<br />
House virus particles to produce an array of novel hybrid<br />
structures. This approach may one day be used to fabricate<br />
unique materials for a variety of applications,<br />
including biofilms with tunable pore sizes, 3-dimensional<br />
scaffolds for production of nanoelectronic devices, and<br />
drug delivery.<br />
PUBLICATIONS<br />
Portney, N.G., Singh, K., Chaudhary, S., Destito, G., Schneemann, A., Manchester, M.,<br />
Ozka, M. Organic and inorganic nanoparticle hybrids. Langmuir 21:2098, 2005.<br />
Schwarcz, W.D., Barroso, S.P., Gomes, S.M., Johnson, J.E., Schneemann, A.,<br />
Oliveira, A.C., Silva, J.L. Virus stability and protein-nucleic acid interaction as<br />
studied by high-pressure effects on nodaviruses. Cell. Mol. Biol. (Noisy-le-grand).<br />
50:419, 2004.<br />
Venter, P.A., Krishna, N.K., Schneemann, A. Capsid protein synthesis from replicating<br />
RNA directs specific packaging of the genome of a multipartite, positivestrand<br />
RNA virus. J. Virol. 79:6239, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
<strong>Molecular</strong> <strong>Biology</strong> of<br />
Retroviruses<br />
J.H. Elder, A.P. de Parseval, Y.-C. Lin, S. de Rozieres,<br />
U. Chatterji,* K. Tam, B.E. Torbett**<br />
* Department of Immunology, <strong>Scripps</strong> <strong>Research</strong><br />
** Department of <strong>Molecular</strong> and Experimental Medicine, <strong>Scripps</strong> <strong>Research</strong><br />
Our research centers on the molecular characterization<br />
of retroviruses, with emphasis on feline<br />
immunodeficiency virus (FIV). FIV causes an<br />
AIDS-like syndrome in domestic cats, and although it<br />
does not infect humans, the feline retrovirus has many<br />
structural and functional similarities to HIV, the causative<br />
agent of AIDS in humans. Thus, study of FIV can<br />
yield insights into ways to interfere with the retrovirus<br />
life cycle that may ultimately result in the development<br />
of treatments for infections in both cats and humans.<br />
During the past year, we focused on 2 major areas:<br />
the molecular characterization of cell-surface receptors<br />
for FIV and the molecular basis for the development of<br />
drug resistance in the aspartic protease encoded by FIV.<br />
RECEPTOR STUDIES<br />
MOLECULAR BIOLOGY 2005 221<br />
Like many strains of HIV, FIV uses the chemokine<br />
receptor CXCR4 to enter the primary target cell, the<br />
CD4 + T cell. However, unlike HIV, FIV does not use<br />
the cell-surface protein CD4 as a primary binding<br />
receptor. Rather, the feline lentivirus initially binds to<br />
another cell-surface molecule, CD134. In the past year,<br />
we characterized the expression of CD134 and showed<br />
that it is upregulated on CD4 + T cells. This observation<br />
explains why FIV can infect and kill this subset of<br />
T cells even though the virus’s surface glycoprotein does<br />
not interact with CD4.<br />
In an extension of these studies, we found that interaction<br />
of the FIV surface glycoprotein gp95 with a soluble<br />
version of CD134 allows the productive infection<br />
of cells that bear the entry receptor, CXCR4, but lack<br />
surface expression of the binding receptor, CD134. <strong>The</strong><br />
results are consistent with the notion that binding of<br />
CD134 causes a conformational change in gp95, which<br />
in turn increases the affinity of interaction with CXCR4<br />
and facilitates infection of the target cell. <strong>The</strong>se effects<br />
are similar to the effects of binding of soluble CD4 by<br />
gp120, the cell-surface glycoprotein of HIV, and indicate<br />
that although different molecules are involved, the<br />
actual mechanisms of infection of FIV and HIV are<br />
strikingly similar. We speculate that the benefit of this<br />
type of binding cascade is to limit exposure of critical
222 MOLECULAR BIOLOGY 2005<br />
regions of the surface glycoproteins to the immune system<br />
until the primary binding event has already occurred,<br />
thus reducing the likelihood of virus neutralization.<br />
We also precisely mapped regions of CD134 involved<br />
in interaction with gp95. CD134 is a member of the<br />
TNF-α receptor superfamily and has a domain structure<br />
similar to that of the TNF-α receptor. Human CD134<br />
does not bind FIV gp95, even though human CD134<br />
shares considerable amino acid homology with feline<br />
CD134. Using chimeric proteins consisting of feline<br />
and human CD134 and site-directed mutagenesis, we<br />
showed that as few as 3 amino acids in the C-terminal<br />
part of outer domain 1 of feline CD134 are sufficient<br />
to impart FIV gp95 binding and receptor function to<br />
human CD134. Structural studies of both receptor and<br />
ligand will establish a molecular basis for the putative<br />
conformational change induced by interaction with the<br />
binding receptor.<br />
DEVELOPMENT OF DRUG RESISTANCE BY FIV<br />
ASPARTIC PROTEASE<br />
<strong>The</strong> aspartic protease of lentiviruses is a particularly<br />
good target for drug therapy because its function in processing<br />
the viral Gag and Pol polyproteins is absolutely<br />
required for generation of infectious virus. Drugs active<br />
against the HIV protease have been keys to the success<br />
of highly active antiretroviral therapy used to treat<br />
patients infected with HIV. <strong>The</strong> substrate and inhibitor<br />
specificity of FIV differs from that of HIV, and we previously<br />
reported the identification of amino acids that<br />
define the different specificities. Comparing FIV with<br />
HIV offers a means to better understand the development<br />
of resistance to therapy, an ongoing problem with<br />
current drugs used to treat HIV disease.<br />
Interestingly, parallels exist between amino acid<br />
positions that dictate differences in substrate specificity<br />
between FIV and HIV aspartic protease and those<br />
that mutate in response to drug treatment. Mutations<br />
in these sites increase the dissociation constant for<br />
complexes consisting of the protease and an inhibitor<br />
drug, but at a cost in catalytic efficiency for the protease.<br />
Over time, compensatory amino acid substitutions<br />
occur that result in an increase in catalytic efficiency,<br />
which results in increased expression of virus despite<br />
drug treatment.<br />
We prepared mutants of FIV protease in which amino<br />
acids found in drug-resistant HIV protease were placed<br />
in the equivalent positions in the FIV enzyme. <strong>The</strong>se<br />
“HIV-inized” FIV proteases had drug sensitivity profiles<br />
similar to those of HIV protease. In studies with cells<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
transduced with gag/pol gene expression vectors encoding<br />
HIV-FIV hybrid proteases, the Gag/Pol polyproteins<br />
were processed with proper fidelity and had the expected<br />
drug sensitivities. When engineered into FIV, these<br />
hybrid proteases will offer a means to study drug resistance<br />
and to develop new inhibitors capable of blocking<br />
replication of drug-resistant viruses, without the<br />
biohazard associated with handling infectious HIV.<br />
PUBLICATIONS<br />
de Parseval, A., Chatterji, U., Morris, G., Sun, P., Olson, A.J., Elder, J.H. Structural<br />
mapping of CD134 residues critical for interaction with feline immunodeficiency<br />
virus. Nat. Struct. Mol. Biol. 12:60, 2005.<br />
de Parseval, A., Chatterji, U., Sun, P., Elder, J.H. Feline immunodeficiency virus<br />
targets activated CD4 + T cells by using CD134 as a binding receptor. Proc. Natl.<br />
Acad. Sci. U. S. A. 101:13044, 2004.<br />
de Rozieres, S., Swan, C.H., Sheeter, D.A., Clingerman, K.J., Lin, Y.-C., Huitrón-<br />
Reséndiz, S. Henriksen, S., Torbett, B.E., Elder, J.H. Assessment of FIV-C infection<br />
of cats as a function of treatment with the protease inhibitor, TL-3.<br />
Retrovirology 1:38, 2004.<br />
Montes-Rodriguez, C.J., Alavez, S., Elder, J.H., Haro, R., Moran, J., Prospero-<br />
Garcia, O. Prolonged waking reduces human immunodeficiency virus glycoprotein<br />
120- or tumor necrosis factor α-induced apoptosis in the cerebral cortex of rats.<br />
Neurosci. Lett. 360:133, 2004.<br />
Metalloenzyme Engineering<br />
D.B. Goodin, C.D. Stout, A.-M.A. Hays, S. Vetter,<br />
E.C. Glazer, A.E. Pond, H.B. Gray,* J.R. Winkler,*<br />
J.H. Dawson,** T.L. Poulos,*** M.A. Marletta****<br />
* California <strong>Institute</strong> of Technology, Pasadena, California<br />
** University of South Carolina, Columbia, South Carolina<br />
*** University of California, Irvine, California<br />
**** University of California, Berkeley, California<br />
Our overall goals are to understand the fundamental<br />
structural features of metalloenzyme catalysts<br />
and to create catalysts for useful chemical reactions.<br />
We use a number of techniques in structural biology<br />
and spectroscopy and strategies of rational protein<br />
redesign and molecular evolution. In the past year, we<br />
made progress in several areas.<br />
One area of recent interest has been the design<br />
and use of molecular wires as probes for the active<br />
sites of enzymes such as cytochrome P450 and nitric<br />
oxide synthase (NOS). In an ongoing collaboration with<br />
H.B. Gray, California <strong>Institute</strong> of Technology, we are<br />
investigating the binding of these wires, which are<br />
specifically designed substrate analogs linked to photochemical<br />
or redox-active sensitizers, to the active<br />
site of metalloproteins. <strong>The</strong> wires are being developed<br />
to serve as reporters of the active-site environment and
as tools to allow rapid deposition or withdrawal of electrons<br />
to drive redox catalysis. In addition, luminescent<br />
wires that are quenched upon either binding or release<br />
from the protein may be useful as imaging agents or as<br />
tools for identifying novel enzyme inhibitors.<br />
P450s make up a large family of enzymes responsible<br />
for a vast range of biologically important oxidation<br />
reactions in mammals, plants, fungi, and bacteria. An<br />
important unresolved question concerns how the deeply<br />
buried heme cofactor of these enzymes achieves regioselective<br />
and stereoselective catalysis of a wide range<br />
of substrates. In the past year, we completed a detailed<br />
