Bacterial Expression of Human Butyrylcholinesterase as a Tool for Nerve Agent Bioscavengers Development

Chronic chlorpyrifos exposure induces oxidative stress, neurological damage, and hepatopancreas enrichment in Chinese mitten crab (Eriocheir sinensis)

The toxic effects of long-term exposure to low doses of chlorpyrifos (CPF) on Eriocheir sinensis were evaluated using acute toxicity tests, transcriptome analyses, and metabolome profiling. Four groups (three replicates per group, 60 crabs)-control (no CPF exposure), high exposure (0.12 mg/L CPF), medium exposure (0.036 mg/L), and low exposure (0.012 mg/L)-were subjected to CPF for 21 days. Tissue damage, antioxidant enzyme activity, transcriptional changes, and metabolic alterations in E. sinensis were analyzed. The results demonstrated that CPF disrupted the regulatory networks of transcription and metabolism in crabs under the experimental concentration conditions, with the severity of effects increasing as the duration of exposure lengthened despite the crabs' efforts to activate key defense mechanisms, such as upregulation of cholinesterase 1-like gene expression, to counteract organophosphorus toxicity and adapt to CPF presence in their environment. Even at low concentrations (0.012 mg/L), neurobehavioral development and the antioxidant kinase system in crabs were impaired, leading to hepatopancreatic tissue lesions that negatively affect their growth and survival rates. Additionally, E. sinensis accumulates significant levels of CPF, which may pose food safety concerns when humans consume them. Therefore, ensuring the rational use of CPF requires maintaining appropriate water concentrations to minimize direct harm to aquatic organisms and indirect impacts on food safety associated with this pesticide.

Effective parallel evaluation of molecular design, expression and bioactivity of novel recombinant butyrylcholinesterase medical countermeasures

Current medical countermeasures (MCMs) for nerve agent poisoning have limited efficacy, and can cause serious adverse effects, prompting the requirement for new broad-spectrum therapeutics. Human plasma-derived butyrylcholinseterase (huBChE) is a promising novel bioscavenger MCM which has shown potential in animal studies, however, is economically prohibitive to manufacture at scale. This study addresses current challenges for the economical production of a bioactive and long-acting recombinant huBChE (rBChE) in mammalian cells by being the first to directly compare novel rBChE design strategies. These include co-expression of a proline rich attachment domain (PRAD) and fusion of BChE with a protein partner. Additionally, a pre-purification screening method developed in this study enables parallel comparison of the expression efficiency, activity and broad-spectrum binding to nerve agents for ten novel rBChE molecular designs. All designed rBChE demonstrated functionality to act as broad-spectrum MCMs to G, V and A series nerve agents. Expression using the ExpiCHO™ Max protocol provided greatest expression levels and activity for all constructs, with most rBChE expressing poorly in Expi293™. Fc- or hSA-fused rBChE significantly outperformed constructs designed to mimic huBChE, including PRAD-BChE, and proved an effective strategy to significantly improve enzyme activity and expression. Choice of protein partner, directionality and the addition of a linker also impacted fusion rBChE activity and expression. Overall, hSA fused rBChE provided greatest expression yield and activity, with BChE-hSA the best performing construct. The purified and characterised BChE-hSA demonstrated similar functionality to huBChE to be inhibited by GD, VX and A-234, supporting the findings of the pre-screening study and validating its capacity to assess and streamline the selection process for rBChE constructs in a cost-effective manner. Collectively, these outcomes contribute to risk mitigation in early-stage development, providing a systematic method to compare rBChE designs and a focus for future development.

Empowering Protein Engineering through Recombination of Beneficial Substitutions

Directed evolution stands as a seminal technology for generating novel protein functionalities, a cornerstone in biocatalysis, metabolic engineering, and synthetic biology. Today, with the development of various mutagenesis methods and advanced analytical machines, the challenge of diversity generation and high-throughput screening platforms is largely solved, and one of the remaining challenges is: how to empower the potential of single beneficial substitutions with recombination to achieve the epistatic effect. This review overviews experimental and computer-assisted recombination methods in protein engineering campaigns. In addition, integrated and machine learning-guided strategies were highlighted to discuss how these recombination approaches contribute to generating the screening library with better diversity, coverage, and size. A decision tree was finally summarized to guide the further selection of proper recombination strategies in practice, which was beneficial for accelerating protein engineering.

Pseudo-irreversible butyrylcholinesterase inhibitors: Structure-activity relationships, computational and crystallographic study of the N-dialkyl O-arylcarbamate warhead

Alongside reversible butyrylcholinesterase inhibitors, a plethora of covalent butyrylcholinesterase inhibitors have been reported in the literature, typically pseudo-irreversible carbamates. For these latter, however, most cases lack full confirmation of their covalent mode of action. Additionally, the available reports regarding the structure-activity relationships of the O-arylcarbamate warhead are incomplete. Therefore, a follow-up on a series of pseudo-irreversible covalent carbamate human butyrylcholinesterase inhibitors and the structure-activity relationships of the N-dialkyl O-arylcarbamate warhead are presented in this study. The covalent mechanism of binding was tested by IC₅₀ time-dependency profiles, and sequentially and increasingly confirmed by kinetic analysis, whole protein LC-MS, and crystallographic analysis. Computational studies provided valuable insights into steric constraints and identified problematic, bulky carbamate warheads that cannot reach and carbamoylate the catalytic Ser198. Quantum mechanical calculations provided further evidence that steric effects appear to be a key factor in determining the covalent binding behaviour of these carbamate cholinesterase inhibitors and their duration of action. Additionally, the introduction of a clickable terminal alkyne moiety into one of the carbamate N-substituents and in situ derivatisation with azide-containing fluorophore enabled fluorescent labelling of plasma human butyrylcholinesterase. This proof-of-concept study highlights the potential of this novel approach and for these compounds to be further developed as clickable molecular probes for investigating tissue localisation and activity of cholinesterases.

Design and production strategies for developing a recombinant butyrylcholinesterase medical countermeasure for Organophosphorus poisoning

Organophosphorus nerve agents represent a serious chemical threat due to their ease of production and scale of impact. The recent use of the nerve agent Novichok has re-emphasised the need for broad-spectrum medical countermeasures (MCMs) to these agents. However, current MCMs are limited. Plasma derived human butyrylcholinesterase (huBChE) is a promising novel bioscavenger MCM strategy, but is prohibitively expensive to isolate from human plasma at scale. Efforts to produce recombinant huBChE (rBChE) in various protein expression platforms have failed to achieve key critical attributes of huBChE such as circulatory half-life. These proteins often lack critical features such as tetrameric structure and requisite post-translational modifications. This review evaluates previous attempts to generate rBChE and assesses recent advances in mammalian cell expression and protein engineering strategies that could be deployed to achieve the required half-life and yield for a viable rBChE MCM. This includes the addition of a proline-rich attachment domain, fusion proteins, post translational modifications, expression system selection and optimised downstream processes. Whilst challenges remain, a combinatorial approach of these strategies demonstrates potential as a technically feasible approach to achieving a bioactive and cost effective bioscavenger MCM.

Insights of conformational dynamics on catalytic activity in the computational stability design of Bacillus subtilis LipA

In protein engineering, the contributions of individual mutations to designed combinatorial mutants are unpredictable. Screening designed mutations that affect enzyme catalytic activity enables evolutions towards efficient activities. Here, Bacillus subtilis LipA (BSLA) was selected as a model protein for thermostabilization designs, and the circular dichroism measurements showed six combinatorial designs with improved stability (from 5.81 °C to 13.61 °C). Based on molecular dynamic simulations, the conformational dynamics of the mutants revealed that mutations alter the populations of conformational states and the increased ensembles of inactive conformations might lead to a reduction in activity. We further demonstrated that the mutations responsible for the reduced enzyme catalytic activity involved a short dynamic correlation path to disturbing the equilibrium conformation of active sites. By removing N82V, which had a close dynamic correlation to the active sites in mutant D3, the redesigned mutant RD3 had an increased activity of 57.6%. By combining computational simulation with experimental verification, this work established that essential sites to counteract the activity-stability trade-off in multipoint combinatorial mutants could be computationally predicted and thus provide a possible strategy by which to indirectly or directly guide protein design.

Computational design and experimental characterisation of a stable human heparanase variant

Heparanase is the only human enzyme known to hydrolyse heparin sulfate and is involved in many important physiological processes. However, it is also unregulated in many disease states, such as cancer, diabetes and Covid-19. It is thus an important drug target, yet the heterologous production of heparanase is challenging and only possible in mammalian or insect expression systems, which limits the ability of many laboratories to study it. Here we describe the computational redesign of heparanase to allow high yield expression in Escherchia coli. This mutated form of heparanase exhibits essentially identical kinetics, inhibition, structure and protein dynamics to the wild type protein, despite the presence of 26 mutations. This variant will facilitate wider study of this important enzyme and contributes to a growing body of literature that shows evolutionarily conserved and functionally neutral mutations can have significant effects on protein folding and expression.

