Berliner E, Young E C, Anderson K, Mahtani H K, Gelles J
Biophysics Program, Brandeis University, Waltham, Massachusetts 02254.
Nature. 1995 Feb 23;373(6516):718-21. doi: 10.1038/373718a0.
Kinesin, a two-headed motor enzyme molecule, hydrolyses ATP to direct organelle transport along microtubules. As it moves along a microtubule, kinesin remains associated with, or 'tracks', microtubule protofilaments. We have prepared truncated kinesin derivatives that contain either two mechanochemical head domains or only a single head. Unlike intact kinesin and the two-headed derivatives, the one-headed enzyme frequently fails to track protofilaments, suggesting that it detaches from microtubules during movement. In this way, the one-headed kinesin derivative is similar to the motor enzyme myosin, which frequently detaches from the actin filament during movement. For myosin (which has two heads), the consequence of this detachment is that single molecules do not appear to drive continuous movement along the filament. Our observations suggest that the ability of single two-headed kinesin molecules to drive continuous movement results from a 'hand-over-hand' mechanism in which one head remains bound to the microtubule while the other detaches and moves forwards.
驱动蛋白是一种双头运动酶分子，它通过水解ATP来沿着微管引导细胞器运输。当驱动蛋白沿着微管移动时，它会与微管原纤维保持结合或“追踪”微管原纤维。我们制备了截短的驱动蛋白衍生物，这些衍生物要么包含两个机械化学头部结构域，要么只包含一个头部。与完整的驱动蛋白和双头衍生物不同，单头酶经常无法追踪原纤维，这表明它在运动过程中会从微管上脱离。通过这种方式，单头驱动蛋白衍生物类似于运动酶肌球蛋白，后者在运动过程中经常从肌动蛋白丝上脱离。对于肌球蛋白（有两个头部），这种脱离的结果是单个分子似乎不会沿着细丝驱动连续运动。我们的观察结果表明，单个双头驱动蛋白分子驱动连续运动的能力源于一种“换手”机制，即一个头部保持与微管结合，而另一个头部脱离并向前移动。