structural analysis by x-ray crystallography of cytochrome<br />
P450 cam complexed with 2 sensitizer-linked<br />
substrate probes, D4A and D8A. <strong>The</strong>se probes differ<br />
in length but bind identically at the substrate end of<br />
the wire (Fig. 1).<br />
Fig. 1. Crystal structure at 1.6 Å of P450cam containing D8A, a<br />
synthetic molecular wire. <strong>The</strong> adamantyl substrate analog is observed<br />
at the camphor binding site for wires of different lengths. Changes<br />
in the F and G helices in response to wire length illustrate the conformational<br />
flexibility in these regions that may be responsible for<br />
the diversity of substrate recognition by P450s.<br />
Significant changes in the protein structure near the<br />
F and G helices accommodate the changes in linker<br />
length. <strong>The</strong>se changes are similar to those that may be<br />
responsible for substrate-binding specificity of mammalian<br />
P450s and indicate that prokaryotic enzymes<br />
have similar conformational flexibility. <strong>The</strong>se changes<br />
also suggest the nature of the dynamic intermediates<br />
that must exist transiently in solution during substrate<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 223<br />
entry and product egress. <strong>The</strong> conformational change<br />
associated with movement of the F and G helices is<br />
transmitted to a backbone carbonyl at the active site<br />
of the enzyme, which has been implicated in gating<br />
the critical peroxy-bond cleavage that activates the<br />
enzyme for catalysis.<br />
In other studies, we are designing and synthesizing<br />
specific pterin-based molecular wires for the active<br />
site of NOS. NOSs are complex enzymes used for the<br />
production of nitric oxide from arginine and play many<br />
critical roles in biological signal transduction. As thiolate<br />
coordinate heme enzymes, they have structural<br />
and functional similarities to P450s. One unique feature<br />
is the role played by the pterin cofactor of NOS.<br />
Recent results suggest that the pterin donates an electron<br />
to either the heme or the substrate at defined steps<br />
in the catalytic mechanism. In the past year, we designed<br />
and synthesized a series of pterin analogs tethered to<br />
sensitizers containing redox-active ruthenium to be used<br />
as specific molecular triggers and probes of the NOS<br />
active site. In addition, we measured the FeIII/II and<br />
FeII/I couples by direct cyclic voltammetry of inducible<br />
NOS in organic films on graphite electrodes.<br />
<strong>The</strong>se studies allow easy and rapid measurements<br />
of electron transfer between the enzyme and the electrode<br />
surface and enabled us to detect the interconversion<br />
of several coordination states of the enzyme.<br />
<strong>The</strong>se studies, coupled with the use of molecular wires<br />
as mediators of electron transfer at electrode surfaces,<br />
will provide a new way to prove the function of NOS<br />
and related enzymes.<br />
PUBLICATIONS<br />
Hays, A.-M., Dunn, A.R., Chiu, R., Gray, H.B., Stout, C.D. Goodin, D.B. Conformational<br />
states of cytochrome P450 cam revealed by trapping of synthetic molecular<br />
wires. J. Mol. Biol. 344:455, 2004.<br />
Udit, A.K., Belliston-Bittner, W., Glazer, E.C., Nguyen, Y.H.L., Gillon M., Hill,<br />
M.G., Marletta, M.A., Goodin, D.B. Gray, H.B. Redox couples of inducible nitric<br />
oxide synthase. J. Am. Chem. Soc. 127:11212, 2005.<br />
Control of Cell Division<br />
S.I. Reed, C. Baskerville, L.-C. Chuang, B. Grünenfelder,<br />
M. Henze, J. Keck, V. Liberal, K. Luo, B. Olson,<br />
S. Ekholm-Reed, S. Rudyak, O. Sangfelt, A. Smith,<br />
C. Spruck, D. Tedesco, F. van Drogen, J. Wohlschlegel, V. Yu<br />
Biological processes of great complexity can be<br />
approached by beginning with a systematic<br />
genetic analysis in which the relevant components<br />
are first identified and the consequences of
224 MOLECULAR BIOLOGY 2005<br />
selectively eliminating the components via mutations<br />
are investigated. We use yeast, which is uniquely<br />
tractable to this type of analysis, to investigate control<br />
of cell division. In recent years, it has become apparent<br />
that the most central cellular processes throughout<br />
the eukaryotic phylogeny are highly conserved in terms<br />
of both the regulatory mechanisms used and the proteins<br />
involved. Thus, it has been possible in many instances to<br />
generalize from yeast cells to human cells.<br />
CONTROL IN YEAST<br />
In recent years, we have focused on the role and<br />
regulation of the Cdc28 protein kinase (Cdk1). Initially<br />
identified by means of a mutational analysis of the yeast<br />
cell cycle, this protein kinase and its analogs are ubiquitous<br />
in eukaryotic cells and are central to a number<br />
of aspects of control of cell-cycle progression.<br />
One current area of interest is regulation of cellular<br />
morphogenesis by Cdk1. <strong>The</strong> activity of Cdk1 driven<br />
by mitotic cyclins modulates polarized growth in yeast<br />
cells. Specifically, these activities depolarize growth by<br />
altering the actin cytoskeleton. We found that several<br />
proteins that modulate actin structure are targeted by<br />
Cdk1, and we are investigating whether these phosphorylation<br />
events control actin depolarization.<br />
A second major area of interest is the regulation of<br />
mitosis. A key aspect of mitotic regulation in yeast is<br />
the accumulation of Cdc20, which triggers the transition<br />
from metaphase to anaphase. Cdc20 is an essential<br />
cofactor of the protein-ubiquitin ligase known as<br />
the anaphase-promoting complex or APC/C. It is through<br />
the ubiquitin-mediated proteolysis of a specific anaphase<br />
inhibitor, securin (Pds1 in yeast), that anaphase<br />
is initiated. We found that cells are prevented from entering<br />
mitosis when DNA replication is blocked by the<br />
drug hydroxyurea, which causes the destabilization of<br />
Cdc20 and inhibition of Cdc20 translation.<br />
While investigating mitosis, we found that Cks1, a<br />
small Cdk1-associated protein, appears to regulate the<br />
proteasome. Proteasomes are complex proteases that<br />
target ubiquitylated proteins, including important cellcycle<br />
regulatory proteins. Surprisingly, we found that<br />
Cks1 regulates a nonproteolytic function of proteasomes,<br />
the transcriptional activation of Cdc20. Specifically,<br />
Cks1 is required to recruit proteasomes to the gene<br />
CDC20 for efficient transcriptional elongation. Our investigations<br />
of CDC20 led to the conclusion that Cks1 is<br />
required for recruitment of proteasomes to and transcriptional<br />
elongation of many other genes, as well.<br />
Currently, we are elucidating the mechanism whereby<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Cks1 recruits proteasomes and facilitates transcriptional<br />
elongation. Our most recent results suggest that Cks1<br />
and proteasomes in conjunction with Cdk1 mediate<br />
remodeling of chromatin.<br />
CONTROL IN MAMMALIAN CELLS<br />
We showed previously that the human homologs<br />
of the Cdc28 protein kinase are so highly conserved,<br />
structurally and functionally, relative to the yeast protein<br />
kinase, that they can function and be regulated<br />
properly in a yeast cell. Analyzing control of the cell<br />
cycle in mammalian cells, we produced evidence for<br />
the existence of regulatory schemes, similar to those<br />
elucidated in yeast, that use networks of both positive<br />
and negative regulators.<br />
A principal research focus is the positive regulator<br />
of Cdk2, cyclin E. Cyclin E is often overexpressed and/or<br />
deregulated in human cancers. Using a tissue culture<br />
model, we showed that deregulation of cyclin E confers<br />
genomic instability, probably explaining the link to<br />
carcinogenesis. <strong>The</strong> observation that deregulation of<br />
cyclin E confers genomic instability led us to hypothesize<br />
a mechanism of cyclin E–mediated carcinogenesis<br />
based on accelerated loss of heterozygosity at tumor<br />
suppressor loci. We are testing this hypothesis in transgenic<br />
mouse models. We showed previously that a<br />
cyclin E transgene expressed in mammary epithelium<br />
markedly increases loss of heterozygosity at the p53<br />
locus, leading to enhanced mammary carcinogenesis.<br />
We are extending these investigations by using mouse<br />
prostate, testis, and skin models.<br />
In an attempt to understand cyclin E–mediated<br />
genomic instability, we are investigating how deregulation<br />
of cyclin E affects both S phase and mitosis. Recent<br />
data suggest that deregulation of cyclin E impairs DNA<br />
replication by interfering with assembly of the prereplication<br />
complex. Cyclin E deregulation also impairs the<br />
transition from metaphase to anaphase by promoting<br />
the accumulation of mitotic checkpoint proteins.<br />
Our interest in cyclin E deregulation in cancer led<br />
us to examine the pathway for turnover of cyclin E.<br />
We showed that phosphorylation-dependent proteolysis<br />
of cyclin E depends on a protein-ubiquitin ligase<br />
known as SCF hCdc4 . <strong>The</strong> F-box protein hCdc4 is the<br />
specificity factor that targets phosphorylated cyclin E.<br />
We are investigating how ubiquitylation of cyclin E is<br />
coordinated with other processes required for its degradation.<br />
We are also investigating SCF hCdc4 ubiquitylation<br />
of other important cellular proteins.<br />
Because of the functional relationship between<br />
hCdc4 and cyclin E, we are studying the role of muta-
tions of hCDC4, the gene that encodes hCdc4, in carcinogenesis.<br />
We found that hCDC4 is mutated and most<br />
likely is a tumor suppressor in endometrial cancer and<br />
breast cancer. In endometrial cancer, tumors with mutations<br />
in hCDC4 are more aggressive than tumors without<br />
mutations in this gene. Because we showed that<br />
loss of hCdc4 leads to deregulation of cyclin E through<br />
the cell cycle, these results confirm the observation that<br />
in some cancers deregulation of cyclin E is associated<br />
with aggressive disease and poor outcome.<br />
Another area of interest is the role of Cks proteins<br />
