The PqsE-RhIR Interaction Regulates RhIR DNA Binding to Control Virulence Factor Production in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that causes disease in immunocompromised individuals and individuals with underlying pulmonary disorders. P. aeruginosa virulence is controlled by quorum sensing (QS), a bacterial cell-cell communication mechanism that underpins transitions between individual and group behaviors. In P. aeruginosa, the PqsE enzyme and the QS receptor RhIR directly interact to control the expression of genes involved in virulence. Here, we show that three surface-exposed arginine residues on PqsE comprise the site required for interaction with RhIR. We show that a noninteracting PqsE variant iPqsE(NI)1 possesses catalytic activity, but is incapable of promoting virulence phenotypes, indicating that interaction with RhIR, and not catalysis, drives these PqsE-dependent behaviors. Biochemical characterization of the PqsE-RhIR interaction coupled with RNA-seq analyses demonstrates that the PqsE-RhIR complex increases the affinity of RhIR for DNA, enabling enhanced expression of genes encoding key virulence factors. These findings provide the mechanism for PqsE-dependent regulation of RhIR and identify a unique regulatory feature of P. aeruginosa QS and its connection to virulence. IMPORTANCE Bacteria use a cell-cell communication process called quorum sensing (QS) to orchestrate collective behaviors. QS relies on the group-wide detection of molecules called autoinducers (AI). QS is required for virulence in the human pathogen Pseudomonas aeruginosa, which can cause fatal infections in patients with underlying pulmonary disorders. In this study, we determine the molecular basis for the physical interaction between two virulence-driving QS components, PqsE and RhIR. We find that the ability of PqsE to bind RhIR correlates with virulence factor production. Since current antimicrobial therapies exacerbate the growing antibiotic resistance problem because they target bacterial growth, we suggest that the PqsE-RhIR interface discovered here represents a new candidate for targeting with small molecule inhibition. Therapeutics that disrupt the PqsE-RhIR interaction should suppress virulence. Targeting bacterial behaviors such as QS, rather than bacterial growth, represents an attractive alternative for exploration because such therapies could potentially minimize the development of resistance.