Acetylcholinesterase In Complex Research Articles

In-silico molecular docking for Potential herbal leads from Withaniasomnifera L. Dunal for the treatment of Alzheimer’s disease

Alzheimer's disease (AD) poses a significant global health challenge, necessitating novel therapeutic interventions. Withaniasomnifera L. Dunal, commonly known as Ashwagandha, has been historically utilized in traditional medicine for its neuroprotective properties. This study employs computational techniques to explore the potential of W. somnifera compounds in targeting key proteins associated with AD. The reported phytoconstituents of W. somnifera were identified and subjected to molecular docking studies against 5NUU (Torpedo californica acetylcholinesterase in complex with a chlorotacrine-tryptophan hybrid inhibitor), as crucial targets. The results revealed several phytoconstituents of W. somnifera exhibiting favorable binding affinities and promising interactions with the target proteins. These findings provide a valuable foundation for further experimental validation and the development of novel therapeutic agents derived from natural sources for the treatment of Alzheimer's.

Two new cyclohexenone derivatives: Synthesis, DFT estimation, biological activities and molecular docking study

Two new cyclohexenone carboxylate derivatives (6a-b) were synthesized through an additional ring-forming chalcone. FT-IR, 1H, 13C NMR, and Mass spectroscopy techniques confirmed the skeletons. The antibacterial, antioxidant, and colon cancer HT-29 cell activity of synthetic substances were assessed. Compound 6a's IC50 is 23.95 and 60.28 for its antioxidant and anticancer activities, whereas Compound 6b's IC50 is 27.56 and 62.72, respectively. MIC values for compound 6a are 15.75 ± 1.12, 10.25 ± 1.27, and 65.61 ± 1.72 against Staphylococcus aureus, Escherichia coli bacterial strains, and Candida albicans, respectively, whereas for compound 6b is equal to 18.32 ± 1.53, 12.63 ± 1.36, and 78.91 ± 1.94. Based on the extent of (B3LYP) and a 6-31G (d, p) basis set, the HOMO and LUMO of synthesized compounds were computed using the density functional theory (DFT) method. Energy gaps for products 6a and 6b are 2.8272 and 2.3360, respectively. Docked products had binding affinities of −9.5 and −9.1 for compounds 6a and 6b, respectively, with the crystal structure of recombinant human acetylcholinesterase in complex with donepezil (PDB ID: 4ey7). Consequently, according to experimental and computational studies, compound 6a is more active than compound 6b.

Crystal structure of human acetylcholinesterase in complex with tacrine: Implications for drug discovery

Alzheimer's disease (AD) is one of the most common, progressive neurodegenerative disorders affecting the aged populations. Though various disease pathologies have been suggested for AD, the impairment of the cholinergic system is one of the critical factors for the disease progression. Restoration of the cholinergic transmission through acetylcholinesterase (AChE) inhibitors is a promising disease modifying therapy. Being the first marketed drug for AD, tacrine reversibly inhibits AChE and thereby slows the breakdown of the chemical messenger acetylcholine (ACh) in the brain. However, the atomic level of interactions of tacrine towards human AChE (hAChE) is unknown for years. Hence, in the current study, we report the X-ray structure of hAChE-tacrine complex at 2.85 Å resolution. The conformational heterogeneity of tacrine within the electron density was addressed with the help of molecular mechanics assisted methods and the low-energy ligand configuration is reported, which provides a mechanistic explanation for the high binding affinity of tacrine towards AChE. Additionally, structural comparison of reported hAChE structures sheds light on the conformational selection and induced fit effects of various active site residues upon binding to different ligands and provides insight for future drug design campaigns against AD where AChE is a drug target.

Inhibitory Mechanism of Baicalein on Acetylcholinesterase: Inhibitory Interaction, Conformational Change, and Computational Simulation.

Alzheimer’s disease (AD) is the most prevalent chronic neurodegenerative disease in elderly individuals, causing dementia. Acetylcholinesterase (AChE) is regarded as one of the most popular drug targets for AD. Herbal secondary metabolites are frequently cited as a major source of AChE inhibitors. In the current study, baicalein, a typical bioactive flavonoid, was found to inhibit AChE competitively, with an associated IC50 value of 6.42 ± 0.07 µM, through a monophasic kinetic process. The AChE fluorescence quenching by baicalein was a static process. The binding constant between baicalein and AChE was an order of magnitude of 104 L mol−1, and hydrogen bonding and hydrophobic interaction were the major forces for forming the baicalein−AChE complex. Circular dichroism analysis revealed that baicalein caused the AChE structure to shrink and increased its surface hydrophobicity by increasing the α-helix and β-turn contents and decreasing the β-sheet and random coil structure content. Molecular docking revealed that baicalein predominated at the active site of AChE, likely tightening the gorge entrance and preventing the substrate from entering and binding with the enzyme, resulting in AChE inhibition. The preceding findings were confirmed by molecular dynamics simulation. The current study provides an insight into the molecular-level mechanism of baicalein interaction with AChE, which may offer new ideas for the research and development of anti-AD functional foods and drugs.

Novel thiophene Chalcones-Coumarin as acetylcholinesterase inhibitors: Design, synthesis, biological evaluation, molecular docking, ADMET prediction and molecular dynamics simulation

A series of around eight novel chalcone based coumarin derivatives (23a-h) was designed, subjected to in-silico ADMET prediction, synthesized, characterized by IR, NMR, Mass analytical techniques and evaluated as acetylcholinesterase (AChE) inhibitor for the treatment of Alzheimer’s disease (AD). The results of predicted ADMET study demonstrated the drug-likeness properties of the titled compounds with developmental challenges in lipophilicity and solubility parameters. The in vitro assessment of the synthesized compounds revealed that all of them showed significant activity (IC50 ranging from 0.42 to 1.296 µM) towards AChE compared to the standard drug, galantamine (IC50 = 1.142 ± 0.027 µM). Among these, compound 23e displayed the most potent inhibitory activity with IC50 value of 0.42 ± 0.019 µM. Cytotoxicity of all compounds was tested on normal human hepatic (THLE-2) cell lines at three different concentrations using the MTT assay, in which none of the compound showed significant toxicity at the highest concentration of 1000 µg/ml compared to the control group. Based on the docking study against AChE, the most active derivative 23e was orientated towards the active site and occupied both catalytic anionic site (CAS) and peripheral anionic site (PAS) of the target enzyme. In-silico studies revealed tested showed better inhibition activity of AChE compared to Butyrylcholinesterase (BuChE). Molecular dynamics simulation explored the stability and dynamic behavior of 23e- AChE complex.

Machine learning models to select potential inhibitors of acetylcholinesterase activity from SistematX: a natural products database.

Alzheimer's disease is the most common form of dementia, representing 60-70% of dementia cases. The enzyme acetylcholinesterase (AChE) cleaves the ester bonds in acetylcholine and plays an important role in the termination of acetylcholine activity at cholinergic synapses in various regions of the nervous system. The inhibition of acetylcholinesterase is frequently used to treat Alzheimer's disease. In this study, a merged BindingDB and ChEMBL dataset containing molecules with reported half-maximal inhibitory concentration (IC50) values for AChE (7032 molecules) was used to build machine learning classification models for selecting potential AChE inhibitors from the SistematX dataset (8593 secondary metabolites). A total of seven fivefold models with accuracy above 80% after cross-validation were obtained using three types of molecular descriptors (VolSurf, DRAGON 5.0, and bit-based fingerprints). A total of 521 secondary metabolites (6.1%) were classified as active in this stage. Subsequently, virtual screening was performed, and 25 secondary metabolites were identified as potential inhibitors of AChE. Separately, the crystal structure of AChE in complex with (-)-galantamine was used to perform molecular docking calculations with the entire SistematX dataset. Consensus analysis of both methodologies was performed. Only eight structures achieved combined probability values above 0.5. Finally, two sesquiterpene lactones, structures 15 and 24, were predicted to be able to cross the blood-brain barrier, which was confirmed in the VolSurf+ quantitative model, revealing these two structures as the most promising secondary metabolites for AChE inhibition among the 8593 molecules tested. A consensus analysis of classification models and molecular docking calculations identified four potential inhibitors of acetylcholinesterase from the SistematX dataset (8593 structures).

Synthesis of novel β-lactams: Antioxidant activity, acetylcholinesterase inhibition and computational studies

A convenient synthesis of some novel β-lactam derivatives with interesting pharmacological activities was described. Some of the synthesized compounds exhibited excellent antioxidant activity and showed acetylcholinesterase inhibition. Theoretical studies were carried out on the most potent compounds 5a and 5b to compare their potential interaction with crystal structure of recombinant human acetylcholinesterase in complex with Donepezil (PDB ID: 4EY7) and binary complex of native hAChE with Donepezil (PDBID:6O4W). The comprehensive theoretical and experimental mechanical studies of compounds 5b were compatible with its FT-IR, 1H NMR,13C NMR and Mass spectral data. The optimized molecular structure and the harmonic vibrational frequencies were examined DFT/B3LYP/6–31G(d) and Hartree-Fock HF/6–31G(d) energies and the difference in bond length and energies between compounds 5a and 5b was confirmed via theoretical studies.

