Regensburg 2016 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 58: Cytoskeletal Filaments

BP 58.9: Vortrag

Donnerstag, 10. März 2016, 12:15–12:30, H44

Stabilization of small myosin II ensembles by mechanical load and ATP concentration — •Thorsten Erdmann, Kathrin Bartelheimer, and Ulrich S. Schwarz — Institute for Theoretical Physics and BioQuant, Heidelberg University, Heidelberg, Germany

Biological systems use ensembles of non-processive myosin II motor molecules to generate contractile forces. In muscle, large myosin II ensembles remain continuously attached to actin filaments to ensure effective force generation. In the cytoskeleton or in reconstituted acto-myosin gels and motility assays, by contrast, small myosin II ensembles detach from actin with probabilities depending on both internal and external parameters. We study the influence of mechanical load and ATP concentration on small myosin II ensembles using a five-state crossbridge model. Increasing mechanical load or decreasing ATP concentration both increase the number of bound motors and stabilize ensemble attachment. While ensemble velocity is always reduced by increased mechanical load, lowering ATP concentration can increase ensemble velocity and stall force due to load-sharing between increased numbers of bound motors. To facilitate the use of our model in higher level modelling, we first reduce it to a three-state cross bridge model with conserved mean-first passage times in the motor cycle. Next, we exploit a separation of time-scales in the motor cycle to project the stochastic reaction network to a one-step master equation. We test the validity of each reduction step by comparison to the full model.