A functional chimera of mammalian guanylyl and adenylyl cyclases

Adenylyl and guanylyl cyclases synthesize second messenger molecules by int ramolecular esterification of purine nucleotides, i.e., cAMP from ATP and c GMP from CTP, respectively. Despite their sequence homology, both families of mammalian cyclases show remarkably different regulatory patterns. In an attempt to define the functional domains in adenylyl cyclase responsible fo r their isotypic-common activation by G alpha(s) or forskolin, dimeric chim eras were constructed from soluble guanylyl cyclase alpha(1) subunit and th e C-terminal halves of adenylyl cyclases type I, II, or V. The cyclase-hybr id generated cAMP and was inhibited by P-site ligands. The data establish s tructural equivalence and the ability of functional complement at the catal ytic sites in both cyclases. Detailed enzymatic characterization of the chi meric cyclase revealed a crucial role of the N-terminal adenylyl cyclase ha lf for stimulatory actions, and a major importance of the C-terminal part f or nucleotide specificity.