Snake three-finger α-neurotoxins and nicotinic acetylcholine receptors: molecules, mechanisms and medicine

Spike protein-related proteinopathies: A focus on the neurological side of spikeopathies

BACKGROUND

The spike protein (SP) is an outward-projecting transmembrane glycoprotein on viral surfaces. SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), responsible for COVID-19 (Coronavirus Disease 2019), uses SP to infect cells that express angiotensin converting enzyme 2 (ACE2) on their membrane. Remarkably, SP has the ability to cross the blood-brain barrier (BBB) into the brain and cause cerebral damage through various pathomechanisms. To combat the COVID-19 pandemic, novel gene-based products have been used worldwide to induce human body cells to produce SP to stimulate the immune system. This artificial SP also has a harmful effect on the human nervous system.

STUDY DESIGN

Narrative review.

OBJECTIVE

This narrative review presents the crucial role of SP in neurological complaints after SARS-CoV-2 infection, but also of SP derived from novel gene-based anti-SARS-CoV-2 products (ASP).

METHODS

Literature searches using broad terms such as "SARS-CoV-2", "spike protein", "COVID-19", "COVID-19 pandemic", "vaccines", "COVID-19 vaccines", "post-vaccination syndrome", "post-COVID-19 vaccination syndrome" and "proteinopathy" were performed using PubMed. Google Scholar was used to search for topic-specific full-text keywords.

CONCLUSIONS

The toxic properties of SP presented in this review provide a good explanation for many of the neurological symptoms following SARS-CoV-2 infection and after injection of SP-producing ASP. Both SP entities (from infection and injection) interfere, among others, with ACE2 and act on different cells, tissues and organs. Both SPs are able to cross the BBB and can trigger acute and chronic neurological complaints. Such SP-associated pathologies (spikeopathies) are further neurological proteinopathies with thrombogenic, neurotoxic, neuroinflammatory and neurodegenerative potential for the human nervous system, particularly the central nervous system. The potential neurotoxicity of SP from ASP needs to be critically examined, as ASPs have been administered to millions of people worldwide.

Utility of binding protein fusions to immunoglobulin heavy chain constant regions from mammalian and avian species

Antibodies are of central importance as reagents for the localization of proteins and other biomolecules in cells and tissues. To expand the repertoire of antibody-based reagents, we have constructed a series of plasmid vectors that permit expression of amino-terminal fusions to the hinge and Fc regions from goat, guinea pig, human, mouse, and rabbit immunoglobulin Gs, and chicken immunogloblin Y. The resulting fusion proteins can be produced in transfected mammalian cells and detected with commercially available and species-specific secondary antibody reagents. We demonstrate the utility of this platform by constructing and testing Fc fusions with DARPin, single-chain Fv, nanobody, toxin, and chemokine partners. The resulting fusion proteins were used to detect their targets in tissue sections or on the surface of transfected cells by immunofluorescent staining or on the surface of immune cells by flow cytometry. By expanding the range of Fc sequences available for fusion protein production, this platform will expand the repertoire of primary antibody reagents for multiplexed immunostaining and fluorescence-activated cell sorting analyses.

Venoms and Extracellular Vesicles: A New Frontier in Venom Biology

Extracellular vesicles (EVs) are nanoparticle-sized vesicles secreted by nearly all cell types under normal physiological conditions. In toxicological research, EVs have emerged as a crucial link between public health and multi-omics approaches, offering insights into cellular responses to disease-causing injury agents such as environmental and biological toxins, contaminants, and drugs. Notably, EVs present a unique opportunity to deepen our understanding of the pathophysiology of envenomation by natural toxins. Recent advancements in isolating and purifying EV cargo, mass spectrometry techniques, and bioinformatics have positioned EVs as potential biomarkers that could elucidate biological signaling pathways and provide valuable information on the relationship between venomous toxins, their mechanisms of action, and the effectiveness of antivenoms. Additionally, EVs hold promise as proxies for various aspects of envenomation, including the toxin dosage, biological characterization, injury progression, and prognosis during therapeutic interventions. These aspects can be explored through multi-omics technology applied to EV contents from the plasma, saliva, or urine samples of envenomated individuals, offering a comprehensive integrative approach to understanding and managing envenomation cases.

Epidemiology and characteristics of coral snake bites reported to the National Poison Data System (2006‒2022)

Objectives

North American coral snake envenomations can result in life-threatening neurotoxicity. Their bites are relatively rare, making large studies difficult. Using the National Poison Data System (NPDS), we sought to investigate the epidemiological trends and clinical outcomes associated with North American coral snake bites over a 17-year period.

Methods

NPDS cases involving coral snakes from January 1, 2006, to December 31, 2022, were analyzed. Data collected included patient age, date, geographic location, clinical effects, treatments administered, and medical outcomes including incidence of "dry bites" (non-envenomation) and death.

Results

During the 17-year period, a total of 1374 cases were reported and analyzed. Cases included adults (≥ 20 years), accounting for 80% (n = 1107), and pediatric patients (≤19 years), accounting for 20% (n = 267) of total cases. Out of 50 US states and District of Columbia, 20 states reported cases. Florida and Texas accounted for 90.5% of all bites (n = 1243) with April being the month with the most reported cases (n = 184). The most bites (n = 96) were reported in 2008 and the fewest (n = 69) in 2016. Male patients predominated for both pediatric (75.7%, n = 202) and adult cases (75.3%, n = 834). Moderate to major clinical outcomes were documented in approximately 30% of total cases; with no reported deaths. Moderate effect is defined as the patient exhibited symptoms as a result of the exposure that were more pronounced, more prolonged, or more of a systemic nature than minor symptoms. Major effect was defined as the patient exhibited symptoms as a result of the exposure that were life threatening or resulted in significant residual disability or disfigurement. The three most reported clinical effects were wound/sting, dermal irritation/pain, and edema. Antivenom was administered in 21% (n = 286) of total cases and 37% (n = 511) of patients were admitted to a critical care unit. Dry bites occurred in 7% (n = 100) of total cases.

Conclusion

Coral snake bites were rare, but consistently reported. While bites were associated with significant morbidity in adult and pediatric patients, there were no deaths reported. Antivenom use declined over the study period but was not associated with an increase in morbidity. An increased incidence of intubations was seen in association with decreased antivenom use.

