Molecule of the Month: Acetylcholinesterase
Acetylcholinesterase stops the signal between a nerve cell and a muscle cell
Acetylcholinesterase in Action
Doctors are now willfully poisoning acetylcholinesterase in an attempt to reverse the symptoms of Alzheimer's disease. People with Alzheimer's disease lose many nerve cells as the disease progresses. By taking a drug that partially blocks acetylcholinesterase, the levels of the neurotransmitter can be raised, strengthening the nerve signals that remain. One drug being used in the way is shown at the bottom, from PDB entry 1eve . It inserts into the active site pocket and temporarily blocks entry of acetylcholine. Other poisons, as shown next, take a more permanent approach.
Exploring the Structure
Acetylcholinesterase with Acetylcholine and Sarin
The nerve toxin sarin and insecticides such as malathion directly attack the active site machinery of acetylcholinesterase. The upper structure, PDB entry 2ace, captures the enzyme in the middle of its cleavage reaction. A serine amino acid, assisted by nearby histidine and glutamate amino acids, forms a bond to the acetyl group of acetylcholine, breaking the molecule. The bond between serine and acetylcholine is then quickly broken by a water molecule, freeing up the enzyme to degrade another molecule.
PDB entry 1cfj (bottom) shows the aftermath of the interaction between acetylcholinesterase and sarin, an organophosphate neurotoxin. Sarin forms a covalent bond to the active site serine and attaches a methylphosphonate group (MeP, yellow) to it. This phosphonate is very stable and will disable the enzyme for hours or days, causing acetylcholine to accumulate and damage neuromuscular function.
Select the JSmol tab to explore these structures in an interactive view. This JSmol was designed and illustrated by Xinyi Christine Zhang.
Related PDB-101 Resources
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- P. Taylor (1991) The Cholinesterases. Journal of Biological Chemistry 266, 4025-4028.
- P. Taylor and Z. Radic (1994) The Cholinesterases: From genes to Proteins. Annual Review of Pharmacology and Toxicology 34, 281-320.
- K. L. Davis (2002) Current and Experimental Therapeutics of Alzheimer Disease. In Neuropsychopharmacology, K.L. Davis, D. Charney, J.T. Coyle, C. Nemeroff editors. Lippincott, Williams and Wilkins, publishers.
- J. L. Sussman, M. Harel, F. Frolow, C. Oefner, A. Goldman, L. Toker and I. Silman (1991) Atomic structure of acetylcholinesterase from Torpedo californica: a prototypic acetylcholine-binding protein. Science 253, 872-879.
June 2004, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2004_6