title: X-ray structure of the EmrE multidrug transporter in complex with a substrate.
abstract: EmrE is a prototype of the Small Multidrug Resistance family of efflux transporters and actively expels positively charged hydrophobic drugs across the inner membrane of Escherichia coli. Here, we report the x-ray crystal structure, at 3.7 angstrom resolution, of one conformational state of the EmrE transporter in complex with a translocation substrate, tetraphenylphosphonium. Two EmrE polypeptides form a homodimeric transporter that binds substrate at the dimerization interface. The two subunits have opposite orientations in the membrane and adopt slightly different folds, forming an asymmetric antiparallel dimer. This unusual architecture likely confers unidirectionality to transport by creating an asymmetric substrate translocation pathway. On the basis of available structural data, we propose a model for the proton-dependent drug efflux mechanism of EmrE.
authors.affiliation: Department of Molecular Biology, The Scripps Institute, 10550 North Torrey Pines Road, CB-105, Jolla, CA 92037, USA.
authors.forename: Owen
authors.initials: O
authors.lastname: Pornillos
authors.forename: Yen-Ju
authors.initials: YJ
authors.lastname: Chen
authors.forename: Andy P
authors.initials: AP
authors.lastname: Chen
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Chang
mesh_terms: D017920:Antiporters / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport; D018360:Crystallography, X-Ray; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D009861:Onium Compounds / Q000737:chemistry* / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D017920:Antiporters; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D009861:Onium Compounds; D009943:Organophosphorus Compounds; C075436:EmrE protein, E coli; C013289:tetraphenylphosphonium