Ekstrom F


Full name : Ekstrom Fredrik

First name : Fredrik

Mail : CBRN Defence and Security\; Swedish Defence Research Agency\; 90182 Umea

Zip Code :

City :

Country : Sweden

Email : fredrik.ekstrom@foi.se

Phone : +4690106815

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Website : \/\/www.researchgate.net\/profile\/Fredrik_Ekstroem

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References (28)

Title : Structure-Activity Relationships Reveal Beneficial Selectivity Profiles of Inhibitors Targeting Acetylcholinesterase of Disease-Transmitting Mosquitoes - Vidal-Albalat_2023_J.Med.Chem__
Author(s) : Vidal-Albalat A , Kindahl T , Rajeshwari R , Lindgren C , Forsgren N , Kitur S , Tengo LS , Ekstrom F , Kamau L , Linusson A
Ref : Journal of Medicinal Chemistry , : , 2023
Abstract : Insecticide resistance jeopardizes the prevention of infectious diseases such as malaria and dengue fever by vector control of disease-transmitting mosquitoes. Effective new insecticidal compounds with minimal adverse effects on humans and the environment are therefore urgently needed. Here, we explore noncovalent inhibitors of the well-validated insecticidal target acetylcholinesterase (AChE) based on a 4-thiazolidinone scaffold. The 4-thiazolidinones inhibit AChE1 from the mosquitoes Anopheles gambiae and Aedes aegypti at low micromolar concentrations. Their selectivity depends primarily on the substitution pattern of the phenyl ring; halogen substituents have complex effects. The compounds also feature a pendant aliphatic amine that was important for activity; little variation of this group is tolerated. Molecular docking studies suggested that the tight selectivity profiles of these compounds are due to competition between two binding sites. Three 4-thiazolidinones tested for in vivo insecticidal activity had similar effects on disease-transmitting mosquitoes despite a 10-fold difference in their in vitro activity.
ESTHER : Vidal-Albalat_2023_J.Med.Chem__
PubMedSearch : Vidal-Albalat_2023_J.Med.Chem__
PubMedID: 37094110

Title : Dual Reversible Coumarin Inhibitors Mutually Bound to Monoamine Oxidase B and Acetylcholinesterase Crystal Structures - Ekstrom_2022_ACS.Med.Chem.Lett_13_499
Author(s) : Ekstrom F , Gottinger A , Forsgren N , Catto M , Iacovino LG , Pisani P , Binda C
Ref : ACS Med Chem Lett , 13 :499 , 2022
Abstract : Multitarget directed ligands (MTDLs) represent a promising frontier in tackling the complexity of multifactorial pathologies. The synergistic inhibition of monoamine oxidase B (MAO B) and acetylcholinesterase (AChE) is believed to provide a potentiated effect in the treatment of Alzheimer's disease. Among previously reported micromolar or sub-micromolar coumarin-bearing dual inhibitors, compound 1 returned a tight-binding inhibition of MAO B (Ki = 4.5 microM) and a +5.5 C increase in the enzyme Tm value. Indeed, the X-ray crystal structure revealed that binding of 1 produces unforeseen conformational changes at the MAO B entrance cavity. Interestingly, 1 showed great shape complementarity with the AChE enzymatic gorge, being deeply buried from the catalytic anionic subsite (CAS) to the peripheral anionic subsite (PAS) and causing significant structural changes in the active site. These findings provide structural templates for further development of dual MAO B and AChE inhibitors.
ESTHER : Ekstrom_2022_ACS.Med.Chem.Lett_13_499
PubMedSearch : Ekstrom_2022_ACS.Med.Chem.Lett_13_499
PubMedID: 35300078
Gene_locus related to this paper: mouse-ACHE

Title : Physical Mechanisms Governing Substituent Effects on Arene-Arene Interactions in a Protein Milieu - Andersson_2020_J.Phys.Chem.B_124_6529
Author(s) : Andersson CD , Mishra BK , Forsgren N , Ekstrom F , Linusson A
Ref : J Phys Chem B , 124 :6529 , 2020
Abstract : Arene-arene interactions play important roles in protein-ligand complex formation. Here, we investigate the characteristics of arene-arene interactions between small organic molecules and aromatic amino acids in protein interiors. The study is based on X-ray crystallographic data and quantum mechanical calculations using the enzyme acetylcholinesterase and selected inhibitory ligands as a model system. It is shown that the arene substituents of the inhibitors dictate the strength of the interaction and the geometry of the resulting complexes. Importantly, the calculated interaction energies correlate well with the measured inhibitor potency. Non-hydrogen substituents strengthened all interaction types in the protein milieu, in keeping with results for benzene dimer model systems. The interaction energies were dispersion-dominated, but substituents that induced local dipole moments increased the electrostatic contribution and thus yielded more strongly bound complexes. These findings provide fundamental insights into the physical mechanisms governing arene-arene interactions in the protein milieu and thus into molecular recognition between proteins and small molecules.
ESTHER : Andersson_2020_J.Phys.Chem.B_124_6529
PubMedSearch : Andersson_2020_J.Phys.Chem.B_124_6529
PubMedID: 32610016
Gene_locus related to this paper: mouse-ACHE

Title : Noncovalent Inhibitors of Mosquito Acetylcholinesterase 1 with Resistance-Breaking Potency - Knutsson_2018_J.Med.Chem_61_10545
Author(s) : Knutsson S , Engdahl C , Kumari R , Forsgren N , Lindgren C , Kindahl T , Kitur S , Wachira L , Kamau L , Ekstrom F , Linusson A
Ref : Journal of Medicinal Chemistry , 61 :10545 , 2018
Abstract : Resistance development in insects significantly threatens the important benefits obtained by insecticide usage in vector control of disease-transmitting insects. Discovery of new chemical entities with insecticidal activity is highly desired in order to develop new insecticide candidates. Here, we present the design, synthesis, and biological evaluation of phenoxyacetamide-based inhibitors of the essential enzyme acetylcholinesterase 1 (AChE1). AChE1 is a validated insecticide target to control mosquito vectors of, e.g., malaria, dengue, and Zika virus infections. The inhibitors combine a mosquito versus human AChE selectivity with a high potency also for the resistance-conferring mutation G122S; two properties that have proven challenging to combine in a single compound. Structure-activity relationship analyses and molecular dynamics simulations of inhibitor-protein complexes have provided insights that elucidate the molecular basis for these properties. We also show that the inhibitors demonstrate in vivo insecticidal activity on disease-transmitting mosquitoes. Our findings support the concept of noncovalent, selective, and resistance-breaking inhibitors of AChE1 as a promising approach for future insecticide development.
ESTHER : Knutsson_2018_J.Med.Chem_61_10545
PubMedSearch : Knutsson_2018_J.Med.Chem_61_10545
PubMedID: 30339371
Gene_locus related to this paper: mouse-ACHE

Title : Influence of Enantiomeric Inhibitors on the Dynamics of Acetylcholinesterase Measured by Elastic Incoherent Neutron Scattering - Andersson_2018_J.Phys.Chem.B_122_8516
Author(s) : Andersson CD , Martinez N , Zeller D , Allgardsson A , Koza MM , Frick B , Ekstrom F , Peters J , Linusson A
Ref : J Phys Chem B , 122 :8516 , 2018
Abstract : The enzyme acetylcholinesterase (AChE) is essential in humans and animals because it catalyzes the breakdown of the nerve-signaling substance acetylcholine. Small molecules that inhibit the function of AChE are important for their use as drugs in the, for example, symptomatic treatment of Alzheimer's disease. New and improved inhibitors are warranted, mainly because of severe side effects of current drugs. In the present study, we have investigated if and how two enantiomeric inhibitors of AChE influence the overall dynamics of noncovalent complexes, using elastic incoherent neutron scattering. A fruitful combination of univariate models, including a newly developed non-Gaussian model for atomic fluctuations, and multivariate methods (principal component analysis and discriminant analysis) was crucial to analyze the fine details of the data. The study revealed a small but clear increase in the dynamics of the inhibited enzyme compared to that of the noninhibited enzyme and contributed to the fundamental knowledge of the mechanisms of AChE-inhibitor binding valuable for the future development of inhibitors.
ESTHER : Andersson_2018_J.Phys.Chem.B_122_8516
PubMedSearch : Andersson_2018_J.Phys.Chem.B_122_8516
PubMedID: 30110543

Title : N-Aryl-N'-ethyleneaminothioureas effectively inhibit acetylcholinesterase 1 from disease-transmitting mosquitoes - Knutsson_2017_Eur.J.Med.Chem_134_415
Author(s) : Knutsson S , Kindahl T , Engdahl C , Nikjoo D , Forsgren N , Kitur S , Ekstrom F , Kamau L , Linusson A
Ref : Eur Journal of Medicinal Chemistry , 134 :415 , 2017
Abstract : Vector control of disease-transmitting mosquitoes by insecticides has a central role in reducing the number of parasitic- and viral infection cases. The currently used insecticides are efficient, but safety concerns and the development of insecticide-resistant mosquito strains warrant the search for alternative compound classes for vector control. Here, we have designed and synthesized thiourea-based compounds as non-covalent inhibitors of acetylcholinesterase 1 (AChE1) from the mosquitoes Anopheles gambiae (An. gambiae) and Aedes aegypti (Ae. aegypti), as well as a naturally occurring resistant-conferring mutant. The N-aryl-N'-ethyleneaminothioureas proved to be inhibitors of AChE1; the most efficient one showed submicromolar potency. Importantly, the inhibitors exhibited selectivity over the human AChE (hAChE), which is desirable for new insecticides. The structure-activity relationship (SAR) analysis of the thioureas revealed that small changes in the chemical structure had a large effect on inhibition capacity. The thioureas showed to have different SAR when inhibiting AChE1 and hAChE, respectively, enabling an investigation of structure-selectivity relationships. Furthermore, insecticidal activity was demonstrated using adult and larvae An. gambiae and Ae. aegypti mosquitoes.
ESTHER : Knutsson_2017_Eur.J.Med.Chem_134_415
PubMedSearch : Knutsson_2017_Eur.J.Med.Chem_134_415
PubMedID: 28433681
Gene_locus related to this paper: anoga-ACHE1

Title : An Unusual Dimeric Inhibitor of Acetylcholinesterase: Cooperative Binding of Crystal Violet - Allgardsson_2017_Molecules_22_
Author(s) : Allgardsson A , David Andersson C , Akfur C , Worek F , Linusson A , Ekstrom F
Ref : Molecules , 22 : , 2017
Abstract : Acetylcholinesterase (AChE) is an essential enzyme that terminates cholinergic transmission by a rapid hydrolysis of the neurotransmitter acetylcholine. AChE is an important target for treatment of various cholinergic deficiencies, including Alzheimer's disease and myasthenia gravis. In a previous high throughput screening campaign, we identified the dye crystal violet (CV) as an inhibitor of AChE. Herein, we show that CV displays a significant cooperativity for binding to AChE, and the molecular basis for this observation has been investigated by X-ray crystallography. Two monomers of CV bind to residues at the entrance of the active site gorge of the enzyme. Notably, the two CV molecules have extensive intermolecular contacts with each other and with AChE. Computational analyses show that the observed CV dimer is not stable in solution, suggesting the sequential binding of two monomers. Guided by the structural analysis, we designed a set of single site substitutions, and investigated their effect on the binding of CV. Only moderate effects on the binding and the cooperativity were observed, suggesting a robustness in the interaction between CV and AChE. Taken together, we propose that the dimeric cooperative binding is due to a rare combination of chemical and structural properties of both CV and the AChE molecule itself.
ESTHER : Allgardsson_2017_Molecules_22_
PubMedSearch : Allgardsson_2017_Molecules_22_
PubMedID: 28867801
Gene_locus related to this paper: mouse-ACHE

Title : Discovery of Selective Inhibitors Targeting Acetylcholinesterase 1 from Disease-Transmitting Mosquitoes - Engdahl_2016_J.Med.Chem_59_9409
Author(s) : Engdahl C , Knutsson S , Ekstrom F , Linusson A
Ref : Journal of Medicinal Chemistry , 59 :9409 , 2016
Abstract : Vector control of disease-transmitting mosquitoes is increasingly important due to the re-emergence and spread of infections such as malaria and dengue. We have conducted a high throughput screen (HTS) of 17,500 compounds for inhibition of the essential AChE1 enzymes from the mosquitoes Anopheles gambiae and Aedes aegypti. In a differential HTS analysis including the human AChE, several structurally diverse, potent, and selective noncovalent AChE1 inhibitors were discovered. For example, a phenoxyacetamide-based inhibitor was identified with a 100-fold selectivity for the mosquito over the human enzyme. The compound also inhibited a resistance conferring mutant of AChE1. Structure-selectivity relationships could be proposed based on the enzymes' 3D structures; the hits' selectivity profiles appear to be linked to differences in two loops that affect the structure of the entire active site. Noncovalent inhibitors of AChE1, such as the ones presented here, provide valuable starting points toward insecticides and are complementary to existing and new covalent inhibitors.
ESTHER : Engdahl_2016_J.Med.Chem_59_9409
PubMedSearch : Engdahl_2016_J.Med.Chem_59_9409
PubMedID: 27598521
Gene_locus related to this paper: anoga-ACHE1 , mouse-ACHE

Title : The Nature of Activated Non-classical Hydrogen Bonds: A Case Study on Acetylcholinesterase-Ligand Complexes - Berg_2016_Chemistry_22_2672
Author(s) : Berg L , Mishra BK , Andersson CD , Ekstrom F , Linusson A
Ref : Chemistry , 22 :2672 , 2016
Abstract : Molecular recognition events in biological systems are driven by non-covalent interactions between interacting species. Here, we have studied hydrogen bonds of the CHY type involving electron-deficient CH donors using dispersion-corrected density functional theory (DFT) calculations applied to acetylcholinesterase-ligand complexes. The strengths of CHY interactions activated by a proximal cation were considerably strong; comparable to or greater than those of classical hydrogen bonds. Significant differences in the energetic components compared to classical hydrogen bonds and non-activated CHY interactions were observed. Comparison between DFT and molecular mechanics calculations showed that common force fields could not reproduce the interaction energy values of the studied hydrogen bonds. The presented results highlight the importance of considering CHY interactions when analysing protein-ligand complexes, call for a review of current force fields, and opens up possibilities for the development of improved design tools for drug discovery.
ESTHER : Berg_2016_Chemistry_22_2672
PubMedSearch : Berg_2016_Chemistry_22_2672
PubMedID: 26751405
Gene_locus related to this paper: mouse-ACHE

Title : Structure of a prereaction complex between the nerve agent sarin, its biological target acetylcholinesterase, and the antidote HI-6 - Allgardsson_2016_Proc.Natl.Acad.Sci.U.S.A_113_5514
Author(s) : Allgardsson A , Berg L , Akfur C , Hornberg A , Worek F , Linusson A , Ekstrom F
Ref : Proc Natl Acad Sci U S A , 113 :5514 , 2016
Abstract : Organophosphorus nerve agents interfere with cholinergic signaling by covalently binding to the active site of the enzyme acetylcholinesterase (AChE). This inhibition causes an accumulation of the neurotransmitter acetylcholine, potentially leading to overstimulation of the nervous system and death. Current treatments include the use of antidotes that promote the release of functional AChE by an unknown reactivation mechanism. We have used diffusion trap cryocrystallography and density functional theory (DFT) calculations to determine and analyze prereaction conformers of the nerve agent antidote HI-6 in complex with Mus musculus AChE covalently inhibited by the nerve agent sarin. These analyses reveal previously unknown conformations of the system and suggest that the cleavage of the covalent enzyme-sarin bond is preceded by a conformational change in the sarin adduct itself. Together with data from the reactivation kinetics, this alternate conformation suggests a key interaction between Glu202 and the O-isopropyl moiety of sarin. Moreover, solvent kinetic isotope effect experiments using deuterium oxide reveal that the reactivation mechanism features an isotope-sensitive step. These findings provide insights into the reactivation mechanism and provide a starting point for the development of improved antidotes. The work also illustrates how DFT calculations can guide the interpretation, analysis, and validation of crystallographic data for challenging reactive systems with complex conformational dynamics.
ESTHER : Allgardsson_2016_Proc.Natl.Acad.Sci.U.S.A_113_5514
PubMedSearch : Allgardsson_2016_Proc.Natl.Acad.Sci.U.S.A_113_5514
PubMedID: 27140636
Gene_locus related to this paper: human-ACHE

Title : Acetylcholinesterases from the Disease Vectors Aedes aegypti and Anopheles gambiae: Functional Characterization and Comparisons with Vertebrate Orthologues - Engdahl_2015_PLoS.One_10_e0138598
Author(s) : Engdahl C , Knutsson S , Fredriksson SA , Linusson A , Bucht G , Ekstrom F
Ref : PLoS ONE , 10 :e0138598 , 2015
Abstract : Mosquitoes of the Anopheles (An.) and Aedes (Ae.) genus are principal vectors of human diseases including malaria, dengue and yellow fever. Insecticide-based vector control is an established and important way of preventing transmission of such infections. Currently used insecticides can efficiently control mosquito populations, but there are growing concerns about emerging resistance, off-target toxicity and their ability to alter ecosystems. A potential target for the development of insecticides with reduced off-target toxicity is the cholinergic enzyme acetylcholinesterase (AChE). Herein, we report cloning, baculoviral expression and functional characterization of the wild-type AChE genes (ace-1) from An. gambiae and Ae. aegypti, including a naturally occurring insecticide-resistant (G119S) mutant of An. gambiae. Using enzymatic digestion and liquid chromatography-tandem mass spectrometry we found that the secreted proteins were post-translationally modified. The Michaelis-Menten constants and turnover numbers of the mosquito enzymes were lower than those of the orthologous AChEs from Mus musculus and Homo sapiens. We also found that the G119S substitution reduced the turnover rate of substrates and the potency of selected covalent inhibitors. Furthermore, non-covalent inhibitors were less sensitive to the G119S substitution and differentiate the mosquito enzymes from corresponding vertebrate enzymes. Our findings indicate that it may be possible to develop selective non-covalent inhibitors that effectively target both the wild-type and insecticide resistant mutants of mosquito AChE.
ESTHER : Engdahl_2015_PLoS.One_10_e0138598
PubMedSearch : Engdahl_2015_PLoS.One_10_e0138598
PubMedID: 26447952
Gene_locus related to this paper: aedae-ACHE1 , anoga-ACHE1