A mutant heparanase that exhibits wild type structure and activity but can be heterologously produced in bacterial protein expression systems.

The structure of natively iodinated bovine thyroglobulin

Thyroglobulin is a homodimeric glycoprotein that is essential for the generation of thyroid hormones in vertebrates. Upon secretion into the lumen of follicles in the thyroid gland, tyrosine residues within the protein become iodinated to produce monoiodotyrosine (MIT) and diiodotyrosine (DIT). A subset of evolutionarily conserved pairs of DIT (and MIT) residues can then engage in oxidative coupling reactions that yield either thyroxine (T4; produced from coupling of a DIT `acceptor' with a DIT `donor') or triiodothyronine (T3; produced from coupling of a DIT acceptor with an MIT donor). Although multiple iodotyrosine residues have been identified as potential donors and acceptors, the specificity and structural context of the pairings (i.e. which donor is paired with which acceptor) have remained unclear. Here, single-particle cryogenic electron microscopy (cryoEM) was used to generate a high-resolution reconstruction of bovine thyroglobulin (2.3 Å resolution in the core region and 2.6 Å overall), allowing the structural characterization of two post-reaction acceptor-donor pairs as well as tyrosine residues modified as MIT and DIT. A substantial spatial separation between donor Tyr149 and acceptor Tyr24 was observed, suggesting that for thyroxine synthesis significant peptide motion is required for coupling at the evolutionarily conserved thyroglobulin amino-terminus.

Organophosphate detoxification by membrane-engineered red blood cells

Biotherapeutics have achieved global economic success due to their high specificity towards their drug targets, providing exceptional safety and efficiency. The ongoing shift away from small molecule drugs towards biotherapeutics heightens the need to further improve the pharmacokinetics of these biological drugs. Three pervasive obstacles that limit the therapeutic capacity of biotherapeutics are proteolytic degradation, circulating half-life, and the development of anti-drug antibodies. These challenges can culminate in limited efficiency and consequently warrant the need for higher drug doses and more frequent administration. We have explored the coupling of biotherapeutics to long-lived and biocompatible red blood cells (RBCs) to address limited pharmacokinetics. Butyrylcholinesterase (BChE), for example, provides prophylactic protection against organophosphate nerve agents (OPNAs), yet the short circulation life of the drug requires extraordinary doses. Herein, we report the rapid and tunable chemical engineering of BChE to RBC membranes to create a cell-based delivery system that retains the enzyme activity and enhances stability. In a three-step process that first pre-modifies BChE with a cell-reactive polymer chain, primes the cells for engineering, and then grafts the conjugates to the cells, we attached over 2 million BChE molecules to the surface of each RBC without diminishing the bioscavenging capacity of the enzyme. Critically, this membrane-engineering approach was cell-tolerated with minimal hemolysis observed. These results provide strong evidence for the ability of engineered RBCs to serve as an enhanced biotherapeutic delivery vehicle. STATEMENT OF SIGNIFICANCE: Organophosphate nerve agents (OPNAs) are one of the most lethal forms of chemical warfare. After exposure to OPNAs, a patient is given life-saving therapeutics, such as atropine and oxime. However, these drugs are limited, and the patient can still suffer from irreparable injuries. Given the toxicity of OPNAs, access to a prophylactic is vital. We have created an enhanced delivery system for prophylactic butyrylcholinesterase (BChE) by engineering this biotherapeutic to the red blood cell (RBC) surface. In three simple steps that first pre-modifies BChE with a cell-reactive polymer, primes the cells for engineering, and then grafts the conjugates to the cells, we attached over 2 million BChE molecules to a single RBC while retaining the enzyme's activity and enhancing its stability.

