Altered functional interactions between CFTR disease mutants ΔF508 and G551D and the protein kinase A catalytic subunit.

The epithelial anion channel cystic fibrosis transmembrane conductance regulator (CFTR) is activated by cAMP-dependent protein kinase (PKA). PKA stimulates CFTR channels through two mechanisms: non-catalytically, by binding to the channel, and catalytically, by phosphorylating its regulatory (R) domain. CFTR mutations that reduce channel activity cause cystic fibrosis (CF), but clinically used modulator drugs that boost channel function can alleviate disease symptoms. The two common CF mutations, ΔF508 and G551D, have been reported to impair CFTR channel activation by PKA, but the mechanisms remain unclear. Here, we aimed to understand how the mutations impact non-catalytic vs. catalytic channel activation by PKA and how these two processes are modulated by clinically used potentiator drugs. Using current recordings from excised inside-out membrane patches superfused with the purified catalytic subunit of PKA, we confirm slowed PKA-dependent activation for both mutants but demonstrate intact binding affinity for the kinase. Furthermore, we find that non-catalytic activation dominates overall channel activity for both mutants and can be strongly enhanced by stabilization of the NBD1-NBD2-TMD interface using the ATP analogue N