title: Small multidrug resistance protein EmrE reduces host pH and osmotic tolerance to metabolic quaternary cation osmoprotectants.
abstract: The small multidrug resistance (SMR) transporter protein EmrE in Escherichia coli is known to confer resistance to toxic antiseptics classified as quaternary cation compounds (QCCs). Naturally derived QCCs synthesized during metabolic activities often act as osmoprotectants, such as betaine and choline, and participate in osmotic homoestasis. The goal of this study was to determine if EmrE proteins transport biological QCC-based osmoprotectants. Plasmid-encoded copies of E. coli emrE and the inactive variant emrE-E14C (emrE with the E → C change at position 14) were expressed in various E. coli strains grown in either rich or minimal media at various pHs (5 to 9) and under hypersaline (0.5 to 1.0 M NaCl and KCl) conditions to identify changes in growth phenotypes induced by osmoprotectant transport. The results demonstrated that emrE expression reduced pH tolerance of E. coli strains at or above neutral pH and when grown in hypersaline media at or above NaCl or KCl concentrations of 0.75 M. Hypersaline growth conditions were used to screen QCC osmoprotectants betaine, choline, l-carnitine, l-lysine, l-proline, and l-arginine. The study identified that betaine and choline are natural QCC substrates of EmrE.
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Denice C
authors.initials: DC
authors.lastname: Bay
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Turner
mesh_terms: D000143:Acids / Q000378:metabolism*; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D009997:Osmotic Pressure; D010957:Plasmids; D011188:Potassium; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D054712:Salinity; D012964:Sodium; D013312:Stress, Physiological
chemical_list: D000143:Acids; D017920:Antiporters; D002412:Cations; D029968:Escherichia coli Proteins; D000644:Quaternary Ammonium Compounds; C075436:EmrE protein, E coli; D012964:Sodium; D011188:Potassium