Community-Wide Experimental Evaluation of the PROSS Stability-Design Method

Recent years have seen a dramatic improvement in protein-design methodology. Nevertheless, most methods demand expert intervention, limiting their widespread adoption. By contrast, the PROSS algorithm for improving protein stability and heterologous expression levels has been successfully applied to a range of challenging enzymes and binding proteins. Here, we benchmark the application of PROSS as a stand-alone tool for protein scientists with no or limited experience in modeling. Twelve laboratories from the Protein Production and Purification Partnership in Europe (P4EU) challenged the PROSS algorithm with 14 unrelated protein targets without support from the PROSS developers. For each target, up to six designs were evaluated for expression levels and in some cases, for thermal stability and activity. In nine targets, designs exhibited increased heterologous expression levels either in prokaryotic and/or eukaryotic expression systems under experimental conditions that were tailored for each target protein. Furthermore, we observed increased thermal stability in nine of ten tested targets. In two prime examples, the human Stem Cell Factor (hSCF) and human Cadherin-Like Domain (CLD12) from the RET receptor, the wild type proteins were not expressible as soluble proteins in E. coli, yet the PROSS designs exhibited high expression levels in E. coli and HEK293 cells, respectively, and improved thermal stability. We conclude that PROSS may improve stability and expressibility in diverse cases, and that improvement typically requires target-specific expression conditions. This study demonstrates the strengths of community-wide efforts to probe the generality of new methods and recommends areas for future research to advance practically useful algorithms for protein science.

A Thermophilic Bacterial Esterase for Scavenging Nerve Agents: A Kinetic, Biophysical and Structural Study

Organophosphorous nerve agents (OPNA) pose an actual and major threat for both military and civilians alike, as an upsurge in their use has been observed in the recent years. Currently available treatments mitigate the effect of the nerve agents, and could be vastly improved by means of scavengers of the nerve agents. Consequently, efforts have been made over the years into investigating enzymes, also known as bioscavengers, which have the potential either to trap or hydrolyze these toxic compounds. We investigated the previously described esterase 2 from Thermogutta terrifontis (TtEst2) as a potential bioscavenger of nerve agents. As such, we assessed its potential against G-agents (tabun, sarin, and cyclosarin), VX, as well as the pesticide paraoxon. We report that TtEst2 is a good bioscavenger of paraoxon and G-agents, but is rather slow at scavenging VX. X-ray crystallography studies showed that TtEst2 forms an irreversible complex with the aforementioned agents, and allowed the identification of amino-acids, whose mutagenesis could lead to better scavenging properties for VX. In conjunction with its cheap production and purification processes, as well as a robust structural backbone, further engineering of TtEst2 could lead to a stopgap bioscavenger useful for in corpo scavenging or skin decontamination.

Counteracting poisoning with chemical warfare nerve agents

Phosphylation of the pivotal enzyme acetylcholinesterase (AChE) by nerve agents (NAs) leads to irreversible inhibition of the enzyme and accumulation of neurotransmitter acetylcholine, which induces cholinergic crisis, that is, overstimulation of muscarinic and nicotinic membrane receptors in the central and peripheral nervous system. In severe cases, subsequent desensitisation of the receptors results in hypoxia, vasodepression, and respiratory arrest, followed by death. Prompt action is therefore critical to improve the chances of victim's survival and recovery. Standard therapy of NA poisoning generally involves administration of anticholinergic atropine and an oxime reactivator of phosphylated AChE. Anticholinesterase compounds or NA bioscavengers can also be applied to preserve native AChE from inhibition. With this review of 70 years of research we aim to present current and potential approaches to counteracting NA poisoning.

PROSS 2: a new server for the design of stable and highly expressed protein variants

Many natural and designed proteins are only marginally stable limiting their usefulness in research and applications. Recently, we described an automated structure and sequence-based design method, called PROSS, for optimizing protein stability and heterologous expression levels that has since been validated on dozens of proteins. Here, we introduce improvements to the method, workflow and presentation, including more accurate sequence analysis, error handling and automated analysis of the quality of the sequence alignment that is used in design calculations. PROSS2 is freely available for academic use at https://pross.weizmann.ac.il.

Enhancing the Butyrylcholinesterase Activity in HEK-293 Cell Line by Dual-Promoter Vector Decorated on Lipofectamine

Purpose

Human butyrylcholinesterase (BChE) serves as a bio scavenger to counteract organophosphate poisoning. It is also a potential drug candidate in several therapeutic fields. Therefore, in the present study, we constructed a new dual-promoter plasmid consisting of Cytomegalovirus (CMV) and human elongation factor 1α (EF-1α) promoters and transfected that into HEK-293 cells using Lipofectamine to enhance the BChE secretion.

