Curr Biol 1995 Oct 01;510:1159-67. doi: 10.1016/s0960-9822(95)00232-6.

Identification and partial characterization of a domain in CFTR that may bind cyclic nucleotides directly.

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BACKGROUND: The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is activated by cAMP-dependent phosphorylation. CFTR channel activity is also stimulated by cGMP-dependent protein kinase and protein kinase C. RESULTS: Here, we show that CFTR channel activation by cGMP may also occur directly. In oocytes from one-third of Xenopus donors, the activation of CFTR by cGMP averaged 87% of the level achieved by cAMP. The currents activated by either cyclic nucleotide displayed similar current-voltage relationships, kinetics, pharmacology and halide selectivity. Sequential stimulation by cAMP and cGMP was not additive, suggesting that both cyclic nucleotides activate the same channel; cGMP was one order of magnitude more potent than cAMP, and its action was insensitive to protein kinase inhibitors. Analysis of the amino-acid sequence of CFTR revealed a domain in the amino-terminal portion of the third cytoplasmic loop that resembles a class of cyclic-nucleotide-binding domains related to that of the catabolite-gene activator protein, CAP. Two CFTR residues in this domain--Val397 and Lys420--were identified which, when changed to alanine, altered the response to cGMP independently of the response to cAMP. CONCLUSIONS: We conclude that direct cyclic nucleotide binding may play a role in channel gating of CFTR. The cGMP-binding domain may provide a useful target for pharmacologic intervention in cystic fibrosis.

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Species referenced: Xenopus laevis
Genes referenced: camp cftr