Mapping the classical crossbridge theory and backward steps in the three-bead laser trap setup for actin-myosin interaction

According to the crossbridge theory (A.F. Huxley 1957), the interaction between myosin and actin is governed by a deterministic process and the myosin molecule pulls the actin filament in one specific direction only. However, studies on single myosin-actin interaction (J.T. Finer et al. 1994) have shown that crossbridges pull actin filaments not only in a preferred but also in the opposite direction, thereby performing what is typically referred to as backward steps (J.E. Molloy et al. 1995). The aim of our study is to investigate whether backward steps could be explained by a crossbridge model strictly based on Huxley’s assumptions, but incorporating perturbations caused by Brownian motion, as observed in single crossbridge-actin interaction. We develop a mathematical model based on Langevin equations describing the classical three-bead laser trap setup and use a semi-analytical approach to study the percentage of backward steps. SeMS – Seminario di Modellazione & Simulazione