Chemical Composition and Anti-Alzheimer's Disease-Related Activities of a Functional Oil from the Edible Seaweed Hizikia fusiforme.

Cholinergic disorder, oxidative stress, and neuroinflammation play important roles in the pathology of Alzheimer's disease. To explore the healthy potential of the edible seaweed Hizikia fusiforme on this aspect, a functional oil (HFFO) was extracted from this alga and investigated on its constituents by gas chromatography-mass spectrometry (GC/MS) in this study. Its anti-Alzheimer's related bioactivities including acetylcholinesterase (AChE) inhibition, antioxidation, and anti-neuroinflammation were evaluated, traced, and simulated by in vitro and in silico methods. GC/MS analysis indicated that HFFO mainly contained arachidonic acid (ARA), 11,14,17-eicosatrienoic acid (ETrA), palmitic acid, phytol, etc. HFFO showed moderate AChE inhibition and antioxidant activity. Bioactivity tracing using commercial standards verified that AChE inhibition of HFFO mainly originated from ARA and ETrA, whereas antioxidant activity mainly from ARA. Lineweaver-Burk plots showed that both ARA and ETrA are noncompetitive AChE inhibitors. A molecular docking study demonstrated low CDOCKER interaction energy of -26.33 kcal/mol for ARA and -43.70 kcal/mol for ETrA when interacting with AChE and multiple interactions in the ARA (or ETrA)-AChE complex. In the anti-neuroinflammatory evaluation, HFFO showed no toxicity toward BV-2 cells at 20 μg/mL and effectively inhibited the production of nitroxide and reduced the level of reactive oxygen species in lipopolysaccharide-induced BV-2 cells. The results indicated that HFFO could be used in functional foods for its anti-Alzheimer's disease-related activities.

From Venom to AChE Inhibitor: Design, Molecular Modeling, and Synthesis of a Peptidic Inhibitor of AChE

Alzheimer’s disease (AD) is an irreversible and progressive brain disorder that slowly destroys memory and cognitive skills. The current treatment of AD mainly focused on the restoring of ACh levels through acetylcholinesterase (AChE) inhibition. Peptides are a unique class of pharmaceutical compounds that have privilege over small molecules, especially in the realm of protein–protein interactions and G protein-coupled receptor (GPCR) inhibitors. We applied a rational structure-based virtual design approach to discover new peptidic inhibitors of AChE. In this regard, conformational space in the fasciculin II (Fas) and AChE complex was evaluated utilizing MD simulation, principal component analysis and clustering to figure out possible interactions of Fas and AChE. Assessment of Fas–AChE interactions by visual evaluation and alanine scanning led to the design of 10 peptides. The highest scored peptide (p2) was selected and synthesized using SPPS. Based on Ellman's test, the inhibitory activity of p2 against AChE was 51.2 ± 8.1 µM. The kinetics study of the enzyme inhibition in accompany with molecular modeling results revealed that p2 was a mixed-type reversible inhibitor of AChE. The DNRMLRTTRY peptide was considerable inhibitor of AChE. Peptides have the merit of being big enough to inhibit PPI and GPCR class B with a wide binding site. But possible peptidic chemical space is too large to be evaluated by the classical peptide synthesis methods. In the present contribution, we introduced a rational in silico peptide design approach that led to the considerable peptidic inhibitor of AChE.

A Second Look at the Crystal Structures of Drosophila melanogaster Acetylcholinesterase in Complex with Tacrine Derivatives Provides Insights Concerning Catalytic Intermediates and the Design of Specific Insecticides.

