Organophosphate Nerve Agents Research Articles

Stimuli-Responsive Pure Protein Organogel Sensors and Biocatalytic Materials.

Utilizing protein chemistry in organic solvents has important biotechnology applications. Typically, organic solvents negatively impact protein structure and function. Immobilizing proteins via cross-links to a support matrix or to other proteins is a common strategy to preserve the native protein function. Recently, we developed methods to fabricate macroscopic responsive pure protein hydrogels by lightly cross-linking the proteins with glutaraldehyde for chemical sensing and enzymatic catalysis applications. The water in the resulting protein hydrogel can be exchanged for organic solvents. The resulting organogel contains pure organic solvents as their mobile phases. The organogel proteins retain much of their native protein function, i.e., protein-ligand binding and enzymatic activity. A stepwise ethylene glycol (EG) solvent exchange was performed to transform these hydrogels into organogels with a very low vapor pressure mobile phase. These responsive organogels are not limited by solvent/mobile phase evaporation. The solvent exchange to pure EG is accompanied by a volume phase transition (VPT) that decreases the organogel volume compared to that of the hydrogel. Our organogel sensor systems utilize shifts in the particle spacing of an attached two-dimensional photonic crystal (2DPC) to report on the volume changes induced by protein-ligand binding. Our 2DPC bovine serum albumin (BSA) organogels exhibit VPT that swell the organogels in response to the BSA binding of charged ligands like ibuprofen and fatty acids. To our knowledge, this is the first report of a pure protein organogel VPT induced by protein-ligand binding. Catalytic protein organogels were also fabricated that utilize the enzyme organophosphorus hydrolase (OPH) to hydrolyze toxic organophosphate (OP) nerve agents. Our OPH organogels retain significant enzymatic activity. The OPH organogel rate of OP hydrolysis is ∼160 times higher than that of un-cross-linked OPH monomers in a 1:1 ethylene glycol/water mixture.

Tuning Butyrylcholinesterase Inactivation and Reactivation by Polymer-Based Protein Engineering.

Organophosphate nerve agents rapidly inhibit cholinesterases thereby destroying the ability to sustain life. Strong nucleophiles, such as oximes, have been used as therapeutic reactivators of cholinesterase‐organophosphate complexes, but suffer from short half‐lives and limited efficacy across the broad spectrum of organophosphate nerve agents. Cholinesterases have been used as long‐lived therapeutic bioscavengers for unreacted organophosphates with limited success because they react with organophosphate nerve agents with one‐to‐one stoichiometries. The chemical power of nucleophilic reactivators is coupled to long‐lived bioscavengers by designing and synthesizing cholinesterase‐polymer‐oxime conjugates using atom transfer radical polymerization and azide‐alkyne “click” chemistry. Detailed kinetic studies show that butyrylcholinesterase‐polymer‐oxime activity is dependent on the electrostatic properties of the polymers and the amount of oxime within the conjugate. The covalent coupling of oxime‐containing polymers to the surface of butyrylcholinesterase slows the rate of inactivation of paraoxon, a model nerve agent. Furthermore, when the enzyme is covalently inhibited by paraoxon, the covalently attached oxime induced inter‐ and intramolecular reactivation. Intramolecular reactivation will open the door to the generation of a new class of nerve agent scavengers that couple the speed and selectivity of biology to the ruggedness and simplicity of synthetic chemicals.

Cloisite Microrobots as Self-Propelling Cleaners for Fast and Efficient Removal of Improvised Organophosphate Nerve Agents

Naturally available microclays are well-known materials with great adsorption capabilities that are available in nature in megatons quantities. On the contrary, artificial nanostructures are often available at high cost via precision manufacturing. Such precision nanomanufacturing is also typically used for fabrication of self-propelled micromotors and nanomachines. Herein, we utilized naturally available Cloisite microclays to fabricate autonomous self-propelled microrobots and demonstrated their excellent performances in pesticide removal due to their excellent adsorption capability. Six different modified Cloisite microrobots were investigated by sputtering their microclays with platinum (Pt) for the fabrication of platinum-Cloisite (Pt-C) microrobots. The obtained microrobots displayed fast velocities (v > 110 μm/s) with fast and efficient enhanced removal of the pesticide fenitrothion, which is also considered as improvised nerve agent. The fabricated Pt-C microrobots exhibited low cytotoxicity even at high concentrations when incubated with human lung carcinoma epithelial cells, which make them safe for human handling.

