STRUCTURAL FEATURES OF CYCLIC NUCLEOTIDE-GATED CHANNELS

Cyclic nucleotide-gated (CNG) cation channels represent a novel class of ion channels that are directly and cooperatively gated by the binding of guanosine 3',5'-cyclic monophosphate (cGMP) or adenosine 3',5'-cyclic monophosphate. Since the first report of a cGMP-gated channel in vertebrate photoreceptors [1], the purification of the channel polypeptide [2] and the molecular cloning of the corresponding cDNA [3] a constantly increasing number of related channels have been discovered. Functionally they belong to the class of ligand-gated channels, because they are directly opened by the binding of a ligand (cyclic nucleotide) to a receptor site. However, the primary structure of CNG channels shows little if any sequence similarity with that of other ligand-gated channels. Instead they share some sequence motifs with members of the family of voltage-gated ion channels. This review examines some structural features of CNG channels and their physiologic implications.