in mammals, complementing our research in yeast.<br />
Mammals express 2 orthologs of yeast Cks1, known as<br />
Cks1 and Cks2. Experiments in mice lacking the gene<br />
for Cks1 and Cks2 revealed that each ortholog has a<br />
specialized function. Cks1 is required as a cofactor for<br />
Skp2-mediated ubiquitylation and turnover of inhibitors<br />
p21, p27, and p130. Cks2 is required for the<br />
transition from metaphase to anaphase in both male<br />
and female meiosis I. Nevertheless, mice nullizygous<br />
at the individual loci are viable. However, doubly nullizygous<br />
mice have not been observed because embryos<br />
die at the morula stage, a finding consistent with an<br />
essential redundant function. We found that this function<br />
most likely is involved in transcriptional elongation<br />
and is linked to chromatin remodeling, as in yeast.<br />
PUBLICATIONS<br />
Huisman, S.M., Bales, O.A.M., Bertrand, M., Smeets, M.F.M.A., Reed, S.I.,<br />
Segal, M. Differential contribution of Bud6p and Kar9p in microtubule capture and<br />
spindle orientation in S. cerevisiae. J. Cell Biol. 167:231, 2004.<br />
Reed, S.I. Cell cycle. In: Cancer: Principles and Practice of Oncology, 7th ed. DeVita<br />
V.T., Jr., Hellman, S., Rosenberg, S.A. (Eds.). Lippincott Williams & Wilkins, Philadelphia,<br />
2004, p. 83.<br />
Reed, S.I., Rothman, J.H. Cell division, growth and death [editorial]. Curr. Opin.<br />
Cell Biol. 16:599, 2004.<br />
Spruck C.H., Smith, A.P.L., Ekholm-Reed, S., Sangfelt, O., Keck, J., Strohmaier, H.,<br />
Méndez, J., Widschwendter, M., Stillman, B., Zetterberg A., Reed, S.I. Deregulation<br />
of cyclin E and genomic Instability. In: Hormonal Carcinogenesis IV. Li, J.J., Li,<br />
S.A., Llombart-Bosch, A. (Eds.). Springer, New York, 2004, p. 98.<br />
Wittenberg, C., Reed, S.I. Cell cycle-dependent transcription in yeast: promoters,<br />
transcription factors, and transcriptomes. Oncogene 24:2746, 2005.<br />
Wohlschlegel, J.A., Johnson, E.S., Reed, S.I., Yates, J.R. III. Global analysis of protein<br />
sumoylation in Saccharomyces cerevisiae. J. Biol. Chem. 279:45662, 2004.<br />
Yu, V.P.C.C., Baskerville, C., Grünenfelder, B., Reed, S.I. A kinase-independent<br />
function of Cks1 and Cdk1 in regulation of transcription. Mol. Cell 17:145, 2005.<br />
Yu, V.P.C.C., Reed, S.I. Cks1 is dispensable for survival in Saccharomyces cerevisiae.<br />
Cell Cycle 3:1402, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Regulating Cell Proliferation:<br />
Flipping Transcriptional and<br />
Proteolytic Switches<br />
C. Wittenberg, M. Ashe, R. de Bruin, M. Guaderrama,<br />
B.-K. Han, T. Kalashnikova, N. Spielewoy<br />
MOLECULAR BIOLOGY 2005 225<br />
Cell proliferation is governed primarily by controlling<br />
the activities of positive and negative<br />
regulators of cell-cycle transitions. Inhibitors<br />
of cyclin-dependent protein kinase (CDK) and the positive<br />
regulatory subunits, cyclins, are critical in establishing<br />
the proper timing of cell-cycle transitions and in<br />
imposing cell-cycle checkpoints. <strong>The</strong> activities of those<br />
proteins are largely regulated via periodic transcriptional<br />
activation coupled with regulated proteolysis. We<br />
focus primarily on those regulatory mechanisms.<br />
As in animal cells, initiation of the cell cycle in the<br />
budding yeast Saccharomyces cerevisiae occurs during<br />
late G 1 phase and is governed by the controlled accumulation<br />
of G 1 CDK activity. A large family of G 1 -specific<br />
genes, including those for the G 1 cyclins Cln1 and<br />
Cln2, are coordinately regulated by 2 transcription factors:<br />
SBF and MBF. As in metazoans, the transcriptional activation<br />
of those genes depends on the activity of a distinct<br />
G 1 cyclin, Cln3, that acts on promoter-bound<br />
transcription factors to promote recruitment of components<br />
of the RNA polymerase II complex.<br />
By analogy with metazoan Rb, an inhibitor of the<br />
E2F transcription factor that is antagonized by cyclin<br />
D/CDK, we predicted the existence of a G 1 -specfic<br />
transcriptional repressor that is inactivated by Cln3/CDK.<br />
Using the combined application of molecular genetics<br />
and mass spectrometry–based multidimensional protein<br />
identification technology, we identified an SBF-specific<br />
transcriptional repressor, Whi5, that is inactivated via<br />
phosphorylation by Cln3/CDK. This discovery provides<br />
a unifying mechanism for initiation of the cell cycle in<br />
yeast and metazoans.<br />
We also identified several other transcriptional regulators,<br />
including Nrm1, a novel cell cycle–dependent<br />
repressor of MBF-dependent transcription. Rather than<br />
repressing expression early in the cell cycle as Whi5<br />
does, Nrm1 acts as cells pass into S phase, thereby limiting<br />
MBF-dependent gene expression to the G 1 phase.<br />
Because expression of the gene for NRM1 depends on<br />
MBF, the gene cannot act until MBF becomes active.<br />
Consequently, the gene confers negative autoregulation
226 MOLECULAR BIOLOGY 2005<br />
on MBF. Additional factors associated with the 2 transcription<br />
factors are under investigation.<br />
One of the primary roles of G 1 cyclin-associated<br />
CDKs is to promote the ubiquitin-dependent proteolysis<br />
of cell-cycle regulators, including the G 1 cyclins<br />
themselves. CDK-dependent phosphorylation of a number<br />
of proteins targets the proteins for recognition by the<br />
Cdc34-SCF ubiquitin ligase complex. Grr1, one of several<br />
distinct F box proteins that associate with that complex,<br />
confers recognition of specific phosphorylated<br />
targets. We are interested in the molecular basis of<br />
that recognition. Previously, we showed that the interaction<br />
between Grr1 and Cln2 requires basic residues<br />
residing in the pocket of the leucine-rich repeat of Grr1<br />
and defined a transferable “degron” in the C terminus<br />
of Cln2 that is phosphorylated by the CDK. <strong>The</strong>se findings,<br />
combined with our understanding of the mechanisms<br />
that govern G 1 -specific transcription, indicate that<br />
an integrated autoregulatory circuit governs the events<br />
of G 1 phase and ensures the orderly progression of<br />
events in the cell cycle.<br />
In addition to its role in cell-cycle control, SCF Grr1<br />
plays a central role in regulating the expression of genes<br />
induced by glucose and amino acids. We showed that<br />
the glucose signal promotes ubiquitin-mediated proteolysis<br />
of Mth1, which is required for maintenance of<br />
transcriptional repression of glucose-inducible genes.<br />
Glucose triggers phosphorylation of Mth1 by casein<br />
kinase I, thereby promoting recognition by SCF Grr1 .<br />
Surprisingly, recognition of phosphorylated Mth1 requires<br />
properties of Grr1 distinct from those required for recognition<br />
of phosphorylated G 1 cyclins. <strong>The</strong> same properties<br />
are also important for Grr1-dependent recognition<br />
of an as yet unknown target required for the activation<br />
of amino acid–regulated genes via SPS signaling. Efforts<br />
are under way to identify novel targets of Grr1 and to<br />
investigate the possibility that Grr1 mediates the coordination<br />
of cell-cycle progression with the availability<br />
of environmental nutrients.<br />
PUBLICATIONS<br />
Flick, K., Wittenberg, C. Multiple pathways for suppression of mutants affecting<br />
G 1 -specific transcription in Saccharomyces cerevisiae. Genetics 169:37, 2005.<br />
Wittenberg, C. Cell cycle: cyclin guides the way. Nature 434:34, 2005.<br />
Wittenberg, C., Reed, S.I. Cell cycle-dependent transcription in yeast: promoters,<br />
transcription factors, and transcriptomes. Oncogene 24:2746, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Cell-Cycle Checkpoints,<br />
DNA Repair, and Oxidative<br />
Stress Response<br />
P. Russell, C. Chahwan, S. Coulon, L.-L. Du, P.-H. Gaillard,<br />
V. Martin, T. Nakamura, C. Noguchi, E. Noguchi,<br />
M. Rodriguez, P. Shanahan, K. Tanaka, H. Zhao<br />
<strong>The</strong> cellular responses to DNA damage and cytotoxic<br />
stress are highly conserved through evolution.<br />
A fortunate consequence of this conservation is<br />
that “simple” eukaryotes such as the fission yeast<br />
Schizosaccharomyces pombe can be used as model<br />
systems for more complex multicellular organisms. We<br />
use S pombe to study cell-cycle checkpoints, DNA<br />
repair, and stress response mechanisms. Defects in<br />
these mechanisms underlie a number of human diseases,<br />
including cancer.<br />
DNA REPLICATION CHECKPOINT<br />
<strong>The</strong> challenging task of replicating a eukaryotic<br />
genome is often made more difficult by conditions that<br />
interfere with progression of the replisome, the complex<br />
formed by the close association of the key proteins used<br />
during DNA replication. Protein complexes bound to<br />
DNA, chemical adducts in DNA, and deoxyribonucleotide<br />
starvation are among the situations that can impede<br />
replisomes. <strong>The</strong> DNA replication checkpoint senses<br />
stalled replication forks and directs cellular responses<br />
that help preserve the integrity of the genome. One<br />
of these responses is the S-M checkpoint. This checkpoint<br />
delays the onset of mitosis (M phase) while DNA<br />
synthesis (S phase) is under way, thereby providing time<br />
to recover from stalled forks. <strong>The</strong> same checkpoint also<br />
controls how damaged DNA is replicated.<br />
DNA-dependent protein kinases, such as ATM and<br />
ATR in humans and Rad3 in fission yeast, are central<br />
components of the replication checkpoint. Acting in<br />
conjunction with regulatory subunits (e.g., Rad26 in<br />
fission yeast) and other protein complexes, these kinases<br />
activate checkpoint effector kinases. <strong>The</strong> effector of<br />
the replication checkpoint in fission yeast is Cds1<br />
(Chk2). A few years ago, we discovered mediator of<br />
replication checkpoint-1 (Mrc1), an adaptor or mediator<br />
protein that directs the replication checkpoint signal<br />
from Rad3 to Cds1. We recently discovered that<br />
the forkhead-associated domain of Cds1 mediates the<br />
binding of Cds1 to Mrc1. This interaction allows Rad3<br />
to activate Cds1.