Antiseizure and neuroprotective effects of delayed treatment with midazolam in a rodent model of organophosphate exposure.

Exposure to organophosphates (OPs) and OP nerve agents (NAs) causes status epilepticus (SE) and irreversible brain damage. Rapid control of seizure activity is important to minimize neuronal injury and the resulting neurological and behavioral disorders; however, early treatment will not be possible after mass release of OPs or NAs. We utilized a delayed-treatment model of OP exposure in adult rats by administration of diisopropyl fluorophosphate (DFP) to study the relationship between the antiseizure and neuroprotective effects of the "standard-of-care" benzodiazepine, midazolam (MDZ), when given at 30, 60, and 120minutes after SE onset. After electroencephalography (EEG) recordings, neural damage in serial brain sections was studied with Fluoro-Jade B staining. MDZ-induced seizure suppression was equivalent in magnitude regardless of treatment delay (ie, seizure duration). When assessed globally (ie, normalized across 10 different brain regions) for each treatment delay, MDZ administration resulted in only nonsignificant reductions in neuronal death. However, when data for MDZ treatment were combined from all three delay times, a small but significant reduction in global neuronal death was detected when compared to vehicle treatment, which indicated that the substantive MDZ-induced seizure suppression led to only a small reduction in neuronal death. In conclusion, MDZ significantly reduced DFP-induced SE intensity when treatment was delayed 30, 60, and even up to 120minutes; however, this reduction in seizure intensity had no detectable effect on neuronal death at each individual delay time. These data show that although MDZ suppressed seizures, additional neuroprotective therapies are needed to mitigate the effects of OP exposure.

Epigenetic and autophagic changes after nerve agent exposure in the rat piriform cortex and hippocampus

The detrimental effects of organophosphate (OP) nerve agents have been reported but the mechanisms mediating these multiple effects are not well understood. Recent use of nerve agents in Syria and the UK illustrate their continuous threat to the modern world. Epigenetic and autophagy studies are useful to address the issues related to regulation of gene and protein expression by which nerve agents could impact on human health. These studies help to understand molecular mechanisms underlying the multiple neurotoxic effects of nerve agents. In the present study, changes in epigenetic (global DNA methylation and histone acetylation) and autophagic marker proteins were studied in the nerve agent sensitive rat brain areas (piriform cortex and hippocampus) after soman (1xLD50) exposure. Global DNA methylation analysis revealed that nerve agent induced hypomethylation in the brain regions at 1 and 7 days post exposure. In contrast, DNA hypermethylation was observed at 30 days post soman exposure, demonstrating a possible compensatory mechanism. Western blot analysis showed significant increase in the histone acetylation levels after soman exposure in the piriform cortex and hippocampus. The present study observed the changes in autophagic proteins of nerve agent poisoning for the first time to the best of our knowledge. Immunoreactivity levels of autophagic proteins (LC3-II, ATG-5 and p62) were transiently increased in the rat piriform cortex and hippocampus after soman exposure. In conclusion, this study provides insight into the epigenetic and autophagic changes in the brain following soman exposure and their possible role in the neuronal damage and development of multiple neurological effects.

Time dependent dual effect of anti-inflammatory treatments on sarin-induced brain inflammation: Suggested role of prostaglandins

A common consequence of exposure to organophosphate nerve agents is the centrally mediated seizure activity that appears even after conventional treatment with atropine and oximes. We have previously demonstrated a major inflammatory response with subsequent brain damage which was correlated with the duration of the sarin-induced seizures (Chapman et al., 2006). In the present work seizures were induced by the nerve agent sarin (1.2 LD50) insufficiently treated 1 min later by atropine and trimedoxime bromide (TA), with additional midazolam treatment either 5 or 30 min after continuous seizure activity. The efficacy of both steroidal and nonsteroidal anti-inflammatory drugs (NSAIDs), as well as other drugs that were reported as beneficial in neuroprotection, were evaluated for their contribution as adjunct treatment against sarin induced seizures and the ensuing inflammatory brain damage. Results show that both steroids and NSAIDs were harmful when administered during convulsions, and steroids were at best ineffective if administered at their termination. However, if administered at termination of convulsions, the NSAID ibuprofen, the selective COX 2 inhibitor nimesulide and the PLA2 inhibitor quinacrine were partially effective in reducing brain inflammatory markers. Administration of exogenous analogs of prostaglandins (PGE2) immediately following sarin-induced convulsions was found to have a beneficial effect in reducing brain inflammatory markers measured at 24 h and one week post sarin exposure. These findings support the hypothesis that elevated levels of PGE2 have a beneficial role immediately following sarin induced seizures, and that early inhibition of PGE2 production by both steroids and NSAID is contraindicative.

