Protein coats deform flat lipid membranes into buds and capture membrane proteins to form transport vesicles. The assembly/disassembly cycle of the COPI coat on Golgi membranes is coupled to the GTP/GDP cycle of the small G protein Arf1. At the heart of this coupling is the specific interaction of membrane-bound Arf1-GTP with coatomer, a complex of seven proteins that forms the building unit of the COPI coat. Although COPI coat disassembly requires the catalysis of GTP hydrolysis in Arf1 by a specific GTPase-activating protein (ArfGAP1), the precise timing of this reaction during COPI vesicle formation is not known. Using time-resolved assays for COPI dynamics on liposomes of controlled size, we show that the rate of ArfGAP1-catalysed GTP hydrolysis in Arf1 and the rate of COPI disassembly increase over two orders of magnitude as the curvature of the lipid bilayer increases and approaches that of a typical transport vesicle. This leads to a model for COPI dynamics in which GTP hydrolysis in Arf1 is organized temporally and spatially according to the changes in lipid packing induced by the coat.

译文

蛋白质外衣将平坦的脂质膜变形为芽,并捕获膜蛋白以形成运输囊泡。高尔基体膜上COPI涂层的组装/拆卸周期与小g蛋白arf1的GTP/GDP周期耦合。这种耦合的核心是膜结合Arf1-GTP与coatomer的特异性相互作用,coatomer是由七个蛋白质组成的复合物,形成了cobi涂层的构建单元。尽管cobi涂层的拆卸需要通过特定的GTPase激活蛋白 (ArfGAP1) 催化Arf1中的GTP水解,但在cobi囊泡形成过程中该反应的确切时间尚不清楚。使用时间分辨测定法对受控大小的脂质体进行COPI动力学,我们表明,随着脂质双层曲率的增加和接近典型运输囊泡的曲率,Arf1中ArfGAP1-catalysed GTP水解的速率和COPI分解的速率增加了两个数量级。这导致了coci动力学模型,其中Arf1中的GTP水解根据涂层引起的脂质堆积的变化在时间和空间上进行组织。

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