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Bilkis I, Silman I, Weiner L. Generation of Reactive Oxygen Species by Photosensitizers and their Modes of Action on Proteins. Curr Med Chem 2019; 25:5528-5539. [PMID: 29303072 DOI: 10.2174/0929867325666180104153848] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Revised: 08/11/2017] [Accepted: 08/11/2017] [Indexed: 12/31/2022]
Abstract
In this review, we first survey the mechanisms underlying the chemical modification of amino acid residues in proteins by singlet oxygen elicited by photosensitizers. Singlet oxygen has the capacity to cause widespread chemical damage to cellular proteins. Its use in photodynamic therapy of tumors thus requires the development of methodologies for specific addressing of the photosensitizer to malignant cells while sparing normal tissue. We describe three targeting paradigms for achieving this objective. The first involves the use of a photosensitizer with a high affinity for its target protein; in this case, the photosensitizer is methylene blue for acetylcholinesterase. The second paradigm involves the use of the hydrophobic photosensitizer hypericin, which has the capacity to interact selectively with partially unfolded forms of proteins, including nascent species in rapidly dividing or virus-infected and cancer cells, acting preferentially at membrane interfaces. In this case, partially unfolded molten globule species of acetylcholinesterase serve as the model system. In the third paradigm, the photodynamic approach takes advantage of a general approach in 'state-of-the-art' chemotherapy, by coupling the photosensitizer emodin to a specific peptide hormone, GnRH, which recognizes malignant cells via specific GnRH receptors on their surface.
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Affiliation(s)
- Itzhak Bilkis
- Robert Smith Faculty of Agriculture, Food & Environment, Hebrew University, Rehovot 76 100, Israel
| | - Israel Silman
- Weizmann Institute of Science, Rehovot, 76 100, Israel
| | - Lev Weiner
- Weizmann Institute of Science, Rehovot, 76 100, Israel
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2
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Dafferner AJ, Schopfer LM, Xiao G, Cashman JR, Yerramalla U, Johnson RC, Blake TA, Lockridge O. Immunopurification of Acetylcholinesterase from Red Blood Cells for Detection of Nerve Agent Exposure. Chem Res Toxicol 2017; 30:1897-1910. [PMID: 28892361 PMCID: PMC5646370 DOI: 10.1021/acs.chemrestox.7b00209] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Nerve agents and
organophosphorus pesticides make a covalent bond
with the active site serine of acetylcholinesterase (AChE), resulting
in inhibition of AChE activity and toxic symptoms. AChE in red blood
cells (RBCs) serves as a surrogate for AChE in the nervous system.
Mass spectrometry analysis of adducts on RBC AChE could provide evidence
of exposure. Our goal was to develop a method of immunopurifying human
RBC AChE in quantities adequate for detecting exposure by mass spectrometry.
For this purpose, we immobilized 3 commercially available anti-human
acetylcholinesterase monoclonal antibodies (AE-1, AE-2, and HR2) plus
3 new monoclonal antibodies. The monoclonal antibodies were characterized
for binding affinity, epitope mapping by pairing analysis, and nucleotide
and amino acid sequences. AChE was solubilized from frozen RBCs with
1% (v/v) Triton X-100. A 16 mL sample containing 5.8 μg of RBC
AChE was treated with a quantity of soman model compound that inhibited
50% of the AChE activity. Native and soman-inhibited RBC AChE samples
were immunopurified on antibody–Sepharose beads. The immunopurified
RBC AChE was digested with pepsin and analyzed by liquid chromatography
tandem mass spectrometry on a 6600 Triple-TOF mass spectrometer. The
aged soman-modified PheGlyGluSerAlaGlyAlaAlaSer (FGESAGAAS) peptide
was detected using a targeted analysis method. It was concluded that
all 6 monoclonal antibodies could be used to immunopurify RBC AChE
and that exposure to nerve agents could be detected as adducts on
the active site serine of RBC AChE.
