The bacterial type VI secretion system (T6SS) uses contraction of a long sheath to quickly thrust a tube with associated effectors across membranes of eukaryotic and bacterial cells ^1-5 . Only limited structural information is available about the inherently unstable precontraction state of the T6SS. Here, we obtain a 3.7 Å resolution structure of a non-contractile sheath-tube complex using cryo-electron microscopy and show that it resembles the extended T6SS inside Vibrio cholerae cells. We build a pseudo-atomic model of the complete sheath-tube assembly, which provides a mechanistic understanding of coupling sheath contraction with pushing and rotating the inner tube for efficient target membrane penetration. Our data further show that sheath contraction exposes a buried recognition domain to specifically trigger the disassembly and recycling of the T6SS sheath by the cognate ATP-dependent unfoldase ClpV.

中文翻译：

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扩展型VI分泌系统鞘管复合体的低温-EM结构。

细菌VI型分泌系统（T6SS）使用长鞘的收缩来快速推动带有相关效应子的管穿过真核和细菌细胞膜^1-5。关于T6SS固有的不稳定预缩状态，只有有限的结构信息可用。在这里，我们获得了使用低温电子显微镜的非收缩鞘管复合物的3.7分辨率结构，并显示它类似于霍乱弧菌细胞内部扩展的T6SS。我们建立了完整的鞘管组件的伪原子模型，该模型提供了对鞘管收缩与推动和旋转内管的耦合机制的有效理解，以实现有效的目标膜穿透。我们的数据进一步表明，鞘收缩暴露了一个隐蔽的识别域，以通过关联的ATP依赖性解折叠酶ClpV特异性触发T6SS鞘的拆卸和循环利用。