A force-dependent state controls the coordination of processive myosin V

Myosin V is an efficient processive molecular motor. Recent experiments have shown how the structure and kinetics of myosin V are specialized to produce a highly processive motor capable of taking multiple 36-nm steps on an actin filament track. Here, we examine how two identical heads coordinate their activity to produce efficient hand-over-hand stepping. We have used a modified laser-trap microscope to apply a approximate to 2-pN forward or backward force on a single-headed myosin V molecule, hypothesized to simulate forces experienced by the rear or lead head, respectively. We found that pulling forward produces only a small change in the kinetics, whereas pulling backward induces a large reduction in the cycling of the head. These results support a model in which the coordination of myosin V stepping is mediated by strain-generated inhibition of the lead head.