A Simple Kinetic Model Describes the Processivity of Myosin-V

TL;DR

This paper presents a simple kinetic model that accurately describes myosin-V's processive movement along actin filaments, including step-size variations and velocity behavior under different loads and ATP concentrations.

Contribution

It introduces a two-state chemical kinetic model for myosin-V that accounts for load-dependent rates and predicts substeps consistent with experimental data.

Findings

Model accurately describes experimental velocity and randomness.

Predicts a substep size of approximately 13-14 nm.

Explains variation in motility with ATP and load conditions.

Abstract

Myosin-V is a motor protein responsible for organelle and vesicle transport in cells. Recent single-molecule experiments have shown that it is an efficient processive motor that walks along actin filaments taking steps of mean size close to 36 nm. A theoretical study of myosin-V motility is presented following an approach used successfully to analyze the dynamics of conventional kinesin but also taking some account of step-size variations. Much of the present experimental data for myosin-V can be well described by a two-state chemical kinetic model with three load-dependent rates. In addition, the analysis predicts the variation of the mean velocity and of the randomness -- a quantitative measure of the stochastic deviations from uniform, constant-speed motion -- with ATP concentration under both resisting and assisting loads, and indicates a {\it sub}step of size $d_{0} \simeq$ 13-14 nm (from the ATP-binding site) that appears to accord with independent observations.