The kinetic mechanism of myosin V
- Enrique M. De La Cruz†,
- Amber L. Wells†,
- Steven S. Rosenfeld‡,
- E. Michael Ostap†, and
- H. Lee Sweeney†,§
- †University of Pennsylvania School of Medicine, Department of Physiology, Pennsylvania Muscle Institute, Philadelphia, PA 19104-6085; and ‡Department of Neurology, University of Alabama, Birmingham, AL 35294-0007
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Edited by Edward D. Korn, National Institutes of Health, Bethesda, MD, and approved October 8, 1999 (received for review June 24, 1999)
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.
Footnotes
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↵ § To whom reprint requests should be addressed at: Department of Physiology, A700 Richards Building, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085. E-mail: lsweeney{at}mail.med.upenn.edu.
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This paper was submitted directly (Track II) to the PNAS office.
- Copyright © 1999, The National Academy of Sciences
