Quantitative Analysis of ATP-Dependent Gating of CFTR

CFTR, the chloride ion channel encoded by the gene mutated in cystic fibrosis patients, has been the subject of intense investigation since its discovery in 1989 (1 ). A member of the ATP Binding Cassette (ABC) superfamily, the CFTR channel possesses two nucleotide-binding domains (NBDs) that hydrolyze ATP in vitro and are thought to use the resulting energy to drive the opening and closing of the channel. In addition to its NBDs and the putative pore-forming transmembrane regions, CFTR also contains a unique domain believed to regulate gating by modulating the activity of the two NBDs. This regulatory (R) domain is a substrate for phosphorylation by protein kinase A (PKA). PKA-dependent phosphorylation not only activates but also finely modulates ATP-dependent gating (2 ).