title: Identification of Gbetagamma binding sites in the third intracellular loop of the M(3)-muscarinic receptor and their role in receptor regulation.
abstract: Gbetagamma binds directly to the third intracellular (i3) loop subdomain of the M(3)-muscarinic receptor (MR). In this report, we identified the Gbetagamma binding motif and G-protein-coupled receptor kinase (GRK2) phosphorylation sites in the M(3)-MR i3 loop via a strategy of deletional and site-directed mutagenesis. The Gbetagamma binding domain was localized to Cys(289)-His(330) within the M(3)-MR-Arg(252)-Gln(490) i3 loop, and the binding properties (affinity, influence of ionic strength) of the M(3)-MR-Cys(289)-His(330) i3 loop subdomain were similar to those observed for the entire i3 loop. Site-directed mutagenesis of the M(3)-MR-Cys(289)-His(330) i3 loop subdomain indicated that Phe(312), Phe(314), and a negatively charged region (Glu(324)-Asp(329)) were required for interaction with Gbetagamma. Generation of the full-length M(3)-MR-Arg(252)-Gln(490) i3 peptides containing the F312A mutation were also deficient in Gbetagamma binding and exhibited a reduced capacity for phosphorylation by GRK2. A similar, parallel strategy resulted in identification of major residues ((331)SSS(333) and (348)SASS(351)) phosphorylated by GRK2, which were just downstream of the Gbetagamma binding motif. Full-length M(3)-MR constructs lacking the 42-amino acid Gbetagamma binding domain (Cys(289)-His(330)) or containing the F312A mutation exhibited ligand recognition properties similar to wild type receptor and also effectively mediated agonist-induced increases in intracellular calcium following receptor expression in Chinese hamster ovary and/or COS 7 cells. However, the M(3)-MRDeltaCys(289)-His(330) and M(3)-MR(F312A) constructs were deficient in agonist-induced sequestration, indicating a key role for the Gbetagamma-M(3)-MR i3 loop interaction in receptor regulation and signal processing.
authors.affiliation: Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: G
authors.initials: G
authors.lastname: Wu
authors.forename: G S
authors.initials: GS
authors.lastname: Bogatkevich
authors.forename: Y V
authors.initials: YV
authors.lastname: Mukhin
authors.forename: J L
authors.initials: JL
authors.lastname: Benovic
authors.forename: J D
authors.initials: JD
authors.lastname: Hildebrandt
authors.forename: S M
authors.initials: SM
authors.lastname: Lanier
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001692:Biological Transport; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D051552:beta-Adrenergic Receptor Kinases
chemical_list: C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D010446:Peptide Fragments; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D012694:Serine; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins; D020962:Heterotrimeric GTP-Binding Proteins