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Plenarvorträge - DPG-Tagungen

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Symposium Life Sciences on the Nanometer Scale - Physics Meets Biology Mittwoch<br />

SYLS 3 Symposium ”Life Sciences on the Nanometer Scale - Physics Meets Biology”<br />

Zeit: Mittwoch 16:00–18:30 Raum: B<br />

SYLS 3.1 Mi 16:00 B<br />

Accumulation and Replication of DNA driven by temperature<br />

gradients — •Dieter Braun — Emmy Noether Gruppe, Experimentalphysik,<br />

Universitaet Muenchen, Amalienstr. 54, 80799 Muenchen<br />

The influence of temperature gradients on DNA is investigated. For the<br />

first time, the thermophoresis of DNA from hot to cold was measured.<br />

Under conditions which also allow for convection, thermophoresis accumulates<br />

DNA thousandfold into microscopic pots [1]. R. Piazza showed<br />

that thermophoresis of ions such as DNA in water is probably driven and<br />

dominated by a gradient of interfacial tension at the nanoscopic interface<br />

between molecule and water [2].<br />

In a similar geometry, the laminar convection can be used to drive the<br />

DNA amplifying reaction of PCR. Such a laminar convective PCR amplifies<br />

DNA specifically and quantitatively at a speed faster than standard<br />

PCR machines [3].<br />

Both studies of mesoscopic open system far away from thermodynamic<br />

equilibrium revealed new effects. Besides biotechnological applications,<br />

the experiments suggests a convective origin of life in porous rock near<br />

submarine hydrothermal vents [4].<br />

[1] D. Braun and A. Libchaber, PRL 89:188103 (2002)<br />

[2] R. Piazza and A. Guarino, PRL 88:208302 (2002)<br />

[3] D. Braun, N.L. Goddard and A. Libchaber, PRL 91:158103 (2003)<br />

[4] D. Braun and A. Libchaber, Physical Biology, submitted<br />

SYLS 3.2 Mi 16:00 B<br />

Modulation of the Nanoscale-Structure of Fibronectin Fibrils —<br />

•Tilo Pompe — Institut für Polymerforschung Dresden e.V. & Max-<br />

Bergmann-Zentrum für Biomaterialien Dresden<br />

The protein fibronectin is a major component of the extracellular matrix<br />

providing cells with binding sites to the surrounding tissue. The<br />

formation of fibrils from single fibronectin molecules is a complex process<br />

which includes binding of cell receptors, like integrins, conformational<br />

changes of fibronectin by mechanical forces exerted from the cell,<br />

and polymerisation of fibronectin molecules at newly exposed binding<br />

sites. Scanning force microscopy analysis revealed that early stages of<br />

fibronectin fibrillogenesis are controlled by the binding strength of fibronectin<br />

molecules to the underlying polymer substrate. Furthermore,<br />

the nano-structure of the fibrils exhibits characteristic distances between<br />

small fibrils with a distinct periodicity of 73 nm. The periodic spacing<br />

implies a mechanism of the fibrillogenesis process directly related to the<br />

force applied to the protein via the cytoskeleton of the cell.<br />

SYLS 3.3 Mi 16:00 B<br />

Interactions of Thionin with DNA-Strands: Intercalation vs<br />

External Stacking — •Christoph Hecht 1 , Josef Friedrich 1 ,<br />

and Ta-Chau Chang 2 — 1 TU München, Physik-Department E14,<br />

Lehrstuhl für Physik Weihenstephan, 85350 Freising — 2 Institute of<br />

Atomic and Molecular Science, Academia Sinica, Taiwan<br />

The interaction of dye-molecules with DNA-strands plays an important<br />

role in anti-cancer drug research. We investigated the binding modes of<br />

thionin with various structures of short stranded DNA-molecules by measuring<br />

the response of a spectral hole to pressure variations. Thionin binds<br />

through Coulomb-interaction via external stacking to DNA-quadruplex<br />

structures. The binding to DNA-duplex structures, however, is different:<br />

One of the two possible isomers of thionin intercalates into the DNAstrands.<br />

SYLS 3.4 Mi 16:00 B<br />

SINGLE VIRUS TRACING: VISUALIZATION OF THE IN-<br />

FECTION PATHWAY OF A VIRUS INTO A LIVING CELL<br />

— •T. Endreß, S. Mugrauer, A. Zumbusch, and C. Bräuchle<br />

— Department Chemie, Universität München, Butenandtstr. 11, 81377<br />

München, Germany<br />

Viruses play a major role in biology and medicine. A detailed analysis<br />

of the different steps of a viral infection is not only necessary to understand<br />