Red-on-Yellow Queen: Bio-Layer Interferometry Reveals Functional Diversity Within Micrurus Venoms and Toxin Resistance in Prey Species

Snakes in the family Elapidae largely produce venoms rich in three-finger toxins (3FTx) that bind to the α 1 subunit of nicotinic acetylcholine receptors (nAChRs), impeding ion channel activity. These neurotoxins immobilize the prey by disrupting muscle contraction. Coral snakes of the genus Micrurus are specialist predators who produce many 3FTx, making them an interesting system for examining the coevolution of these toxins and their targets in prey animals. We used a bio-layer interferometry technique to measure the binding interaction between 15 Micrurus venoms and 12 taxon-specific mimotopes designed to resemble the orthosteric binding region of the muscular nAChR subunit. We found that Micrurus venoms vary greatly in their potency on this assay and that this variation follows phylogenetic patterns rather than previously reported patterns of venom composition. The long-tailed Micrurus tend to have greater binding to nAChR orthosteric sites than their short-tailed relatives and we conclude this is the likely ancestral state. The repeated loss of this activity may be due to the evolution of 3FTx that bind to other regions of the nAChR. We also observed variations in the potency of the venoms depending on the taxon of the target mimotope. Rather than a pattern of prey-specificity, we found that mimotopes modeled after snake nAChRs are less susceptible to Micrurus venoms and that this resistance is partly due to a characteristic tryptophan → serine mutation within the orthosteric site in all snake mimotopes. This resistance may be part of a Red Queen arms race between coral snakes and their prey.

The role of venom proteomics and single-domain antibodies for antivenoms: Progress in snake envenoming treatment

Single-domain antibodies (sdAbs) hold promise for developing new biopharmaceuticals to treat neglected tropical diseases (NTDs), including snakebites, which are severe and occur frequently. In addition, limitations of conventional snakebite treatments, especially in terms of local action, and the global antivenom crisis incentivize the use of this biotechnological tool to design next-generation snakebite antivenoms. Conventional antivenoms for snakebite treatment are usually composed of immunoglobulin G or F(ab')2 fragments derived from the plasma of immunized animals. sdAbs, the smallest antigen-binding fragments, are derived from the variable domains of camelid heavy-chain antibodies. sdAbs may have some advantages over conventional antivenoms for local toxicity, such as better penetration into tissues due to their small size, and high solubility and affinity for venom antigens due to their unique antigen-binding loops and ability to access cryptic epitopes. We present an overview of current antivenom therapy in the context of sdAb development for toxin neutralization. Furthermore, strategies are presented for identifying snake venom's major toxins as well as for developing antisnake toxin sdAbs by employing proteomic tools for toxin neutralization.

The Cloning and Characterization of a Three-Finger Toxin Homolog (NXH8) from the Coralsnake Micrurus corallinus That Interacts with Skeletal Muscle Nicotinic Acetylcholine Receptors

Coralsnakes (Micrurus spp.) are the only elapids found throughout the Americas. They are recognized for their highly neurotoxic venom, which is comprised of a wide variety of toxins, including the stable, low-mass toxins known as three-finger toxins (3FTx). Due to difficulties in venom extraction and availability, research on coralsnake venoms is still very limited when compared to that of other Elapidae snakes like cobras, kraits, and mambas. In this study, two previously described 3FTx from the venom of M. corallinus, NXH1 (3SOC1_MICCO), and NXH8 (3NO48_MICCO) were characterized. Using in silico, in vitro, and ex vivo experiments, the biological activities of these toxins were predicted and evaluated. The results showed that only NXH8 was capable of binding to skeletal muscle cells and modulating the activity of nAChRs in nerve-diaphragm preparations. These effects were antagonized by anti-rNXH8 or antielapidic sera. Sequence analysis revealed that the NXH1 toxin possesses eight cysteine residues and four disulfide bonds, while the NXH8 toxin has a primary structure similar to that of non-conventional 3FTx, with an additional disulfide bond on the first loop. These findings add more information related to the structural diversity present within the 3FTx class, while expanding our understanding of the mechanisms of the toxicity of this coralsnake venom and opening new perspectives for developing more effective therapeutic interventions.

A comparative study of the performance of E. coli and K. phaffii for expressing α-cobratoxin

Three-finger toxins (3FTxs) have traditionally been obtained via venom fractionation of whole venoms from snakes. This method often yields functional toxins, but it can be difficult to obtain pure isoforms, as it is challenging to separate the many different toxins with similar physicochemical properties that generally exist in many venoms. This issue can be circumvented via the use of recombinant expression. However, achieving the correct disulfide bond formation in recombinant toxins is challenging and requires extensive optimization of expression and purification methods to enhance stability and functionality. In this study, we investigated the expression of α-cobratoxin, a well-characterized 3FTx from the monocled cobra (Naja kaouthia), in three different expression systems, namely Escherichia coli BL21 (DE3) cells with the csCyDisCo plasmid, Escherichia coli SHuffle cells, and Komagataella phaffii (formerly known as Pichia pastoris). While none of the tested systems yielded α-cobratoxin identical to the variant isolated from whole venom, the His6-tagged α-cobratoxin expressed in K. phaffii exhibited a comparable secondary structure according to circular dichroism spectra and similar binding properties to the α7 subunit of the nicotinic acetylcholine receptor. The findings presented here illustrate the advantages and limitations of the different expression systems and can help guide researchers who wish to express 3FTxs.

Synthetic development of a broadly neutralizing antibody against snake venom long-chain α-neurotoxins

Snakebite envenoming is a major global public health concern for which improved therapies are urgently needed. The antigenic diversity present in snake venom toxins from various species presents a considerable challenge to the development of a universal antivenom. Here, we used a synthetic human antibody library to find and develop an antibody that neutralizes long-chain three-finger α-neurotoxins produced by numerous medically relevant snakes. Our antibody bound diverse toxin variants with high affinity, blocked toxin binding to the nicotinic acetylcholine receptor in vitro, and protected mice from lethal venom challenge. Structural analysis of the antibody-toxin complex revealed a binding mode that mimics the receptor-toxin interaction. The overall workflow presented is generalizable for the development of antibodies that target conserved epitopes among antigenically diverse targets, and it offers a promising framework for the creation of a monoclonal antibody-based universal antivenom to treat snakebite envenoming.

