title: Unconventional Coupling between Ligand Recognition and Allosteric Control in the Multidrug Resistance Gene Regulator, BmrR.
abstract: BmrR is a multidrug resistance (MDR) regulator that responds to diverse ligands. To obtain insight into signal recognition, allosteric control, and cooperativity, we used a quantitative in vitro transcription assay to determine the ligand-dependent activation profiles for a diverse set of cations, zwitterions, and uncharged ligands. As for many other biological switch systems, the data are well described by a modified Hill equation. Parameters extracted from curve fits to the data include L50, RMAXand N. We found that L50values correlate directly with ΔGBINDvalues, suggesting that the parameter reflects binding, whereas RMAXand N reflect allosteric control and cooperativity, respectively. Our results suggest unconventional coupling between ligand binding and allosteric control, with weakly interacting ligands exhibiting the highest levels of activation. Such properties are in stark contrast to those often exhibited by biological switch proteins, whereby ligand binding and allostery are tightly coupled, yielding both high selectivity and ultrasensitivity. We propose that weakened coupling, as observed for BmrR, may be important for providing robust activation responses to unrelated ligands. We also propose that other MDR proteins and other polyspecific switch systems will show similar features.
authors.affiliation: Laboratory of RNA Biophysics and Cellular Physiology, Biochemistry and Biophysics Center, National Institutes of Health, 50 South Drive, MSC, Bethesda, MD, 20892-8012, USA.
authors.forename: Sharrol
authors.identifier: 0000-0002-0662-1030
authors.initials: S
authors.lastname: Bachas
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University, School of Medicine, 725 North Wolfe Street, Baltimore, MD, 21205, USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Kohrs
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University, School of Medicine, 725 North Wolfe Street, Baltimore, MD, 21205, USA.
authors.forename: Herschel
authors.identifier: 0000-0003-1095-7888
authors.initials: H
authors.lastname: Wade
mesh_terms: D000494:Allosteric Regulation; D000634:Aminoquinolines / Q000737:chemistry / Q000494:pharmacology; D001412:Bacillus subtilis / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects; D008024:Ligands; D011401:Promoter Regions, Genetic; D011798:Quinaldines / Q000737:chemistry / Q000494:pharmacology; D013816:Thermodynamics; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D000634:Aminoquinolines; D001426:Bacterial Proteins; C098722:BmrR protein, bacteria; D008024:Ligands; D011798:Quinaldines; D015534:Trans-Activators; C507002:4-amino-2-methylquinoline
keywords: allosterism; biosensors; in vitro transcription; molecular recognition; multidrug resistance