Investigating the Quorum Sensing Protein PqsE Active Site in Pseudomonas Aeruginosa

Abstract

Quorum sensing in Pseudomonas aeruginosa is a chemical communication process that promotes density dependent regulation of virulence and other behaviors. The quinolone-based quorum-sensing system of P. aeruginosa regulates downstream quorum-sensing traits. The pqsABCDE operon encodes the PqsA, PqsB, PqsC and PqsD enzymes that are involved in the synthesis of 4-quinolone compounds (HHQ and PQS). pqsE is a part of the pqsABCDE operon, but PqsE is not required for the synthesis of HHQ or PQS. Instead, PqsE forms a ligand synthase-receptor pair with RhlR. RhlR is a receptor that is sensitive to a signal molecule, called an autoinducer, and RhlR is activated in response to the buildup of autoinducer. Activation of RhlR results in transcriptional regulation of genes involved in P. aeruginosa virulence. The exact involvement of PqsE in this process remains unclear. This project was designed to determine the active site of the PqsE protein to better understand the function of PqsE and its role in quorum sensing. Random and site-directed mutagenesis of pqsE were performed and the ensuing PqsE-dependent pyocyanin production levels and PrhlA-mNeongreen reporter activity were analyzed to assess the role of each altered PqsE residue. These assays enabled assessment of essential amino acids in PqsE for proper control of pyocyanin production and rhlA transcription.