Efficient Expression in Leishmania tarentolae (LEXSY) of the Receptor-Binding Domain of the SARS-CoV-2 S-Protein and the Acetylcholine-Binding Protein from Lymnaea stagnalis

Leishmania tarentolae (LEXSY) system is an inexpensive and effective expression approach for various research and medical purposes. The stated advantages of this system are the possibility of obtaining the soluble product in the cytoplasm, a high probability of correct protein folding with a full range of post-translational modifications (including uniform glycosylation), and the possibility of expressing multi-subunit proteins. In this paper, a LEXSY expression system has been employed for obtaining the receptor binding domain (RBD) of the spike-protein of the SARS-CoV-2 virus and the homopentameric acetylcholine-binding protein (AChBP) from Lymnaea stagnalis. RBD is actively used to obtain antibodies against the virus and in various scientific studies on the molecular mechanisms of the interaction of the virus with host cell targets. AChBP represents an excellent structural model of the ligand-binding extracellular domain of all subtypes of nicotinic acetylcholine receptors (nAChRs). Both products were obtained in a soluble glycosylated form, and their structural and functional characteristics were compared with those previously described.

Regulation of Inflammation by IRAK-M Pathway Can Be Associated with nAchRalpha7 Activation and COVID-19

In spite of the vaccine development and its importance, the SARS-CoV-2 pandemic is still impacting the world. It is known that the COVID-19 severity is related to the cytokine storm phenomenon, being inflammation a common disease feature. The nicotinic cholinergic system has been widely associated with COVID-19 since it plays a protective role in inflammation via nicotinic receptor alpha 7 (nAchRalpha7). In addition, SARS-CoV-2 spike protein (Spro) subunits can interact with nAchRalpha7. Moreover, Spro causes toll-like receptor (TLR) activation, leading to pro- and anti-inflammatory pathways. The increase and maturation of the IL-1 receptor-associated kinase (IRAK) family are mediated by activation of membrane receptors, such as TLRs. IRAK-M, a member of this family, is responsible for negatively regulating the activity of other active IRAKs. In addition, IRAK-M can regulate microglia phenotype by specific protein expression. Furthermore, there exists an antagonist influence of SARS-CoV-2 Spro and the cholinergic system action on the IRAK-M pathway and microglia phenotype. We discuss the overexpression and suppression of IRAK-M in inflammatory cell response to inflammation in SARS-CoV-2 infection when the cholinergic system is constantly activated via nAchRalpha7.

Deep-STP: a deep learning-based approach to predict snake toxin proteins by using word embeddings

Snake venom contains many toxic proteins that can destroy the circulatory system or nervous system of prey. Studies have found that these snake venom proteins have the potential to treat cardiovascular and nervous system diseases. Therefore, the study of snake venom protein is conducive to the development of related drugs. The research technologies based on traditional biochemistry can accurately identify these proteins, but the experimental cost is high and the time is long. Artificial intelligence technology provides a new means and strategy for large-scale screening of snake venom proteins from the perspective of computing. In this paper, we developed a sequence-based computational method to recognize snake toxin proteins. Specially, we utilized three different feature descriptors, namely g-gap, natural vector and word 2 vector, to encode snake toxin protein sequences. The analysis of variance (ANOVA), gradient-boost decision tree algorithm (GBDT) combined with incremental feature selection (IFS) were used to optimize the features, and then the optimized features were input into the deep learning model for model training. The results show that our model can achieve a prediction performance with an accuracy of 82.00% in 10-fold cross-validation. The model is further verified on independent data, and the accuracy rate reaches to 81.14%, which demonstrated that our model has excellent prediction performance and robustness.

Synthetic Peptide Fragments of the Wtx Toxin Reduce Blood Pressure in Rats under General Anesthesia

Previously, it was shown that the non-conventional toxin WTX from the venom of the cobra Naja kaouthia, when administered intravenously, caused a decrease in blood pressure (BP) and an increase in heart rate (HR) in rats [13]. To identify the site of the toxin molecule responsible for these effects, we studied the influence of synthetic peptide fragments of the WTX on BP and HR in normotensive male Sprague-Dawley rats under general anesthesia induced by Telazol and Xylazine. It was found that peptides corresponding to the WTX central polypeptide loop, stabilized by a disulfide bond, at intravenous injection at concentrations from 0.1 to 1.0 mg/mL caused a dose-dependent decrease in BP, with the HR increasing only in the first 5-10 min after administration. Thus, WTX fragments corresponding to the central polypeptide loop reproduce the decrease in blood pressure caused by the toxin.

Comparison of Conformations and Interactions with Nicotinic Acetylcholine Receptors for E. coli-Produced and Synthetic Three-Finger Protein SLURP-1

SLURP-1 is a three-finger human protein targeting nicotinic acetylcholine receptors (nAChRs). The recombinant forms of SLURP-1 produced in E. coli differ in added fusion fragments and in activity. The closest in sequence to the naturally occurring SLURP-1 is the recombinant rSLURP-1, differing by only one additional N-terminal Met residue. sSLURP-1 can be prepared by peptide synthesis and its amino acid sequence is identical to that of the natural protein. In view of recent NMR analysis of the conformational mobility of rSLURP-1 and cryo-electron microscopy structures of complexes of α-bungarotoxin (a three-finger snake venom protein) with Torpedo californica and α7 nAChRs, we compared conformations of sSLURP-1 and rSLURP-1 by Raman spectroscopy and CD-controlled thermal denaturation, analyzed their competition with α-bungarotoxin for binding to the above-mentioned nAChRs, compared the respective receptor complexes with computer modeling and compared their inhibitory potency on the α9α10 nAChR. The CD revealed a higher thermostability of sSLURP-1; some differences between sSLURP-1 and rSLURP-1 were observed in the regions of disulfides and tyrosine residues by Raman spectroscopy, but in binding, computer modeling and electrophysiology, the proteins were similar. Thus, sSLURP-1 and rSLURP-1 with only one additional Met residue appear close in structure and functional characteristics, being appropriate for research on nAChRs.

Molecular Mechanisms of Animal Toxins, Venoms and Antivenoms

In many animals belonging to different taxa, venoms evolved as a means of defense and/or a means of attack/hunting [...].

