Chemical probes to modulate acyl-homoserine lactone quorum signal synthesis

Abstract Gram-negative bacteria count specific, N-acyl-L-homoserine lactone (AHL) quorum sensing (QS) signals in the environment to estimate local population densities, facilitate cell-cell communication and virulence. AHL synthases make AHL autoinducer signals by enzymatically coupling acyl-ACP/acyl-CoA and S-adenosyl-L- methionine metabolites to facilitate quorum sensing for the bacterium. Small molecule inhibitors of AHL synthase enzymes would limit signal synthesis, interrupt quorum sensing and thus hold significant promise as chemical tools to investigate QS networks in bacteria. Designing AHL synthase-specific inhibitors, however, does remain a significant challenge. To develop AHL synthase selective inhibitors, we recently embarked on a proof-of-concept study to evaluate the potential of AHL signal derivatives as product analog inhibitors of Pseudomonas aeruginosa RhlI AHL synthase. In this study, we demonstrated that AHL analogs could serve as ‘chemical probes’ to uncover novel inhibition and activation binding pockets that could be tapped to develop potent AHL synthase-specific modulators. In this grant application, we extend this approach on a broader scale to evaluate the utility of AHL analog chemical probes in discovering novel binding pockets, determining the mechanistic basis of AHL synthase modulation, and formulating the rules of AHL engagement in short, medium and long-chain preferring AHL synthases. Additionally, we will determine how the inhibition and activation pockets could be leveraged to develop novel substrates and substrate analog inhibitors of AHL synthases. Successful completion of these studies should inform the rational design of inhibition and activation pocket directed AHL synthase modulators. Finally, the goals described in this application are tightly aligned with the objectives of AREA program, which are to a) support meritorious research at an undergraduate focused institution, b) strengthen the research environment at the home institution and c) provide opportunity for undergraduate students to get involved in biomedical research.