On the mechanism of gating defects caused by the R117H mutation in cystic fibrosis transmembrane conductance regulator
Two functional abnormalities of cystic fibrosis transmembrane conductance regulator (CFTR), a 25% reduction of the single‐channel conductance (g) and a ∼13‐fold lower open probability (Po), were found with the R117H mutation that is associated with mild forms of cystic fibrosis. Characterizations of the gating defects of R117H‐CFTR led to the conclusion that the mutation decreases Po by perturbing the gating conformational changes in CFTR's transmembrane domains (TMDs) without altering the function of the nucleotide binding domains (NBDs). Nonetheless, gating of the R117H‐CFTR can be improved by a variety of pharmacological reagents supposedly acting on NBDs such as ATP analogues, or TMDs (e.g. VX‐770 or nitrate). These reagents potentiate synergistically R117H‐CFTR gating to a level that allows accurate assessments of its gating deficits. Our studies not only elucidate the mechanism underpinning gating dysfunction of R117H‐CFTR, but also provide a mechanistic understanding of how VX‐770 ameliorates the gating defects in the R117H mutant.