An in vitro assay to investigate venom neurotoxin activity on muscle-type nicotinic acetylcholine receptor activation and for the discovery of toxin-inhibitory molecules

Snakebite envenoming is a neglected tropical disease that causes over 100,000 deaths annually. Envenomings result in variable pathologies, but systemic neurotoxicity is among the most serious and is currently only treated with difficult to access and variably efficacious commercial antivenoms. Venom-induced neurotoxicity is often caused by α-neurotoxins antagonising the muscle-type nicotinic acetylcholine receptor (nAChR), a ligand-gated ion channel. Discovery of therapeutics targeting α-neurotoxins is hampered by relying on binding assays that do not reveal restoration of receptor activity or more costly and/or lower throughput electrophysiology-based approaches. Here, we report the validation of a screening assay for nAChR activation using immortalised TE671 cells expressing the γ-subunit containing muscle-type nAChR and a fluorescent dye that reports changes in cell membrane potential. Assay validation using traditional nAChR agonists and antagonists, which either activate or block ion fluxes, was consistent with previous studies. We then characterised antagonism of the nAChR by a variety of elapid snake venoms that cause muscle paralysis in snakebite victims, before defining the toxin-inhibiting activities of commercial antivenoms, and new types of snakebite therapeutic candidates, namely monoclonal antibodies, decoy receptors, and small molecules. Our findings show robust evidence of assay uniformity across 96-well plates and highlight the amenability of this approach for the future discovery of new snakebite therapeutics via screening campaigns. The described assay therefore represents a useful first-step approach for identifying α-neurotoxins and their inhibitors in the context of snakebite envenoming, and it should provide wider value for studying modulators of nAChR activity from other sources.

Fifty Years of Animal Toxin Research at the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS

This review covers briefly the work carried out at our institute (IBCh), in many cases in collaboration with other Russian and foreign laboratories, for the last 50 years. It discusses the discoveries and studies of various animal toxins, including protein and peptide neurotoxins acting on the nicotinic acetylcholine receptors (nAChRs) and on other ion channels. Among the achievements are the determination of the primary structures of the α-bungarotoxin-like three-finger toxins (TFTs), covalently bound dimeric TFTs, glycosylated cytotoxin, inhibitory cystine knot toxins (ICK), modular ICKs, and such giant molecules as latrotoxins and peptide neurotoxins from the snake, as well as from other animal venoms. For a number of toxins, spatial structures were determined, mostly by 1H-NMR spectroscopy. Using this method in combination with molecular modeling, the molecular mechanisms of the interactions of several toxins with lipid membranes were established. In more detail are presented the results of recent years, among which are the discovery of α-bungarotoxin analogs distinguishing the two binding sites in the muscle-type nAChR, long-chain α-neurotoxins interacting with α9α10 nAChRs and with GABA-A receptors, and the strong antiviral effects of dimeric phospholipases A2. A summary of the toxins obtained from arthropod venoms includes only highly cited works describing the molecules' success story, which is associated with IBCh. In marine animals, versatile toxins in terms of structure and molecular targets were discovered, and careful work on α-conotoxins differing in specificity for individual nAChR subtypes gave information about their binding sites.

'Spikeopathy': COVID-19 Spike Protein Is Pathogenic, from Both Virus and Vaccine mRNA

The COVID-19 pandemic caused much illness, many deaths, and profound disruption to society. The production of 'safe and effective' vaccines was a key public health target. Sadly, unprecedented high rates of adverse events have overshadowed the benefits. This two-part narrative review presents evidence for the widespread harms of novel product COVID-19 mRNA and adenovectorDNA vaccines and is novel in attempting to provide a thorough overview of harms arising from the new technology in vaccines that relied on human cells producing a foreign antigen that has evidence of pathogenicity. This first paper explores peer-reviewed data counter to the 'safe and effective' narrative attached to these new technologies. Spike protein pathogenicity, termed 'spikeopathy', whether from the SARS-CoV-2 virus or produced by vaccine gene codes, akin to a 'synthetic virus', is increasingly understood in terms of molecular biology and pathophysiology. Pharmacokinetic transfection through body tissues distant from the injection site by lipid-nanoparticles or viral-vector carriers means that 'spikeopathy' can affect many organs. The inflammatory properties of the nanoparticles used to ferry mRNA; N1-methylpseudouridine employed to prolong synthetic mRNA function; the widespread biodistribution of the mRNA and DNA codes and translated spike proteins, and autoimmunity via human production of foreign proteins, contribute to harmful effects. This paper reviews autoimmune, cardiovascular, neurological, potential oncological effects, and autopsy evidence for spikeopathy. With many gene-based therapeutic technologies planned, a re-evaluation is necessary and timely.

Metabolomics analyses of serum metabolites perturbations associated with Naja atra bite

Naja atra bite is one of the most common severe snakebites in emergency departments. Unfortunately, the pathophysiological changes caused by Naja atra bite are unclear due to the lack of good animal models. In this study, an animal model of Naja atra bite in Guangxi Bama miniature pigs was established by intramuscular injection at 2 mg/kg of Naja atra venom, and serum metabolites were systematically analyzed using untargeted metabolomic and targeted metabolomic approaches. Untargeted metabolomic analysis revealed that 5045 chromatographic peaks were obtained in ESI+ and 3871 chromatographic peaks were obtained in ESI-. Screening in ESI+ modes and ESI- modes identified 22 and 36 differential metabolites compared to controls. The presence of 8 core metabolites of glutamine, arginine, proline, leucine, phenylalanine, inosine, thymidine and hippuric acid in the process of Naja atra bite was verified by targeted metabolomics significant difference (P<0.05). At the same time, during the verification process of the serum clinical samples with Naja atra bite, we found that the contents of three metabolites of proline, phenylalanine and inosine in the serum of the patients were significantly different from those of the normal human serum (P<0.05). By conducting functional analysis of core and metabolic pathway analysis, we revealed a potential correlation between changes in key metabolites after the Naja atra bite and the resulting pathophysiological alterations, and our research aims to establish a theoretical foundation for the prompt diagnosis and treatment of Naja atra bite.

