Ecosystem and Public Health; Snyder Institute for Chronic Diseases; Biochemistry and Molecular Biology, Cumming School of Medicine, University of Calgary, Calgary, AB, T2N4Z6, Canada.
State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, China.
Nat Commun. 2020 Oct 8;11(1):5065. doi: 10.1038/s41467-020-18807-9.
The type VI protein secretion system (T6SS) is a powerful needle-like machinery found in Gram-negative bacteria that can penetrate the cytosol of receiving cells in milliseconds by physical force. Anchored by its membrane-spanning complex (MC) and a baseplate (BP), the T6SS sheath-tube is assembled in a stepwise process primed by TssA and terminated by TagA. However, the molecular details of its assembly remain elusive. Here, we systematically examined the initiation and termination of contractile and non-contractile T6SS sheaths in MC-BP, tssA and tagA mutants by fluorescence microscopy. We observe long pole-to-pole sheath-tube structures in the non-contractile MC-BP defective mutants but not in the Hcp tube or VgrG spike mutants. Combining overexpression and genetic mutation data, we demonstrate complex effects of TssM, TssA and TagA interactions on T6SS sheath-tube dynamics. We also report promiscuous interactions of TagA with multiple T6SS components, similar to TssA. Our results demonstrate that priming of the T6SS sheath-tube assembly is not dependent on TssA, nor is the assembly termination dependent on the distal end TssA-TagA interaction, and highlight the tripartite control of TssA-TssM-TagA on sheath-tube initiation and termination.
VI 型蛋白分泌系统（T6SS）是革兰氏阴性菌中一种强大的针状机械装置，能够在毫秒内通过物理力穿透受体细胞的细胞质。T6SS 的膜跨复合物（MC）和基板（BP）锚定，其鞘管通过 TssA 和 TagA 逐步组装。然而，其组装的分子细节仍然难以捉摸。在这里，我们通过荧光显微镜系统地检查了 MC-BP、tssA 和 tagA 突变体中收缩和非收缩 T6SS 鞘管的起始和终止。我们观察到非收缩性 MC-BP 缺陷突变体中的长极对极鞘管结构，但在 Hcp 管或 VgrG 刺突突变体中没有。结合过表达和遗传突变数据，我们证明了 TssM、TssA 和 TagA 相互作用对 T6SS 鞘管动力学的复杂影响。我们还报告了 TagA 与多种 T6SS 组件的混杂相互作用，类似于 TssA。我们的研究结果表明，T6SS 鞘管组装的引发不依赖于 TssA，组装的终止也不依赖于远端 TssA-TagA 相互作用，突出了 TssA-TssM-TagA 对鞘管起始和终止的三分控制。
