Hancock W O, Howard J
Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195-7290, USA.
J Cell Biol. 1998 Mar 23;140(6):1395-405. doi: 10.1083/jcb.140.6.1395.
A single kinesin molecule can move for hundreds of steps along a microtubule without dissociating. One hypothesis to account for this processive movement is that the binding of kinesin's two heads is coordinated so that at least one head is always bound to the microtubule. To test this hypothesis, the motility of a full-length single-headed kinesin heterodimer was examined in the in vitro microtubule gliding assay. As the surface density of single-headed kinesin was lowered, there was a steep fall both in the rate at which microtubules landed and moved over the surface, and in the distance that microtubules moved, indicating that individual single-headed kinesin motors are not processive and that some four to six single-headed kinesin molecules are necessary and sufficient to move a microtubule continuously. At high ATP concentration, individual single-headed kinesin molecules detached from microtubules very slowly (at a rate less than one per second), 100-fold slower than the detachment during two-headed motility. This slow detachment directly supports a coordinated, hand-over-hand model in which the rapid detachment of one head in the dimer is contingent on the binding of the second head.
单个驱动蛋白分子能够沿着微管移动数百步而不解离。解释这种持续运动的一种假说是，驱动蛋白两个头部的结合是协同的，以便至少有一个头部始终与微管结合。为了验证这一假说，在体外微管滑动实验中检测了全长单头驱动蛋白异二聚体的运动性。随着单头驱动蛋白表面密度的降低，微管在表面着陆和移动的速率以及微管移动的距离都急剧下降，这表明单个单头驱动蛋白分子不是持续运动的，并且大约四到六个单头驱动蛋白分子对于微管的持续移动是必要且充分的。在高ATP浓度下，单个单头驱动蛋白分子从微管上解离的速度非常慢（每秒少于一次），比双头运动时的解离速度慢100倍。这种缓慢的解离直接支持了一种协同的、交替式模型，即二聚体中一个头部的快速解离取决于另一个头部的结合。
