Title: A Simplified Flexible Chain Model of Calcium Regulated Myosin-Actin Interaction
Abstract: While the process of muscle contraction is relatively well understood at the molecular level, the collective behavior of many molecular motors has become an interesting topic for computer simulations in recent years. Duke's model has proven to provide a good description of the myosin-actin interaction and the Flexible Chain Model can be used to describe the regulatory behavior of the troponin-tropomyosin complex. Based on these models, we developed and implemented a simple computational motility assay that covers calcium-regulated muscle activation and allows to study the cooperative effects of many motormolecules working in parallel as well as the relationships between contraction speed and isometric force versus calcium concentration. Like in Duke's model, myosin heads are modeled using a simple 3-state system corresponding to detached, attached and strongly attached to actin. The behavior of the troponin-tropomyosin complex, located at every 7th actin binding site, is treated using a simple 2-state model, allowing troponin to be attached or detached to actin. Both troponin and myosin control a continuous energy landscape that models the steric blocking of actin binding sites by tropomyosin. This troponin-potential is computed using radial basis interpolation. It is locally reduced, if a myosin head binds to actin and increased, if a binding site is occupied by troponin, causing the system to act cooperatively.