Molecular mechanism of regulated branching nucleation by Arp2/3 complex and WASP proteins - admin supplement

摘要/摘要 为了协调运动和内吞等复杂的过程，细胞依赖于肌动蛋白细丝的调节。 控制肌动蛋白细丝网络的动力学和结构的蛋白质。肌动蛋白细丝核心子有 关键的肌动蛋白调节器，因为它们允许细胞启动新的肌动蛋白网络，但它们也决定了 这些网络的架构。Arp2/3复合体是一个7个亚基250kD的肌动蛋白成核机，它 专门产生分枝的肌动蛋白细丝。需要Arp2/3复合体调节的分支 组装分支肌动蛋白网络，对内吞作用和生长锥体的运动等过程非常重要， 以及在宿主细胞被细菌感染或肿瘤细胞转移等致病过程中。大多数人 对Arp2/3复合体调控的研究主要集中在对NPF研究最深入的WASP蛋白上。这些研究 揭示了WASP介导的激活的基本原理；它与复杂的、新招募的肌动蛋白单体结合， 并刺激激活的构象变化。然而，WASP介导的激活的一个关键方面 该复合体仍不清楚：WASP蛋白如何激活Arp2/3复合体以产生独有的分支 肌动蛋白细丝？根据多个实验室的努力，我们现在知道除了WASP和WASP- 被招募的单体，Arp2/3复合体也必须结合预形成的肌动蛋白细丝才能允许WASP介导 激活。尽管预制丝在确保分支方面起着重要作用，但几乎什么都不知道。 关于细丝是如何促进激活的。此外，尚不清楚WASP、WASP招募的单体、 和肌动蛋白细丝以严格的双峰开关行为协调激活分枝成核，其中 所有的激活因子都需要启动复合体。在这里，我们使用了一系列生化、结构和 解决这些问题的计算方法。我们预计，破译分子机制 或者WASP调节的分支将帮助我们了解细胞如何控制 肌动蛋白细胞骨架。

Summary / Abstract To orchestrate complex processes like motility and endocytosis, cells rely on actin filament regulatory proteins to control both the dynamics and architectures of actin filament networks. Actin filament nucleators are critical actin regulators, because they allow cells to initiate new actin networks, but they also dictate the architectures of these networks. Arp2/3 complex is a seven subunit 250 kD actin nucleating machine that specifically generates branched actin filaments. Regulated branching by Arp2/3 complex is required to assemble branched actin networks important for processes such as endocytosis and motility of growth cones, and in pathogenic processes like host cell infection by bacteria or metastasis of tumor cells. The majority of studies on Arp2/3 complex regulation have focused on WASP proteins, the best studied NPF. These studies revealed the basic tenets of WASP mediated activation; that it binds to the complex, recruits actin monomers, and stimulates an activating conformational change. However, a critical facet of WASP-mediated activation of the complex remains unknown: how do WASP proteins activate Arp2/3 complex to create exclusively branched actin filaments? Based on the efforts of several labs, we now know that in addition to WASP and WASP- recruited monomers, Arp2/3 complex must also bind preformed actin filaments to permit WASP-mediated activation. Despite the essential role for preformed filaments in ensuring a branch, almost nothing is known about how filaments contribute to activation. Further, it is not known how WASP, WASP-recruited monomers, and actin filaments coordinately activate branching nucleation with strict bimodal switch-like behavior, in which all activating factors are required to turn on the complex. Here we use a series of biochemical, structural, and computational approaches to address these issues. We anticipate that deciphering the molecular mechanism or WASP-regulated branching will help us understand how cells control the dynamics and architectures of the actin cytoskeleton.