Acetylcholinesterase
This enzyme is found in, or attached to, cellular or basement membranes of presynaptic cholinergic neurons and postsynaptic cholinoceptive cells within the neuromuscular junction. Signal transmission at the neuromuscular junction involves the release of acylcholine, its interaction with the acycholine receptor and hydrolysis, all occuring in a period of a few milliseconds. Rapid hydrolysis of the newly released aceytlcholine is vital in order to prevent continuous firing of the nerve impulses [PMID:8161450].
Reference Protein and Structure
- Sequence
-
P21836
(3.1.1.7)
(Sequence Homologues)
(PDB Homologues)
- Biological species
-
Mus musculus (house mouse)
- PDB
-
1mah
- FASCICULIN2-MOUSE ACETYLCHOLINESTERASE COMPLEX
(3.2 Å)
- Catalytic CATH Domains
-
3.40.50.1820
(see all for 1mah)
Enzyme Reaction (EC:3.1.1.7)
+
→
+
+
Alternative enzyme names: AcCholE, Acetyl.beta-methylcholinesterase, Acetylcholine hydrolase, Acetylthiocholinesterase, Choline esterase I, Cholinesterase, True cholinesterase,
Enzyme Mechanism
Introduction
Acetylcholine esterase functions via classic Ser-His-Asp/Glu triad mechanism. Acetylcholine is guided into the site via Phe290 and Phe292. Ser203 is deprotonated and activated by His447. Ser203 then performs a nucleophilic attack on the acly carbon of the substrate creating a intermediate stabilised by Gly121, Gly120 and Ala204 forming an oxyanion hole. His447 then proceeds to donate the newly gained proton to the substrate releasing choline from the substrate molecule. His447 then deprotonates a water molecule which then attacks the acyl carbon forming a new intermediate again stabilised by the oxyanion hole previously mentioned. This intermediate then collapses as His447 donates his proton to Ser203 severing the enzyme-substrate covalent bond.
Catalytic Residues Roles
| UniProt | PDB* (1mah) | ||
| Glu365 | Glu334A | Part of the catalytic Ser-His-Glu triad. It modifies the pKa of the histidine of the triad, allowing it to act as the general acid/base. | modifies pKa, electrostatic stabiliser |
| His478 | His447A | Part of the catalytic Ser-His-Glu triad. Acts as a general acid/base. Initially it activates the catalytic serine, in the latter stages of the reaction it activates the catalytic water molecule. | activator, hydrogen bond donor, proton acceptor, proton donor |
| Ser234 | Ser203A | Part of the catalytic Ser-His-Glu triad. Acts as the nucleophile, becoming covalently attached to the substrate during the course of the reaction. | covalently attached, nucleofuge, nucleophile, proton acceptor, proton donor |
| Gly152 (main-N), Gly153 (main-N), Ala235 (main-N) | Gly121A (main-N), Gly122A (main-N), Ala204A (main-N) | These residues form the oxyanion hole that stabilises the reactive intermediates and transition states formed during the course of the reaction. | electrostatic stabiliser |
| Phe326, Phe369 | Phe295A, Phe338A | These residues are responsible for maintaining the functional positioning of the catalytic histidine. | steric locator |
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file;
y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain;
C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.
Chemical Components
bimolecular nucleophilic addition, enzyme-substrate complex formation, intermediate formation, proton transfer, hydrogen transfer, unimolecular elimination by the conjugate base, intermediate collapse, overall reactant used, overall product formed, enzyme-substrate complex cleavage, native state of enzyme regeneratedReferences
- Zhou Y et al. (2010), J Phys Chem B, 114, 8817-8825. Catalytic reaction mechanism of acetylcholinesterase determined by Born-Oppenheimer ab initio QM/MM molecular dynamics simulations. DOI:10.1021/jp104258d. PMID:20550161.
- Qiao Y et al. (2013), Biochemistry, 52, 6467-6479. Fundamental reaction pathway and free energy profile for butyrylcholinesterase-catalyzed hydrolysis of heroin. DOI:10.1021/bi400709v. PMID:23992153.
- Ekström F et al. (2009), PLoS One, 4, e5957-. Structure of HI-6*sarin-acetylcholinesterase determined by X-ray crystallography and molecular dynamics simulation: reactivator mechanism and design. DOI:10.1371/journal.pone.0005957. PMID:19536291.
- Paz A et al. (2009), J Med Chem, 52, 2543-2549. The crystal structure of a complex of acetylcholinesterase with a bis-(-)-nor-meptazinol derivative reveals disruption of the catalytic triad. DOI:10.1021/jm801657v. PMID:19326912.
- Shafferman A et al. (2008), Chem Biol Interact, 175, 166-172. Flexibility versus "rigidity" of the functional architecture of AChE active center. DOI:10.1016/j.cbi.2008.03.013. PMID:18471807.
- Hörnberg A et al. (2007), Biochemistry, 46, 4815-4825. Crystal structures of acetylcholinesterase in complex with organophosphorus compounds suggest that the acyl pocket modulates the aging reaction by precluding the formation of the trigonal bipyramidal transition state. DOI:10.1021/bi0621361. PMID:17402711.
