title: Trapping the transition state of an ATP-binding cassette transporter: evidence for a concerted mechanism of maltose transport.
abstract: High-affinity uptake into bacterial cells is mediated by a large class of periplasmic binding protein-dependent transport systems, members of the ATP-binding cassette superfamily. In the maltose transport system of Escherichia coli, the periplasmic maltose-binding protein binds its substrate maltose with high affinity and, in addition, stimulates the ATPase activity of the membrane-associated transporter when maltose is present. Vanadate inhibits maltose transport by trapping ADP in one of the two nucleotide-binding sites of the membrane transporter immediately after ATP hydrolysis, consistent with its ability to mimic the transition state of the gamma-phosphate of ATP during hydrolysis. Here we report that the maltose-binding protein becomes tightly associated with the membrane transporter in the presence of vanadate and simultaneously loses its high affinity for maltose. These results suggest a general model explaining how ATP hydrolysis is coupled to substrate transport in which a binding protein stimulates the ATPase activity of its cognate transporter by stabilizing the transition state.
authors.affiliation: Howard Hughes Medical Institute, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.forename: S
authors.initials: S
authors.lastname: Sharma
authors.forename: F A
authors.initials: FA
authors.lastname: Quiocho
authors.forename: A L
authors.initials: AL
authors.lastname: Davidson
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008320:Maltose / Q000378:metabolism*; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D014638:Vanadates / Q000494:pharmacology
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; C079123:MalG protein, E coli; C068021:MalK protein, Bacteria; C489398:MalK protein, E coli; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; C461599:maltose transport system, E coli; D014638:Vanadates; D000244:Adenosine Diphosphate; D008320:Maltose; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases