title: Introduction of the most common cystic fibrosis mutation (Delta F508) into human P-glycoprotein disrupts packing of the transmembrane segments.
abstract: The most common mutation in cystic fibrosis (deletion of phenylalanine 508 (DeltaF508) in the cystic fibrosis conductance transmembrane regulator (CFTR) gene) causes defective synthesis of CFTR protein. To understand how this deletion interferes with protein folding, we made the equivalent deletion (DeltaY490) in P-glycoprotein (P-gp). A Cys-less P-gp with cysteines in transmembrane (TM) 4 or TM5 can be cross-linked with a cysteine in TM12. Deleting Tyr(490) in P-gp resulted in an inactive and defectively processed mutant in which no cross-linking between TM4 or TM5 and TM12 was detected. Expression of the DeltaY490 mutant in the presence of a chemical chaperone corrected the processing defect and yielded active P-gp mutants that could be cross-linked between TM4 or TM5 and TM12. Cross-linking between TM4 or TM5 and TM12 was also detected when residues (483)TIAENIRYG(491) in P-gp were replaced with residues (501)TIKENIIFG(509) from CFTR (P-gp/CFTR). Deleting Phe(508) in the P-gp/CFTR chimera, however, caused defective processing of the mutant protein and no detectable cross-linking between TM4 or TM5 and TM12. The processing defect was corrected with a chemical chaperone and yielded active P-gp/CFTR mutant proteins that could be cross-linked. These results show that deletion at residue 490 disrupts packing of the TM segments possibly by affecting interaction between the first nucleotide-binding domain (Tyr(490)) and the first cytoplasmic loop (Glu(184)).
authors.affiliation: Canadian Institutes for Health Research (CIHR) Group in Membrane Biology, Department of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Tip W
authors.initials: TW
authors.lastname: Loo
authors.forename: M Claire
authors.initials: MC
authors.lastname: Bartlett
authors.forename: David M
authors.initials: DM
authors.lastname: Clarke
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019943:Amino Acid Substitution; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003432:Cross-Linking Reagents; D003545:Cysteine; D003550:Cystic Fibrosis / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D016296:Mutagenesis; D009154:Mutation; D010084:Oxidation-Reduction; D010649:Phenylalanine; D017510:Protein Folding; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D014162:Transfection
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; C505032:CFTR protein, human; D003432:Cross-Linking Reagents; D011994:Recombinant Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D010649:Phenylalanine; D003545:Cysteine