3 AMINO-ACIDS IN THE C-LINKER ARE MAJOR DETERMINANTS OF GATING IN CYCLIC NUCLEOTIDE-GATED CHANNELS

The activation of cyclic nucleotide-gated (CNG) channels is a complex process comprising the initial ligand binding and a consecutive allost eric transition from a closed to an open configuration, The cone and o lfactory CNG channels differ considerably in cyclic nucleotide affinit y and efficacy. In each channel, the cyclic nucleotide-binding site is connected to the last transmembrane segment of the channel by a linke r peptide (C-linker) of similar to 90 amino acids. Here we report that replacement of three amino acids in the cone C-linker by the correspo nding amino acids of the olfactory channel (I439V, D481A and D494S) pr ofoundly enhanced the cAMP efficacy and increased the affinities for c AMP and cGMP. Unlike the wild-type cone channel, the mutated channel e xhibited similar single-channel kinetics for both cGMP and cAMP, expla ining the increase in cAMP efficacy. We thus conclude that the identif ied amino acids are major determinants of channel gating.