Cross-reactivity trends when selecting scFv antibodies against snake toxins using a phage display-based cross-panning strategy

Antibodies with cross-reactive binding and broad toxin-neutralizing capabilities are advantageous for treating indications such as infectious diseases and animal envenomings. Such antibodies have been successfully selected against closely related antigens using phage display technology. However, the mechanisms driving antibody cross-reactivity typically remain to be elucidated. Therefore, we sought to explore how a previously reported phage display-based cross-panning strategy drives the selection of cross-reactive antibodies using seven different snake toxins belonging to three protein (sub-)families: phospholipases A2, long-chain α-neurotoxins, and short-chain α-neurotoxins. We showcase how cross-panning can increase the chances of discovering cross-reactive single-chain variable fragments (scFvs) from phage display campaigns. Further, we find that the feasibility of discovering cross-reactive antibodies using cross-panning cannot easily be predicted by analyzing the sequence, structural, or surface similarity of the antigens alone. However, when antigens share the (exact) same functions, this seems to increase the chances of selecting cross-reactive antibodies, which may possibly be due to the existence of structurally similar motifs on the antigens.

What Are the Neurotoxins in Hemotoxic Snake Venoms?

Snake venoms as tools for hunting are primarily aimed at the most vital systems of the prey, especially the nervous and circulatory systems. In general, snakes of the Elapidae family produce neurotoxic venoms comprising of toxins targeting the nervous system, while snakes of the Viperidae family and most rear-fanged snakes produce hemotoxic venoms directed mainly on blood coagulation. However, it is not all so clear. Some bites by viperids results in neurotoxic signs and it is now known that hemotoxic venoms do contain neurotoxic components. For example, viperid phospholipases A₂ may manifest pre- or/and postsynaptic activity and be involved in pain and analgesia. There are other neurotoxins belonging to diverse families ranging from large multi-subunit proteins (e.g., C-type lectin-like proteins) to short peptide neurotoxins (e.g., waglerins and azemiopsin), which are found in hemotoxic venoms. Other neurotoxins from hemotoxic venoms include baptides, crotamine, cysteine-rich secretory proteins, Kunitz-type protease inhibitors, sarafotoxins and three-finger toxins. Some of these toxins exhibit postsynaptic activity, while others affect the functioning of voltage-dependent ion channels. This review represents the first attempt to systematize data on the neurotoxins from "non-neurotoxic" snake venom. The structural and functional characteristic of these neurotoxins affecting diverse targets in the nervous system are considered.

Peptides from the Sea Anemone Metridium senile with Modified Inhibitor Cystine Knot (ICK) Fold Inhibit Nicotinic Acetylcholine Receptors

Nicotinic acetylcholine receptors (nAChRs) play an important role in the functioning of the central and peripheral nervous systems, and other organs of living creatures. There are several subtypes of nAChRs, and almost all of them are considered as pharmacological targets in different pathological states. The crude venom of the sea anemone Metridium senile showed the ability to interact with nAChRs. Four novel peptides (Ms11a-1-Ms11a-4) with nAChR binding activity were isolated. These peptides stabilized by three disulfide bridges have no noticeable homology with any known peptides. Ms11a-1-Ms11a-4 showed different binding activity towards the muscle-type nAChR from the Torpedo californica ray. The study of functional activity and selectivity for the most potent peptide (Ms11a-3) revealed the highest antagonism towards the heterologous rat α9α10 nAChR compared to the muscle and α7 receptors. Structural NMR analysis of two toxins (Ms11a-2 and Ms11a-3) showed that they belong to a new variant of the inhibitor cystine knot (ICK) fold but have a prolonged loop between the fifth and sixth cysteine residues. Peptides Ms11a-1-Ms11a-4 could represent new pharmacological tools since they have structures different from other known nAChRs inhibitors.

Neurotoxins Acting at Synaptic Sites: A Brief Review on Mechanisms and Clinical Applications

Neurotoxins generally inhibit or promote the release of neurotransmitters or bind to receptors that are located in the pre- or post-synaptic membranes, thereby affecting physiological functions of synapses and affecting biological processes. With more and more research on the toxins of various origins, many neurotoxins are now widely used in clinical treatment and have demonstrated good therapeutic outcomes. This review summarizes the structural properties and potential pharmacological effects of neurotoxins acting on different components of the synapse, as well as their important clinical applications, thus could be a useful reference for researchers and clinicians in the study of neurotoxins.

Current situation of snakebites envenomation in the Neotropics: Biotechnology, a versatile tool in the production of antivenoms

Snakebite envenomation is a neglected tropical disease that affects millions of people around the world with a great impact on health and the economy. Unfortunately, public health programs do not include this kind of disease as a priority in their social programs. Cases of snakebite envenomations in the Neotropics are inaccurate due to inadequate disease management from medical records to the choice of treatments. Victims of snakebite envenomation are primarily found in impoverished agricultural areas where remote conditions limit the availability of antivenom. Antivenom serum is the only Food and Drug Administration-approved treatment used up to date. However, it has several disadvantages in terms of safety and effectiveness. This review provides a comprehensive insight dealing with the current epidemiological status of snakebites in the Neotropics and technologies employed in antivenom production. Also, modern biotechnological tools such as transcriptomic, proteomic, immunogenic, high-density peptide microarray and epitope mapping are highlighted for producing new-generation antivenom sera. These results allow us to propose strategic solutions in the Public Health Sector for managing this disease. Keywords: antivenom, biotechnology, neglected tropical disease, omics, recombinant antibody.

Membrane-mediated interaction of non-conventional snake three-finger toxins with nicotinic acetylcholine receptors

Nicotinic acetylcholine receptor of α7 type (α7-nAChR) presented in the nervous and immune systems and epithelium is a promising therapeutic target for cognitive disfunctions and cancer treatment. Weak toxin from Naja kaouthia venom (WTX) is a non-conventional three-finger neurotoxin, targeting α7-nAChR with weak affinity. There are no data on interaction mode of non-conventional neurotoxins with nAChRs. Using α-bungarotoxin (classical three-finger neurotoxin with high affinity to α7-nAChR), we showed applicability of cryo-EM to study complexes of α7-nAChR extracellular ligand-binding domain (α7-ECD) with toxins. Using cryo-EM structure of the α7-ECD/WTX complex, together with NMR data on membrane active site in the WTX molecule and mutagenesis data, we reconstruct the structure of α7-nAChR/WTX complex in the membrane environment. WTX interacts at the entrance to the orthosteric site located at the receptor intersubunit interface and simultaneously forms the contacts with the membrane surface. WTX interaction mode with α7-nAChR significantly differs from α-bungarotoxin's one, which does not contact the membrane. Our study reveals the important role of the membrane for interaction of non-conventional neurotoxins with the nicotinic receptors.

