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Type VI secretion system, TssF This is a family of Gram-negative bacterial proteins that form part of the type VI pathogenicity secretion system (T6SS), including TssF. TssF is homologs to phage tail proteins and is required for proper assembly of the Hcp tube (the T6SS inner tube) in bacteria. T6SSs are toxin delivery systems. It is a multiprotein complex requiring numerous core proteins (Tss proteins) including cytoplasmic, transmembrane, and outer membrane components. The needle or tube apparatus is comprised of a phage-like complex, similar to the T4 contractile bacteriophage tail, which is thought to be anchored to the membrane by a trans-envelope complex. T6SSs contain 13 conserved components (TssA-TssM) which are thought to form the core apparatus and to enable effector proteins to be injected into target cells in a single cell-contact-dependent step. TssF one of the core components of T6SSs machinery, has been shown to be recruited by TssK into the membrane-associated T6SS complex, contributing to the dynamic mechanism of the system. Furthermore, it has been reported to interact with TssG proteins stabilizing each other while making contact with TssE, TssK and VgrG as well as with tube and sheath components. Bioinformatic analysis suggest that TssF and TssG share similarities with the J and I proteins of the bacteriophage P2 baseplate respectively. Further experimental studies show that functional TssF and TssK proteins assemble into static foci near the cell envelope. Moreover, biochemical and cytological approaches provide support to the role of TssE, TssF, TssG, TssK and VgrG as T6SS baseplate components and to a sequential recruitment hierarchy (membrane complex, baseplate, tail tube/sheath) during T6SS biogenesis. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",