The kinetic mechanism of myosin V

EM De La Cruz, AL Wells… - Proceedings of the …, 1999 - National Acad Sciences
EM De La Cruz, AL Wells, SS Rosenfeld, EM Ostap, HL Sweeney
Proceedings of the National Academy of Sciences, 1999National Acad Sciences
Myosin V is an unconventional myosin proposed to be processive on actin filaments,
analogous to kinesin on a microtubule [Mehta, AD, 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 …
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.
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