Cds1 controls repair systems that are required to<br />
tolerate stalled replication forks. We hope to better<br />
understand these systems by identifying proteins that<br />
associate with the forkhead-associated domain of Cds1.<br />
Mus81, a novel protein related to the XPF nucleotide<br />
excision repair protein, was identified in a screen for<br />
such proteins. We found that Mus81 associates with<br />
another protein, Eme1, to form a structure-specific<br />
endonuclease that resolves X-shaped Holliday junctions.<br />
In recent studies with T. Wang, Stanford University,<br />
Stanford, California, and M.N. Boddy, Department of<br />
<strong>Molecular</strong> <strong>Biology</strong>, we discovered that phosphorylation<br />
of Mus81 by Cds1 helps preserve genome integrity<br />
when replication forks arrest. We hypothesize that the<br />
phosphorylation prevents the Mus81-Eme1 complex<br />
from cleaving stalled replication forks.<br />
Stalled forks are potentially unstable structures<br />
prone to rearrangement and collapse. We previously<br />
reported that the protein Swi1 helps preserve stalled<br />
forks and is necessary for strong activation of Cds1.<br />
Recent studies with J.R. Yates, Department of Cell<br />
<strong>Biology</strong>, indicated that Swi1 associates with Swi3 to<br />
form a fork-protection complex. We found that the<br />
complex travels with the replisome during DNA replication.<br />
It is therefore ideally placed to detect, stabilize,<br />
and signal stalled replication forks (Fig. 1). We<br />
speculate that Swi1 and Swi3 homologs in humans<br />
have equivalent functions.<br />
Fig. 1. Stabilization of stalled replication forks. <strong>The</strong> fork-protection<br />
complex (FPC), which consists of Swi1 and Swi3, travels with<br />
the replisome. Mrc1 also appears to travel with the fork. When the<br />
replisome stalls at obstructions in the fork or for other reasons, the<br />
fork-protection complex and Mrc1 are required for activation of Cds1<br />
by Rad3-Rad26 kinase. <strong>The</strong> Rad9-Rad1-Hus1 (9-1-1) complex is<br />
also required for Cds1 activation.<br />
DNA DAMAGE CHECKPOINT<br />
<strong>The</strong> DNA damage checkpoint prevents the onset of<br />
mitosis when DNA is damaged (Fig. 2). This checkpoint<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
is enforced by the protein kinase Chk1, which is activated<br />
by Rad3. Activation of Chk1 requires the adaptor protein<br />
Crb2. Crb2 is rapidly recruited to double-stranded<br />
breaks in DNA. We recently found that Rad3 and Tel1<br />
(the ATM homolog in fission yeast) stimulate Crb2<br />
recruitment by phosphorylating histone H2A at the<br />
DNA break site. We also found that the tandem C-terminal<br />
BRCT domains in Crb2 are essential for Crb2<br />
homo-oligomerization.<br />
Recently, we investigated how Tel1/ATM is recruited<br />
for sites of DNA damage and how it is activated. <strong>The</strong>se<br />
studies, done in collaboration with T. Hunter, the Salk<br />
<strong>Institute</strong>, La Jolla, California, revealed that Tel1/ATM<br />
interacts with the extreme C terminus of Nbs1. Nbs1<br />
is a subunit of the Mre11-Rad50-Nbs1 complex that<br />
associates with and processes double-stranded breaks.<br />
We found that the interaction with Nbs1 is essential<br />
for ATM activation.<br />
OXIDATIVE STRESS RESPONSE<br />
MOLECULAR BIOLOGY 2005 227<br />
Fig. 2. <strong>The</strong> unicellular yeast S pombe divides by medial fission<br />
(top left panel). It has 3 chromosomes and approximately 4000<br />
genes. <strong>The</strong> DNA damage checkpoint arrests division in cells<br />
exposed to ionizing radiation (+IR) (top right panel). Pulse-field gel<br />
electrophoresis shows that the chromosomes are fragmented by<br />
120 Gy of ionizing radiation (bottom panel). About 3 hours are<br />
required to repair the DNA, necessitating a checkpoint that prevents<br />
mitosis while DNA repair is under way.<br />
Oxidative stress caused by reactive oxygen species<br />
can be highly toxic, causing damage to proteins, lipids,
228 MOLECULAR BIOLOGY 2005<br />
and nucleic acids. Oxidative stress elicits a complex<br />
gene expression response that is orchestrated in large<br />
part by MAP kinase cascades. <strong>The</strong> fission yeast Spc1<br />
MAP kinase pathway is homologous to the p38 pathway<br />
in humans. We recently discovered Csx1, a protein<br />
that collaborates with Spc1 to control gene expression<br />
in response to oxidative stress. Csx1 is an RNA-binding<br />
protein that mediates global control of gene expression<br />
in response to oxidative stress by binding and stabilizing<br />
mRNA that encodes Atf1, a transcription factor that<br />
is also regulated by Spc1. Most recently, we focused<br />
on a newly discovered family of proteins that interact<br />
with Csx1.<br />
PUBLICATIONS<br />
Du, L.L., Moser, B.A., Russell, P. Homo-oligomerization is the essential function of<br />
the tandem BRCT domains in the checkpoint protein Crb2. J. Biol. Chem.<br />
279:38409, 2004.<br />
Kai, M., Boddy, M.N., Russell, P., Wang, T.S.F. Replication checkpoint kinase<br />
Cds1 regulates Mus81 to preserve genome integrity during replication stress.<br />
Genes Dev. 19:919, 2005.<br />
McGowan, C.H., Russell, P. <strong>The</strong> DNA damage response: sensing and signaling.<br />
Curr. Opin. Cell Biol. 16:629, 2004.<br />
Nakamura, T.M., Moser, B.A., Du, L.L., Russell, P. Cooperative control of Crb2 by<br />
ATM-family and Cdc2 kinases is essential for the DNA damage checkpoint in fission<br />
yeast. Mol. Cell. Biol., in press.<br />
Noguchi, E., Noguchi, C., McDonald, W.H., Yates, J.R. III, Russell, P. Swi1 and<br />
Swi3 are components of a replication fork protection complex in fission yeast. Mol.<br />
Cell. Biol. 24:8342, 2004.<br />
Tanaka, K., Russell, P. Cds1 phosphorylation by Rad3-Rad26 kinase is mediated by<br />
forkhead-associated domain interaction with Mrc1. J. Biol. Chem. 279:32079, 2004.<br />
You, Z., Chahwan, C., Bailis, J., Hunter, T. Russell, P. ATM activation and its recruitment<br />
to damaged DNA require binding to the C terminus of Nbs1. Mol. Cell. Biol.<br />
25:5363, 2005.<br />
Zhao, H., Russell, P. DNA binding domain in the replication checkpoint protein<br />
Mrc1 of Schizosaccharomyces pombe. J. Biol. Chem. 279:53023, 2004.<br />
DNA Damage Responses in<br />
Human Cells<br />
C.H. McGowan, V. Blais, H. Gao, E. Langley, A. MacLaren,<br />
J. Scorah, E. Taylor<br />
Complex multicellular organisms, such as humans,<br />
have large numbers of mitotically competent cells<br />
that are capable of renewal, repair, and, to some<br />
extent, regeneration. <strong>The</strong> advantages of being able to<br />
replace damaged or aged cells are off set by the inherent<br />
susceptibility of mitotic cells to acquiring mutations and<br />
becoming cancerous. DNA is inherently vulnerable to<br />
many sorts of chemical and physical modification; thus,<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
as they duplicate and divide, cells can acquire mutations.<br />
Both spontaneous and induced DNA damage must<br />
be repaired with minimal changes if growth, renewal,<br />
and repair are to be successful. Our overall objective is<br />
to understand how mammalian cells protect themselves<br />
from DNA damage and thus from cancer.<br />
Eukaryotic cells have evolved with a complex network<br />
of DNA repair processes and cell-cycle checkpoint<br />
responses that ensure that damaged DNA is repaired<br />
before it is replicated and becomes fixed in the genome.<br />
<strong>The</strong>se pathways are highly conserved through evolution,<br />
and much information about human responses to DNA<br />
damage has been gained from studies of simple genetically<br />
tractable organisms such as yeast. We use a combination<br />
of molecular, cellular, and genetic techniques<br />
to determine how these pathways operate in human cells.<br />
Checkpoints control the order and timing of events<br />
in the cell cycle; they ensure that biochemically independent<br />
processes are coupled so that a delay in a critical<br />
cell-cycle process will cause a delay in all other aspects<br />
of progression of the cycle. In addition, checkpoints<br />
coordinate repair with delays in progression of the cell<br />
cycle and promote the use of the most appropriate repair<br />
pathway. We used genetic models to identify 2 checkpoint<br />
kinases in humans that limit progression of the<br />
cell cycle when DNA is damaged. One of these kinases,<br />
Chk2, is activated in response to DNA damage. Chk2<br />
physically interacts with Mus81-Eme1, a conserved<br />
DNA repair protein that has homology to the xeroderma<br />
pigmentosum F family of endonucleases. Xeroderma<br />
pigmentosum is a cancer-prone disorder that results<br />
from a failure to appropriately repair damaged DNA.<br />
Biochemical analysis indicates that Mus81-Eme1<br />
has associated endonuclease activity against structurespecific<br />
DNA substrates, including Holliday junctions.<br />
Enzymatic analysis, immunofluorescence studies, and the<br />
use of RNA interference have all contributed to the conclusion<br />
that Mus81-Eme1 is required for recombination<br />
repair in human cells. We are also using gene targeting to<br />
study the function of the Mus81-Eme1 endonuclease in<br />
mice. Inactivation of Mus81 in mice increases genomic<br />
instability and sensitivity to DNA damage but does not<br />
promote tumorogenesis. In addition, we showed that<br />
Mus81-Eme1 is specifically required for survival after<br />
exposure to cisplatin, mitomycin C, and other commonly<br />
used anticancer drugs. As a point of interaction between<br />
checkpoint control and DNA repair, the relationship<br />
between Mus81-Eme1 and Chk2 most likely will provide<br />
information critical to understanding the responses to<br />
DNA damage as a whole.
Anticancer therapy is largely based on the use of<br />
genotoxic agents that damage DNA and thus kill dividing<br />
cells. Coordination of cell-cycle checkpoints and<br />
DNA repair is especially important when unusually<br />
high amounts of DNA damage occur after radiation or<br />
genotoxic chemotherapy. Hence, a detailed understanding<br />
of cellular responses to DNA damage is essential<br />
to understanding both the development and the treatment<br />
of disease in humans.<br />
PUBLICATIONS<br />
Dendouga, N., Gao, H., Moechars, D., Janicot, M., Vialard, J., McGowan, C.H.<br />
Disruption of murine Mus81 increases genomic instability and DNA damage sensitivity<br />
but does not promote tumorigenesis. Mol. Cell. Biol. 25:7569, 2005.<br />
McGowan, C.H., Russell, P. <strong>The</strong> DNA damage response: sensing and signaling.<br />
Curr Opin. Cell Biol. 16:629, 2004.<br />
Zhang, R., Sengupta, S., Yang, Q,, Linke, S.P., Yanaihara, N., Bradsher, J., Blais, V,.<br />
McGowan, C.H., Harris, C.C. BLM helicase facilitates Mus81 endonuclease activity<br />
in human cells. Cancer Res. 65:2526, 2005.<br />
DNA Repair and the Maintenance<br />
of Genomic Stability<br />
M.N. Boddy, Y. Pavlova, S. Pebenard, G. Raffa<br />
DNA repair pathways have evolved to protect the<br />
genome from ever-present genotoxic agents.<br />
Highlighting the importance of the pathways,<br />
defects in DNA repair mechanisms strongly predispose<br />
the host to cancer and to neurologic and developmental<br />
disorders. <strong>The</strong> DNA repair systems we study in fission<br />
yeast are evolutionarily conserved, and therefore<br />
our investigations provide a valuable framework for<br />
understanding genome maintenance in human cells.<br />
Although many DNA repair mechanisms have been<br />
described, information on how they are coordinated<br />
with necessary changes in chromatin structure is limited.<br />
We are studying the essential structural maintenance<br />
of chromosomes (SMC) complex Smc5-Smc6.<br />
<strong>The</strong> molecular functions of Smc5-Smc6 are unknown,<br />
but the complex is related to the SMC complexes that<br />
hold replicated sister chromatids together (cohesin)<br />
and condense chromatin before its segregation at<br />
mitosis (condensin).<br />
In collaboration with J.R. Yates, Department of Cell<br />
<strong>Biology</strong>, we purified the Smc5-Smc6 complex and determined<br />
the identity of the core components. <strong>The</strong> holocomplex<br />
consists of the Smc5-Smc6 heterodimer and<br />
6 additional non-SMC elements, Nse1–Nse6 (Fig. 1).<br />
We expressed and purified individual components of<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 229<br />
Fig. 1. Architecture of the Smc5-Smc6 holocomplex. Nse1, Nse3,<br />
and Nse4 form a stable heterotrimer that then associates with<br />
Smc5. Nse2 interacts directly with Smc5 in the absence of the<br />
other Nse proteins. Smc6 interacts directly with Smc5 but none of<br />
the other components. Nse5 and Nse6 form a stable heterodimer<br />
