Development of novel anti-microbial drugs targeting quorum sensing in Gram-positive bacteria

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The expression of two Enterococcus feacalis virulence-related proteases, gelatinase and serine protease, is positively regulated by a quorum sensing system encoded by the fsr gene cluster. In this system, E. feacalis secretes an autoinducing peptide, gelatinase biosynthesis-activating pheromone(GBAP), which triggers the FsrC-FsrA two component regulatory system controlling the expression of two transcripts, fsrBDC and gelE-sprE. To aim anti-pathogenic compounds targeting cyclic peptide-mediated quorum sensing in Gram-positive bacteria, we have studied on (1) biosynthetic molecular mechanism of cyclic peptide quormone 'GBAP' and (2) screening for inhibitors of GBAP-mediated quorum sensing 'fir regulatory system'.(1) In this study, we demonstrated the existence offsrD, encoding the GBAP propeptide, which is in frame with fsrB but is translated independently of fsrB. It was also demonstrated that FsrB', an FsrD-truncated FsrB, functions as a cysteine protease-like processing enzyme to generate GBAP from FsrD. This revised model is consistent with the staphylococcal agr system.(2) We have screened for inhibitors of the fsr quorum sensing from actinomycetes metabolites, and identified a known peptide antibiotic, siamycin I. Quantitative analysis offsrBDC and gelE-sprE transcript suggested that siamycin I inhibited the GBAP-signaling via FsrC-FsrA two component regulatory system in a noncompetitive maner. The sublethal concentration of siamysin I also attenuated biofilm formation. Overrall, siamycin I would offer a novel means of treating enterococcal infections.