PhD Scientific Days 2026

Molecular Medicine 4.

Functional interactions between ΔF508 and G551D CFTR variants and the protein kinase A catalytic subunit

Name of the presenter

Závoti, Olivér

Institute/workplace of the presenter

Department of Biochemistry

Authors

Olivér Závoti¹, Márton A. Simon¹, László Csanády¹
1: Department of Biochemistry

Text of the abstract

The epithelial anion channel cystic fibrosis transmembrane conductance regulator (CFTR) is activated by cyclic AMP-dependent protein kinase A (PKA) through two complementary mechanisms: noncatalytic activation via direct kinase binding and catalytic activation via phosphorylation of the regulatory (R) domain. Mutations that impair CFTR function cause cystic fibrosis (CF), including the two highly prevalent variants ΔF508 and G551D. Although clinically approved modulators (ETI; elexacaftor-tezacaftor-ivacaftor) mitigate disease symptoms, the molecular mechanisms by which these mutations disrupt PKA-dependent activation – and how potentiator drugs modify these processes – remain unclear.
We determined the relative contributions of catalytic and noncatalytic PKA activation in ΔF508 and G551D CFTR using current recordings from excised inside-out membrane patches superfused with purified PKA catalytic subunit. Although kinase binding affinity remained intact, both variants exhibited slowed PKA-dependent activation kinetics. Quantitative analysis revealed that noncatalytic activation constitutes the dominant component of overall channel activity in both mutants. This noncatalytic contribution was markedly enhanced by the high-affinity ATP analogue N6-(2-phenylethyl)-ATP (P-ATP), which stabilises the NBD1-NBD2-TMD interface.
We further examined the impact of the clinically employed potentiator drug combination elexacaftor and ivacaftor. For both variants, the drug combination preferentially enhanced catalytic channel activation relative to noncatalytic activation. Surprisingly, in ΔF508 CFTR, elexacaftor plus ivacaftor induced substantial PKA-independent channel activity while effectively suppressing PKA-mediated noncatalytic activation.
Together, these findings demonstrate how two common CF variants selectively disrupt PKA-dependent gating mechanisms and reveal and reveal distinct drug effects on catalytic versus noncatalytic activation. These mechanistic insights highlight opportunities to further optimise CFTR potentiator strategies to improve therapeutic efficacy in cystic fibrosis.