Lockhart A, Cross R A
Molecular Motors Group, Marie Curie Research Institute, Surrey, UK.
EMBO J. 1994 Feb 15;13(4):751-7. doi: 10.1002/j.1460-2075.1994.tb06317.x.
The head or motor domain of the ncd (non-claret disjunctional) molecular motor is 41% identical to that of kinesin, yet moves along microtubules in the opposite direction to kinesin. We show here that despite the reversed directionality of ncd, its kinetics in solution are homologous in key respects to those of kinesin. The rate limiting step, ADP release, occurs at 0.0033 s-1 at 100 mM NaCl and is accelerated approximately 1000-fold when the motor binds to microtubules. Other reaction steps are all very fast (> 0.1 s-1) compared with ADP release, and the motor is consequently paused in the ncd.ADP state until microtubule binding occurs (Kd = 2 microM), at which point ADP release is triggered and the motor locks onto the microtubule in a rigor-like state. These data identify close functional homology between the strong binding states of kinesin and ncd, and in view of this we discuss a possible mechanism for directional reversal, in which the strong binding states of ncd and kinesin are functionally identical, but the weak binding states are biased in opposite directions.
非清晰分离（ncd）分子马达的头部或运动结构域与驱动蛋白的该结构域有41%的同源性，但它沿微管的运动方向与驱动蛋白相反。我们在此表明，尽管ncd的方向性相反，但其在溶液中的动力学在关键方面与驱动蛋白的动力学是同源的。限速步骤，即ADP释放，在100 mM NaCl条件下的发生速率为0.0033 s-1，当马达与微管结合时，该速率会加快约1000倍。与ADP释放相比，其他反应步骤都非常快（> 0.1 s-1），因此马达会在ncd.ADP状态下暂停，直到发生微管结合（Kd = 2 microM），此时触发ADP释放，马达以类似僵直的状态锁定在微管上。这些数据表明驱动蛋白和ncd的强结合状态之间存在密切的功能同源性，鉴于此，我们讨论了一种可能的方向反转机制，即ncd和驱动蛋白的强结合状态在功能上是相同的，但弱结合状态偏向相反的方向。
