AChE inhibitors and substrates

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<applet load='Soman1.pdb' size='500' frame='true' align='right' scene='2wfz/Al/1' />
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<StructureSection load='Soman1.pdb' size='500' frame='true' align='right' scene='2wfz/Al/1' >
As was mentioned above, AChE hydrolysizes the neurotransmitter <scene name='2wfz/Al/2'>ACh</scene>, producing <scene name='2wfz/Al/3'>choline and an acetate</scene> group. <scene name='2wfz/Al/2'>ACh</scene> directly binds catalytic <scene name='2wfz/Al/4'>Ser200</scene> (via its nucleophilic Oγ atom). <scene name='2wfz/Al/5'>Soman</scene>, [http://en.wikipedia.org/wiki/Soman O-(1,2,2-trimethylpropyl) methylphosphonofluoridate] (<font color='violet'><b>fluorine atom is colored violet</b></font> and <font color='darkmagenta'><b>phosphorus atom is colored darkmagenta</b></font>), is one of the most toxic OPs. Soman inhibits AChE by <scene name='2wfz/Al/6'>covalent binding</scene> to catalytic Ser200, <scene name='2wfz/Al/7'>mimicking ACh</scene>. This process <scene name='2wfz/Al/8'>(phosphonylation)</scene> implicates nucleophilic attack of the Ser200 nucleophilic Oγ atom on the phosphorus atom of soman, with concomitant departure of its fluoride atom. After that AChE catalyzes the <scene name='2wfz/Al/9'>dealkylation ("aging")</scene> of the soman or other OP. This causes irreversible inhibition of AChE, "aged" soman/AChE conjugate can not be reactivated. However, before “aging”, at the step of <scene name='2wfz/Al/8'>phosphonylation</scene>, AChE can be <scene name='2wfz/Al/11'>reactivated</scene> by nucleophiles, such as pralidoxime (2-PAM), resulting in <scene name='2wfz/Al/12'>cleavage</scene> of the phosphonyl adduct from Ser200 Oγ.
As was mentioned above, AChE hydrolysizes the neurotransmitter <scene name='2wfz/Al/2'>ACh</scene>, producing <scene name='2wfz/Al/3'>choline and an acetate</scene> group. <scene name='2wfz/Al/2'>ACh</scene> directly binds catalytic <scene name='2wfz/Al/4'>Ser200</scene> (via its nucleophilic Oγ atom). <scene name='2wfz/Al/5'>Soman</scene>, [http://en.wikipedia.org/wiki/Soman O-(1,2,2-trimethylpropyl) methylphosphonofluoridate] (<font color='violet'><b>fluorine atom is colored violet</b></font> and <font color='darkmagenta'><b>phosphorus atom is colored darkmagenta</b></font>), is one of the most toxic OPs. Soman inhibits AChE by <scene name='2wfz/Al/6'>covalent binding</scene> to catalytic Ser200, <scene name='2wfz/Al/7'>mimicking ACh</scene>. This process <scene name='2wfz/Al/8'>(phosphonylation)</scene> implicates nucleophilic attack of the Ser200 nucleophilic Oγ atom on the phosphorus atom of soman, with concomitant departure of its fluoride atom. After that AChE catalyzes the <scene name='2wfz/Al/9'>dealkylation ("aging")</scene> of the soman or other OP. This causes irreversible inhibition of AChE, "aged" soman/AChE conjugate can not be reactivated. However, before “aging”, at the step of <scene name='2wfz/Al/8'>phosphonylation</scene>, AChE can be <scene name='2wfz/Al/11'>reactivated</scene> by nucleophiles, such as pralidoxime (2-PAM), resulting in <scene name='2wfz/Al/12'>cleavage</scene> of the phosphonyl adduct from Ser200 Oγ.
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<br /><applet load="1som" size="350" color="white" frame="true" align="right" spinBox="true"
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To understand the basis for [http://en.wikipedia.org/wiki/Enzyme_inhibitor#Irreversible_inhibitors irreversible inhibition], the <scene name='1som/Ache_soman/1'>structure of the aged conjugate</scene> obtained by reaction of ''Tc''AChE with soman was solved by X-ray crystallography to 2.2Å resolution ([[1som]]). The highest positive difference density peak corresponded to the OP phosphorus and was located within covalent bonding distance of the active-site serine (S200). The <scene name='1som/Soman_active_site/3'>OP-oxygen atoms</scene> are within hydrogen-bonding distance of four potential donors from catalytic subsites of the enzyme, suggesting that electrostatic forces significantly stabilize the aged enzyme. The methyl group of soman occupies the <scene name='1som/Soman_acyl_binding/2'>acyl binding pocket</scene>, bounded by Trp233, Phe288, and Phe290.
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caption="1som, resolution 2.20&Aring;" scene="1som/Ache_soman/1"/> <br />
