WPI Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan.
PLoS One. 2010 Aug 18;5(8):e12224. doi: 10.1371/journal.pone.0012224.
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.
V 类肌球蛋白（myosin-V）是一种沿着肌动蛋白丝运动的货物转运蛋白，它以大的（约 36nm）连续步长移动。它由两个头部组成，每个头部都包含一个马达结构域和一个长（23nm）的颈部结构域。描述这些步骤的一个更流行的模型是手拉手模型，它假设双头部结构是强制性的。然而，我们之前通过优化肌球蛋白与肌动蛋白相互作用的角度成功地观察到了单头部肌球蛋白-V 的连续大步。此外，据报道，野生型肌球蛋白-VI 和肌球蛋白-IX，都是单头部肌球蛋白，也可以产生连续的大步。在这里，我们描述了单头部和双头部肌球蛋白-V 的连续大步的机械特性（步长和步进动力学）。这项研究表明，单头部肌球蛋白-V 的步长和步进动力学与双头部肌球蛋白-V 非常相似。然而，在稳定性和多步的数量方面存在差异。单头部肌球蛋白-V 也表现出单向运动，类似于双头部肌球蛋白-V，需要 3.5kBT 的 ATP 水解才能产生。这个值也与非运动性肌球蛋白-II（smooth muscle myosin-II）相似，表明肌球蛋白家族无论是否是运动性的，都使用一种共同的机制进行步进。在本文中，我们得出结论，单头部肌球蛋白-V 可以产生连续的大步，而不需要遵循手拉手的机制。
