Oguchi Yusuke, Mikhailenko Sergey V, Ohki Takashi, Olivares Adrian O, De La Cruz Enrique M, Ishiwata Shin'ichi
Department of Physics, Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan.
Proc Natl Acad Sci U S A. 2008 Jun 3;105(22):7714-9. doi: 10.1073/pnas.0800564105. Epub 2008 May 28.
Dimeric myosins V and VI travel long distances in opposite directions along actin filaments in cells, taking multiple steps in a "hand-over-hand" fashion. The catalytic cycles of both myosins are limited by ADP dissociation, which is considered a key step in the walking mechanism of these motors. Here, we demonstrate that external loads applied to individual actomyosin V or VI bonds asymmetrically affect ADP affinity, such that ADP binds weaker under loads assisting motility. Model-based analysis reveals that forward and backward loads modulate the kinetics of ADP binding to both myosins, although the effect is less pronounced for myosin VI. ADP dissociation is modestly accelerated by forward loads and inhibited by backward loads. Loads applied in either direction slow ADP binding to myosin V but accelerate binding to myosin VI. We calculate that the intramolecular load generated during processive stepping is approximately 2 pN for both myosin V and myosin VI. The distinct load dependence of ADP binding allows these motors to perform different cellular functions.
二聚体肌球蛋白V和VI在细胞内沿着肌动蛋白丝向相反方向移动很长距离，以“手拉手”的方式迈出多步。这两种肌球蛋白的催化循环都受ADP解离的限制，ADP解离被认为是这些分子马达行走机制中的关键步骤。在这里，我们证明施加到单个肌动球蛋白V或VI键上的外部负载不对称地影响ADP亲和力，使得在辅助运动的负载下ADP结合较弱。基于模型的分析表明，向前和向后的负载调节ADP与这两种肌球蛋白结合的动力学，尽管对肌球蛋白VI的影响不太明显。向前的负载适度加速ADP解离，向后的负载则抑制ADP解离。向任一方向施加的负载都会减慢ADP与肌球蛋白V的结合，但会加速与肌球蛋白VI的结合。我们计算得出，在连续步移过程中产生的分子内负载对于肌球蛋白V和肌球蛋白VI来说都约为2皮牛。ADP结合对负载的不同依赖性使这些分子马达能够执行不同的细胞功能。
