Functional homology between signal-coupling proteins. Cholera toxin inactivates the GTPase activity of transducin

• Published in: The Journal of biological chemistry 1982-09, Vol.257 (18), p.10540-10543
• Main Authors: Abood, M E, Hurley, J B, Pappone, M C, Bourne, H R, Stryer, L
• Format: Article
• Language: English
• Subjects: Adenosine Diphosphate Ribose - metabolism; Animals; Cell Membrane - enzymology; Cholera Toxin - pharmacology; GTP Phosphohydrolases - antagonists & inhibitors; Guanylyl Imidodiphosphate - pharmacology; Kinetics; Light; Membrane Proteins - antagonists & inhibitors; NAD - metabolism; Phosphoric Monoester Hydrolases - antagonists & inhibitors; Photoreceptor Cells - enzymology; Rod Cell Outer Segment - enzymology; Transducin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)33851-1

Both the light-stimulated cGMP phosphodiesterase of retinal rod outer segments (ROS) and hormone-stimulated adenylate cyclase are regulated by guanine nucleotide-binding regulatory proteins (N). Transducin serves as the signal-carrying regulatory protein in ROS, and the N protein (also called G or G/F) performs this role in the adenylate cyclase system. The GTP form of these regulatory proteins activates the corresponding enzyme, whereas the GDP form does not. Both transducin and the N protein possess a GTPase activity that restores the regulatory protein to the unstimulated state. Cholera enterotoxin catalyzes the transfer of ADP-ribose from NAD+ to the N protein, which inhibits its GTPase activity and activates adenylate cyclase. We report here that the toxin also catalyzes ADP-ribosylation of the alpha-subunit of transducin in ROS membranes. This modification of the guanine nucleotide-binding subunit of transducin is markedly enhanced by the bleaching of rhodopsin and by the addition of guanosine-5'-(beta, gamma-imino)triphosphate. In contrast, GDP, GTP, and guanosine-5'-(3-O)thiotriphosphate inhibit the reaction, while GMP and ATP have no effect. Under optimal conditions, toxin catalyzes labeling of 0.7 mol of the alpha-subunit of transducin/mol of bound [3H]guanosine-5'-(beta, gamma-imido)triphosphate and causes 70% inhibition of the light-dependent GTPase activity of transducin in ROS. These results indicate close functional homology between transducin of ROS and the N protein of adenylate cyclase.