| Title: | Direct evidence for the modulation of the activity of the Erwinia chrysanthemi quorum-sensing regulator ExpR by acylhomoserine lactone pheromone |
| Author(s): | Castang S; Reverchon S; Gouet P; Nasser W; |
| Address: | "Unite de Microbiologie et Genetique, Unite Mixte de Recherche CNRS-Universite Lyon 1-Institut National des Sciences Appliquees de Lyon 5122, Domaine Scientifique de la Doua, batiment Andre Lwoff 10 rue Raphael Dubois, 69622 Villeurbanne Cedex, France" |
| ISSN/ISBN: | 0021-9258 (Print) 0021-9258 (Linking) |
| Abstract: | "In Erwinia chrysanthemi production of pectic enzymes is controlled by a complex network involving several regulators. Among them is ExpR, the quorum-sensing regulatory protein. ExpR is a member of the LuxR family of transcriptional regulators, the activity of which is modulated by the binding of diffusible N-acylhomoserine lactone pheromones to the N-terminal receptor site of the proteins. Previous in vitro DNA-ExpR binding studies suggested that ExpR might activate pectic enzyme production and repress its cognate gene expression. This report presents genetic evidence that ExpR represses its own gene expression in the absence of pheromone and that the addition of pheromone promotes concentration-dependent de-repression. In vitro experiments show that (i) ExpR binds target DNA in the absence of pheromone and that the pheromone dissociates ExpR-DNA complexes, (ii) ExpR binds target DNA in a non-cooperative fashion, and (iii) two molecules of pheromone are bound per molecule of ExpR dimer. In the absence of N-(3-oxo-hexanoyl)-homoserine lactone, ExpR prevents RNA polymerase access to the expR promoter, thereby directly repressing transcription initiation. The presence of pheromone renders the expR promoter accessible to RNA polymerase and results in the de-repression of transcription initiation. Overall we have established that there is a direct modulation of the repressive activity of a LuxR family regulator by a pheromone. Furthermore, site-directed mutagenesis experiments strongly suggest that the ExpR residues Leu-19, Tyr-31, and Ser-125 are involved in the transduction of conformational changes induced by ligand binding, and this provides new insights into the structure-function relationship of this bacterial regulator family" |
| Keywords: | 4-Butyrolactone/*analogs & derivatives/physiology Amino Acid Sequence Bacterial Proteins/genetics/*metabolism Base Sequence Dickeya chrysanthemi/genetics/*metabolism Molecular Sequence Data Pheromones/*physiology Trans-Activators/genetics/*metabolism; |
| Notes: | "MedlineCastang, Sandra Reverchon, Sylvie Gouet, Patrice Nasser, William eng Research Support, Non-U.S. Gov't 2006/07/13 J Biol Chem. 2006 Oct 6; 281(40):29972-87. doi: 10.1074/jbc.M601666200. Epub 2006 Jul 10" |
