title: Analysis of the properties of the N-terminal nucleotide-binding domain of human P-glycoprotein.
abstract: Human P-glycoprotein, the MDR1 gene product, requires both Mg(2+)-ATP binding and hydrolysis to function as a drug transporter; however, the mechanism(s) defining these events is not understood. In the present study, we explored the nature of Mg(2+)-ATP binding in the N-terminal nucleotide-binding domain of human P-glycoprotein and identified the minimal functional unit required for specific ATP binding. Recombinant proteins encompassing amino acids within the region beginning at 348 and ending at 707 were expressed in Escherichia coli, purified from inclusion bodies under denaturing conditions, and renatured by rapid dilution. The ability of ATP to interact with these proteins was examined by use of the photoactive ATP analogue [alpha-(32)P]-8-azido-ATP. Photoaffinity labeling of recombinant proteins identified the region between amino acids 375 and 635 as the region necessary to obtain specific ATP-binding properties. Specific protein labeling was saturable, enhanced by Mg(2+), and inhibited by ATP. Recombinant proteins confined within the region beginning at amino acid 392 and ending at amino acid 590 demonstrated nonspecific [alpha-(32)P]-8-azido-ATP labeling. Nonspecific labeling was not enhanced by Mg(2+) and was inhibited only by high concentrations of ATP. Using a D555N mutated protein, we found that the conserved aspartate residue in the Walker B motif plays a role in magnesium-enhanced ATP-binding. Taken together, these data define the region of the N-terminal nucleotide-binding domain of P-glycoprotein that is required for specific ATP binding and suggest that magnesium may play a role in stabilizing the ATP-binding site.
authors.affiliation: Laboratories of Molecular Biology and Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Booth
authors.forename: L
authors.initials: L
authors.lastname: Pulaski
authors.forename: M M
authors.initials: MM
authors.lastname: Gottesman
authors.forename: I
authors.initials: I
authors.lastname: Pastan
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry* / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D001386:Azides / Q000737:chemistry; D001665:Binding Sites; D004926:Escherichia coli; D006801:Humans; D007700:Kinetics; D009154:Mutation; D009711:Nucleotides / Q000378:metabolism*; D019920:Photoaffinity Labels; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001386:Azides; D009711:Nucleotides; D019920:Photoaffinity Labels; D011994:Recombinant Proteins; C017040:8-azidoadenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases