title: Alteration of substrate specificity by mutations at the His61 position in predicted transmembrane domain 1 of human MDR1/P-glycoprotein.
abstract: In CFTR, a member of the ABC superfamily and a chloride channel, amino acid substitutions in its transmembrane domains 1 and 6 (TM1, TM6) have been reported to modulate the anion selectivity or ion conductance of the ion channel. In P-glycoprotein, no amino acid substitution in TM1, but some in TM6, have been reported to modify the substrate specificity of this protein. In this work, we demonstrated the involvement of His61, which is in the middle of the predicted TM1, in the function of P-glycoprotein. His61 was replaced by all other amino acid residues, and each of the mutant cDNAs was introduced into drug-sensitive human carcinoma cells, KB3-1. The drug-resistance profile of cells stably expressing each mutated P-glycoprotein was investigated by comparing their relative resistance to vinblastine, colchicine, VP16, and adriamycin. The resistance to vinblastine was increased by replacing His61 by amino acids with smaller side chains, while it was lowered by replacing by amino acids with bulkier side chains. The reverse effect was observed for resistance to colchicine and VP16. The resistance to adriamycin was increased by replacing by amino acids with bulkier side chains except Lys or Arg, which have a basic side chain. We also showed that the replacement of His61 by Phe and Lys greatly impaired the efflux of calcein AM, while the replacement had no effect on the efflux of rhodamine 123. These results suggest that an amino acid residue at position 61 in TM1 is important in deciding the substrate specificity of P-glycoprotein.
authors.affiliation: Laboratory of Biochemistry, Division of Applied Life Science, Kyoto University Graduate School of Agriculture, Kyoto 606-01, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Taguchi
authors.forename: K
authors.initials: K
authors.lastname: Kino
authors.forename: M
authors.initials: M
authors.lastname: Morishima
authors.forename: T
authors.initials: T
authors.lastname: Komano
authors.forename: S E
authors.initials: SE
authors.lastname: Kane
authors.forename: K
authors.initials: K
authors.lastname: Ueda
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000502:physiology*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D001665:Binding Sites / Q000235:genetics; D003078:Colchicine / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000502:physiology; D004252:DNA Mutational Analysis; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005047:Etoposide / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D006639:Histidine / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D020112:Rhodamine 123; D012235:Rhodamines / Q000378:metabolism; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; C505032:CFTR protein, human; D005452:Fluoresceins; D005456:Fluorescent Dyes; D012235:Rhodamines; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C085925:calcein AM; D020112:Rhodamine 123; D006639:Histidine; D014747:Vinblastine; D005047:Etoposide; D004317:Doxorubicin; D003078:Colchicine