biostudies-literatureSingh HMedical Research CouncilBiotechnology and Biological Sciences Research Council12387https://www.ebi.ac.uk/biostudies/studies/S-EPMC4979069biostudies-literatureUnknown7ATP-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.Nature communicationsATP-dependent substrate transport by the ABC transporter MsbA is proton-coupled.PMC4979069G0401165BB/I002383/1BB/K017713/1BB/C004663/1MC_PC_14116Singh Hvan Veen HWHoward JWei SLDeery MJVelamakanni SfalseATP-dependent substrate transport by the ABC transporter MsbA is proton-coupled.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.2016-01-01T00:00:00Z2016 Aug2025-04-21T18:59:37.564Z2019-03-27T02:20:16ZS-EPMC49790692749901310.1038/ncomms12387