We aim to make pro- and anti-quorum-sensing modulators to use as probes to further our basic research and to demonstrate their potential as novel therapeutics. We screened for inhibitors of quorum sensing in Pseudomonas aeruginosa, a pathogen that uses quorum sensing to control virulence and biofilm formation. The most potent molecule identified, meta-bromothiolactone (mBTL), is a competitive inhibitor that binds in the autoinducer binding sites of both the LasR and RhlR receptors. mBTL prevents virulence factor expression and biofilm formation and also protects the nematode Caenorhabditis elegans and human A549 lung epithelial cells from killing by P. aeruginosa. To my knowledge, mBTL is the first anti-quorum-sensing molecule discovered that is capable of terminating an infection in an animal.
We discovered compounds that interfere with V. cholerae quorum sensing by acting on CqsS and LuxO. LuxO is an AAA+ ATPase superfamily member that is the signal integrator in the vibrio quorum-sensing circuit.. LuxO exists in all vibrios but not in other sequenced bacterial species. One of our LuxO inhibitors, AzaU, is a broad spectrum virulence inhibitor in pathogenic vibrios.. In collaboration with Fred Hughson, we crystallized and solved structures of apo-LuxO, ATP-bound LuxO, and AzaU-bound LuxO. We discovered an unprecedented natural mechanism of LuxO regulation mediated by an intra-protein linker domain that acts competitively by occupying the ATP binding site and preventing ATP binding. Phosphorylation by the quorum-sensing receptors alters the conformation of the linker, allowing ATP to bind. AzaU also occupies the ATP binding site, and thus acts as a competitive inhibitor by preventing ATP binding.