that also binds directly to Smc5. Double-headed arrows indicate<br />
interactions between subcomplexes. Nse5-Nse6 may recruit the<br />
holocomplex to stalled replication forks and certain DNA damage<br />
sites (black oval on leading-strand template of replication fork).<br />
the complex and determined the architecture of the<br />
holocomplex. Nse1–Nse4 are essential for growth, and<br />
hypomorphic mutants of these proteins cause cellular<br />
sensitivity to genotoxic agents such as ultraviolet light<br />
and x-rays. Nse5 and Nse6 are nonessential, but cells<br />
lacking either protein also are hypersensitive to DNAdamaging<br />
agents. Notably, Nse1 and Nse2 contain<br />
certain zinc finger domains that implicate these 2 elements<br />
in the modification of target proteins with ubiquitin<br />
and the small ubiquitin-like protein SUMO. Such<br />
protein modifications play roles in DNA repair and<br />
chromatin remodeling.<br />
Our genetic analyses support a role for the Smc5-<br />
Smc6 complex in stabilizing replication forks that have<br />
stalled at sites of DNA damage. We have also identified<br />
a critical role for the Smc5-Smc6 complex in meiosis,<br />
the process that generates gametes for reproduction<br />
and genetic diversity. A critical feature of meiosis is<br />
the programmed formation of DNA double-strand breaks<br />
followed by repair of the breaks via homologous recombination.<br />
We found that the Smc5-Smc6 complex functions<br />
in the correct repair of the breaks and that mutants
230 MOLECULAR BIOLOGY 2005<br />
of Smc5-Smc6 do not segregate homologous chromosomes<br />
at the first meiotic division.<br />
Finally, we identified a physical interaction between<br />
the Smc5-Smc6 complex and Rad60, an essential DNA<br />
repair factor required for the homologous recombination<br />
repair of DNA. Rad60 is regulated by the replication<br />
checkpoint, and thus we can study the important<br />
but poorly defined interface between DNA repair and<br />
cell-cycle checkpoints.<br />
PUBLICATIONS<br />
Kai, M., Boddy, M.N., Russell, P., Wang, T.S. Replication checkpoint kinase Cds1<br />
regulates Mus81 to preserve genome integrity during replication stress. Genes Dev.<br />
19:919, 2005.<br />
Pebernard, S., McDonald, W.H., Pavlova, Y., Yates, J.R., III, Boddy, M.N. Nse1,<br />
Nse2, and a novel subunit of the Smc5-Smc6 complex, Nse3, play a crucial role in<br />
meiosis. Mol. Biol. Cell 15:4866, 2004.<br />
Delineation of Oncogenic and<br />
Tumor-Suppressing Pathways<br />
via Genetic Approaches<br />
P. Sun, Q. Deng, C. Kannemeier, R. Liao, B. Moser<br />
Our major interests are the genetic alterations<br />
involved in tumorigenesis and the cellular pathways<br />
that must be altered during oncogenic<br />
transformation. To this end, we analyzed the behaviors<br />
of primary, normal human cells after stable transduction<br />
of oncogenes, such as ras and MPM2.<br />
Members of the ras family of oncogenes encode<br />
small GTP-binding proteins that transduce growth signals.<br />
Constitutive activation of ras often occurs in tumors<br />
and contributes to tumor development. In normal cells,<br />
activation of ras triggers an antioncogenic response<br />
called premature senescence, a stable growth arrest<br />
that must be overcome before transformation occurs.<br />
We showed that ras induces senescence through sequential<br />
activation of 2 MAP kinase pathways. Initially, ras<br />
activates the MAP kinase kinase (MEK)–extracellular signal–regulated<br />
kinase (ERK) pathway. Sustained activation<br />
of MEK-ERK turns on the stress-induced p38 pathway,<br />
which subsequently causes senescence.<br />
<strong>The</strong>se results revealed a novel, tumor-suppressing<br />
function of p38, in addition to its known roles in inflammation<br />
and stress responses. In other studies, we identified<br />
additional signaling components, either upstream or<br />
downstream of p38, that mediate premature senescence.<br />
To determine how premature senescence is bypassed<br />
in tumors, we dissected the functions of an adenovi-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
rus-encoded oncoprotein, E1A, that can rescue cells<br />
from ras-induced senescence. E1A directly binds to<br />
and inhibits the functions of several cellular proteins,<br />
such as members of the Rb family, p300/CBP, and p400,<br />
that have been implicated in tumor-suppressing pathways.<br />
Our results indicated that senescence-bypassing<br />
activity resides in the N terminus of E1A and requires<br />
binding of both Rb and p300/CBP, but not binding of<br />
p400. Although interference with the p16 INK4A /Rb<br />
pathway or with p300/CBP functions alone did not<br />
result in bypassing of senescence, these 2 types of<br />
genetic alterations complemented mutants of E1A with<br />
defects in Rb binding and p300/CBP binding, respectively,<br />
to rescue cells from ras-induced senescence and<br />
lead to cellular transformation. <strong>The</strong>refore, genetic alterations<br />
that disrupt the p16 INK4A /Rb pathway and those<br />
that perturb the p300/CBP functions cooperate to<br />
bypass ras-induced senescence. <strong>The</strong>se results indicate<br />
that p300 and CBP are integral components of the<br />
senescence pathway. Both p300 and CBP have tumorsuppressing<br />
functions. <strong>The</strong> critical role of p300 and<br />
CBP in the senescence response has provided a mechanistic<br />
basis for the tumor-suppressing function of<br />
these proteins.<br />
Another focus of our research is MDM2, an oncogene<br />
that can mediate transformation primarily through inactivation<br />
of the tumor suppressor protein p53. However, we<br />
found that MDM2 confers resistance to a growth-inhibitory<br />
cytokine, transforming growth factor β, through a<br />
p53-independent mechanism. Currently, we are delineating<br />
this p53-independent activity of MDM2, which<br />
may play an important role in tumorigenesis.<br />
In other studies, we are systematically searching<br />
for genetic alterations that contribute to specific tumorassociated<br />
phenotypes, such as drug resistance, cellular<br />
immortalization, and metastasis. For these investigations,<br />
we are using cDNA expression libraries or libraries<br />
of short interfering RNAs.<br />
PUBLICATIONS<br />
de Parseval, A., Chatterji, U., Morris, G., Sun, P., Elder, J.H. Fine mapping of<br />
CD134 residues critical for interaction with feline immunodeficiency virus. Nat.<br />
Struct. Mol. Biol. 12:60, 2005.<br />
de Parseval, A., Chatterji, U., Sun, P., Elder, J.H. Feline immunodeficiency virus<br />
targets activated CD4 + T cells by using CD134 as a binding receptor. Proc. Natl.<br />
Acad. Sci. U. S. A. 101:13044, 2004.<br />
de Parseval, A., Ngo, S., Sun, P., Elder, J.H. Factors that increase the effective<br />
concentration of CXCR4 dictate feline immunodeficiency virus tropism and kinetics<br />
of replication. J. Virol. 78:9132, 2004.<br />
Deng, Q., Li, Y., Tedesco, D., Liao, R., Fuhrmann, G., Sun, P. <strong>The</strong> ability of E1A to<br />
rescue ras-induced premature senescence and confer transformation relies on inactivation<br />
of both p300/CBP and Rb family proteins. Cancer Res. 65:8298, 2005.
<strong>The</strong> 5-HT 7 Receptor as a Target<br />
in Depression and Schizophrenia<br />
P.B. Hedlund, P.E. Danielson, S. Huitrón-Reséndiz,<br />
S.J. Hendriksen, S. Semenova, M.A. Geyer, A. Markou,<br />
J.G. Sutcliffe<br />
Serotonin (5-HT) is produced by a small group of<br />
nuclei in the brain stem that send their projections<br />
to a vast number of receptive fields. <strong>The</strong> family<br />
of receptors for 5-HT is the most diverse family that<br />
binds a single ligand; it has at least 14 members. One<br />
of these is the 5-HT 7 receptor, which we previously discovered.<br />
In earlier studies, we showed that this receptor<br />
mediates resetting of circadian rhythms by the hypothalamus.<br />
Despite vast differences in amino acid sequence<br />
between the 5-HT 7 receptor and the 5-HT 1A receptor,<br />
the 2 share considerable pharmacology and have been<br />
implicated in some of the same functions. 5-HT 1A is<br />
more abundant than 5-HT 7 , but the areas of the brain<br />
that express the 2 receptors overlap considerably.<br />
We produced mutant mice in which the gene for<br />
the 5-HT 7 receptor was inactivated. Studies with these<br />
mice and SB-266970, a 5-HT 7 -selective antagonist,<br />
indicated that this receptor mediates serotonin-induced<br />
hypothermia and is important for fine tuning of temperature<br />
homeostasis.<br />
Sleep, circadian rhythm, and mood are related phenomena.<br />
5-HT 7 -selective antagonists increase REM sleep<br />
latency and decrease the cumulative duration of REM<br />
sleep, patterns the opposite of those found in patients<br />
with clinical depression. Several antidepressants activate<br />
5-HT 7 neurons in the circadian control area of the<br />
hypothalamus, and chronic treatment with antidepressants<br />
diminishes both activation and 5-HT 7 binding<br />
there. We examined sleep parameters in the mutant<br />
mice in which the gene for the 5-HT 7 receptor was<br />
inactivated. We found that they spent less time than<br />
normal mice in REM sleep. This pattern is the opposite<br />
of that found in humans with depression.<br />
Two models of behavioral despair, the forced swim<br />
test and the tail suspension test, make rats and mice<br />
immobile. This immobility, or helplessness, is likened<br />
to depression in humans because a high correlation<br />
exists between the ability of antidepressant drugs to<br />
reverse immobility in rodents and to be effective clinically<br />
in humans. Furthermore, mice selectively bred to<br />
have increased helplessness in these behavioral despair<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 231<br />
tests resemble patients with clinical depression. <strong>The</strong><br />
mice have decreased REM latency and more cumulative<br />
REM sleep, elevated levels of corticosterone, a decreased<br />
5-HT metabolism index, and altered serotonin-induced<br />
hypothermia. We examined unmedicated 5-HT 7 mutant<br />
mice in these tests and found that the mice remained<br />
significantly more mobile than unmedicated normal<br />
mice during both the forced swim and the tail suspension<br />
tests. Normal mice medicated with the 5-HT 7 -selective<br />
antagonist SB-266970 mimicked the mobility of<br />
unmedicated mutant mice, whereas the selective antagonist<br />
had no effect on the mobility of mutant mice. A<br />
selective serotonin reuptake inhibitor increased mobility<br />
in both types of mice (albeit at a lower concentration<br />
in the mutant mice), suggesting that the inhibitor<br />
worked through an independent mechanism.<br />
<strong>The</strong>se results are consistent with the notion that<br />
the 5-HT 7 mutant mice have characteristics of a partially<br />
“antidepressed” state: they spend less time in<br />
REM sleep, have reduced immobility in the forced swim<br />
and tail suspension tests, and have decreases in serotonin-induced<br />
hypothermia. Normal mice medicated<br />
with 5-HT 7 -selective antagonists resemble unmedicated<br />
5-HT 7 mutant mice in these measures. <strong>The</strong>se findings<br />
suggest that 5-HT 7 -selective antagonists might be sufficient<br />
treatment for some aspects of clinical depression.<br />
Several antipsychotic drugs have high affinity for<br />
the 5-HT 7 receptor. We examined the role of 5-HT 7<br />
receptors in an animal model of schizophrenia: phencyclidine-induced<br />
disruption of prepulse inhibition of<br />
the acoustic startle reflex. In untreated mice, we<br />
found no difference between mice in which the gene<br />
for the 5-HT 7 receptor was inactivated and wild-type<br />
mice in startle response or in prepulse inhibition regardless<br />
of prepulse intensity, interstimulus interval, or pulse<br />
intensity. SB-269970 had no effect on prepulse inhibition.<br />
<strong>The</strong> disruption of prepulse inhibition produced<br />
by phencyclidine in wild-type mice did not occur in<br />
the mutant mice. Similarly, the effect of phencyclidine<br />
on prepulse inhibition was reduced by SB-269970 in<br />
wild-type mice. <strong>The</strong> results indicate a specific role for<br />
the 5-HT 7 receptor in the glutamatergic prepulse inhibition<br />
model of schizophrenia.<br />
PUBLICATIONS<br />
de Lecea, L., Sutcliffe, J.G. Hypocretin as a wakefulness regulatory peptide. In:<br />
<strong>The</strong> Orexin/Hypocretin System: Physiology and Pathophysiology. Nishino, S., Sakurai,<br />
T. (Eds.). Humana Press, Totowa, NJ, 2005, p. 143. A volume in the series<br />
Contemporary Clinical Neuroscience.<br />
de Lecea, L., Sutcliffe, J.G. (Eds.). <strong>The</strong> Hypocretins: Integrators of Physiological<br />
Functions. Plenum Press, New York, 2005.