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Affiliation(s)
- Alicia J Dafferner
- Eppley Institute, University of Nebraska Medical Center , Omaha, Nebraska 68198, United States
| | - Lawrence M Schopfer
- Eppley Institute, University of Nebraska Medical Center , Omaha, Nebraska 68198, United States
| | - Gaoping Xiao
- Syd Labs, Inc , Natick, Massachusetts 01760, United States
| | - John R Cashman
- Human BioMolecular Research Institute , 5310 Eastgate Mall, San Diego, California 92121, United States
| | - Udaya Yerramalla
- Precision Antibody , 91330 Red Branch Rd, Columbia, Maryland 21045, United States
| | - Rudolph C Johnson
- Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention , 4770 Buford Highway, Chamblee, Georgia 30341, United States
| | - Thomas A Blake
- Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention , 4770 Buford Highway, Chamblee, Georgia 30341, United States
| | - Oksana Lockridge
- Eppley Institute, University of Nebraska Medical Center , Omaha, Nebraska 68198, United States
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Silman I, Sussman JL. Recent developments in structural studies on acetylcholinesterase. J Neurochem 2017; 142 Suppl 2:19-25. [PMID: 28503857 DOI: 10.1111/jnc.13992] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This review focuses on several recent developments concerning structure-function relationships in vertebrate acetylcholinesterase. These include studies on high-resolution structures of human acetylcholinesterase and its complexes; the first crystal structure of a snake venom acetylcholinesterase, in which open and closed states of the 'back door' are visualized; a powerful algorithm for redesigning proteins for enhanced expression in prokaryotic systems, as applied to human acetylcholinesterase, which has hitherto been an intractable target; in situ implementation of 'click chemistry' in crystalline acetylcholinesterase, which yields novel insights into the steric and dynamic changes involved in the reaction within the active-site gorge; and a study that demonstrates the effect of crystallization conditions on ligand alignment within a protein complex, in this case the methylene blue-Torpedo californica acetylcholinesterase complex, which highlights the relevance of the precipitant employed to structure-based drug design. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.
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Affiliation(s)
- Israel Silman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
| | - Joel L Sussman
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
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Dym O, Song W, Felder C, Roth E, Shnyrov V, Ashani Y, Xu Y, Joosten RP, Weiner L, Sussman JL, Silman I. The impact of crystallization conditions on structure-based drug design: A case study on the methylene blue/acetylcholinesterase complex. Protein Sci 2016; 25:1096-114. [PMID: 26990888 DOI: 10.1002/pro.2923] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 03/07/2016] [Indexed: 11/05/2022]
Abstract
Structure-based drug design utilizes apoprotein or complex structures retrieved from the PDB. >57% of crystallographic PDB entries were obtained with polyethylene glycols (PEGs) as precipitant and/or as cryoprotectant, but <6% of these report presence of individual ethyleneglycol oligomers. We report a case in which ethyleneglycol oligomers' presence in a crystal structure markedly affected the bound ligand's position. Specifically, we compared the positions of methylene blue and decamethonium in acetylcholinesterase complexes obtained using isomorphous crystals precipitated with PEG200 or ammonium sulfate. The ligands' positions within the active-site gorge in complexes obtained using PEG200 are influenced by presence of ethyleneglycol oligomers in both cases bound to W84 at the gorge's bottom, preventing interaction of the ligand's proximal quaternary group with its indole. Consequently, both ligands are ∼3.0Å further up the gorge than in complexes obtained using crystals precipitated with ammonium sulfate, in which the quaternary groups make direct π-cation interactions with the indole. These findings have implications for structure-based drug design, since data for ligand-protein complexes with polyethylene glycol as precipitant may not reflect the ligand's position in its absence, and could result in selecting incorrect drug discovery leads. Docking methylene blue into the structure obtained with PEG200, but omitting the ethyleneglycols, yields results agreeing poorly with the crystal structure; excellent agreement is obtained if they are included. Many proteins display features in which precipitants might lodge. It will be important to investigate presence of precipitants in published crystal structures, and whether it has resulted in misinterpreting electron density maps, adversely affecting drug design.
