Acetylcholinesterase anionic sites

Acetylcholinesterase can be inhibited by two general mechanisms. In the first mechanism, positively charged quaternary ammonium compounds bind to the anionic site and prevent ACh from binding—a simple competitive inhibition. In the second mechanism, the agents act either as a false substrate for the cholinesterase or directly attack the esteratic site in both cases they covalently modify the esteratic site and non-competitively prevent further hydrolytic activity. Either mechanism can be effective in preventing the hydroly-... 

Wilson, I.B 1955. Promotion of acetylcholinesterase activity by the anionic site. Disc. Faraday Soc. 20 119-125. 

We can draw schematically the interaction of ammonium ions with the anionic site of acetylcholinesterase in Fig. 5 based upon Eq. 36 since the informations for the steric and hydrophobic effects of substituents do not change practically even if la is used for the analysis 26). 

Fig. 5. Susceptibility of the binding vicinal to the anionic site of acetylcholinesterase to the hydrophobicity of N-substitu-ents26) (reproduced with permission from Pure and Applied Chemistry, IUPAC)...

The reversible inhibitors, which have a short to moderate duration of action, fall into two categories. Type one, exemplified by edrophonium, forms an ionic bond at the anionic site and a weak hydrogen bond at the esteratic site of acetylcholinesterase. Type two, exemplified by neostigmine, forms an ionic bond at the anionic site and a hydrolyzable covalent bond at the esteratic site. The irreversible inhibitors, exemplified by organophosphorus compounds (diisopropyl fluorophosphate, parathion,... 

Bourne, Y., Taylor, P., Radic, Z., March-ot, P. Structural Insights into Ligand Interactions at the Acetylcholinesterase Peripheral Anionic Site. EMBO J. 2003, 22, 1-12. 

Acetylcholinesterase is only cholinesterase in insects. It is mainly located in the neuropile (area of synapses between nerve fibers) of the CNS in insects (Toutant, 1989). AChE contains two active sites, the esteratic site and the anionic site. The esteratic site possesses the hydroxyl group of serine and a basic nucleophilic imidazole group of histidine. The anionic site has a free carboxyl group (aspartic acid and/or glutamic acid). The interaction of ACh with AChE can be divided into three steps, as shown in Figure 7.13. The first... 

Johnson, G., Moore, S.W. (2003). Human acetylcholinesterase binds to mouse laminin-1 and human collagen IV by an electrostatic mechanism at the peripheral anionic site. Neuro-sci. Lett. 337 37-40. 

Lin G, Lai CY, Liao WC. Molecular recognition by acetylcholinesterase at the peripheral anionic site Structure-activity relationships for inhibitions by aryl carbamates. Bioorg Med Chem 1999 7 2683-9. 

Fluorescence data for the interaction with acetylcholinesterase (EC 3.1.1.7, ACHE) from the electric eel Electrophorus electricus with some quaternary protoberberine and benzophenanthridine alkaloids was obtained. Berberine and other related compounds were bound to the gamma y-anionic site of ACHE via a comparison with known inhibitors of acetylcholinesterase, including tetramethylammonium and tacrine. Furthermore, during the interaction, two molecules of the ligand were bound to one molecule of the enzyme [226]. 

A series of novel l, 3-dihydroxyxanthone Mannich base derivatives were synthesized, structure elucidated, and evaluated for anticholinesterase activity. Most of the target compounds exhibited moderate to good inhibitory activities with the IC50 values at micromole level concentration against both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Among them, 2 - ((diethylamino )methyl) -1 -hydroxy- 3 - (3 -methylbut-2-enyloxy) -9H-xanthen-9-one showed potent inhibitory activity against AChE and the best inhibitory activity against BuChE. The Mannich base derivatives were likely to bind to the active site (AS) and the peripheral anionic site (PAS) of cholinesterases [169]. 

There are three primary cholinesterases (ChE) in the body. Acetylcholinesterase is located in the vicinity of ACh receptors at neuronal and neuromuscular junctions. Acetylcholinesterase terminates ACh activity via hydrolysis into choline and acetic acid. The positively charged choline portion of the ACh molecule attaches to the anionic site and the acetyl region attaches to the esteratic site on the AChE molecule. Eollowing the attachment of the two regions, choline is rapidly released to be recycled back into the presynaptic nerve terminal, and the acetyl group reacts with... 

