Structural basis of the interaction between RalA and Sec5, a subunit of the sec6/8 complex
Structural basis of the interaction between RalA and Sec5, a subunit of the sec6/8 complex
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DOI：
10.1093/emboj/cdg329
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发表时间：
2003-07-01
期刊：
影响因子：
11.4
通讯作者：
Brunger, AT
中科院分区：
文献类型：
--
作者：
Fukai, S;Matern, HT;Brunger, AT
sec6/8 复合物或外囊是一种八聚体蛋白复合物，在细胞极化过程中通过调节外吐囊泡与质膜对接的位点与小型 GTP 结合蛋白协同发挥作用。哺乳动物 sec6/8 复合物的 Sec5 亚基以 GTP 依赖性方式结合 Ral。在这里，我们以 2.1 埃的分辨率报道了 Sec5 的 Ral 结合域和与不可水解的 GTP 类似物 (GppNHp) 结合的 RalA 之间复合物的晶体结构，为 sec6/8 调节的机制和特异性提供了第一个结构见解。 Sec5 Ral 结合结构域折叠成免疫球蛋白样 β 夹心结构，这代表了 GTP 结合蛋白效应子的一种新折叠方式。两种蛋白质之间的界面涉及连续的反平行 β 折叠，类似于其他效应器/G 蛋白复合物（例如 Ras 和 Rap1A）中发现的界面。 RalA.Sec5 复合物特有的特定相互作用包括 Sec5 Thr11 和 Arg27 以及 RalA Glu38，我们证明这些相互作用是通过等温滴定量热法形成复合物所必需的。比较 GppNHp 和 GDP 结合的 RalA 的结构表明 Sec5 结合存在核苷酸依赖性开关机制。
The sec6/8 complex or exocyst is an octameric protein complex that functions during cell polarization by regulating the site of exocytic vesicle docking to the plasma membrane, in concert with small GTP-binding proteins. The Sec5 subunit of the mammalian sec6/8 complex binds Ral in a GTP-dependent manner. Here we report the crystal structure of the complex between the Ral-binding domain of Sec5 and RalA bound to a non-hydrolyzable GTP analog (GppNHp) at 2.1 Angstrom resolution, providing the first structural insights into the mechanism and specificity of sec6/8 regulation. The Sec5 Ral-binding domain folds into an immunoglobulin-like beta-sandwich structure, which represents a novel fold for an effector of a GTP-binding protein. The interface between the two proteins involves a continuous antiparallel beta-sheet, similar to that found in other effector/G-protein complexes, such as Ras and Rap1A. Specific interactions unique to the RalA.Sec5 complex include Sec5 Thr11 and Arg27, and RalA Glu38, which we show are required for complex formation by isothermal titration calorimetry. Comparison of the structures of GppNHp- and GDP-bound RalA suggests a nucleotide-dependent switch mechanism for Sec5 binding.