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Affiliation(s)
- Orly Dym
- Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot, 76100, Israel.,Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Wanling Song
- CAS Key Laboratory of Receptor Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai (22), China
| | - Clifford Felder
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Esther Roth
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Valery Shnyrov
- Department of Biochemistry and Molecular Biology, Universidad de Salamanca, Salamanca, 37007, Spain
| | - Yacov Ashani
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Yechun Xu
- CAS Key Laboratory of Receptor Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences (CAS), Shanghai (22), China
| | - Robbie P Joosten
- Department of Biochemistry, Netherlands Cancer Institute, Amsterdam, CX, 1066, the Netherlands
| | - Lev Weiner
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Joel L Sussman
- Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot, 76100, Israel.,Department of Structural Biology, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - Israel Silman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, 76100, Israel
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Ehrenshaft M, Deterding LJ, Mason RP. Tripping up Trp: Modification of protein tryptophan residues by reactive oxygen species, modes of detection, and biological consequences. Free Radic Biol Med 2015; 89:220-8. [PMID: 26393422 PMCID: PMC4684788 DOI: 10.1016/j.freeradbiomed.2015.08.003] [Citation(s) in RCA: 96] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 08/07/2015] [Accepted: 08/08/2015] [Indexed: 01/22/2023]
Abstract
Proteins comprise a majority of the dry weight of a cell, rendering them a major target for oxidative modification. Oxidation of proteins can result in significant alterations in protein molecular mass such as breakage of the polypeptide backbone and/or polymerization of monomers into dimers, multimers, and sometimes insoluble aggregates. Protein oxidation can also result in structural changes to amino acid residue side chains, conversions that have only a modest effect on protein size but can have widespread consequences for protein function. There are a wide range of rate constants for amino acid reactivity, with cysteine, methionine, tyrosine, phenylalanine, and tryptophan having the highest rate constants with commonly encountered biological oxidants. Free tryptophan and tryptophan protein residues react at a diffusion-limited rate with hydroxyl radical and also have high rate constants for reactions with singlet oxygen and ozone. Although oxidation of proteins in general and tryptophan residues specifically can have effects detrimental to the health of cells and organisms, some modifications are neutral, whereas others contribute to the function of the protein in question or may act as a signal that damaged proteins need to be replaced. This review provides a brief overview of the chemical mechanisms by which tryptophan residues become oxidized, presents both the strengths and the weaknesses of some of the techniques used to detect these oxidative interactions, and discusses selected examples of the biological consequences of tryptophan oxidation in proteins from animals, plants, and microbes.
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Affiliation(s)
- Marilyn Ehrenshaft
- Immunity, Inflammation and Disease Laboratory and National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
| | - Leesa J Deterding
- Epigenetics and Stem Cell Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Ronald P Mason
- Immunity, Inflammation and Disease Laboratory and National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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Silman I, Roth E, Paz A, Triquigneaux MM, Ehrenshaft M, Xu Y, Shnyrov VL, Sussman JL, Deterding LJ, Ashani Y, Mason RP, Weiner L. The specific interaction of the photosensitizer methylene blue with acetylcholinesterase provides a model system for studying the molecular consequences of photodynamic therapy. Chem Biol Interact 2013; 203:63-6. [PMID: 23159732 PMCID: PMC11326041 DOI: 10.1016/j.cbi.2012.10.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 10/22/2012] [Accepted: 10/30/2012] [Indexed: 11/22/2022]
Abstract
The photosensitizer, methylene blue (MB), generates singlet oxygen ((1)O2) that irreversibly inhibits Torpedo californica acetylcholinesterase (TcAChE). In the dark MB inhibits reversibly, binding being accompanied by a bathochromic shift that can be used to show its displacement by other reversible inhibitors binding to the catalytic 'anionic' subsite (CAS), the peripheral 'anionic' subsite (PAS), or bridging them. Data concerning both reversible and irreversible inhibition are here reviewed. MB protects TcAChE from thermal denaturation, and differential scanning calorimetry reveals a ~8 °C increase in the denaturation temperature. The crystal structure of the MB/TcAChE complex reveals a single MB stacked against W279 in the PAS, pointing down the gorge towards the CAS. The intrinsic fluorescence of the irreversibly inhibited enzyme displays new emission bands that can be ascribed to N'-formylkynurenine (NFK); this was indeed confirmed using anti-NFK antibodies. Mass spectroscopy revealed that two Trp residues, Trp84 in the CAS, and Trp279 in the PAS, were the only Trp residues, out of a total of 14, significantly modified by photo-oxidation, both being converted to NFK. In the presence of competitive inhibitors that displace MB from the gorge, their modification is completely prevented. Thus, photo-oxidative damage caused by MB involves targeted release of (1)O2 by the bound photosensitizer within the aqueous milieu of the active-site gorge.
