The kinetic mechanism of myosin V

TLDR

Myosin V is an unconventional myosin proposed to be processive on actin filaments, analogous to kinesin on a microtubule. The study aims to determine the unique properties of myosin V that enable its processivity by conducting a detailed kinetic analysis. The authors used a truncated, single‑headed myosin V construct bound to a single light chain to perform kinetic measurements, revealing that increased pre‑strong‑binding rates and a slowed ADP release extend the strongly bound state. The data show that more than 70 % of the cycle is spent strongly bound to actin, with ADP release becoming the rate‑limiting step, thereby enabling processive movement and cargo transport at lower motor densities than other myosins. Published in Nature (London) 1999, 400:590–593.

Abstract

Myosin V is an unconventional myosin proposed to be processive on actin filaments, analogous to kinesin on a microtubule [Mehta, A. D., et al . (1999) Nature (London) 400, 590–593]. To ascertain the unique properties of myosin V that permit processivity, we undertook a detailed kinetic analysis of the myosin V motor. We expressed a truncated, single-headed myosin V construct that bound a single light chain to study its innate kinetics, free from constraints imposed by other regions of the molecule. The data demonstrate that unlike any previously characterized myosin a single-headed myosin V spends most of its kinetic cycle (>70%) strongly bound to actin in the presence of ATP. This kinetic tuning is accomplished by increasing several of the rates preceding strong binding to actin and concomitantly prolonging the duration of the strongly bound state by slowing the rate of ADP release. The net result is a myosin unlike any previously characterized, in that ADP release is the rate-limiting step for the actin-activated ATPase cycle. Thus, because of a number of kinetic adaptations, myosin V is tuned for processive movement on actin and will be capable of transporting cargo at lower motor densities than any other characterized myosin.