Rational design of a global inhibitor of the virulence response in Staphylococcus aureus , based in part on localization of the site of inhibition to the receptor-histidine kinase, AgrC

Abstract

Two-component signaling systems involving receptor-histidine kinases are ubiquitous in bacteria and have been found in yeast and plants. These systems provide the major means by which bacteria communicate with each other and the outside world. Remarkably, very little is known concerning the extracellular ligands that presumably bind to receptor-histidine kinases to initiate signaling. The two-component agr signaling circuit in Staphylococcus aureus is one system where the ligands are known in chemical detail, thus opening the door for detailed structure-activity relationship studies. These ligands are short (8-to 9-aa) peptides containing a thiolactone structure, in which the ␣-carboxyl group of the C-terminal amino acid is linked to the sulfhydryl group of a cysteine, which is always the fifth amino acid from the C terminus of the peptide. One unique aspect of the agr system is that peptides that activate virulence expression in one group of S. aureus strains also inhibit virulence expression in other groups of S. aureus strains. Herein, it is demonstrated by switching the receptor-histidine kinase, AgrC, between strains of different agr specificity types, that intragroup activation and intergroup inhibition are both mediated by the same group-specific receptors. These results have facilitated the development of a global inhibitor of virulence in S. aureus, which consists of a truncated version of one of the naturally occurring thiolactone peptides.

Surface-attached molecules control Staphylococcus aureus quorum sensing and biofilm development

“…A plasmid carrying a transcriptional fusion to monitor S. aureus Agr quorum-sensing activity was constructed by replacing the lacZ gene from vector pRN7062 54 ( agrP3-lacZ ) with the mkate2 gene. pRN7062 also harbors the genes encoding the Agr quorum-sensing detection components agrCA under their native agrP2 promoter but driven in the opposite direction.…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…The exceptions to this are the AIPs of of groups I and IV, which differ by only a single endocyclic residue; AIP-I strongly activates its cognate AgrC receptor while weakly activating AgrC of group IV strains, while AIP-IV strongly activates the agr response in both groups I and IV (218). The molecular determinants for AIP specificity have been shown to reside entirely in the interaction between the AIP signal and the AgrC receptor (130). Both cognate activation and heterologous inhibition activities require the ring structure of AIP, as linear AIPs have no detectable activity in any agr group (219,220), but the requirement of the thioester linkage has been debated (218)(219)(220).…”

“…Both cognate activation and heterologous inhibition activities require the ring structure of AIP, as linear AIPs have no detectable activity in any agr group (219,220), but the requirement of the thioester linkage has been debated (218)(219)(220). The tail of the AIP molecule is required only for activation, as mutation of the tail amino acid residues or removal of the tail did not alter inhibition of the agr response in heterologous groups despite eliminating self-activation activity (130,219). Numerous SAR studies have mapped amino acid residues critical for AIP activity, and overall the results demonstrate that critical amino acids differ between AIP groups (218)(219)(220).…”

“…Lyon et al described an AIP-II derivative lacking the exocyclic tail portion of the molecule, designated trAIP-II (Table 3), which functioned as an inhibitor in all four agr groups, including in cognate group II strains, making this molecule the first known AIP-based global inhibitor of S. aureus agr activation (130). Furthermore, addition of trAIP-II to S. aureus cultures reduced production of ␦-toxin, a known virulence factor (130), indicating a reduction in virulence potential.…”

“…Lyon et al described an AIP-II derivative lacking the exocyclic tail portion of the molecule, designated trAIP-II (Table 3), which functioned as an inhibitor in all four agr groups, including in cognate group II strains, making this molecule the first known AIP-based global inhibitor of S. aureus agr activation (130). Furthermore, addition of trAIP-II to S. aureus cultures reduced production of ␦-toxin, a known virulence factor (130), indicating a reduction in virulence potential. Separately, 14 macrocyclic peptide-peptoid hybrid molecules lacking thioester linkages were designed as AIP-1 analogues, and one was found to alter S. aureus biofilm formation in vitro, a known AIP-modulated behavior, although the mechanism of action by the molecule was not investigated (223).…”