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To understand the basis for [http://en.wikipedia.org/wiki/Enzyme_inhibitor#Irreversible_inhibitors irreversible inhibition], the structure of the aged conjugate obtained by reaction of ''Tc''AChE with soman was solved by X-ray crystallography to 2.2Å resolution ([[1som]]). The highest positive difference density peak corresponded to the OP phosphorus and was located within covalent bonding distance of the active-site serine (S200). The <scene name='1som/Soman_active_site/3'>OP-oxygen atoms</scene> are within hydrogen-bonding distance of four potential donors from catalytic subsites of the enzyme, suggesting that electrostatic forces significantly stabilize the aged enzyme. The methyl group of soman occupies the <scene name='1som/Soman_acyl_binding/2'>acyl binding pocket</scene>, bounded by Trp233, Phe288, and Phe290.
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<applet load='1cfj.pdb' size='500' frame='true' align='left' scene='1cfj/Cv/1' />
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<scene name='1cfj/Cv/1'>Sarin.</scene> [http://en.wikipedia.org/wiki/Sarin Sarin], O-''iso''propylmethylphosponofluoridate, is an other toxic OP compound. It is also inhibits AChE by covalent binding to the catalytic Ser200. The active sites of aged <scene name='1cfj/Cv/2'>sarin-TcAChE</scene> ([[1cfj]]) and aged soman-TcAChE ([[1som]] and [[2wg0]]) are almost identical and provided structural models for the negatively charged, tetrahedral intermediate that occurs during deacylation with the ACh.
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[http://en.wikipedia.org/wiki/Sarin Sarin], O-''iso''propylmethylphosponofluoridate, is an other toxic OP compound. It is also inhibits AChE by covalent binding to the catalytic Ser200. The active sites of aged <scene name='1cfj/Cv/2'>sarin-TcAChE</scene> ([[1cfj]]) and aged soman-TcAChE ([[1som]] and [[2wg0]]) are almost identical and provided structural models for the negatively charged, tetrahedral intermediate that occurs during deacylation with the ACh.
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There are four hydrogen bond donors <font color='red'><b>(red dotted lines)</b></font> to the anionic phosphonyl oxygen atoms: the backbone amide nitrogen atoms of Ala201, Gly118, and Gly119, as well as His440 Nε2. The sarin <font color='cyan'><b>methyl carbon (colored cyan)</b></font> is within non-bonded contact distances '''(black dotted lines)''' of Phe288 and Phe290 in the acyl binding pocket.
There are four hydrogen bond donors <font color='red'><b>(red dotted lines)</b></font> to the anionic phosphonyl oxygen atoms: the backbone amide nitrogen atoms of Ala201, Gly118, and Gly119, as well as His440 Nε2. The sarin <font color='cyan'><b>methyl carbon (colored cyan)</b></font> is within non-bonded contact distances '''(black dotted lines)''' of Phe288 and Phe290 in the acyl binding pocket.
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<scene name='2dfp/Cv/3'>DFP</scene>, di''iso''propylphosphorofluoridate, is an other toxic OP nerve agent. It is also inhibits AChE by covalent binding to the catalytic Ser200. As in the case with soman ([[1som]]) and sarin ([[1cfj]]), there are four hydrogen bond donors (dotted lines) to the anionic phosphonyl oxygen atoms: the backbone amide nitrogen atoms of Ala201, Gly118, and Gly119, as well as His440 Nε2 at the <scene name='2dfp/Cv/4'>active site</scene> of aged DFP-TcAChE ([[2dfp]]). Phosphorylation with DFP caused an unexpected distortion in the main chain of a loop that includes residues F288 and F290 of the TcAChE acyl binding pocket. F288 and F290 move significantly in the <font color='lime'><b>DFP-TcAChE structure (lime)</b></font>, in comparison to their positions in the <font color='magenta'><b>native enzyme</b></font> ([[2ace]]). This is the first major conformational change reported in the active site of any AChE−ligand complex, and it offers a structural explanation for the substrate selectivity of AChE.
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DFP, di''iso''propylphosphorofluoridate, is an other toxic OP nerve agent. It is also inhibits AChE by covalent binding to the catalytic Ser200. As in the case with soman ([[1som]]) and sarin ([[1cfj]]), there are four hydrogen bond donors (dotted lines) to the anionic phosphonyl oxygen atoms: the backbone amide nitrogen atoms of Ala201, Gly118, and Gly119, as well as His440 Nε2 at the <scene name='2dfp/Cv/4'>active site</scene> of aged DFP-TcAChE ([[2dfp]]). Phosphorylation with DFP caused an unexpected distortion in the main chain of a loop that includes residues F288 and F290 of the TcAChE acyl binding pocket. F288 and F290 move significantly in the <font color='lime'><b>DFP-TcAChE structure (lime)</b></font>, in comparison to their positions in the <font color='magenta'><b>native enzyme</b></font> ([[2ace]]). This is the first major conformational change reported in the active site of any AChE−ligand complex, and it offers a structural explanation for the substrate selectivity of AChE.
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</StructureSection>
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Revision as of 06:52, 28 November 2010

