Purification of transgenic plant-derived recombinant human acetylcholinesterase-R

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.

Plant-expressed cocaine hydrolase variants of butyrylcholinesterase exhibit altered allosteric effects of cholinesterase activity and increased inhibitor sensitivity

Butyrylcholinesterase (BChE) is an enzyme with broad substrate and ligand specificities and may function as a generalized bioscavenger by binding and/or hydrolyzing various xenobiotic agents and toxicants, many of which target the central and peripheral nervous systems. Variants of BChE were rationally designed to increase the enzyme’s ability to hydrolyze the psychoactive enantiomer of cocaine. These variants were cloned, and then expressed using the magnICON transient expression system in plants and their enzymatic properties were investigated. In particular, we explored the effects that these site-directed mutations have over the enzyme kinetics with various substrates of BChE. We further compared the affinity of various anticholinesterases including organophosphorous nerve agents and pesticides toward these BChE variants relative to the wild type enzyme. In addition to serving as a therapy for cocaine addiction-related diseases, enhanced bioscavenging against other harmful agents could add to the practicality and versatility of the plant-derived recombinant enzyme as a multivalent therapeutic.

New biorecognition molecules in biosensors for the detection of toxins

Biological and synthetic recognition elements are at the heart of the majority of modern bioreceptor assays. Traditionally, enzymes and antibodies have been integrated in the biosensor designs as a popular choice for the detection of toxin molecules. But since 1970s, alternative biological and synthetic binders have been emerged as a promising alternative to conventional biorecognition elements in detection systems for laboratory and field-based applications. Recent research has witnessed immense interest in the use of recombinant enzymatic methodologies and nanozymes to circumvent the drawbacks associated with natural enzymes. In the area of antibody production, technologies based on the modification of in vivo synthesized materials and in vitro approaches with development of "display "systems have been introduced in the recent years. Subsequently, molecularly-imprinted polymers and Peptide nucleic acid (PNAs) were developed as an attractive receptor with applications in the area of sample preparation and detection systems. In this article, we discuss all alternatives to conventional biomolecules employed in the detection of various toxin molecules We review recent developments in modified enzymes, nanozymes, nanobodies, aptamers, peptides, protein scaffolds and DNazymes. With the advent of nanostructures and new interface materials, these recognition elements will be major players in future biosensor development.

Plant expression and characterization of the transmission-blocking vaccine candidate PfGAP50

BACKGROUND

Despite the limited success after decades of intensive research and development efforts, vaccination still represents the most promising strategy to significantly reduce the disease burden in malaria endemic regions. Besides the ultimate goal of inducing sterile protection in vaccinated individuals, the prevention of transmission by so-called transmission blocking vaccines (TBVs) is being regarded as an important feature of an efficient malaria eradication strategy. Recently, Plasmodium falciparum GAP50 (PfGAP50), a 44.6 kDa transmembrane protein that forms an essential part of the invasion machinery (glideosome) multi-protein complex, has been proposed as novel potential transmission-blocking candidate. Plant-based expression systems combine the advantages of eukaryotic expression with a up-scaling potential and a good product safety profile suitable for vaccine production. In this study we investigated the feasibility to use the transient plant expression to produce PfGAP50 suitable for the induction of parasite specific inhibitory antibodies.

RESULTS

We performed the transient expression of recombinant PfGAP50 in Nicotiana benthamiana leaves using endoplasmatic reticulum (ER) and plastid targeting. After IMAC-purification the protein yield and integrity was investigated by SDS-PAGE and Western Blot. Rabbit immune IgG derived by the immunization with the plastid-targeted variant of PfGAP50 was analyzed by immune fluorescence assay (IFA) and zygote inhibition assay (ZIA). PfGAP50 could be produced in both subcellular compartments at different yields IMAC (Immobilized Metal Affinity Chromatography) purification from extract yielded up to 4.1 μg/g recombinant protein per fresh leaf material for ER-retarded and16.2 μg/g recombinant protein per fresh leave material for plasmid targeted PfGAP50, respectively. IgG from rabbit sera generated by immunization with the recombinant protein specifically recognized different parasite stages in immunofluorescence assay. Furthermore up to 55 % inhibition in an in vitro zygote inhibition assay could be achieved using PfGAP50-specific rabbit immune IgG.

