Issue 10 Volume 41 May 16, 2003

across membranes separating the interior of the cell from the environment, capture and utilization of energy, and transduction
of environmental signals, is a key question in protobiological evolution. On the basis of detailed, molecular-level computer
simulations we investigate how these peptides insert into membranes, self-assemble into higher-order structures and acquire
functions. We have studied the insertion of an a-helical peptide containing leucine (L) and serine (S) of the form (LSLLLSL)S
into a model membrane. The transmembrane state is metastable, and approximately 15 kcal/mol is required to insert the
peptide into the membrane. Investigations of dimers formed by (LSLLLSL)S and glycophorin A demonstrate how the
favorable free energy of helix association can offset the unfavorable free energy of insertion, leading to self- assembly of
peptide helices in the membrane. An example of a self-assembled structure is the tetrameric transmembrane pore of the
influenza virus M2 protein, which is an efficient and selective voltage-gated proton channel. Our simulations explain the gating
mechanism and provide guidelines how to reengineering the channel to act as a simple proton pump. In general, emergence
of integral membrane proteins appears to be quite feasible and may be easier to envision than the emergence of water-soluble
proteins.
Author
Biological Evolution; Peptides; Membranes; Ions; Transferring; Organic Materials; Cells (Biology); Protobiology
20030032467 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Optimal Extraction with Sub-sampled Line-Spread Functions
Collins, Nicholas R.; Gull, Theodore; Bowers, Chuck; Lindler, Don; [2002]; 4 pp.; In English; Hubble Space Telescope
Workshop, 17-18 Oct. 2002, Baltimore, MD, USA; Copyright; Avail: CASI; A01, Hardcopy
STIS long-slit medium resolution spectra reduced in CALSTIS extended-source mode with narrow extraction heights
(GWIDTH=3 pixels) show photometric uncertainties of +/- 3\% relative to point-source extractions. These uncertainties are
introduced through interpolation in the spectral image rectification processing stage, and are correlated with the number of
pixel crossings the spectral profile core encounters in the spatial direction. The line-spread-function may be determined as a
function of pixel crossing- position from calibration data sub-sampled in the spatial direction. This line spread function will
be applied to science data to perform optimal extractions and point- source de-blending. Wavelength and breathing effects will
be studied. Viability of the method to de-convolve extended source ‘blobs’ will be investigated.
Author
Image Processing; Spectral Resolution; Line Spectra; Image Analysis; Astronomical Photometry; Data Processing; Computer
Programs
20030032964 Oxford Univ., Oxford
ICA-Based Segmentation of the Brain on Perfusion Data
Tasciyan, T. A.; Beckmann, C. F.; Morris, E. D.; Smith, S. M.; Oct 2001; 5 pp.; In English; Original contains color illustrations
Report No.(s): AD-A410449; No Copyright; Avail: CASI; A01, Hardcopy
An Independent Component Analysis (ICA) based segmentation technique is presented allowing the quantitative
assessment of cerebral blood volume (CBV), cerebral blood flow (CBF) and mean transit time (MTT) from dynamic
susceptibility contrast magnetic resonance (MR) images of the brain. Tissue types such as gray matter (GM), white matter
(WM), and pathology appear as different ICA components as a result of their distinct temporal response to the first passage
of contrast agent through the brain. The average CBV, CBF, and MTT values calculated for each component/tissue type could
help evaluate the evolution of pathology and provide the opportunity for intersubject comparisons.
DTIC
Image Processing; Numerical Analysis
20030033088 Army Engineer Research and Development Center, Vicksburg, MS, USA
Development of a Rapid, Inexpensive Bioassay for Screening Contaminant Bioavailability in Sediment Using mRNA
Profiling
Perkins, Edward; Frederickson, Herbert L.; Lotufo, Gilherme; Dec. 2002; 8 pp.; In English
Report No.(s): AD-A410566; ERDC/TN EEDP-04-34; No Copyright; Avail: CASI; A02, Hardcopy
This technical note describes how the stress responses of common bioassay organisms can be used to identify toxic
contaminants and their bioavailability in sediment. The freshwater non-biting midge, Chironomus tentans, responds to
contaminant exposure by making proteins to detoxify chemicals or repair damage, in addition to other responses. Midges make
new proteins by transcription, or copying, of genes into messenger RNA (mRNA) that are used to make many copies of a
protein. A snapshot of what the midge is sensing and how it is responding can be found by looking at the mRNAs that are
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