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Structure of the minor pseudopilin XcpW from the Pseudomonas aeruginosa type II secretion system.

ABSTRACT: Pseudomonas aeruginosa utilizes the type II secretion machinery to transport virulence factors through the outer membrane into the extracellular space. Five proteins in the type II secretion system share sequence homology with pilin subunits of type IV pili and are called the pseudopilins. The major pseudopilin XcpT(G) assembles into an intraperiplasmic pilus and is thought to act in a piston-like manner to push substrates through an outer membrane secretin. The other four minor pseudopilins, XcpU(H), XcpV(I), XcpW(J) and XcpX(K), play less well defined roles in pseudopilus formation. It was recently discovered that these four minor pseudopilins form a quaternary complex that is presumed to initiate the formation of the pseudopilus and to localize to its tip. Here, the structure of XcpW(J) was refined to 1.85?Å resolution. The structure revealed the type IVa pilin fold with an embellished variable antiparallel ?-sheet as also found in the XcpW(J) homologue enterotoxigenic Escherichia coli GspJ(W) and the XcpU(H) homologue Vibrio cholerae EpsU(H). It is proposed that the exposed surface of this sheet may cradle the long N-terminal ?1 helix of another pseudopilin. The final 31 amino acids of the XcpW(J) structure are instrinsically disordered. Deletion of this unstructured region of XcpW(J) did not prevent type II secretion in vivo.

SUBMITTER: Franz LP

PROVIDER: S-EPMC3045273 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

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Structure of the minor pseudopilin XcpW from the Pseudomonas aeruginosa type II secretion system.

Franz Laura P LP Douzi Badreddine B Durand Eric E Dyer David H DH Voulhoux Romé R Forest Katrina T KT

Acta crystallographica. Section D, Biological crystallography 20110115 Pt 2

Pseudomonas aeruginosa utilizes the type II secretion machinery to transport virulence factors through the outer membrane into the extracellular space. Five proteins in the type II secretion system share sequence homology with pilin subunits of type IV pili and are called the pseudopilins. The major pseudopilin XcpT(G) assembles into an intraperiplasmic pilus and is thought to act in a piston-like manner to push substrates through an outer membrane secretin. The other four minor pseudopilins, Xc ...[more]

PMID: 21245534

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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

Structure of the minor pseudopilin XcpW from the Pseudomonas aeruginosa type II secretion system.

Publications

Structure of the minor pseudopilin XcpW from the Pseudomonas aeruginosa type II secretion system.

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