Stagg Scott M, Gürkan Cemal, Fowler Douglas M, LaPointe Paul, Foss Ted R, Potter Clinton S, Carragher Bridget, Balch William E
National Resource for Automated Molecular Microscopy, Departments of Cell, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Nature. 2006 Jan 12;439(7073):234-8. doi: 10.1038/nature04339.
Endomembranes of eukaryotic cells are dynamic structures that are in continuous communication through the activity of specialized cellular machineries, such as the coat protein complex II (COPII), which mediates cargo export from the endoplasmic reticulum (ER). COPII consists of the Sar1 GTPase, Sec23 and Sec24 (Sec23/24), where Sec23 is a Sar1-specific GTPase-activating protein and Sec24 functions in cargo selection, and Sec13 and Sec31 (Sec13/31), which has a structural role. Whereas recent results have shown that Sec23/24 and Sec13/31 can self-assemble to form COPII cage-like particles, we now show that Sec13/31 can self-assemble to form minimal cages in the absence of Sec23/24. We present a three-dimensional reconstruction of these Sec13/31 cages at 30 A resolution using cryo-electron microscopy and single particle analysis. These results reveal a novel cuboctahedron geometry with the potential to form a flexible lattice and to generate a diverse range of containers. Our data are consistent with a model for COPII coat complex assembly in which Sec23/24 has a non-structural role as a multivalent ligand localizing the self-assembly of Sec13/31 to form a cage lattice driving ER cargo export.
真核细胞的内膜是动态结构，它们通过特殊细胞机制的活动持续进行通讯，比如介导货物从内质网（ER）输出的II型被膜小泡蛋白复合体（COPII）。COPII由Sar1 GTP酶、Sec23和Sec24（Sec23/24）组成，其中Sec23是一种Sar1特异性GTP酶激活蛋白，Sec24在货物选择中发挥作用，还有具有结构作用的Sec13和Sec31（Sec13/31）。尽管最近的研究结果表明Sec23/24和Sec13/31能够自我组装形成COPII笼状颗粒，但我们现在发现，在没有Sec23/24的情况下，Sec13/31也能自我组装形成最小的笼状结构。我们使用冷冻电子显微镜和单颗粒分析，以30埃的分辨率对这些Sec13/31笼状结构进行了三维重建。这些结果揭示了一种新颖的立方八面体几何结构，它有形成灵活晶格并产生多种容器的潜力。我们的数据与COPII被膜复合体组装模型一致，在该模型中，Sec23/24作为一种多价配体，具有非结构作用，可定位Sec13/31的自我组装，以形成驱动内质网货物输出的笼状晶格。
