Analysis of intra-specific variations in the venom of individual snakes based on Raman spectroscopy

The knowledge of variations in the composition of venoms from different snakes is important from both theoretical and practical points of view, in particular, at developing and selecting an antivenom. Many studies on this topic are conducted with pooled venoms, while the existence and significance of variations in the composition of venoms between individual snakes of the same species are emphasized by many authors. It is important to study both inter- and intra-specific, including intra-population, venom variations, because intra-specific variations in the venom composition may affect the effectiveness of antivenoms as strongly as inter-specific. In this work, based on venom Raman spectroscopy with principal component analysis, we assessed the variations in venoms of individual snakes of the Vipera nikolskii species from two populations and compared these intra-specific variations with inter-specific variations (with regard to the other related species). We demonstrated intra-specific (inter- and intra-population) differences in venom compositions which are smaller than inter-specific variations. We also assessed the compositions of V. nikolskii venoms from two populations to explain inter-population differences. The method used is rapid and requires virtually no preparation of samples, used in extremely small quantities, allowing the venoms of individual snakes to be analyzed. In addition, the method is informative and capable of detecting fairly subtle differences in the composition of venoms.

Effects of Cobra Cardiotoxins on Intracellular Calcium and the Contracture of Rat Cardiomyocytes Depend on Their Structural Types

Cardiotoxins (CaTx) of the three-finger toxin family are one of the main components of cobra venoms. Depending on the structure of the N-terminal or the central polypeptide loop, they are classified into either group I and II or P- and S-types, respectively, and toxins of different groups or types interact with lipid membranes variably. While their main target in the organism is the cardiovascular system, there is no data on the effects of CaTxs from different groups or types on cardiomyocytes. To evaluate these effects, a fluorescence measurement of intracellular Ca²⁺ concentration and an assessment of the rat cardiomyocytes' shape were used. The obtained results showed that CaTxs of group I containing two adjacent proline residues in the N-terminal loop were less toxic to cardiomyocytes than group II toxins and that CaTxs of S-type were less active than P-type ones. The highest activity was observed for Naja oxiana cobra cardiotoxin 2, which is of P-type and belongs to group II. For the first time, the effects of CaTxs of different groups and types on the cardiomyocytes were studied, and the data obtained showed that the CaTx toxicity to cardiomyocytes depends on the structures both of the N-terminal and central polypeptide loops.

The Potassium Channel Blocker β-Bungarotoxin from the Krait Bungarus multicinctus Venom Manifests Antiprotozoal Activity

Protozoal infections are a world-wide problem. The toxicity and somewhat low effectiveness of the existing drugs require the search for new ways of protozoa suppression. Snake venom contains structurally diverse components manifesting antiprotozoal activity; for example, those in cobra venom are cytotoxins. In this work, we aimed to characterize a novel antiprotozoal component(s) in the Bungarus multicinctus krait venom using the ciliate Tetrahymena pyriformis as a model organism. To determine the toxicity of the substances under study, surviving ciliates were registered automatically by an original BioLaT-3.2 instrument. The krait venom was separated by three-step liquid chromatography and the toxicity of the obtained fractions against T. pyriformis was analyzed. As a result, 21 kDa protein toxic to Tetrahymena was isolated and its amino acid sequence was determined by MALDI TOF MS and high-resolution mass spectrometry. It was found that antiprotozoal activity was manifested by β-bungarotoxin (β-Bgt) differing from the known toxins by two amino acid residues. Inactivation of β-Bgt phospholipolytic activity with p-bromophenacyl bromide did not change its antiprotozoal activity. Thus, this is the first demonstration of the antiprotozoal activity of β-Bgt, which is shown to be independent of its phospholipolytic activity.

Membrane-Disrupting Activity of Cobra Cytotoxins Is Determined by Configuration of the N-Terminal Loop

In aqueous solutions, cobra cytotoxins (CTX), three-finger folded proteins, exhibit conformational equilibrium between conformers with either cis or trans peptide bonds in the N-terminal loop (loop-I). The equilibrium is shifted to the cis form in toxins with a pair of adjacent Pro residues in this loop. It is known that CTX with a single Pro residue in loop-I and a cis peptide bond do not interact with lipid membranes. Thus, if a cis peptide bond is present in loop-I, as in a Pro-Pro containing CTX, this should weaken its lipid interactions and likely cytotoxic activities. To test this, we have isolated seven CTX from Naja naja and N. haje cobra venoms. Antibacterial and cytotoxic activities of these CTX, as well as their capability to induce calcein leakage from phospholipid liposomes, were evaluated. We have found that CTX with a Pro-Pro peptide bond indeed exhibit attenuated membrane-perturbing activity in model membranes and lower cytotoxic/antibacterial activity compared to their counterparts with a single Pro residue in loop-I.

New Plant Species Showing Antiprotozoian Activity

The effects of extracts of ten plant species from Russia and five species from Vietnam on the growth and survival of ciliates Tetrahymena pyriformis were studied. T. pyriformis belongs to the subkingdom Protozoa, which also includes pathogens of protozoan infections. Extraction of dried plants was carried out with acidic and alkaline aqueous solutions, as well as with an aqueous ethanol. Various amounts of extracts were added to the ciliate cells, and the number of cells survived after incubation for 1 and 24 h was recorded. We found that our samples of several plants, including wormwood, harmala, and licorice, similarly to those studied earlier, exhibit antiprotozoal activity, which may indicate that the secondary metabolites are the same in plants from different regions. Using the ciliate T. pyriformis as a model organism, the presence of antiprotozoal activity in extracts of lilac, chondrilla, cinquefoil, hop, and elm was shown for the first time.

