Adenylylcyclase

Adenylyl cyclases (ACs) are enzymes that catalyze the conversion of ATP to cyclic adenosine monophosphate (cAMP) and pyrophosphate. In many cells, cAMP acts as a key second messenger that transmits signals from hormones and neurotransmitters to intracellular targets, regulating metabolism, gene expression, ion channels, and neuronal activity. ACs are found as membrane-bound enzymes and as cytosolic forms in various organisms.

Most mammalian ACs are membrane-bound isoforms (commonly designated AC1–AC9) with multiple transmembrane segments and cytosolic catalytic domains. A soluble form, ADCY10 (soluble adenylyl cyclase or sAC), lacks transmembrane regions and is regulated by factors such as bicarbonate and calcium. The active site comprises two catalytic lobes (C1 and C2) that come together to convert ATP to cAMP. Activity is modulated by G proteins (Gs stimulates; Gi inhibits) and by activators such as forskolin.

cAMP produced by ACs activates downstream effectors including protein kinase A (PKA), exchange proteins directly activated by cAMP (Epac), and cyclic nucleotide-gated channels, thereby controlling diverse responses such as glucose metabolism, muscle contraction, memory formation, and heart rate. Phosphodiesterases degrade cAMP, providing dynamic regulation of signaling.

In bacteria, adenylyl cyclases (e.g., cyaA) generate cAMP to regulate transcription via the CRP–cAMP complex, linking nutrient sensing to gene expression. Dysregulation of AC signaling is implicated in various diseases and is a focus of pharmacological research, with agents that modulate AC activity used as research tools and potential therapies.