Title : Benefits of statistical molecular design, covariance analysis, and reference models in QSAR: a case study on acetylcholinesterase - Andersson_2015_J.Comput.Aided.Mol.Des_29_199
Author(s) : Andersson CD , Hillgren JM , Lindgren C , Qian W , Akfur C , Berg L , Ekstrom F , Linusson A
Ref : J Comput Aided Mol Des , 29 :199 , 2015
Abstract : Scientific disciplines such as medicinal- and environmental chemistry, pharmacology, and toxicology deal with the questions related to the effects small organic compounds exhort on biological targets and the compounds' physicochemical properties responsible for these effects. A common strategy in this endeavor is to establish structure-activity relationships (SARs). The aim of this work was to illustrate benefits of performing a statistical molecular design (SMD) and proper statistical analysis of the molecules' properties before SAR and quantitative structure-activity relationship (QSAR) analysis. Our SMD followed by synthesis yielded a set of inhibitors of the enzyme acetylcholinesterase (AChE) that had very few inherent dependencies between the substructures in the molecules. If such dependencies exist, they cause severe errors in SAR interpretation and predictions by QSAR-models, and leave a set of molecules less suitable for future decision-making. In our study, SAR- and QSAR models could show which molecular sub-structures and physicochemical features that were advantageous for the AChE inhibition. Finally, the QSAR model was used for the prediction of the inhibition of AChE by an external prediction set of molecules. The accuracy of these predictions was asserted by statistical significance tests and by comparisons to simple but relevant reference models.
ESTHER : Andersson_2015_J.Comput.Aided.Mol.Des_29_199
PubMedSearch : Andersson_2015_J.Comput.Aided.Mol.Des_29_199
PubMedID: 25351962

Title : Evaluation of novel carbamate insecticides for neurotoxicity to non-target species - Jiang_2013_Pestic.Biochem.Physiol_106_156
Author(s) : Jiang Y , Swale D , Carlier PR , Hartsel JA , Ma M , Ekstrom F , Bloomquist JR
Ref : Pesticide Biochemistry and Physiology , 106 :156 , 2013
Abstract : Malaria is an urgent world health concern and vector control is one important option for reducing disease prevalence. Increased reports of pyrethroid-resistant mosquito strains have amplified the need for new vector-control chemicals. We compared three commercially available carbamate insecticides (carbofuran, bendiocarb, and propoxur) to eight experimental compounds 1-8 for activity against Anopheles gambiae acetylcholinesterase, as well as enzymes from mammalian, avian, and aquatic species. The experimental compounds (except 7) were less potent than the commercial inhibitors against the mosquito enzyme, but had higher selectivity values (up to near 600-fold, IC50 of non-target species/IC50 An. gambiae) because of their low potency for acetylcholinesterases from nontarget species. Neurotoxic esterase assay showed that none of the experimental carbamates (1 mM) displayed NTE inhibition, while bendiocarb did (24% inhibition at 1 mM), although the effect was much less than that of mipafox. In vivo bioassays using Daphnia magna showed that all novel carbamates were of similar killing potency as bendiocarb (24 h LC50 = 611 nM), with the exception of experimental compound 1 (LC50 = 172 nM). Overall, the results suggested that the novel carbamate insecticides 4-8 presented in this study were safer to mammals than the commercial compounds and were promising insecticides for malaria vector control usage on bednets or indoor residual sprays.
ESTHER : Jiang_2013_Pestic.Biochem.Physiol_106_156
PubMedSearch : Jiang_2013_Pestic.Biochem.Physiol_106_156

Title : Effects of Anticholinesterases on Catalysis and Induced Conformational Change of the Peripheral Anionic Site of Murine Acetylcholinesterase - Tong_2013_Pestic.Biochem.Physiol_106_79
Author(s) : Tong F , Islam RM , Carlier PR , Ma M , Ekstrom F , Bloomquist JR
Ref : Pesticide Biochemistry and Physiology , 106 :79 , 2013
Abstract : Conventional insecticides targeting acetylcholinesterase (AChE) typically show high mammalian toxicities and because there is resistance to these compounds in many insect species, alternatives to established AChE inhibitors used for pest control are needed. Here we used a fluorescence method to monitor interactions between various AChE inhibitors and the AChE peripheral anionic site, which is a novel target for new insecticides acting on this enzyme. The assay uses thioflavin-T as a probe, which binds to the peripheral anionic site of AChE and yields an increase in fluorescent signal. Three types of AChE inhibitors were studied: catalytic site inhibitors (carbamate insecticides, edrophonium, and benzylpiperidine), peripheral site inhibitors (tubocurarine, ethidium bromide, and propidium iodide), and bivalent inhibitors (donepezil, BW284C51, and a series of bis(n)-tacrines). All were screened on murine AChE to compare and contrast changes of peripheral site conformation in the TFT assay with catalytic inhibition. All the inhibitors reduced thioflavin-T fluorescence in a concentration-dependent manner with potencies (IC50) ranging from 8 nM for bis(6)-tacrine to 159 muM for benzylpiperidine. Potencies in the fluorescence assay were correlated well with their potencies for enzyme inhibition (R2 = 0.884). Efficacies for reducing thioflavin-T fluorescence ranged from 23-36% for catalytic site inhibitors and tubocurarine to near 100% for ethidium bromide and propidium iodide. Maximal efficacies could be reconciled with known mechanisms of interaction of the inhibitors with AChE. When extended to pest species, we anticipate these findings will assist in the discovery and development of novel, selective bivalent insecticides acting on AChE.
ESTHER : Tong_2013_Pestic.Biochem.Physiol_106_79
PubMedSearch : Tong_2013_Pestic.Biochem.Physiol_106_79
PubMedID: 24003261

Title : Divergent Structure-Activity Relationships of Structurally Similar Acetylcholinesterase Inhibitors - Andersson_2013_J.Med.Chem_56_7615
Author(s) : Andersson CD , Forsgren N , Akfur C , Allgardsson A , Berg L , Engdahl C , Qian W , Ekstrom F , Linusson A
Ref : Journal of Medicinal Chemistry , 56 :7615 , 2013
Abstract : The molecular interactions between the enzyme acetylcholinesterase (AChE) and two compound classes consisting of N-[2-(diethylamino)ethyl]benzenesulfonamides and N-[2-(diethylamino)ethyl]benzenemethanesulfonamides have been investigated using organic synthesis, enzymatic assays, X-ray crystallography, and thermodynamic profiling. The inhibitors' aromatic properties were varied to establish structure-activity relationships (SAR) between the inhibitors and the peripheral anionic site (PAS) of AChE. The two structurally similar compound classes proved to have distinctly divergent SARs in terms of their inhibition capacity of AChE. Eight X-ray structures revealed that the two sets have different conformations in PAS. Furthermore, thermodynamic profiles of the binding between compounds and AChE revealed class-dependent differences of the entropy/enthalpy contributions to the free energy of binding. Further development of the entropy-favored compound class resulted in the synthesis of the most potent inhibitor and an extension beyond the established SARs. The divergent SARs will be utilized to develop reversible inhibitors of AChE into reactivators of nerve agent-inhibited AChE.
ESTHER : Andersson_2013_J.Med.Chem_56_7615
PubMedSearch : Andersson_2013_J.Med.Chem_56_7615
PubMedID: 23984975
Gene_locus related to this paper: mouse-ACHE

