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 bindi ng of guanosine 3',5'-cyclic monophosphate (cGMP) or adenosine 3',5'-c yclic monophosphate. Since the first report of a cGMP-gated channel in vertebrate photoreceptors [1], the purification of the channel polype ptide [2] and the molecular cloning of the corresponding cDNA [3] a co nstantly increasing number of related channels have been discovered. F unctionally they belong to the class of ligand-gated channels, because they are directly opened by the binding of a ligand (cyclic nucleotid e) to a receptor site. However, the primary structure of CNG channels shows little if any sequence similarity with that of other ligand-gate d channels. Instead they share some sequence motifs with members of th e family of voltage-gated ion channels. This review examines some stru ctural features of CNG channels and their physiologic implications.