Plenarvorträge - DPG-Tagungen

Symposium Life Sciences on the Nanometer Scale - Physics Meets Biology Donnerstag
of loading rate-dependent behaviour were identified. A thermal off-rate
koff = (1.2 ± 1.0) × 10 −3 s −1 was derived from the lower loading rate
regime for all DNA fragments. In the upper loading rate regime, however,
these fragments exhibited distinct differences which are attributed
to sequence specific details of the binding mechanism.
SYLS 4.3 Do 10:15 H 37
Fast Folding Dynamics of α-Helical Peptides — •Martin Volk,
Angela Pozo Ramajo, Edmund Leary, and Sarah A. Petty —
Department of Chemistry, University of Liverpool, UK
The dynamics of secondary structure formation, which is generally believed
to be the first phase of protein folding, has attracted much attention
recently, particularly since the application of the temperature jump
technique. Using nanosecond lasers, a sudden temperature increase is
induced; the ensuing (un)folding can then be observed by suitable timeresolved
methods, such as IR-spectroscopy. Previous studies on α-helical
model peptides investigated alanine-based peptides containing a repeat
motif of the type -(AAAXA)n- (X: hydrophilic amino acid, n = 2-4),
which show helix-coil relaxation on the time scale of 150-300 ns.
Here, we report results on longer and more complex helical peptides.
We found that the helix-coil relaxation in Poly-N 5 -(3-hydroxypropyl)-Lglutamine
(DP 230) occurs on the same time scale as in alanine-based
peptides, in spite of the peptide length and the complex and bulky side
chain. On the other hand, the helix-coil relaxation in the random copolymer
Poly(Ala, Lys, Glu, Tyr) 6:5:2:1 (DP 180) is much more complex. At
high concentrations, it occurs on the µs-time scale and seems to be limited
by strong interpeptide interactions of the abundant charged residues,
whereas at lower concentrations it shows major deviations from monoexponentiality
due to sequence heterogeneity.
SYLS 4.4 Do 10:30 H 37
Photomodulation of conformational states — •Christian
Renner, Alexander Milbradt, Markus Schütt, Raymond
Behrend, Simone Krupka, Eva-Karthin Sinner, Ciara
Cabrele, and Luis Moroder — Max-Planck-Institut für Biochemie
Every living cell, be it bacterial or human, contains a variety of proteins
that turn the static information encoded in the genes into the densely
packed activity of life. Although protein functions are built on well-known
fundamental physical laws the sheer complexity of such macromolecules
due to their size and variability renders experimental as well as theoretical
investigations a difficult challenge. A productive and helpful approach
has been the reduction to simpler albeit artificial model systems. We
have constructed peptide models that combine small functional protein
fragments of a few amino acid residues with a light-switch allowing for
photomodulation of properties like spatial structure, redox potential or
affinity for ligands. The light induced changes could be exploited for a
limited photo-control of peptide structure (1), protein binding (2) and
oxidative protein refolding (3). The consequences observed upon applying
well-defined changes to the system through the photoisomerization
process should allow for a better understanding of the functional protein
parts that are contained in our model systems.
(1) Biopolymers 63 (2002), 382-393.; (2) Angew. Chem. Int. Ed. 41
(2002), 289-292.; (3) Chem. Biol. 10, 487-490.
SYLS 4.5 Do 10:45 H 37
Electro-Manipulation of Oligonucleotides Tethered to Au-
Surfaces — •Ulrich Rant 1 , Kenji Arinaga 1,2 , Shozo Fujita 2 ,
Naoki Yokoyama 2 , Gerhard Abstreiter 1 , and Marc Tornow 1
— 1 Walter Schottky Institut, Technische Universitaet Muenchen,
85748 Garching, Germany — 2 Fujitsu Laboratories Ltd., 10-1
Morinosato-Wakamiya, Atsugi 243-0197, Japan
We present electro-optical investigations of short DNA strands, tethered
to Au-electrodes in aqueous solutions. By controlling the bias potential
at the supporting electrodes, we are able to study multiple phenomena
related to electrostatic interactions between polyelectrolytes and
metal interfaces in electrolyte environment:
DNA-desorption at highly negative electrode potentials can be utilized
to study the electrostatic nature of DNA, revealing a new regime of excessive
counterion condensation in solutions of high salt concentrations.
