Article

Structural biology of Type VI secretion systems

CNRS, Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UMR 7255, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Philosophical Transactions of The Royal Society B Biological Sciences (Impact Factor: 7.06). 04/2012; 367(1592):1102-11. DOI: 10.1098/rstb.2011.0209
Source: PubMed

ABSTRACT

Type VI secretion systems (T6SSs) are transenvelope complexes specialized in the transport of proteins or domains directly into target cells. These systems are versatile as they can target either eukaryotic host cells and therefore modulate the bacteria-host interaction and pathogenesis or bacterial cells and therefore facilitate access to a specific niche. These molecular machines comprise at least 13 proteins. Although recent years have witnessed advances in the role and function of these secretion systems, little is known about how these complexes assemble in the cell envelope. Interestingly, the current information converges to the idea that T6SSs are composed of two subassemblies, one resembling the contractile bacteriophage tail, whereas the other subunits are embedded in the inner and outer membranes and anchor the bacteriophage-like structure to the cell envelope. In this review, we summarize recent structural information on individual T6SS components emphasizing the fact that T6SSs are composite systems, adapting subunits from various origins.

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    • "By motif and profile HMM analysis, we identified presumed functional equivalents of nine of these 13 Proteobacterial core proteins in gut Bacteroidales T6SS loci; however, genes encoding identifiable TssA, TssJ, TssL and TssM proteins were not detected. The function of TssA is currently unknown; however, TssJ, TssL, and TssM likely form a transenvelope complex that anchors the phage tail structure[27,28]. There are five proteins of unknown function encoded within the Bacteroidales T6SS of all three genetic architectures. "
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    • "The C. jejuni T6SS was found to have pleiotropic effects ranging from virulence, influencing cell adhesion, cytotoxicity towards erythrocytes and colonisation of mice (Lertpiriyapong et al., 2012; Bleumink-Pluym et al., 2013; Harrison et al., 2014). Current structural models of T6SS consist of a bacteriophage-like structure and a cell envelope-spanning membrane-associated assembly that translocates protein effectors into different cell types (Cascales and Cambillau, 2012; Silverman et al., 2012). A loci containing 13 ORFs can be subdivided into three groups; group one genes tssJ, tssL and tssM encode for membrane-associated proteins; group two genes tssB, tssC, tssD (hcp), tssE and tssI (vgrG) encode for proteins with function related to tailed bacteriophage components; group three genes tssA, tssF, tssG, tssH (tagH) and tssK encode for proteins with unknown function (Silverman et al., 2012; Fritsch et al., 2013). "
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    • "Bacteroidetes T6SS in Interbacterial Antagonism membrane for function, and so far a T6SS iii -conserved predicted outer membrane-localized protein has not been identified. It is worth noting that TssJ, TssL, and TssM interact stably to form a trans-envelope complex (Cascales and Cambillau, 2012). While it has been postulated that this complex facilitates the passage of bacteriophage-like proteins and effectors out of the recipient cell, there are little experimental data to support this notion. "
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