Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Freitag
AKB 50.95 Fr 10:30 B
Global pattern formation from local cell-to-cell communication
— •Thimo Rohlf and Stefan Bornholdt — IZBI, University of
Leipzig, Kreuzstr. 7b, 04103 Leipzig, Germany
A central observation in developmental biology is the self-organization
of spatial gene expression patterns on scales much larger than cell size. In
existing models, this is often explained by morphogen gradients, which
are established by Turing instability of activator-inhibitor systems [1].
However, pattern formation in these models depends on parameter tuning
of, e.g., diffusion constants. The role of gene regulation in development
is neglected. Here we sketch a new process of global pattern formation
from local information transfer without the need for parameter tuning.
We study a three-state cellular automaton which reproduces two basic
experimental observations at the polyp Hydra: de novo pattern regeneration
and regulation of expression domain size proportional to system
size.
The model shows remarkable robustness with respect to noise and cell
movement. Similar mechanisms could in principle occur in biological organisms
where direct contact induction is present.
[1] Gierer, A. and Meinhardt, H., Kybernetik 12, 30 (1972)
AKB 50.96 Fr 10:30 B
A biological solar energy generator — •Dieter F. Ihrig 1 , H.
Michael Heise 2 , Alexander Moor 2 , Manuel Gemuend 1 , Darius
Wilczek 1 , Ruediger Kuckuk 2 , and Martin Poschmann 1 —
1 FH Suedwestfalen Iserlohn, Germany — 2 Institut fuer Spektrochemie
und angewandte Spektrometrie, Dortmund, Germany
Biomass production by micro algae is by a factor of 10 more efficient
then plants. This gives the chance to create an economic process of solar
energy harvesting. In view of the very low dry mass content of algal
suspensions the most promising way of conversion to a high exoergic and
transportable form of energy is the anearobic production of biogas.
We are actually developing such processes especially micro algal reactors,
a method to separate micro algal cells, a method to treat the micro
algal biomass and a two stage anaerobic process. First results of these
project sections are shown. The developed anaerobic process is very efficient
but also very unstable. To get a better process management it is
necessary to understand the influences between the parameters of process
engineering and biochemical parameters like the concentration of
carboxylic acids. Goal of this part of the project is the development of
an inline sensor. The project was funded by the German Federal Ministry
for Education and Research (BMBF).
AKB 50.97 Fr 10:30 B
FCS used to study translational mobilities in plasma membranes
of living cells — •Margarita Khazarchyan 1 , Elmar
Thews 1 , Carsten Tietz 1 , Jörg Wrachtrup 1 , Sylvia Willi 2 ,
Anja Krippner-Heidenreich 2 , and Peter Scheurich 2 —
1 3.Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring
57, 70569 Stuttgart — 2 Institut für Zellbiologie und Immunologie,
Universität Stuttgart, Allmandring 31, 70569 Stuttgart
Fluorescence correlation spectroscopy (FCS) is an attractivce method
of measuring molecular concentrations, chemical kinetics and diffusion
processes in living cells. We use one- and two-photon excitation for the
investigation of translational mobility in cytoplasm and in plasma membranes
using different fluorophores for intracellular applications of FCS.
Measurements in living cells and in plasma membranes are feasible with
reasonable signal-to-noise ratios, even with fluorophore concentrations on
a single molecule level in the detection volume.
We present an application of this method to study TNF(Tumor Necrosis
Factor)-R1, TNF-R2 in plasma membranes and TRAF2-protein in
cytoplasm of living cells. Other investigations demonstrated that TNF-R
and TRAF-proteins involved in the cells apoptotic pathway. Apoptosis is
the specific controlled mechanism of cell death which is distinct from uncontrolled
necrotic cell death. Apoptosis requires tight regulation. Lack of
such regulation leads to either too much or too little apoptosis, resulting
in pathological conseqeunces, such as Alzheimer disease or cancer.
Diffusion coefficients of the signal TNF-R and TRAF2-protein were
determined before and after stimulation with TNF ligand.
