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首页> 外文期刊>Physical Review X >Stochastic Ratcheting on a Funneled Energy Landscape Is Necessary for Highly Efficient Contractility of Actomyosin Force Dipoles
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Stochastic Ratcheting on a Funneled Energy Landscape Is Necessary for Highly Efficient Contractility of Actomyosin Force Dipoles

机译：肌动蛋白力偶极子的高效收缩性在漏斗的能量景观上随机棘轮是必要的。

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Current understanding of how contractility emerges in disordered actomyosin networks of nonmuscle cells is still largely based on the intuition derived from earlier works on muscle contractility. In addition, in disordered networks, passive cross-linkers have been hypothesized to percolate force chains in the network, hence, establishing large-scale connectivity between local contractile clusters. This view, however, largely overlooks the free energy of cross-linker binding at the microscale, which, even in the absence of active fluctuations, provides a thermodynamic drive towards highly overlapping filamentous states. In this work, we use stochastic simulations and mean-field theory to shed light on the dynamics of a single actomyosin force dipole—a pair of antiparallel actin filaments interacting with active myosin II motors and passive cross-linkers. We first show that while passive cross-linking without motor activity can produce significant contraction between a pair of actin filaments, driven by thermodynamic favorability of cross-linker binding, a sharp onset of kinetic arrest exists at large cross-link binding energies, greatly diminishing the effectiveness of this contractility mechanism. Then, when considering an active force dipole containing nonmuscle myosin II, we find that cross-linkers can also serve as a structural ratchet when the motor dissociates stochastically from the actin filaments, resulting in significant force amplification when both molecules are present. Our results provide predictions of how actomyosin force dipoles behave at the molecular level with respect to filament boundary conditions, passive cross-linking, and motor activity, which can explicitly be tested using an optical trapping experiment.
机译：当前对如何在非肌肉细胞的无序放线肌球蛋白网络中出现收缩力的理解仍主要基于对肌肉收缩力早期工作的直觉。另外，在无序的网络中，已经假设无源交联剂可以渗透网络中的力链，因此可以在局部可收缩簇之间建立大规模的连通性。然而，这种观点在很大程度上忽略了交联剂结合在微观尺度上的自由能，即使在没有主动波动的情况下，该自由能也提供了向高度重叠的丝状态的热力学驱动。在这项工作中，我们使用随机模拟和均值场理论来揭示单个肌动球蛋白力偶极子的动力学-一对反平行肌动蛋白丝与主动肌球蛋白II电机和被动交联剂相互作用。我们首先显示，虽然没有运动活性的被动交联可以在一对肌动蛋白丝之间产生显着的收缩，这是由交联剂结合的热力学偏好所驱动的，但是在大的交联结合能下，动力学阻滞作用会急剧发作，从而大大减少这种收缩机制的有效性。然后，当考虑包含非肌肉肌球蛋白II的主动力偶极子时，我们发现当电动机从肌动蛋白丝随机分离时，交联剂也可以用作结构棘轮，当两个分子都存在时，会导致显着的力放大。我们的结果提供了关于肌动蛋白力偶极子在细丝边界条件，被动交联和运动活动方面在分子水平上表现的预测，可以使用光阱实验对其进行明确测试。

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