Plenarvorträge - DPG-Tagungen

Symposium Life Sciences on the Nanometer Scale - Physics Meets Biology Mittwoch
Fachsitzungen
– Haupt-, Kurzvorträge und Posterbeiträge –
SYLS 1 Symposium ”Life Sciences on the Nanometer Scale - Physics Meets Biology”
Zeit: Mittwoch 14:00–15:00 Raum: H 37
Hauptvortrag SYLS 1.1 Mi 14:00 H 37
Aquaporin Proteins: Perfect filters — •Helmut Grubmüller and
Bert L. de Groot — Theoretische und computergestützte Biophysik
MPI für biophysikalische Chemie, 37075 Göttingen
Aquaporins are highly selective water channels. Molecular dynamics
simulations of water permeation correctly predict the permeation rate,
explain why these channels are so efficient, and suggest that protons are
blocked by an electrostatic barrier.
Hauptvortrag SYLS 1.2 Mi 14:30 H 37
Single-Molecule Cellular Signaling — •Thomas Schmidt —
Physics of Life Processes, Leiden Institute of Physics, Leiden University
Recent studies showed that several types of membrane microdomains
are involved in H-Ras signal transduction. However, our knowledge about
the in vivo dynamics of these domains is still in its infancy. In this study,
the effect of plasma membrane organization on the activation of the small
GTPase H-Ras was studied by single-molecule fluorescence microscopy.
Diffusion analysis revealed a major, fast diffusing population and a minor,
slow diffusion population for both inactive and active H-Ras. Activation
of H-Ras resulted in a transfer from free diffusion to confinement into
200 nm-sized domains for the minor, slowly diffusing fraction. This is a
first indication for the relevance of membrane ultrastructure on cellular
signalling.
SYLS 2 Symposium ”Life Sciences on the Nanometer Scale - Physics Meets Biology”
Zeit: Mittwoch 15:15–16:00 Raum: H 37
SYLS 2.1 Mi 15:15 H 37
Nucleo-Cytoplasmic Transport of Single Molecules — •Ulrich
Kubitscheck, Andreas Hoekstra, David Grünwald, Jan Peter
Siebrasse, and Reiner Peters — Institute of Medical Physics
and Biophysics, Westfälische Wilhelms-Universität, D-48149 Münster
Understanding the intracellular exchange of matter and information
across the envelopes of cell nuclei presents a central biophysical problem.
Single-molecule microscopy was used to examine the topography and
transport properties of the large pore complexes (NPCs) in the nuclear
envelopes of digitonin-permeabilized cells. The nucleoporins POM121,
Nup358 and Nup153 could be localized along the NPC axis with a precision
of ±25 nm. Binding sites of NTF2 were detected on cytoplasmic
filaments and in the central framework of the NPC. Binding sites of an
import complex containing karyopherin β, however, were localized to the
central framework, and extended up to 200 nm into the nuclear basket.
In order to monitor the interaction of the transport substrates with the
NPC in real-time, we used an electron-multiplying CCD for fast kinetic
measurements. The dwell times of NTF2 and import complex at their
NPC binding sites were determined as 8.2±0.4 and 16±0.6 ms, respectively.
Together with the known transport rates these data suggest that
nucleocytoplasmic transport occurs via multiple parallel pathways within
single NPCs.
SYLS 2.2 Mi 15:30 H 37
Biophysical Applications of Quantum Dots: Labeling of Single
Biomolecules — •Colin D. Heyes 1 , Andrei Yu. Kobitski 1 , Elza
V. Amirgoulova 1 , Vladimir V. Breus 1 , Kirill V. Anikin 1 , and
G. Ulrich Nienhaus 1,2 — 1 Department of Biophysics, University of
Ulm, D - 89069 Ulm, Germany — 2 Department of Physics, University of
Illinois Urbana-Champaign, Urbana, IL 61801, USA
Fluorescent quantum dots (QDs) have several important properties,
which render them extremely useful in ultrasensitive studies of biomolecular
dynamics. They are bright, easily tunable in emission color, can be
chemically modified at the surface to recognize specific biomolecules without
changing the color, and are extremely stable against photobleaching.
We have studied the single particle photophysics, such as fluorescence
blinking and brightness, under various conditions to evaluate their usefulness
in single biomolecular experiments. We then present examples
in which they can be used to evaluate ultrasensitive and long timescale
biophysical processes as well as, or better than, conventional fluorescent
dyes. In the first example, we have studied the lateral diffusion of labeled
lipid molecules. This allows us to track lipid molecules for long periods of
time without significantly affecting the diffusion kinetics, as has been observed
with latex bead tracking. In the second example, we have studied
enzyme-substrate interactions of single enzyme molecules. Both examples
highlight the fact that QDs will continue to increase in importance for
biophysical applications, and the photophysics of such species needs to
be thoroughly understood.
SYLS 2.3 Mi 15:45 H 37
Detection and spectroscopy of 5 nm gold particles using
white-light confocal microscopy — •Patrick Stoller 1 , Klas
Lindfors 2 , Thomas Kalkbrenner 3 , and Vahid Sandoghdar 1 —
1 Physical Chemistry Laboratory; Swiss Federal Institute of Technology
(ETH); CH-8093, Zurich; Switzerland — 2 Department of Physics;
Helsinki University of Technology; P. O. Box 1000; FIN-02015 HUT;
Finland — 3 FOM Institute for Atomic and Molecular Physics (AMOLF);
Kruislaan 407; 1098 SJ Amsterdam; The Netherlands
The interaction of fluorescently labeled biological molecules can be
observed dynamically using optical microscopy. Gold nanoparticles can
also be used to optically label biological molecules because of their welldefined
plasmon resonance spectrum. Gold nanoparticles are biocompatible
and, unlike fluorophores, they do not bleach. To avoid interference
with the molecular interaction, it is important to minimize the size of
the labels. Recently, Boyer et. al. succeeded in detecting 2.5 nm gold
nanoparticles using photothermal imaging [Science. 297. 1160-1163]. In
our work, we used white light confocal microscopy not only to detect but
also to observe the plasmon resonance spectrum of single gold nanoparticles
with diameters as small as 5 nm [submitted]. An ultra-short pulse
laser and a photonic crystal fiber were used to generate a collimated beam
of quasi-continuum white light, which was tightly focused onto the sample
using a high numerical aperture microscope objective; the scattered
light was collected confocally and detected using an imaging spectrometer.
Our goal is to apply this technique to studying the interaction of
biological molecules at the single molecule level.