title: ATP alone triggers the outward facing conformation of the maltose ATP-binding cassette transporter.
abstract: The maltose transporter MalFGK(2) is a study prototype for ABC importers. During catalysis, the MalFG membrane domain alternates between inward and outward facing conformations when the MalK dimer closes and hydrolyzes ATP. Because a rapid ATP hydrolysis depends on MalE and maltose, it has been proposed that closed liganded MalE facilitates the transition to the outward facing conformation. Here we find that, in contrast to the expected, ATP is sufficient for the closure of MalK and for the conversion of MalFG to the outward facing state. The outward facing transporter binds MalE with nanomolar affinity, yet neither MalE nor maltose is necessary or facilitates the transition. Thus, the rapid hydrolysis of ATP observed in the presence of MalE and maltose is not because closed liganded MalE accelerates the formation of the outward facing conformation. These findings have fundamental implications for the description of the transport reaction.
authors.affiliation: Department of Biochemistry & Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Huan
authors.initials: H
authors.lastname: Bao
authors.forename: Franck
authors.initials: F
authors.lastname: Duong
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D005453:Fluorescence; D007700:Kinetics; D008320:Maltose / Q000378:metabolism*; D033902:Periplasmic Binding Proteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation; D011510:Proteolipids / Q000378:metabolism; D017186:Titrimetry
chemical_list: D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D033902:Periplasmic Binding Proteins; D011510:Proteolipids; C461599:maltose transport system, E coli; C020485:proteoliposomes; D008320:Maltose; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases