title: Identification of residues within the drug-binding domain of the human multidrug resistance P-glycoprotein by cysteine-scanning mutagenesis and reaction with dibromobimane.
abstract: P-glycoprotein (P-gp) can transport a wide variety of cytotoxic compounds that have diverse structures. Therefore, the drug-binding domain of the human multidrug resistance P-gp likely consists of residues from multiple transmembrane (TM) segments. In this study, we completed cysteine-scanning mutagenesis of all the predicted TM segments of P-gp (TMs 1-5 and 7-10) and tested for inhibition by a thiol-reactive substrate (dibromobimane) to identify residues within the drug-binding domain. The activities of 189 mutants were analyzed. Verapamil-stimulated ATPase activities of seven mutants (Y118C and V125C (TM2), S222C (TM4), I306C (TM5), S766C (TM9), and I868C and G872C (TM10)) were inhibited by more than 50% by dibromobimane. The activities of mutants S222C (TM4), I306C (TM5), I868C (TM10), and G872C (TM10), but not that of mutants Y118C (TM2), V125C (TM2), and S776C (TM9), were protected from inhibition by dibromobimane by pretreatment with verapamil, vinblastine, or colchicine. These results and those from previous studies (Loo, T. W. and Clarke, D. M. (1997) J. Biol. Chem. 272, 31945-31948; Loo, T. W. and Clarke, D. M. (1999) J. Biol. Chem. 274, 35388-35392) indicate that the drug-binding domain of P-gp consists of residues in TMs 4, 5, 6, 10, 11, and 12.
authors.affiliation: Canadian Institute for Health Research Group in Membrane Biology, Departments of Medicine and Biochemistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: T W
authors.initials: TW
authors.lastname: Loo
authors.forename: D M
authors.initials: DM
authors.lastname: Clarke
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D003545:Cysteine / Q000737:chemistry*; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D001643:Bridged Bicyclo Compounds; D002121:Calcium Channel Blockers; D003432:Cross-Linking Reagents; D014747:Vinblastine; C037094:dibromobimane; D014700:Verapamil; D000251:Adenosine Triphosphatases; D003545:Cysteine; D003078:Colchicine