Evidence for a single heptahelical domain being turned on upon activation of a dimeric GPCR

EMBO J. 2005 Feb 9;24(3):499-509. doi: 10.1038/sj.emboj.7600557. Epub 2005 Jan 20.


G-protein-coupled receptors (GPCRs) have been shown to form dimers, but the relevance of this phenomenon in G-protein activation is not known. Among the large GPCR family, metabotropic glutamate (mGlu) receptors are constitutive dimers. Here we examined whether both heptahelical domains (HDs) are turned on upon full receptor activation. To that aim, we measured G-protein coupling efficacy of dimeric mGlu receptors in which one subunit bears specific mutations. We show that a mutation in the third intracellular loop (i3 loop) known to prevent G-protein activation in a single subunit decreases coupling efficacy. However, when a single HD is blocked in its inactive state using an inverse agonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP), no decrease in receptor activity is observed. Interestingly, in a receptor dimer in which the subunit that binds MPEP is mutated in its i3 loop, MPEP enhances agonist-induced activity, reflecting a 'better' activation of the adjacent HD. These data are consistent with a model in which a single HD is turned on upon activation of such homodimeric receptors and raise important issues in deciphering the functional role of GPCR dimer formation for G-protein activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • Dimerization
  • Excitatory Amino Acid Antagonists / pharmacology
  • Humans
  • In Vitro Techniques
  • Kinetics
  • Models, Biological
  • Mutagenesis, Site-Directed
  • Protein Structure, Tertiary
  • Protein Subunits
  • Pyridines / pharmacology
  • Receptors, Metabotropic Glutamate / antagonists & inhibitors
  • Receptors, Metabotropic Glutamate / chemistry*
  • Receptors, Metabotropic Glutamate / genetics
  • Receptors, Metabotropic Glutamate / metabolism*
  • Recombinant Fusion Proteins / antagonists & inhibitors
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Recombinant Proteins / antagonists & inhibitors
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Transfection


  • Excitatory Amino Acid Antagonists
  • Protein Subunits
  • Pyridines
  • Receptors, Metabotropic Glutamate
  • Recombinant Fusion Proteins
  • Recombinant Proteins
  • metabotropic glutamate receptor type 1
  • 6-methyl-2-(phenylethynyl)pyridine