The power stroke driven muscle contraction

Overview & Synopsis

This thesis is devoted to the modeling of mechanical functioning of myosin II/actin in- teraction, responsible for active force generation in skeletal muscles at nanometer scale. The muscle contractile units contain actin filament and myosin II filaments formed by an assembly of myosins II. The myosin II is molecular motor that periodically attaches and detaches to the actin filament in presence of ATP. In order to understand the phenomenon of muscle contraction from mechanical point of view, we follow the approach developed by the Brownian ratchets community, which replaced the conventional chemistry-based interpretation of active force generation by a study of Langevin dynamics of mechanical systems with well defined energy landscapes. We focus on the role of the conformational change known as power stroke in the functioning of myosin II. We identify the power stroke as the main driver of contractility. The attribution of active role to power stroke reflects the biological reality imprinted in the molecular motor functional cycle. We propose an innovative mechanical model and by emphasizing the active role of the power stroke we are therefore building a bridge between processive and nonprocessive motors. In this Thesis we present the first examples of models of nonprocessive motors driven exclusively by the power stroke and exploiting the well known phenomenon of stochastic resonance.