Comparative Study of the Effect of Snake Venoms on the Growth of Ciliates Tetrahymena pyriformis: Identification of Venoms with High Antiprotozoal Activity

To search for compounds with antiprotozoal activity, effects of snake venoms on the ciliates Tetrahymena pyriformis was studied. T. pyriformis from subkingdom of Protozoa, including the protozoal pathogens, was used as a model organism to select the venoms that are the most active against parasitic protozoans. Various concentrations of venoms were added to the cells, and the cells that survived after 24 h were counted. Among the six snake species from the Viperidae family, the venom of the viper Vipera berus, which completely killed the cells at 49 μg/mL, was the most active. Among four species from the Elapidae family, the previously studied cobra venoms containing cytotoxins with strong antiprotozoal activity as well as the venom of krait Bungarus multicinctus (10 μg/mL) were the most active. The venoms of the pit vipers and Nikolsky's viper did not show any activity at 12.5 mg/mL. Thus, the venoms of V. berus and B. multicinctus are promising for the isolation of new antiprotozoal compounds.

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.

Effects of Cardiotoxins from Naja oxiana Cobra Venom on Rat Heart Muscle and Aorta: A Comparative Study of Toxin-Induced Contraction Mechanisms

Cardiotoxins (CaTxs) are a group of snake toxins that affect the cardiovascular system (CVS). Two types (S and P) of CaTxs are known, but the exact differences in the effects of these types on CVS have not been thoroughly studied. We investigated cellular mechanisms of action on CVS for Naja oxiana cobra CaTxs CTX-1 (S-type) and CTX-2 (P-type) focusing on the papillary muscle (PM) contractility and contraction of aortic rings (AR) supplemented by pharmacological analysis. It was found that CTX-1 and CTX-2 exerted dose-dependent effects manifested in PM contracture and AR contraction. CTX-2 impaired functions of PM and AR more strongly than CTX-1. Effects of CaTxs on PM were significantly reduced by nifedipine, an L-type Ca2+ channel blocker, and by KB-R7943, an inhibitor of reverse-mode Na+/Ca2+ exchange. Furthermore, 2-aminoethoxydiphenyl borate, an inhibitor of store-operated calcium entry, partially restored PM contractility damaged by CaTxs. The CaTx influence on AR contracture was significantly reduced by nifedipine and KB-R7943. The involvement of reverse-mode Na+/Ca2+ exchange in the effect of CaTxs on the rat aorta was shown for the first time. The results obtained indicate that CaTx effects on CVS are mainly associated with disturbance of transporting systems responsible for the Ca2+ influx.

S- and P-type cobra venom cardiotoxins differ in their action on isolated rat heart

Background:

The cardiovascular system is one of the first systems to be affected by snake toxins; but not many toxins exert a direct effect on the heart. Cobra venom cardiotoxins are among those few toxins that attack the heart. Although the two cardiotoxin types (S and P) differ in their central-loop structure, it is not known whether they differ in their effect on the mammalian heart. We compared the effects of S- and P-type cardiotoxins, CTХ-1 and CTХ-2, respectively, from the cobra Naja oxiana, on the isolated rat heart.

Methods:

An isolated rat heart perfused according to the Langendorff technique was used in this study to investigate the activity of cardiotoxins CTX-1 and CTX-2. The following parameters were registered: the left ventricular developed pressure, calculated as the difference between systolic and diastolic pressure in the left ventricle, the end-diastolic pressure, the heart rate, time to maximal end-diastolic pressure (heart contracture), and time to depression of the heart contraction.

Results:

Both cardiotoxins at the concentration of 5 μg/mL initially produce a slight increase in systolic intraventricular pressure, followed by its rapid decrease with a simultaneous increase in diastolic intraventricular pressure until reaching contracture. CTX-2 blocks cardiac contractions faster than CTX-1; in its presence the maximum diastolic pressure is reached faster and the magnitude of the developed contracture is higher.

Conclusion:

The P-type cardiotoxin CTX-2 more strongly impairs rat heart functional activity than the S-type cardiotoxin CTX-1, as expressed in its faster blockage of cardiac contractions as well as in more rapid development and greater magnitude of contracture in its presence.

The omega-loop of cobra cytotoxins tolerates multiple amino acid substitutions

Cobra cytotoxins (CTs), the three-fingered proteins, feature high amino acid sequence homology in the beta-strands and variations in the loop regions. We selected a pair of cytotoxins from Naja kaouthia crude venom to clarify the sequence-structure relationships. Using chromatography and mass spectroscopy, we separated and identified the mixture of cytotoxins 2 and 3, differentiated by the only Val 41/Ala 41 substitution. Here, using natural abundance ¹³C, ¹⁵N NMR-spectroscopy we performed chemical shift assignments of the signals of the both toxins in aqueous solution in the major and minor forms. Combining NOE and chemical shift data, the toxins' spatial structure was determined. Finally, we proved that the tip of the "finger"-2, or the loop-2 of cytotoxins adopts the shape of an omega-loop with a tightly-bound water molecule in its cavity. Comparison with other NMR and X-ray structures of cytotoxins possessing different amino acid sequences reveals spatial similarity in this family of proteins, including the loop-2 region, previously considered to be flexible.