Title : Catalytic-site conformational equilibrium in nerve-agent adducts of acetylcholinesterase: possible implications for the HI-6 antidote substrate specificity - Artursson_2013_Biochem.Pharmacol_85_1389
Author(s) : Artursson E , Andersson PO , Akfur C , Linusson A , Borjegren S , Ekstrom F
Ref : Biochemical Pharmacology , 85 :1389 , 2013
Abstract : Nerve agents such as tabun, cyclosarin and Russian VX inhibit the essential enzyme acetylcholinesterase (AChE) by organophosphorylating the catalytic serine residue. Nucleophiles, such as oximes, are used as antidotes as they can reactivate and restore the function of the inhibited enzyme. The oxime HI-6 shows a notably low activity on tabun adducts but can effectively reactivate adducts of cyclosarin and Russian VX. To examine the structural basis for the pronounced substrate specificity of HI-6, we determined the binary crystal structures of Mus musculus AChE (mAChE) conjugated by cyclosarin and Russian VX and found a conformational mobility of the side chains of Phe338 and His447. The interaction between HI-6 and tabun-adducts of AChE were subsequently investigated using a combination of time resolved fluorescence spectroscopy and X-ray crystallography. Our findings show that HI-6 binds to tabun inhibited Homo sapiens AChE (hAChE) with an IC50 value of 300muM and suggest that the reactive nucleophilic moiety of HI-6 is excluded from the phosphorus atom of tabun. We propose that a conformational mobility of the side-chains of Phe338 and His447 is a common feature in nerve-agent adducts of AChE. We also suggest that the conformational mobility allow HI-6 to reactivate conjugates of cyclosarin and Russian VX while a reduced mobility in tabun conjugated AChE results in steric hindrance that prevents efficient reactivation.
ESTHER : Artursson_2013_Biochem.Pharmacol_85_1389
PubMedSearch : Artursson_2013_Biochem.Pharmacol_85_1389
PubMedID: 23376121
Gene_locus related to this paper: mouse-ACHE

Title : Similar but different: thermodynamic and structural characterization of a pair of enantiomers binding to acetylcholinesterase - Berg_2012_Angew.Chem.Int.Ed.Engl_51_12716
Author(s) : Berg L , Niemiec MS , Qian W , Andersson CD , Wittung-Stafshede P , Ekstrom F , Linusson A
Ref : Angew Chem Int Ed Engl , 51 :12716 , 2012
Abstract : Take a closer look: Unexpectedly, a pair of enantiomeric ligands proved to have similar binding affinities for acetylcholinesterase. Further studies indicated that the enantiomers exhibit different thermodynamic profiles. Analyses of the noncovalent interactions in the protein-ligand complexes revealed that these differences are partly due to nonclassical hydrogen bonds between the ligands and aromatic side chains of the protein.
ESTHER : Berg_2012_Angew.Chem.Int.Ed.Engl_51_12716
PubMedSearch : Berg_2012_Angew.Chem.Int.Ed.Engl_51_12716
PubMedID: 23161758
Gene_locus related to this paper: mouse-ACHE

Title : Targeting acetylcholinesterase: identification of chemical leads by high throughput screening, structure determination and molecular modeling - Berg_2011_PLoS.One_6_e26039
Author(s) : Berg L , Andersson CD , Artursson E , Hornberg A , Tunemalm AK , Linusson A , Ekstrom F
Ref : PLoS ONE , 6 :e26039 , 2011
Abstract : Acetylcholinesterase (AChE) is an essential enzyme that terminates cholinergic transmission by rapid hydrolysis of the neurotransmitter acetylcholine. Compounds inhibiting this enzyme can be used (inter alia) to treat cholinergic deficiencies (e.g. in Alzheimer's disease), but may also act as dangerous toxins (e.g. nerve agents such as sarin). Treatment of nerve agent poisoning involves use of antidotes, small molecules capable of reactivating AChE. We have screened a collection of organic molecules to assess their ability to inhibit the enzymatic activity of AChE, aiming to find lead compounds for further optimization leading to drugs with increased efficacy and/or decreased side effects. 124 inhibitors were discovered, with considerable chemical diversity regarding size, polarity, flexibility and charge distribution. An extensive structure determination campaign resulted in a set of crystal structures of protein-ligand complexes. Overall, the ligands have substantial interactions with the peripheral anionic site of AChE, and the majority form additional interactions with the catalytic site (CAS). Reproduction of the bioactive conformation of six of the ligands using molecular docking simulations required modification of the default parameter settings of the docking software. The results show that docking-assisted structure-based design of AChE inhibitors is challenging and requires crystallographic support to obtain reliable results, at least with currently available software. The complex formed between C5685 and Mus musculus AChE (C5685*mAChE) is a representative structure for the general binding mode of the determined structures. The CAS binding part of C5685 could not be structurally determined due to a disordered electron density map and the developed docking protocol was used to predict the binding modes of this part of the molecule. We believe that chemical modifications of our discovered inhibitors, biochemical and biophysical characterization, crystallography and computational chemistry provide a route to novel AChE inhibitors and reactivators.
ESTHER : Berg_2011_PLoS.One_6_e26039
PubMedSearch : Berg_2011_PLoS.One_6_e26039
PubMedID: 22140425
Gene_locus related to this paper: mouse-ACHE