CONCLUSIONS

The results of this study demonstrate that the plant-produced PfGAP50 is functional regarding the presentation of inhibitory epitopes and could be considered as component of a transmission-blocking malaria vaccine formulation.

Optimization of Ammonium Sulfate Concentration for Purification of Colorectal Cancer Vaccine Candidate Recombinant Protein GA733-FcK Isolated from Plants

A protein purification procedure is required to obtain high-value recombinant injectable vaccine proteins produced in plants as a bioreactor. However, existing purification procedures for plant-derived recombinant proteins are often not optimized and are inefficient, with low recovery rates. In our previous study, we used 25-30% ammonium sulfate to precipitate total soluble proteins (TSPs) in purification process for recombinant proteins from plant leaf biomass which has not been optimized. Thus, the objective in this study is to optimize the conditions for plant-derived protein purification procedures. Various ammonium sulfate concentrations (15-80%) were compared to determine their effects on TSPs yield. With 50% ammonium sulfate, the yield of precipitated TSP was the highest, and that of the plant-derived colorectal cancer-specific surface glycoprotein GA733 fused to the Fc fragment of human IgG tagged with endoplasmic reticulum retention signal KDEL (GA733(P)-FcK) protein significantly increased 1.8-fold. SDS-PAGE analysis showed that the purity of GA733(P)-FcK protein band appeared to be similar to that of an equal dose of mammalian-derived GA733-Fc (GA733(M)-Fc). The binding activity of purified GA733(P)-FcK to anti-GA733 mAb was as efficient as the native GA733(M)-Fc. Thus, the purification process was effectively optimized for obtaining a high yield of plant-derived antigenic protein with good quality. In conclusion, the purification recovery rate of large quantities of recombinant protein from plant expression systems can be enhanced via optimization of ammonium sulfate concentration during downstream processes, thereby offering a promising solution for production of recombinant GA733-Fc protein in plants.

Drug development for the management of organophosphorus poisoning

INTRODUCTION

The continuous application of organophosphate pesticides in developing countries, in addition to the remaining stock piles of chemical warfare nerve agents and their possible use is a significant threat to the public. Yet, today's options for a treatment of organophosphorus poisonings are still inadequate.

AREAS COVERED

This article provides a concise overview of current and future research trying to improve both prophylaxis and treatment of organophosphorus intoxications. The authors provide a summary of current oxime therapy and highlight several new concepts to overcome existing gaps. This overview of therapeutic options is accompanied by two sections on cyclodextrins, related compounds and bioscavengers, which may be used for either prophylaxis or treatment. For both groups, the authors review current drug design and screening approaches, the resulting developments and future challenges.

EXPERT OPINION

While the search for one multipotent oxime has been a fruitless endeavor, combination of multiple oximes with complemental and systemic reactivity appears as a valuable concept. Development of potential scavengers, be it cyclodextrins or bioscavengers, is still hampered by insufficient efficacy of these compounds. Future strategies will aim at improving their catalytic efficacy while minimizing immunogenicity.

Plants as a source of butyrylcholinesterase variants designed for enhanced cocaine hydrolase activity

Cocaine addiction affects millions of people with disastrous personal and social consequences. Cocaine is one of the most reinforcing of all drugs of abuse, and even those who undergo rehabilitation and experience long periods of abstinence have more than 80% chance of relapse. Yet there is no FDA-approved treatment to decrease the likelihood of relapse in rehabilitated addicts. Recent studies, however, have demonstrated a promising potential treatment option with the help of the serum enzyme butyrylcholinesterase (BChE), which is capable of breaking down naturally occurring (-)-cocaine before the drug can influence the reward centers of the brain or affect other areas of the body. This activity of wild-type (WT) BChE, however, is relatively low. This prompted the design of variants of BChE which exhibit significantly improved catalytic activity against (-)-cocaine. Plants are a promising means to produce large amounts of these cocaine hydrolase variants of BChE, cheaply, safely with no concerns regarding human pathogens and functionally equivalent to enzymes derived from other sources. Here, in expressing cocaine-hydrolyzing mutants of BChE in Nicotiana benthamiana using the MagnICON virus-assisted transient expression system, and in reporting their initial biochemical analysis, we provide proof-of-principle that plants can express engineered BChE proteins with desired properties.