- Bourne Y et al. (2003), EMBO J, 22, 1-12. Structural insights into ligand interactions at the acetylcholinesterase peripheral anionic site. DOI:10.1093/emboj/cdg005. PMID:12505979.
- Nicolet Y et al. (2003), J Biol Chem, 278, 41141-41147. Crystal structure of human butyrylcholinesterase and of its complexes with substrate and products. DOI:10.1074/jbc.M210241200. PMID:12869558.
- Dvir H et al. (2002), Biochemistry, 41, 10810-10818. X-ray structures of Torpedo californica acetylcholinesterase complexed with (+)-huperzine A and (-)-huperzine B: structural evidence for an active site rearrangement. PMID:12196020.
- Kaplan D et al. (2001), Biochemistry, 40, 7433-7445. Does "butyrylization" of acetylcholinesterase through substitution of the six divergent aromatic amino acids in the active center gorge generate an enzyme mimic of butyrylcholinesterase? PMID:11412096.
- Harel M et al. (2000), Protein Sci, 9, 1063-1072. Three-dimensional structures of Drosophila melanogaster acetylcholinesterase and of its complexes with two potent inhibitors. DOI:10.1110/ps.9.6.1063. PMID:10892800.
- Raves ML et al. (1997), Nat Struct Biol, 4, 57-63. Structure of acetylcholinesterase complexed with the nootropic alkaloid, (–)-huperzine A. DOI:10.1038/nsb0197-57. PMID:8989325.
- Primo-Parmo SL et al. (1996), Am J Hum Genet, 58, 52-64. Characterization of 12 silent alleles of the human butyrylcholinesterase (BCHE) gene. PMID:8554068.
- Anglister L et al. (1994), Neuron, 12, 783-794. Acetylcholinesterase density and turnover number at frog neuromuscular junctions, with modeling of their role in synaptic function. PMID:8161450.
- Shafferman A et al. (1992), J Biol Chem, 267, 17640-17648. Mutagenesis of human acetylcholinesterase. Identification of residues involved in catalytic activity and in polypeptide folding. PMID:1517212.
- NACHMANSOHN D et al. (1951), Adv Enzymol Relat Subj Biochem, 12, 259-339. The enzymic hydrolysis and synthesis of acetylcholine. DOI:10.1002/9780470122570.ch5. PMID:14885021.
Step 1. Ser203 is deprotonated by His447 after which Ser203 attacks the acyl carbon on the substrate.
Download: Image, Marvin FileCatalytic Residues Roles
| Residue | Roles |
|---|---|
| His447A | activator, proton acceptor |
| Ser203A | nucleophile, proton donor |
| Phe295A | steric locator |
| Phe338A | steric locator |
| Glu334A | electrostatic stabiliser, modifies pKa |
| Gly121A (main-N) | electrostatic stabiliser |
| Gly122A (main-N) | electrostatic stabiliser |
| Ala204A (main-N) | electrostatic stabiliser |
Chemical Components
ingold: bimolecular nucleophilic addition, enzyme-substrate complex formation, intermediate formation, proton transfer
Step 2. The intermediate collapses due to His447 donating a proton to the leaving choline group.
Download: Image, Marvin FileCatalytic Residues Roles
| Residue | Roles |
|---|---|
| Glu334A | electrostatic stabiliser |
| Gly121A (main-N) | electrostatic stabiliser |
| Gly122A (main-N) | electrostatic stabiliser |
| Ala204A (main-N) | electrostatic stabiliser |
| Phe295A | steric locator |
| Phe338A | steric locator |
| Ser203A | covalently attached |
| Glu334A | modifies pKa |
| His447A | proton donor, hydrogen bond donor |
Chemical Components
hydrogen transfer, ingold: unimolecular elimination by the conjugate base, intermediate collapse
Step 3. His447 deprotonates a water molecule from solution and the resulting hydroxide binds to the remaining acly group bound to Ser203.
Download: Image, Marvin FileCatalytic Residues Roles
| Residue | Roles |
|---|---|
| Glu334A | electrostatic stabiliser |
| Gly121A (main-N) | electrostatic stabiliser |
| Gly122A (main-N) | electrostatic stabiliser |
| Ala204A (main-N) | electrostatic stabiliser |
| Glu334A | modifies pKa |
| Phe295A | steric locator |
| Phe338A | steric locator |
| Ser203A | covalently attached |
| His447A | proton acceptor, hydrogen bond donor |
Chemical Components
intermediate formation, ingold: bimolecular nucleophilic addition, proton transfer, overall reactant used
Step 4. His447 donate a proton to Ser203 which collapses the intermediate and releases the acyl group in the form of acetate.
Download: Image, Marvin FileCatalytic Residues Roles
| Residue | Roles |
|---|---|
| Glu334A | electrostatic stabiliser |
| Gly121A (main-N) | electrostatic stabiliser |
| Gly122A (main-N) | electrostatic stabiliser |
| Ala204A (main-N) | electrostatic stabiliser |
| His447A | proton donor, hydrogen bond donor |
| Ser203A | nucleofuge, proton acceptor |
Download: