Myosin X is a high duty ratio motor
Myosin X is a high duty ratio motor
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DOI：
10.1074/jbc.m504779200
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发表时间：
2005-08-12
影响因子：
4.8
通讯作者：
Ikebe, M
中科院分区：
文献类型：
--
作者：
Homma, K;Ikebe, M
Myosin X在多种细胞类型中表达，并在货物运动和丝状足延伸中发挥作用，但其机械酶特性尚不完全清楚。本文采用单头结构体（M10IQ1）分析了肌动蛋白X ATP水解循环的动力学机制。Myosin X具有弱的“强肌动蛋白结合状态”（AMD）， K-d为1.6 μ M，这是由于它的解离速率常数很大（2.1 s(-1)）。M10IQ1肌动蛋白激活的ATPase活性的V-max和K-ATPase分别为13.5 s（-1）和17.4 μ M。ATP水解速率（> 100 s(-1)）和肌动蛋白X的磷酸盐释放速率（> 100 s(-1)）比整个ATP酶循环速率快得多，因此不是限速的。肌动蛋白X的ADP脱除率为23 s(-1)，是V-max的2倍。P-i-burst大小较低（0.46 mol/ mol），表明平衡向预水解中间体明显转移。稳态atp酶速率可以解释为水解步骤的不利平衡常数和相对缓慢的ADP速率的组合。我们的动力学模型计算的占空比为0.6，与K-m atp酶和K-m运动性比较得出的占空比为0.7一致。我们的结果表明肌凝蛋白X是一个高占空比马达。
Myosin X is expressed in a variety of cell types and plays a role in cargo movement and filopodia extension, but its mechanoenzymatic characteristics are not fully understood. Here we analyzed the kinetic mechanism of the ATP hydrolysis cycle of acto-myosin X using a single-headed construct (M10IQ1). Myosin X was unique for the weak "strong actin binding state" (AMD) with a K-d of 1.6 mu M attributed to the large dissociation rate constant (2.1 s(-1)). V-max and K-ATPase of the actin-activated ATPase activity of M10IQ1 were 13.5 s(-1) and 17.4 mu M, respectively. The ATP hydrolysis rate (> 100 s(-1)) and the phosphate release rate from acto-myosin X (> 100 s(-1)) were much faster than the entire ATPase cycle rate and, thus, not rate-limiting. The ADP off-rate from acto-myosin X was 23 s(-1), which was two times larger than the V-max. The P-i-burst size was low (0.46 mol/ mol), indicating that the equilibrium is significantly shifted toward the prehydrolysis intermediate. The steady-state ATPase rate can be explained by a combination of the unfavorable equilibrium constant of the hydrolysis step and the relatively slow ADP off-rate. The duty ratio calculated from our kinetic model, 0.6, was consistent with the duty ratio, 0.7, obtained from comparison of K-m ATPase and K-m motility. Our results suggest that myosin X is a high duty ratio motor.