09.12.2012 Views

Plenarvorträge - DPG-Tagungen

Plenarvorträge - DPG-Tagungen

Plenarvorträge - DPG-Tagungen

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Arbeitskreis Biologische Physik Freitag<br />

the molecule. Small cantilevers (length: < 30µm, width: < 10µm, thickness:<br />

< 200nm) show all necessary properties for force spectroscopy:<br />

small spring constants, low viscous damping and high resonance frequencies.<br />

We present an AFM that is capable of using small cantilevers for force<br />

spectroscopy experiments of single biomolecules and our current results.<br />

AKB 50.82 Fr 10:30 B<br />

X-ray scattering and microscopy on spider silk fibers — •Anja<br />

Glisovic, Juergen Thieme, Peter Guttmann, and Tim Salditt<br />

— Institut fuer Roentgenphysik, Universitaet Goettingen<br />

We report on the structural characterization of different types of spider<br />

silk. Spider silk is a high performance biomaterial with a unique combination<br />

of elastic properties consisting of only one to two proteins. The<br />

structural basis for these properties on the molecular and mesoscopic<br />

scale of the silk fiber is a matter of intensive scientific debate [1]. We<br />

have used synchrotron based x-ray diffraction as well as x-ray microscopy<br />

to investigate single as well as bundle of fibers. Some technical aspects<br />

(beam collimation, background to noise, analysis of crystalline domains)<br />

and first results of these experiments will be discussed. [1] F. Vollrath,<br />

Knight DP, Nature 410, 541 (2001), and references therein.<br />

AKB 50.83 Fr 10:30 B<br />

Transistor Array probes Release of Vesicles of Chromaffin Cells<br />

— •Janosch Lichtenberger and Peter Fromherz — Membran<br />

and Neurophysics,MPI for Biohemistry<br />

We monitored the release of large dense core vesicles from bovine chromaffin<br />

cells using a linear array of open field effect transistors with a pitch<br />

of 3.6 µm. When secretion was induced by barium, brief spikes in the<br />

transistor current were observed. The events were well localized on the<br />

transistor array with an amplitude of effective gate voltage up to 17 mV.<br />

We assign the events to the local drop of pH in the narrow cleft between<br />

cell and chip that is caused by the release of ATP by individual vesicles.<br />

The pH change affects the threshold of the transistor by proton binding<br />

to the exposed gate oxide. We found good agreement for amplitude,<br />

duration and localization of the signals with the change of the electrical<br />

surface potential that is computed with a model that takes into account<br />

(i) local release of ATP from a vesicle at pH 5.5 into the cleft with an extracellular<br />

buffer at pH 7.2, (ii) diffusion of protons, buffer and ions along<br />

the cleft and (iii) binding of protons to the negatively charged oxide. The<br />

investigation establishes the first chemical neuron-silicon synapse.<br />

AKB 50.84 Fr 10:30 B<br />

Effective pair–potential approach to entangled stiff polymers —<br />

•Sven van Teeffelen, Erwin Frey, and Klaus Kroy — Hahn-<br />

Meitner Institut, Berlin<br />

The entanglement of stiff polymers in solution is remarkably well described<br />

by an effective tube model, in complete analogy to the well–known<br />

blob model for flexible polymers. We extend the scope of this (so far homogeneous)<br />

model to account for spatial density fluctuations by reformulating<br />

it in terms of a microscopically motivated effective pair potential.<br />

This allows us to straightforwardly include additional interactions (depletion,<br />

van der Waals, electrostatic...), and thus turns the model into<br />

a versatile tool for predicting the static structure factor and the equilibrium<br />

phase behavior of stiff polymer solutions. Non–equilibrium (kinetic<br />

arrest) scenarios are also considered. Finally we discuss applications to<br />

biopolymer solutions.<br />

AKB 50.85 Fr 10:30 B<br />

Silicon chip with cultured rat hippocampus slice interfaced with<br />

arrays of capacitors and transistors — •Michael Hutzler and<br />

Peter Fromherz — Max Planck Institute of Biochemistry, Martinsried,<br />

Germany<br />

In the past, field potentials of cultured hippocampal slices evoked by<br />

tungsten electrode stimulation could be recorded by electrolyte-oxidesilicon<br />

field effect transistors. We developed a new silicon chip with a<br />

TiO2-coated surface, containing capacitor arrays for eliciting as well as<br />

transistor arrays for detecting neuronal activity. After cultivating the<br />

brain slices on the silicon chips for one week, we were able to capacitively<br />

stimulate the slices in CA3 by application of defined voltage pulses. The<br />

resulting field potential in CA1 could be recorded with the transistors.<br />

By combining a row of capacitors with a row of transistors we also determined<br />

a simple transfer matrix from CA3 to CA1. This novel type<br />

of purely capacitive interfacing allows a mechanically noninvasive and<br />

electrically minimally interfering contact compared to traditional electrophysiological<br />