Complement and myasthenia gravis

Myasthenia gravis is a neuromuscular disease associated with antibodies against components of the neuromuscular junction, most often against the acetylcholine receptor (AChR). Although several mechanisms have been postulated to explain how these autoantibodies can lead to the pathology of the disease, convincing evidence suggests that destruction of the receptor-bearing postsynaptic membrane by complement membrane attack complex is of central importance. In this review, evidence for the importance of complement, and possible relationships between autoantigen, autoantibodies, complement activation, and the destruction of the membrane are discussed. More recent insights from the results of the complement-inhibiting therapeutic antibody eculizumab are also described, and the mechanisms connecting antibody binding to complement activation are considered from a structural viewpoint.

Isolation and Characterization of Two Postsynaptic Neurotoxins From Indian Cobra (Naja Naja) Venom

The Indian Cobra (Naja naja) is among the “Big Four” responsible for most of the snakebite envenoming cases in India. Although recent proteomic studies suggest the presence of postsynaptic neurotoxins in N. naja venom, little is known about the pharmacology of these toxins. We isolated and characterized α-Elapitoxin-Nn2a (α-EPTX-Nn2a; 7020 Da) and α-Elapitoxin-Nn3a (α-EPTX-Nn3a; 7807 Da), a short-chain and long-chain postsynaptic neurotoxin, respectively, which constitute 1 and 3% of N. naja venom. α-EPTX-Nn2a (100–300 nM) and α-EPTX-Nn3a (100–300 nM) both induced concentration-dependent inhibition of indirect twitches and abolished contractile responses of tissues to exogenous acetylcholine and carbachol, in the chick biventer cervicis nerve-muscle preparation. The prior incubation of tissues with Indian polyvalent antivenom (1 ml/0.6 mg) prevented the in vitro neurotoxic effects of α-EPTX-Nn2a (100 nM) and α-EPTX-Nn3a (100 nM). The addition of Indian polyvalent antivenom (1 ml/0.6 mg), at the t₉₀ time point, could not reverse the in vitro neurotoxicity of α-EPTX-Nn2a (100 nM). The in vitro neurotoxicity of α-EPTX-Nn3a (100 nM) was partially reversed by the addition of Indian polyvalent antivenom (1 ml/0.6 mg), as well as repeated washing of the tissue. α-EPTX-Nn2a displayed non-competitive antagonism of concentration-response curves to carbachol, with a pA₂ of 8.01. In contrast, α-EPTX-Nn3a showed reversible antagonism of concentration-response curves to carbachol, with a pA₂ of 8.17. De novo sequencing of α-EPTX-Nn2a and α-EPTX-Nn3a showed a short-chain and long-chain postsynaptic neurotoxin, respectively, with 62 and 71 amino acids. The important observation made in this study is that antivenom can reverse the neurotoxicity of the clinically important long-chain neurotoxin, but not the short-chain neurotoxin, from N. naja venom.

Preparation and Evaluation of a Horse Antiserum against the Venom of Sea Snake Hydrophis curtus from Hainan, China

Sea snake venom is extremely toxic, and it can induce severe respiratory failure and cause high mortality. The most effective first aid treatment for sea snake bites is to inject antivenom as soon as possible. However, in China, there are only four types of terrestrial snake antivenoms, none of which are effective in the treatment of sea snake bites. In order to develop an antivenom for the dominant species of sea snakes in Chinese seas, Hydrophis curtus venom (HcuV) was chosen as the antigen to immunize horses. From immune plasma, a high-titer Hydrophis curtus antivenom (HcuAV) was prepared. In vitro assessment showed that HcuAV had a cross-neutralizing capacity against HcuV and Hydrophis cyanocinctus venom (HcyV). In vivo assessment indicated that HcuAV injection could significantly improve the survival rates of the HcuV and HcyV envenomated mice (0% to 100% and 87.5%, respectively) when it was injected at a sufficient amount within the shortest possible time. In addition, HcuAV could also effectively alleviate multiple organ injuries caused by HcuV. These results provide experimental support for the future clinical application of HcuAV.

The rise of genomics in snake venom research: recent advances and future perspectives

Snake venoms represent a danger to human health, but also a gold mine of bioactive proteins that can be harnessed for drug discovery purposes. The evolution of snakes and their venom has been studied for decades, particularly via traditional morphological and basic genetic methods alongside venom proteomics. However, while the field of genomics has matured rapidly over the past 2 decades, owing to the development of next-generation sequencing technologies, snake genomics remains in its infancy. Here, we provide an overview of the state of the art in snake genomics and discuss its potential implications for studying venom evolution and toxinology. On the basis of current knowledge, gene duplication and positive selection are key mechanisms in the neofunctionalization of snake venom proteins. This makes snake venoms important evolutionary drivers that explain the remarkable venom diversification and adaptive variation observed in these reptiles. Gene duplication and neofunctionalization have also generated a large number of repeat sequences in snake genomes that pose a significant challenge to DNA sequencing, resulting in the need for substantial computational resources and longer sequencing read length for high-quality genome assembly. Fortunately, owing to constantly improving sequencing technologies and computational tools, we are now able to explore the molecular mechanisms of snake venom evolution in unprecedented detail. Such novel insights have the potential to affect the design and development of antivenoms and possibly other drugs, as well as provide new fundamental knowledge on snake biology and evolution.

