Quorum sensing in Gram-negative bacteria is typically mediated by low molecular weight molecules. Our lab focuses on the LuxR/I-type quorum sensing system in a variety of species, including the medically relevant opportunistic pathogens common in humans (Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cepacia), economically important plant pathogens (Pectobacterium versatile, Agrobacterium tunefaciens, Pantoea stewartii), symbiotic bacteria (Vibrio fischeri, Rhizhobia species), and other important model systems (Chromobacterium species, Rhodopseudomonas palustris). Over the years, we have developed numerous collections of small molecules aimed at targeting LuxR/I quorum sensing, which have provided both receptor selective and pan-active inhibitors, along with numerous non-native activators of LuxR-type receptors. We apply these novel chemical tools to (1) understand the fundamental biochemical mechanisms that allow bacteria to perceive quorum sensing signals and (2) modulate quorum sensing-regulated phenotypes in biological systems.
Featured Projects
Novel quorum sensing modulators
Several projects aim to understand structure-activity relationships among synthetic small molecule quorum sensing modulators. Our lab’s expertise in chemical biology allows us to rationally design and synthesize analogs of native quorum sensing signals and other small molecule leads, test novel compounds in cell-based reporter assays for LuxR-type receptor activity, and further validate lead compounds in assays measuring quorum sensing phenotypes.
A recent high-throughput compound screen identified several new classes of non-native modulators of LasR, an important LuxR-type receptor and virulence regulator in Pseudomonas aeruginosa. We are developing robust synthetic routes to these compounds and structural analogs thereof to with the goal of identifying LasR inhibitors with increased potency and stability.
In another project, we are interested in developing chemical probes that will allow us to visualize quorum sensing ligand localization within cells and understand ligand interactions with cell membranes. Recent collaborative research in our lab has shown that lipid-like lactone quorum sensing signals can aggragate and interact with membranes at quorate signal concentrations. We are developing routes to label these lactone signals and track their distribution in living cells.
Read more:
Interactions of Bacterial Quorum Sensing Signals with Model Lipid Membranes: Influence of Membrane Composition on Membrane Remodeling
LuxR receptor structure and mechanism
Cell-based and in vitro assays with quorum sensing receptors help us to understand mechanisms of ligand response. We use a FRET-based assay developed by our lab to directly measure ligand affinity, electromobility shift assays (EMSAs) and fluorescence polarization (FP) to measure changes in protein conformation, and differential scanning fluorimetry (DSF), proteolysis, and western blot assays to determine protein stability.
We also design targeted receptor mutants to dissect the role of individual residues and larger structural features on LuxR function. Understanding the 3D structures of these proteins, bound to agonist or antagonist, is a major motivation, and collaborative structural studies of QscR and LasR (from P. aeruginosa) bound to agonists have begun to further illuminate mechanism of ligand response. An improved mechanistic understanding of LuxR-type receptor will provide fundamental insights into this sociomicrobiology phenomenon. This knowledge will also advance the design of small molecule modulators with improved potency, efficacy, and receptor specificity.
Read more:
Autoinducer-fluorophore conjugates enable FRET in LuxR proteins in vitro and in cells
