title: An antibody directed against the carboxyl-terminal decapeptide of the alpha subunit of the retinal GTP-binding protein, transducin. Effects on transducin function.
abstract: An antibody (AS/7) prepared against the carboxyl-terminal decapeptide of the alpha subunit of transducin (alpha T) has been used in various reconstitution studies aimed at characterizing the role of the carboxyl-terminal domain in the different functional activities of transducin. The peptide-specific antibody is a potent inhibitor of the rhodopsin-stimulated GTPase activity in phospholipid vesicle systems containing pure rhodopsin and pure holo-transducin, or rhodopsin and the purified alpha T and beta/gamma (beta gamma T) subunit components, with the highest levels of inhibition (80-95%) occurring under conditions where the molar ratio of holo-transducin (or alpha T) to AS/7 approximately equal to 1. The inhibition of the receptor-stimulated GTPase does not represent an interference in the interactions between the alpha T subunit and the beta gamma T complex, since essentially identical levels of inhibition are observed when AS/7 is preincubated with either free alpha T, holo-transducin, or alpha T in the presence of excess beta gamma T, prior to assay. The AS/7-induced inhibition also does not appear to reflect an alteration in the ability of alpha T to bind or hydrolyze GTP and, in fact, the incubation of alpha T with AS/7 results in a stimulation of the intrinsic GTPase activity for alpha T alone (i.e. in the absence of rhodopsin). Thus, we conclude that the inhibition of the rhodopsin-stimulated GTPase activity by AS/7 is due to the direct blocking (by the antibody) of rhodopsin-alpha T interactions. While AS/7 is capable of uncoupling rhodopsin-transducin interactions, it appears to promote the stimulation of the cyclic GMP phosphodiesterase (PDE) by an activated alpha T subunit. Specifically, when the pure alpha T-guanosine 5-O-(3-thiotriphosphate) (alpha TGTP gamma S) species is preincubated with AS/7 prior to its addition to an assay solution containing PDE, there is at least a 4-fold increase in the resultant cyclic GMP hydrolysis relative to the activities measured with alpha TGTP gamma S, alone, or with alpha TGTP gamma S preincubated with nonimmune (control) rabbit IgG. The AS/7-induced promotion is specific for the active form of alpha T; the inactive alpha TGDP species does not stimulate PDE activity either in the presence or absence of the antibody. The different effects by AS/7 on the various activities of the alpha T subunit highlight the existence of distinct functional domains on alpha T.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Pharmacology, New York State College of Veterinary Medicine, Cornell University, Ithaca 14853-6401.
authors.forename: R A
authors.initials: RA
authors.lastname: Cerione
authors.forename: S
authors.initials: S
authors.lastname: Kroll
authors.forename: R
authors.initials: R
authors.lastname: Rajaram
authors.forename: C
authors.initials: C
authors.lastname: Unson
authors.forename: P
authors.initials: P
authors.lastname: Goldsmith
authors.forename: A M
authors.initials: AM
authors.lastname: Spiegel
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D000906:Antibodies; D002417:Cattle; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000378:metabolism; D013873:Thionucleotides / Q000378:metabolism; D015293:Transducin
chemical_list: D000906:Antibodies; D046911:Macromolecular Substances; D008565:Membrane Proteins; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D012243:Rhodopsin; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D015293:Transducin