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A Simple Kinetic Model Describes the Processivity of Myosin-V

Anatoly B. Kolomeisky^* and Michael E. Fisher

^* Department of Chemistry, Rice University, Houston, Texas 77005-1892; and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742

Correspondence: Address reprint requests to Anatoly B. Kolomeisky, Rice University, 6100 Main St., Houston, TX 77005-1892. Tel.: 713-348-5672; Fax: 713-348-5155; E-mail: tolya{at}rice.edu.

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 substep of size d₀ 13–14 nm (from the ATP-binding state) that appears to accord with independent observations.

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