Methods

The new dual-promoter construction (pBudCE dual BChE) including two copies of the BChE gene was designed and transfected into cells by liposomal structures. The cloned plasmids were evaluated by enzyme digestion and gel electrophoresis analysis. Experimental groups were categorized into the cells transfected by pBudCE dual BChE (treatment), pCMV (positive control) vectors, and nontransfected cells (negative control). BChE gene expression was evaluated by qRT-PCR and the enzyme activity was assessed using modified Ellman’s method. The freeze-thaw process was carried out for analyzing the stability of the pBudCE dual BChE vector.

Results

Validation examination of the cloned plasmids confirmed the successful cloning process. The gene expression level and Ellman’s method value in pBudCE dual BChE was higher than the other groups. CMV promoter has also increased the enzyme activity, although the difference was not significant compared with the control group. Interestingly, freeze-thaw cycles followed by several passages did not affect the enzyme activity.

Conclusion

The designed construction with CMV and EF-1α promoters could increase BChE gene expression and the activity of the BChE enzyme in HEK-293 cell line. Large-scale production of BChE enzyme can be achieved by using dual-promoter plasmid construction compared to a single-promoter vector to be used in clinical trials.

Practically useful protein-design methods combining phylogenetic and atomistic calculations

Our ability to design new or improved biomolecular activities depends on understanding the sequence-function relationships in proteins. The large size and fold complexity of most proteins, however, obscure these relationships, and protein-optimization methods continue to rely on laborious experimental iterations. Recently, a deeper understanding of the roles of stability-threshold effects and biomolecular epistasis in proteins has led to the development of hybrid methods that combine phylogenetic analysis with atomistic design calculations. These methods enable reliable and even single-step optimization of protein stability, expressibility, and activity in proteins that were considered outside the scope of computational design. Furthermore, ancestral-sequence reconstruction produces insights on missing links in the evolution of enzymes and binders that may be used in protein design. Through the combination of phylogenetic and atomistic calculations, the long-standing goal of general computational methods that can be universally applied to study and optimize proteins finally seems within reach.

Gene therapy delivering a paraoxonase 1 variant offers long-term prophylactic protection against nerve agents in mice

Chemical warfare nerve agents are organophosphorus chemical compounds that induce cholinergic crisis, leaving little or no time for medical intervention to prevent death. The current chemical treatment regimen may prevent death but does not prevent postexposure complications such as brain damage and permanent behavioral abnormalities. In the present study, we have demonstrated an adeno-associated virus 8 (AAV8)-mediated paraoxonase 1 variant IF-11 (PON1-IF11) gene therapy that offers asymptomatic prophylactic protection to mice against multiple lethal doses of G-type chemical warfare nerve agents, namely, tabun, sarin, cyclosarin, and soman, for up to 5 months in mice. A single injection of liver-specific adeno-associated viral particles loaded with PON1-IF11 gene resulted in expression and secretion of recombinant PON1-IF11 in milligram quantities, which has the catalytic power to break down G-type chemical warfare nerve agents into biologically inactive products in vitro and in vivo in rodents. Mice containing milligram concentrations of recombinant PON1-IF11 in their blood displayed no clinical signs of toxicity, as judged by their hematological parameters and serum chemistry profiles. Our study unfolds avenues to develop a one-time application of gene therapy to express a near-natural and circulating therapeutic PON1-IF11 protein that can potentially protect humans against G-type chemical warfare nerve agents for several weeks to months.

Dimerization of human butyrylcholinesterase expressed in bacterium for development of a thermally stable bioscavenger of organophosphorus compounds

Human butyrylcholinesterase (BChE) is a widely distributed plasma enzyme. For decades, numerous research efforts have been directed at engineering BChE as a bioscavenger of organophosphorus insecticides and chemical warfare nerve agents. However, it has been a grand challenge to cost-efficiently produce BChE in large-scale. Recently reported studies have successfully designed a truncated BChE mutant (with amino-acid substitutions on 47 residues that are far away from the catalytic site), denoted as BChE-M47 for convenience, which can be expressed in E. coli without loss of its catalytic activity. In this study, we aimed to dimerize the truncated BChE mutant protein expressed in a prokaryotic system (E. coli) in order to further improve its thermal stability by introducing a pair of cross-subunit disulfide bonds to the BChE-M47 structure. Specifically, the E377C/A516C mutations were designed and introduced to BChE-M47, and the obtained new protein entity, denoted as BChE-M48, with a pair of cross-subunit disulfide bonds indeed exists as a dimer with significantly improved thermostability and unaltered catalytic activity and reactivity compared to BChE-M47. These results provide a new strategy for optimizing protein stability for production in a cost-efficient prokaryotic system. Our enzyme, BChE-M48, has a half-life of almost one week at a 37°C, suggesting that it could be utilized as a highly stable bioscavenger of OP insecticides and chemical warfare nerve agents.

