The molecular motor myosin V transports cargo by stepping on actin filaments, executing a random diffusive search for actin binding sites at each step. A recent experiment suggests that the joint between the myosin lever arms may not rotate freely, as assumed in earlier studies, but instead has a preferred angle giving rise to structurally constrained diffusion. We address this controversy through comprehensive analytical and numerical modeling of myosin V diffusion and stepping. When the joint is constrained, our model reproduces the experimentally observed diffusion, allowing us to estimate bounds on the constraint energy. We also test the consistency between the constrained diffusion model and previous measurements of step size distributions and the load dependence of various observable quantities. The theory lets us address the biological significance of the constrained joint and provides testable predictions of new myosin behaviors, including the stomp distribution and the run length under off-axis force.

中文翻译：

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Myosin V通过结构受约束的扩散执行可变长度的步骤

分子马达肌球蛋白V通过踩在肌动蛋白丝上来运输货物，并在每个步骤中随机搜索肌动蛋白结合位点。最近的一项实验表明，肌球蛋白杠杆臂之间的关节可能不会像早期研究中所假定的那样自由旋转，而是具有优选的角度，从而导致结构受约束的扩散。我们通过对肌球蛋白V扩散和步进进行全面的分析和数值建模来解决这一争议。当关节受约束时，我们的模型将再现实验观察到的扩散，从而使我们能够估算约束能的边界。我们还测试了约束扩散模型与步长分布的先前测量值以及各种可观察量的负载依赖性之间的一致性。