Subchapter 20C - Caerulein

Abstract

Caerulein was first purified and identified in the Australian frog Hyla caerulea in 1967, and has since been detected in several frog species. This protein is a decapeptide that contains the C-terminal four amino-acid sequence (Gly–Trp–Met–Asp–Phe–NH2) that is conserved in vertebrate gastrin and CCK. In addition, caerulein possesses a sulfated tyrosine located seven residues from the C terminus. These similarities suggest that caerulein is an orthologous peptide of vertebrate gastrin and CCK. Synthesis of the caerulein peptide occurs in the skin of frogs. Caerulein is processed from preprocaerulein, which also contains an antimicrobial peptide called the caerulein precursor fragment. Caerulein activates endogenous gastrin and CCK signaling in vertebrates through CCK1R and CCK2R, suggesting that the preprocaerulein gene functions as a defensive peptide against microbes and predators.