Elucidation of the molecular nature of another cholinergic receptor system, the enzyme acetylcholinesterase. is also being attempted through the use of specific, irreversible inhibitors. Belleau and Tanl have recently demonstrated that N,N-dlmethyl-2-chloro-2 phenylethylamine inactivates erythrocyte acetylcholinesterase when acetylcholine is the substrate.. Other workers have provided evidence that the action of this compound involves alkylation at or near the anionic site of the enzyme, rather then at the esteratlc site. Future studies of this system may well be conducted with pure, crystalline enzyme, if a recent report" of the crystallization of acetylcholinesterase from eel electric tissue can be confirmed. 

D. Synaptic Acetylcholinesterase and Butyrylcholinesterase Have High Homology BUT Distinct Peripheral Anionic Sites and C Termini... 

It has already been mentioned that there are some doubts A26) about the existence of an anionic site in human or horse cholinesterase. Comparative kinetic studies using a series of pyridylcarbinol acetates as substrates have shown that acetylcholinesterase from T. marmorata electric organ and the plasma cholinesterases from horse and man have similar esteratic sites. It was also shown that the electric eel organ enzyme has an anionic site, whereas the second site of butyrylcholine... 

The hydrophobic area surrounding the anionic site plays a more important role for butyrylcholinesterase than for acetylcholinesterase. The greater importance of this hydrophobic area for butyrylcholinesterase could help to explain and resolve some of the opposing views of earlier workers (A26). Kabachnik et al. (Kl) also proposed that in the vicinity of the esteratic site of butyrylcholinesterase there are two hydrophobic areas separated by a hydrophilic group. Differences in length and structure of the hydrophobic areas of the active surfaces of butyryl- and... 

A28. Augustinsson, K. B., The nature of an anionic site in butyrylcholinesterase compared with that of a similar site in acetylcholinesterase. Biochim. Biophys. Acta 128, 351-362 (1966). 

The action of OP nerve agents on the nervous system results from their effects on enzymes, particularly esterases. The most notable of these esterases is acetylcholinesterase. The active site of acetylcholinesterase comprises a catalytic triad of serine, histidine and glutamic acid residues and other important features of the enzyme are a gorge connecting the active site to the surface of the protein and a peripheral anionic site (Bourne etal., 1995,1999 Sussman etal., 1991 Thompson and Richardson, 2004), The OPs phosphy-late1 the serine hydroxyl group in the active site of the enzyme. 

The most important part of the enzyme is its active site, where the acetylcholine and the many inhibitors bind. The classical model shown in Figure 5.3 (Nachmansohn and Wilson, 1951) is still very useful, although not exactly correct. The model says that acetylcholinesterase has two subsites in the active site called the esteratic and anionic sites. Because acetylcholine is an ester where the alcoholic part (choline) carries a positive charge, this part... 

Figure 1. Schematic of the probable physical structure of acetylcholinesterase. One physical region carries the esteratic site, which is proximal to one anionic site (Site I) the other region would carry at least four anionic sites, and would be homologous to the acetylcholine receptor of the motor end plate excitable membrane. Sites I and II are masked by DPA, but Site II can be regenerated at alkaline pH. Decamethonium (C10) would interact at least with Sites I and II whereas curare would bind at III and TV, and perhaps at II and III. Most quaternary salt substituents bind on the anionic chain [exo-binding (26, 36, 42.

Ordentlich, A., Barak, D., Kronman, C, Flashner, V, Leitncr. M., Segall, Y., Ariel, N., Cohen. S Velan, B, and Shafferman, A, (1993). Dis.seciion of the human acetylcholinesterase active center deteiminant.s of substrate specificity. Identification of residues constituting the anionic site, the hydrophobic site, and the acyl pocket. J. Biol. Chem. 268, 17083-17095. 

John.son, G., and Moore, S, W, (1999). The adhesion function on acetylcholinesterase is located at the peripheral anionic site. Btochem. Biophys Res, Commun. 258, 758-762. 

Rl. Radio, Z., Reiner, E., and Taylor, P., Role of the peripheral anionic site on acetylcholinesterase Inhibition by substrates and coumarin derivatives. Mol. Pharmacol. 39, 98-104 (1991). 

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