Function of the second nucleotide-binding fold in the CFTR chloride channel

To test the role of nucleotide-binding fold (NBF) 2 and its interaction with the regulatory (R) domain in the function of the cystic fibrosis transmembrane conductance regulator (CFTR) channel, we used three deletion mutants of CFTR: ΔR(708-835), ΔNBF2(1185-1349) and ΔR-ΔNBF2. In lipid bilayers, ΔNBF2 channel activity is ATP- and cAMP-dependent protein kinase (PKA)-dependent, but unlike wild-type (wt) CFTR, it displays a reduced activity and insensitivity to 5′-adenylylimidodiphosphate (AMP-PNP). Both ΔR and ΔR-ΔNBF2 channels are PKA-independent, but ΔR activity is reduced whereas ΔR-ΔNBF2 activity is increased. Deletion of NBF2 from CFTR affects protein trafficking and channel gating kinetics. The data suggest that NBF2 could have inhibitory and stimulatory roles in CFTR activity by interaction with NBF1 directly or indirectly via the R domain.