Human umbilical cord perivascular cells: A novel source of the organophosphate antidote butyrylcholinesterase

Human butyrylcholinesterase (BChE) is a well-characterized bioscavenger with significant potential as a prophylactic or post-exposure treatment for organophosphate poisoning. Despite substantial efforts, BChE has proven technically challenging to produce in recombinant systems. Recombinant BChE tends to be insufficiently or incorrectly glycosylated, and consequently exhibits a truncated half-life, compromised activity, or is immunogenic. Thus, expired human plasma remains the only reliable source of the benchmark BChE tetramer, but production is costly and time intensive and presents possible blood-borne disease hazards. Here we report a human BChE production platform that produces functionally active, tetrameric BChE enzyme, without the addition of external factors such as polyproline peptides or chemical or gene modification required by other systems. Human umbilical cord perivascular cells (HUCPVCs) are a rich population of mesenchymal stromal cells (MSCs) derived from Wharton's jelly. We show that HUCPVCs naturally and stably secrete BChE during culture in xeno- and serum-free media, and can be gene-modified to increase BChE output. However, BChE secretion from HUCPVCs is limited by innate feedback mechanisms that can be interrupted by addition of miR 186 oligonucleotide mimics or by competitive inhibition of muscarinic cholinergic signalling receptors by addition of atropine. By contrast, adult bone marrow-derived mesenchymal stromal cells neither secrete measurable levels of BChE naturally, nor after gene modification. Further work is required to fully characterize and disable the intrinsic ceiling of HUCPVC-mediated BChE secretion to achieve commercially relevant enzyme output. However, HUCPVCs present a unique opportunity to produce both native and strategically engineered recombinant BChE enzyme in a human platform with the innate capacity to secrete the benchmark human plasma form.

Protein engineers turned evolutionists-the quest for the optimal starting point

The advent of laboratory directed evolution yielded a fruitful crosstalk between the disciplines of molecular evolution and bio-engineering. Here, we outline recent developments in both disciplines with respect to how one can identify the best starting points for directed evolution, such that highly efficient and robust tailor-made enzymes can be obtained with minimal optimization. Directed evolution studies have highlighted essential features of engineer-able enzymes: highly stable, mutationally robust enzymes with the capacity to accept a broad range of substrates. Robust, evolvable enzymes can be inferred from the natural sequence record. Broad substrate spectrum relates to conformational plasticity and can also be predicted by phylogenetic analyses and/or by computational design. Overall, an increasingly powerful toolkit is becoming available for identifying optimal starting points including network analyses of enzyme superfamilies and other bioinformatics methods.

Purification of recombinant human butyrylcholinesterase on Hupresin®

Affinity chromatography on procainamide-Sepharose has been an important step in the purification of butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) since its introduction in 1978. The procainamide affinity gel has limitations. In the present report a new affinity gel called Hupresin® was evaluated for its ability to purify truncated, recombinant human butyrylcholinesterase (rHuBChE) expressed in a stably transfected Chinese Hamster Ovary cell line. We present a detailed example of the purification of rHuBChE secreted into 3940 mL of serum-free culture medium. The starting material contained 13,163 units of BChE activity (20.9 mg). rHuBChE was purified to homogeneity in a single step by passage over 82 mL of Hupresin® eluted with 0.1 M tetramethylammonium bromide in 20 mM TrisCl pH 7.5. The fraction with the highest specific activity of 630 units/mg contained 11 mg of BChE. Hupresin® is superior to procainamide-Sepharose for purification of BChE, but is not suitable for purifying native AChE because Hupresin® binds AChE so tightly that AChE is not released with buffers, but is desorbed with denaturing solvents such as 50% acetonitrile or 1% trifluoroacetic acid. Procainamide-Sepharose will continue to be useful for purification of AChE.

