CyclaseC

CyclaseC is a protein designation used in genome and proteome annotations to refer to a cyclase enzyme subfamily labeled with the letter C. The term is not tied to a single universally defined protein, and its exact identity varies by organism and database. In general, cyclaseC proteins are predicted members of the cyclic nucleotide cyclase family, enzymes that synthesize cyclic nucleotides from nucleoside triphosphates. Depending on the member, the catalytic reaction may produce cyclic adenosine monophosphate (cAMP) from ATP or cyclic guanosine monophosphate (cGMP) from GTP; some sequences remain of uncertain substrate specificity.

Most cyclaseC proteins contain a catalytic cyclase domain with conserved motifs necessary for metal-dependent catalysis, and many are associated with regulatory regions or membrane anchors that influence signaling. Localization ranges from soluble cytosolic forms to multi-pass membrane proteins, reflecting diverse regulatory strategies across organisms.

Regulation of cyclaseC activity is context dependent. It can be controlled by divalent cations such as Mg2+ or Mn2+, allosteric regulators, dimerization state, and interacting proteins. In certain lineages, calcium/calmodulin or G-protein subunits modulate activity, linking cyclic nucleotide production to broader signaling networks.

Biological roles attributed to cyclaseC-like enzymes center on the generation of secondary messengers that influence metabolism, ion transport, gene expression, development, and sensory responses. Distribution is broad in genome annotations, with predictions reported in bacteria, archaea, and eukaryotes; however, experimental validation varies.

Further study through activity assays, mutagenesis, and structural biology continues to clarify substrate specificities, regulatory mechanisms, and physiological functions of cyclaseC proteins.