title: Function of the ABC signature sequences in the human multidrug resistance protein 1.
abstract: Human multidrug resistance protein 1 (MRP1) is a membrane ATP-binding cassette transporter that confers multidrug resistance to tumor cells by effluxing intracellular drugs in an ATP-dependent manner. The mechanisms by which transport occurs and by which ATP hydrolysis is coupled to drug transport are not fully elucidated. In particular, the function of the signature sequences in the nucleotide binding domains (NBDs) of MRP1 is unknown. We therefore investigated the effect of mutation of the signature sequences (G771D and G1433D) and of the Walker A motifs (K684M and K1333M) in the NBDs on the 8-azido-[alpha-32P]ATP photolabeling and 8-azido-[alpha-32P]ADP vanadate trapping of MRP1. Both mutations in the Walker A motif almost completely inhibited the labeling of the mutated NBD with 8-azido-[alpha-32P]ATP but not the labeling of the other intact NBD. In contrast, the G771D mutation in the signature sequence of NBD1 enhanced the labeling of NBD1 but slightly decreased the labeling of NBD2. The G1433D mutation in the signature motif of NBD2 enhanced the labeling of NBD2 but did not affect the labeling of NBD1. These effects were all substrate-independent. Photolabeling of NBD2 and a very slight photolableing of NBD1 were detectable under vanadate trapping conditions with 8-azido-[alpha-32P]ATP. Trapping at both NBD1 and NBD2 was almost completely inhibited by K684M and K1333M mutations and by the K684M/K1333M double mutation. The G771D mutation completely inhibited trapping at NBD2 and considerably inhibited trapping at NBD1. However, whereas the G1433D mutation also considerably inhibited trapping at NBD1, it only partially inhibited trapping of NBD2, and the trapping could still be enhanced by leukotriene C4. Our findings suggest that both signature sequences of MRP1 are involved in ATP hydrolysis and must be intact for the ATP hydrolysis and the transport by MRP1.
authors.affiliation: Department of Molecular Oncology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Xiao-Qin
authors.initials: XQ
authors.lastname: Ren
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Furukawa
authors.forename: Misako
authors.initials: M
authors.lastname: Haraguchi
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Sumizawa
authors.forename: Shunji
authors.initials: S
authors.lastname: Aoki
authors.forename: Motomasa
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Akiyama
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001386:Azides / Q000494:pharmacology; D001692:Biological Transport; D002478:Cells, Cultured; D006801:Humans; D007313:Insecta / Q000166:cytology; D017997:Leukotriene C4 / Q000378:metabolism; D009154:Mutation; D010761:Phosphorus Radioisotopes; D017434:Protein Structure, Tertiary / Q000235:genetics; D014638:Vanadates / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D001386:Azides; D010761:Phosphorus Radioisotopes; D017997:Leukotriene C4; D014638:Vanadates; C017040:8-azidoadenosine 5'-triphosphate; D000255:Adenosine Triphosphate