title: The homodimeric ATP-binding cassette transporter LmrA mediates multidrug transport by an alternating two-site (two-cylinder engine) mechanism.
abstract: The bacterial LmrA protein and the mammalian multidrug resistance P-glycoprotein are closely related ATP-binding cassette (ABC) transporters that confer multidrug resistance on cells by mediating the extrusion of drugs at the expense of ATP hydrolysis. The mechanisms by which transport is mediated, and by which ATP hydrolysis is coupled to drug transport, are not known. Based on equilibrium binding experiments, photoaffinity labeling and drug transport assays, we conclude that homodimeric LmrA mediates drug transport by an alternating two-site transport (two-cylinder engine) mechanism. The transporter possesses two drug-binding sites: a transport-competent site on the inner membrane surface and a drug-release site on the outer membrane surface. The interconversion of these two sites, driven by the hydrolysis of ATP, occurs via a catalytic transition state intermediate in which the drug transport site is occluded. The mechanism proposed for LmrA may also be relevant for P-glycoprotein and other ABC transporters.
authors.affiliation: Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, NL-9751 NN Haren, The Netherlands. h.w.van.veen@biol.rug.nl
authors.forename: H W
authors.initials: HW
authors.lastname: van Veen
authors.forename: A
authors.initials: A
authors.lastname: Margolles
authors.forename: M
authors.initials: M
authors.lastname: Müller
authors.forename: C F
authors.initials: CF
authors.lastname: Higgins
authors.forename: W N
authors.initials: WN
authors.lastname: Konings
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000502:physiology; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000502:physiology*; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D001562:Benzimidazoles / Q000378:metabolism; D001665:Binding Sites; D001693:Biological Transport, Active; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D019281:Dimerization; D018432:Drug Resistance, Multiple / Q000502:physiology*; D007546:Isoquinolines / Q000494:pharmacology; D013294:Lactococcus lactis; D008081:Liposomes; D008958:Models, Molecular; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D016297:Mutagenesis, Site-Directed; D019920:Photoaffinity Labels; D017434:Protein Structure, Tertiary; D011799:Quinazolines / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014638:Vanadates / Q000494:pharmacology; D014747:Vinblastine / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D001426:Bacterial Proteins; D001562:Benzimidazoles; D002121:Calcium Channel Blockers; D007546:Isoquinolines; D008081:Liposomes; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D019920:Photoaffinity Labels; D011799:Quinazolines; D011993:Recombinant Fusion Proteins; D014638:Vanadates; D014747:Vinblastine; C101824:LmrA protein, Lactococcus lactis; C087168:CP 100356; C017807:bisbenzimide ethoxide trihydrochloride