Plenarvorträge - DPG-Tagungen

Symposium Life Sciences on the Nanometer Scale - Physics Meets Biology Mittwoch
SYLS 3.42 Mi 16:00 B
Diffusion in live cells: A combined optical sectioning and single
particle tracking approach — •Ralf Bausinger 1 , Christoph
Bräuchle 1 , Sabine Boeckle 2 , Katharina von Gersdorff 2 ,
Ernst Wagner 2 , and Andreas Zumbusch 1 — 1 Department Chemie -
LMU München - Butenandtstr. 5-13 - D-81377 München — 2 Department
Pharmazie - LMU München - Butenandtstr. 5-13 - D-81377 München
Single particle tracking methods with sensitivities down to the single
molecule detection limit have become important tools for the study of
diffusion processes. For their application to studies of trafficking in live
cells, the trajectories have to be analyzed in the context of the complex
cellular structures. In order to visualize these structures in three dimensions,
confocal fluorescence microscopy is commonly applied because of
its high axial resolution. This raster scanning method however contradicts
the simultaneous usage of wide-field microscopy usually employed
for particle tracking. Classical wide-field microscopy in turn does not offer
sufficient axial resolution in order to reconstruct the three dimensional
image of the cell.
For this reason we use structured wide-field illumination in order to
achieve high axial resolution. Like this, fast switching between high resolution
cellular imaging and tracking with single molecule sensitivity becomes
possible. The application of this setup to studies of artificial virus
diffusion in live cells is demonstrated.
SYLS 3.43 Mi 16:00 B
Investigating structure and function of single citrate transport
proteins — •Michael Prummer 1 , Horst Vogel 1 , Beate Sick 2 ,
Alois Renn 3 , Urs P. Wild 3 , Christopher N. Kästner 4 , and Peter
Dimroth 4 — 1 Institute of Biomolecular Sciences, EPFL, CH-1015
Lausanne — 2 DNA-Array Facility, University of Lausanne, CH-1015 Lausanne
— 3 Physical Chemistry Laboratory, ETH-Hönggerberg, CH-8093
Zürich — 4 Institute of Microbiology, ETH-Zentrum, CH-8092 Zürich
We have utilized fluorescence quenching to study functional conformational
changes in single membrane transport proteins upon substrate
binding. The fluorescence of a fluorophore, specifically attached to the citrate
carrier CitS, was completely quenched upon addition of citrate, but
not DL-isocitrate. After exclusion of other possible reasons we attribute
the quenching to conformational changes of CitS in the citrate transport
cycle. Many membrane proteins are thought to obtain their functional
state upon dimerization. To test the hypothesis in a very direct way,
whether or not also CitS occurs as a dimer, we conducted a dual-color
colocalization experiment and found strong evidence for a homo-dimeric
arrangement of CitS.
SYLS 3.44 Mi 16:00 B
Single-molecule microscopy of the rotary motor F0F1 ATP
synthase at work — •Michael Prummer 1 , Horst Vogel 1 ,
Beate Sick 2 , Alois Renn 3 , Gert Zumofen 3 , Urs P. Wild 3 ,
Georg Kaim 4 , and Peter Dimroth 4 — 1 Institute of Biomolecular
Sciences, EPFL, CH-1015 Lausanne — 2 DNA-Array Facility, University
of Lausanne, CH-1015 Lausanne — 3 Physical Chemistry Laboratory,
ETH-Hönggerberg, CH-8093 Zürich — 4 Institute of Microbiology,
ETH-Zentrum, CH-8092 Zürich
The universal ATP factory F0F1 ATP synthase is the smallest rotary
motor in nature. The driving force for rotation during ATP production
is a trans-membrane potential together with a H + /Na + gradient. Vice
versa, F0F1 can act as an ion pump by consuming ATP and is thus a
completely reversible rotor. We have investigated the rotation of individual
immobilized and functionally coupled F0F1 rotary motors during ATP
synthesis and hydrolysis by single-fluorophore multi-parameter confocal
microscopy. Simultaneously, a number of parameters have been recorded,
like the emission polarization, the fluorescence lifetime, the anisotropy decay
time, and the spectral relaxation time. These fluorescence quantities
can be correlated with structural and functional features of the protein
being part of the nano-environment of the fluorophore.
