Regensburg 2004 – scientific programme

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AKB: Biologische Physik

AKB 50: Poster Session "Biological Physics"

AKB 50.126: Poster

Friday, March 12, 2004, 10:30–13:00, B

Molecular motors in cells: an analogue for thermotropic ordering — •David Smith and Josef Käs — Linne Str 5, 04103, Leipzig

All eukaryotic cells rely on the self-assembly of protein filaments to form an intracellular cytoskeleton. The need for motility and reaction additionally requires pathways that restructure and disassemble cytoskeletal structures. Temperature-driven increases in disorder are the most obvious method, thermodynamically, for dissolving complex structures, yet could denature cellular components. This is exemplified in the unfolding of double-stranded DNA for duplication. While de-hybridization of the strands by a temperature increase represents the simplest pathway, molecular motors are present to perform the same function in the nucleus without heat-induced damage to the cell. We report another fundamental mechanism whereby changes in the activity of the molecular motor myosin II induce order-disorder transitions in actin networks. In near-chemical-rest states, aggregates of myosin II motors acting as crosslinkers induce a compounded state of aligned actin filaments and motors. This results in the self-assembly of various macro-molecular structures such as asters, neuron-like networks, and condensed super-precipitates. However, when the molecular motors are turned on and the system assumes an active nonequilibrium state, the myosin II-induced filament motility maintains a disordered high-entropy state. Experiments with photo-activated motors show the rapid dynamics of disassembly of actomyosin structures and the reversibility of the changes. This ability for rapid transitions of the entropic state by motor activity indicates that molecular motors, in general, may substantially contribute to dynamic cellular organization.