232 MOLECULAR BIOLOGY 2005<br />
Hedlund, P.B., Huitrón-Reséndiz, S., Henriksen, S.J., Sutcliffe, J.G. 5-HT 7 receptor<br />
inhibition and inactivation induce antidepressantlike behavior and sleep pattern.<br />
Biol. Psychiatry, in press.<br />
Hedlund, P.B., Sutcliffe, J.G. Functional, molecular and pharmacological advances<br />
in 5-HT 7 receptor research. Trends Pharmacol. Sci. 25:481, 2004.<br />
Hedlund, P.B., Sutcliffe, J.G. 5-HT 7 receptors as favorable pharmacological targets<br />
for drug discovery. In: <strong>The</strong> Serotonin Receptors: From <strong>Molecular</strong> Pharmacology to<br />
Human <strong>The</strong>rapeutics. Roth, B.L. (Ed.). Humana Press, Totowa, NJ, in press.<br />
Sutcliffe, J.G., de Lecea, L. <strong>The</strong> hypocretin/orexin system. In: Handbook of Contemporary<br />
Neuropharmacology. Sibley, D. (Ed.). Wiley & Sons, Hoboken, NJ, in press.<br />
Sutcliffe, J.G., de Lecea, L. Hypocretins/orexins in brain function. In: Handbook of Neurochemistry<br />
and <strong>Molecular</strong> Neurobiology. Lim, R. (Ed.). Springer, New York, in press.<br />
Sutcliffe J.G., de Lecea, L. Not asleep, not quite awake. Nat. Med. 10:673, 2004.<br />
Ziolkowska, B., Gieryk, A., Bilecki, W., Wawrzczak-Bargiela, A., Wedzony, K.,<br />
Chocyk, A., Danielson, P.E., Thomas, E.A., Hilbush, B.S., Sutcliffe, J.G.,<br />
Przewlocki, R. Regulation of α-synuclein expression in limbic and motor brain<br />
regions of morphine-treated mice. J. Neurosci. 25:4996, 2005.<br />
<strong>Molecular</strong> Neurobiology of<br />
CNS Disorders<br />
E.A. Thomas, J.G. Sutcliffe, P.A. Desplats, S. Narayan,<br />
K.E. Kass, W. Huang<br />
GENE EXPRESSION IN STRIATAL DISORDERS<br />
We have identified and cataloged approximately<br />
50 genes that are predominantly expressed<br />
in the striatum in the brain. Our long-standing<br />
hypothesis is that such genes most likely encode<br />
proteins that are preferentially associated with particular<br />
physiologic processes in the striatum and therefore<br />
may be relevant to striatal disorders. Using oligonucleotide<br />
microarrays, we measured expression of these<br />
genes simultaneously in the striatum of R6/1 mice, a<br />
transgenic model of Huntington’s disease.<br />
A total of 81% of striatal genes had increased<br />
expression in mice in presymptomatic and/or symptomatic<br />
stages of illness. Changes in expression of genes<br />
associated with G protein signaling and calcium homeostasis<br />
are of particular interest for future studies. <strong>The</strong><br />
most striking decrease occurred in β4, a newly identified<br />
subunit of the sodium channel. Changes in expression<br />
began when the mice were 8 weeks old, and expression<br />
had progressively decreased almost 10-fold by the time<br />
the mice were 8 months old. Two novel sequences with<br />
highly specific striatal expression also had differences in<br />
expression throughout the life span of the mutant mice,<br />
as determined by in situ hybridization analysis.<br />
Expression differences of 15 of the striatum-enriched<br />
genes were tested in rats treated with 6-hydroxydopamine,<br />
a rodent model of Parkinson’s disease. No<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
changes in expression were detected in any of the<br />
genes tested.<br />
<strong>The</strong>se findings indicate that mutant huntingtin<br />
protein causes selective deficits in the expression of<br />
mRNAs responsible for striatum-specific physiologic<br />
changes. Furthermore, the results suggest that although<br />
both Huntington’s disease and Parkinson’s disease<br />
involve striatal dysfunction, the differences in the<br />
molecular pathologic changes associated with the 2<br />
diseases are distinct.<br />
MOLECULAR MARKERS OF SCHIZOPHRENIA<br />
Schizophrenia is a life-long mental illness with variable<br />
expression and unknown etiology. <strong>The</strong> major clinical<br />
manifestations of schizophrenia at the time of onset<br />
of the illness are psychotic symptoms; however, as the<br />
illness progresses, the negative symptoms become more<br />
predominant. In addition, many other neurologic aspects<br />
change during the course of the illness. We are interested<br />
in the molecular factors that influence manifestation<br />
of the symptoms and the course of schizophrenia<br />
after its onset and how treatment modifies the effects<br />
of illness.<br />
Using oligonucleotide microarrays, we generated<br />
gene expression profiles from tissue samples obtained<br />
at autopsy from the prefrontal cortex of patients with<br />
schizophrenia of short and long duration. Because correct<br />
treatment early in the illness is thought to have a<br />
beneficial effect on the outcome of schizophrenia, the<br />
identification of genes involved in the early and late<br />
stages of disease will be important for understanding<br />
the progression of the illness.<br />
PUBLICATIONS<br />
Dean, B., Keriakous, D., Thomas, E.A., Scarr, E. Understanding the pathology of<br />
schizophrenia: the impact of high-throughput screening of the genome and proteome<br />
in postmortem CNS. Curr. Psychiatry Rev. 1:1, 2005.<br />
Digney, A., Keriakous, D., Scarr, E., Thomas, E.A., Dean, B. Differential changes<br />
in apolipoprotein E in schizophrenia and bipolar I disorder. Biol. Psychiatry<br />
57:711, 2005.<br />
Yao, J.K., Thomas, E.A., Reddy, R.D., Keshavan, M.S. Association of plasma<br />
apolipoproteins D with RBC membrane arachidonic acid levels in schizophrenia.<br />
Schizophr. Res. 72:259, 2005.<br />
Ziolkowska, B., Gieryk, A., Bilecki, W., Wawrzczak-Bargiela, A., Wedzony, K.,<br />
Chocyk, A., Danielson, P.E., Thomas, E.A., Hilbush, B.S., Sutcliffe, J.G.,<br />
Przewlocki, R. Regulation of α-synuclein expression in limbic and motor brain<br />
regions of morphine-treated mice. J. Neurosci. 25:4996, 2005.
<strong>Molecular</strong> <strong>Biology</strong> of Sleep<br />
L. de Lecea, C. Suzuki, C. Pañeda, B. Boutrel,* R. Winsky-<br />
Sommerer, A. Coda, S. Huitrón-Reséndiz,* A.J. Roberts,*<br />
J.G. Sutcliffe, G.F. Koob,* S.J. Henriksen*<br />
* <strong>Molecular</strong> and Integrative Neurosciences Department, <strong>Scripps</strong> <strong>Research</strong><br />
Our goal is to understand the cellular and molecular<br />
components that modulate cortical activity<br />
and sleep. In particular, we focus on the characterization<br />
of neuropeptides first described by our group:<br />
cortistatin and the hypocretins.<br />
CORTISTATIN<br />
Cortistatin is a neuropeptide expressed in the cerebral<br />
cortex. Of its 14 residues, 11 also occur in the<br />
neuropeptide somatostatin. However, cortistatin and<br />
somatostatin have different physiologic functions. Cortistatin<br />
is neuroinhibitory and promotes sleep.<br />
We generated mice deficient in cortistatin and determined<br />
their behavioral profile in collaboration with<br />
A.J. Roberts, <strong>Molecular</strong> and Integrative Neurosciences<br />
Department. Because cortistatin has anticonvulsant<br />
activity, we tested seizure susceptibility in cortistatindeficient<br />
mice. We also did gene array studies to determine<br />
the consequences of cortistatin deficiency in mice<br />
lacking the gene for this neuropeptide. Our results<br />
suggest that cortistatin has multiple functions in the<br />
maintenance of cortical excitability.<br />
THE HYPOCRETINS<br />
<strong>The</strong> hypocretins, 2 neuropeptides derived from the<br />
same precursor, are produced in a few thousand cells<br />
in the lateral part of the hypothalamus. <strong>The</strong> hypocretins<br />
are key molecules for the stability of the states of vigilance.<br />
Lack of hypocretin peptides or hypocretin-producing<br />
neurons produces narcolepsy, a sleep disorder<br />
characterized by uninvited intrusions of sleep into wakefulness.<br />
Patients with narcolepsy experience excessive<br />
daytime sleepiness and cataplexy, a sudden loss of<br />
muscle tone upon certain stimuli. Recent studies<br />
indicated that patients with narcolepsy lack hypocretin-expressing<br />
cells, suggesting that narcolepsy is a<br />
neurodegenerative disease of the hypocretinergic system.<br />
In anatomic and electrophysiologic experiments,<br />
we found that neurons expressing hypocretin are contacted<br />
by neurons expressing corticotropin-releasing<br />
factor (CRF), a major component of the stress response.<br />
Hypocretin neurons contain CRF receptors. Intracellular<br />
recordings in hypothalamic slices from transgenic<br />
mice that express green fluorescent protein under the<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 233<br />
control of the hypocretin promoter indicated that CRF<br />
depolarizes hypocretin neurons through the CRF 1 receptor.<br />
Further, hypocretin neurons are not activated upon<br />
stress in mice that lack the gene for this receptor. <strong>The</strong>se<br />
data suggest a close association between the CRF and<br />
hypocretin systems in the acute stress response.<br />
Because CRF is involved in addiction and because<br />
hypocretin neurons project to key areas involved in brain<br />
reward, we hypothesized that hypocretin neurons might<br />
be involved in addiction-related behaviors. We found<br />
that hypocretin-1 leads to the reinstatement of previously<br />
extinguished cocaine-seeking behavior but does<br />
not alter cocaine intake in rats. In collaboration with<br />
P.J. Kenny and A. Markou, <strong>Molecular</strong> and Integrative<br />
Neurosciences Department, we discovered that hypocretin-1<br />
negatively regulates the activity of brain reward<br />
circuitries. Hypocretin-induced reinstatement of cocaine<br />
seeking can be prevented by simultaneous blockade of<br />
noradrenergic and CRF systems but not by blockade of<br />
either system alone. <strong>The</strong>se findings reveal a previously<br />
unidentified role for hypocretins in drug craving and<br />
relapse behavior. Moreover, hypocretins may drive drug<br />
seeking through induction of a negative affective state<br />
by activation of stress pathways in the brain.<br />
NEUROPEPTIDE S<br />
Neuropeptide S is a newly discovered neuropeptide<br />
expressed prominently in a few hundred neurons in the<br />
area near the locus coeruleus. We found that infusion of<br />
neuropeptide S into the brain ventricles in mice dramatically<br />
enhanced wakefulness and suppressed anxiety. <strong>The</strong><br />
neuropeptide activated several brain nuclei related to<br />
arousal. We showed that neurons expressing neuropeptide<br />
S project to and depolarize neurons expressing hypocretin.<br />
Our data strongly suggest that neuropeptide S<br />
is an important modulator of sleep and waking.<br />
PUBLICATIONS<br />
de Lecea, L. Reverse genetics and the study of sleep. In: Sleep: Circuits and Functions.<br />
Luppi, P.-H. (Ed.). CRC Press, Boca Raton, FL, 2004, p. 109.<br />
de Lecea, L., Sutcliffe, J.G. <strong>The</strong> hypocretins and sleep. FEBS J., in press.<br />
de Lecea, L., Sutcliffe, J.G. (Eds.) Hypocretins: Integrators of Physiological Functions.<br />
Springer, New York, 2005.<br />
Huitrón-Reséndiz, S., Kristensen, M.P., Sánchez-Alavez, M., Clark, S.D., Grupke,<br />
S.L., Tyler, C., Suzuki, C., Nothacker, H.P., Civelli, O., Criado, J.R., Henriksen, S.J.,<br />
Leonard, C.S., de Lecea, L. Urotensin II modulates rapid eye movement sleep<br />
through activation of brainstem cholinergic neurons. J. Neurosci. 25:5465, 2005.<br />
Levine, A.S., Winsky-Sommerer, R., Huitrón-Reséndiz, S., Grace, M.K., de Lecea, L.<br />
Injection of neuropeptide W into paraventricular nucleus of hypothalamus increases<br />
food intake. Am. J. Physiol. Regul. Integr. Comp. Physiol. 288:R1727, 2005.<br />
Martin, G., Guadaño-Ferraz, A., Morte, B., Ahmed, S., Koob, G.F., de Lecea, L.<br />
Siggins, G.R. Chronic morphine treatment alters N-methyl-D-aspartate receptors in<br />
freshly isolated neurons from nucleus accumbens. J. Pharmacol. Exp. <strong>The</strong>r.<br />
311:265-73, 2004.
