Bigay Joëlle, Gounon Pierre, Robineau Sylviane, Antonny Bruno
Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, 660 route des Lucioles, 06560 Valbonne-Sophia-Antipolis, France.
Nature. 2003 Dec 4;426(6966):563-6. doi: 10.1038/nature02108.
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.
蛋白质衣壳将扁平的脂质膜变形为芽状，并捕获膜蛋白以形成运输小泡。高尔基体膜上 COPI 衣壳的组装/拆卸循环与小 G 蛋白 Arf1 的 GTP/GDP 循环相偶联。这种偶联的核心是膜结合的 Arf1-GTP 与衣被蛋白复合物的特异性相互作用，衣被蛋白复合物由七种蛋白质组成，是 COPI 衣壳的构建单元。尽管 COPI 衣壳的拆卸需要一种特异性 GTP 酶激活蛋白（ArfGAP1）催化 Arf1 中的 GTP 水解，但在 COPI 小泡形成过程中该反应的精确时间尚不清楚。通过对大小可控的脂质体上的 COPI 动力学进行时间分辨测定，我们发现随着脂质双层曲率增加并接近典型运输小泡的曲率，ArfGAP1 催化 Arf1 中 GTP 水解的速率以及 COPI 拆卸的速率增加了两个数量级。这导致了一个关于 COPI 动力学的模型，其中 Arf1 中的 GTP 水解根据衣壳诱导的脂质堆积变化在时间和空间上进行组织。
