Laboratoire d'Ingénierie des Systèmes Macromoléculaires, Institut de Microbiologie de la Méditerranée, CNRS UMR7255, Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Architecture et Fonction des Macromolécules Biologiques, Centre National de la Recherche Scientifique, UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France.
Nature. 2016 Mar 3;531(7592):59-63. doi: 10.1038/nature17182. Epub 2016 Feb 24.
Contractile tails are composed of an inner tube wrapped by an outer sheath assembled in an extended, metastable conformation that stores mechanical energy necessary for its contraction. Contraction is used to propel the rigid inner tube towards target cells for DNA or toxin delivery. Although recent studies have revealed the structure of the contractile sheath of the type VI secretion system, the mechanisms by which its polymerization is controlled and coordinated with the assembly of the inner tube remain unknown. Here we show that the starfish-like TssA dodecameric complex interacts with tube and sheath components. Fluorescence microscopy experiments in enteroaggregative Escherichia coli reveal that TssA binds first to the type VI secretion system membrane core complex and then initiates tail polymerization. TssA remains at the tip of the growing structure and incorporates new tube and sheath blocks. On the basis of these results, we propose that TssA primes and coordinates tail tube and sheath biogenesis.
收缩尾由一个内管组成，该内管被一个在外鞘包裹，组装成一种伸展的、亚稳态构象，该构象储存着收缩所需的机械能量。收缩用于将刚性内管推向靶细胞，以进行 DNA 或毒素的传递。尽管最近的研究揭示了 VI 型分泌系统的收缩鞘的结构，但聚合的机制以及与内管组装的协调机制仍然未知。在这里，我们展示了海星状的 TssA 十二聚体复合物与管和鞘成分相互作用。在肠聚集性大肠杆菌中的荧光显微镜实验表明，TssA 首先与 VI 型分泌系统膜核心复合物结合，然后启动尾部聚合。TssA 留在生长结构的尖端，并整合新的管和鞘块。基于这些结果，我们提出 TssA 启动和协调尾部管和鞘的生物发生。