methods.<br />

AKB 50.86 Fr 10:30 B<br />

Growth of the Mineral Particles in Bone - Combined Study of<br />

Small Angle X-ray Scattering (SAXS) and Electron Backscattering<br />

(qBEI) — •A. Valenta 1,2 , P. Roschger 2 , B.M. Misof 2 ,<br />

O. Paris 3 , W. Tesch 1,2 , S. Bernstorff 4 , H. Amenitsch 5 , K.<br />

Klaushofer 2 , and P. Fratzl 3 — 1 Erich Schmid Inst. of Material Science,<br />

Austrian Academy of Sciences and Inst. of Metal Physics, University<br />

of Leoben, Leoben, Austria — 2 L. Boltzmann Inst. of Osteology,<br />

4th Med. Dept., Hanusch Hospital & UKH-Meidling, Vienna, Austria<br />

— 3 Max Planck Inst. of Colloids and Interfaces, Dept. of Biomaterials,<br />

Potsdam, Germany — 4 Sincrotrone Trieste S.C.p.A., Basovizza, Trieste,<br />

Italy — 5 IBR, Austrian Academy of Sciences, Graz, Austria<br />

Bone is a nanofiber composite formed by mineralized collagen fibrils.<br />

In this study bone areas from human biopsies with different degree of<br />

mineralization were investigated. The mineral volume fraction (φ) was<br />

assessed by qBEI, and then the particle surface per volume (σ) was determined<br />

by scanning-SAXS using a micro focus (20 micron) synchrotron<br />

x-ray beam. A biphasic correlation between φ and σ was found: In the<br />

φ-range of 0-27 vol% mineral σ showed a monotone increase, whereas<br />

in the range of 27-40 vol% σ remained constant. This finding suggests,<br />

that after nucleation, mineralization proceeds by a rapid predominant-<br />

2-dimensional growth of the mineral particles, followed by a slow increase<br />

in thickness.<br />

AKB 50.87 Fr 10:30 B<br />

SARS membrane protein E in model membranes: structural<br />

— •Ziad Khattari 1 , Guillaume Brotons 1 , Tim Salditt 1 , and<br />

Shy Arkin 2 — 1 Institut fuer Roentgenphysik, Universitaet Goettingen,<br />

Goettingen — 2 Department of Biological Chemistry, Hebrew University,<br />

Jerusalm<br />

We present a structural investigation of the SARS membrane protein<br />

E in model membranes by x-ray reflectivity. After the recent publication<br />

of the SARS coronavirus genome [1], structural characterization of its<br />

membrane active proteins is of great importance. The SARS membrane<br />

protein E is believed to be a viral ion channel, but it may also exhibit<br />

fusiogenic functions. The structure and interaction of the membrane active<br />

part of the protein is therefore investigated in model membranes.<br />

Using x-ray reflectivity on highly aligned stacks of membranes on silicon<br />

surfaces in the fluid La phase [2,3], we can determine the electron<br />

density profile of the lipid bilayer as a function of peptide-lipid (P/L)<br />

ratio. Structural properties of the peptide can be determined, as well as<br />

changes in lipid bilayer properties as a function of protein concentration<br />

may be assessed, ranging from bilayer thickness to acyl chain ordering<br />

and head-group hydration. In addition we use site-specific iodination as<br />

a marker in the density profile. Measurements have been performed at<br />

the D4 bending magnet station of HASYLAB/DESY. The results are<br />

complemented by spatial restraints from FTIR spectroscopy on samples<br />

containing site-specific isotopic labels (peptidic 13C=18O). [1] Marra et<br />

al. Science 300, 1399 (2003). [2] T. Salditt et al, Eur. Phys. J. E 7, 105<br />

(2002). [3] Li, C. et al, accepted in J. Phys. D.<br />

AKB 50.88 Fr 10:30 B<br />

Dynamics of Lipid and Protein Domains in Biomembranes<br />

— •Karin John and Markus Bär — Max-Planck-Institute für die<br />

Physik komplexer Systeme, Nöthnitzer Strasse 38, D-01187 Dresden<br />

Acidic lipids such as PIP2 and PIP3 are thought to elicit localized responses,<br />

e.g. for remodeling the cytoskeleton in response to external stimuli.<br />

We consider a mechanism that accounts for a nonrandom distribution<br />

of acidic lipids in the plasma membrane: electrostatic sequestration by<br />

basic proteins such as GMC (MARCKS, CAP23, GAP43) proteins. Our<br />

strategy is to incorporate the different properties of GMC proteins into<br />

a reaction-diffusion model:<br />

1. GMC proteins are cytosolic proteins. Membrane association depends<br />

on a basic effector domain, which interacts with acidic lipids in the membrane<br />

and can lead to the formation of domains enriched in acidic lipids<br />

and GMC.<br />

2. GMC proteins are probably integrators of PKC and Ca 2+ signalling<br />

pathways. Upon phosphorylation of residues within the basic effector domain<br />

by a protein kinase C or interaction with Ca ++ /calmodulin GMC<br />

proteins translocate from the membrane into the cytosol. Upon dephosphorylation<br />

or a decrease in cytosolic Ca ++ GMC proteins reassociates<br />

with the membrane. This cycle is called myristoyl-electrostatic switch

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!