234 MOLECULAR BIOLOGY 2005<br />
Pañeda, C., Winsky-Sommerer, R., Boutrel, B., de Lecea, L. <strong>The</strong> corticotropinreleasing<br />
factor-hypocretin connection: implications in stress response and addiction.<br />
Drug News Perspect. 18:250, 2005.<br />
Spier, A.D., Fabre, V., de Lecea, L. Cortistatin radioligand binding in wild-type and<br />
somatostatin receptor-deficient mouse brain. Regul. Pept. 124:179, 2005.<br />
Sutcliffe, J.G., de Lecea L. Not asleep, not quite awake. Nat. Med. 10:673, 2004.<br />
Tallent, M.K., Fabre, V., Qiu, C., Calbet, M., Lamp, T., Baratta, M.V., Suzuki, C.,<br />
Siggins, G.R., Henriksen, S.J., Criado, J.R., Roberts, A., de Lecea, L., Cortistatin<br />
overexpression in transgenic mice produces deficits in synaptic plasticity and learning.<br />
Mol. Cell. Neurosci., in press.<br />
Ureña, J.M., La Torre, A., Martínez, A., Lowenstein, E., Franco, N., Winsky-Sommerer,<br />
R., Fontana, X., Casaroli-Marano, R., Ibáñez-Sabio, M.A., Pascual, M., del<br />
Rio, J.A., de Lecea, L., Soriano, E. Expression, synaptic localization, and developmental<br />
regulation of Ack1/Pyk1, a cytoplasmic tyrosine kinase highly expressed in<br />
the developing and adult brain. J. Comp. Neurol. 490:119, 2005.<br />
Winsky-Sommerer, R., Boutrel, B., de Lecea , L. Stress and arousal: the corticotropin-releasing<br />
factor/hypocretin circuitry. J. Mol. Neurobiol., in press.<br />
Winsky-Sommerer, R., Yamanaka, A., Diano, S., Borok, E., Roberts, A., Sakurai, T.,<br />
Kilduff, T.S., Horvath, T.L., de Lecea, L. Interaction between the corticotropinreleasing<br />
factor system and hypocretins (orexins): a novel circuit mediating stress<br />
response. J. Neurosci. 24:11439, 2004.<br />
Xu, Y., Reinscheid, R.R., Huitrón-Reséndiz, S., Clark, S.D., Wang, Z., Lin, S.H.,<br />
Brucher, F.A., Zeng, J., Ly, H.K., Henriksen, S.J., de Lecea, L., Civelli, O. Neuropeptide<br />
S: a novel neuropeptide promoting arousal and anxiolytic-like effects.<br />
Neuron 43:487, 2004.<br />
<strong>Molecular</strong> Neuroscience:<br />
Lysophospholipid Signaling,<br />
Neural Aneuploidy<br />
J. Chun, B. Almeida, B. Anliker, E. Birgbauer, M. Fontanoz,<br />
S. Gardell, C. Paczkowski, D. Herr, D. Kaushal, G. Kennedy,<br />
M. Kingsbury, C.W. Lee, M. McConnell, M. McCreight,<br />
S. Peterson, S. Rehen, R. Rivera, M. Lu, W. Westra,<br />
A.H. Yang, X.Q. Ye, Y. Yung, L. Zhu<br />
Understanding the nervous system—how it arises<br />
developmentally and how it carries out its myriad<br />
complex tasks in normal and diseased states—<br />
is a major challenge. We are studying 2 topics with<br />
both basic and potentially therapeutic relevance: the<br />
role of lysophospholipid signaling and the role of genomic<br />
alterations within individual neurons as manifested<br />
by aneuploidy.<br />
LYSOPHOSPHOLIPID SIGNALING<br />
Lysophospholipids are simple phospholipids containing<br />
a glycerophosphate or glycerosphingoid backbone<br />
and single acyl chain of varied length and saturation.<br />
Two major forms of lysophospholipids are lysophosphatidic<br />
acid and sphingosine 1-phosphate (Fig. 1). It<br />
is now clear from our research and that of many oth-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
Fig. 1. Chemical structures of lysophosphatidic acid and sphingosine<br />
1-phosphate.<br />
ers that most important actions of lysophospholipids<br />
are mediated by cognate G protein–coupled receptors.<br />
A growing range of neurobiological functions is being<br />
identified, particularly effects on Schwann cells and oligodendrocytes,<br />
which are involved in myelination, and<br />
on neuroprogenitor cells of the cerebral cortex. To<br />
determine receptor selectivity and actual neurobiological<br />
function, we are producing mice that lack the genes<br />
for single and multiple receptors. In collaboration with<br />
other scientists at <strong>Scripps</strong> <strong>Research</strong>, we are developing<br />
chemical tools to dissect the in vivo function of lysophosphatidic<br />
acid and sphingosine 1-phosphate.<br />
During 2004, the range of new biological functions<br />
for receptor-mediated lysophospholipid signaling continued<br />
to grow. With collaborators from around the world,<br />
we showed that lysophospholipid signaling influences<br />
the cardiovascular system, the immune system, cancer<br />
cell motility, and, especially, neuropathic pain and<br />
multiple sclerosis.<br />
Neuropathic pain is pain due to nerve damage or<br />
dysfunction. Mechanisms for the initiation of this type<br />
of pain are poorly understood. In a murine model of<br />
neuropathic pain, activation of a single lysophospholipid<br />
receptor was necessary for the initiation of pain;<br />
such pain did not develop in mice that lacked the gene<br />
for the receptor. Another medically important disease,<br />
multiple sclerosis, can be approximated in animals by<br />
immunization with myelin antigens to produce experimental<br />
autoimmune encephalomyelitis. Agonists for<br />
lysophospholipid receptors (specifically, sphingosine<br />
1-phosphate receptor agonists) abrogated the disability<br />
normally produced by experimental autoimmune<br />
encephalomyelitis, suggesting a role for this signaling<br />
pathway in the medical biology and a possible therapy
for multiple sclerosis. We are expanding these themes<br />
in previously identified and new biological systems.<br />
NORMAL NEURAL ANEUPLOIDY<br />
Are all neurons of the brain genetically identical,<br />
as is widely assumed, or are differences encoded within<br />
individual genomes? Using a combination of spectral<br />
karyotyping, which “paints” chromosomes to allow their<br />
unambiguous detection, and fluorescence in situ hybridization,<br />
which uses labeled point-probes to identify discrete<br />
genetic loci in interphase cells, we detected a<br />
substantial degree of genomic variation in the normal<br />
brain. During neurogenesis, approximately one third of<br />
all cells are aneuploid, produced, at least in part, by<br />
chromosome missegregation mechanisms. In postmitotic<br />
neurons, in which spectral karyotyping cannot be<br />
used because neurons are in interphase, fluorescence<br />
in situ hybridization of sex chromosomes revealed a<br />
high percentage of aneuploidy, and the total number<br />
of aneuploid cells is certainly higher if the remaining<br />
autosomes are considered (Fig. 2).<br />
Fig. 2. Examples of neural aneuploidy in different regions of the<br />
brain in adult mice as revealed by fluorescence in situ hybridization.<br />
During 2004, by analyzing mice deficient in DNA<br />
surveillance or repair molecules, we detected a new<br />
influence on the generation of aneuploidy. One of these<br />
molecules, the mutated protein ATM, is the cause of<br />
the rare genetic disease ataxia-telangiectasia. Elimination<br />
of the gene for ATM or the gene for XRCC5, another molecule<br />
involved in DNA surveillance and repair, resulted<br />
in major increases in the number and severity of aneuploid<br />
neural progenitor/stem cells, indicating a positive<br />
biological link between aneuploidy and molecules involved<br />
with genome integrity. Currently, we are exploring the<br />
basic phenomenologic aspects and functional importance<br />
of neural aneuploidy during development and in<br />
disease processes.<br />
PUBLICATIONS<br />
Anliker, B., Chun, J. Cell surface receptors in lysophospholipid signaling. Semin.<br />
Cell Dev. Biol. 15:457, 2004.<br />
Anliker, B., Chun, J. Lysophospholipid G protein-coupled receptors. J. Biol. Chem.<br />
279:20555, 2004.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 235<br />
Baudhuin, L.M., Jiang, Y., Zaslavsky, A., Ishii, I., Chun, J., Xu, Y. S1P 3 -mediated<br />
Akt activation and cross-talk with platelet-derived growth factor receptor (PDGFR).<br />
FASEB J. 18:341, 2004.<br />
Chun, J. Choices, choices, choices. Nat. Neurosci. 7:323, 2004.<br />
Girkontaite, I., Sakk, V., Wagner, M., Borggrefe, T., Tedford, K., Chun, J., Fischer,<br />
K.-D. <strong>The</strong> sphingosine-1-phosphate (S1P) lysophospholipid receptor S1P 3 regulates<br />
MAdCAM-1 + endothelial cells in splenic marginal sinus organization. J. Exp.<br />
Med. 200:1491, 2004.<br />
Hama, K., Aoki, J., Fukaya, M., Kishi, Y., Sakai, T., Suzuki, R., Ohta, H., Yamori, T.,<br />
Watanabe, M., Chun, J., Arai, H. Lysophosphatidic acid and autotaxin stimulate<br />
cell motility of neoplastic and non-neoplastic cells through LPA1. J. Biol. Chem.<br />
279:17634, 2004.<br />
Inoue, M., Rashid, M.H., Fujita, R., Contos, J.J., Chun, J., Ueda, H. Initiation of<br />
neuropathic pain requires lysophosphatidic acid receptor signaling [published correction<br />
appears in Nat. Med. 10:755, 2004]. Nat. Med. 10:712, 2004.<br />
Ishii, I., Fukushima, N., Ye, X., Chun, J. Lysophospholipid receptors: signaling and<br />
biology. Annu. Rev. Biochem. 73:321, 2004.<br />
Kingsbury, M.A., Rehen, S.K., Ye, X., Chun, J. Genetics and cell biology of lysophosphatidic<br />
acid receptor-mediated signaling during cortical neurogenesis. J. Cell. Biochem.<br />
92:1004, 2004.<br />
Levkau, B., Hermann, S., <strong>The</strong>ilmeier, G., van der Giet, M., Chun, J., Schober, O.,<br />
Schäfers, M. High-density lipoprotein stimulates myocardial perfusion in vivo. Circulation<br />
110:3355, 2004.<br />
McConnell, M.J., Kaushal, D., Yang, A.H., Kingsbury, M.A., Rehen, S.K., Treuner, K.,<br />
Helton, R., Annas, E.G., Chun, J., Barlow, C. Failed clearance of aneuploid embryonic<br />
neural progenitor cells leads to excess aneuploidy in ATM-deficient but not the<br />
Trp53-deficient adult cerebral cortex. J. Neurosci. 24:8090, 2004.<br />
Nofer, J.-R., van der Giet, M., Tölle, M., Wolinska, I., von Wnuck-Lipinski, K.,<br />
