Modelling and simulation of motility in actomyosin systems.

We present a model mechanism for simulating the diffusive motion and fluctuations inherent in myofibrillar sarcomere and its subunits at the molecular level. The model couples Langevin dynamics with Huxley kinetics to reproduce the transient patterns of momentum transfer, force generation and resulting motility due to the interactive activities of actin and myosin crossbridges. When myosin is detached from actin, our model predicts Brownian displacements centered at 0 +/- 8 nm (mean +/- SD, n = 265,308) and it is broadly distributed due to the Brownian noise. Attachment events produced displacements with step sizes of approximately 8 +/- 6 nm (mean +/- SD, n = 34,693), which is in agreement with some recent optical-tweezers transducer experimental results. The proposed model could form the basis for a complete qualitative and quantitative description of the evolving complex interactions of the molecular proteins--actin and myosin--in the overall framework of muscular contraction studies.