Variability in the Spatial Structure of the Central Loop in Cobra Cytotoxins Revealed by X-ray Analysis and Molecular Modeling

Cobra cytotoxins (CTs) belong to the three-fingered protein family and possess membrane activity. Here, we studied cytotoxin 13 from Naja naja cobra venom (CT13Nn). For the first time, a spatial model of CT13Nn with both “water” and “membrane” conformations of the central loop (loop-2) were determined by X-ray crystallography. The “water” conformation of the loop was frequently observed. It was similar to the structure of loop-2 of numerous CTs, determined by either NMR spectroscopy in aqueous solution, or the X-ray method. The “membrane” conformation is rare one and, to date has only been observed by NMR for a single cytotoxin 1 from N. oxiana (CT1No) in detergent micelle. Both CT13Nn and CT1No are S-type CTs. Membrane-binding of these CTs probably involves an additional step—the conformational transformation of the loop-2. To confirm this suggestion, we conducted molecular dynamics simulations of both CT1No and CT13Nn in the Highly Mimetic Membrane Model of palmitoiloleoylphosphatidylglycerol, starting with their “water” NMR models. We found that the both toxins transform their “water” conformation of loop-2 into the “membrane” one during the insertion process. This supports the hypothesis that the S-type CTs, unlike their P-type counterparts, require conformational adaptation of loop-2 during interaction with lipid membranes.

α5-nAChR associated with Ly6E modulates cell migration via TGF-β1/Smad signaling in non-small cell lung cancer

The α5-nicotinic acetylcholine receptor (α5-nAChR) is closely associated with nicotine-related lung cancer, offering a novel perspective for investigating the molecular pathogenesis of this disease. However, the mechanism by which α5-nAChR functions in lung carcinogenesis remains to be elucidated. Lymphocyte antigen 6 (Ly6) proteins, like snake three-finger alpha toxins such as α-bungarotoxin, can modulate nAChR signaling. Ly6E, a member of the Ly6 family, is a biomarker of poor prognosis in smoking-induced lung carcinogenesis and is involved in the regulation of TGF-β1/Smad signaling. Here, we explored the underlying mechanisms linking α5-nAChR and Ly6E in non-small cell lung cancer (NSCLC). The expression of α5-nAChR was correlated with Ly6 expression, smoking status and lower survival in NSCLC tissues. In vitro, α5-nAChR mediated Ly6E, the phosphorylation of the TGF-β1 downstream molecule Smad3 (pSmad3, a key mediator of TGF-β1 signaling), the epithelial-mesenchymal transition (EMT) markers Zeb1, N-cadherin and vimentin expression in NSCLC cells. The downregulation of Ly6E reduced α5-nAChR, pSmad3, Zeb1, N-cadherin and vimentin expression. Functionally, silencing both α5-nAChR and Ly6E significantly inhibited cell migration compared to silencing α5-nAChR or Ly6E alone. Furthermore, the functional effects of α5-nAchR and Ly6E were confirmed in chicken embryo chorioallantoic membrane (CAM) and mouse xenograft models. Therefore, our findings uncover a new interaction between α5-nAChR and Ly6E that inhibits cancer cell migration by modulating the TGF-β1/Smad signaling pathway in NSCLC, which may serve as a novel target for therapeutic intervention.

Proteomics and neutralization of Bungarus multicinctus (Many-banded Krait) venom: Intra-specific comparisons between specimens from China and Taiwan

The Many-banded Krait (Bungarus multicinctus) is a medically important venomous snake in East Asia. This study investigated the venom proteomes of B. multicinctus from Guangdong, southern China (BM-China) and insular Taiwan (BM-Taiwan), and the neutralization activities of two antivenom products (produced separately in China and Taiwan) against the lethal effect of the venoms. The venom proteomes of both specimens contained similar toxin families, notwithstanding small variations in the subtypes and abundances of minor components. More than 90% of the total venom proteins belong to three-finger toxins (3FTx, including alpha-neurotoxins) and phospholipases A₂ (PLA₂, including beta-bungarotoxins), supporting their key involvement in the pathophysiology of krait envenomation which manifests as pre- and post-synaptic neurotoxicity. The venoms exhibited potent neurotoxic and lethal effects with extremely low i.v. LD₅₀ of 0.027 μg/g (Bm-China) and 0.087 μg/g (Bm-Taiwan), respectively, in mice. Bungarus multicinctus monovalent antivenom (BMMAV) produced in China and Neuro bivalent antivenom (NBAV) produced in Taiwan were immunoreactive toward both venoms and their toxin fractions. The antivenoms neutralized the venom lethality variably, with BMMAV being more efficacious than NBAV by approximately two-fold. Findings suggest that the monovalent antivenom has a higher potency presumably due to its species-specificity toward the krait venom.

Therapeutic Targeting of α7 Nicotinic Acetylcholine Receptors

The α7-type nicotinic acetylcholine receptor is one of the most unique and interesting of all the members of the cys-loop superfamily of ligand-gated ion channels. Since it was first identified initially as a binding site for α-bungarotoxin in mammalian brain and later as a functional homomeric receptor with relatively high calcium permeability, it has been pursued as a potential therapeutic target for numerous indications, from Alzheimer disease to asthma. In this review, we discuss the history and state of the art for targeting α7 receptors, beginning with subtype-selective agonists and the basic pharmacophore for the selective activation of α7 receptors. A key feature of α7 receptors is their rapid desensitization by standard "orthosteric" agonist, and we discuss insights into the conformational landscape of α7 receptors that has been gained by the development of ligands binding to allosteric sites. Some of these sites are targeted by positive allosteric modulators that have a wide range of effects on the activation profile of the receptors. Other sites are targeted by direct allosteric agonist or antagonists. We include a perspective on the potential importance of α7 receptors for metabotropic as well as ionotropic signaling. We outline the challenges that exist for future development of drugs to target this important receptor and approaches that may be considered to address those challenges. SIGNIFICANCE STATEMENT: The α7-type nicotinic acetylcholine receptor (nAChR) is acknowledged as a potentially important therapeutic target with functional properties associated with both ionotropic and metabotropic signaling. The functional properties of α7 nAChR can be regulated in diverse ways with the variety of orthosteric and allosteric ligands described in this review.

Venom-Derived Neurotoxins Targeting Nicotinic Acetylcholine Receptors

Acetylcholine was the first neurotransmitter described. The receptors targeted by acetylcholine are found within organisms spanning different phyla and position themselves as very attractive targets for predation, as well as for defense. Venoms of snakes within the Elapidae family, as well as those of marine snails within the Conus genus, are particularly rich in proteins and peptides that target nicotinic acetylcholine receptors (nAChRs). Such compounds are invaluable tools for research seeking to understand the structure and function of the cholinergic system. Proteins and peptides of venomous origin targeting nAChR demonstrate high affinity and good selectivity. This review aims at providing an overview of the toxins targeting nAChRs found within venoms of different animals, as well as their activities and the structural determinants important for receptor binding.

