Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR, USA.
Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR, USA
EMBO J. 2018 Nov 15;37(22). doi: 10.15252/embj.2018100005. Epub 2018 Oct 15.
Unlike the WASP family of Arp2/3 complex activators, WISH/DIP/SPIN90 (WDS) family proteins activate actin filament nucleation by the Arp2/3 complex without the need for a preformed actin filament. This allows WDS proteins to initiate branched actin network assembly by providing seed filaments that activate WASP-bound Arp2/3 complex. Despite their important role in actin network initiation, it is unclear how WDS proteins drive the activating steps that require both WASP and pre-existing actin filaments during WASP-mediated nucleation. Here, we show that SPIN90 folds into an armadillo repeat domain that binds a surface of Arp2/3 complex distinct from the two WASP sites, straddling a hinge point that may stimulate movement of the Arp2 subunit into the activated short-pitch conformation. SPIN90 binds a surface on Arp2/3 complex that overlaps with actin filament binding, explaining how it could stimulate the same structural rearrangements in the complex as pre-existing actin filaments. By revealing how WDS proteins activate the Arp2/3 complex, these data provide a molecular foundation to understand initiation of dendritic actin networks and regulation of Arp2/3 complex by its activators.
不像 Arp2/3 复合物激活因子 WASP 家族，WISH/DIP/SPIN90（WDS）家族蛋白通过 Arp2/3 复合物激活肌动蛋白丝成核，而无需预先形成肌动蛋白丝。这使得 WDS 蛋白能够通过提供激活 WASP 结合的 Arp2/3 复合物的种丝来启动分支肌动蛋白网络组装。尽管它们在肌动蛋白网络起始中具有重要作用，但不清楚 WDS 蛋白如何驱动在 WASP 介导的成核过程中需要 WASP 和预先存在的肌动蛋白丝的激活步骤。在这里，我们表明 SPIN90 折叠成一个富含亮氨酸重复的结构域，该结构域结合 Arp2/3 复合物的一个不同于两个 WASP 结合位点的表面，跨越一个铰链点，该铰链点可能刺激 Arp2 亚基向激活的短螺距构象移动。SPIN90 结合 Arp2/3 复合物上的一个表面，该表面与肌动蛋白丝结合重叠，解释了它如何能够刺激复合物发生与预先存在的肌动蛋白丝相同的结构重排。通过揭示 WDS 蛋白如何激活 Arp2/3 复合物，这些数据为理解树突状肌动蛋白网络的起始和其激活因子对 Arp2/3 复合物的调节提供了分子基础。
