Focal Area Infection Biology, Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056, Basel, Switzerland.
Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, Mattenstrasse 26, CH-4058, Basel, Switzerland.
Nat Microbiol. 2017 Nov;2(11):1507-1512. doi: 10.1038/s41564-017-0020-7. Epub 2017 Sep 25.
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 . 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.
细菌的 VI 型分泌系统（T6SS）使用长鞘的收缩，迅速将带有相关效应器的管穿过真核和细菌细胞的膜。关于 T6SS 的固有不稳定预收缩状态，只有有限的结构信息可用。在这里，我们使用冷冻电子显微镜获得了一个非收缩鞘-管复合物的 3.7Å 分辨率结构，并表明它类似于霍乱弧菌细胞内伸展的 T6SS。我们构建了完整鞘-管组件的拟原子模型，该模型提供了对鞘收缩与推动和旋转内部管以进行有效靶膜穿透的机械耦合的理解。我们的数据还表明，鞘的收缩暴露了一个埋藏的识别域，以特异性触发同源 ATP 依赖性解折叠酶 ClpV 触发 T6SS 鞘的解组装和再循环。
