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Structural and DNA binding properties of the cytoplasmic domain of Vibrio cholerae transcription factor ToxR.

ABSTRACT: ToxR represents an essential transcription factor of Vibrio cholerae, which is involved in the regulation of multiple, mainly virulence associated genes. Its versatile functionality as activator, respressor or co-activator suggests a complex regulatory mechanism, whose clarification is essential for a better understanding of the virulence expression system of V. cholerae. Here, we provide structural information elucidating the organization and binding behaviour of the cytoplasmic DNA binding domain of ToxR (cToxR), containing a winged helix-turn-helix (wHTH) motif. Our analysis reveals unexpected structural features of this domain expanding our knowledge of a poorly-defined subfamily of wHTH proteins. cToxR forms an extraordinary long α-loop and furthermore has an additional C-terminal beta strand, contacting the N-terminus and thus leading to a compact fold. The identification of the exact interactions between ToxR and DNA contributes to a deeper understanding of this regulatory process. Our findings not only show general binding of the soluble cytoplasmic domain of ToxR to DNA, but also indicate a higher affinity for the toxT motif. These results support the current theory of ToxR being a 'DNA-catcher' to enable binding of the transcription factor TcpP and thus activation of virulence-associated toxT transcription. Although, TcpP and ToxR interaction is assumed to be crucial in the activation of the toxT genes, we could not detect an interaction event of their isolated cytoplasmic domains. We therefore conclude that other factors are needed to establish this protein-protein interaction, e.g., membrane attachment, the presence of their full-length proteins and/or other intermediary proteins that may facilitate binding.

SUBMITTER: Gubensak N

PROVIDER: S-EPMC8517210 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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Structural and DNA-binding properties of the cytoplasmic domain of Vibrio cholerae transcription factor ToxR.

Gubensäk Nina N Schrank Evelyne E Hartlmüller Christoph C Göbl Christoph C Falsone Fabio S FS Becker Walter W Wagner Gabriel E GE Pulido Sergio S Meyer N Helge NH Pavkov-Keller Tea T Madl Tobias T Reidl Joachim J Zangger Klaus K

The Journal of biological chemistry 20210904 4

ToxR represents an essential transcription factor of Vibrio cholerae, which is involved in the regulation of multiple, mainly virulence associated genes. Its versatile functionality as activator, repressor or coactivator suggests a complex regulatory mechanism, whose clarification is essential for a better understanding of the virulence expression system of V. cholerae. Here, we provide structural information elucidating the organization and binding behavior of the cytoplasmic DNA-binding domain ...[more]

PMID: 34487759

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Project description:UnlabelledVibrio cholerae is an aquatic organism that causes the severe acute diarrheal disease cholera. The ability of V. cholerae to cause disease is dependent upon the production of two critical virulence determinants, cholera toxin (CT) and the toxin-coregulated pilus (TCP). The expression of the genes that encode for CT and TCP production is under the control of a hierarchical regulatory system called the ToxR regulon, which functions to activate virulence gene expression in response to in vivo stimuli. Cyclic dipeptides have been found to be produced by numerous bacteria, yet their biological function remains unknown. V. cholerae has been shown to produce cyclo(Phe-Pro). Previous studies in our laboratory demonstrated that cyclo(Phe-Pro) inhibited V. cholerae virulence factor production. For this study, we report on the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We have demonstrated that exogenous cyclo(Phe-Pro) activated the expression of leuO, a LysR-family regulator that had not been previously associated with V. cholerae virulence. Increased leuO expression repressed aphA transcription, which resulted in downregulation of the ToxR regulon and attenuated CT and TCP production. The cyclo(Phe-Pro)-dependent induction of leuO expression was found to be dependent upon the virulence regulator ToxR. Cyclo(Phe-Pro) did not affect toxR transcription or ToxR protein levels but appeared to enhance the ToxR-dependent transcription of leuO. These results have identified leuO as a new component of the ToxR regulon and demonstrate for the first time that ToxR is capable of downregulating virulence gene expression in response to an environmental cue.ImportanceThe ToxR regulon has been a focus of cholera research for more than three decades. During this time, a model has emerged wherein ToxR functions to activate the expression of Vibrio cholerae virulence factors upon host entry. V. cholerae and other enteric bacteria produce cyclo(Phe-Pro), a cyclic dipeptide that we identified as an inhibitor of V. cholerae virulence factor production. This finding suggested that cyclo(Phe-Pro) was a negative effector of virulence factor production and represented a molecule that could potentially be exploited for therapeutic development. In this work, we investigated the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We found that cyclo(Phe-Pro) signaled through ToxR to activate the expression of leuO, a new virulence regulator that functioned to repress virulence factor production. Our results have identified a new arm of the ToxR regulon and suggest that ToxR may play a broader role in pathogenesis than previously known.

Dataset Information

Structural and DNA binding properties of the cytoplasmic domain of Vibrio cholerae transcription factor ToxR.

Publications

Structural and DNA-binding properties of the cytoplasmic domain of Vibrio cholerae transcription factor ToxR.

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