Sed4p Stimulates Sar1p GTP Hydrolysis and Promotes Limited Coat Disassembly
Sed4p Stimulates Sar1p GTP Hydrolysis and Promotes Limited Coat Disassembly
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DOI：
10.1111/j.1600-0854.2011.01173.x
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发表时间：
2011-05-01
期刊：
影响因子：
4.5
通讯作者：
Sato, Ken
中科院分区：
文献类型：
--
作者：
Kodera, Chie;Yorimitsu, Tomohiro;Sato, Ken
外壳蛋白复合物 II (COPII) 产生介导内质网 (ER) 蛋白质输出的转运囊泡。 COPII 囊泡形成的第一步涉及通过鸟嘌呤核苷酸交换因子 (GEF) Sec12p 将 Sar1p-GDP 转化为 Sar1p-GTP。在酿酒酵母中，Sed4p 是 Sec12p 的结构同源物，但尚未发现 GEF 对 Sar1p 的活性。尽管 Sed4p 在 COPII 囊泡形成中的作用是由与 SAR1 的遗传相互作用暗示的，但 Sed4p 促进这一过程的分子基础尚不清楚。这项研究表明，Sed4p 的胞质结构域优先结合 Sar1p 的无核苷酸形式，并且 Sed4p 结合会刺激 Sar1p 的内在 GTP 酶激活蛋白 (GAP) 和 Sec23p GTP 酶激活蛋白 (GAP) 加速的 GTP 酶活性。 Sed4p 对 Sec23p GAP 活性的刺激导致外壳蛋白从膜上加速解离。然而，只有当货物不与 Sar1p 关联时，Sed4p 才会与 Sar1p 结合。基于这些发现，Sed4p 似乎加速了 Sec23/24p 外壳从膜上的解离，但效果仅限于不捕获货物蛋白的 Sar1p 分子。我们推测这种受限的外壳分解可能有助于特定货物分子浓缩到 COPII 囊泡中。
The coat protein complex II (COPII) generates transport vesicles that mediate protein export from the endoplasmic reticulum (ER). The first step of COPII vesicle formation involves conversion of Sar1p-GDP to Sar1p-GTP by guanine-nucleotide-exchange factor (GEF) Sec12p. In Saccharomyces cerevisiae, Sed4p is a structural homolog of Sec12p, but no GEF activity toward Sar1p has been found. Although the role of Sed4p in COPII vesicle formation is implied by the genetic interaction with SAR1, the molecular basis by which Sed4p contributes to this process is unclear. This study showed that the cytoplasmic domain of Sed4p preferentially binds the nucleotide-free form of Sar1p and that Sed4p binding stimulates both the intrinsic and Sec23p GTPase-activating protein (GAP)-accelerated GTPase activity of Sar1p. This stimulation of Sec23p GAP activity by Sed4p leads to accelerated dissociation of coat proteins from membranes. However, Sed4p binding to Sar1p occurs only when cargo is not associated with Sar1p. On the basis of these findings, Sed4p appears to accelerate the dissociation of the Sec23/24p coat from the membrane, but the effect is limited to Sar1p molecules that do not capture cargo protein. We speculate that this restricted coat disassembly may contribute to the concentration of specific cargo molecules into the COPII vesicles.