Over recent decades, crystallographic software for data processing and structure refinement has improved dramatically, resulting in more accurate and detailed crystal structures. It is, therefore, sometimes valuable to have a second look at “old” diffraction data, especially when earlier interpretation of the electron density maps was rather difficult. Here, we present updated crystal structures of Drosophila melanogaster acetylcholinesterase (DmAChE) originally published in [Harel et al., Prot Sci (2000) 9:1063-1072], which reveal features previously unnoticed. Thus, previously unmodeled density in the native active site can be interpreted as stable acetylation of the catalytic serine. Similarly, a strong density in the DmAChE/ZA complex originally attributed to a sulfate ion is better interpreted as a small molecule that is covalently bound. This small molecule can be modeled as either a propionate or a glycinate. The complex is reminiscent of the carboxylate butyrylcholinesterase complexes observed in crystal structures of human butyrylcholinesterases from various sources, and demonstrates the remarkable ability of cholinesterases to stabilize covalent complexes with carboxylates. A very strong peak of density (10 σ) at covalent distance from the Cβ of the catalytic serine is present in the DmAChE/ZAI complex. This can be undoubtedly attributed to an iodine atom, suggesting an unanticipated iodo/hydroxyl exchange between Ser238 and the inhibitor, possibly driven by the intense X-ray irradiation. Finally, the binding of tacrine-derived inhibitors, such as ZA (1DX4) or the iodinated analog, ZAI (1QON) results in the appearance of an open channel that connects the base of the active-site gorge to the solvent. This channel, which arises due to the absence of the conserved tyrosine present in vertebrate cholinesterases, could be exploited to design inhibitors specific to insect cholinesterases. The present study demonstrates that updated processing of older diffraction images, and the re-refinement of older diffraction data, can produce valuable information that could not be detected in the original analysis, and strongly supports the preservation of the diffraction images in public data banks.

Discovery of Novel Acetylcholinesterase Inhibitors as Potential Candidates for the Treatment of Alzheimer's Disease.

Acetylcholinesterase (AChE) catalyzes the hydrolysis of neurotransmitter acetylcholine to acetate and choline in a synaptic cleft. Deficits in cholinergic neurotransmitters are linked closely with the progression of Alzheimer’s disease (AD), which is a neurodegenerative disorder characterized by memory impairment, and a disordered cognitive function. Since the previously approved AChE inhibitors, donepezil (Aricept), galantamine (Reminyl), and rivastigmine (Exelon), have side effects and several studies are being carried out out to develop novel AD drugs, we have applied a three-dimensional quantitative structure−activity relationship (3D QSAR) and structure-based pharmacophore modeling methodologies to identify potential candidate inhibitors against AChE. Herein, 3D QSAR and structure-based pharmacophore models were built from known inhibitors and crystal structures of human AChE in complex with donepezil, galantamine, huperzine A, and huprine W, respectively. The generated models were used as 3D queries to screen new scaffolds from various chemical databases. The hit compounds obtained from the virtual screening were subjected to an assessment of drug-like properties, followed by molecular docking. The final hit compounds were selected based on binding modes and molecular interactions in the active site of the enzyme. Furthermore, molecular dynamics simulations for AChE in complex with the final hits were performed to evaluate that they maintained stable interactions with the active site residues. The binding free energies of the final hits were also calculated using molecular mechanics/Poisson-Boltzmann surface area method. Taken together, we proposed that these hits can be promising candidates for anti-AD drugs.

1-Naphthyl acetate: A chromogenic substrate for the detection of erythrocyte acetylcholinesterase activity

Erythrocyte acetylcholinesterase (AChE) is a preferred biomarker for the detection of organophosphorus poisoning. Acetylthiocholine (ATCh) is the most popular substrate for the detection of AChE activity. However, oximolysis is a prominent feature with ATCh. In this context, we have searched alternative substrates for AChE using in silico tools for screening of a better substrate. The in silico approach was performed to understand the fitness and the Total Interaction Energy (TIE) of substrates for AChE. The alternative substrates for AChE were screened in terms of high Goldscore and favorable TIE in comparison to acetylcholine (ACh)-AChE complex and other relevant esterases. Among the screened substrates, 1-Naphthyl acetate (1-NA) exhibited the most favorable interaction with AChE in terms of highest TIE and corresponding high Goldscore. The Molecular Dynamic (MD) simulation of the 1-NA-AChE complex showed a stable complex formation over a period of 5 ns. The results obtained in the in silico studies were validated in vitro using pure erythrocyte AChE and hemolysate. We observed 1-NA to be a better alternative substrate for AChE than ATCh in terms of lower Km value. Its specificity appeared at least similar to ATCh. Therefore, we propose that 1-NA can be an attractive chromogenic substrate for the measurement of AChE activity, and it possess the potential to detect organophosphorus pesticide (OP) poisoning.