Characterization of butyrylcholinesterase from porcine milk

Human butyrylcholinesterase (HuBChE) is under development for use as a pretreatment antidote against nerve agent toxicity. Animals are used to evaluate the efficacy of HuBChE for protection against organophosphorus nerve agents. Pharmacokinetic studies of HuBChE in minipigs showed a mean residence time of 267 h, similar to the half-life of HuBChE in humans, suggesting a high degree of similarity between BChE from 2 sources. Our aim was to compare the biochemical properties of PoBChE purified from porcine milk to HuBChE purified from human plasma. PoBChE hydrolyzed acetylthiocholine slightly faster than butyrylthiocholine, but was sensitive to BChE-specific inhibitors. PoBChE was 50-fold less sensitive to inhibition by DFP than HuBChE and 5-fold slower to reactivate in the presence of 2-PAM. The amino acid sequence of PoBChE determined by liquid chromatography tandem mass spectrometry was 91% identical to HuBChE. Monoclonal antibodies 11D8, mAb2, and 3E8 (HAH 002) recognized both PoBChE and HuBChE. Assembly of 4 identical subunits into tetramers occurred by noncovalent interaction with polyproline-rich peptides in PoBChE as well as in HuBChE, though the set of polyproline-rich peptides in milk-derived PoBChE was different from the set in plasma-derived HuBChE tetramers. It was concluded that the esterase isolated from porcine milk is PoBChE.

Optimization of Cholinesterase-Based Catalytic Bioscavengers Against Organophosphorus Agents

Organophosphorus agents (OPs) are irreversible inhibitors of acetylcholinesterase (AChE). OP poisoning causes major cholinergic syndrome. Current medical counter-measures mitigate the acute effects but have limited action against OP-induced brain damage. Bioscavengers are appealing alternative therapeutic approach because they neutralize OPs in bloodstream before they reach physiological targets. First generation bioscavengers are stoichiometric bioscavengers. However, stoichiometric neutralization requires administration of huge doses of enzyme. Second generation bioscavengers are catalytic bioscavengers capable of detoxifying OPs with a turnover. High bimolecular rate constants (k_cat/K_m > 10⁶ M⁻¹min⁻¹) are required, so that low enzyme doses can be administered. Cholinesterases (ChE) are attractive candidates because OPs are hemi-substrates. Moderate OP hydrolase (OPase) activity has been observed for certain natural ChEs and for G117H-based human BChE mutants made by site-directed mutagenesis. However, before mutated ChEs can become operational catalytic bioscavengers their dephosphylation rate constant must be increased by several orders of magnitude. New strategies for converting ChEs into fast OPase are based either on combinational approaches or on computer redesign of enzyme. The keystone for rational conversion of ChEs into OPases is to understand the reaction mechanisms with OPs. In the present work we propose that efficient OP hydrolysis can be achieved by re-designing the configuration of enzyme active center residues and by creating specific routes for attack of water molecules and proton transfer. Four directions for nucleophilic attack of water on phosphorus atom were defined. Changes must lead to a novel enzyme, wherein OP hydrolysis wins over competing aging reactions. Kinetic, crystallographic, and computational data have been accumulated that describe mechanisms of reactions involving ChEs. From these studies, it appears that introducing new groups that create a stable H-bonded network susceptible to activate and orient water molecule, stabilize transition states (TS), and intermediates may determine whether dephosphylation is favored over aging. Mutations on key residues (L286, F329, F398) were considered. QM/MM calculations suggest that mutation L286H combined to other mutations favors water attack from apical position. However, the aging reaction is competing. Axial direction of water attack is not favorable to aging. QM/MM calculation shows that F329H+F398H-based multiple mutants display favorable energy barrier for fast reactivation without aging.

Hot Spots for Protein Partnerships at the Surface of Cholinesterases and Related α/β Hydrolase Fold Proteins or Domains-A Structural Perspective

The hydrolytic enzymes acetyl- and butyryl-cholinesterase, the cell adhesion molecules neuroligins, and the hormonogenic macromolecule thyroglobulin are a few of the many members of the α/β hydrolase fold superfamily of proteins. Despite their distinctive functions, their canonical subunits, with a molecular surface area of ~20,000 Ų, they share binding patches and determinants for forming homodimers and for accommodating structural subunits or protein partners. Several of these surface regions of high functional relevance have been mapped through structural or mutational studies, while others have been proposed based on biochemical data or molecular docking studies. Here, we review these binding interfaces and emphasize their specificity versus potentially multifunctional character.