Myosin learns to walk

Recent experiments, drawing upon single-molecule, solution kinetic and structural techniques, have clarified our mechanistic understanding of class V myosins. The findings of the past two years can be summarized as follows: (1) Myosin V is a highly efficient processive motor, surpassing even conventional kinesin in the distance that individual molecules can traverse. (2) The kinetic scheme underlying ATP turnover resembles those of myosins I and II but with rate constants tuned to favor strong binding to actin. ADP release precedes dissociation from actin and is rate-limiting in the cycle. (3) Myosin V walks in strides averaging approximately 36 nm, the long pitch pseudo-repeat of the actin helix, each step coupled to a single ATP hydrolysis. Such a unitary displacement, the largest molecular step size measured to date, is required for a processive myosin motor to follow a linear trajectory along a helical actin track.