Structural Insights into Streptococcal Competence Regulation by the Cell-to-Cell Communication System ComRS.

Antoine Talagas,Noureddine Lazar,Sylvie Nessler,Magali Aumont-Nicaise,Laura Ledesma-Garca,Inès Li De La Sierra-Gallay,Johann Mignolet,Pascal Hols,Gerd Prehna,Laetitia Fontaine,Michael J Federle,Gongyi Zhang

doi:10.1371/journal.ppat.1005980

Abstract

In Gram-positive bacteria, cell-to-cell communication mainly relies on extracellular signaling peptides, which elicit a response either indirectly, by triggering a two-component phosphorelay, or directly, by binding to cytoplasmic effectors. The latter comprise the RNPP family (Rgg and original regulators Rap, NprR, PrgX and PlcR), whose members regulate important bacterial processes such as sporulation, conjugation, and virulence. RNPP proteins are increasingly considered as interesting targets for the development of new antibacterial agents. These proteins are characterized by a TPR-type peptide-binding domain, and except for Rap proteins, also contain an N-terminal HTH-type DNA-binding domain and display a transcriptional activity. Here, we elucidate the structure-function relationship of the transcription factor ComR, a new member of the RNPP family, which positively controls competence for natural DNA transformation in streptococci. ComR is directly activated by the binding of its associated pheromone XIP, the mature form of the comX/sigX-inducing-peptide ComS. The crystal structure analysis of ComR from Streptococcus thermophilus combined with a mutational analysis and in vivo assays allows us to propose an original molecular mechanism of the ComR regulation mode. XIP-binding induces release of the sequestered HTH domain and ComR dimerization to allow DNA binding. Importantly, we bring evidence that this activation mechanism is conserved and specific to ComR orthologues, demonstrating that ComR is not an Rgg protein as initially proposed, but instead constitutes a new member of the RNPP family. In addition, identification of XIP and ComR residues important for competence activation constitutes a crucial step towards the design of antagonistic strategies to control gene exchanges among streptococci.

Highlights

Within Gram-positive bacteria, cell-to-cell communication processes, called quorumsensing (QS), are regulated via oligopeptidic pheromones[1, 2] whose production and secretion are initiated in response to specific environmental stimuli or stresses [1, 2]
Bacterial cell-cell communication systems are based on the secretion of signal molecules
These quorum-sensing systems allow bacteria to coordinate genes expression according to the density of their local population

Summary

Introduction

Within Gram-positive bacteria, cell-to-cell communication processes, called quorumsensing (QS), are regulated via oligopeptidic pheromones[1, 2] whose production and secretion are initiated in response to specific environmental stimuli or stresses [1, 2]. The first identified examples of cytoplasmic QS regulators were grouped in a superfamily called RNPP (for the original members Rap/NprR/PlcR/PrgX) [5]. They regulate important physiological processes such as sporulation [6, 7] and virulence [8] in bacilli or conjugation in enterococci [9]. The TPR consensus sequence defined by a pattern of small and large amino acids is poorly conserved and TPR motifs are difficult to predict Their repetition forms a right-handed super-helical domain involved in pheromone binding and dimerization [10]. The induced molecular rearrangements and the detailed molecular mechanisms of protein activation/de-repression greatly differ among RNPP regulators

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Discussion

Conclusion