Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2014 Oct 28;4:152.
doi: 10.3389/fcimb.2014.00152. eCollection 2014.

An Evolving Perspective on the Pseudomonas Aeruginosa Orphan Quorum Sensing Regulator QscR

Affiliations
Free PMC article
Review

An Evolving Perspective on the Pseudomonas Aeruginosa Orphan Quorum Sensing Regulator QscR

Sudha Chugani et al. Front Cell Infect Microbiol. .
Free PMC article

Erratum in

  • Front Cell Infect Microbiol. 2015;4:181

Abstract

Many Proteobacteria govern responses to changes in cell density by using acyl-homoserine lactone (AHL) quorum-sensing (QS) signaling. Similar to the LuxI-LuxR system described in Vibrio fischeri, a minimal AHL QS circuit comprises a pair of genes, a luxI-type synthase gene encoding an enzyme that synthesizes an AHL and a luxR-type AHL-responsive transcription regulator gene. In most bacteria that utilize AHL QS, cognate luxI and luxR homologs are found in proximity to each other on the chromosome. However, a number of recent reports have identified luxR homologs that are not linked to luxI homologs; in some cases luxR homologs have been identified in bacteria that have no luxI homologs. A luxR homolog without a linked luxI homologs is termed an orphan or solo. One of the first reports of an orphan was on QscR in Pseudomonas aeruginosa. The qscR gene was revealed by whole genome sequencing and has been studied in some detail. P. aeruginosa encodes two AHL synthases and three AHL responsive receptors, LasI-LasR form a cognate synthase-receptor pair as do RhlI-RhlR. QscR lacks a linked synthase and responds to the LasI-generated AHL. QS regulation of gene expression in P. aeruginosa employs multiple signals and occurs in the context of other interconnected regulatory circuits that control diverse physiological functions. QscR affects virulence of P. aeruginosa, and although it shows sensitivity to the LasI-generated AHL, 3-oxo-dodecanoylhomoserine lactone, it's specificity is relaxed compared to LasR and can respond equally well to several AHLs. QscR controls a set of genes that overlaps the set regulated by LasR. QscR is comparatively easy to purify and study in vitro, and has become a model for understanding the biochemistry of LuxR homologs. In fact there is a crystal structure of QscR bound to the LasI-generated AHL. Here, we review the current state of research concerning QscR and highlight recent advances in our understanding of its structure and biochemistry.

Keywords: acylhomoserine lactone; bacterial communication; cell-cell signaling; gene activation; sociomicrobiology.

Figures

Figure 1
Figure 1
An alignment of the QscR sequence with previously characterized LuxR homologs TraR, LuxR, RhlR, LasR, and BviR. We have also included sequences of three ORFs annotated as LuxR-family transcriptional regulators showing significant identity to QscR; Methylosarcina lacus (41% identity), Burkholderia ambifaria (46% identity), and Acinetobacter baumannii (35% identity). Conserved amino acids are shaded in black. Gray shading indicates that 100% of the residues are similar at that position. The numbers at the end of each sequence indicate the percent identity with QscR. The alignment was generated by using the MUSCLE multiple sequence alignment program and the degree of residue shading was determined by using Boxshade. The sequences used in the alignment and their GenBank or NCBI Reference Sequence (RefSeq) accession numbers are Agrobacterium tumefaciens TraR (RefSeq: YP_001967610.1), V. fischeri LuxR (GenBank: M96844), P. aeruginosa LasR (GenBank: M59425), P. aeruginosa RhlR (GenBank: L08962), Burkholderia cepacia BviR(GenBank: AAK35156.1), Burkholderia ambifaria (RefSeq: WP_006749592.1), Methylosarcina lacus (RefSeq: WP_024298126.1), and Acinetobacter baumannii (GenBank: EXS59053.1).
Figure 2
Figure 2
QscR, unlike LasR, responds to multiple AHLs. Shown are lacZ reporter expression levels for (A) E. coli containing a qscR expression vector and the PA1897–lacZ reporter and (B) E. coli containing a lasR expression vector and the lasIlacZ reporter. The acyl chains of each AHL are indicated on the right from Lee et al. (2006).
Figure 3
Figure 3
A model for biochemical states of QscR in vivo. Nascent QscR polypeptides can fold into active forms and exist as monomers at low concentrations. The monomers can either refold into inactive forms that are subsequently proteolyzed or they can bind AHLs and form homodimers capable of binding target DNA from Oinuma and Greenberg (2011).
Figure 4
Figure 4
Structure of QscR bound to 3OC12-HSL. The QscR monomers are shown in cyan and green and 3OC12-HSL is shown in orange. The ligand-binding domain (LBD) and the DNA- binding domain (DBD) are also indicated for each chain from Lintz et al. (2011).

Similar articles

See all similar articles

Cited by 15 articles

See all "Cited by" articles

References

    1. Bottomley M. J., Muraglia E., Bazzo R., Carfi A. (2007). Molecular insights into quorum sensing in the human pathogen Pseudomonas aeruginosa from the structure of the virulence regulator LasR bound to its autoinducer. J. Biol. Chem. 282, 13592–13600. 10.1074/jbc.M700556200 - DOI - PubMed
    1. Brint J. M., Ohman D. E. (1995). Synthesis of multiple exoproducts in Pseudomonas aeruginosa is under the control of RhlR-RhlI, another set of regulators in strain PAO1 with homology to the autoinducer-responsive LuxR-LuxI family. J. Bacteriol. 177, 7155–7163. - PMC - PubMed
    1. Chen G., Swem L. R., Swem D. L., Stauff D. L., O'Loughlin C. T., Jeffrey P. D., et al. . (2011). A strategy for antagonizing quorum sensing. Mol. Cell 42, 199–209. 10.1016/j.molcel.2011.04.003 - DOI - PMC - PubMed
    1. Chugani S. A., Whiteley M., Lee K. M., D'Argenio D., Manoil C., Greenberg E. P. (2001). QscR, a modulator of quorum-sensing signal synthesis and virulence in Pseudomonas aeruginosa. Proc. Natl. Acad. Sci. U.S.A. 98, 2752–2757. 10.1073/pnas.051624298 - DOI - PMC - PubMed
    1. Fagerlind M. G., Rice S. A., Nilsson P., Harlen M., James S., Charlton T., et al. . (2003). The role of regulators in the expression of quorum-sensing signals in Pseudomonas aeruginosa. J. Mol. Microbiol. Biotechnol. 6, 88–100. 10.1159/000076739 - DOI - PubMed

Publication types

MeSH terms

LinkOut - more resources

Feedback