Studies of human MDR1-MDR2 chimeras demonstrate the functional exchangeability of a major transmembrane segment of the multidrug transporter and phosphatidylcholine flippase.
P-glycoprotein (P-gp), encoded by the MDR1 gene, is a plasma membrane transporter which effluxes a large number of structurally nonrelated hydrophobic compounds. The molecular basis of the broad substrate recognition of P-gp is not well understood. Despite the 78% amino acid sequence identity of the MDR1 and MDR2 transporter, MDR2, which has been identified as a phosphatidylcholine transporter, does not transport most MDR1 substrates. The structural and functional differences between MDR1 and MDR2 provide an opportunity to identify the residues essential for the broad substrate spectrum of MDR1. Using an approach involving exchanging homologous segments of MDR1 and MDR2 and site-directed mutagenesis, we have demonstrated that MDR1 residues Q330, V331, and L332 in transmembrane domain 6 are sufficient to allow an MDR2 backbone in the N-terminal half of P-gp to transport several MDR1 substrates, including bisantrene, colchicine, vinblastine, and rhodamine-123. These studies help define some residues important for multidrug transport and indicate the close functional relationship between the multidrug transporter (MDR1) and phosphatidylcholine flippase (MDR2).
Zhou
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Y
Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Gottesman
M M
MM
Pastan
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I
D016475:3T3 Cells; D018435:ATP Binding Cassette Transporter, Subfamily B / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000345:Affinity Labels; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010713:Phosphatidylcholines / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000345:Affinity Labels; D010713:Phosphatidylcholines; D011993:Recombinant Fusion Proteins; C095122:multidrug resistance protein 3