Division of Structural Biology, Department of Biology/Chemistry, University of Osnabrück, Barbarastraße 13, Osnabrück 49076, Germany.
Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, Barbarastraße 13, Osnabrück 49076, Germany.
Nat Commun. 2017 Jan 4;8:14034. doi: 10.1038/ncomms14034.
The Mon1-Ccz1 complex (MC1) is the guanine nucleotide exchange factor (GEF) for the Rab GTPase Ypt7/Rab7 and is required for endosomal maturation and fusion at the vacuole/lysosome. Here we present the overall architecture of MC1 from Chaetomium thermophilum, and in combining biochemical studies and mutational analysis in yeast, we identify the domains required for catalytic activity, complex assembly and localization of MC1. The crystal structure of a catalytic MC1 core complex bound to Ypt7 provides mechanistic insight into its function. We pinpoint the determinants that allow for a discrimination of the Rab7-like Ypt7 over the Rab5-like Vps21, which are both located on the same membrane. MC1 shares structural similarities with the TRAPP complex, but employs a novel mechanism to promote nucleotide exchange that utilizes a conserved lysine residue of Ypt7, which is inserted upon MC1 binding into the nucleotide-binding pocket of Ypt7 and contributes to specificity.
Mon1-Ccz1 复合物（MC1）是 Rab GTPase Ypt7/Rab7 的鸟嘌呤核苷酸交换因子（GEF），对于液泡/溶酶体中的内体成熟和融合是必需的。在这里，我们展示了嗜热毛壳菌 MC1 的整体结构，并通过酵母中的生化研究和突变分析，确定了催化活性、复合物组装和 MC1 定位所需的结构域。与 Ypt7 结合的催化 MC1 核心复合物的晶体结构提供了其功能的机制见解。我们确定了允许区分位于同一膜上的 Rab7 样 Ypt7 与 Rab5 样 Vps21 的决定因素。MC1 与 TRAPP 复合物具有结构相似性，但采用了一种新的机制来促进核苷酸交换，该机制利用了 MC1 结合后插入 Ypt7 核苷酸结合口袋的 Ypt7 保守赖氨酸残基，有助于特异性。
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