SYLS 3.45 Mi 16:00 B
Optical Tweezers: A Single Molecule Biosensor for molecular
DNA manipulation and detection of individual receptors on
cells — •A. Sischka 1 , K. Toensing 1 , A. Grabbe 2 , K. Leffhalm 1 ,
R. Eckel 1 , S.D. Wilking 3 , N. Sewald 3 , J. Wienands 2 , R. Ros 1 ,
and D. Anselmetti 1 — 1 Experimental Biophysics and Applied
Nanosciences, Faculty of Physics, Bielefeld University, Germany —
2 Organic and Bioorganic Chemistry, Faculty of Chemistry, Bielefeld
University, 33615 Bielefeld, Germany — 3 Biochemistry, Faculty of
Chemistry, Bielefeld University, 33615 Bielefeld, Germany
We used a compact, single beam optical tweezers system to investigate
mechanical properties of double stranded DNA in the presence of different
binding ligands. Individual binding modes could be distinguished by
analyzing the mechanic response of a lambda-DNA molecule to an applied
external force. We compared the effects of the minor groove binder
distamycin-A, a major groove binding a-helical peptide, the intercalators
ethidium bromide, YO-1 and daunomycin as well as the bisintercalator
YOYO-1 on lambda-DNA.
Significant force hysteresis effects occurring during stretching/relaxation
cycles with velocities in the range between 100 nm/s
and 12,000 nm/s were found for daunomycin and YOYO-1. These time
dependent mechanical properties were found to directly reflect the
kinetics of the binding and unbinding behaviour.
Futhermore, specific interactions and rupture force properties of an
antibody against a receptor on a living chicken-B-cell were successfully
measured.
SYLS 3.46 Mi 16:00 B
Modulation of protein exchange by the physicochemical characteristics
of copolymer substrates — •Tilo Pompe, Lars Renner,
Katrin Salchert, and Carsten Werner — Institut für Polymerforschung
Dresden e.V. & Max-Bergmann-Zentrum für Biomaterialien
Dresden
The kinetics of adsorption, desorption, and exchange of the proteins
fibronectin and human serum albumin were studied in their dependency
on the physicochemical surface characteristics of different maleic anhydride
copolymer films. The analysis of the kinetics indicates two kinds
of populations - a fast desorbing species and a species with a slow exchange
rate. By a multivariate regression analysis the variation of the
surface energy of the substrate was identified as an important parameter
for the description of the desorption and exchange characteristics. The
exchange was further shown to depend significantly on the kind of the
pre-adsorbed protein and the protein competing for adsorption sites in
a size dependent manner related to the diffusion constant and the area
of exclusion on the surface. A higher exchange efficiency is observed for
fibronectin on hydrophobic and for human serum albumin on hydrophilic
surfaces.
SYLS 3.47 Mi 16:00 B
Influence of water on the mechanical properties of wood —
•Ingo Grotkopp 1 , Klaas Kölln 1 , Sergio S. Funari 2 , Martin
Dommach 2 , and Martin Müller 1 — 1 IEAP, Uni Kiel, 24098 Kiel —
2 MPIKG Golm c/o HASYLAB, Hamburg
The unique mechanical properties of the biological material wood
strongly depend on the water content. Water is not only present in the
lumina of the wood cells but is adsorbed to the cell walls. These are a
composite of nanocrystalline cellulose microfibrils embedded in a disordered
matrix. We investigated dry and wet wood using X–ray diffraction
techniques using synchrotron radiation. Tensile tests were carried out in
situ. The changes in the fibre diffraction diagrams upon stretching enable
us to conclude on the microscopic mechanisms responsible for the dependence
of wood properties on water content. Implications for the use of
wood as a biomaterial in trees (wet) and construction material (variable
moisture content) are discussed.
SYLS 3.48 Mi 16:00 B
Exact Enumeration of 3D Lattice Proteins — •Reinhard Schiemann,
Michael Bachmann, and Wolfhard Janke — Institut für
Theoretische Physik, Universität Leipzig, Augustusplatz 10/11, 04109
Leipzig (Germany)
We investigate the properties of native, i.e. non–degenerate, ground
states of lattice proteins in the HP model[1] on the three–dimensional
simple cubic lattice. In order to do so, the complete sets of sequences
and conformations were enumerated exhaustively for chains of up to 19
monomers. The identification of native ground states was accelerated by