Cross-linking of human multidrug resistance P-glycoprotein by the substrate, tris-(2-maleimidoethyl)amine, is altered by ATP hydrolysis. Evidence for rotation of a transmembrane helix.
We identified a thiol-reactive substrate, Tris-(2-maleimidoethyl)amine (TMEA), to explore the contribution of the TM segments 6 and 12 of the human multidrug resistance P-glycoprotein (P-gp) during transport. TMEA is a trifunctional maleimide and stimulated the ATPase activity of Cys-less P-gp about 7-fold. Cysteine-scanning mutagenesis of TM12 showed that the activity of mutant V982C was inhibited by TMEA. P-gp mutants containing V982C (TM12) and another cysteine in TM6 were constructed and tested for cross-linking with TMEA. A cross-linked product was observed in SDS-polyacrylamide gel electrophoresis for mutant L339C(TM6)/V982C(TM12). Cross-linking by TMEA also inhibited the ATPase activity of the mutant protein. Substrates such as cyclosporin A, vinblastine, colchicine, or verapamil inhibited cross-linking by TMEA. In the presence of ATP at 37 degrees C, cross-linking of mutant L339C/V982C was decreased. In contrast, there was enhanced cross-linking of mutant F343C(TM6)/V982C(TM12) in the presence of ATP. These results show that cross-linking must be within the drug-binding domain, that residues L339C(TM6)/V982C(TM12) must be at least 10 A apart, and that ATP hydrolysis promotes rotation of one or both TM helices.
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Canadian Institutes for Health Research Group in Membrane Biology, Department of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Clarke
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D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D002460:Cell Line; D003432:Cross-Linking Reagents / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008301:Maleimides / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D013379:Substrate Specificity; D014638:Vanadates / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003432:Cross-Linking Reagents; D008301:Maleimides; C434955:tris(2-maleimidoethyl)amine; D014638:Vanadates; D000255:Adenosine Triphosphate