Identification of novel acetylcholinesterase inhibitors through e-pharmacophore-based virtual screening and molecular dynamics simulations

Alzheimer’s disease (AD), a progressive neurodegenerative disorder is the most common cause of dementia among elderly people. To date, the successful therapeutic strategy to treat AD is maintaining the levels of acetylcholine via inhibiting acetylcholinesterase (AChE). The present study involves identification of newer AChE inhibitors by dual approach of e-pharmacophore and structure-based virtual screening of Asinex library. Robustness of docking protocol was validated by enrichment calculation with ROC value .71 and BEDROC value .028. Among 11 selected hits, ZINC72338524 with best MM-GBSA dG binding shows optimal range of CNS properties and ligand–AChE complex stability. Further, molecular dynamics study revealed its molecular interactions with Trp86, Phe338, and Tyr341 amino acid residues of catalytic anionic site and Tyr124, Ser125, and Trp286 amino acid residues of peripheral anionic site. Physicochemical properties and ADMET risk prediction indicates their potential in druggability and safety.

Structures of paraoxon-inhibited human acetylcholinesterase reveal perturbations of the acyl loop and the dimer interface.

Irreversible inhibition of the essential nervous system enzyme acetylcholinesterase by organophosphate nerve agents and pesticides may quickly lead to death. Oxime reactivators currently used as antidotes are generally less effective against pesticide exposure than nerve agent exposure, and pesticide exposure constitutes the majority of cases of organophosphate poisoning in the world. The current lack of published structural data specific to human acetylcholinesterase organophosphate-inhibited and oxime-bound states hinders development of effective medical treatments. We have solved structures of human acetylcholinesterase in different states in complex with the organophosphate insecticide, paraoxon, and oximes. Reaction with paraoxon results in a highly perturbed acyl loop that causes a narrowing of the gorge in the peripheral site that may impede entry of reactivators. This appears characteristic of acetylcholinesterase inhibition by organophosphate insecticides but not nerve agents. Additional changes seen at the dimer interface are novel and provide further examples of the disruptive effect of paraoxon. Ternary structures of paraoxon-inhibited human acetylcholinesterase in complex with the oximes HI6 and 2-PAM reveals relatively poor positioning for reactivation. This study provides a structural foundation for improved reactivator design for the treatment of organophosphate intoxication. Proteins 2016; 84:1246-1256. © 2016 Wiley Periodicals, Inc.

Crystal Structure of Snake Venom Acetylcholinesterase in Complex with Inhibitory Antibody Fragment Fab410 Bound at the Peripheral Site: EVIDENCE FOR OPEN AND CLOSED STATES OF A BACK DOOR CHANNEL

The acetylcholinesterase found in the venom of Bungarus fasciatus (BfAChE) is produced as a soluble, non-amphiphilic monomer with a canonical catalytic domain but a distinct C terminus compared with the other vertebrate enzymes. Moreover, the peripheral anionic site of BfAChE, a surface site located at the active site gorge entrance, bears two substitutions altering sensitivity to cationic inhibitors. Antibody Elec410, generated against Electrophorus electricus acetylcholinesterase (EeAChE), inhibits EeAChE and BfAChE by binding to their peripheral sites. However, both complexes retain significant residual catalytic activity, suggesting incomplete gorge occlusion by bound antibody and/or high frequency back door opening. To explore a novel acetylcholinesterase species, ascertain the molecular bases of inhibition by Elec410, and document the determinants and mechanisms for back door opening, we solved a 2.7-Å resolution crystal structure of natural BfAChE in complex with antibody fragment Fab410. Crystalline BfAChE forms the canonical dimer found in all acetylcholinesterase structures. Equally represented open and closed states of a back door channel, associated with alternate positions of a tyrosine phenol ring at the active site base, coexist in each subunit. At the BfAChE molecular surface, Fab410 is seated on the long Ω-loop between two N-glycan chains and partially occludes the gorge entrance, a position that fully reflects the available mutagenesis and biochemical data. Experimentally based flexible molecular docking supports a similar Fab410 binding mode onto the EeAChE antigen. These data document the molecular and dynamic peculiarities of BfAChE with high frequency back door opening, and the mode of action of Elec410 as one of the largest peptidic inhibitors targeting the acetylcholinesterase peripheral site.

Structures of Human Acetylcholinesterase Bound to Dihydrotanshinone I and Territrem B Show Peripheral Site Flexibility

Acetylcholinesterase is a critical enzyme that regulates neurotransmission by degrading the neurotransmitter acetylcholine in synapses of the nervous system. It is an important target for both therapeutic drugs that treat Alzheimer's disease and chemical warfare agents that cripple the nervous system and cause death through paralysis. The enzyme has both catalytic and peripheral sites to which inhibitors may bind. Structures of recombinant human acetylcholinesterase in complex with the natural product inhibitors dihydrotanshinone I and territrem B reveal dihydrotanshinone I binding that is specific to only the peripheral site and territrem B binding that spans both sites and distorts the protein backbone in the peripheral site. These inhibitors may function as important molecular templates for therapeutics used for treatment of disease and protection against nerve agents.

