Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Freitag
crease, which may occur either by releasing intra-molecular voids or by
contraction of the solvent near the newly exposed protein surface. The
latter involves changes in structure of the protein-solvent network. By
dynamic neutron scattering we probe the pressure evolution of proteinsolvent
bonds. At the unfolding transition, we observe a reduction of the
structural inter-conversion rates and of water fluctuational amplitudes,
related to a compressibility change. This result suggests that stronger
protein-solvent interactions in the unfolded form destabilize the native
state at high pressure. Neutron diffraction experiments reveal a reorganisation
in the hydration shell upon unfolding in parallel with a decrease in
helix content. About 40 intact in the pressure-unfolded state indicative
of a molten globular conformation.
AKB 50.62 Fr 10:30 B
Collective dynamics of lipid membranes studied by inelastic
neutron scattering — •Maikel C. Rheinstädter 1,2 , Christoph
Ollinger 3 , Giovanna Fragneto 1 , and Tim Salditt 3 — 1 Institut
Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble, France — 2 IFF,
FZ-Jülich, 52425 Jülich, Germany — 3 Institut für Röntgenphysik, Georg-
August-Universität Göttingen, Geiststr. 11, 37073 Göttingen, Germany
The collective dynamics of lipid molecules are believed to affect significantly
the physical properties of phospholipid membranes. In the context
of more complex biological membranes, collective molecular motions may
play a significant role for different biological functions [1]. We present a
first time inelastic neutron scattering study on the collective dynamics of
the lipid acyl chains in the model system DMPC -d54. We have measured
the dynamical structure factor S(Qr, ω) in the gel (Lβ) and the fluid (Lα)
phase of the lipid bilayer. The dispersion relation we find is similar to
those found in liquids, with a distinct minimum at Q0, the maximum of
the static structure factor S(Qr), and can be compared to recent Molecular
Dynamics simulations [2]. Furthermore, we investigated the temperature
dependence of the excitations in the minimum in the vicinity of
the main phase transition. Our discussion may shed light on the gel-fluid
phase transition and coexistence of the two phases. By combining neutron
diffraction and inelastic measurements, we gain information about
structure and (collective) dynamics of model membranes on a molecular
length scale. [1] R. Lipowsky and E. Sackmann, Handbook of Biological
Physics, vol. 1, Elsevier (1995); [2] M. Tarek et al., Phys. Rev. Lett. 87,
238101 (2001).
AKB 50.63 Fr 10:30 B
Investigation of the N-terminal domain of LHCII using single
molecule techniques — •Felix Neugart 1 , Sebastian Schuler 1 ,
Carsten Tietz 1 , Jörg Wrachtrup 1 , Stephanie Boggasch 2 , and
Manuel Lion 2 — 1 3. Physikalisches Institut, Universität Stuttgart —
2 Institut für Allgemeine Botanik, Universität Mainz
The light-harvesting complex II (LHCII) is the most abundant
chlorophyll-binding complex in photosynthesis of green plants. The
native LHCII trimer is responsible for the absorption of half the photons
involved in photosynthesis of algae and higher plants.
The structure of the transmembrane part of the protein of the LHCII
is well known (Kühlbrandt et al. 1994, Nature 367, 614-621) whereas the
N-terminal region of the LHCII complex is not resolved and its function,
orientation and dynamic is still under debate.
One possibility to gather information about the motion of the Nterminal
domain is to attach an artificial fluorophor to the N-terminus
and observe the energy transfer to the Chlorophylls of the LHCII. Different
conformations of the N-terminal domain lead to different energy
transfer rates. Hence, the observation of single labeled LHCII-Monomers
in a confocal setup monitors the dynamics of the N-terminal region and
reveal subensembles of different conformations.
AKB 50.64 Fr 10:30 B
Continuum theory of filamental self-organization —
•Alexander Zumdieck, Karsten Kruse, and Frank Jülicher
— Max-Planck-Institut für Physik komplexer Systeme
The cytoskeleton is a dynamic complex network of protein filaments
which is involved in many active cellular processes. The polymerization
and depolymerization of filaments as well as the interaction with other
proteins such as molecular motors induce mechanical stresses and dynamic
processes in these structures.Linear filament bundles are important
substructures of the cytoskeleton.
