title: G protein antagonists. A novel hydrophobic peptide competes with receptor for G protein binding.
abstract: A substance P (SP) analog, [D-Pro4,D-Trp7,9,10] SP4-11, is known to inhibit the actions of various structurally unrelated messenger molecules as well as SP. Our studies on the effects of this peptide on the regulation of purified G proteins by receptor showed that at least some of the biological effects of the peptide can be explained by the ability of the peptide to block the activation of G proteins by receptors. Here we report that a novel truncated SP-related peptide, pGlu-Gln-D-Trp-Phe-D-Trp-D-Trp-Met-NH2, inhibited the activation of G(i) or G(o) by M2 muscarinic cholinergic receptor (M2 mAChR) or of Gs by beta-adrenergic receptor in the reconstituted phospholipid vesicles, assayed by receptor-promoted GTP hydrolysis. The inhibition by the peptide was apparently reversible and competitive with respect to receptor binding to G proteins; the inhibition could be overcome by increasing the concentration of receptor in the vesicles and was not altered by changes in the concentration of G protein. The competing effects of the peptide were used to analyze the effect of agonist on receptor-G protein interaction. The concentration change of muscarinic agonist did not alter the inhibitory effects of the peptide on M2 mAChR-promoted GTPase by G(o), which is consistent with the idea that agonist increases the regulatory efficiency of the receptor but does not alter its affinity for G proteins. This new group of compounds (G protein antagonists) is a promising tool to study receptor-G protein interaction quantitatively.
authors.affiliation: Department of Pharmacology, University of Texas, Southwestern Medical Center, Dallas 75235-9041.
authors.forename: H
authors.initials: H
authors.lastname: Mukai
authors.forename: E
authors.initials: E
authors.lastname: Munekata
authors.forename: T
authors.initials: T
authors.lastname: Higashijima
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007313:Insecta; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology; D010446:Peptide Fragments; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013373:Substance P / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014162:Transfection; D014422:Turkeys
chemical_list: D046911:Macromolecular Substances; D009842:Oligopeptides; D010446:Peptide Fragments; D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; D013373:Substance P; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C040436:substance P (4-11), Pro(4)-Trp(7,9,10)-; D006160:Guanosine Triphosphate; D002217:Carbachol; D019204:GTP-Binding Proteins