Interaction of the two cytosolic domains of mammalian adenylyl cyclase

Adenylyl cyclase activity can be reconstituted by simple mixture of the two cytosolic domains of the enzyme after their independent synthesis in Escherichia coli, We have synthesized and purified the C-1a domain of type I adenylyl cyclase and the C-2 domain of the type II enzyme to assess their interactions with each other and with the activators G(s alpha) and forskolin, In the absence of an activator, the fragments associate with low affinity and display low catalytic activity, This basal activity can be stimulated more than 100-fold by either forskolin or activated G(s alpha). Further, the addition of these activators increases the apparent affinity of the fragments for each other, Stimulation of catalysis by G(s alpha) and forskolin is synergistic. These data suggest a model wherein either G(s alpha) or forskolin enhances association of the other activator with adenylyl cyclase, as well as facilitating the interaction between the C-1 and C-2 domains of the enzyme.