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effector domain of the CAP family of transcription factors; members include CAP (or cAMP receptor protein (CRP)), which binds cAMP, FNR (fumarate and nitrate reduction), which uses an iron-sulfur cluster to sense oxygen) and CooA, a heme containing CO sensor. In all cases binding of the effector leads to conformational changes and the ability to activate transcription. Cyclic nucleotide-binding domain similar to CAP are also present in cAMP- and cGMP-dependent protein kinases (cAPK and cGPK) and vertebrate cyclic nucleotide-gated ion-channels. Cyclic nucleotide-monophosphate binding domain; proteins that bind cyclic nucleotides (cAMP or cGMP) share a structural domain of about 120 residues; the best studied is the prokaryotic catabolite gene activator, CAP, where such a domain is known to be composed of three alpha-helices and a distinctive eight-stranded, antiparallel beta-barrel structure; three conserved glycine residues are thought to be essential for maintenance of the structural integrity of the beta-barrel; CooA is a homodimeric transcription factor that belongs to CAP family; cAMP- and cGMP-dependent protein kinases (cAPK and cGPK) contain two tandem copies of the cyclic nucleotide-binding domain; cAPK's are composed of two different subunits, a catalytic chain and a regulatory chain, which contains both copies of the domain; cGPK's are single chain enzymes that include the two copies of the domain in their N-terminal section; also found in vertebrate cyclic nucleotide-gated ion-channels
Jiyao W et al.(2023). "The conserved domain database in 2023.",