1. Identification of Gbetagamma binding sites in the third intracellular loop of the M(3)-muscarinic receptor and their role in receptor regulation.
- Author
-
Wu G, Bogatkevich GS, Mukhin YV, Benovic JL, Hildebrandt JD, and Lanier SM
- Subjects
- Amino Acid Sequence, Binding Sites, Biological Transport, GTP-Binding Proteins genetics, Molecular Sequence Data, Mutagenesis, Site-Directed, Peptide Fragments metabolism, Phosphorylation, Receptor, Muscarinic M3, Receptors, Muscarinic genetics, Recombinant Proteins metabolism, Serine metabolism, Signal Transduction, beta-Adrenergic Receptor Kinases, Cyclic AMP-Dependent Protein Kinases metabolism, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, GTP-Binding Proteins metabolism, Heterotrimeric GTP-Binding Proteins, Receptors, Muscarinic metabolism
- 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.
- Published
- 2000
- Full Text
- View/download PDF