Select small core structure carbamates exhibit high contact toxicity to "carbamate-resistant" strain malaria mosquitoes, Anopheles gambiae (Akron)

Acetylcholinesterase (AChE) is a proven target for control of the malaria mosquito (Anopheles gambiae). Unfortunately, a single amino acid mutation (G119S) in An. gambiae AChE-1 (AgAChE) confers resistance to the AChE inhibitors currently approved by the World Health Organization for indoor residual spraying. In this report, we describe several carbamate inhibitors that potently inhibit G119S AgAChE and that are contact-toxic to carbamate-resistant An. gambiae. PCR-RFLP analysis was used to confirm that carbamate-susceptible G3 and carbamate-resistant Akron strains of An. gambiae carry wild-type (WT) and G119S AChE, respectively. G119S AgAChE was expressed and purified for the first time, and was shown to have only 3% of the turnover number (k(cat)) of the WT enzyme. Twelve carbamates were then assayed for inhibition of these enzymes. High resistance ratios (>2,500-fold) were observed for carbamates bearing a benzene ring core, consistent with the carbamate-resistant phenotype of the G119S enzyme. Interestingly, resistance ratios for two oxime methylcarbamates, and for five pyrazol-4-yl methylcarbamates were found to be much lower (4- to 65-fold). The toxicities of these carbamates to live G3 and Akron strain An. gambiae were determined. As expected from the enzyme resistance ratios, carbamates bearing a benzene ring core showed low toxicity to Akron strain An. gambiae (LC(50)>5,000 μg/mL). However, one oxime methylcarbamate (aldicarb) and five pyrazol-4-yl methylcarbamates (4a-e) showed good to excellent toxicity to the Akron strain (LC(50) = 32-650 μg/mL). These results suggest that appropriately functionalized "small-core" carbamates could function as a resistance-breaking anticholinesterase insecticides against the malaria mosquito.

Butyrylcholinesterase interactions with amylin may protect pancreatic cells in metabolic syndrome

The metabolic syndrome (MetS) is a risk factor for type 2 diabetes mellitus (T2DM). However, the mechanisms underlying the transition from MetS to T2DM are unknown. Our goal was to study the potential contribution of butyrylcholinesterase (BChE) to this process. We first determined the hydrolytic activity of BChE in serum from MetS, T2DM and healthy individuals. The ‘Kalow’ variant of BChE (BChE-K), which has been proposed to be a risk factor for T2DM, was genotyped in the last two groups. Our results show that in MetS patients serum BChE activity is elevated compared to T2DM patients and healthy controls (P < 0.001). The BChE-K genotype showed similar prevalence in T2DM and healthy individuals, excluding this genotype as a risk factor for T2DM. However, the activity differences remained unexplained. Previous results from our laboratory have shown BChE to attenuate the formation of β-amyloid fibrils, and protect cultured neurons from their cytotoxicity. Therefore, we next studied the in vitro interactions between recombinant human butyrylcholinesterase and amylin by surface plasmon resonance, Thioflavine T fluorescence assay and cross-linking, and used cultured pancreatic β cells to test protection by BChE from amylin cytotoxicity. We demonstrate that BChE interacts with amylin through its core domain and efficiently attenuates both amylin fibril and oligomer formation. Furthermore, application of BChE to cultured β cells protects them from amylin cytotoxicity. Taken together, our results suggest that MetS-associated BChE increases could protect pancreatic β-cells in vivo by decreasing the formation of toxic amylin oligomers.

Plant-derived human butyrylcholinesterase, but not an organophosphorous-compound hydrolyzing variant thereof, protects rodents against nerve agents

The concept of using cholinesterase bioscavengers for prophylaxis against organophosphorous nerve agents and pesticides has progressed from the bench to clinical trial. However, the supply of the native human proteins is either limited (e.g., plasma-derived butyrylcholinesterase and erythrocytic acetylcholinesterase) or nonexisting (synaptic acetylcholinesterase). Here we identify a unique form of recombinant human butyrylcholinesterase that mimics the native enzyme assembly into tetramers; this form provides extended effective pharmacokinetics that is significantly enhanced by polyethylene glycol conjugation. We further demonstrate that this enzyme (but not a G117H/E197Q organophosphorus acid anhydride hydrolase catalytic variant) can prevent morbidity and mortality associated with organophosphorous nerve agent and pesticide exposure of animal subjects of two model species.

