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Common and distinct structural features of Salmonella injectisome and flagellar basal body.

ABSTRACT: Bacterial pathogens use an injectisome to deliver virulence proteins into eukaryotic host cells. The bacterial flagellum and injectisome export their component proteins for self-assembly. These two systems show high structural similarities and are classified as the type III secretion system, but it remains elusive how similar they are in situ because the structures of these complexes isolated from cells and visualized by electron cryomicroscopy have shown only the export channel and housing for the export apparatus. Here we report in situ structures of Salmonella injectisome and flagellum by electron cryotomography. The injectisome lacks the flagellar basal body C-ring, but a wing-like disc and a globular density corresponding to the export gate platform and ATPase hexamer ring, respectively, are stably attached through thin connectors, revealing yet unidentified common architectures of the two systems. The ATPase ring is far from the disc, suggesting that both apparatuses are observed in an export-off state.

SUBMITTER: Kawamoto A

PROVIDER: S-EPMC3842551 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Common and distinct structural features of Salmonella injectisome and flagellar basal body.

Kawamoto Akihiro A Morimoto Yusuke V YV Miyata Tomoko T Minamino Tohru T Hughes Kelly T KT Kato Takayuki T Namba Keiichi K

Scientific reports 20131128

Bacterial pathogens use an injectisome to deliver virulence proteins into eukaryotic host cells. The bacterial flagellum and injectisome export their component proteins for self-assembly. These two systems show high structural similarities and are classified as the type III secretion system, but it remains elusive how similar they are in situ because the structures of these complexes isolated from cells and visualized by electron cryomicroscopy have shown only the export channel and housing for ...[more]

PMID: 24284544

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Project description:UnlabelledThe opportunistic pathogen Pseudomonas aeruginosa utilizes an injectisome-type III secretion system (injectisome-T3SS) to elicit cytotoxicity toward epithelial cells and macrophages. Macrophage killing results from the cytotoxic properties of the translocated effector proteins (ExoS, ExoT, ExoU, and ExoY) and inflammasome-mediated induction of pyroptosis. Inflammasome activation can occur following Nlrc4-mediated recognition of cytosolic translocated flagellin (FliC). In the present study, we demonstrate that FliC is a secretion substrate of both the injectisome- and flagellum-associated T3SSs. Molecular analyses indicate that the first 20 amino-terminal residues of FliC are sufficient for secretion by the injectisome-T3SS and that the first 100 residues are sufficient for translocation of FliC into host cells. Although maximal inflammasome activation requires FliC, activation can also occur in the absence of FliC. This prompted us to examine whether other flagellar components might also be translocated into cells to elicit inflammasome activation. Indeed, we find that the flagellar cap (FliD), hook-associated (FlgK and FlgL), hook (FlgE), and rod (FlgE) proteins are secretion substrates of the injectisome-T3SS. None of these proteins, however, result in increased inflammasome activation when they are overexpressed in a fliC mutant and appear to be translocated into host cells. While a role in inflammasome activation has been excluded, these data raise the possibility that flagellar components, which are highly conserved between different bacterial species, trigger other specific host responses from the extracellular milieu or contribute to the pathogenesis of P. aeruginosa.ImportanceThe inflammasome is a host defense mechanism that recognizes invading bacteria and triggers an inflammatory immune response. The opportunistic pathogen P. aeruginosa produces both inflammasome agonists and antagonists. In this study, we demonstrate that overexpression of an agonist suppresses the activity of an antagonist, thereby resulting in inflammasome activation. Since the relative expression levels of agonists and antagonists likely vary between strains, these differences could be important predictors of whether a particular P. aeruginosa strain elicits inflammasome activation.

Dataset Information

Common and distinct structural features of Salmonella injectisome and flagellar basal body.

Publications

Common and distinct structural features of Salmonella injectisome and flagellar basal body.

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