Program in Molecular Medicine and Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Proc Natl Acad Sci U S A. 2013 Aug 27;110(35):14213-8. doi: 10.1073/pnas.1301883110. Epub 2013 Aug 12.
Membrane recruitment of cytohesin family Arf guanine nucleotide exchange factors depends on interactions with phosphoinositides and active Arf GTPases that, in turn, relieve autoinhibition of the catalytic Sec7 domain through an unknown structural mechanism. Here, we show that Arf6-GTP relieves autoinhibition by binding to an allosteric site that includes the autoinhibitory elements in addition to the PH domain. The crystal structure of a cytohesin-3 construct encompassing the allosteric site in complex with the head group of phosphatidyl inositol 3,4,5-trisphosphate and N-terminally truncated Arf6-GTP reveals a large conformational rearrangement, whereby autoinhibition can be relieved by competitive sequestration of the autoinhibitory elements in grooves at the Arf6/PH domain interface. Disposition of the known membrane targeting determinants on a common surface is compatible with multivalent membrane docking and subsequent activation of Arf substrates, suggesting a plausible model through which membrane recruitment and allosteric activation could be structurally integrated.
细胞松弛素家族 Arf 鸟嘌呤核苷酸交换因子的膜募集依赖于与磷酸肌醇和活性 Arf GTPase 的相互作用，反过来，通过未知的结构机制，通过活性 Arf GTPase 解除催化 Sec7 结构域的自动抑制。在这里，我们表明，Arf6-GTP 通过结合别构位点来解除自动抑制，该别构位点除了 PH 结构域外还包含自动抑制元件。包含别构位点的细胞松弛素-3 构建体的晶体结构与磷脂酰肌醇 3,4,5-三磷酸的头部基团和 N 端截断的 Arf6-GTP 复合物，揭示了一个大的构象重排，通过竞争性隔离 Arf6/PH 结构域界面凹槽中的自动抑制元件，可以解除自动抑制。已知的膜靶向决定因素在共同表面上的配置与多价膜对接和随后的 Arf 底物激活兼容，这表明了一个合理的模型，通过该模型，膜募集和别构激活可以在结构上整合。