Transgenic plants as a source for the bioscavenging enzyme, human butyrylcholinesterase

Organophosphorous pesticides and nerve agents inhibit the enzyme acetylcholinesterase at neuronal synapses and in neuromuscular junctions. The resulting accumulation of acetylcholine overwhelms regulatory mechanisms, potentially leading to seizures and death from respiratory collapse. While current therapies are only capable of reducing mortality, elevation of the serum levels of the related enzyme butyrylcholinesterase (BChE) by application of the purified protein as a bioscavenger of organophosphorous compounds is effective in preventing all symptoms associated with poisoning by these toxins. However, BChE therapy requires large quantities of enzyme that can easily overwhelm current sources. Here, we report genetic optimization, cloning and high-level expression of human BChE in plants. Plant-derived BChE is shown to be biochemically similar to human plasma-derived BChE in terms of catalytic activity and inhibitor binding. We further demonstrate the ability of the plant-derived bioscavenger to protect animals against an organophosphorous pesticide challenge.

Hairy-root organ cultures for the production of human acetylcholinesterase

BACKGROUND

Human cholinesterases can be used as a bioscavenger of organophosphate toxins used as pesticides and chemical warfare nerve agents. The practicality of this approach depends on the availability of the human enzymes, but because of inherent supply and regulatory constraints, a suitable production system is yet to be identified.

RESULTS

As a promising alternative, we report the creation of "hairy root" organ cultures derived via Agrobacterium rhizogenes-mediated transformation from human acetylcholinesterase-expressing transgenic Nicotiana benthamiana plants. Acetylcholinesterase-expressing hairy root cultures had a slower growth rate, reached to the stationary phase faster and grew to lower maximal densities as compared to wild type control cultures. Acetylcholinesterase accumulated to levels of up to 3.3% of total soluble protein, ~3 fold higher than the expression level observed in the parental plant. The enzyme was purified to electrophoretic homogeneity. Enzymatic properties were nearly identical to those of the transgenic plant-derived enzyme as well as to those of mammalian cell culture derived enzyme. Pharmacokinetic properties of the hairy-root culture derived enzyme demonstrated a biphasic clearing profile. We demonstrate that master banking of plant material is possible by storage at 4 degrees C for up to 5 months.

CONCLUSION

Our results support the feasibility of using plant organ cultures as a successful alternative to traditional transgenic plant and mammalian cell culture technologies.

Increased organophosphate scavenging in a butyrylcholinesterase mutant

Nicotiana benthamiana plant lines expressing a reengineered human butyrylcholinesterase (BChE) with enhanced cocaine hydrolase activity were created. Subsequent purification and biochemical analysis revealed that compared to wild-type butyrylcholinesterase, the cocaine hydrolase displayed increased affinity to the organophosphate (OP) pesticides paraoxon (6.8 4x 10(-10)M vs. 1.11 x 10(-8)M) and malaoxon (9.81 x 10(-8)M vs. 5.99 x 10(-7)M). Furthermore, the cocaine hydrolase retained identical anticholinesterase binding profiles for all other compounds tested. Thus we have demonstrated a potential large-scale production platform for a multivalent antidote for cocaine and anticholinesterase poisoning.

Acetylcholinesterase-R increases germ cell apoptosis but enhances sperm motility

Changes in protein subdomains through alternative splicing often modify protein-protein interactions, altering biological processes. A relevant example is that of the stress-induced up-regulation of the acetylcholinesterase (AChE-R) splice variant, a common response in various tissues. In germ cells of male transgenic TgR mice, AChE-R excess associates with reduced sperm differentiation and sperm counts. To explore the mechanism(s) by which AChE-R up-regulation affects spermatogenesis, we identified AChE-R's protein partners through a yeast two-hybrid screen. In meiotic spermatocytes from TgR mice, we detected AChE-R interaction with the scaffold protein RACK1 and elevated apoptosis. This correlated with reduced scavenging by RACK1 of the pro-apoptotic TAp73, an outcome compatible with the increased apoptosis. In contrast, at later stages in sperm development, AChE-R's interaction with the glycolytic enzyme enolase-α elevates enolase activity. In transfected cells, enforced AChE-R excess increased glucose uptake and adenosine tri-phosphate (ATP) levels. Correspondingly, TgR sperm cells display elevated ATP levels, mitochondrial hyperactivity and increased motility. In human donors' sperm, we found direct association of sperm motility with AChE-R expression. Interchanging interactions with RACK1 and enolase-α may hence enable AChE-R to affect both sperm differentiation and function by participating in independent cellular pathways.