The structural and biochemical impacts of monomerizing human acetylcholinesterase.

Serving a critical role in neurotransmission, human acetylcholinesterase (hAChE) is the target of organophosphate nerve agents. Hence, there is an active interest in studying the mechanism of inhibition and recovery of enzymatic activity, which could lead to better countermeasures against nerve agents. As hAChE is found in different oligomeric assemblies, certain approaches to studying it have been problematic. Herein, we examine the biochemical and structural impact of monomerizing hAChE by using two mutations: L380R/F535K. The activities of monomeric hAChE L380R/F535K and dimeric hAChE were determined to be comparable utilizing a modified Ellman's assay. To investigate the influence of subunit–subunit interactions on the structure of hAChE, a 2.1 Å X‐ray crystallographic structure was determined. Apart from minor shifts along the dimer interface, the overall structure of the hAChE L380R/F535K mutant is similar to that of dimeric hAChE. To probe whether the plasticity of the active site was overtly impacted by monomerizing hAChE, the kinetic constants of (PR/S) − VX (ethyl({2‐[bis(propan‐2‐yl)amino]ethyl}sulfanyl)(methyl)phosphinate) inhibition and subsequent rescue of hAChE L380R/F535K activity with HI‐6 (1‐(2′‐hydroxyiminomethyl‐1′‐pyridinium)‐3‐(4′‐carbamoyl‐1‐pyridinium)) were determined and found to be comparable to those of dimeric hAChE. Thus, hAChE L380R/F535K could be used as a substitute for dimeric hAChE when experimentally probing the ability of the hAChE active site to accommodate future nerve agent threats or judge the ability of new therapeutics to access the active site.

Magnetic integrated metal/enzymatic nanoreactor for chemical warfare agent degradation

The combination of metal nanoparticle-catalysts and biocatalysts to perform cascade catalytic strategy is a powerful platform for synthesis or degradation of complex molecules. In this work, an integrated nanoreactor (INR) was successfully prepared via immobilizing organophosphorus hydrolase (OPH) onto porous carbon materials containing Co nanoparticles (C/Co). The C/Co was synthesized conveniently by pyrolysis of a metal-organic framework (MOF) named ZIF-67. This INR can reduce the toxicity of organophosphate nerve agent up to 208-fold by cascade degradation route. In this INR, C/Co not only acts as chemocatalyst but also serves as support for OPH, which allows an easy separation and reuse due to its magnetic properties. Moreover, this INR shows outstanding universal applicability, reusability and stability. With this proof-of-concept, it is foreseeable that the future metal nanoparticles that formed by pyrolyzing MOF will combine more other biocatalysts for perspective applications in more fields.

A long-lasting poison scavenger

Drug Development Nerve agents are neurotoxic compounds found in pesticides and chemical weapons. They act by blocking the transmission of nerve impulses to the muscles, and exposure can be fatal within minutes. Zhang et al. developed a nanoparticle-based bioscavenger that breaks down organophosphate nerve agents into innocuous compounds. Prophylactic treatment of rats and guinea pigs confirmed low immunogenicity and good biodistribution. Treated animals were protected from repeated exposure to the nerve agent sarin over 7 days. This nanoscavenger might thus help prevent nerve-agent poisoning in at-risk subjects. Sci. Transl. Med. 11 , eaau7091 (2019).