We discuss a general continuum description of the dynamics of such
active networks[1] and focus on one-dimensional bundle geometries. We
show that polymerization and depolymerization play a key role for the
dynamic properties of a bundle, they for example introduce a new length
scale in the system which governs instabilities leading to inhomogenous
states. We relate this continuum theory to a more microscopic description
of active filament systems and show that de-/polymerization could play
a similar role as motors for bundle dynamics. The continuum description
can also be applied to higher dimensional filament geometries that are
for example relevant to the formation of filament rings on cell surfaces.
[1] K. Kruse, A. Zumdieck and F. Jülicher, Europhys. Lett. 64, 716
(2003)
AKB 50.65 Fr 10:30 B
Spontaneous Oscillations by hair bundles from the vertebrate
inner ear — •Björn Nadrowski 1 , Pascal Martin 2 , and Frank
Jülicher 1 — 1 Max-Planck-Institut für Physik komplexer Systeme,
Nöthnitzer Straße 38, D-01187 Dresden, Germany — 2 Laboratoire
Physico-Chimie Curie, Unité Mixte de Recherche 168, Institut Curie, 26
rue d’Ulm, F-75248 Paris Cedex 05, France
Hearing relies on active filtering to achieve exquisite sensitivity and
sharp frequency selectivity. In a quiet environment, the ears of many
vertebrates emit one to several tones. These spontaneous otoacoustic
emissions, the most striking manifestation of the inner ear’s active process,
must result from self-sustained mechanical oscillations of aural constituents.
As early as 1948, Thomas Gold proposed that the ear contains
an active amplifier, and predicted oto-acoustic emissions for malfunctioning,
i.e. over-amplified ears. It has recently been shown that the
mechanosensitive hair bundles of vestibular cells from the frog ear have
the ability to oscillate spontaneously. This spontaneous oscillation leads
to frequency-selective amplification and nonlinearity in the bundles mechanical
response. We discuss the physical principles behind detection
based on critical oscillation as well as specific mechanisms that can lead
to oscillations and active behaviors by hair bundles. A simple theoretical
description of the hair bundle is presented, and its implications are
studied. The hair bundles non-linear response to mechanical stimuli is
described. We pay special attention to the role of noise in the system.
AKB 50.66 Fr 10:30 B
Structure and Fluctuations of Highly Oriented and Charged
Membranes Under Osmotic Stress. — •Guillaume Brotons, Ulrike
Mennicke, and Tim Salditt — Institut fuer Roentgenphysik,
Universitaet Goettingen
Imposing osmotic pressure to multilamellar membranes is a unique
method for studing lipid bilayer interactions [1]. We have extended this
approach to charged lamellar phases oriented on flat solid support, which
are then probed by interface sensitive X-ray scattering. In this first study
we used the anionic phospholipid POPS [2] and synthetic cationic surfactant
DDABr [3], at controlled osmotic stress corresponding to water
layer thicknesses in the range of a few water molecules up to more than
15 times the bilayer thickness. High-pressures (deshydrated) are obtained
by controlled water vapour, while lower pressures (full hydration) are imposed
by direct contact with a polyelectrolyte solution of same sign as
the lamellar phase under investigation. Under these conditions, specular
and non-specular reflectivity can be carried out within the different symmetry
axes of the oriented membranes (Fig.1) which opens new routes
for establishing the Equations Of State (Pressure-Distance diagram) of
bio-molecular assemblies and studing bilayer undulations or compressibility
fluctuations as a function of pressure. [1] Parsegian,V.A. et all,
Methods in Enzymology; Academic-Press 1986; Vol.127. [2] Mennicke,U.,
PhD-Dissertation, Göttingen-Universität, 08/2003. [3] Brotons,G. et all,
Langmuir 2003, 19, 8235-8244.
AKB 50.67 Fr 10:30 B
X-ray and neutron reflectivity analysis of peptide-lipid model
systems — •Chenghao Li und Tim Salditt — Institut fuer Roentgenphysik,
Universitaet Goettingen
Using x-ray and neutron reflectivity, we have investigated the structure
of solid-supported, multilamellar lipid membranes with and without
membrane active, antimicrobial peptides. To analyse the measured
reflectivity curve we fit the curves to a model bilayer profile
of adjustable resolution and deduce detailed structural parameters
of the bilayers on an absolute scale of the scattering length
density. The model is implemented in the framework of a semikinematical
scattering theory. We have analysed reflectivity curves
for lipids POPC (1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine),
DMPC (1,2-Dimyristoyl-sn-Glycero-3-Phosphatidylcholin, mixture of
POPC/POPS (1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine]) )