Key result
One-headed myosin-V can produce successive large steps of approximately 32 nm with stepping kinetics similar to two-headed myosin-V, demonstrating processive movement without a hand-over-hand mechanism.
Absolute Event Rate: 32% vs 34%
One-headed myosin-V can produce successive large steps with similar kinetics to two-headed myosin-V, challenging the necessity of the hand-over-hand mechanism for processive movement.
Questions hand-over-hand necessity for myosin-V processivity; hypothesis-generating for motor mechanics.
Class V myosin (myosin-V) is a cargo transporter that moves along an actin filament with large (approximately 36-nm) successive steps. It consists of two heads that each includes a motor domain and a long (23 nm) neck domain. One of the more popular models describing these steps, the hand-over-hand model, assumes the two-headed structure is imperative. However, we previously succeeded in observing successive large steps by one-headed myosin-V upon optimizing the angle of the acto-myosin interaction. In addition, it was reported that wild type myosin-VI and myosin-IX, both one-headed myosins, can also generate successive large steps. Here, we describe the mechanical properties (stepsize and stepping kinetics) of successive large steps by one-headed and two-headed myosin-Vs. This study shows that the stepsize and stepping kinetics of one-headed myosin-V are very similar to those of the two-headed one. However, there was a difference with regards to stability against load and the number of multisteps. One-headed myosin-V also showed unidirectional movement that like two-headed myosin-V required 3.5 k(B)T from ATP hydrolysis. This value is also similar to that of smooth muscle myosin-II, a non-processive motor, suggesting the myosin family uses a common mechanism for stepping regardless of the steps being processive or non-processive. In this present paper, we conclude that one-headed myosin-V can produce successive large steps without following the hand-over-hand mechanism.
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Watanabe et al. (2010) studied this question. One-headed myosin-V (M5SH) vs. Two-headed myosin-V (M5DH) was evaluated on Forward stepsize during successive steps (nm). One-headed myosin-V can produce successive large steps of approximately 32 nm with stepping kinetics similar to two-headed myosin-V, demonstrating processive movement without a hand-over-hand mechanism.
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