Snake venom phospholipase A2s exhibit strong virucidal activity against SARS-CoV-2 and inhibit the viral spike glycoprotein interaction with ACE2

The COVID-19 pandemic caused by SARS-CoV-2 requires new treatments both to alleviate the symptoms and to prevent the spread of this disease. Previous studies demonstrated good antiviral and virucidal activity of phospholipase A₂s (PLA₂s) from snake venoms against viruses from different families but there was no data for coronaviruses. Here we show that PLA₂s from snake venoms protect Vero E6 cells against SARS-CoV-2 cytopathic effects. PLA₂s showed low cytotoxicity to Vero E6 cells with some activity at micromolar concentrations, but strong antiviral activity at nanomolar concentrations. Dimeric PLA₂ from the viper Vipera nikolskii and its subunits manifested especially potent virucidal effects, which were related to their phospholipolytic activity, and inhibited cell-cell fusion mediated by the SARS-CoV-2 spike glycoprotein. Moreover, PLA₂s interfered with binding both of an antibody against ACE2 and of the receptor-binding domain of the glycoprotein S to 293T/ACE2 cells. This is the first demonstration of a detrimental effect of PLA₂s on β-coronaviruses. Thus, snake PLA₂s are promising for the development of antiviral drugs that target the viral envelope, and could also prove to be useful tools to study the interaction of viruses with host cells.

Snake C-type lectin-like proteins inhibit nicotinic acetylcholine receptors

Venoms of viperid snakes affect mostly hemostasis, while C-type lectin-like proteins (CTLPs), one of the main components of viperid venoms, act as anticoagulants, procoagulants, or agonists/antagonists of platelet activation. However, we have shown earlier that CTLPs from the saw-scaled viper Echis multisquamatus, called emunarecins EM1 and EM2, were able to inhibit nicotinic acetylcholine receptors (nAChRs) in neurons of a pond snail (Lymnaea stagnalis). Here we analysed the structure of the emunarecins by mass spectrometry and report that EM1 and EM2 inhibit fluorescent α-bungarotoxin binding to both muscle-type nAChRs from Torpedo californica and human neuronal α7 nAChRs. EM1 at 23µM and EM2 at 9µM almost completely prevented fluorecsent α-bungarotoxin binding to muscle-type nAChRs. Interaction with human neuronal α7 nAChR was weaker; EM1 at the concentration of 23µM blocked the α-bungarotoxin binding only by about 40% and EM2 at 9µM by about 20%. The efficiency of the EM2 interaction with nAChRs was comparable to that of a non-conventional toxin, WTX, from Naja kaouthia cobra venom. Together with the data obtained earlier, these results show that CTLPs may represent new nAChR ligands.

Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins

Snake venoms possess lethal activities against different organisms, ranging from bacteria to higher vertebrates. Several venoms were shown to be active against protozoa, however, data about the anti-protozoan activity of cobra and viper venoms are very scarce. We tested the effects of venoms from several snake species on the ciliate Tetrahymena pyriformis. The venoms tested induced T. pyriformis immobilization, followed by death, the most pronounced effect being observed for cobra Naja sumatrana venom. The active polypeptides were isolated from this venom by a combination of gel-filtration, ion exchange and reversed-phase HPLC and analyzed by mass spectrometry. It was found that these were cytotoxins of the three-finger toxin family. The cytotoxins from several cobra species were tested and manifested toxicity for infusorians. Light microscopy revealed that, because of the cytotoxin action, the infusorians’ morphology was changed greatly, from teardrop-like to an almost spherical shape, this alteration being accompanied by a leakage of cell contents. Fluorescence microscopy showed that the fluorescently labelled cytotoxin 2 from cobra N. oxiana was localized mainly at the membrane of killed infusorians, indicating that cytotoxins may kill T. pyriformis by causing membrane rupture. This work is the first evidence of the antiprotozoal activity of cobra venom cytotoxins, as demonstrated by the example of the ciliate T. pyriformis.

Dimeric Disintegrins from the Steppe Viper V. ursinii Venom

Four dimeric disintegrins were isolated from the venom of the steppe viper V. ursinii using liquid chromatography. Disintegrins prevented adhesion of MCF7 cells to fibronectin, which indicates their interaction with integrin receptors of the αVβ1 type. According to mass spectrometry data, the molar masses of disintegrins are about 14 kDa. The method of peptide mapping established the structure of a new heterodimeric disintegrin weighing 13 995.5 Da and shows that it belongs to the class of RGD/KGD-containing disintegrins.

Encapsulation of Neurotoxins, Blockers of Nicotinic Acetylcholine Receptors, in Nanomaterials Based on Sulfated Polysaccharides

Three-finger snake neurotoxins are selective antagonists of some nicotinic acetylcholine receptor subtypes and are widely used to study these receptors. The peptide neurotoxin azemiopsin, recently isolated from the venom of Azemipos feae, is a selective blocker of muscle-type nicotinic acetylcholine receptor. In order to reduce their toxicity and increase resistance under physiological conditions, we have encapsulated these toxins into nanomaterials. The study of nanomaterials after interaction with neurotoxins by the methods of transmission electron microscopy and dynamic light scattering revealed an increase in the size of nanoparticles, which indicates the inclusion of neurotoxins in nanomaterials.