Baba, H.A., Gödecke, A., Tietge, U.J., Ishii, I., Kleuser, B., Schäfers, M., Fobker, M.,<br />
Zidek, W., Assmann, G., Chun, J., Levkau, B. HDL induces NO-dependent vasorelaxation<br />
via the lysophospholipid receptor S1P 3 . J. Clin. Invest. 113:569, 2004.<br />
Rao, T.S., Lariosa-Willingham, K.D., Lin, F.-F. Yu, N., Tham, C.-S., Chun, J., Webb, M.<br />
Growth factor pre-treatment differentially regulates phosphoinositide turnover downstream<br />
of lysophospholipid receptor and metabotropic glutamate receptors in cultured<br />
rat cerebrocortical astrocytes. Int. J. Dev. Neurosci. 22:131, 2004.<br />
Sanna, M.G., Liao, J., Jo, E., Alfonso, C., Ahn, M.Y., Peterson, M.S., Webb, B.,<br />
Lefebvre, S., Chun, J., Gray, N., Rosen, H. Sphingosine 1-phosphate (S1P) receptor<br />
subtypes S1P 1 and S1P 3 , respectively, regulate lymphocyte recirculation and<br />
heart rate. J. Biol. Chem. 279:13839, 2004.<br />
Webb, M., Tham, C.-S., Lin, F.-F., Lariosa-Willingham, K., Yu, N., Hale, J., Mandala,<br />
S., Chun, J., Rao, T.S. Sphingosine 1-phosphate receptor agonists attenuate<br />
relapsing-remitting experimental autoimmune encephalitis in SJL mice. J. Neuroimmunol.<br />
153:108, 2004.<br />
Chemical Glycobiology in the<br />
Immune System<br />
J.C. Paulson, P. Bengtson, O. Blixt, B.E. Collins, S. Han,<br />
T. Islam, H. Tateno, Q. Yan<br />
We investigate the roles of glycan-binding proteins<br />
that mediate cellular processes central<br />
to immunoregulation and human disease. We<br />
work at the interface of biology and chemistry to understand<br />
how the interaction of glycan-binding proteins<br />
with their ligands modulates the functions of the pro-
236 MOLECULAR BIOLOGY 2005<br />
teins in cell-cell adhesion and cell signaling. Projects<br />
fall into 2 main areas: (1) functions of glycan-binding<br />
proteins expressed on leukocytes and (2) regulation of<br />
the synthesis of the carbohydrate ligands of the proteins<br />
during leukocyte activation and differentiation. Our multidisciplinary<br />
approach is complemented by a diverse<br />
group of chemists, biochemists, cell biologists, and<br />
molecular biologists.<br />
SIGLEC FAMILY OF CELL ADHESION PROTEINS<br />
A total of 11 human and 8 mouse siglecs have been<br />
identified so far, and most siglecs are expressed on<br />
leukocytes. <strong>The</strong> siglecs are a subfamily of the immunoglobulin<br />
superfamily. <strong>The</strong>y have variable numbers of<br />
extracellular Ig domains, including a unique, homologous<br />
N-terminal Ig domain that confers the ability to bind<br />
to sialic acid–containing carbohydrate groups (sialosides)<br />
of glycoproteins and glycolipids. <strong>The</strong> cytoplasmic<br />
domains of the siglecs typically contain one or more<br />
immunoreceptor tyrosine-based inhibitory motifs characteristic<br />
of accessory proteins that regulate transmembrane<br />
signaling of cell-surface receptor proteins.<br />
To dissect the biology of the siglecs, we use novel<br />
carbohydrate probes that modulate the function of the<br />
proteins. We use chemoenzymatic approaches to synthesize<br />
sialoside analogs recognized by siglecs. <strong>The</strong><br />
analogs range from potent inhibitors to multivalent<br />
probes of siglec binding to monovalent sialic acid analogs<br />
that can be fed to cells and incorporated into cell-surface<br />
glycoproteins to add chemical functionality or alter the<br />
affinity of sialoside ligands for cell-surface siglecs. Projects<br />
on several members of the siglec family are ongoing.<br />
CD22 (siglec-2) is an accessory molecule of the<br />
B-cell receptor complex; it has both positive and negative<br />
effects on receptor signaling. <strong>The</strong> carbohydrate<br />
ligand recognized by CD22 is the sequence sialic acid<br />
α-2-6-galactose, which commonly terminates N-linked<br />
carbohydrate groups of glycoproteins. Significantly, ablation<br />
of the gene that encodes β-galactoside α-2,6-sialyltransferase<br />
I, the enzyme responsible for synthesis of<br />
this carbohydrate in mice, causes a marked deficiency<br />
in antibody production in response to vaccination with<br />
T cell–dependent or T cell–independent antigens, establishing<br />
the importance of the ligand in CD22 function.<br />
We developed a novel method for in situ photoaffinity<br />
cross-linking of CD22 to its ligands on the same cell<br />
(cis) or on an adjacent cell (trans); we use a 9-arylazide-sialic<br />
acid that is taken up by cells and incorporated<br />
into cell-surface glycoproteins, allowing the<br />
glycoproteins to be cross-linked to CD22 upon expo-<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
sure to ultraviolet light (Fig. 1). <strong>The</strong> striking finding is<br />
that microdomain localization of CD22, not glycan<br />
structure alone, strongly influences the glycoprotein<br />
ligands CD22 interacts with, providing insights into<br />
how glycan ligands influence the function of this molecule.<br />
This basic observation on siglec-ligand interactions<br />
most likely is recapitulated by other members of<br />
the siglec family.<br />
Fig. 1. Bioengineering of cell-surface glycoproteins to carry 9-arylazide-sialic<br />
acids for in situ photoaffinity cross-linking of CD22 to<br />
its ligands.<br />
Other members of the siglec family differ from CD22<br />
both in cellular distribution and in specificity for recognition<br />
of sialic acid–containing oligosaccharides. We are<br />
evaluating the roles of siglec-7 and siglec-9 in regulation<br />
of human T-cell receptor signaling, the role of siglec-F<br />
in the biology of eosinophils in mice, and the role of<br />
myelin-associated glycoprotein (siglec-4) in regulation<br />
of neurite formation. We recently developed a novel<br />
approach in which a robotically printed glycan array is<br />
used for combinatorial assessment of the effects of sialoside<br />
analogs on the affinity of siglecs. This method<br />
should be a rapid one for developing high-affinity sialoside<br />
probes for each of the siglecs to facilitate investigations<br />
into siglec biology.<br />
REGULATION OF LEUKOCYTE GLYCOSYLATION<br />
Activation of lymphocytes and other leukocytes<br />
induces programmed changes in glycosylation. Such<br />
changes regulate leukocyte trafficking and can modulate<br />
the functions of carbohydrate-binding proteins. We<br />
are systematically investigating the changes in glycosylation<br />
that occur in B and T lymphocytes after activation<br />
in order to elucidate the underlying molecular<br />
mechanisms for these changes and their biological relevance.<br />
To this end, in collaboration with S. Head and<br />
the Consortium for Functional Glycomics (http://www<br />
.functionalglycomics.org), we participated in the development<br />
and use of a custom microarray of glycosyl-
transferase genes, and in collaboration with A. Dell,<br />
Imperial College London, London, England, we correlated<br />
dramatic changes in gene expression with changes<br />
in the glycan profiles of the resting and activated B<br />
and T cells.<br />
PUBLICATIONS<br />
Amado, M., Yan, Q., Comelli, E.M., Collins, B.D. Paulson, J.C. Peanut agglutinin<br />
high phenotype of activated CD8 + T cells results from de novo synthesis of CD45<br />
glycans. J. Biol. Chem. 279:36689, 2004.<br />
Blixt, O., Head, S., Mondala, T., Scanlan, C., Huflejt, M.E., Alvarez, R., Bryan,<br />
M.C., Fazio, F., Calarese, D., Stevens, J., Razi, N., Stevens, D.J., Skehel, J.J.,<br />
van Die, I., Burton, D.R., Wilson, I.A., Cummings, R., Bovin, N., Wong, C-H.,<br />
Paulson, J.C. Printed covalent glycan array for ligand profiling of diverse glycan<br />
binding proteins. Proc. Natl. Acad. Sci. U. S. A. 101:17033, 2004.<br />
Blixt, O., Vasiliu, D., Allin, K., Jacobsen, N., Warnock, D., Razi, N., Paulson, J.C.,<br />
Bernatchez, S., Gilbert, M., Wakarchuk, W. Chemoenzymatic synthesis of 2-azidoethyl-ganglio-oligosaccharides<br />
GD3, GT3, GM2, GD2, GT2, GM1, and GD1a.<br />
Carbohydr. Res. 340:1963, 2005.<br />
Bryan, M.C., Fazio, F., Lee, H.-K., Huang, C.-Y., Chang, A., Best, M.D., Calarese, D.A.,<br />
Blixt, O., Paulson, J.C., Burton, D., Wilson, I.A., Wong, C.-H. Covalent display of<br />
oligosaccharide arrays in microtiter plates. J. Am. Chem. Soc. 126:8640, 2004.<br />
Collins, B.E., Paulson, J.C. Cell surface biology mediated by low affinity multivalent<br />
protein-glycan interactions. Curr. Opin. Chem. Biol. 8:617, 2004.<br />
Goldberg, D., Sutton-Smith, M., Paulson, J.C., Dell, A. Automatic annotation of<br />
matrix-assisted laser desorption/ionization N-glycan spectra. Proteomics 5:865, 2005.<br />
Han, S., Collins, B.E., Bengtson, P., Paulson, J.C. Homomultimeric complexes of CD22<br />
in B cells revealed by protein-glycan cross-linking. Nat. Chem. Biol. 1:93, 2005.<br />
Ikehara, Y., Ikehara, S.K., Paulson, J.C. Negative regulation of T cell receptor signaling<br />
by Siglec-7 (p70/AIRM) and Siglec-9. J. Biol. Chem. 279:43117, 2004.<br />
Kitazume, S., Nakagawa, K., Oka, R., Tachida, Y., Ogawa, K., Luo, Y., Citron, M.,<br />
Shitara, H., Taya, C., Yonekawa, H., Paulson, J.C., Miyoshi, E., Taniguchi, N.,<br />
Hashimoto, Y. In vivo cleavage of α2,6-sialyltransferase by Alzheimer’s β-secretase.<br />
J. Biol. Chem. 280:8589, 2005.<br />
Vyas, A.A., Blixt, O., Paulson, J.C., Schnaar, R.L. Potent glycan inhibitors of<br />
myelin-associated glycoprotein enhance axon outgrowth in vitro. J. Biol. Chem.<br />
280:16305, 2005.<br />
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.<br />
MOLECULAR BIOLOGY 2005 237
Published by TSRI Press ®. ©Copyright 2005,<br />
<strong>The</strong> <strong>Scripps</strong> <strong>Research</strong> <strong>Institute</strong>. All rights reserved.