The physics of biological molecular motors
The physics of biological molecular motors
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DOI：
10.1088/0022-3727/31/3/002
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发表时间：
1998-02
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影响因子：
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通讯作者：
N. Thomas;R. A. Thornhill
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文献类型：
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作者：
N. Thomas;R. A. Thornhill
分子马达是生物体运动的基本动因。一个最好的例子是肌动球蛋白马达，它为肌肉收缩提供动力。我们使用一个简化的三态模型来说明这种马达的非凡物理特性，在这个模型中，肌球蛋白的交叉桥连接到肌动蛋白细丝上，倾斜，然后分离。除了分子系统是随机的之外，这个由三磷酸腺苷水解酶驱动的‘跨桥循环’类似于热力学循环。因此，周期中的随机转变会产生张力波动，这是最近在单分子实验中观察到的。此外，由于附着和倾斜的速率常数取决于跨桥弹簧中的弹性能量，因此分子马达是一个高度非线性的机械系统。一个偏向的张力“拉伸”激活了马达，然后它产生了“负粘度”的显著特性，这使它能够像一个自我维持的机械振荡器一样工作。然而，当一系列附着点可用时，电机作为棘轮运行，在轻负载下快速向前拉动肌动蛋白细丝，而重负载仅非常缓慢地向相反方向拉动细丝。类似的想法可能适用于为纤毛和鞭毛提供动力的动力蛋白-微管马达，以及用于细胞内运输的动力蛋白-微管马达。
Molecular motors are the fundamental agents of movement in living organisms. A prime example is the actomyosin motor that powers muscle contraction. We illustrate the remarkable physics of this motor using a simplified three-state model, in which a myosin cross-bridge attaches to an actin filament, tilts over and then detaches. This `cross-bridge cycle', driven by ATP hydrolysis, is similar to a thermodynamic cycle, except that the molecular system is stochastic. Random transitions in the cycle therefore produce tension fluctuations, which have recently been observed in single-molecule experiments. Furthermore, since the rate constants for attachment and tilting depend on the elastic energy in the cross-bridge spring, the molecular motor is a highly nonlinear mechanical system. A bias tension `stretch activates' the motor, and it then develops the remarkable property of `negative viscosity', which allows it to perform as a self-sustained mechanical oscillator. However, when a series of attachment sites is available, the motor operates instead as a ratchet, pulling the actin filament rapidly forwards against a light load, whilst a heavy load pulls the filament only very slowly in the opposite direction. Similar ideas may apply to the dynein-tubulin motor that powers cilia and flagella and the kinesin-tubulin motor used in intracellular transport.