Sar1p N-terminal helix initiates membrane curvature and completes the fission of a COPII vesicle
Sar1p N-terminal helix initiates membrane curvature and completes the fission of a COPII vesicle
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DOI：
10.1016/j.cell.2005.07.025
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发表时间：
2005-08-26
期刊：
影响因子：
64.5
通讯作者：
Schekman, R
中科院分区：
文献类型：
--
作者：
Lee, MCS;Orci, L;Schekman, R
分泌蛋白通过copii包被的运输囊泡从内质网运输到高尔基体。五个核心COPII蛋白（Sar1p， Sec23/24p和Sec13/31p）协同作用，捕获货物蛋白并将内质网膜雕刻成定义几何形状的囊泡。外壳蛋白如何使脂质双分子层变形成囊泡的分子细节尚不清楚。在这里，我们发现小的GTPase Sar1p在囊泡生物发生过程中直接启动膜曲率。当GTP被Sar1p结合时，n端两性α螺旋的膜插入使合成脂质体变形成狭窄的小管。用丙氨酸取代a螺旋中庞大的疏水残基产生Sar1p突变体，这些突变体不能产生高度弯曲的膜，并且在天然内质网膜中形成囊泡时存在缺陷，尽管可以正常募集外壳和货物蛋白。因此，Sar1p引发的囊泡出芽将膜曲率的产生与衣蛋白组装和货物捕获结合在一起。
Secretory proteins traffic from the ER to the Golgi via COPII-coated transport vesicles. The five core COPII proteins (Sar1p, Sec23/24p, and Sec13/31p) act in concert to capture cargo proteins and sculpt the ER membrane into vesicles of defined geometry. The molecular details of how the coat proteins deform the lipid bilayer into vesicles are not known. Here we show that the small GTPase Sar1p directly initiates membrane curvature during vesicle biogenesis. Upon GTP binding by Sar1p, membrane insertion of the N-terminal amphipathic alpha helix deforms synthetic liposomes into narrow tubules. Replacement of bulky hydrophobic residues in the a helix with alanine yields Sar1p mutants that are unable to generate highly curved membranes and are defective in vesicle formation from native ER membranes despite normal recruitment of coat and cargo proteins. Thus, the initiation of vesicle budding by Sar1p couples the generation of membrane curvature with coat-protein assembly and cargo capture.