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Characterization of a periplasmic thiol:disulfide interchange protein required for the functional maturation of secreted virulence factors of Vibrio cholerae.

ABSTRACT: A number of ToxR-regulated genes that encode products required for the biogenesis or function of the toxin-coregulated colonization pilus (TCP) of Vibrio cholerae have been identified previously by TnphoA fusions. In this study we have examined the role of the product of one of these genes, tcpG, to which a fusion results in a piliated cell lacking all of the in vivo and in vitro functions associated with TCP. Our results show that TcpG is not an ancillary pilus adhesin component as suggested by the mutant phenotype but instead is a 24-kDa periplasmic protein that shares active-site homology with several different bacterial thioredoxins and protein disulfide isomerase, as well as overall homology with the disulfide bond-forming DsbA periplasmic oxidoreductase protein of E. coli. Corresponding activity can be demonstrated in vitro for TcpG-enriched fractions from a wild-type strain but is absent in a similarly fractionated tcpG-phoA mutant. The phenotype conferred by a tcpG mutation was found to be pleiotropic in nature, also affecting the extracellular secretion of cholera toxin A subunit and a major protease. This suggests a general role for TcpG in allowing a group of virulence-associated (and perhaps other) proteins that contain disulfide bonds to assume a secretion or functionally competent state.

SUBMITTER: Peek JA

PROVIDER: S-EPMC402152 | biostudies-other | 1992 Jul

REPOSITORIES: biostudies-other

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Characterization of a periplasmic thiol:disulfide interchange protein required for the functional maturation of secreted virulence factors of Vibrio cholerae.

Peek J A JA Taylor R K RK

Proceedings of the National Academy of Sciences of the United States of America 19920701 13

A number of ToxR-regulated genes that encode products required for the biogenesis or function of the toxin-coregulated colonization pilus (TCP) of Vibrio cholerae have been identified previously by TnphoA fusions. In this study we have examined the role of the product of one of these genes, tcpG, to which a fusion results in a piliated cell lacking all of the in vivo and in vitro functions associated with TCP. Our results show that TcpG is not an ancillary pilus adhesin component as suggested by ...[more]

PMID: 1631111

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Project description:LysR-type transcriptional regulators (LTTRs) are the largest, most diverse family of prokaryotic transcription factors, with regulatory roles spanning metabolism, cell growth and division, and pathogenesis. Using a sequence-defined transposon mutant library, we screened a panel of V. cholerae El Tor mutants to identify LTTRs required for host intestinal colonization. Surprisingly, out of 38 LTTRs, only one severely affected intestinal colonization in the suckling mouse model of cholera: the methionine metabolism regulator, MetR. Genetic analysis of genes influenced by MetR revealed that glyA1 and metJ were also required for intestinal colonization. Chromatin immunoprecipitation of MetR and quantitative reverse transcription-PCR (qRT-PCR) confirmed interaction with and regulation of glyA1, indicating that misregulation of glyA1 is likely responsible for the colonization defect observed in the metR mutant. The glyA1 mutant was auxotrophic for glycine but exhibited wild-type trimethoprim sensitivity, making folate deficiency an unlikely cause of its colonization defect. MetJ regulatory mutants are not auxotrophic but are likely altered in the regulation of amino acid-biosynthetic pathways, including those for methionine, glycine, and serine, and this misregulation likely explains its colonization defect. However, mutants defective in methionine, serine, and cysteine biosynthesis exhibited wild-type virulence, suggesting that these amino acids can be scavenged in vivo. Taken together, our results suggest that glycine biosynthesis may be required to alleviate an in vivo nutritional restriction in the mouse intestine; however, additional roles for glycine may exist. Irrespective of the precise nature of this requirement, this study illustrates the importance of pathogen metabolism, and the regulation thereof, as a virulence factor. Vibrio cholerae continues to be a severe cause of morbidity and mortality in developing countries. Identification of V. cholerae factors critical to disease progression offers the potential to develop or improve upon therapeutics and prevention strategies. To increase the efficiency of virulence factor discovery, we employed a regulator-centric approach to multiplex our in vivo screening capabilities and allow whole regulons in V. cholerae to be interrogated for pathogenic potential. We identified MetR as a new virulence regulator and serine hydroxymethyltransferase GlyA1 as a new MetR-regulated virulence factor, both required by V. cholerae to colonize the infant mouse intestine. Bacterial metabolism is a prerequisite to virulence, and current knowledge of in vivo metabolism of pathogens is limited. Here, we expand the known role of amino acid metabolism and regulation in virulence and offer new insights into the in vivo metabolic requirements of V. cholerae within the mouse intestine.

Project description:UnlabelledTcpP and ToxR coordinately regulate transcription of toxT, the master regulator of numerous virulence factors in Vibrio cholerae. TcpP and ToxR are membrane-localized transcription factors, each with a periplasmic domain containing two cysteines. In ToxR, these cysteines form an intramolecular disulfide bond and a cysteine-to-serine substitution affects activity. We determined that the two periplasmic cysteines of TcpP also form an intramolecular disulfide bond. Disruption of this intramolecular disulfide bond by mutation of either cysteine resulted in formation of intermolecular disulfide bonds. Furthermore, disruption of the intramolecular disulfide bond in TcpP decreased the stability of TcpP. While the decreased stability of TcpP-C207S resulted in a nearly complete loss of toxT activation and cholera toxin (CT) production, the second cysteine mutant, TcpP-C218S, was partially resistant to proteolytic degradation and maintained ?50% toxT activation capacity. TcpP-C218S was also TcpH independent, since deletion of tcpH did not affect the stability of TcpP-C218S, whereas wild-type TcpP was degraded in the absence of TcpH. Finally, TcpH was also unstable when intramolecular disulfides could not be formed in TcpP, suggesting that the single periplasmic cysteine in TcpH may assist with disulfide bond formation in TcpP by interacting with the periplasmic cysteines of TcpP. Consistent with this finding, a TcpH-C114S mutant was unable to stabilize TcpP and was itself unstable. Our findings demonstrate a periplasmic disulfide bond in TcpP is critical for TcpP stability and virulence gene expression.ImportanceThe Vibrio cholerae transcription factor TcpP, in conjunction with ToxR, regulates transcription of toxT, the master regulator of numerous virulence factors in Vibrio cholerae. TcpP is a membrane-localized transcription factor with a periplasmic domain containing two cysteines. We determined that the two periplasmic cysteines of TcpP form an intramolecular disulfide bond and disruption of the intramolecular disulfide bond in TcpP decreased the stability of TcpP and reduced virulence gene expression. Normally TcpH, another membrane-localized periplasmic protein, protects TcpP from degradation. However, we found that TcpH was also unstable when intramolecular disulfides could not be formed in TcpP, indicating that the periplasmic cysteines of TcpP are required for functional interaction with TcpH and that this interaction is required for both TcpP and TcpH stability.

Dataset Information

Characterization of a periplasmic thiol:disulfide interchange protein required for the functional maturation of secreted virulence factors of Vibrio cholerae.

Publications

Characterization of a periplasmic thiol:disulfide interchange protein required for the functional maturation of secreted virulence factors of Vibrio cholerae.

Similar Datasets

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