title: Role of carboxylate residues adjacent to the conserved core Walker B motifs in the catalytic cycle of multidrug resistance protein 1 (ABCC1).
abstract: MRP1 belongs to subfamily "C" of the ABC transporter superfamily. The nucleotide-binding domains (NBDs) of the C family members are relatively divergent compared with many ABC proteins. They also differ in their ability to bind and hydrolyze ATP. In MRP1, NBD1 binds ATP with high affinity, whereas NBD2 is hydrolytically more active. Furthermore, ATP binding and/or hydrolysis by NBD2 of MRP1, but not NBD1, is required for MRP1 to shift from a high to low affinity substrate binding state. Little is known of the structural basis for these functional differences. One minor structural difference between NBDs is the presence of Asp COOH-terminal to the conserved core Walker B motif in NBD1, rather than the more commonly found Glu present in NBD2. We show that the presence of Asp or Glu following the Walker B motif profoundly affects the ability of the NBDs to bind, hydrolyze, and release nucleotide. An Asp to Glu mutation in NBD1 enhances its hydrolytic capacity and affinity for ADP but markedly decreases transport activity. In contrast, mutations that eliminate the negative charge of the Asp side chain have little effect. The decrease in transport caused by the Asp to Glu mutation in NBD1 is associated with an inability of MRP1 to shift from high to low affinity substrate binding states. In contrast, mutation of Glu to Asp markedly increases the affinity of NBD2 for ATP while decreasing its ability to hydrolyze ATP and to release ADP. This mutation eliminates transport activity but potentiates the conversion from a high to low affinity binding state in the presence of nucleotide. These observations are discussed in the context of catalytic models proposed for MRP1 and other ABC drug transport proteins.
authors.affiliation: Cancer Research Laboratories, Queen's University, Kingston, Ontario, Canada.
authors.forename: Lea F
authors.initials: LF
authors.lastname: Payen
authors.forename: Mian
authors.initials: M
authors.lastname: Gao
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Westlake
authors.forename: Susan P C
authors.initials: SP
authors.lastname: Cole
authors.forename: Roger G
authors.initials: RG
authors.lastname: Deeley
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D001692:Biological Transport; D002264:Carboxylic Acids / Q000737:chemistry*; D002384:Catalysis; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D018432:Drug Resistance, Multiple; D004591:Electrophoresis, Polyacrylamide Gel; D018698:Glutamic Acid / Q000737:chemistry; D006801:Humans; D006868:Hydrolysis; D007313:Insecta; D017997:Leukotriene C4 / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000737:chemistry*; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014638:Vanadates / Q000494:pharmacology
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D001224:Aspartic Acid; D002264:Carboxylic Acids; D018076:DNA, Complementary; D018698:Glutamic Acid; D017997:Leukotriene C4; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011994:Recombinant Proteins; D014638:Vanadates; C022571:adenosine 5'-O-(3-thiotriphosphate); C421109:multidrug resistance-associated protein 1