Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo, Japan.
Mol Biol Cell. 2012 Aug;23(15):2930-42. doi: 10.1091/mbc.E12-05-0356. Epub 2012 Jun 6.
COPII-coated buds are formed at endoplasmic reticulum exit sites (ERES) to mediate ER-to-Golgi transport. Sec16 is an essential factor in ERES formation, as well as in COPII-mediated traffic in vivo. Sec16 interacts with multiple COPII proteins, although the functional significance of these interactions remains unknown. Here we present evidence that full-length Sec16 plays an important role in regulating Sar1 GTPase activity at the late steps of COPII vesicle formation. We show that Sec16 interacts with Sec23 and Sar1 through its C-terminal conserved region and hinders the ability of Sec31 to stimulate Sec23 GAP activity toward Sar1. We also find that purified Sec16 alone can self-assemble into homo-oligomeric complexes on a planar lipid membrane. These features ensure prolonged COPII coat association within a preformed Sec16 cluster, which may lead to the formation of ERES. Our results indicate a mechanistic relationship between COPII coat assembly and ERES formation.
COPII 被膜小泡在内质网出口位点（ERES）处形成，以介导内质网到高尔基体的运输。Sec16 是 ERES 形成以及体内 COPII 介导的运输所必需的因素。Sec16 与多种 COPII 蛋白相互作用，尽管这些相互作用的功能意义尚不清楚。在这里，我们提供的证据表明全长 Sec16 在调节 COPII 囊泡形成后期 Sar1 GTPase 活性方面发挥着重要作用。我们表明 Sec16 通过其 C 端保守结构域与 Sec23 和 Sar1 相互作用，并阻碍 Sec31 对 Sar1 的 Sec23 GAP 活性的刺激能力。我们还发现，纯化的 Sec16 本身可以在平面脂质膜上自组装成同源寡聚复合物。这些特征确保了在预先形成的 Sec16 簇内 COPII 外壳的持续结合，这可能导致 ERES 的形成。我们的结果表明 COPII 外壳组装和 ERES 形成之间存在机制关系。
