Dresden 2014 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 1: Molecular Motors
BP 1.7: Vortrag
Montag, 31. März 2014, 11:30–11:45, HÜL 386
Stochastic dynamics of small ensembles of non-processive molecular motors: The parallel cluster model — •Thorsten Erdmann1,2, Philipp J. Albert1,2, and Ulrich S. Schwarz1,2 — 1Institute for Theoretical Physics, Heidelberg University, Heidelberg, Germany — 2BioQuant, Heidelberg University, Heidelberg, Germany
Forces in the actin cytoskeleton are generated by small groups of non-processive myosin II motors. For such small groups comprising few tens of myosin II molecules, stochastic effects are highly relevant. Using a three-state crossbridge model with the assumptions of fast powerstroke kinetics and equal load sharing between motors in equivalent states, the stochastic reaction network is reduced to a one-step master equation for binding and unbinding dynamics (parallel cluster model) together with rules for ensemble movement. For constant external load, ensemble dynamics is determined by the catch bond character of myosin II, leading to an increase of the fraction of bound motors under load and firm attachment of small ensembles. This adaptation to load results in a concave force-velocity relation described by a Hill relation. When working against an external linear spring, myosin II ensembles adjust themselves to an isometric state with constant average position and load. Ensemble dynamics is now determined by the distribution of motors over different bound states. Above a critical spring stiffness, myosin II can no longer perform the power stroke. This stalls ensemble movement but slow unbinding from the pre-power-stroke state protects the ensembles against detachment. [Reference: T. Erdmann, P.J. Albert & U.S. Schwarz, J. Chem. Phys. 139, 175104 (2013).]