Catalyzes the formation of the signaling molecule cAMP in response to G-protein coupled receptor signaling (PubMed:10603085, PubMed:23929551). Probably downstream of gustatory receptors, involved in taste perception of sucrose, trehalose and caffeine (PubMed:19046378). Has no role in bitter perception (PubMed:19046378). In the circadian brain neuron evening cells (E-cells), involved in circadian pacemaker synchronization by playing a role in signaling downstream of the G protein-coupled receptor Pdfr, probably in conjunction with other, as yet unidentified, adenylate cyclases (PubMed:23929551). Does not have adenylyl cyclase activity and it is not involved in taste perception. ATP = 3',5'-cyclic AMP + diphosphate Binds 2 magnesium ions per subunit. Is also active with manganese (in vitro). Expressed in labella, particularly in sugar-sensitive gustatory receptor neurons (GRNs). Isoform B: Ubiquitously expressed in embryos, larvae and adult (PubMed:10603085). Isoform C: Temporally restricted to the earliest hours of embryogenesis before cellularization (PubMed:10603085). As germ band extension commences, expression decreases along the entire ventral surface of the embryo and is restricted to the cephalic furrow (CF) and anterior and posterior dorsal transverse folds (DTFs) (PubMed:10603085). By state 7, restricted expression in the CF and DTFs on the dorsal and lateral surfaces of the embryo (PubMed:10603085). The protein contains two modules with six transmembrane helices each; both are required for catalytic activity. Isolated N-terminal or C-terminal guanylate cyclase domains have no catalytic activity, but when they are brought together, enzyme activity is restored. The active site is at the interface of the two domains. Both contribute substrate-binding residues, but the catalytic metal ions are bound exclusively via the N-terminal guanylate cyclase domain. RNAi-mediated knockdown in sugar gustatory neurons results in reduced sucrose response and no alteration in response to water (PubMed:19046378). RNAi-mediated knockdown in the pacemaker dorsal lateral neurons (LNDs) results in reduced Pigment-dispersing factor (Pdf) response in the circadian brain neurons evening cells (E-cells) (PubMed:23929551). Isoform B: Results in reduced sucrose and trehalose substances response and no alteration of water response or bitter perception (PubMed:19046378). Catalytically inactive. Belongs to the adenylyl cyclase class-4/guanylyl cyclase family.