Three-Finger Toxins from Brazilian Coral Snakes: From Molecular Framework to Insights in Biological Function

Studies on 3FTxs around the world are showing the amazing diversity in these proteins both in structure and function. In Brazil, we have not realized the broad variety of their amino acid sequences and probable diversified structures and targets. In this context, this work aims to conduct an in silico systematic study on available 3FTxs found in Micrurus species from Brazil. We elaborated a specific guideline for this toxin family. First, we grouped them according to their structural homologue predicted by HHPred server and further curated manually. For each group, we selected one sequence and constructed a representative structural model. By looking at conserved features and comparing with the information available in the literature for this toxin family, we managed to point to potential biological functions. In parallel, the phylogenetic relationship was estimated for our database by maximum likelihood analyses and a phylogenetic tree was constructed including the homologous 3FTx previously characterized. Our results highlighted an astonishing diversity inside this family of toxins, showing some groups with expected functional similarities to known 3FTxs, and pointing out others with potential novel roles and perhaps structures. Moreover, this classification guideline may be useful to aid future studies on these abundant toxins.

Spatial Structure and Activity of Synthetic Fragments of Lynx1 and of Nicotinic Receptor Loop C Models

Lynx1, membrane-bound protein co-localized with the nicotinic acetylcholine receptors (nAChRs) and regulates their function, is a three-finger protein (TFP) made of three β-structural loops, similarly to snake venom α-neurotoxin TFPs. Since the central loop II of α-neurotoxins is involved in binding to nAChRs, we have recently synthesized the fragments of Lynx1 central loop, including those with the disulfide between Cys residues introduced at N- and C-termini, some of them inhibiting muscle-type nAChR similarly to the whole-size water-soluble Lynx1 (ws-Lynx1). Literature shows that the main fragment interacting with TFPs is the C-loop of both nAChRs and acetylcholine binding proteins (AChBPs) while some ligand-binding capacity is preserved by analogs of this loop, for example, by high-affinity peptide HAP. Here we analyzed the structural organization of these peptide models of ligands and receptors and its role in binding. Thus, fragments of Lynx1 loop II, loop C from the Lymnaea stagnalis AChBP and HAP were synthesized in linear and Cys-cyclized forms and structurally (CD and NMR) and functionally (radioligand assay on Torpedo nAChR) characterized. Connecting the C- and N-termini by disulfide in the ws-Lynx1 fragment stabilized its conformation which became similar to the loop II within the ¹H-NMR structure of ws-Lynx1, the activity being higher than for starting linear fragment but lower than for peptide with free cysteines. Introduced disulfides did not considerably change the structure of HAP and of loop C fragments, the former preserving high affinity for α-bungarotoxin, while, surprisingly, no binding was detected with loop C and its analogs.

Immunoreactivity and neutralization study of Chinese Bungarus multicinctus antivenin and lab-prepared anti-bungarotoxin antisera towards purified bungarotoxins and snake venoms

Bungarus multicinctus is the most venomous snake distributed in China and neighboring countries of Myanmar, Laos, north Vietnam and Thailand. The high mortality rate of B. multicinctus envenomation is attributed to the lethal components of α-, β-, γ- and κ- bungarotoxins contained in the venom. Although anti-B. multicinctus sera were produced in Shanghai, Taiwan and Vietnam, the most widely clinic used product was term as B. multicinctus antivenin and manufactured by Shanghai Serum Bio-technology Co. Ltd. In the present investigation, high purity α-, β- and γ-bungarotoxins were separately isolated from B. multicinctus crude venom. Rabbit anti- α-, β- and γ-bungarotoxin antisera were prepared by common methods, respectively. LD50 values of α-, β- and γ-bungarotoxins were systematically determined via three administration pathways (intraperitoneal, intramuscular and intravenous injections) in Kunming mice. LD50 values of β-bungarotoxin were closely related with injection routines but those of both α- and γ-bungarotoxins were not dependent on the injection routines. Commercial B. multicinctus antivenin showed strong immunoreaction with high molecular weight fractions of the B. multicinctus but weakly recognized low molecular weight fractions like α- and γ-bungarotoxins. Although B. multicinctus antivenin showed immunoreaction with high molecular weight fractions of Bungarus fasciatus, Naja atra, Ophiophagus hannah venoms but the antivenin only demonstrated animal protection efficacy against O. hannah venom. These results indicated that the high molecular weight fractions of the O. hannah played an important role in venom lethality but those of B. fasciatus and N. atra did not have such a role.

A unique snake venom neuritogenesis mechanism: A cornerstone in the treatment of neurodegenerative diseases?: An Editorial Highlight for "Transcriptomic, proteomic, and biochemical analyses reveal a novel neuritogenesis mechanism of Naja naja venom α-elapitoxin post binding to TrkA receptor of rat pheochromocytoma cells" on 612

Neurodegenerative diseases are a worldwide health problem and are a major cause of death and disability. A progressive loss of defined neuronal populations is triggered by a diverse array of stimuli that converge in deficient neurotrophic signaling. Therefore, much effort has been placed in recent years in the characterization of the molecular mechanisms associated with the structure and function of neurotrophins, its receptors, signaling strategies, and their target genes. This Editorial highlights an impressive study by the group of Prof. Ashis K. Mukherjee, a renowned specialist in snake venoms, in which a component of the Indian Cobra N.naja venom with no significant similarity to nerve growth factor, is shown to induce sustained neuritogenesis. An elegant transcriptomic and functional analysis of this component, named Nn-α-elapitoxin, mapped novel domains in mammalian neurotrophic receptors that trigger both conventional and novel signal cascades that support neurite extension in the PC-12 neuronal model system. The authors discuss their findings in the context of the paradoxical neurite outgrowth properties of this toxin which originate in their unique receptor binding site. This study takes an important step towards a better understanding of the complexity of neuronal development and maintenance of the nervous system and provides a potential target to improve neurotrophic signaling, independent of endogenous growth factors, in the diseased brain.