Ali M Yusuf, Uemura Sotaro, Adachi Kengo, Itoh Hiroyasu, Kinosita Kazuhiko, Ishiwata Shin'ichi
Center for Integrative Bioscience, Okazaki National Research Institutes, Higashiyama 5-1, Myodaiji, Okazaki 444-8585, Japan.
Nat Struct Biol. 2002 Jun;9(6):464-7. doi: 10.1038/nsb803.
Myosin V is a two-headed, actin-based molecular motor implicated in organelle transport. Previously, a single myosin V molecule has been shown to move processively along an actin filament in discrete approximately 36 nm steps. However, 36 nm is the helical repeat length of actin, and the geometry of the previous experiments may have forced the heads to bind to, or halt at, sites on one side of actin that are separated by 36 nm. To observe unconstrained motion, we suspended an actin filament in solution and attached a single myosin V molecule carrying a bead duplex. The duplex moved as a left-handed spiral around the filament, disregarding the right-handed actin helix. Our results indicate a stepwise walking mechanism in which myosin V positions and orients the unbound head such that the head will land at the 11th or 13th actin subunit on the opposing strand of the actin double helix.
肌球蛋白V是一种双头的、基于肌动蛋白的分子马达，参与细胞器运输。此前，已证明单个肌球蛋白V分子能沿肌动蛋白丝以约36纳米的离散步长进行持续移动。然而，36纳米是肌动蛋白的螺旋重复长度，先前实验的几何结构可能迫使头部结合到或停留在肌动蛋白一侧相隔36纳米的位点上。为了观察无约束运动，我们将一根肌动蛋白丝悬浮在溶液中，并连接了一个携带珠子双链体的单个肌球蛋白V分子。双链体围绕细丝以左旋螺旋的形式移动，而忽略了右旋的肌动蛋白螺旋。我们的结果表明了一种逐步行走机制，其中肌球蛋白V定位并定向未结合的头部，使得该头部将落在肌动蛋白双螺旋相对链上的第11或13个肌动蛋白亚基处。