Plant-derived human acetylcholinesterase-R provides protection from lethal organophosphate poisoning and its chronic aftermath

Therapeutically valuable proteins are often rare and/or unstable in their natural context, calling for production solutions in heterologous systems. A relevant example is that of the stress-induced, normally rare, and naturally unstable "read-through" human acetylcholinesterase variant, AChE-R. AChE-R shares its active site with the synaptic AChE-S variant, which is the target of poisonous organophosphate anticholinesterase insecticides such as the parathion metabolite paraoxon. Inherent AChE-R overproduction under organophosphate intoxication confers both short-term protection (as a bioscavenger) and long-term neuromuscular damages (as a regulator). Here we report the purification, characterization, and testing of human, endoplasmic reticulum-retained AChE-R(ER) produced from plant-optimized cDNA in Nicotiana benthamiana plants. AChE-R(ER) purified to homogeneity showed indistinguishable biochemical properties, with IC50 = 10(-7) M for the organophosphate paraoxon, similar to mammalian cell culture-derived AChE. In vivo titration showed dose-dependent protection by intravenously injected AChE-R(ER) of FVB/N male mice challenged with a lethal dose of paraoxon, with complete elimination of short-term clinical symptoms at near molar equivalence. By 10 days postexposure, AChE-R prophylaxis markedly limited postexposure increases in plasma murine AChE-R levels while minimizing the organophosphate-induced neuromuscular junction dismorphology. Our findings present plant-produced AChE-R(ER) as a bimodal agent, conferring both short- and long-term protection from organophosphate intoxication.

Arabidopsis thaliana plants expressing human beta-defensin-2 are more resistant to fungal attack: functional homology between plant and human defensins

Human beta-defensin-2 (hBD-2) is a small antimicrobial peptide with potent activity against different Gram-negative bacteria and fungal/yeast species. Since human beta-defensins and plant defensins share structural homology, we set out to analyse whether there also exists a functional homology between these defensins of different eukaryotic kingdoms. To this end, we constructed a plant transformation vector harbouring the hBD-2 coding sequence, which we transformed to Arabidopsis thaliana plants, giving rise to A. thaliana plants indeed expressing hBD-2. Furthermore, we could demonstrate that this heterologously produced hBD-2 possesses antifungal activity in vitro. Finally, we could show that hBD-2 expressing A. thaliana plants are more resistant against the broad-spectrum fungal pathogen Botrytis cinerea as compared to untransformed A. thaliana plants, and that this resistance is correlated with the level of active hBD-2 produced in these transgenic plants. Hence, we demonstrated a functional homology, next to the already known structural homology, between defensins originating from different eukaryotic kingdoms. To our knowledge, this is the first time that this is specifically demonstrated for plant and mammalian defensins.

Adaptive changes in acetylcholinesterase gene expression as mediators of recovery from chemical and biological insults

Both organophosphate (OP) exposure and bacterial infection notably induce short- and long-term cholinergic responses. These span the central and peripheral nervous system, neuromuscular pathway and hematopoietic cells and involve over-expression of the "readthrough" variant of acetylcholinesterase, AChE-R, and its naturally cleavable C-terminal peptide ARP. However, the causal involvement of these changes with post-exposure recovery as opposed to apoptotic events remained to be demonstrated. Here, we report the establishment of stably transfected cell lines expressing catalytically active human "synaptic" AChE-S or AChE-R which are fully viable and non-apoptotic. In addition, intraperitoneally injected synthetic mouse ARP (mARP) elevated serum AChE levels post-paraoxon exposure. Moreover, mARP treatment ameliorated post-exposure increases in corticosterone and decreases in AChE gene expression and facilitated earlier retrieval of motor activity following both paraoxon and lipopolysaccharide (LPS) exposures. Our findings suggest a potential physiological role for overproduction of AChE-R and the ARP peptide following exposure to both chemical warfare agents and bacterial LPS.