Effects of the S1347G mutation on ligand exchange. (A) Stereoview of interactions of ATP with key residues at the NBD dimer interface. The crystal structure of Escherichia coli MalK NBD dimer (Protein Data Bank accession no. 1Q12) was used to illustrate these interactions. The residue numbers in the parentheses represent the equivalent amino acids in CFTR. Arrow, the side chain of S1347. (B) A representative single S1347G-CFTR channel trace from seven similar recordings. (C) The channel entered longer openings without an obvious delay after ATP/PATP change. (D) Macroscopic currents from S1347G channels. PATP-induced current increase can be fitted well with a double-exponential function (inset).