Title : Kinetic analysis of interactions between alkylene-linked bis-pyridiniumaldoximes and human acetylcholinesterases inhibited by various organophosphorus compounds - Wille_2010_Biochem.Pharmacol_80_941
Author(s) : Wille T , Ekstrom F , Lee JC , Pang YP , Thiermann H , Worek F
Ref : Biochemical Pharmacology , 80 :941 , 2010
Abstract : The therapeutic approach of organophosphorus compound (OP) intoxications is to reactivate the inhibited enzyme acetylcholinesterase (AChE). Numerous studies demonstrated a limited efficacy of standard oxime-based reactivators against different nerve agents such as tabun and cyclosarin. This emphasizes research for more effective oximes. In the present study, reactivation kinetics of tabun-, sarin-, cyclosarin-, VX- or paraoxon-ethyl-inhibited human AChE (hAChE) with a homologous series of bis-ortho-pyridiniumaldoximes, Ortho-4 - Ortho-9, was investigated with a robot-assisted setting, allowing determination of second-order reactivation rate constants as well as model calculations. The reactivation constants of Ortho-4 - Ortho-9 resulted in marked differences of affinity and reactivity depending on the OP structure and the linker length of the oximes. In general, the K(D) values decreased with increasing linker length. Reactivity increased from Ortho-4 to Ortho-6 for PXE- and VX-inhibited hAChE and from Ortho-4 to Ortho-7 for GA-inhibited hAChE and decreased again with Ortho-8 and Ortho-9. In contrast, k(r) decreased with increasing linker length for sarin- and cyclosarin-inhibited hAChE. In view of the pronounced decrease of K(D) from Ortho-4 to Ortho-9, the k(r2) values increased with all tested OP. Hence, the ratios of K(I)/K(D) and of K(I)/k(r2) showed that in almost all cases the affinity of Ortho-N to the native hAChE was higher than to OP-inhibited enzyme. Model calculations indicated that Ortho-6 - Ortho-9 could be superior to obidoxime in reactivating tabun-inhibited hAChE. Finally, these data emphasize the need to develop oximes with a higher selective affinity towards OP-inhibited hAChE in order to minimize possible side effects.
ESTHER : Wille_2010_Biochem.Pharmacol_80_941
PubMedSearch : Wille_2010_Biochem.Pharmacol_80_941
PubMedID: 20510679

Title : Crystal structures of oxime-bound fenamiphos-acetylcholinesterases: reactivation involving flipping of the His447 ring to form a reactive Glu334-His447-oxime triad - Hornberg_2010_Biochem.Pharmacol_79_507
Author(s) : Hornberg A , Artursson E , Warme R , Pang YP , Ekstrom F
Ref : Biochemical Pharmacology , 79 :507 , 2010
Abstract : Organophosphorus insecticides and nerve agents inhibit the vital enzyme acetylcholinesterase by covalently bonding to the catalytic serine residue of the enzyme. Oxime-based reactivators, such as [(E)-[1-[(4-carbamoylpyridin-1-ium-1-yl)methoxymethyl]pyridin-2-ylidene]methyl]-o xoazanium dichloride (HI-6) and 1,7-heptylene-bis-N,N'-2-pyridiniumaldoxime dichloride (Ortho-7), restore the organophosphate-inhibited enzymatic activity by cleaving the phosphorous conjugate. In this article, we report the intermolecular interactions between Mus musculus acetylcholinesterase inhibited by the insecticide fenamiphos (fep-mAChE) and HI-6 or Ortho-7 revealed by a combination of crystallography and kinetics. The crystal structures of the two oxime-bound fep-mAChE complexes show that both oximes interact with the peripheral anionic site involving different conformations of Trp286 and different peripheral-site residues (Tyr124 for HI-6 and Tyr72 for Ortho-7). Moreover, residues at catalytic site of the HI-6-bound fep-mAChE complex adopt conformations that are similar to those in the apo mAChE, whereas significant conformational changes are observed for the corresponding residues in the Ortho-7-bound fep-mAChE complex. Interestingly, flipping of the His447 imidazole ring allows the formation of a hydrogen bonding network among the Glu334-His447-Ortho-7 triad, which presumably deprotonates the Ortho-7 oxime hydroxyl group, increases the nucleophilicity of the oxime group, and leads to cleavage of the phosphorous conjugate. These results offer insights into a detailed reactivation mechanism for the oximes and development of improved reactivators.
ESTHER : Hornberg_2010_Biochem.Pharmacol_79_507
PubMedSearch : Hornberg_2010_Biochem.Pharmacol_79_507
PubMedID: 19732756
Gene_locus related to this paper: mouse-ACHE

Title : Reactivation of tabun-hAChE investigated by structurally analogous oximes and mutagenesis - Artursson_2009_Toxicology_265_108
Author(s) : Artursson E , Akfur C , Hornberg A , Worek F , Ekstrom F
Ref : Toxicology , 265 :108 , 2009
Abstract : The nerve agent tabun inhibits the essential enzyme acetylcholinesterase (AChE) by a rapid phosphoramidation of the catalytic serine residue. Oximes, such as K027 and HLo-7, can reactivate tabun-inhibited human AChE (tabun-hAChE) whereas the activity of their close structural analogue HI-6 is notably low. To investigate HI-6, K027 and HLo-7, residues lining the active-site gorge of hAChE were substituted and the effects on kinetic parameters for reactivation were determined. None of the mutants (Asp74Asn, Asp74Glu, Tyr124Phe, Tyr337Ala, Tyr337Phe, Phe338Val and Tyr341Ala) were able to facilitate HI-6-mediated reactivation of tabun-hAChE. In contrast, Tyr124Phe and Tyr337Phe induce a 2-2.5-fold enhancement of the bimolecular rate constant for K027 and HLo-7. The largest effects on the dissociation constant (3.5-fold increase) and rate constant (20-fold decrease) were observed for Tyr341Ala and Asp74Asn, respectively. These findings demonstrate the importance of residues located distant from the conjugate during the reactivation of tabun-hAChE.
ESTHER : Artursson_2009_Toxicology_265_108
PubMedSearch : Artursson_2009_Toxicology_265_108
PubMedID: 19761810

