CAPcAMP

CAP-cAMP refers to the complex formed when cyclic adenosine monophosphate (cAMP) binds to the catabolite activator protein (CAP), also known as the cAMP receptor protein (CRP). CAP is a homodimeric transcriptional regulator found in many bacteria, most notably Escherichia coli. Each CAP subunit has a cAMP-binding domain and a DNA-binding domain; binding of one cAMP molecule per subunit induces a conformational change that enables high-affinity DNA binding.

Functionally, the CAP–cAMP complex recognizes and binds to a specific DNA motif called the CAP binding site, located upstream of certain promoters such as those of the lac, gal, and ara operons. Upon binding, CAP–cAMP interacts with RNA polymerase—principally through contacts with the RNA polymerase alpha subunit—to promote transcription initiation. Thus CAP–cAMP acts as a transcriptional activator for genes involved in the metabolism of non-glucose carbon sources.

Regulation of CAP–cAMP levels is tightly linked to cellular energy status and carbon source availability. Intracellular cAMP concentration rises when preferred carbon sources like glucose are scarce, activating CAP–cAMP and promoting transcription of catabolic operons. Conversely, high glucose availability suppresses adenylate cyclase activity, lowering cAMP and inactivating CAP–cAMP.

Biologically, CAP–cAMP is central to carbon catabolite repression in many bacteria, coordinating the utilization of available nutrients. Similar CRP–cAMP regulatory systems exist in other species and participate in broader transcriptional control, responding to environmental and metabolic cues.