Correctors Enhance Maturation of ΔF508 CFTR by Promoting Interactions between the Two Halves of the Molecule

Deletion or Phe508 in cystic fibrosis transmembrane conductance regulator (Delta F508 CFTR) causes cystic fibrosis. CFTR consists of two homologous halves with each containing 4 nucleotide-binding domain (NBD) and a transmembrane domain (TMD). Delta F508 CFTR appears to be trapped in an incompletely folded state. Small molecules (correctors) promote folding of Delta F508 CFTR with relatively low efficiency. Understanding the mechanism of repair may lead to the development of more effective correctors, Here we tested the effect of correctors and the Delta F508 Mutation on interactions between the halves of CFTR when expressed as separate polypeptides. Glycosylation of C-half CFTR was defective when expressed alone as a mixture of core and unglycosylated proteins was detected. Coexpression of C-half CFTR with either wild-type N-half or Delta F508/N-hair CFTR, however, increased the amount of core-glycosylated protein, but only coexpression with wild-type N-half promoted maturation of C-half CFTR (Endo H resistant). This suggested that the Delta F508 mutation inhibited some interactions between N-half and C-half CFTRs. Interaction of Delta 52-tagged wild-type N-half or Delta F508/N-half CFTR with histidine-tagged C-half CFTR was then followed by nickel-chelate chromatography. Coexpression of Delta 52-tagged wild-type N-half or Delta F508/N-half CFTR with histidine-tagged C-half CFTR resulted in the wild-type N-half CFTR but not Delta F508/N-half CFTR. protein being retained on the column. Coexpression of Delta F508/N-half and C-half CFTR in the presence correctors VX-325 and corr-4a, however, restored interactions between the two halves. An interaction that was restored was that between NBD1 and TMD2 as the correctors restored cross-linking of mutant Delta F508/NBD1-(V510C)/TMD2(Delta 1067C). Therefore, correctors promote proper interactions between the two halves of CFTR.