Nature2014-06-18 6:10 PM

一个4-型分泌系统的结构 Structure of a type IV secretion system

论文摘要 


这项研究报告了使用电子显微镜来重构来自大肠杆菌的细菌4-型分泌(T4S)系统的一个较大的、3-megadalton的复合物,它由以复杂的化学计量关系聚集在一起的8个蛋白组成,形成一个穿过细胞膜的柄,将一个与核心外膜相关的复合物和一个内膜复合物结为一体。该结构显示了一个新颖的架构,它明显不同于从其他细菌分泌系统所知道的那些架构。T4S系统被很多细菌病原体用来输送毒性因子和转移遗传材料,同时它们也显示了用作对人类细胞进行遗传修饰的一种工具的潜力。


Abstract 


Bacterial type IV secretion systems translocate virulence factors into eukaryotic cells, distribute genetic material between bacteria and have shown potential as a tool for the genetic modification of human cells. Given the complex choreography of the substrate through the secretion apparatus, the molecular mechanism of the type IV secretion system has proved difficult to dissect in the absence of structural data for the entire machinery. Here we use electron microscopy to reconstruct the type IV secretion system encoded by the Escherichia coli R388 conjugative plasmid. We show that eight proteins assemble in an intricate stoichiometric relationship to form an approximately 3 megadalton nanomachine that spans the entire cell envelope. The structure comprises an outer membrane-associated core complex connected by a central stalk to a substantial inner membrane complex that is dominated by a battery of 12 VirB4 ATPase subunits organized as side-by-side hexameric barrels. Our results show a secretion system with markedly different architecture, and consequently mechanism, to other known bacterial secretion systems.

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