Mapping of single amino acid residues required for selective activation of Gq/11 by the m3 muscarinic acetylcholine receptor

J Biol Chem. 1995 Jul 28;270(30):17741-8. doi: 10.1074/jbc.270.30.17741.

Abstract

Each G protein-coupled receptor can interact only with a limited number of the many structurally similar G proteins expressed within a cell. This study was undertaken to identify single amino acids required for selectively coupling the m3 muscarinic acetylcholine receptor to G proteins of the Gq/11 family. To this goal, distinct intracellular segments/amino acids of the m3 receptor were systematically substituted into the structurally closely related m2 muscarinic receptor, which couples to Gi/o proteins, not Gq/11 proteins. The resultant mutant receptors were expressed in COS-7 cells and studied for their ability to induce agonist-dependent stimulation of phosphatidylinositol hydrolysis, a response known to be mediated by G proteins of the Gq/11 class. Using this approach, we were able to identify four amino acids in the second intracellular loop and four amino acids at the C terminus of the third intracellular loop of the m3 muscarinic receptor that are essential for efficient Gq/11 activation. We could demonstrate that these amino acids, together with a short segment at the N terminus of the third intracellular loop, fully account for the G protein coupling preference of the m3 muscarinic receptor. Taken together, our data strongly suggest that only a limited number of amino acids, located on different intracellular regions, are required to determine the functional profile of a given G protein-coupled receptor.

MeSH terms

  • Amino Acid Sequence
  • Amino Acids / metabolism*
  • Animals
  • Carbachol / pharmacology
  • Cell Line
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / metabolism*
  • Humans
  • Hydrolysis
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Phosphatidylinositols / metabolism
  • Receptors, Muscarinic / metabolism*
  • Sequence Alignment

Substances

  • Amino Acids
  • Phosphatidylinositols
  • Receptors, Muscarinic
  • Carbachol
  • GTP-Binding Proteins