Inactive-state preassembly of G(q)-coupled receptors and G(q) heterotrimers

Nat Chem Biol. 2011 Aug 28;7(10):740-7. doi: 10.1038/nchembio.642.


G protein-coupled receptors (GPCRs) transmit signals by forming active-state complexes with heterotrimeric G proteins. It has been suggested that some GPCRs also assemble with G proteins before ligand-induced activation and that inactive-state preassembly facilitates rapid and specific G protein activation. However, no mechanism of preassembly has been described, and no functional consequences of preassembly have been demonstrated. Here we show that M(3) muscarinic acetylcholine receptors (M3R) form inactive-state complexes with G(q) heterotrimers in intact cells. The M3R C terminus is sufficient, and a six-amino-acid polybasic sequence distal to helix 8 ((565)KKKRRK(570)) is necessary for preassembly with G(q). Replacing this sequence with six alanine residues prevents preassembly, slows the rate of G(q) activation and decreases steady-state agonist sensitivity. That other G(q)-coupled receptors possess similar polybasic regions and also preassemble with G(q) suggests that these GPCRs may use a common preassembly mechanism to facilitate activation of G(q) heterotrimers.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Sequence
  • Cells, Cultured
  • GTP-Binding Protein alpha Subunits, Gq-G11 / chemistry*
  • GTP-Binding Protein alpha Subunits, Gq-G11 / metabolism*
  • HEK293 Cells
  • Humans
  • Molecular Sequence Data
  • Protein Binding
  • Protein Structure, Quaternary
  • Receptor, Muscarinic M3 / chemistry*
  • Receptor, Muscarinic M3 / metabolism*
  • Signal Transduction
  • Time Factors


  • Receptor, Muscarinic M3
  • GTP-Binding Protein alpha Subunits, Gq-G11