Department of Biochemistry, University of Washington, Seattle, Washington, USA.
Nat Struct Mol Biol. 2010 Oct;17(10):1226-32. doi: 10.1038/nsmb.1910. Epub 2010 Sep 19.
The type II secretion system (T2SS) is a macromolecular complex spanning the inner and outer membranes of Gram-negative bacteria. Remarkably, the T2SS secretes folded proteins, including multimeric assemblies such as cholera toxin and heat-labile enterotoxin from Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. The major outer membrane T2SS protein is the 'secretin' GspD. Cryo-EM reconstruction of the V. cholerae secretin at 19-Å resolution reveals a dodecameric structure reminiscent of a barrel, with a large channel at its center that contains a closed periplasmic gate. The GspD periplasmic domain forms a vestibule with a conserved constriction, and it binds to a pentameric exoprotein and to the trimeric tip of the T2SS pseudopilus. By combining our results with structures of the cholera toxin and T2SS pseudopilus tip, we provide a structural basis for a possible secretion mechanism of the T2SS.
II 型分泌系统（T2SS）是一种跨越革兰氏阴性菌内外膜的大分子复合物。值得注意的是，T2SS 分泌折叠蛋白，包括霍乱毒素和肠产毒性大肠杆菌的耐热肠毒素等多聚体组装体。主要的外膜 T2SS 蛋白是“分泌蛋白”GspD。19 埃分辨率的霍乱弧菌分泌蛋白的冷冻电镜重建揭示了一个十二聚体结构，类似于桶状结构，其中心有一个大通道，包含一个封闭的周质门。GspD 周质结构域形成一个带有保守收缩的前庭，它与五聚体外蛋白和 T2SS 假菌毛的三聚体尖端结合。通过将我们的结果与霍乱毒素和 T2SS 假菌毛尖端的结构相结合，我们为 T2SS 的可能分泌机制提供了结构基础。
