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Abstract：
Cortactin coactivates Arp2/3 complex synergistically with WASP-family nucleation-promoting factors (NPFs) and stabilizes branched networks by linking Arp2/3 complex to F-actin. It is poorly understood how cortactin performs these functions. We describe the 2.89 Å resolution cryo-EM structure of cortactin\'s N-terminal domain (Cort1-76) bound to Arp2/3 complex. Cortactin binds Arp2/3 complex through an inverted Acidic domain (D20-V29), which targets the same site on Arp3 as the Acidic domain of NPFs but with opposite polarity. Sequences N- and C-terminal to cortactin\'s Acidic domain do not increase its affinity for Arp2/3 complex but contribute toward coactivation with NPFs. Coactivation further increases with NPF dimerization and for longer cortactin constructs with stronger binding to F-actin. The results suggest that cortactin contributes to Arp2/3 complex coactivation with NPFs in two ways, by helping recruit the complex to F-actin and by stabilizing the short-pitch (active) conformation, which are both byproducts of cortactin\'s core function in branch stabilization.
摘要：
Cortactin与WASP家族成核促进因子（NPF）协同激活Arp2/3复合物，并通过将Arp2/3复合物连接到F-肌动蛋白来稳定分支网络。人们对cortactin如何执行这些功能知之甚少。我们描述了与Arp2/3复合物结合的cortactin的N端结构域（Cort1-76）的2.89µ分辨率低温EM结构。Cortactin通过反向酸性结构域（D20-V29）结合Arp2/3复合物，其靶向Arp3上与NPF的酸性结构域相同的位点,但具有相反的极性。cortactin酸性结构域的N-和C-末端序列不会增加其对Arp2/3复合物的亲和力，但有助于与NPF的共激活。随着NPF二聚化和与F-肌动蛋白结合更强的更长的皮质肌动蛋白构建体,共激活进一步增加。结果表明，皮质肌动蛋白以两种方式促进Arp2/3复合物与NPF的共激活，通过帮助将复合物招募到F-肌动蛋白并稳定短间距（活性）构象，这两种都是cortactin在分支稳定中的核心功能的副产物。