Structures of Human Acetylcholinesterase in Complex with Pharmacologically Important Ligands

Human acetylcholinesterase (AChE) is a significant target for therapeutic drugs. Here we present high resolution crystal structures of human AChE, alone and in complexes with drug ligands; donepezil, an Alzheimer's disease drug, binds differently to human AChE than it does to Torpedo AChE. These crystals of human AChE provide a more accurate platform for further drug development than previously available.

Backdoor opening mechanism in acetylcholinesterase based on X‐ray crystallography and molecular dynamics simulations

The transient opening of a backdoor in the active-site wall of acetylcholinesterase, one of nature's most rapid enzymes, has been suggested to contribute to the efficient traffic of substrates and products. A crystal structure of Torpedo californica acetylcholinesterase in complex with the peripheral-site inhibitor aflatoxin is now presented, in which a tyrosine at the bottom of the active-site gorge rotates to create a 3.4-Å wide exit channel. Molecular dynamics simulations show that the opening can be further enlarged by movement of Trp84. The crystallographic and molecular dynamics simulation data thus point to the interface between Tyr442 and Trp84 as the key element of a backdoor, whose opening permits rapid clearance of catalysis products from the active site. Furthermore, the crystal structure presented provides a novel template for rational design of inhibitors and reactivators, including anti-Alzheimer drugs and antidotes against organophosphate poisoning.

Structure of HI-6*sarin-acetylcholinesterase determined by X-ray crystallography and molecular dynamics simulation: reactivator mechanism and design.

Organophosphonates such as isopropyl metylphosphonofluoridate (sarin) are extremely toxic as they phosphonylate the catalytic serine residue of acetylcholinesterase (AChE), an enzyme essential to humans and other species. Design of effective AChE reactivators as antidotes to various organophosphonates requires information on how the reactivators interact with the phosphonylated AChEs. However, such information has not been available hitherto because of three main challenges. First, reactivators are generally flexible in order to change from the ground state to the transition state for reactivation; this flexibility discourages determination of crystal structures of AChE in complex with effective reactivators that are intrinsically disordered. Second, reactivation occurs upon binding of a reactivator to the phosphonylated AChE. Third, the phosphorous conjugate can develop resistance to reactivation. We have identified crystallographic conditions that led to the determination of a crystal structure of the sarinnonaged-conjugated mouse AChE in complex with [(E)-[1-[(4-carbamoylpyridin-1-ium-1-yl)methoxymethyl]pyridin-2-ylidene]methyl]-oxoazanium dichloride (HI-6) at a resolution of 2.2 Å. In this structure, the carboxyamino-pyridinium ring of HI-6 is sandwiched by Tyr124 and Trp286, however, the oxime-pyridinium ring is disordered. By combining crystallography with microsecond molecular dynamics simulation, we determined the oxime-pyridinium ring structure, which shows that the oxime group of HI-6 can form a hydrogen-bond network to the sarin isopropyl ether oxygen, and a water molecule is able to form a hydrogen bond to the catalytic histidine residue and subsequently deprotonates the oxime for reactivation. These results offer insights into the reactivation mechanism of HI-6 and design of better reactivators.

Novel Nerve-Agent Antidote Design Based on Crystallographic and Mass Spectrometric Analyses of Tabun-Conjugated Acetylcholinesterase in Complex with Antidotes

Organophosphorus compound-based nerve agents inhibit the essential enzyme acetylcholinesterase (AChE) causing acute toxicity and death. Clinical treatment of nerve-agent poisoning is to use oxime-based antidotes to reactivate the inhibited AChE. However, the nerve agent tabun is resistant to oximes. To design improved oximes, crystal structures of a tabun-conjugated AChE in complex with different oximes are needed to guide the structural modifications of known antidotes. However, this type of structure is extremely challenging to obtain because both deamidation of the tabun conjugate and reactivation of AChE occur during crystallographic experiments. Here we report, for the first time, the crystal structures of Ortho-7 and HLö-7 in complex with AChE that is conjugated to an intact tabun. These structures were determined by our new strategy of combining crystallographic and mass spectrometric analyses of AChE crystals. The results explain the relative reactivation potencies of the two oximes and offer insights into improving known medical antidotes.