Pancreatic and snake venom presynaptically active phospholipases A2 inhibit nicotinic acetylcholine receptors

Phospholipases A₂ (PLA₂s) are enzymes found throughout the animal kingdom. They hydrolyze phospholipids in the sn-2 position producing lysophospholipids and unsaturated fatty acids, agents that can damage membranes. PLA₂s from snake venoms have numerous toxic effects, not all of which can be explained by phospholipid hydrolysis, and each enzyme has a specific effect. We have earlier demonstrated the capability of several snake venom PLA₂s with different enzymatic, cytotoxic, anticoagulant and antiproliferative properties, to decrease acetylcholine-induced currents in Lymnaea stagnalis neurons, and to compete with α-bungarotoxin for binding to nicotinic acetylcholine receptors (nAChRs) and acetylcholine binding protein. Since nAChRs are implicated in postsynaptic and presynaptic activities, in this work we probe those PLA₂s known to have strong presynaptic effects, namely β-bungarotoxin from Bungarus multicinctus and crotoxin from Crotalus durissus terrificus. We also wished to explore whether mammalian PLA₂s interact with nAChRs, and have examined non-toxic PLA₂ from porcine pancreas. It was found that porcine pancreatic PLA₂ and presynaptic β-bungarotoxin blocked currents mediated by nAChRs in Lymnaea neurons with IC₅₀s of 2.5 and 4.8 μM, respectively. Crotoxin competed with radioactive α-bungarotoxin for binding to Torpedo and human α7 nAChRs and to the acetylcholine binding protein. Pancreatic PLA₂ interacted similarly with these targets; moreover, it inhibited radioactive α-bungarotoxin binding to the water-soluble extracellular domain of human α9 nAChR, and blocked acetylcholine induced currents in human α9α10 nAChRs heterologously expressed in Xenopus oocytes. These and our earlier results show that all snake PLA₂s, including presynaptically active crotoxin and β-bungarotoxin, as well as mammalian pancreatic PLA₂, interact with nAChRs. The data obtained suggest that this interaction may be a general property of all PLA₂s, which should be proved by further experiments.

Cobra Venom Factor and Ketoprofen Abolish the Antitumor Effect of Nerve Growth Factor from Cobra Venom

We showed recently that nerve growth factor (NGF) from cobra venom inhibited the growth of Ehrlich ascites carcinoma (EAC) inoculated subcutaneously in mice. Here, we studied the influence of anti-complementary cobra venom factor (CVF) and the non-steroidal anti-inflammatory drug ketoprofen on the antitumor NGF effect, as well as on NGF-induced changes in EAC histological patterns, the activity of lactate and succinate dehydrogenases in tumor cells and the serum level of some cytokines. NGF, CVF and ketoprofen reduced the tumor volume by approximately 72%, 68% and 30%, respectively. The antitumor effect of NGF was accompanied by an increase in the lymphocytic infiltration of the tumor tissue, the level of interleukin 1β and tumor necrosis factor α in the serum, as well as the activity of lactate and succinate dehydrogenases in tumor cells. Simultaneous administration of NGF with either CVF or ketoprofen abolished the antitumor effect and reduced all other effects of NGF, whereas NGF itself significantly decreased the antitumor action of both CVF and ketoprofen. Thus, the antitumor effect of NGF critically depended on the status of the immune system and was abolished by the disturbance of the complement system; the disturbance of the inflammatory response canceled the antitumor effect as well.

New paradoxical three-finger toxin from the cobra Naja kaouthia venom: Isolation and characterization

A new three-finger toxin nakoroxin was isolated from the cobra Naja kaouthia venom, and its complete amino acid sequence was established. Nakoroxin belongs to the group of "orphan" toxins, data on the biological activity of which are practically absent. Nakoroxin shows no cytotoxicity and does not inhibit the binding of α-bungarotoxin to nicotinic acetylcholine receptors of muscle and α7 types. However, it potentiates the binding of α-bungarotoxin to the acetylcholine-binding protein from Lymnaea stagnalis. This is the first toxin with such an unusual property.

N-methyl serotonin analogues from the Bufo bufo toad venom interact efficiently with the α7 nicotinic acetylcholine receptors

Two low-molecular-weight compounds were isolated from the parotid gland secret of the toad Bufo bufo, which by absorption spectra and HPLC-MS/MS chromatography data correspond to di- and trimethyl derivatives of serotonin (5-hydorxytryptamine): bufotenine (confirmed by counter synthesis) and bufotenidine (5-HTQ). In experiments on competitive radioligand binding, these compounds showed a higher affinity and selectivity for neuronal α7 nicotinic acetylcholine receptors compared with the muscular cholinergic receptors. The most efficient compound in terms of binding value was bufotenine, the efficiency of 5-HTQ was an order of magnitude lower, and the minimal activity was exhibited by serotonin.

Peptides from puff adder Bitis arietans venom, novel inhibitors of nicotinic acetylcholine receptors

Phospholipase A₂ (named bitanarin) possessing capability to block nicotinic acetylcholine receptors (nAChRs) was isolated earlier (Vulfius et al., 2011) from puff adder Bitis arietans venom. Further studies indicated that low molecular weight fractions of puff adder venom inhibit nAChRs as well. In this paper, we report on isolation from this venom and characterization of three novel peptides called baptides 1, 2 and 3 that reversibly block nAChRs. To isolate the peptides, the venom of B. arietans was fractionated by gel-filtration and reversed phase chromatography. The amino acid sequences of peptides were established by de novo sequencing using MALDI mass spectrometry. Baptide 1 comprised 7, baptides 2 and 3-10 amino acid residues, the latter being acetylated at the N-terminus. This is the first indication for the presence of such post-translational modification in snake venom proteins. None of the peptides contain cysteine residues. For biological activity studies the peptides were prepared by solid phase peptide synthesis. Baptide 3 and 2 blocked acetylcholine-elicited currents in isolated Lymnaea stagnalis neurons with IC₅₀ of about 50 μM and 250 μM, respectively. In addition baptide 2 blocked acetylcholine-induced currents in muscle nAChR heterologously expressed in Xenopus oocytes with IC₅₀ of about 3 μM. The peptides did not compete with radioactive α-bungarotoxin for binding to Torpedo and α7 nAChRs at concentration up to 200 μM that suggests non-competitive mode of inhibition. Calcium imaging studies on α7 and muscle nAChRs heterologously expressed in mouse neuroblastoma Neuro2a cells showed that on α7 receptor baptide 2 inhibited acetylcholine-induced increasing intracellular calcium concentration with IC₅₀ of 20.6 ± 3.93 μM. On both α7 and muscle nAChRs the suppression of maximal response to acetylcholine by about 50% was observed at baptide 2 concentration of 25 μM, the value being close to IC₅₀ on α7 nAChR. These data are in accord with non-competitive inhibition as follows from α-bungarotoxin binding experiments. The described peptides are the shortest peptides without disulfide bridges isolated from animal venom and capable to inhibit nAChR by non-competitive way.

Quantitative Proteomic Analysis of Venoms from Russian Vipers of Pelias Group: Phospholipases A₂ are the Main Venom Components

Venoms of most Russian viper species are poorly characterized. Here, by quantitative chromato-mass-spectrometry, we analyzed protein and peptide compositions of venoms from four Vipera species (V. kaznakovi, V. renardi, V. orlovi and V. nikolskii) inhabiting different regions of Russia. In all these species, the main components were phospholipases A₂, their content ranging from 24% in V. orlovi to 65% in V. nikolskii. Altogether, enzyme content in venom of V. nikolskii reached ~85%. Among the non-enzymatic proteins, the most abundant were disintegrins (14%) in the V. renardi venom, C-type lectin like (12.5%) in V. kaznakovi, cysteine-rich venom proteins (12%) in V. orlovi and venom endothelial growth factors (8%) in V. nikolskii. In total, 210 proteins and 512 endogenous peptides were identified in the four viper venoms. They represented 14 snake venom protein families, most of which were found in the venoms of Vipera snakes previously. However, phospholipase B and nucleotide degrading enzymes were reported here for the first time. Compositions of V. kaznakovi and V. orlovi venoms were described for the first time and showed the greatest similarity among the four venoms studied, which probably reflected close relationship between these species within the “kaznakovi” complex.

Nonconventional three-finger toxin BMLCL from krait Bungarus multicinctus venom with high affinity interacts with nicotinic acetylcholine receptors

Nonconventional three-finger toxin BMLCL was isolated from B. multicinctus venom, and its interaction with different subtypes of nicotinic acetylcholine receptor (nAChR) was studied. It was found that BMLCL is able to interact with high efficiency with both α7 and muscle type nAChRs.

Neurotoxins from snake venoms and α-conotoxin ImI inhibit functionally active ionotropic γ-aminobutyric acid (GABA) receptors

Ionotropic receptors of γ-aminobutyric acid (GABAAR) regulate neuronal inhibition and are targeted by benzodiazepines and general anesthetics. We show that a fluorescent derivative of α-cobratoxin (α-Ctx), belonging to the family of three-finger toxins from snake venoms, specifically stained the α1β3γ2 receptor; and at 10 μm α-Ctx completely blocked GABA-induced currents in this receptor expressed in Xenopus oocytes (IC50 = 236 nm) and less potently inhibited α1β2γ2 ≈ α2β2γ2 > α5β2γ2 > α2β3γ2 and α1β3δ GABAARs. The α1β3γ2 receptor was also inhibited by some other three-finger toxins, long α-neurotoxin Ls III and nonconventional toxin WTX. α-Conotoxin ImI displayed inhibitory activity as well. Electrophysiology experiments showed mixed competitive and noncompetitive α-Ctx action. Fluorescent α-Ctx, however, could be displaced by muscimol indicating that most of the α-Ctx-binding sites overlap with the orthosteric sites at the β/α subunit interface. Modeling and molecular dynamic studies indicated that α-Ctx or α-bungarotoxin seem to interact with GABAAR in a way similar to their interaction with the acetylcholine-binding protein or the ligand-binding domain of nicotinic receptors. This was supported by mutagenesis studies and experiments with α-conotoxin ImI and a chimeric Naja oxiana α-neurotoxin indicating that the major role in α-Ctx binding to GABAAR is played by the tip of its central loop II accommodating under loop C of the receptors.

Nerve growth factor from cobra venom inhibits the growth of Ehrlich tumor in mice

The effects of nerve growth factor (NGF) from cobra venom (cvNGF) on growth of Ehrlich ascites carcinoma (EAC) cells inoculated subcutaneously in mice have been studied. The carcinoma growth slows down, but does not stop, during a course of cvNGF injections and restores after the course has been discontinued. The maximal anti-tumor effect has been observed at a dose of 8 nmoles cvNGF/kg body weight. cvNGF does not impact on lifespan of mice with grafted EAC cells. K252a, a tyrosine kinase inhibitor, attenuates the anti-tumor effect of cvNGF indicating the involvement of TrkA receptors in the process. cvNGF has induced also increase in body weight of the experimental animals. In overall, cvNGF shows the anti-tumor and weight-increasing effects which are opposite to those described for mammalian NGF (mNGF). However in experiments on breast cancer cell line MCF-7 cvNGF showed the same proliferative effects as mNGF and had no cytotoxic action on tumor cells in vitro. These data suggest that cvNGF slows down EAC growth via an indirect mechanism in which TrkA receptors are involved.

Azemiopsin from Azemiops feae viper venom, a novel polypeptide ligand of nicotinic acetylcholine receptor

Azemiopsin, a novel polypeptide, was isolated from the Azemiops feae viper venom by combination of gel filtration and reverse-phase HPLC. Its amino acid sequence (DNWWPKPPHQGPRPPRPRPKP) was determined by means of Edman degradation and mass spectrometry. It consists of 21 residues and, unlike similar venom isolates, does not contain cysteine residues. According to circular dichroism measurements, this peptide adopts a β-structure. Peptide synthesis was used to verify the determined sequence and to prepare peptide in sufficient amounts to study its biological activity. Azemiopsin efficiently competed with α-bungarotoxin for binding to Torpedo nicotinic acetylcholine receptor (nAChR) (IC₅₀ 0.18 ± 0.03 μm) and with lower efficiency to human α7 nAChR (IC₅₀ 22 ± 2 μm). It dose-dependently blocked acetylcholine-induced currents in Xenopus oocytes heterologously expressing human muscle-type nAChR and was more potent against the adult form (α1β1ϵδ) than the fetal form (α1β1γδ), EC₅₀ being 0.44 ± 0.1 μm and 1.56 ± 0.37 μm, respectively. The peptide had no effect on GABA_A (α1β3γ2 or α2β3γ2) receptors at a concentration up to 100 μm or on 5-HT₃ receptors at a concentration up to 10 μm. Ala scanning showed that amino acid residues at positions 3–6, 8–11, and 13–14 are essential for binding to Torpedo nAChR. In biological activity azemiopsin resembles waglerin, a disulfide-containing peptide from the Tropidechis wagleri venom, shares with it a homologous C-terminal hexapeptide, but is the first natural toxin that blocks nAChRs and does not possess disulfide bridges.

Dimeric α-cobratoxin X-ray structure: localization of intermolecular disulfides and possible mode of binding to nicotinic acetylcholine receptors

In Naja kaouthia cobra venom, we have earlier discovered a covalent dimeric form of α-cobratoxin (αCT-αCT) with two intermolecular disulfides, but we could not determine their positions. Here, we report the αCT-αCT crystal structure at 1.94 Å where intermolecular disulfides are identified between Cys(3) in one protomer and Cys(20) of the second, and vice versa. All remaining intramolecular disulfides, including the additional bridge between Cys(26) and Cys(30) in the central loops II, have the same positions as in monomeric α-cobratoxin. The three-finger fold is essentially preserved in each protomer, but the arrangement of the αCT-αCT dimer differs from those of noncovalent crystallographic dimers of three-finger toxins (TFT) or from the κ-bungarotoxin solution structure. Selective reduction of Cys(26)-Cys(30) in one protomer does not affect the activity against the α7 nicotinic acetylcholine receptor (nAChR), whereas its reduction in both protomers almost prevents α7 nAChR recognition. On the contrary, reduction of one or both Cys(26)-Cys(30) disulfides in αCT-αCT considerably potentiates inhibition of the α3β2 nAChR by the toxin. The heteromeric dimer of α-cobratoxin and cytotoxin has an activity similar to that of αCT-αCT against the α7 nAChR and is more active against α3β2 nAChRs. Our results demonstrate that at least one Cys(26)-Cys(30) disulfide in covalent TFT dimers, similar to the monomeric TFTs, is essential for their recognition by α7 nAChR, although it is less important for interaction of covalent TFT dimers with the α3β2 nAChR.

[Molecular cloning and analysis of cDNA sequences encoding serine proteinase and Kunitz type inhibitor in venom gland of Vipera nikolskii viper]

Serine proteinases and Kunitz type inhibitors are widely represented in venoms of snakes from different genera. During the study of the venoms from snakes inhabiting Russia we have cloned cDNAs encoding new proteins belonging to these protein families. Thus, a new serine proteinase called nikobin was identified in the venom gland of Vipera nikolskii viper. By amino acid sequence deduced from the cDNA sequence, nikobin differs from serine proteinases identified in other snake species. Nikobin amino acid sequence contains 15 unique substitutions. This is the first serine proteinase of viper from Vipera genus for which a complete amino acid sequence established. The cDNA encoding Kunitz type inhibitor was also cloned. The deduced amino acid sequence of inhibitor is homologous to those of other proteins from that snakes of Vipera genus. However there are several unusual amino acid substitutions that might result in the change of biological activity of inhibitor.

[New weak toxins from the cobra venom]

A protein with M 7485 Da containing five disulfide bonds was isolated from the venom of cobra Naja oxiana using various types of liquid chromatography. The complete amino acid sequence of the protein was determined by protein chemistry methods, which permitted us to assign it to the group of weak toxins. This is the first weak toxin isolated from the venom of N. oxiana. In a similar way, two new toxins with M 7628 and 7559 Da, which fall into the range of weak toxin masses, were isolated from the venom of the cobra N. kaouthia. The characterization of these proteins using Edman degradation and MALDI mass spectrometry has shown that one of these proteins is a novel weak toxin and the other is the known weak toxin WTX with an oxidized methionine residue in position 9. Such a modification was detected in weak toxins for the first time. A study of the biological activity of the toxin from N. oxiana showed that, like other weak toxins, it can be bound by muscle nicotinic cholinoreceptors and alpha7 nicotinic cholinoreceptors.

Cysteine-rich venom proteins from the snakes of Viperinae subfamily - molecular cloning and phylogenetic relationship

Cysteine-rich proteins found in animal venoms (CRISP-Vs) are members of a large family of cysteine-rich secretory proteins (CRISPs). CRISP-Vs acting on different ion channels were found in venoms or mRNA (cDNA) encoding CRISP-Vs were cloned from snakes of three main families (Elapidae, Colubridae and Viperidae). About thirty snake CRISP-Vs were sequenced so far, however no complete sequence for CRISP-V from Viperinae subfamily was reported. We have cloned and sequenced for the first time cDNAs encoding CRISP-Vs from Vipera nikolskii and Vipera berus vipers (Viperinae). The deduced mature CRISP-V amino acid sequences consist of 220 amino acid residues. Phylogenetic analysis showed that viper proteins are closely related to those of Crotalinae snakes. The presence of CRISP-V in the V. berus venom was revealed using a combination of gel-filtration chromatography, electrophoresis and MALDI mass spectrometry. The finding of the putative channel blocker in viper venom may indicate its action on prey nervous system.

Naturally occurring disulfide-bound dimers of three-fingered toxins: a paradigm for biological activity diversification

Disulfide-bound dimers of three-fingered toxins have been discovered in the Naja kaouthia cobra venom; that is, the homodimer of alpha-cobratoxin (a long-chain alpha-neurotoxin) and heterodimers formed by alpha-cobratoxin with different cytotoxins. According to circular dichroism measurements, toxins in dimers retain in general their three-fingered folding. The functionally important disulfide 26-30 in polypeptide loop II of alpha-cobratoxin moiety remains intact in both types of dimers. Biological activity studies showed that cytotoxins within dimers completely lose their cytotoxicity. However, the dimers retain most of the alpha-cobratoxin capacity to compete with alpha-bungarotoxin for binding to Torpedo and alpha7 nicotinic acetylcholine receptors (nAChRs) as well as to Lymnea stagnalis acetylcholine-binding protein. Electrophysiological experiments on neuronal nAChRs expressed in Xenopus oocytes have shown that alpha-cobratoxin dimer not only interacts with alpha7 nAChR but, in contrast to alpha-cobratoxin monomer, also blocks alpha3beta2 nAChR. In the latter activity it resembles kappa-bungarotoxin, a dimer with no disulfides between monomers. These results demonstrate that dimerization is essential for the interaction of three-fingered neurotoxins with heteromeric alpha3beta2 nAChRs.

Toxicity of venoms from vipers of Pelias group to crickets Gryllus assimilis and its relation to snake entomophagy

The existing data indicate that snake venom is most toxic towards the natural vertebrate preys. Several species of snake include arthropods in their food. However, there is no available data on the toxicity of venom from entomophagous snakes towards their prey. We have studied the toxicity of venom from vipers of Pelias group towards crickets Gryllus assimilis. The Pelias group includes several closely related viper species inhabiting mainly the South European part of Russia, and they differ in their feeding preferences. Snakes from the Vipera renardi, Vipera lotievi, Vipera kaznakovi, and Vipera orlovi species feed on wide range of animals including insects, whereas snakes from Vipera berus and Vipera nikolskii species do not include insects in their diet. We have found that the venom from vipers that include insects in their diet possesses greater toxicity towards crickets. The greatest toxicity was observed for the venom from V. lotievi, which displays a preference for insects in its diet. Therefore, based on our data, we suggest that the viper entomophagy is not a result of behavior plasticity, but is probably determined at a genetic level.

Naja melanoleuca cobra venom contains two forms of complement-depleting factor (CVF)

Two forms of complement-depleting cobra venom factor (CVFm1 and CVFm2), possessing molecular masses of 142.6 kDa (CVFm1) and 143.1 kDa (CVFm2), according to MALDI mass-spectrometry, were isolated from the Naja melanoleuca cobra venom. As shown by polyacrylamide gel electrophoresis in the presence of SDS, both forms similarly to factor from the Naja kaouthia cobra venom (CVFk) consist of three polypeptide chains with molecular masses of about 70, 50, and 30 kDa, the two large subunits being glycosylated. As determined by MALDI mass-spectrometry, 30 kDa subunits of CVFm1 and CVFm2 have considerably different finger-prints of tryptic digests that suggests differences in their amino acid sequences. A study of activity in vivo has shown no significant differences in C3 consumption by CVFm1, CVFm2 and CVFk in mouse blood. However, as shown by an immunoassay method, they differ in their ability to activate the complement system via C3 conversion, the ratio of these activities for CVFm1:CVFm2:CVFk being 2.5:1.6:1. Kinetic studies using a hemolytic test showed that complement depletion by CVFm1 is faster than that by CVFm2. Thus, for the first time the presence in a single venom of two forms of CVF differing by both amino acid sequence and biological activity has been shown.

Isolation and preliminary crystallographic studies of two new phospholipases A2 from Vipera nikolskii venom

Snake-venom phospholipases A2 (PLA2s) represent a good model for studies of structure-function relationships, mainly because of their small size and diverse pharmacological and toxicological activities. To obtain new members of the abundant PLA2 family, the venom of the viper Vipera nikolskii was fractionated for the first time and two new proteins, VN5-3 and VN4-3, were isolated. Both proteins show phospholipase A2 activity and may possess neurotoxic activity. Based on the determined partial amino-acid sequences, the new proteins can be classified as basic Asp49 phospholipases A2. They were crystallized using the hanging-drop vapour-diffusion method and crystals of both proteins belong to space group R32, with similar unit-cell parameters: a = b = 76.29, c = 303.35 A for protein VN5-3 and a = b = 76.28, c = 304.39 A for protein VN4-3. Diffraction data sets to 3.0 and 2.2 A resolution were collected and processed for the VN5-3 and VN4-3 crystals, respectively. Preliminary analysis indicates that there are two molecules in the asymmetric unit for both crystals. Further crystallographic studies will help in understanding the structural basis for the multiple functions of snake-venom PLA2s.

Toxicity of cobra venom components to cockroach Gromphadorhina portentosa

The toxicity of the Thailand and Middle-Asian cobra venoms as well as of their isolated components (neurotoxins, cytotoxins, phospholipases and some others) for cockroach Gromphadorhina portentosa was studied. It was found that, as compared to mammals, cockroaches are more resistant to cobra venoms and their components. At intraabdominal injection the most toxic for cockroaches were cytotoxins (LD(50) 1.5-2.3 nmol/g). Acidic phospholipase A(2) CM II is less active (2.85 nmol/g), while alpha-neurotoxins, being the most toxic venom components for mice (LD(50) 0.01-0.03 nmol/g), are not toxic for cockroaches at doses up to 15 nmol/g.

First tryptophan-containing weak neurotoxin from cobra venom

With the purpose of studying structure-function relationships among weak neurotoxins (called so because of their low toxicity), we have isolated a toxin (WTX) from the venom of cobra Naja kaouthia using a combination of gel-filtration and ion-exchange chromatography. The amino acid sequence of the isolated toxin was determined by means of Edman degradation and MALDI mass spectrometry, the primary structure obtained being confirmed by 1H-NMR in the course of spatial structure analysis. The WTX sequence differs slightly from that of the toxin CM-9a isolated earlier from the same venom (Joubert and Taljaard, Hoppe-Seyler's Z. Physiol. Chem., 361 (1980) 425). The differences include an extra residue (Trp36) between Ser35 and Arg37 as well as interchanging of two residues (Tyr52 and Lys50) in the C-terminal part of the toxin molecule. These changes improve the alignment that can be made with other weak neurotoxin sequences. An extended sequence comparison reveals that WTX is the first case of a tryptophan-containing weak neurotoxin isolated from cobra venom. WTX was found to compete with radioiodinated alpha-bungarotoxin for binding to the membrane-bound nicotinic acetylcholine receptor from Torpedo californica.

Muscarinic toxin-like proteins from cobra venom

Three new polypeptides were isolated from the venom of the Thailand cobra Naja kaouthia and their amino-acid sequences determined. They consist of 65-amino-acid residues and have four disulfide bridges. A comparison of the amino-acid sequences of the new polypeptides with those of snake toxins shows that two of them (MTLP-1 and MTLP-2) share a high degree of similarity (55-74% sequence identity) with muscarinic toxins from the mamba. The third polypeptide (MTLP-3) is similar to muscarinic toxins with respect to the position of cysteine residues and the size of the disulfide-confined loops, but shows less similarity to these toxins (30-34% sequence identity). It is almost identical with a neurotoxin-like protein from Bungarus multicinctus (TrEMBL accession number Q9W727), the sequence of which has been deduced from cloned cDNA only. The binding affinities of the isolated muscarinic toxin-like proteins towards the different muscarinic acetylcholine receptor (mAChR) subtypes (m1-m5) was determined in competition experiments with N-[3H]methylscopolamine using membrane preparations from CHO-K1 cells, which express these receptors. We found that MTLP-1 competed weakly with radioactive ligand for binding to all mAChR subtypes. The most pronounced effect was observed for the m3 subtype; here an IC50 value of about 3 microM was determined. MTLP-2 had no effect on ligand binding to any of the mAChR subtypes at concentrations up to 1 microM. MTLP-1 showed no inhibitory effect on alpha-cobratoxin binding to the nicotinic acetylcholine receptor from Torpedo californica at concentrations up to 20 microM.

[MALDI-mass spectrometry for identification of new proteins in snake venoms]

By MALDI MS, we searched cobra venoms for new low-content polypeptides. A number of new proteins with molecular masses 7-25 kDa, characteristic of the known snake protein toxins, were identified, with the content of one of them less than 0.02%.