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Affiliation(s)
- Israel Silman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel.
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Targeted oxidation of Torpedo californica acetylcholinesterase by singlet oxygen: identification of N-formylkynurenine tryptophan derivatives within the active-site gorge of its complex with the photosensitizer methylene blue. Biochem J 2013; 448:83-91. [PMID: 22888904 DOI: 10.1042/bj20120992] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The principal role of AChE (acetylcholinesterase) is termination of impulse transmission at cholinergic synapses by rapid hydrolysis of the neurotransmitter acetylcholine. The active site of AChE is near the bottom of a long and narrow gorge lined with aromatic residues. It contains a CAS (catalytic 'anionic' subsite) and a second PAS (peripheral 'anionic' site), the gorge mouth, both of which bind acetylcholine via π-cation interactions, primarily with two conserved tryptophan residues. It was shown previously that generation of (1)O(2) by illumination of MB (Methylene Blue) causes irreversible inactivation of TcAChE (Torpedo californica AChE), and suggested that photo-oxidation of tryptophan residues might be responsible. In the present study, structural modification of the TcAChE tryptophan residues induced by MB-sensitized oxidation was investigated using anti-N-formylkynurenine antibodies and MS. From these analyses, we determined that N-formylkynurenine derivatives were specifically produced from Trp(84) and Trp(279), present at the CAS and PAS respectively. Peptides containing these two oxidized tryptophan residues were not detected when the competitive inhibitors, edrophonium and propidium (which should displace MB from the gorge) were present during illumination, in agreement with their efficient protection against the MB-induced photo-inactivation. Thus the bound MB elicited selective action of (1)O(2) on the tryptophan residues facing on to the water-filled active-site gorge. The findings of the present study thus demonstrate the localized action and high specificity of MB-sensitized photo-oxidation of TcAChE, as well as the value of this enzyme as a model system for studying the mechanism of action and specificity of photosensitizing agents.
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Tacal O, Li B, Lockridge O, Schopfer LM. Resistance of human butyrylcholinesterase to methylene blue-catalyzed photoinactivation; mass spectrometry analysis of oxidation products. Photochem Photobiol 2012; 89:336-48. [PMID: 23136924 DOI: 10.1111/php.12016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Accepted: 10/30/2012] [Indexed: 12/01/2022]
Abstract
Methylene blue, 3, 7-bis(dimethylamino)-phenothiazin-5-ium chloride, is a reversible inhibitor of human butyrylcholinesterase (BChE) in the absence of light. In the presence of light and oxygen, methylene blue promotes irreversible inhibition of human BChE as a function of time, requiring 3 h irradiation to inhibit 95% activity. Inactivation was accompanied by a progressive loss of Coomassie-stained protein bands on native and denaturing polyacrylamide gels, suggesting backbone fragmentation. Aggregation was not detected. MALDI-TOF/TOF mass spectrometry identified oxidized tryptophan (W52, 56, 231, 376, 412, 490, 522), oxidized methionine (M81, 144, 302, 532, 554, 555), oxidized histidine (H214), oxidized proline (P230), oxidized cysteine (C519) and oxidized serine (S215). A 20 min irradiation in the presence of methylene blue resulted in 17% loss of BChE activity, suggesting that BChE is relatively resistant to methylene blue-catalyzed photoinactivation and that therefore this process could be used to sterilize BChE preparations.
