title: ATP-dependent substrate transport by the ABC transporter MsbA is proton-coupled.
abstract: ATP-binding cassette transporters mediate the transbilayer movement of a vast number of substrates in or out of cells in organisms ranging from bacteria to humans. Current alternating access models for ABC exporters including the multidrug and Lipid A transporter MsbA from Escherichia coli suggest a role for nucleotide as the fundamental source of free energy. These models involve cycling between conformations with inward- and outward-facing substrate-binding sites in response to engagement and hydrolysis of ATP at the nucleotide-binding domains. Here we report that MsbA also utilizes another major energy currency in the cell by coupling substrate transport to a transmembrane electrochemical proton gradient. The dependence of ATP-dependent transport on proton coupling, and the stimulation of MsbA-ATPase by the chemical proton gradient highlight the functional integration of both forms of metabolic energy. These findings introduce ion coupling as a new parameter in the mechanism of this homodimeric ABC transporter.
authors: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
authors: Himansha
authors: H
authors: Singh
authors: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
authors: Saroj
authors: S
authors: Velamakanni
authors: Department of Biochemistry, Cambridge Centre for Proteomics, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK.
authors: Michael J
authors: MJ
authors: Deery
authors: Department of Biochemistry, Cambridge Centre for Proteomics, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK.
authors: Julie
authors: J
authors: Howard
authors: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
authors: Shen L
authors: SL
authors: Wei
authors: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
authors: Hendrik W
authors: HW
authors: van Veen
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002701:Chloramphenicol / Q000494:pharmacology; D004563:Electrochemistry; D004996:Ethidium / Q000378:metabolism; D006868:Hydrolysis; D007477:Ions; D011510:Proteolipids / Q000378:metabolism; D011522:Protons; D013379:Substrate Specificity / Q000187:drug effects
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D007477:Ions; C079726:MsbA protein, Bacteria; D011510:Proteolipids; D011522:Protons; C020485:proteoliposomes; D002701:Chloramphenicol; D000255:Adenosine Triphosphate; D004996:Ethidium