title: Activation of a GTP-binding protein and a GTP-binding-protein-coupled receptor kinase (beta-adrenergic-receptor kinase-1) by a muscarinic receptor m2 mutant lacking phosphorylation sites.
abstract: A mutant of the human muscarinic acetylcholine receptor m2 subtype (m2 receptor), lacking a large part of the third intracellular loop, was expressed and purified using the baculovirus/insect cell culture system. The mutant was not phosphorylated by beta-adrenergic-receptor kinase, as expected from the previous assignment of phosphorylation sites to the central part of the third intracellular loop. However, the m2 receptor mutant was capable of stimulating beta-adrenergic-receptor-kinase-1-mediated phosphorylation of a glutathione S-transferase fusion protein containing the m2 phosphorylation sites in an agonist-dependent manner. Both mutant and wild-type m2 receptors reconstituted with the guanine-nucleotide-binding regulatory proteins (G protein), G(o) and G(i)2, displayed guanine-nucleotide-sensitive high-affinity agonist binding, as assessed by displacement of [3H]quinuclidinyl-benzilate binding with carbamoylcholine, and both stimulated guanosine 5'-3-O-[35S]thiotriphosphate ([35S]GTP[S]) binding in the presence of carbamoylcholine and GDP. The Ki values of carbamoylcholine effects on [3H]quinuclidinyl-benzilate binding were indistinguishable for the mutant and wild-type m2 receptors. Moreover, the phosphorylation of the wild-type m2 receptor by beta-adrenergic-receptor kinase-1 did not affect m2 interaction with G proteins as assessed by the binding of [3H]quinuclidinyl benzilate or [35S]GTP[S]. These results indicate that (a) the m2 receptor serves both as an activator and as a substrate of beta-adrenergic-receptor kinase, and (b) a large part of the third intracellular loop of the m2 receptor does not contribute to interaction with G proteins and its phosphorylation by beta-adrenergic-receptor kinase does not uncouple the receptor and G proteins in reconstituted lipid vesicles.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, University of Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kameyama
authors.forename: K
authors.initials: K
authors.lastname: Haga
authors.forename: T
authors.initials: T
authors.lastname: Haga
authors.forename: O
authors.initials: O
authors.lastname: Moro
authors.forename: W
authors.initials: W
authors.lastname: Sadée
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D001665:Binding Sites; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D018411:Spodoptera / Q000378:metabolism; D013329:Structure-Activity Relationship; D013552:Swine; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D011976:Receptors, Muscarinic; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D011813:Quinuclidinyl Benzilate; D002217:Carbachol; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins