Snake venom toxins: toxicity and medicinal applications

Investigating the cytotoxic effects of the venom proteome of two species of the Viperidae family (Cerastes cerastes and Cryptelytrops purpureomaculatus) from various habitats

Animal secretions are of great interest in terms of drug development due to their complex protein and peptide composition. Especially, in the field of therapeutic medications such as anti-cancer drugs snake venoms receive attention. In this study, we address two Viperidae species from various habitats with a particular focus on the cytotoxic potential along with the decomplexation of the venom proteome: the horned desert viper (Cerastes cerastes), native to desert regions of North Africa and the mangrove pit viper (Cryptelytrops purpureomaculatus), found in coastal forests of Southeast Asia. Initial cytotoxic screenings of the crude venoms revealed diverse activity, with the highest effect against SHSY5Y human glioblastoma carcinoma cells compared to other cancerous and non-cancerous cell lines. In-depth cytotoxicity studies of SHSY5Y cells with purified venom fractions revealed heterodimeric disintegrins from C. cerastes venom, which exerted a high cytotoxic activity with IC₅₀ values from 0.11 to 0.58 μM and a disintegrin-like effect on SHSY5Y morphology was observed due to cell detachment. Furthermore, two polyproline BPP-related peptides, one PLA₂ and a peptide-rich fraction were determined for C. purpureomaculatus with moderate IC₅₀ values between 3 and 51 μM. Additionally, the decryption of the venom proteomes by snake venomic mass spectrometry and comparison of the same species from different habitats revealed slight differences in the composition.

Are peptides a solution for the treatment of hyperactivated JAK3 pathways?

While the inactivation mutations that eliminate JAK3 function lead to the immunological disorders such as severe combined immunodeficiency, activation mutations, causing constitutive JAK3 signaling, are known to trigger various types of cancer or are responsible for autoimmune diseases, such as rheumatoid arthritis, psoriasis, or inflammatory bowel diseases. Treatment of hyperactivated JAK3 is still an obstacle, due to different sensibility of mutation types to conventional drugs and unwanted side effects, because these drugs are not absolutely specific for JAK3, thus inhibiting other members of the JAK family, too. Lack of information, in which way sole inhibition of JAK3 is necessary for elimination of the disease, calls for the development of isoform-specific JAK3 inhibitors. Beside this strategy, up to date peptides are a rising alternative as chemo- or immunotherapeutics, but still sparsely represented in drug development and clinical trials. Beyond a possible direct inhibition function, crossing the cancer cell membrane and interfering in disease-causing pathways or triggering apoptosis, peptides could be used in future as adjunct remedies to potentialize traditional therapy and preserve non-affected cells. To discuss such feasible topics, this review deals with the knowledge about the structure-function of JAK3 and the actual state-of-the-art of isoform-specific inhibitor development, as well as the function of currently approved drugs or those currently being tested in clinical trials. Furthermore, several strategies for the application of peptide-based drugs for cancer therapy and the physicochemical and structural relations to peptide efficacy are discussed, and an overview of peptide sequences, which were qualified for clinical trials, is given.

BmK AEP, an Anti-Epileptic Peptide Distinctly Affects the Gating of Brain Subtypes of Voltage-Gated Sodium Channels

BmK AEP, a scorpion peptide purified form the venom of Buthus martensii Karsch, has been reported to display anti-epileptic activity. Voltage-gated sodium channels (VGSCs) are responsible for the rising phase of action potentials (APs) in neurons and, therefore, controlling neuronal excitability. To elucidate the potential molecular mechanisms responsible for its anti-epileptic activity, we examined the influence of BmK AEP on AP firing in cortical neurons and how BmK AEP influences brain subtypes of VGSCs (Na_v1.1–1.3 and Na_v1.6). BmK AEP concentration-dependently suppresses neuronal excitability (AP firing) in primary cultured cortical neurons. Consistent with its inhibitory effect on AP generation, BmK AEP inhibits Na⁺ peak current in cortical neurons with an IC₅₀ value of 2.12 µM by shifting the half-maximal voltage of activation of VGSC to hyperpolarized direction by ~7.83 mV without affecting the steady-state inactivation. Similar to its action on Na⁺ currents in cortical neurons, BmK AEP concentration-dependently suppresses the Na⁺ currents of Na_v1.1, Na_v1.3, and Na_v1.6, which were heterologously expressed in HEK-293 cells, with IC₅₀ values of 3.20, 1.46, and 0.39 µM with maximum inhibition of 82%, 56%, and 93%, respectively. BmK AEP shifts the voltage-dependent activation in the hyperpolarized direction by ~15.60 mV, ~9.97 mV, and ~6.73 mV in Na_v1.1, Na_v1.3, and Na_v1.6, respectively, with minimal effect on steady-state inactivation. In contrast, BmK AEP minimally suppresses Na_v1.2 currents (~15%) but delays the inactivation of the channel with an IC₅₀ value of 1.69 µM. Considered together, these data demonstrate that BmK AEP is a relatively selective Na_v1.6 gating modifier which distinctly affects the gating of brain subtypes of VGSCs.

Intradermal Application of Crotamine Induces Inflammatory and Immunological Changes In Vivo

Crotamine is a single-chain polypeptide with cell-penetrating properties, which is considered a promising molecule for clinical use. Nevertheless, its biosafety data are still scarce. Herein, we assessed the in vivo proinflammatory properties of crotamine, including its local effect and systemic serum parameters. Sixty male Wistar rats were intradermically injected with 200, 400 and 800 µg crotamine and analyzed after 1, 3 and 7 days. Local effect of crotamine was assessed by determination of MPO and NAG activities, NO levels and angiogenesis. Systemic inflammatory response was assessed by determination of IL-10, TNF-α, CRP, NO, TBARS and SH groups. Crotamine induced macrophages and neutrophils chemotaxis as evidenced by the upregulation of both NAG (0.5–0.6 OD/mg) and MPO (0.1–0.2 OD/mg) activities, on the first and third day of analysis, respectively. High levels of NO were observed for all concentrations and time-points. Moreover, 800 μg crotamine resulted in serum NO (64.7 μM) and local tissue NO (58.5 μM) levels higher or equivalent to those recorded for their respective histamine controls (55.7 μM and 59.0 μM). Crotamine also induced a significant angiogenic response compared to histamine. Systemically, crotamine induced a progressive increase in serum CRP levels up to the third day of analysis (22.4–45.8 mg/mL), which was significantly greater than control values. Crotamine (400 μg) also caused an increase in serum TNF-α, in the first day of analysis (1095.4 pg/mL), however a significant increase in IL-10 (122.2 pg/mL) was also recorded for the same time-point, suggesting the induction of an anti-inflammatory effect. Finally, crotamine changed the systemic redox state by inducing gradual increase in serum levels of TBARS (1.0–1.8 μM/mL) and decrease in SH levels (124.7–19.5 μM/mL) throughout the experimental period of analysis. In summary, rats intradermally injected with crotamine presented local and systemic acute inflammatory responses similarly to histamine, which limits crotamine therapeutic use on its original form.

Vipers of the Middle East: A Rich Source of Bioactive Molecules

Snake venom serves as a tool of defense against threat and helps in prey digestion. It consists of a mixture of enzymes, such as phospholipase A2, metalloproteases, and l-amino acid oxidase, and toxins, including neurotoxins and cytotoxins. Beside their toxicity, venom components possess many pharmacological effects and have been used to design drugs and as biomarkers of diseases. Viperidae is one family of venomous snakes that is found nearly worldwide. However, three main vipers exist in the Middle Eastern region: Montivipera bornmuelleri, Macrovipera lebetina, and Vipera (Daboia) palaestinae. The venoms of these vipers have been the subject of many studies and are considered as a promising source of bioactive molecules. In this review, we present an overview of these three vipers, with a special focus on their venom composition as well as their biological activities, and we discuss further frameworks for the exploration of each venom.

Cell migration inhibition activity of a non-RGD disintegrin from Crotalus durissus collilineatus venom

BACKGROUND

In recent decades, snake venom disintegrins have received special attention due to their potential use in anticancer therapy. Disintegrins are small and cysteine-rich proteins present in snake venoms and can interact with specific integrins to inhibit their activities in cell-cell and cell-ECM interactions. These molecules, known to inhibit platelet aggregation, are also capable of interacting with certain cancer-related integrins, and may interfere in important processes involved in carcinogenesis. Therefore, disintegrin from Crotalus durissus collilineatus venom was isolated, structurally characterized and evaluated for its toxicity and ability to interfere with cell proliferation and migration in MDA-MB-231, a human breast cancer cell line.

METHODS

Based on previous studies, disintegrin was isolated by FPLC, through two chromatographic steps, both on reversed phase C-18 columns. The isolated disintegrin was structurally characterized by Tris-Tricine-SDS-PAGE, mass spectrometry and N-terminal sequencing. For the functional assays, MTT and wound-healing assays were performed in order to investigate cytotoxicity and effect on cell migration in vitro, respectively.

RESULTS

Disintegrin presented a molecular mass of 7287.4 Da and its amino acid sequence shared similarity with the disintegrin domain of P-II metalloproteases. Using functional assays, the disintegrin showed low cytotoxicity (15% and 17%, at 3 and 6 μg/mL, respectively) after 24 h of incubation and in the wound-healing assay, the disintegrin (3 μg/mL) was able to significantly inhibit cell migration (24%, p < 0.05), compared to negative control.

CONCLUSION

Thus, our results demonstrate that non-RGD disintegrin from C. d. collilineatus induces low cytotoxicity and inhibits migration of human breast cancer cells. Therefore, it may be a very useful molecular tool for understanding ECM-cell interaction cancer-related mechanisms involved in an important integrin family that highlights molecular aspects of tumorigenesis. Also, non-RGD disintegrin has potential to serve as an agent in anticancer therapy or adjuvant component combined with other anticancer drugs.

Harnessing snake venom phospholipases A2 to novel approaches for overcoming antibiotic resistance

The emergence of antibiotic resistance drives an essential race against time to reveal new molecular structures capable of addressing this alarming global health problem. Snake venoms are natural catalogs of multifunctional toxins and privileged frameworks, which serve as potential templates for the inspiration of novel treatment strategies for combating antibiotic resistant bacteria. Phospholipases A₂ (PLA₂ s) are one of the main classes of antibacterial biomolecules, with recognized therapeutic value, found in these valuable secretions. Recently, a number of biomimetic oligopeptides based on small fragments of primary structure from PLA₂ toxins has emerged as a meaningful opportunity to overcome multidrug-resistant clinical isolates. Thus, this review will highlight the biochemical and structural properties of antibacterial PLA₂ s and peptides thereof, as well as their possible molecular mechanisms of action and key roles in development of effective therapeutic strategies. Chemical strategies possibly useful to convert antibacterial peptides from PLA₂ s to efficient drugs will be equally addressed.

Crotalus atrox disintegrin reduces hemorrhagic transformation by attenuating matrix metalloproteinase-9 activity after middle cerebral artery occlusion in hyperglycemic male rats

Hemorrhagic transformation after ischemic stroke is an independent predictor for poor outcome and is characterized by blood vessel rupture leading to brain edema. To date, no therapies for preventing hemorrhagic transformation exist. Disintegrins from the venom of Crotalus atrox have targets within the coagulation cascade, including receptors on platelets. We hypothesized that disintegrins from C. atrox venom can attenuate hemorrhagic transformation by preventing activation of matrix metalloproteinase after middle cerebral artery occlusion (MCAO) in hyperglycemic rats. We subjected 48 male Sprague-Dawley rats weighing 240-260 g to MCAO and hyperglycemia to induce hemorrhagic transformation of the infarction. At reperfusion, we administered either saline (vehicle), whole C. atrox venom (two doses were used), or fractionated C. atrox venom (HPLC Fraction 2). Rats were euthanized 24 hr post-ictus for measurement of infarction and hemoglobin volume. Reversed-phase HPLC was performed to fractionate the whole venom and peaks were combined to form Fraction 2, which contained the disintegrin Crotatroxin. Fraction 2 protected against hemorrhagic transformation after MCAO, and attenuated activation of matrix metalloproteinase-9. Administering matrix metalloproteinase antagonists prevented the protection by Fraction 2. The results of this study indicate that disintegrins found in C. atrox venom may have therapeutic potential for reducing hemorrhagic transformation after ischemic stroke. Moreover, the RP-HPLC fractions retained sufficient protein activity to suggest that gentler and less efficient orthogonal chromatographic methods may be unnecessary to isolate proteins and explore their function.

Snake Venoms in Cancer Therapy: Past, Present and Future

Cancer is one of the leading causes of morbidity and mortality worldwide, and the discovery of new drugs for cancer therapy is one of the most important objectives for the pharmaceutical industry. Snake venoms are complex mixtures containing different peptides, proteins, enzymes, carbohydrates and other bioactive molecules, which are secreted by the snake in the predation or defending against threats. Understanding the snake venoms may turn the toxins into a valuable source of new lead compounds in drug discovery. Captopril, the first angiotensin-converting enzyme inhibitor approved in 1981 by FDA, was designed based on the structure of a peptide isolated from the snake venom. The earliest reports about snake venoms used in cancer treatments appeared in the 1930s. Since then, numerous studies on the activities, isolations, purifications and structure elucidations of the components from snake venoms were published. The comprehensive structural and functional investigations of snake venoms would contribute to the development of novel anti-cancer drugs. Our review will focus on the past, present and the future of the studies on snake venoms in cancer target therapy.

A Case Series of Snake Venom Pharmacopuncture for Chemotherapy-Induced Peripheral Neuropathy: A Retrospective Observational Study

Objective

This case series aims to report the efficacy and the safety of using snake venom pharmacopuncture (SVP) for chemotherapy-induced peripheral neuropathy (CIPN).

Methods

Three heterogeneous cancer (1 endometrium, 1 cervix, and 1 prostate cancer) patients were referred to the East-West Cancer Center (EWCC), Dunsan Korean Medicine Hospital of Daejeon University, from August 02, 2017, to September 15, 2017, for treatment with SVP, and they were treated with SVP 4 times, 6 times, and 8 times, respectively. During the treatment period, the efficacy of SVP therapy was assessed by using the Numerical Rating Scale (NRS) and the Common Terminology Criteria for Adverse Events (CTCAE), and the stability was evaluated by using blood tests. Following each session, all patients were examined closely for any allergenic responses or adverse effects.

Results

All patients showed noticeable improvements of their NRS and CTCAE scores. Except for bleeding and bruising at the SVP injection site, no major side effects were noted. One of the patients reported mild chilling and a sore throat after receiving the second treatment; those symptoms went away after a few hours. No hematologic toxicity, hepatotoxicity, or nephrotoxicity was found on the blood test.

Conclusion

The results of this research suggest positive potential benefits of using SVP for treating patients with CIPN. Also, the excellent safety results of SVP seen in this research should lead to larger clinical trials aimed at developing SVP into a potential intervention for managing patients with the symptoms of CIPN.

Assigning biological function using hidden signatures in cystine-stabilized peptide sequences

Cystine-stabilized peptides have great utility as they naturally block ion channels, inhibit acetylcholine receptors, or inactivate microbes. However, only a tiny fraction of these peptides has been characterized. Exploration for novel peptides most efficiently starts with the identification of candidates from genome sequence data. Unfortunately, though cystine-stabilized peptides have shared structures, they have low DNA sequence similarity, restricting the utility of BLAST and even more powerful sequence alignment-based annotation algorithms, such as PSI-BLAST and HMMER. In contrast, a supervised machine learning approach may improve discovery and function assignment of these peptides. To this end, we employed our previously described m-NGSG algorithm, which utilizes hidden signatures embedded in peptide primary sequences that define and categorize structural or functional classes of peptides. From the generalized m-NGSG framework, we derived five specific models that categorize cystine-stabilized peptide sequences into specific functional classes. When compared with PSI-BLAST, HMMER and existing function-specific models, our novel approach (named CSPred) consistently demonstrates superior performance in discovery and function-assignment. We also report an interactive version of CSPred, available through download ( https://bitbucket.org/sm_islam/cystine-stabilized-proteins/src ) or web interface (watson.ecs.baylor.edu/cspred), for the discovery of cystine-stabilized peptides of specific function from genomic datasets and for genome annotation. We fully describe, in the Availability section following the Discussion, the quick and simple usage of the CsPred website to automatically deliver function assignments for batch submissions of peptide sequences.

Microbial production of toxins from the scorpion venom: properties and applications

Scorpion venom are composed mainly of bioactive proteins and peptides that may serve as lead compounds for the design of biotechnological tools and therapeutic drugs. However, exploring the therapeutic potential of scorpion venom components is mainly impaired by the low yield of purified toxins from milked venom. Therefore, production of toxin-derived peptides and proteins by heterologous expression is the strategy of choice for research groups and pharmaceutical industry to overcome this limitation. Recombinant expression in microorganisms is often the first choice, since bacteria and yeast systems combine high level of recombinant protein expression, fast cell growth and multiplication and simple media requirement. Herein, we present a comprehensive revision, which describes the scorpion venom components that were produced in their recombinant forms using microbial systems. In addition, we highlight the pros and cons of performing the heterologous expression of these compounds, regarding the particularities of each microorganism and how these processes can affect the application of these venom components. The most used microbial system in the heterologous expression of scorpion venom components is Escherichia coli (85%), and among all the recombinant venom components produced, 69% were neurotoxins. This review may light up future researchers in the choice of the best expression system to produce scorpion venom components of interest.

Short-chain consensus alpha-neurotoxin: a synthetic 60-mer peptide with generic traits and enhanced immunogenic properties

The three-fingered toxin family and more precisely short-chain α-neurotoxins (also known as Type I α-neurotoxins) are crucial in defining the elapid envenomation process, but paradoxically, they are barely neutralized by current elapid snake antivenoms. This work has been focused on the primary structural identity among Type I neurotoxins in order to create a consensus short-chain α-neurotoxin with conserved characteristics. A multiple sequence alignment considering the twelve most toxic short-chain α-neurotoxins reported from the venoms of the elapid genera Acanthophis, Oxyuranus, Walterinnesia, Naja, Dendroaspis and Micrurus led us to propose a short-chain consensus α-neurotoxin, here named ScNtx. The synthetic ScNtx gene was de novo constructed and cloned into the expression vector pQE30 containing a 6His-Tag and an FXa proteolytic cleavage region. Escherichia coli Origami cells transfected with the pQE30/ScNtx vector expressed the recombinant consensus neurotoxin in a soluble form with a yield of 1.5 mg/L of culture medium. The 60-amino acid residue ScNtx contains canonical structural motifs similar to α-neurotoxins from African elapids and its LD₅₀ of 3.8 µg/mice is similar to the most toxic short-chain α-neurotoxins reported from elapid venoms. Furthermore, ScNtx was also able to antagonize muscular, but not neuronal, nicotinic acetylcholine receptors (nAChR). Rabbits immunized with ScNtx were able to immune-recognize short-chain α-neurotoxins within whole elapid venoms. Type I neurotoxins are difficult to isolate and purify from natural sources; therefore, the heterologous expression of molecules such ScNtx, bearing crucial motifs and key amino acids, is a step forward to create common immunogens for developing cost-effective antivenoms with a wider spectrum of efficacy, quality and strong therapeutic value.

Biochemical and pharmacological characterization of Trimersurus malabaricus snake venom

Trimeresurus malabaricus is a venomous pit viper species endemic to southwestern part of India. In earlier reports, we have shown that envenomation by T. malabaricus venom leading to strong local tissue damage but the mechanism of action is not clearly revealed. Local tissue damage affected by T. malabaricus venom is of great importance since the poison has serious systemic effects including death in the case of multiple attacks. The present study details the major manifestations of T. malabaricus venom and the induction of local tissue damage, which suggests that most toxins are present in the form of hydrolytic enzymes. Hydrolytic activity of the enzymes was measured and the data indicated that protease and phospholipase A₂ activity was high which is responsible for local tissue damage. Furthermore, the role of hydrolytic enzymes in the induction of pathological events such as hemorrhage, edema, myotoxicity, and blood coagulation examination were assessed through animal models.

Computational Studies of Snake Venom Toxins

Most snake venom toxins are proteins, and participate to envenomation through a diverse array of bioactivities, such as bleeding, inflammation, and pain, cytotoxic, cardiotoxic or neurotoxic effects. The venom of a single snake species contains hundreds of toxins, and the venoms of the 725 species of venomous snakes represent a large pool of potentially bioactive proteins. Despite considerable discovery efforts, most of the snake venom toxins are still uncharacterized. Modern bioinformatics tools have been recently developed to mine snake venoms, helping focus experimental research on the most potentially interesting toxins. Some computational techniques predict toxin molecular targets, and the binding mode to these targets. This review gives an overview of current knowledge on the ~2200 sequences, and more than 400 three-dimensional structures of snake toxins deposited in public repositories, as well as of molecular modeling studies of the interaction between these toxins and their molecular targets. We also describe how modern bioinformatics have been used to study the snake venom protein phospholipase A2, the small basic myotoxin Crotamine, and the three-finger peptide Mambalgin.

Evaluation in zebrafish model of the toxicity of rhodamine B-conjugated crotamine, a peptide potentially useful for diagnostics and therapeutics

Crotamine is defensin-like cationic peptide from rattlesnake venom that possesses anticancer, antimicrobial, and antifungal properties. Despite these promising biological activities, toxicity is a major concern associated with the development of venom-derived peptides as therapeutic agents. In the present study, we used zebrafish as a system model to evaluate the toxicity of rhodamine B-conjugated (RhoB) crotamine derivative. The lethal toxic concentration of RhoB-crotamine was as low as 4 μM, which effectively kill zebrafish larvae in less than 10 min. With non-lethal concentrations (<1 μM), crotamine caused malformation in zebrafish embryos, delayed or completely halted hatching, adversely affected embryonic developmental programming, decreased the cardiac functions, and attenuated the swimming distance of zebrafish. The RhoB-crotamine translocated across vitelline membrane and accumulated in zebrafish yolk sac. These results demonstrate the sensitive responsivity of zebrafish to trial crotamine analogues for the development of novel therapeutic peptides with improved safety, bioavailability, and efficacy profiles.

Combined venom profiling and cytotoxicity screening of the Radde's mountain viper (Montivipera raddei) and Mount Bulgar Viper (Montivipera bulgardaghica) with potent cytotoxicity against human A549 lung carcinoma cells

Here we report the first characterization of the endemic Mount Bulgar Viper (Montivipera bulgardaghica) and Radde's mountain viper (Montivipera raddei) venom by a combined approach using intact mass profiling and bottom-up proteomics. The cytotoxicity screening of crude venom as well as isolated serine proteases revealed a high activity against A549 human lung carcinoma cells. By means of intact mass profiling of native and reduced venom we observed basic and acidic phospholipases type A₂. Moreover, the analysis revealed snake venom metalloproteases, cysteine-rich secretory proteins, disintegrins, snake venom serine proteases, C-type lectins, a vascular endothelial growth factor and an L-amino acid oxidase.

Wasp venomic: Unravelling the toxins arsenal of Polybia paulista venom and its potential pharmaceutical applications

Polybia paulista (Hymenoptera: Vespidae) is a neotropical social wasp from southeast Brazil. As most social Hymenoptera, venom from P. paulista comprises a complex mixture of bioactive toxins ranging from low molecular weight compounds to peptides and proteins. Several efforts have been made to elucidate the molecular composition of the P. paulista venom. Data derived from proteomic, peptidomic and allergomic analyses has enhanced our understanding of the whole envenoming process caused by the insect sting. The combined use of bioinformatics, -omics- and molecular biology tools have allowed the identification, characterization, in vitro synthesis and recombinant expression of several wasp venom toxins. Some of these P. paulista - derived bioactive compounds have been evaluated for the rational design of antivenoms and the improvement of allergy specific diagnosis and immunotherapy. Molecular characterization of crude venom extract has enabled the description and isolation of novel toxins with potential biotechnological applications. Here, we review the different approaches that have been used to unravel the venom composition of P. paulista. We also describe the main groups of P. paulista - venom toxins currently identified and analyze their potential in the development of component-resolved diagnosis of allergy, and in the rational design of antivenoms and novel bioactive drugs.

Towards universal approach for bacterial production of three-finger Ly6/uPAR proteins: Case study of cytotoxin I from cobra N. oxiana

Cytotoxins or cardiotoxins is a group of polycationic toxins from cobra venom belonging to the 'three-finger' protein superfamily (Ly6/uPAR family) which includes small β-structural proteins (60-90 residues) with high disulfide bond content (4-5 disulfides). Due to a high cytotoxic activity for cancer cells, cytotoxins are considered as potential anticancer agents. Development of the high-throughput production methods is required for the prospective applications of cytotoxins. Here, efficient approach for bacterial production of recombinant analogue of cytotoxin I from N. oxiana containing additional N-terminal Met-residue (rCTX1) was developed. rCTX1 was produced in the form of E. coli inclusion bodies. Refolding in optimized conditions provided ∼6 mg of correctly folded protein from 1 L of bacterial culture. Cytotoxicity of rCTX1 for C6 rat glioma cells was found to be similar to the activity of wild type CTX1. The milligram quantities of ¹³C,¹⁵N-labeled rCTX1 were obtained. NMR study confirmed the similarity of the spatial structures of recombinant and wild-type toxins. Additional Met residue does not perturb the overall structure of the three-finger core. The analysis of available data for different Ly6/uPAR proteins of snake and human origin revealed that efficiency of their folding in vitro is correlated with the number of proline residues in the third loop and the surface area of hydrophobic residues buried within the protein interior. The obtained data indicate that hydrophobic core is important for the folding of proteins with high disulfide bond content. Developed expression method opens new possibilities for structure-function studies of CTX1 and other related three-finger proteins.