Center for Theoretical Biological Physics, Rice University, Houston, Texas, United States of America.
Systems, Synthetic, and Physical Biology, Rice University, Houston, Texas, United States of America.
PLoS Comput Biol. 2022 May 9;18(5):e1010105. doi: 10.1371/journal.pcbi.1010105. eCollection 2022 May.
Actin networks are essential for living cells to move, reproduce, and sense their environments. The dynamic and rheological behavior of actin networks is modulated by actin-binding proteins such as α-actinin, Arp2/3, and myosin. There is experimental evidence that actin-binding proteins modulate the cooperation of myosin motors by connecting the actin network. In this work, we present an analytical mean field model, using the Flory-Stockmayer theory of gelation, to understand how different actin-binding proteins change the connectivity of the actin filaments as the networks are formed. We follow the kinetics of the networks and estimate the concentrations of actin-binding proteins that are needed to reach connectivity percolation as well as to reach rigidity percolation. We find that Arp2/3 increases the actomyosin connectivity in the network in a non-monotonic way. We also describe how changing the connectivity of actomyosin networks modulates the ability of motors to exert forces, leading to three possible phases of the networks with distinctive dynamical characteristics: a sol phase, a gel phase, and an active phase. Thus, changes in the concentration and activity of actin-binding proteins in cells lead to a phase transition of the actin network, allowing the cells to perform active contraction and change their rheological properties.
肌动蛋白网络对于活细胞的运动、繁殖和感知环境至关重要。肌动蛋白结合蛋白（如α-辅肌动蛋白、Arp2/3 和肌球蛋白）调节肌动蛋白网络的动态和流变行为。有实验证据表明，肌动蛋白结合蛋白通过连接肌动蛋白网络来调节肌球蛋白马达的协同作用。在这项工作中，我们使用 Flory-Stockmayer 凝胶化理论提出了一个分析的平均场模型，以了解不同的肌动蛋白结合蛋白如何改变网络形成时肌动蛋白丝的连接性。我们跟踪网络的动力学，并估计达到连接性渗滤和达到刚性渗滤所需的肌动蛋白结合蛋白浓度。我们发现 Arp2/3 以非单调的方式增加了网络中肌球蛋白的连接性。我们还描述了改变肌球蛋白网络的连接性如何调节马达施加力的能力，导致具有独特动力学特征的网络的三个可能相：溶胶相、凝胶相和活性相。因此，细胞中肌动蛋白结合蛋白的浓度和活性的变化导致肌动蛋白网络的相变，使细胞能够进行主动收缩并改变其流变性质。
