Kinetic analysis of the fastest motor protein, Chara myosin.

革质轮藻Xi类肌球蛋白是迄今为止最快的分子马达。为了研究这种快速运动的分子机制，我们对轮藻肌球蛋白的重组马达结构域进行了动力学分析。我们估计所花费的时间与肌动蛋白的强结合状态，通过测量ADP解离肌动蛋白-运动域复合物和ATP诱导的解离肌动蛋白的运动域的速率常数。ADP从动作-运动域解离的速率常数&gt; 2，800 s^<-1>，在生理ATP浓度下ATP诱导的运动域从肌动蛋白解离的速率常数为2，200 s^<-1>。从这些数据中，在与肌动蛋白的强结合状态下花费的时间估计为&lt;0.82 ms。该值是各种肌球蛋白的已知值中最短的，并且产生&lt;0.3的占空比，其中肌动蛋白激活的ATP酶活性的Vmax值为390 s-1。除了长颈域的肌球蛋白Va的Chara电机域大大增加了运动的速度，而不增加ATP水解周期率，与摆动杠杆模型一致。此外，这项研究揭示了一些显着的动力学特征轮藻肌球蛋白，适合快速运动：一个戏剧性的加速ADP释放肌动蛋白（1,000倍）和极快的ATP结合率。

Chara corallina class XI myosin is by far the fastest molecular motor. To investigate the molecular mechanism of this fast movement, we performed a kinetic analysis of a recombinant motor domain of Chara myosin. We estimated the time spent in the strongly bound state with actin by measuring rate constants of ADP dissociation from actin-motor domain complex and ATP-induced dissociation of the motor domain from actin. The rate constant of ADP dissociation from acto-motor domain was >2,800 s^<-1> and the rate constant of ATP-induced dissociation of the motor domain from actin at physiological ATP concentration was 2,200 s^<-1>. From these data, the time spent in the strongly bound state with actin was estimated to be <0.82 ms. This value is the shortest among known values for various myosins, and yields the duty ratio of <0.3 with the Vmax value of the actin-activated ATPase activity of 390 s 1. The addition of the long neck domain of myosin Va to the Chara motor domain largely increased the velocity of the motility without increasing the ATP hydrolysis cycle rate, consistent with the swinging lever model. In addition, this study reveals some striking kinetic features of Chara myosin that are suited for the fast movement: a dramatic acceleration of ADP release by actin (1,000-fold) and extremely fast ATP binding rate.