Clathrin-mediated endocytosis depends on polymerization of a branched actin network to provide force for membrane invagination. A key regulator in branched actin network formation is actin capping protein (CP), which binds to the barbed end of actin filaments to prevent the addition or loss of actin subunits. CP was thought to stochastically bind actin filaments, but recent evidence shows CP is regulated by a group of proteins containing CP-interacting (CPI) motifs. Importantly, how CPI motif proteins function together to regulate CP is poorly understood. Here, we show Aim21 and Bsp1 work synergistically to recruit CP to the endocytic actin network in budding yeast through their CPI motifs, which also allosterically modulate capping strength. In contrast, twinfilin works downstream of CP recruitment, regulating the turnover of CP through its CPI motif and a non-allosteric mechanism. Collectively, our findings reveal how three CPI motif proteins work together to regulate CP in a stepwise fashion during endocytosis.

中文翻译：

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网格蛋白介导的内吞作用期间肌动蛋白加帽蛋白招募和周转的机制


网格蛋白介导的内吞作用依赖于分支肌动蛋白网络的聚合来为膜内陷提供力。分支肌动蛋白网络形成的关键调节因子是肌动蛋白加帽蛋白 (CP)，它与肌动蛋白丝的倒刺末端结合，以防止肌动蛋白亚基的添加或丢失。 CP 被认为随机结合肌动蛋白丝，但最近的证据表明 CP 受到一组含有 CP 相互作用 (CPI) 基序的蛋白质的调节。重要的是，人们对 CPI 基序蛋白如何共同发挥作用来调节 CP 知之甚少。在这里，我们展示了 Aim21 和 Bsp1 协同作用，通过它们的 CPI 基序将 CP 招募到芽殖酵母中的内吞肌动蛋白网络，这也变构调节加帽强度。相比之下，twinfilin 在 CP 募集下游发挥作用，通过其 CPI 基序和非变构机制调节 CP 的周转。总的来说，我们的研究结果揭示了三种 CPI 基序蛋白如何协同作用，在内吞作用过程中逐步调节 CP。