Journal of Computer Science & Systems Biology

S2 Diode Model of Muscle Crossbridge Dynamics

Abstract

Peter R Greene

This report explores the contribution of lateral myosin bending to the developed crossbridge force and power stroke. The equipartition theorem and Boltzmann distribution are used to calculate crossbridge force and displacement, consistent with experimental values. Negligible buckling strength of the S2-myosin link means that the muscle crossbridge is effectively a one-way force transducer, a mechanical diode, transmitting axial tension forces only. Crossbridge stiffness surfaces as an important factor. Power-stroke displacement is found to decrease with increasing stiffness, whereas axial force increases. The transverse thermal fluctuations of the myosin molecule are significant. Equipartition is used to calculate the mode amplitudes for myosin bending. Crossbridge axial force Fx and power stroke Δx develop from transverse in-plane fluctuations along the y and z axes. Single and doubleheaded actin-myosin attachment configurations are calculated in detail. Practical applications include the effects of temperature on the flexibility of the myosin molecule stiffness and tension, relevant to man-made fabrication of synthetic muscle using micro-machines. Scaling laws for the S2 bending amplitude depend on mode number, filament length, and stiffness, as (n)-2, (L)2, and (EI)-1.