cAMP (cyclic adenosine 3′,5′-monophosphate) is a small nucleotide-based second messenger produced from ATP by adenylyl cyclase in response to activation of Gs-coupled receptors. Gi-coupled receptors inhibit adenylyl cyclase and therefore lower cAMP.
cAMP acts primarily by binding the regulatory subunits of protein kinase A (PKA), releasing its catalytic subunits and allowing phosphorylation of downstream substrates. It also activates Epac guanine-nucleotide exchange factors and cyclic nucleotide-gated ion channels. Intracellular cAMP is degraded by phosphodiesterases, allowing the signal to be tightly time- and space-limited.
Intracellular cAMP is the standard functional readout for Gs-coupled receptors including GLP-1R, GIPR, GCGR and melanocortin receptors — the receptor families underlying most peptides in this catalogue.