viral biology, but also for the development of efficient antiviral<br />

drugs and save viral gene therapy vectors. Single Virus Tracing allows<br />

visualization of the infection pathway of an individual virus labeled with<br />

fluorescent dye molecules (even in the case of labeling with a single dye<br />

molecule). The fluorescence of the marker molecule is imaged and used<br />

to follow the pathway of the virus with high spatial (≥ 40 nm) and time<br />

(≥ 10 ms) resolution. As a first model system we have investigated the<br />

infection pathway of Adeno-associated viruses (AAV) into HeLa cells.<br />

AAV shows promising results for the use in gene therapy applications.<br />

A sequence of events can be tracked starting with a virus approaching<br />

the cell surface, successive receptor binding, membrane penetration, endosome<br />

formation and trafficking, virus release from the endosome and<br />

virus trafficking in the cytoplasm as well as penetration into the nuclear<br />

area.<br />

Besides AAV the studies have been extended to other viral particles like<br />

HIV. HIV is an enveloped virus, which was labeled at its matrix protein<br />

(MA) and its viral protein (Vpr) with GFP and GFP mutants. First<br />

results from these studies will also be presented.<br />

SYLS 3.5 Mi 16:00 B<br />

Interactions of biopolymers of fixed topology with thermal fluctuations<br />

— •Ralf Metzler 1 and Andreas Hanke 2 — 1 NORDITA,<br />

Blegdamsvej 17, DK-2100 Copenhagen OE — 2 Theoretical Physics, University<br />

of Oxford, Oxford OX1 3NP, United Kingdom<br />

DNA knots of different complexity effect different mobility of the chain,<br />

and they pose an intricate problem to a biological cell in respect to transcription<br />

or replication. Specific enzymes remove knots very efficiently<br />

despite having access to local information, only. I will discuss ideas on<br />

how interaction of thermal fluctuations with the fixed topology of the<br />

chain may assist the enzymes in their task, and under which conditions<br />

this may actually work in vivo.<br />

Double-stranded DNA even at physiological temperatures undergoes<br />

fluctuations, during which single-stranded bubbles open up along the<br />

strand. Increasing the temperature, dsDNA eventually undergoes a melting<br />

transition. Starting from a microscopic model for the Free energy, we<br />

derive a Fokker-Planck equation to the bubble fluctuations, whose predictions<br />

close to physiological temperatures reproduce recent experimental<br />

results on single bubble fluctuations.<br />

References: R. Metzler, A. Hanke, P. G. Dommersnes, Y. Kantor, and<br />

M. Kardar, Phys. Rev. Lett. 88 (2002) 188101; Phys. Rev. E 65 (2002)<br />

061103. A. Hanke and R. Metzler, Phys. Rev. Lett. 90 (2003) 159801, A.<br />

Hanke and R. Metzler, J. Phys. A (Lett.) 36 (2003) L473.<br />

SYLS 3.6 Mi 16:00 B<br />

Tuning of microcapsule adhesion by varying capsule stiffness —<br />

•Nils Elsner and Andreas Fery — MPI for Colloids and Interfaces<br />

14424 Potsdam<br />

We have been studying the adhesion polyelectrolyte (PE) capsules<br />

composed from Polyallylamine (PAH) and Polystyrenesulfonate (PSS).<br />

These PE capsule can be produced in sizes up to 20 mm, while the thickness<br />

remains tunable on the nanometer scale. This makes it possible to<br />

vary the elastic properties by changing the wall thickness, which has been<br />

shown by us recently [1].<br />

The interaction of these capsules with a glass surface was studied by<br />

Reflective Interference Contrast Microscopy measurements. It was found,<br />

that negatively charged capsules adhere to glass, which was coated with<br />

positively charged polyelectrolyte, whereas these capsules do not adhere<br />

to bare glass. We found that the adhesion area increases with decreasing<br />

shell thickness for shells with identical surface interactions. The data for<br />

the adhesion area for different thicknesses and different radii could be<br />

fitted with a simple model based on [2], having the surface energy as the<br />

only fitting parameter.<br />

In pH-experiments, the stiffness of the capsules is found to decrease<br />

upon increasing pH as revealed by force spectroscopy measurements.<br />

Consequently, we observe an increase of the adhesion areas although the<br />

surface interactions are not strongly changed in this pH range.<br />

[1] F. Dubreil, N. Elsner, and A. Fery, Eur. Phys. J. E in press (2003).<br />

[2] L. D. Landau and E. M. Lifschitz, Elastizitätstheorie (Akademie<br />

Verlag, Berlin, 1991).<br />

SYLS 3.7 Mi 16:00 B<br />

Persistent Spectral Labeling of Proteins via UV-<br />

Photochemistry of their Aromatic Amino Acids — •Christoph<br />

Schnell, Christoph Hecht, Markus Stübner, and Josef<br />

Friedrich — Physik-Department E14, Lehrstuhl für Physik<br />

Weihenstephan, Technische Universität Müenchen, 85350 Freising<br />

We used hole burning techniques for high resolution frequency label-

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