Overdamped mechanical model of myosin II

Due to their small size molecular systems are often overdamped and they are affected by significant fluctuations due to thermal forces. In this paper we investigate the effect of overdamping on a simple mechanical model of myosin II, the motor protein responsible for muscle contraction. We demonstrate that this model, based on the experimentally observed shape of the protein’s subdomains, is consistent with the available experimental results. We also shed new light on the debate whether the powerstroke is a sudden conformational change followed by relaxation to equilibrium or a thermal fluctuation followed by a fixation by a ratchet-like mechanism in an energetically favourable conformation: we propose that these mechanisms coexist.