Systematic Dissection of the Agrobacterium Type VI Secretion System Reveals Machinery and Secreted Components for Subcomplex FormationReport as inadecuate




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The type VI secretion system T6SS is widely distributed in pathogenic Proteobacteria. Sequence and structural analysis of T6SS reveals a resemblance to the T4 bacteriophage tail, in which an outer sheath structure contracts an internal tube for injecting nucleic acid into bacterial cells. However, the molecular details of how this phage tail-like T6SS structure is assembled in vivo and executed for exoprotein or effector secretion remain largely unknown. Here, we used a systematic approach to identify T6SS machinery and secreted components and investigate the interaction among the putative sheath and tube components of Agrobacterium tumefaciens. We showed that 14 T6SS components play essential roles in the secretion of the T6SS hallmark exoprotein Hcp. In addition, we discovered a novel T6SS exoprotein, Atu4347, that is dispensable for Hcp secretion. Interestingly, Atu4347 and the putative tube components, Hcp and VgrG, are mainly localized in the cytoplasm but also detected on the bacterial surface. Atu4342 TssB and Atu4341 TssC41 interact with and stabilize each other, which suggests that they are functional orthologs of the sheath components TssB VipA and TssC VipB, respectively. Importantly, TssB interacts directly with the three exoproteins Hcp, VgrG, and Atu4347, in which Hcp also interacts directly with VgrG-1 on co-purification from Escherichia coli. Further co-immunoprecipitation and pulldown assays revealed these subcomplexes in A. tumefaciens and thereby support T6SS functioning as a contractile phage tail-like structure.



Author: Jer-Sheng Lin, Lay-Sun Ma, Erh-Min Lai

Source: http://plos.srce.hr/



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