title: Acyl-homoserine lactone binding to and stability of the orphan Pseudomonas aeruginosa quorum-sensing signal receptor QscR.
abstract: The Pseudomonas aeruginosa transcription factor QscR responds to a variety of fatty acyl-homoserine lactones (HSLs), including N-3-oxododecanoyl-HSL (3OC12-HSL), which is produced and detected by the P. aeruginosa quorum-sensing circuit LasI and LasR. As is true for LasR and many other acyl-HSL-dependent transcription factors, production of soluble QscR in sufficient amounts for purification requires growth of recombinant bacteria in the presence of an appropriate acyl-HSL. QscR is thought to bind 3OC12-HSL relatively weakly compared to LasR, and unlike LasR, binding of purified QscR to target DNA was shown to strongly depend on exogenously added 3OC12-HSL. We show that purified QscR is dimeric at sufficiently high concentrations and monomeric at lower concentrations. Furthermore, QscR bound 3OC12-HSL more tightly than previously believed. Purified QscR retained 3OC12-HSL, and at sufficiently high concentrations, it bound target DNA in the absence of added 3OC12-HSL. We also obtained soluble QscR from recombinant Escherichia coli grown in the presence of N-3-oxohexanoyl-HSL (3OC6-HSL) instead of 3OC12-HSL, and because 3OC6-HSL bound much more loosely to QscR than other acyl-HSLs tested, we were able to exchange 3OC6-HSL with other acyl-HSLs in vitro and then estimate binding affinities of QscR for different acyl-HSLs and for target DNA. Our data support a model whereby QscR polypeptides fold properly in the absence of an acyl-HSL, but soluble, acyl-HSL-free QscR does not accumulate because it is subject to rapid aggregation or proteolysis.
authors.affiliation: Department of Microbiology, University of Washington School of Medicine, Seattle, WA 98195-7242, USA.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Oinuma
authors.forename: E Peter
authors.initials: EP
authors.lastname: Greenberg
mesh_terms: D054742:Acyl-Butyrolactones / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D011485:Protein Binding; D055503:Protein Multimerization; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D053038:Quorum Sensing; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*
chemical_list: D054742:Acyl-Butyrolactones; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C434259:QscR protein, Pseudomonas aeruginosa; D011994:Recombinant Proteins; D012097:Repressor Proteins