Quaternary ligand binding to aromatic residues in the active-site gorge of acetylcholinesterase

Proc Natl Acad Sci U S A. 1993 Oct 1;90(19):9031-5. doi: 10.1073/pnas.90.19.9031.


Binding sites of Torpedo acetylcholinesterase (EC for quaternary ligands were investigated by x-ray crystallography and photoaffinity labeling. Crystal structures of complexes with ligands were determined at 2.8-A resolution. In a complex with edrophonium, and quaternary nitrogen of the ligand interacts with the indole of Trp-84, and its m-hydroxyl displays bifurcated hydrogen bonding to two members of the catalytic triad, Ser-200 and His-440. In a complex with tacrine, the acridine is stacked against the indole of Trp-84. The bisquaternary ligand decamethonium is oriented along the narrow gorge leading to the active site; one quaternary group is apposed to the indole of Trp-84 and the other to that of Trp-279, near the top of the gorge. The only major conformational difference between the three complexes is in the orientation of the phenyl ring of Phe-330. In the decamethonium complex it lies parallel to the surface of the gorge; in the other two complexes it is positioned to make contact with the bound ligand. This close interaction was confirmed by photoaffinity labelling by the photosensitive probe 3H-labeled p-(N,N-dimethylamino)benzenediazonium fluoroborate, which labeled, predominantly, Phe-330 within the active site. Labeling of Trp-279 was also observed. One mole of label is incorporated per mole of AcChoEase inactivated, indicating that labeling of Trp-279 and that of Phe-330 are mutually exclusive. The structural and chemical data, together, show the important role of aromatic groups as binding sites for quaternary ligands, and they provide complementary evidence assigning Trp-84 and Phe-330 to the "anionic" subsite of the active site and Trp-279 to the "peripheral" anionic site.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acetylcholine / metabolism
  • Acetylcholinesterase / chemistry*
  • Acetylcholinesterase / metabolism
  • Affinity Labels / metabolism
  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Chromatography, High Pressure Liquid
  • Crystallography, X-Ray / methods
  • Decamethonium Compounds / metabolism
  • Edrophonium / metabolism
  • Hydrogen Bonding
  • Ligands
  • Peptide Fragments / isolation & purification
  • Protein Conformation*
  • Protein Structure, Secondary
  • Quaternary Ammonium Compounds / metabolism
  • Tacrine / metabolism
  • Torpedo


  • Affinity Labels
  • Decamethonium Compounds
  • Ligands
  • Peptide Fragments
  • Quaternary Ammonium Compounds
  • Tacrine
  • Edrophonium
  • decamethonium
  • Acetylcholinesterase
  • tetramethylammonium
  • Acetylcholine