AKB 50.98 Fr 10:30 B
Stepwise rotation of the epsilon-subunit of EFoF1-ATP synthase
during ATP synthesis and hydrolysis - a single-molecule
FRET approach — •Michael Börsch 1 , Boris Zimmermann 2 ,
Nawid Zarrabi 1 , Manuel Diez 2 , and Peter Gräber 2 —
1 3. Physikalisches Institut, Universität Stuttgart — 2 Institut für
Physikalische Chemie, Universität Freiburg
F-type ATP synthases catalyze the formation of ATP by coupling
two rotary motions of subunits within the enzyme. We attached
tetramethylrhodamine-maleimide at the rotating epsilon-subunit and
Cy5-bismaleimide crosslinking the two b-subunits, and reconstituted the
enzymes fully functional into liposomes. Fluorescence resonance energy
transfer (FRET) was monitored in photon bursts of freely diffusing ATP
synthases with a confocal setup for single-molecule detection. Incubation
with non-hydrolysable AMPPNP resulted in stable intensity ratios
within a burst and three different FRET efficiencies corresponding to
the three possible orientations of the epsilon-subunit.
Upon addition of ATP at mM concentrations, a consecutive order of
three distinguishable FRET efficiencies was observed indicating a stepwise
movement of the epsilon-subunit, comparable to the stepwise rotation
of the gamma-subunit in EFoF1 [1,2]. Under the conditions for ATP
synthesis stepwise rotation of the epsilon-subunit was observed in opposite
direction. Dwell-time analysis revealed heterogeneity of the three
catalytic binding sites.
[1] M. Borsch et al. (2002) FEBS lett. 527, 147-152.
[2] M. Diez et al. (2004) Nat. Struct. Mol. Biol., in press.
AKB 50.99 Fr 10:30 B
DNA translocation through a biological nanopore — •Ulrich F.
Keyser 1 , N. Wennersbusch 1 , D. J. Bonthuis 1 , N. H. Dekker 1 ,
X. S. Ling 2 , and Cees Dekker 1 — 1 Molecular Biophysics, Delft University
of Technology, Lorentzweg , 2628 CJ Delft, The Netherlands1 —
2 Brown University, Providence, USA
We study the translocation of single-stranded DNA (ss-DNA)
molecules through a single biological nanopore, viz., an alpha-Hemolysin
pore from Staphylococcus aureus assembled within a lipid membrane.
The inner diameter of this nanopore is only 1.5 nm and ss-DNA molecules
can be transferred one by one. Applying a bias voltage at high salt concentrations
gives rise to an ionic current through the nanopore. If a ss-DNA
molecule enters the pore the current is partly blocked and the passage
of a molecule is detected. We are investigating different types of ss-DNA
with various lengths and sequences to study the influence on the translocation
speed and current. The experimental results will be compared to
recent theoretical models.
AKB 50.100 Fr 10:30 B
Immobilisation of the Light harvesting complex LH1 of
Rhodospirillum rubrum on nanostructured surfaces — •Britta
Götze, Carsten Tietz, and Jörg Wrachtrup — 3. Physikalisches
Institut, Universität Stuttgart, Germany
Sunlight is the driving force on this planet. To make it useable plants
and bacteria have created a sofisticated system- the photosynthetic apparatus
-.The final product of this system is ATP - the most common
transporter of energy in every living thing.
The first step in this apparatus is to capture sunlight as excitation
energy and transfer it to the reaction center. Here a charge seperation
takes place as a initializing step in photosynthesis.
In this work the light harvesting complex LH1, a pigment protein complex
of the purple bacterium Rhodospirillum rubrum is investigated. The
studies have been performed on nanostructured as well as on modified
surfaces. The aim of this work is to investigate the possibility of long
range 1d energy transfer between light harvesting complexes on nanostructured
surfaces.
The structures are made using electron beam lithography and consist
of gold/titanium on SiO2. A self assembled monolayer is formed on top
of them using different types of mercaptanes.
First step was to figure out what kind of mercaptane offers the best adsorbance
properties for the light harvesting complexes./par Second step
was to proof a specific binding / adsorbance of the proteins on the modified
surface./par Third step will be to get a densly package of proteins
on these structures.