Title : Selective and irreversible inhibitors of mosquito acetylcholinesterases for controlling malaria and other mosquito-borne diseases - Pang_2009_PLoS.One_4_e6851
Author(s) : Pang YP , Ekstrom F , Polsinelli GA , Gao Y , Rana S , Hua DH , Andersson B , Andersson PO , Peng L , Singh SK , Mishra RK , Zhu KY , Fallon AM , Ragsdale DW , Brimijoin S
Ref : PLoS ONE , 4 :e6851 , 2009
Abstract : New insecticides are urgently needed because resistance to current insecticides allows resurgence of disease-transmitting mosquitoes while concerns for human toxicity from current compounds are growing. We previously reported the finding of a free cysteine (Cys) residue at the entrance of the active site of acetylcholinesterase (AChE) in some insects but not in mammals, birds, and fish. These insects have two AChE genes (AP and AO), and only AP-AChE carries the Cys residue. Most of these insects are disease vectors such as the African malaria mosquito (Anopheles gambiae sensu stricto) or crop pests such as aphids. Recently we reported a Cys-targeting small molecule that irreversibly inhibited all AChE activity extracted from aphids while an identical exposure caused no effect on the human AChE. Full inhibition of AChE in aphids indicates that AP-AChE contributes most of the enzymatic activity and suggests that the Cys residue might serve as a target for developing better aphicides. It is therefore worth investigating whether the Cys-targeting strategy is applicable to mosquitocides. Herein, we report that, under conditions that spare the human AChE, a methanethiosulfonate-containing molecule at 6 microM irreversibly inhibited 95% of the AChE activity extracted from An. gambiae s. str. and >80% of the activity from the yellow fever mosquito (Aedes aegypti L.) or the northern house mosquito (Culex pipiens L.) that is a vector of St. Louis encephalitis. This type of inhibition is fast ( approximately 30 min) and due to conjugation of the inhibitor to the active-site Cys of mosquito AP-AChE, according to our observed reactivation of the methanethiosulfonate-inhibited AChE by 2-mercaptoethanol. We also note that our sulfhydryl agents partially and irreversibly inhibited the human AChE after prolonged exposure (>4 hr). This slow inhibition is due to partial enzyme denaturation by the inhibitor and/or micelles of the inhibitor, according to our studies using atomic force microscopy, circular dichroism spectroscopy, X-ray crystallography, time-resolved fluorescence spectroscopy, and liquid chromatography triple quadrupole mass spectrometry. These results support our view that the mosquito-specific Cys is a viable target for developing new mosquitocides to control disease vectors and to alleviate resistance problems with reduced toxicity toward non-target species.
ESTHER : Pang_2009_PLoS.One_4_e6851
PubMedSearch : Pang_2009_PLoS.One_4_e6851
PubMedID: 19714254
Gene_locus related to this paper: mouse-ACHE , mouse-acnt1

Title : Structure of HI-6*sarin-acetylcholinesterase determined by X-ray crystallography and molecular dynamics simulation: reactivator mechanism and design - Ekstrom_2009_PLoS.One_4_e5957
Author(s) : Ekstrom F , Hornberg A , Artursson E , Hammarstrom LG , Schneider G , Pang YP
Ref : PLoS ONE , 4 :e5957 , 2009
Abstract : 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 sarin(nonaged)-conjugated mouse AChE in complex with [(E)-[1-[(4-carbamoylpyridin-1-ium-1-yl)methoxymethyl]pyridin-2-ylidene]methyl]-o xoazanium dichloride (HI-6) at a resolution of 2.2 A. 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.
ESTHER : Ekstrom_2009_PLoS.One_4_e5957
PubMedSearch : Ekstrom_2009_PLoS.One_4_e5957
PubMedID: 19536291
Gene_locus related to this paper: mouse-ACHE

Title : Aging of cholinesterases phosphylated by tabun proceeds through O-dealkylation - Carletti_2008_J.Am.Chem.Soc_130_16011
Author(s) : Carletti E , Li H , Li B , Ekstrom F , Nicolet Y , Loiodice M , Gillon E , Froment MT , Lockridge O , Schopfer LM , Masson P , Nachon F
Ref : Journal of the American Chemical Society , 130 :16011 , 2008
Abstract : Human butyrylcholinesterase (hBChE) hydrolyzes or scavenges a wide range of toxic esters, including heroin, cocaine, carbamate pesticides, organophosphorus pesticides, and nerve agents. Organophosphates (OPs) exert their acute toxicity through inhibition of acetylcholinesterase (AChE) by phosphorylation of the catalytic serine. Phosphylated cholinesterase (ChE) can undergo a spontaneous, time-dependent process called "aging", during which the OP-ChE conjugate is dealkylated. This leads to irreversible inhibition of the enzyme. The inhibition of ChEs by tabun and the subsequent aging reaction are of particular interest, because tabun-ChE conjugates display an extraordinary resistance toward most current oxime reactivators. We investigated the structural basis of oxime resistance for phosphoramidated ChE conjugates by determining the crystal structures of the non-aged and aged forms of hBChE inhibited by tabun, and by updating the refinement of non-aged and aged tabun-inhibited mouse AChE (mAChE). Structures for non-aged and aged tabun-hBChE were refined to 2.3 and 2.1 A, respectively. The refined structures of aged ChE conjugates clearly show that the aging reaction proceeds through O-dealkylation of the P(R) enantiomer of tabun. After dealkylation, the negatively charged oxygen forms a strong salt bridge with protonated His438N epsilon2 that prevents reactivation. Mass spectrometric analysis of the aged tabun-inhibited hBChE showed that both the dimethylamine and ethoxy side chains were missing from the phosphorus. Loss of the ethoxy is consistent with the crystallography results. Loss of the dimethylamine is consistent with acid-catalyzed deamidation during the preparation of the aged adduct for mass spectrometry. The reported 3D data will help in the design of new oximes capable of reactivating tabun-ChE conjugates.
ESTHER : Carletti_2008_J.Am.Chem.Soc_130_16011
PubMedSearch : Carletti_2008_J.Am.Chem.Soc_130_16011
PubMedID: 18975951
Gene_locus related to this paper: human-BCHE , mouse-ACHE

Title : Novel nerve-agent antidote design based on crystallographic and mass spectrometric analyses of tabun-conjugated acetylcholinesterase in complex with antidotes - Ekstrom_2007_Clin.Pharmacol.Ther_82_282
Author(s) : Ekstrom F , Astot C , Pang YP
Ref : Clinical Pharmacology & Therapeutics , 82 :282 , 2007
Abstract : 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 HLo-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.
ESTHER : Ekstrom_2007_Clin.Pharmacol.Ther_82_282
PubMedSearch : Ekstrom_2007_Clin.Pharmacol.Ther_82_282
PubMedID: 17443135
Gene_locus related to this paper: mouse-ACHE

