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

总结/摘要 为了协调复杂的过程，如运动和内吞作用，细胞依赖于肌动蛋白丝调节 蛋白质来控制肌动蛋白丝网络的动力学和结构。肌动蛋白丝成核剂是 关键的肌动蛋白调节因子，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。Arp 2/3复合物是一个7亚基的250 kD肌动蛋白成核机器， 专门产生分支肌动蛋白丝。需要Arp 2/3复合物调节分支， 组装对于生长锥的内吞作用和运动性等过程重要的分支肌动蛋白网络， 以及在致病过程如宿主细胞被细菌感染或肿瘤细胞转移中。大多数 Arp 2/3复合物调节的研究集中在WASP蛋白上，WASP蛋白是研究得最好的NPF。这些研究 揭示了WASP介导的激活的基本原理;它与复合物结合，募集肌动蛋白单体， 并刺激激活构象变化。然而，WASP介导的激活的一个关键方面是， 该复合物仍然未知：WASP蛋白如何激活Arp 2/3复合物， 肌动蛋白丝？根据几个实验室的努力，我们现在知道，除了WASP和WASP- 招募的单体，Arp 2/3复合物也必须结合预制的肌动蛋白丝，以允许WASP介导的 activation.尽管预成形长丝在确保分支方面起着重要作用，但几乎一无所知 纤维是如何激活的此外，还不知道WASP，WASP募集的单体， 和肌动蛋白丝协调激活具有严格双峰开关样行为的分支成核，其中 需要所有激活因子来启动复合物。在这里，我们使用一系列的生物化学，结构， 计算方法来解决这些问题。我们预计破译分子机制 或WASP调节的分支将帮助我们了解细胞如何控制细胞的动力学和结构， 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.