Crystal Structure of Torpedo californica acetylcholinesterase, 2ace
Crystal Structure of Torpedo californica acetylcholinesterase, 2ace

Template:STRUCTURE 2ace

Dear readers, this page presents only a small part of the great world of the acetylcholinesterase inhibitors. So, please see also our pages AChE inhibitors and substrates (Part II), AChE inhibitors and substrates (Part III), AChE bivalent inhibitors and AChE bivalent inhibitors (Part II). The images at the left and at the right correspond to one representative acetylcholinesterase with substrate structure, i.e. crystal structure of Torpedo californica acetylcholinesterase with acetylcholine (2ace).

Contents

AChE substrate

Drag the structure with the mouse to rotate

Solution of the three-dimensional (3D) structure of Torpedo californica acetylcholinesterase (TcAChE) in 1991 (Sussman et al. & Silman (1991)) opened up new horizons in research on an enzyme that had already been the subject of intensive investigation. The unanticipated structure of this extremely rapid enzyme, in which the active site was found to be buried at the bottom of a , lined by (colored dark magenta), led to a revision of the views then held concerning substrate traffic, recognition and hydrolysis (Botti et al. Sussman & Silman (1999)). This led to a series of theoretical and experimental studies, which took advantage of recent advances in theoretical techniques for treatment of proteins, such as molecular dynamics and electrostatics and to site-directed mutagenesis, utilizing suitable expression systems. Acetylcholinesterase hydrolysizes the neurotransmitter acetylcholine , producing group. directly binds (via its nucleophilic Oγ atom) within the catalytic triad (ACh/TcAChE structure 2ace). The residues are also important in the ligand recognition .

AChE monovalent inhibitors

Organophosphorus acid anhydride nerve agents

Organophosphorus (OP) acid anhydride nerve agents are potent inhibitors which rapidly phosphonylate AChE and then may undergo an internal dealkylation reaction (called "aging") to produce an OP-enzyme conjugate that cannot be reactivated.

Reaction between Ser200Oγ and Soman, assuming an in-line attack by the Oγ, followed by spontaneous dealkylation of the O-pinacolyl group.
Reaction between Ser200Oγ and Soman, assuming an in-line attack by the Oγ, followed by spontaneous dealkylation of the O-pinacolyl group.


Drag the structure with the mouse to rotate


Treatment of Alzheimer's disease

Please see pages AChE inhibitors and substrates (Part II) and AChE inhibitors and substrates (Part III).

AChE bivalent inhibitors

Please see pages AChE bivalent inhibitors and AChE bivalent inhibitors (Part II)

Selected 3D Structures of AChE

  • 2ace This is the original solved structure for Torpedo Californica
  • 1ea5 This is one of the highest quality representative X-ray structures in the PDB.
  • 1eve The E2020 (Aricept) complex.
  • 1ax9 Endrophonium complex.
  • 1vot Complex with Huperzine, a Chinese folk medicine.
  • 1fss Complex with snake venum toxin Fasciculin-II.
  • 1acj Complex with tacrine.
  • 1e66 Complex with huprine X.
  • 1dx6 Complex with galanthamine.
  • 1qti Complex with galanthamine.
  • 1w6r Complex with galanthamine iminium derivative.
  • 2ack Complex with edrophonium.
  • 1vzj Structure of the tetramerization domain of acetylcholinesterase.
  • 1gqr Complex with rivastigmine.
  • 1gqs Complex with NAP alone.
  • 1vxr Complex with VX.
  • 2vja Complex with OTMA.
  • 1som Complex with soman.
  • 2wfz Complex with nonaged soman.
  • 2wg0 Complex with aged soman.
  • 2wg1 Complex with aged soman and 2-PAM.
  • 1cfj Complex with aged sarin.
  • 2dfp Complex with aged DFP.