Title : 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 - Hornberg_2007_Biochemistry_46_4815
Author(s) : Hornberg A , Tunemalm AK , Ekstrom F
Ref : Biochemistry , 46 :4815 , 2007
Abstract : Organophosphorus compounds (OPs), such as nerve agents and a group of insecticides, irreversibly inhibit the enzyme acetylcholinesterase (AChE) by a rapid phosphorylation of the catalytic Ser203 residue. The formed AChE-OP conjugate subsequently undergoes an elimination reaction, termed aging, that results in an enzyme completely resistant to oxime-mediated reactivation by medical antidotes. In this study, we present crystal structures of the non-aged and aged complexes between Mus musculus AChE (mAChE) and the nerve agents sarin, VX, and diisopropyl fluorophosphate (DFP) and the OP-based insecticides methamidophos (MeP) and fenamiphos (FeP). Non-aged conjugates of MeP, sarin, and FeP and aged conjugates of MeP, sarin, and VX are very similar to the noninhibited apo conformation of AChE. A minor structural change in the side chain of His447 is observed in the non-aged conjugate of VX. In contrast, an extensive rearrangement of the acyl loop region (residues 287-299) is observed in the non-aged structure of DFP and in the aged structures of DFP and FeP. In the case of FeP, the relatively large substituents of the phosphorus atom are reorganized during aging, providing a structural support of an aging reaction that proceeds through a nucleophilic attack on the phosphorus atom. The FeP aging rate constant is 14 times lower than the corresponding constant for the structurally related OP insecticide MeP, suggesting that tight steric constraints of the acyl pocket loop preclude the formation of a trigonal bipyramidal intermediate.
ESTHER : Hornberg_2007_Biochemistry_46_4815
PubMedSearch : Hornberg_2007_Biochemistry_46_4815
PubMedID: 17402711
Gene_locus related to this paper: mouse-ACHE

Title : Crystal structures of acetylcholinesterase in complex with HI-6, Ortho-7 and obidoxime: structural basis for differences in the ability to reactivate tabun conjugates - Ekstrom_2006_Biochem.Pharmacol_72_597
Author(s) : Ekstrom F , Pang YP , Boman M , Artursson E , Akfur C , Borjegren S
Ref : Biochemical Pharmacology , 72 :597 , 2006
Abstract : Inhibition of acetylcholinesterase (AChE) by organophosphorus compounds (OPs) such as pesticides and nerve agents causes acute toxicity or death of the intoxicated individual. The inhibited AChE may be reactivated by certain oximes as antidotes for clinical treatment of OP-intoxications. Crystal structures of the oximes HI-6, Ortho-7 and obidoxime in complex with Mus musculus acetylcholinesterase (mAChE) reveal different roles of the peripheral anionic site (PAS) in the binding of the oximes. A limited structural change of the side chains of Trp286 and Asp74 facilitates the intercalation of the 4-carboxylamide pyridinium ring of HI-6 between the side chains of Tyr124 and Trp286. The 2-carboxyimino pyridinium ring of HI-6 is accommodated at the entrance of the catalytic site with the oximate forming a hydrogen bond to the main-chain nitrogen atom of Phe295. In contrast to HI-6, the coordination of Ortho-7 and obidoxime within the PAS is facilitated by an extended structural change of Trp286 that allows one of the carboxyimino pyridinium rings to form a cation-pi interaction with the aromatic groups of Tyr72 and Trp286. The central chain of Ortho-7 and obidoxime is loosely coordinated in the active-site gorge, whereas the second carboxyimino pyridinium ring is accommodated in the vicinity of the phenol ring of Tyr337. The structural data clearly show analogous coordination of Ortho-7 and obidoxime within the active-site gorge of AChE. Different ability to reactivate AChE inhibited by tabun is shown in end-point reactivation experiments where HI-6, Ortho-7 and obidoxime showed an efficiency of 1, 45 and 38%, respectively. The low efficiency of HI-6 and the significantly higher efficiency of Ortho-7 and obidoxime may be explained by the differential binding of the oximes in the PAS and active-site gorge of AChE.
ESTHER : Ekstrom_2006_Biochem.Pharmacol_72_597
PubMedSearch : Ekstrom_2006_Biochem.Pharmacol_72_597
PubMedID: 16876764
Gene_locus related to this paper: mouse-ACHE

Title : Structural changes of phenylalanine 338 and histidine 447 revealed by the crystal structures of tabun-inhibited murine acetylcholinesterase - Ekstrom_2006_Biochemistry_45_74
Author(s) : Ekstrom F , Akfur C , Tunemalm AK , Lundberg S
Ref : Biochemistry , 45 :74 , 2006
Abstract : Organophosphorus compounds (OPs) interfere with the catalytic mechanism of acetylcholinesterase (AChE) by rapidly phosphorylating the catalytic serine residue. The inhibited enzyme can at least partly be reactivated with nucleophilic reactivators such as oximes. The covalently attached OP conjugate may undergo further intramolecular dealkylation or deamidation reactions, a process termed "aging" that results in an enzyme considered completely resistant to reactivation. Of particular interest is the inhibition and aging reaction of the OP compound tabun since tabun conjugates display an extraordinary resistance toward most reactivators of today. To investigate the structural basis for this resistance, we determined the crystal structures of Mus musculus AChE (mAChE) inhibited by tabun prior to and after the aging reaction. The nonaged tabun conjugate induces a structural change of the side chain of His447 that uncouples the catalytic triad and positions the imidazole ring of His447 in a conformation where it may form a hydrogen bond to a water molecule. Moreover, an unexpected displacement of the side chain of Phe338 narrows the active site gorge. In the crystal structure of the aged tabun conjugate, the side chains of His447 and Phe338 are reversed to the conformation found in the apo structure of mAChE. A hydrogen bond between the imidazole ring of His447 and the ethoxy oxygen of the aged tabun conjugate stabilizes the side chain of His447. The displacement of the side chain of Phe338 into the active site gorge of the nonaged tabun conjugate may interfere with the accessibility of reactivators and thereby contribute to the high resistance of tabun conjugates toward reactivation.
ESTHER : Ekstrom_2006_Biochemistry_45_74
PubMedSearch : Ekstrom_2006_Biochemistry_45_74
PubMedID: 16388582
Gene_locus related to this paper: mouse-ACHE