Cryo-EM structure of the native butyrylcholinesterase tetramer reveals a dimer of dimers stabilized by a superhelical assembly

The quaternary structures of the cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), are essential for their localization and function. Of practical importance, BChE is a promising therapeutic candidate for intoxication by organophosphate nerve agents and insecticides, and for detoxification of addictive substances. Efficacy of the recombinant enzyme hinges on its having a long circulatory half-life; this, in turn, depends strongly on its ability to tetramerize. Here, we used cryoelectron microscopy (cryo-EM) to determine the structure of the highly glycosylated native BChE tetramer purified from human plasma at 5.7 Å. Our structure reveals that the BChE tetramer is organized as a staggered dimer of dimers. Tetramerization is mediated by assembly of the C-terminal tryptophan amphiphilic tetramerization (WAT) helices from each subunit as a superhelical assembly around a central lamellipodin-derived oligopeptide with a proline-rich attachment domain (PRAD) sequence that adopts a polyproline II helical conformation and runs antiparallel. The catalytic domains within a dimer are asymmetrically linked to the WAT/PRAD. In the resulting arrangement, the tetramerization domain is largely shielded by the catalytic domains, which may contribute to the stability of the human BChE (HuBChE) tetramer. Our cryo-EM structure reveals the basis for assembly of the native tetramers and has implications for the therapeutic applications of HuBChE. This mode of tetramerization is seen only in the cholinesterases but may provide a promising template for designing other proteins with improved circulatory residence times.

Polymer-Bound 4-Pyridyl-5-hydroxyethyl-thiazole Fluorescent Chemosensors for the Detection of Organophosphate Nerve Agent Simulants.

Fluorescent sensors have been synthesized for organophosphate nerve agent detection. The resulting 4-pyridyl-5-hydroxyethyl structures react with organophosphate nerve agent simulants such as diethylchlorophosphate and diisopropylfluorophosphate and cyclize to form a dihydroquinolizinium ring that results in an increased fluorescence response to long-wave UV excitation. These sensors have been functionalized with monomeric substitutions that allow for covalent incorporation into a polymer matrix for organophosphate detection to develop a fieldable sensor. In addition, inclusion of silicon dioxide into the polymer matrix eliminated false-positive responses from mineral acids, greatly advancing this class of sensors.

Purification and site-specific N-glycosylation analysis of human recombinant butyrylcholinesterase from Nicotiana benthamiana

Butyrylcholinesterase (BChE) is a glycosylated serine hydrolase found in human serum that has been shown to protect against various cholinesterase-inhibiting organophosphate nerve agents. The supply of plasma-derived butyrylcholinesterase (hBChE) is constrained by the availability of human blood and a complex purification process and its high cost. This constraints necessitates the development of expression platforms capable of large-scale, low-cost production of an active recombinant BChE (rBChE). Traditionally, procainamide affinity chromatography has been used to purify BChE. Recently, an effective affinity chromatography resin based on a potent cholinesterase inhibitor (tacrine-huperzine A hybrid; huperine X termed as Hupresin®) was developed. Here, we describe a purification scheme of rBChE from Nicotiana benthamiana plants. Different extraction buffers were screened for their ability to extract rBChE and native plant proteins. Citrate buffer at pH 4 was selected to minimize extraction of host plant proteins and showed a 4.5-fold enhancement in rBChE specific activity compared to Tris buffer, pH 8. DEAE-Sepharose chromatography increased the purity of rBChE by 70% by removing major host plant protein impurities. The rBChE was then adsorbed to Hupresin® and purified to homogeneity for an overall process yield of 34%. The purification process represents a threefold higher product yield over the established process. Mass spectrometry confirmed the protein sequence and site-specific N-glycosylation analysis was performed.

Automated Design of Efficient and Functionally Diverse Enzyme Repertoires

Substantial improvements in enzyme activity demand multiple mutations at spatially proximal positions in the active site. Such mutations, however, often exhibit unpredictable epistatic (non-additive) effects on activity. Here we describe FuncLib, an automated method for designing multipoint mutations at enzyme active sites using phylogenetic analysis and Rosetta design calculations. We applied FuncLib to two unrelated enzymes, a phosphotriesterase and an acetyl-CoA synthetase. All designs were active, and most showed activity profiles that significantly differed from the wild-type and from one another. Several dozen designs with only 3-6 active-site mutations exhibited 10- to 4,000-fold higher efficiencies with a range of alternative substrates, including hydrolysis of the toxic organophosphate nerve agents soman and cyclosarin and synthesis of butyryl-CoA. FuncLib is implemented as a web server (http://FuncLib.weizmann.ac.il); it circumvents iterative, high-throughput experimental screens and opens the way to designing highly efficient and diverse catalytic repertoires.

