Functional exchange of components between light-activated photoreceptor phosphodiesterase and hormone-activated adenylate cyclase systems.

Abstract

Previous studies have noted profound similarities between the regulation of light-activated 3'',5''-cyclic nucleotide phosphodiesterase (3'',5''-cyclic-nucleotide 5''-nucleotidohydrolase, EC 3.1.4.17) in retinal rods and hormone-activated adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in a variety of tissues. The functional exchange of components isolated from the photoreceptor system, which displayed predicted functional characteristics when incubated with recipient adenylate cyclase systems from rat cerebral cortical and hypothalamic synaptic membranes and frog erythrocye ghosts is reported. Functional exchange of photoreceptor components at each of 3 loci: the hormone receptor, the GTP-binding (GBP), and the catalytic moiety of adenylate cyclase is demonstrated. Illuminated (but not unilluminated) rhodopsin mimicked the hormone-receptor complex, causing GTP-dependent activation of adenylate cyclase. The photoreceptor GBP complexed with guanosine 5''-[.beta.,.gamma.]imidotriphosphate (p[NH]ppG) produced a marked activation of recipient adenylate cyclase systems. Much smaller activation was observed when GBP was not complexed with p[NH]ppG. A heat-stable photoreceptor phosphodiesterase inhibitor reduced both basal and Mn2+-activated adenylate cyclase activities and this inhibition was reversed by photoreceptor GBP.cntdot.p[NH]ppG. These data demonstrate a remarkable functional compatibility between subunits of both systems and furthermore imply that specialized peptide domains responsible for protein-protein interactions are highly conserved.