Veigel Claudia, Schmitz Stephan, Wang Fei, Sellers James R
Physical Biochemistry, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
Nat Cell Biol. 2005 Sep;7(9):861-9. doi: 10.1038/ncb1287. Epub 2005 Aug 14.
Recent studies provide strong evidence that single myosin class V molecules transport vesicles and organelles processively along F-actin, taking several 36-nm steps, 'hand over hand', for each diffusional encounter. The mechanisms regulating myosin-V's processivity remain unknown. Here, we have used an optical-tweezers-based transducer to measure the effect of load on the mechanical interactions between rabbit skeletal F-actin and a single head of mouse brain myosin-V, which produces its working stroke in two phases. We found that the lifetimes of the first phase of the working stroke changed exponentially and about 10-fold over a range of pushing and pulling forces of +/- 1.5 pN. Stiffness measurements suggest that intramolecular forces could approach 3.6 pN when both heads are bound to F-actin, in which case extrapolation would predict the detachment kinetics of the front head to slow down 50-fold and the kinetics of the rear head to accelerate respectively. This synchronizing effect on the chemo-mechanical cycles of the heads increases the probability of the trail head detaching first and causes a strong increase in the number of forward steps per diffusional encounter over a system with no strain dependence.
近期研究提供了有力证据，表明单个肌球蛋白V类分子沿着F-肌动蛋白持续地运输囊泡和细胞器，每次扩散相遇时采取几个36纳米的“手拉手”步骤。调节肌球蛋白V持续运动性的机制仍然未知。在这里，我们使用了基于光镊的传感器来测量负载对兔骨骼肌F-肌动蛋白与小鼠脑肌球蛋白V的单个头部之间机械相互作用的影响，该肌球蛋白V的工作冲程分两个阶段产生。我们发现，在+/- 1.5皮牛顿的推拉力范围内，工作冲程第一阶段的寿命呈指数变化，变化幅度约为10倍。刚度测量表明，当两个头部都与F-肌动蛋白结合时，分子内力可能接近3.6皮牛顿，在这种情况下，外推法预测前头部分离动力学将减慢50倍，而后头部分离动力学将分别加速。这种对头部化学机械循环的同步效应增加了拖尾头部首先分离的概率，并导致每次扩散相遇时向前步数相对于无应变依赖性系统大幅增加。
