title: Demonstration of conformational changes associated with activation of the maltose transport complex.
abstract: In Escherichia coli, interaction of a periplasmic maltose-binding protein with a membrane-associated ATP-binding cassette transporter stimulates ATP hydrolysis, resulting in translocation of maltose into the cell. The maltose transporter contains two transmembrane subunits, MalF and MalG, and two copies of a nucleotide-hydrolyzing subunit, MalK. Mutant transport complexes that function in the absence of binding protein are thought to be stabilized in an ATPase-active conformation. To probe the conformation of the nucleotide-binding site and to gain an understanding of the nature of the conformational changes that lead to activation, cysteine 40 within the Walker A motif of the MalK subunit was modified by the fluorophore 2-(4'-maleimidoanilino)naphthalene-6-sulfonic acid. Fluorescence differences indicated that residues involved in nucleotide binding were less accessible to aqueous solvent in the binding protein independent transporter than in the wild-type transporter. Similar differences in fluorescence were seen when a vanadate-trapped transition state conformation was compared with the ground state in the wild-type transporter. Our results and recent crystal structures are consistent with a model in which activation of ATPase activity is associated with conformational changes that bring the two MalK subunits closer together, completing the nucleotide-binding sites and burying ATP in the interface.
authors.affiliation: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Mannering
authors.forename: S
authors.initials: S
authors.lastname: Sharma
authors.forename: A L
authors.initials: AL
authors.lastname: Davidson
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000251:Adenosine Triphosphatases / Q000378:metabolism; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008320:Maltose / Q000378:metabolism*; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011487:Protein Conformation; D012997:Solvents; D013050:Spectrometry, Fluorescence
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; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D012997:Solvents; C461599:maltose transport system, E coli; D008320:Maltose; D000251:Adenosine Triphosphatases