Figure 1.

A free energy landscape for the coupled refolding–stepping processes. (A) A contour plot of the free energy landscape as a function of x, the position of the myosin head along the actin filament, and ρ, the order parameter of refolding. The multiple intermediate states at ρ = 0.1, 0.3, 0.5, 0.7, and the rigor state at ρ = 0.9 are positioned periodically along the actin filament with a period of 5.5 nm. There is a global bias of decreasing free energy with increasing ρ, and kinetic connectivity between the intermediate states is in favor of stepping movement. (B) Kinetic representation of actomyosin binding as a sequential process through multiple intermediate states, I(x,ρ), toward rigor states, R(x,ρ).