Acute and long-term consequences of exposure to organophosphate nerve agents in humans.

Nerve agents are organophosphate (OP) compounds and among the most powerful poisons known to man. A terrorist attack on civilian or military populations causing mass casualties is a real threat. The OP nerve agents include soman, sarin, cyclosarin, tabun, and VX. The major mechanism of acute toxicity is the irreversible inhibition of acetylcholinesterase. Acetylcholinesterase inhibition results in the accumulation of excessive acetylcholine levels in synapses, leading to progression of toxic signs including hypersecretions, tremors, status epilepticus, respiratory distress, and death. Miosis and rhinorrhea are the most common clinical findings in those individuals acutely exposed to OP nerve agents. Prolonged seizures are responsible for the neuropathology. The brain region that shows the most severe damage is the amygdala, followed by the piriform cortex, hippocampus, cortex, thalamus, and caudate/putamen. Current medical countermeasures are only modestly effective in attenuating the seizures and neuropathology. Anticonvulsants such as benzodiazepines decrease seizure activity and improve outcome, but their efficacy depends upon the administration time after exposure to the nerve agent. Administration of benzodiazepines may increase the risk for seizure recurrence. Recent studies document long-term neurologic and behavior deficits, and technological advances demonstrate structural brain changes on magnetic resonance imaging.

Investigation of dried blood sampling with liquid chromatography tandem mass spectrometry to confirm human exposure to nerve agents

A method was developed to detect and quantify organophosphate nerve agent (OPNA) metabolites in dried blood samples. Dried blood spots (DBS) and microsampling devices are alternatives to traditional blood draws, allowing for safe handling, extended stability, reduced shipping costs, and potential self-sampling. DBS and microsamplers were evaluated for precision, accuracy, sensitivity, matrix effects, and extraction recovery following collection of whole blood containing five OPNA metabolites. The metabolites of VX, Sarin (GB), Soman (GD), Cyclosarin (GF), and Russian VX (VR) were quantitated from 5.0 to 500 ng mL−1 with precision of ≤16% and accuracy between 93 and 108% for QC samples with controlled volumes. For unknown spot volumes, OPNA metabolite concentrations were normalized to total blood protein to improve interpretation of nerve agent exposures. This study provides data to support the use of DBS and microsamplers to collect critical exposure samples quickly, safely, and efficiently following large-scale chemical exposure events.

Catalytic degradation of organophosphorous nerve agent simulants by polymer beads@graphene oxide with organophosphorus hydrolase-like activity based on rational design of functional bimetallic nuclear ligand

The degradation of organophosphorous nerve agents is of primary concern due to the severe toxicity of these agents. Based on the active center of organophosphorus hydrolase (OPH), a bimetallic nuclear ligand, (5-vinyl-1,3-phenylene)bis(di(1H-imidazol-2-yl) methanol) (VPIM), was designed and synthesized, which contains four imidazole groups to mimic the four histidines at OPH active center. By grafting VPIM on graphene oxide (GO) surface via polymerization, the VPIM-polymer beads@GO was produced. The obtained OPH mimics has an impressive activity in dephosphorylation reactions (turnover frequency (TOF) towards paraoxon: 2.3 s−1). The synergistic catalytic effect of the bimetallic Zn2+ nuclear center and carboxyl groups on surface of GO possibly contributes to the high hydrolysis on organophosphate substrate. Thus, a biomimetic catalyst for efficient degradation of some organophosphorous nerve agent simulants, such as paraoxon and chlorpyrifos, was prepared by constructing catalytic active sites. The proposed mechanism and general synthetic strategy open new avenues for the engineering of functional GOs for biomimetic catalysts.

Crystallographic studies of human acetylcholinesterase inhibition by organophosphates and reactivation by oximes

