title: Discovery of an auto-regulation mechanism for the maltose ABC transporter MalFGK2.
abstract: The maltose transporter MalFGK(2), together with the substrate-binding protein MalE, is one of the best-characterized ABC transporters. In the conventional model, MalE captures maltose in the periplasm and delivers the sugar to the transporter. Here, using nanodiscs and proteoliposomes, we instead find that MalE is bound with high-affinity to MalFGK2 to facilitate the acquisition of the sugar. When the maltose concentration exceeds the transport capacity, MalE captures maltose and dissociates from the transporter. This mechanism explains why the transport rate is high when MalE has low affinity for maltose, and low when MalE has high affinity for maltose. Transporter-bound MalE facilitates the acquisition of the sugar at low concentrations, but also captures and dissociates from the transporter past a threshold maltose concentration. In vivo, this maltose-forced dissociation limits the rate of transport. Given the conservation of the substrate-binding proteins, this mode of allosteric regulation may be universal to ABC importers.
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, 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*; D001692:Biological Transport; D004789:Enzyme Activation; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis; D008320:Maltose / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D009154:Mutation; D033902:Periplasmic Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011510:Proteolipids / Q000378:metabolism
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