In contrast, by employing moderate AC-potentials with respect to the
potential of zero charge, we are able to attain persistent conformational
switching with formidable long term stability of the DNA layer on the Au-
surface, alternating the orientation of the strands between a lying‘ and a
’
’ standing‘ state. We elucidate the capability of the presented modulation
experiments to provide information on collective monolayer properties
such as steric interactions between adsorbed molecules, as well as the
possibilities to study molecular dynamics of tethered DNA subjected to
electric fields at the metal/solution interface.
SYLS 5 Symposium ”Life Sciences on the Nanometer Scale - Physics Meets Biology”
Zeit: Donnerstag 11:15–12:30 Raum: H 37
Hauptvortrag SYLS 5.1 Do 11:15 H 37
Mechano-Chemical Coupling in F1-ATPase — •Kazuhiko Kinosita
— Center for Integrative Bioscience, Okazaki National Research
Institutes
The protein F1-ATPase is a rotary motor made of a single molecule.
Its central γ subunit rotates against a surrounding cylinder made of α3β3
subunits. This rotary motor is powered by sequential ATP hydrolysis in
the three β subunits, and reverse rotation of the motor is expected to
drive ATP synthesis. We have shown, by single-molecule imaging, that
(i) the rotary torque is nearly independent of the rotation angle, (ii) 80-
90 pN nm of mechanical work can be done per ATP hydrolyzed, (iii)
binding of ATP causes ∼90 o rotation, and (iv) release of the last hydrolysis
product causes further ∼30 o rotation. Point ii implies that the
efficiency of chemo-mechanical conversion may reach ∼100 %. Points i-iv
allowed us to infer the angle-dependent potential energies for γ rotation
for each of chemical intermediates that appear during rotation. Details
of the coupling scheme between chemical reactions on the three catalytic
sites and mechanical rotation of the rotor are beginning to unravel.
SYLS 5.2 Do 11:45 H 37
Probing individual F0F1 ATP synthases by multi-parameter
fluorescence spectroscopy — •Michael Prummer 1 , Horst Vogel
1 , Beate Sick 2 , Alois Renn 3 , Gert Zumofen 3 , Urs P. Wild 3 ,
Georg Kaim 4 und Peter Dimroth 4 — 1 Institute of Biomolecular
Sciences, EPFL, CH-1015 Lausanne — 2 DNA-Array Facility, University
of Lausanne, CH-1015 Lausanne — 3 Physical Chemistry Laboratory,
ETH-Hönggerberg, CH-8093 Zürich — 4 Institute of Microbiology, ETH-
Zentrum, CH-8092 Zürich
The rotary motor F0F1 ATP synthase is the universal ATP factory
in most cells from bacteria to plants and animals. The driving force for
ATP production is a trans-membrane potential plus a H + /Na + gradient.
Vice versa, F0F1 can act as an ion pump by consuming ATP and is thus
a completely reversible rotor. We have simultaneously measured several
fluorescence quantities from individual immobilized and functionally coupled
F0F1 rotary motors by single-fluorophore multi-parameter confocal
microscopy. By analyzing these quantities we could monitor the rotation
of F0F1 during ATP synthesis and hydrolysis. We could further correlate
for example the different distributions of the fluorescence lifetime or
the emission spectral ratio with structural and functional features of the
protein.
SYLS 5.3 Do 12:00 H 37
Molecular dynamics simulations of isolated β-subunits of F1-
ATPase — •U. Kleinekathöfer 1 , B. Isralewitz 2 , M. Dittrich 2 ,
and K. Schulten 2 — 1 International University Bremen, 28725 Bremen
— 2 Beckman Institute, University of Illinois, Urbana-Champaign, USA.
The F1 unit of ATPase has three-fold symmetry and consists of three
noncatalytic α and three catalytic β-subunits. The β-subunits furnish
the binding sites where ADP is transformed into ATP. We have investigated
the properties of isolated β-subunits as a step towards explaining
the function of the integral F1 unit. The β-subunits exist in different
conformations at any moment of the F1 unit reaction cycle.
The open conformation of the AlF3-inhibited β-subunit of bovine
ATPase had been equilibrated for about 10 ns and a spontaneous change
in conformation was observed. The change can be decomposed into two
rotations: one around an axis parallel to the pseudo-symmetry axis of F1-
ATPase and one around an axis perpendicular to the first axis . In several
runs the equilibrated subunit was in a conformation about half-way between
the open and the closed conformation. This partially confirms the