Human acetylcholinesterase (hAChE; EC 3.1.1.7) is responsible for degrading neurotransmitter acetylcholine at synapses of the nervous system. Organophosphate (OP) nerve agents and pesticides inactivate hAChE through chemical modifications of the enzyme's active center leading to a life‐threatening increase of acetylcholine (ACh) concentration. Exposure to OPs may be fatal if not treated. The current generation of oxime antidotes is not highly efficient; the rates of nucleophilic reactivation are far slower than the catalytic rate of ACh hydrolysis. Insights into the molecular structures of Torpedo and mammalian AChEs reveal the underlying limitations in enhancing reactivation rates, but limited in their ability to resolve positions of hydrogens important for understanding proton transfer in reactivation of OP‐inhibited AChEs. The only experimental method that can provide this information is macromolecular neutron crystallography.In preparation for the neutron diffraction studies we have obtained several new X‐ray structures of native and phosphonylated (with VX and/or POX) hAChE in complex with oxime reactivators, RS2‐170B and RS‐194B, at 2.15–2.45 Å resolution range. In these complexes the enzyme forms crystals in previously unseen unit cell (a=b=124.3, c=129.1 Å; space group P31) amenable to neutron crystallography. Ternary structures with RS2‐170B reveal that the oxime binds in two conformations to non‐modified and OP‐conjugated active center suggesting that conformational changes can happen inside the active center cavity for this reactivator. In one conformation the oxime moiety extends towards the catalytic Ser203 and could represent reactive orientation of the oxime. Conversely, in our structures RS‐194B binds with the oximate pointing away from Ser203 and towards the entrance to the gorge in the non‐modified active center and the entire molecule is pushed out of the active center to bind in the peripheral site in the VX‐modified structure. POX binding induces significant changes in the acyl pocket loop conformation expelling the weakly binding RS‐194B from the active site gorge completely. This alternation may hinder oxime binding for reactivation.In addition, we have determined the first room temperature (RT) structure of hAChE in complex with the oxime reactivator RS2‐170B at 2.8 Å. Detailed analysis of interactions between the reactivator and the enzyme in both 100K and room‐temperature structures will be presented.Support or Funding InformationSupported by Grant 1U01NS083451 by the COUNTERACT program from NINDSThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Purification, characterization, and N-glycosylation of recombinant butyrylcholinesterase from transgenic rice cell suspension cultures.

Recombinant butyrylcholinesterase produced in a metabolically regulated transgenic rice cell culture (rrBChE) was purified to produce a highly pure (95%), active form of enzyme. The developed downstream process uses common manufacturing friendly operations including tangential flow filtration, anion-exchange chromatography, and affinity chromatography to obtain a process recovery of 42% active rrBChE. The purified rrBChE was then characterized to confirm its comparability to the native human form of the molecule (hBChE). The recombinant and native enzyme demonstrated comparable enzymatic behavior and had an identical amino acid sequence. However, rrBChE differs in that it contains plant-type complex N-glycans, including an α-1,3 linked core fucose, and a β-1,2 xylose, and lacking a terminal sialic acid. Despite this difference, rrBChE is demonstrated to be an effective stoichiometric bioscavenger for five different organophosphorous nerve agents in vitro. Together, the efficient downstream processing scheme and functionality of rrBChE confirm its promise as a cost-effective alternative to hBChE for prophylactic and therapeutic use.

First-Principles Calculations of Sarin Adsorption on Anatase Surfaces

We report density functional theory calculations investigating the adsorption of the organophosphate nerve agent sarin (GB) on clean (101), (001)-(1 × 4), and (001)-(1 × 1) surfaces of anatase titanium dioxide (TiO2). Our calculations show that GB chemisorbs on all three surfaces by the formation of a dative bond between the phosphoryl oxygen and a five-coordinated titanium atom in the surface. The adsorption of GB on the (001)-(1 × 4) and (001)-(1 × 1) surfaces (−45.1 and −34.8 kcal mol–1) is substantially stronger than on the (101) surface (−18.2 kcal mol–1). This could be a result of reactive surface states observed within the TiO2 band gap at the (001) surfaces but not the (101) surface. Our calculations show that the GB adsorption passivates these surface states. GB adsorption also breaks a bridging oxygen bond on both (001) surfaces, leading to a titanyl group that is also predicted to occur in adsorption of the simulant dimethyl methylphosphonate (DMMP) on anatase (001). The ordering of the three a...

An integrated nanocatalyst combining enzymatic and metal-organic framework catalysts for cascade degradation of organophosphate nerve agents.

An integrated nanocatalyst (INC), denoted OPH@MIL-100(Fe), was synthesized by immobilizing a biocatalyst onto a metal-organic framework (MOF)-based catalyst, which can cascadingly degrade organophosphate nerve agents to 4-aminophenol (4-AP) and result in a sharp decrease of their toxicity up to 208-fold.