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: Delta R(708-835), Delta NBF2(1185-1349) and Delta R-Delta NBF2. In lipid bilayers, Delta BF2 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 Delta R and Delta R-NBF2 channels are PKA-independent, but Delta R activity is reduced whereas Delta R-Delta NBF2 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. (C) 1999 Federation of European Biochemical Societies.