Antagonistic Rgg Regulators Mediate Quorum Sensing via Competitive DNA Binding in Streptococcus pyogenes

Abstract

Recent studies have established the fact that multiple members of the Rgg family of transcriptional regulators serve as key components of quorum sensing (QS) pathways that utilize peptides as intercellular signaling molecules. We previously described a novel QS system in Streptococcus pyogenes which utilizes two Rgg-family regulators (Rgg2 and Rgg3) that respond to neighboring signaling peptides (SHP2 and SHP3) to control gene expression and biofilm formation. We have shown that Rgg2 is a transcriptional activator of target genes, whereas Rgg3 represses expression of these genes, and that SHPs function to activate the QS system. The mechanisms by which Rgg proteins regulate both QS-dependent and QS-independent processes remain poorly defined; thus, we sought to further elucidate how Rgg2 and Rgg3 mediate gene regulation. Here we provide evidence that S. pyogenes employs a unique mechanism of direct competition between the antagonistic, peptide-responsive proteins Rgg2 and Rgg3 for binding at target promoters. The highly conserved, shared binding sites for Rgg2 and Rgg3 are located proximal to the −35 nucleotide in the target promoters, and the direct competition between the two regulators results in concentration-dependent, exclusive occupation of the target promoters that can be skewed in favor of Rgg2 in vitro by the presence of SHP. These results suggest that exclusionary binding of target promoters by Rgg3 may prevent Rgg2 binding under SHP-limiting conditions, thereby preventing premature induction of the quorum sensing circuit.

Discovery of scmR as a global regulator of secondary metabolism and virulence in Burkholderia thailandensis E264

“…One would involve competition of ScmR with MalR for the mal promoter, with ScmR binding leading to silencing of the mal cluster. This kind of competition among two transcriptional regulators for one binding site has been observed in other systems before (39,40). Alternatively, because MalR has been shown to be an orphan LuxR with an unknown ligand (35,41), a small molecule coinducer, only present under conditions of lowly expressed scmR (or ΔscmR), could also be invoked.…”

Enterococcal Rgg-Like Regulator ElrR Activates Expression of the elrA Operon

“…which switches the oligomeric status of the regulator from a tetramer to a dimer and relieves repression (60,69,70). More recently, it was also proposed that Rgg3-mediated repression in S. pyogenes was relieved upon interaction with the signaling peptide (71). At this stage of our knowledge, further investigation is required to analyze the elrR-dependent activation of elrA at the molecular level.…”

Rgg protein structure–function and inhibition by cyclic peptide compounds

“…1B) with similar affinities, and Rgg2 Sp and Rgg3 Sp bind to identical DNA-regulatory elements upstream of their target promoters (21,26). The net response of S. pyogenes to SHP pheromone is the robust expression of Rgg2/3-controlled promoters; however, Rgg2 Sp and Rgg3 Sp affect transcription by different mechanisms.…”

“…For example, Streptococcus pyogenes, which contains a thoroughly studied Rgg regulatory system, expresses four Rgg paralogs: Rgg2 Sp , Rgg3 Sp , ComR Sp , and RopB Sp . Rgg2 Sp , Rgg3 Sp , and ComR Sp are transcription factors whose activity is regulated via interactions with pheromones (4,21,22). RopB is a transcription factor as well, and its role in pathogenesis has been thoroughly documented; however, the exact identity of RopB's cognate regulatory pheromone has not been determined (23)(24)(25).…”