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Affiliation(s)
- Ozden Tacal
- Department of Biochemistry, School of Pharmacy, Hacettepe University, Ankara, Turkey
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Paz A, Roth E, Ashani Y, Xu Y, Shnyrov VL, Sussman JL, Silman I, Weiner L. Structural and functional characterization of the interaction of the photosensitizing probe methylene blue with Torpedo californica acetylcholinesterase. Protein Sci 2012; 21:1138-52. [PMID: 22674800 PMCID: PMC3537235 DOI: 10.1002/pro.2101] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2012] [Revised: 05/16/2012] [Accepted: 05/16/2012] [Indexed: 11/09/2022]
Abstract
The photosensitizer, methylene blue (MB), generates singlet oxygen that irreversibly inhibits Torpedo californica acetylcholinesterase (TcAChE). In the dark, it inhibits reversibly. Binding is accompanied by a bathochromic absorption shift, used to demonstrate displacement by other acetylcholinesterase inhibitors interacting with the catalytic "anionic" subsite (CAS), the peripheral "anionic" subsite (PAS), or bridging them. MB is a noncompetitive inhibitor of TcAChE, competing with reversible inhibitors directed at both "anionic" subsites, but a single site is involved in inhibition. MB also quenches TcAChE's intrinsic fluorescence. It binds to TcAChE covalently inhibited by a small organophosphate (OP), but not an OP containing a bulky pyrene. Differential scanning calorimetry shows an ~8° increase in the denaturation temperature of the MB/TcAChE complex relative to native TcAChE, and a less than twofold increase in cooperativity of the transition. The crystal structure reveals a single MB stacked against Trp279 in the PAS, oriented down the gorge toward the CAS; it is plausible that irreversible inhibition is associated with photooxidation of this residue and others within the active-site gorge. The kinetic and spectroscopic data showing that inhibitors binding at the CAS can impede binding of MB are reconciled by docking studies showing that the conformation adopted by Phe330, midway down the gorge, in the MB/TcAChE crystal structure, precludes simultaneous binding of a second MB at the CAS. Conversely, binding of ligands at the CAS dislodges MB from its preferred locus at the PAS. The data presented demonstrate that TcAChE is a valuable model for understanding the molecular basis of local photooxidative damage.
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Affiliation(s)
- Aviv Paz
- Department of Neurobiology, Weizmann Institute of ScienceRehovot 76100, Israel
- Department of Structural Biology, Weizmann Institute of ScienceRehovot 76100, Israel
| | - Esther Roth
- Department of Neurobiology, Weizmann Institute of ScienceRehovot 76100, Israel
| | - Yacov Ashani
- Department of Neurobiology, Weizmann Institute of ScienceRehovot 76100, Israel
| | - Yechun Xu
- Department of Neurobiology, Weizmann Institute of ScienceRehovot 76100, Israel
- Department of Structural Biology, Weizmann Institute of ScienceRehovot 76100, Israel
| | - Valery L Shnyrov
- Department of Biochemistry and Molecular Biology, Universidad de SalamancaSalamanca 37007, Spain
| | - Joel L Sussman
- Department of Structural Biology, Weizmann Institute of ScienceRehovot 76100, Israel
| | - Israel Silman
- Department of Neurobiology, Weizmann Institute of ScienceRehovot 76100, Israel
| | - Lev Weiner
- Department of Chemical Research Support, Weizmann Institute of ScienceRehovot 76100, Israel
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Wildman SA, Zheng X, Sept D, Auletta JT, Rosenberry TL, Marshall GR. Drug-like Leads for Steric Discrimination between Substrate and Inhibitors of Human Acetylcholinesterase. Chem Biol Drug Des 2011; 78:495-504. [DOI: 10.1111/j.1747-0285.2011.01157.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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