Additional Resources

For additional information, see: Alzheimer's Disease

References




  • Raves ML, Harel M, Pang YP, Silman I, Kozikowski AP, Sussman JL. Structure of acetylcholinesterase complexed with the nootropic alkaloid, (-)-huperzine A. Nat Struct Biol. 1997 Jan;4(1):57-63. PMID:8989325
  • Harel M, Schalk I, Ehret-Sabatier L, Bouet F, Goeldner M, Hirth C, Axelsen PH, Silman I, Sussman JL. 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. PMID:8415649
  • Greenblatt HM, Guillou C, Guenard D, Argaman A, Botti S, Badet B, Thal C, Silman I, Sussman JL. The complex of a bivalent derivative of galanthamine with torpedo acetylcholinesterase displays drastic deformation of the active-site gorge: implications for structure-based drug design. J Am Chem Soc. 2004 Dec 1;126(47):15405-11. PMID:15563167 doi:http://dx.doi.org/10.1021/ja0466154
  • Ravelli RB, Raves ML, Ren Z, Bourgeois D, Roth M, Kroon J, Silman I, Sussman JL. Static Laue diffraction studies on acetylcholinesterase. Acta Crystallogr D Biol Crystallogr. 1998 Nov 1;54(Pt 6 Pt 2):1359-66. PMID:10089512
  • Haviv H, Wong DM, Greenblatt HM, Carlier PR, Pang YP, Silman I, Sussman JL. Crystal packing mediates enantioselective ligand recognition at the peripheral site of acetylcholinesterase. J Am Chem Soc. 2005 Aug 10;127(31):11029-36. PMID:16076210 doi:http://dx.doi.org/10.1021/ja051765f
  • Carlier PR, Du DM, Han Y, Liu J, Pang YP. Potent, easily synthesized huperzine A-tacrine hybrid acetylcholinesterase inhibitors. Bioorg Med Chem Lett. 1999 Aug 16;9(16):2335-8. PMID:10476864
  • Wong DM, Greenblatt HM, Dvir H, Carlier PR, Han YF, Pang YP, Silman I, Sussman JL. Acetylcholinesterase complexed with bivalent ligands related to huperzine a: experimental evidence for species-dependent protein-ligand complementarity. J Am Chem Soc. 2003 Jan 15;125(2):363-73. PMID:12517147 doi:http://dx.doi.org/10.1021/ja021111w
  • Sussman JL, Harel M, Frolow F, Oefner C, Goldman A, Toker L, Silman I. Atomic structure of acetylcholinesterase from Torpedo californica: a prototypic acetylcholine-binding protein. Science. 1991 Aug 23;253(5022):872-9. PMID:1678899
  • Greenblatt HM, Kryger G, Lewis T, Silman I, Sussman JL. Structure of acetylcholinesterase complexed with (-)-galanthamine at 2.3 A resolution. FEBS Lett. 1999 Dec 17;463(3):321-6. PMID:10606746
  • Bar-On P, Millard CB, Harel M, Dvir H, Enz A, Sussman JL, Silman I. Kinetic and structural studies on the interaction of cholinesterases with the anti-Alzheimer drug rivastigmine. Biochemistry. 2002 Mar 19;41(11):3555-64. PMID:11888271
  • Colletier JP, Bourgeois D, Sanson B, Fournier D, Sussman JL, Silman I, Weik M. Shoot-and-Trap: use of specific x-ray damage to study structural protein dynamics by temperature-controlled cryo-crystallography. Proc Natl Acad Sci U S A. 2008 Aug 19;105(33):11742-7. Epub 2008 Aug 13. PMID:18701720
  • Dvir H, Wong DM, Harel M, Barril X, Orozco M, Luque FJ, Munoz-Torrero D, Camps P, Rosenberry TL, Silman I, Sussman JL. 3D structure of Torpedo californica acetylcholinesterase complexed with huprine X at 2.1 A resolution: kinetic and molecular dynamic correlates. Biochemistry. 2002 Mar 5;41(9):2970-81. PMID:11863435
  • Millard CB, Kryger G, Ordentlich A, Greenblatt HM, Harel M, Raves ML, Segall Y, Barak D, Shafferman A, Silman I, Sussman JL. Crystal structures of aged phosphonylated acetylcholinesterase: nerve agent reaction products at the atomic level. Biochemistry. 1999 Jun 1;38(22):7032-9. PMID:10353814 doi:http://dx.doi.org/10.1021/bi982678l
  • Sanson B, Nachon F, Colletier JP, Froment MT, Toker L, Greenblatt HM, Sussman JL, Ashani Y, Masson P, Silman I, Weik M. Crystallographic Snapshots of Nonaged and Aged Conjugates of Soman with Acetylcholinesterase, and of a Ternary Complex of the Aged Conjugate with Pralidoxime (dagger). J Med Chem. 2009 Jul 30. PMID:19642642 doi:10.1021/jm900433t
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