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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Crystal structure of the Sec4p·Sec2p complex in the nucleotide exchanging intermediate state
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Crystal structure of the Sec4p·Sec2p complex in the nucleotide exchanging intermediate state

机译：核苷酸交换中间态下Sec4p·Sec2p复合物的晶体结构

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摘要

Vesicular transport during exocytosis is regulated by Rab GTPase (Sec4p in yeast), which is activated by a guanine nucleotide exchange factor (GEF) called Sec2p. Here, we report the crystal structure of the Sec2p GEF domain in a complex with the nucleotide-free Sec4p at 2.7 A resolution. Upon complex formation, the Sec2p helices approach each other, flipping the side chain of Phe-109 toward Leu-104 and Leu-108 of Sec2p. These three residues provide a hydrophobic platform to attract the side chains of Phe-49, Ile-53, and Ile-55 in the switch Ⅰ region as well as Phe-57 and Trp-74 in the inters witch region of Sec4p. Consequently, the switch Ⅰ and Ⅱ regions are largely deformed, to create a flat hydrophobic interface that snugly fits the surface of the Sec2p coiled coil. These drastic conformational changes disrupt the interactions between switch Ⅰ and the bound guanine nucleotide, which facilitates the GDP release. Unlike the recently reported 3.3 A structure of the Sec4p·Sec2p complex, our structure contains a phosphate ion bound to the P-loop, which may represent an intermediate state of the nucleotide exchange reaction.
机译：胞吐过程中的囊泡运输受Rab GTPase（酵母中的Sec4p）调节，Rab GTPase被称为Sec2p的鸟嘌呤核苷酸交换因子（GEF）激活。在这里，我们报告与2.7 A分辨率的无核苷酸Sec4p复杂的Sec2p GEF域的晶体结构。复合体形成后，Sec2p螺旋彼此靠近，将Phe-109的侧链向Sec2p的Leu-104和Leu-108翻转。这三个残基提供了一个疏水平台，以吸引开关Ⅰ区域中Phe-49，Ile-53和Ile-55的侧链，以及Sec4p间区域中的Phe-57和Trp-74的侧链。因此，开关Ⅰ和Ⅱ区大大变形，形成一个平坦的疏水界面，紧密地适合Sec2p盘绕线圈的表面。这些剧烈的构象变化破坏了开关Ⅰ与结合的鸟嘌呤核苷酸之间的相互作用，从而促进了GDP的释放。与最近报道的Sec4p·Sec2p复合物的3.3 A结构不同，我们的结构包含与P环结合的磷酸根离子，这可能代表核苷酸交换反应的中间状态。

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