title: Evidence for two interacting ligand binding sites in human multidrug resistance protein 2 (ATP binding cassette C2).
abstract: Multidrug resistance protein 2 (MRP2) belongs to the ATP binding cassette family of transporters. Its substrates include organic anions and anticancer drugs. We have used transport assays with vesicles derived from Sf9 insect cells overproducing MRP2 to study the interactions of drugs, organic anions, and bile acids with three MRP2 substrates: estradiol-17-beta-d-glucuronide (E217betaG), methotrexate, and glutathione-S-dinitrophenol. Complex inhibition and stimulation patterns were obtained, different from those observed with the related transporters MRP1 and MRP3. In contrast to a previous report, we found that the rate of E217betaG transport by MRP2 increases sigmoidally with substrate concentration indicative of homotropic cooperativity. Half-maximal transport was obtained at 120 microm E217betaG, in contrast to values < 20 microm for MRP1 and 3. MRP2 stimulators, such as indomethacin and sulfanitran, strongly increased the affinity of MRP2 for E217betaG (half-maximal transport rates at 65 and 16 microm E217betaG, respectively) and shifted the sigmoidal dependence of transport rate on substrate concentration to a more hyperbolic one, without substantially affecting the maximal transport rate. Sulfanitran also stimulated MRP2 activity in cells, i.e. the transport of saquinavir through monolayers of Madin-Darby canine kidney II cells. Some compounds that stimulate E217betaG transport, such as penicillin G or pantoprazole, are not detectably transported by MRP2, suggesting that they allosterically stimulate transport without being cotransported with E217betaG. We propose that MRP2 contains two similar but nonidentical ligand binding sites: one site from which substrate is transported and a second site that regulates the affinity of the transport site for the substrate.
authors.affiliation: Division of Molecular Biology and Center of Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Noam
authors.initials: N
authors.lastname: Zelcer
authors.forename: Maarten T
authors.initials: MT
authors.lastname: Huisman
authors.forename: Glen
authors.initials: G
authors.lastname: Reid
authors.forename: Peter
authors.initials: P
authors.lastname: Wielinga
authors.forename: Pauline
authors.initials: P
authors.lastname: Breedveld
authors.forename: Annemieke
authors.initials: A
authors.lastname: Kuil
authors.forename: Puck
authors.initials: P
authors.lastname: Knipscheer
authors.forename: Jan H M
authors.initials: JH
authors.lastname: Schellens
authors.forename: Alfred H
authors.initials: AH
authors.lastname: Schinkel
authors.forename: Piet
authors.initials: P
authors.lastname: Borst
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002460:Cell Line; D004958:Estradiol / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008727:Methotrexate / Q000378:metabolism; D024101:Mitochondrial Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D014161:Transduction, Genetic
chemical_list: D004958:Estradiol; D008024:Ligands; D008727:Methotrexate; D024101:Mitochondrial Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C093947:MRP2 protein, S cerevisiae; C025483:estradiol-17 beta-glucuronide; C114462:multidrug resistance-associated protein 3; C421109:multidrug resistance-associated protein 1