DISTINCT INHIBITORY ATP-REGULATED MODULATORY DOMAIN (ARM(I)) IN MEMBRANE GUANYLATE CYCLASES

Depending upon the cofactors Mg2+ Or Mn2+, ATP stimulates or inhibits the signal transduction activities of the natriuretic factor receptor guanylate cyclases, ANF-RGC and CNP-RGC: there is stimulation in the p resence of Mg2+ and inhibition in the presence of Mn2+. A defined core ATP-regulated modulatory (ARM) sequence motif within the intracellula r 'kinase-like' domain of the cyclases is critical for stimulation, bu t the mechanism of the inhibitory transduction process is not known. I n addition, ATP inhibits the basal cyclase activity of a rod outer seg ment membrane guanylate cyclase (ROS-GC). The mechanism of this inhibi tory transduction process is also not known. These issues have been ad dressed in the present investigation through a program of deletion mut agenesis/expression studies of the cyclases. The study shows that the ATP-mediated inhibitory transduction processes of the natriuretic fact or receptor cyclases and of ROS-GC are identical. The ATP-regulated in hibitory domain of all these cyclases resides within the C-terminal se gment of the cyclase. This domain is in a different location from the one representing the ATP-stimulatory ARM. The identification of the in hibitory domain in the C-terminal segment of the cyclase indicates tha t this segment is composed of two separate domains: one representing a catalytic cyclase domain and the other an ATP-regulated inhibitory (A RM,) domain. These findings establish a novel ATE-mediated inhibitory transduction mechanism of the membrane guanylate cyclases which is dis tinct from that of its counterpart, the stimulatory ATP-mediated hormo nal signal transduction mechanism. Thus, they define a new paradigm of guanylate cyclase-linked signal transduction pathways.