A potential binding site for a regulatory control element. A) Structure of the mammalian adenylate cyclase catalytic domain bound to the activator Gsα (PDB ID 1CJU) . The switch II helix of Gsα binds in a groove on the C2 domain between the α1–α2 and α3-β4a loops, priming the catalytic domain for nucleotide binding. A surface representation of the adenylate cyclase catalytic domain is shown, and Gsα is shown as a ribbon cartoon. The C1 domain is colored blue, the C2 domain is colored orange, and Gsα is colored teal. B) Surface representation of the guanylate cyclase catalytic domain in the same orientation as the adenylate cyclase domain in A. A groove similar to that used by adenylate cyclase to bind to Gsα is located between the α1–α2 and α3-β4a loops, and may serve as a site for interaction of control elements with the guanylate cyclase catalytic domain. Monomer A is colored teal, and monomer B is colored green.