Conformation of ligands bound to the muscarinic acetylcholine receptor

Mol Pharmacol. 2002 Oct;62(4):778-87. doi: 10.1124/mol.62.4.778.


Many biogenic amines evoke a variety of physiological responses by acting on G protein-coupled receptors. We have determined the conformation of two acetylcholine analogs, (S)-methacholine and (2S,4R,5S)-muscarine, bound to the M(2) muscarinic acetylcholine receptor (M(2) mAChR) by NMR spectroscopy. The analysis of the transferred nuclear Overhauser effect indicated that the receptor selectively recognized the conformers of (S)-methacholine and (2S,4R,5S)-muscarine with the gauche O-C2-C1-N dihedral angle at +60 degrees. This is distinct from the predominant conformations of these ligands in solution with O-C2-C1-N dihedral angle (+80 to approximately 85 degrees ) in the absence of the M(2) mAChR, as assessed by analyses of the coupling constants and nuclear Overhauser effect spectroscopy. We have also built a molecular model of the M(2) mAChR-(S)-methacholine complex, based on the X-ray crystallographic structure of rhodopsin. This model indicated that the conformation with the gauche O-C2-C1-N dihedral angle at +55.5 degrees, which is similar to the one determined by NMR measurement, is energetically favored in the binding of (S)-methacholine to the receptor. We suggest that this conformation represents the binding of the agonist to the M(2) mAChR in the absence of G protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Cells, Cultured
  • GTP-Binding Proteins / metabolism
  • Insecta
  • Methacholine Chloride / chemistry
  • Methacholine Chloride / metabolism*
  • Models, Molecular
  • Molecular Conformation
  • Muscarine / chemistry
  • Muscarine / metabolism*
  • Muscarinic Agonists / chemistry
  • Muscarinic Agonists / metabolism*
  • Mutation
  • Receptor, Muscarinic M2
  • Receptors, Muscarinic / chemistry
  • Receptors, Muscarinic / genetics
  • Receptors, Muscarinic / metabolism*
  • Structure-Activity Relationship


  • Muscarinic Agonists
  • Receptor, Muscarinic M2
  • Receptors, Muscarinic
  • Methacholine Chloride
  • Muscarine
  • GTP-Binding Proteins