Proteins that bind cyclic nucleotides (cAMP or cGMP) share a structural domain of about 120 residues [ PUBMED:14638413 PUBMED:10550204 PUBMED:1710853 ]. The best studied … expand

Proteins that bind cyclic nucleotides (cAMP or cGMP) share a structural domain of about 120 residues [ PUBMED:14638413 PUBMED:10550204 PUBMED:1710853 ]. The best studied of these proteins is the prokaryotic catabolite gene activator (alsoknown as the cAMP receptor protein) (gene crp) where such a domain is known to be composed of three α-helices and a distinctive eight-stranded, antiparallel β-barrel structure. There are six invariant amino acids in this domain, three of which are glycine residues that are thought to be essential for maintenance of the structural integrity of the β-barrel. cAMP- and cGMP-dependent protein kinases (cAPK and cGPK) contain two tandem copies of the cyclic nucleotide-binding domain. The cAPK's are composed of two different subunits, a catalytic chain and a regulatory chain, which contains both copies of the domain. The cGPK's are single chain enzymes that include the two copies of the domain in their N-terminal section. Vertebrate cyclic nucleotide-gated ion-channels also contain this domain. Two such cations channels have been fully characterised, one is found in rod cells where it plays a role in visual signal transduction.