Structural Characterization And Regulatory Mechanisms Of Quorum-sensing Repressor RsaL In Pseudomonas Aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium which exists in various environments.It is the third pathogenic bacteria which causes the infections of patients in the nosocomium and difficult to treat due to the high resistance to multiple antibiotics.Therefore,the urgent work at present is developing new antibiotics to combat this pathogen.Quorum-sensing is a cell-cell communication system.In Pseudomonas aeruginosa,there are at least three systems including Las,Rhl and PQS,which controls many important physiological functions.RsaL is a QS repressor,that provides homeostasis of signal molecule by functioning in opposition to Las R.It also controls virulence factor expression and biofilm formation.In this study,we conducted a ChIP-seq assay and revealed that RsaL bound to two new targets,the intergenic regions of PA2228/PA2229 and pqsH/cdpR,which are required for PQS.Deletion of rsaL reduced transcription of pqsH and cdpR,thus decreasing PQS signal production.The?rsaL strain exhibited increased pyocyanin production and reduced biofilm formation,which are dependent on CdpR or PqsH activity.In addition,we solved the structure of the RsaL-DNA complex.Although the overall sequence similarity is quite low,RsaL folds into a HTH-like structure,which is conserved among many transcriptional regulators.Complementation results of the rsaL knockout cells with different rsaL mutants further confirmed the critical role of the DNA-binding residues(including Arg20,Gln27,Gln38,Gly35,Ser37 and Ser42)are essential for DNA binding.This research give us a clearer understanding of the complex regulatory network of RsaL.It also provide a new clue and basis to explore the unknown regulatory protein in QS.