Use of a synthetic biosensor for neutralizing activity-biased selection of monoclonal antibodies against atroxlysin-I, an hemorrhagic metalloproteinase from Bothrops atrox snake venom

Development of a neutralizing monoclonal antibody targeting Bothrops atrox venom metalloproteinases

Snakebites are classified as a neglected tropical disease by the World Health Organization. In South America's tropical rainforests, Bothrops genus, particularly Bothrops atrox, is responsible for most incidents. Severe local effects, such as hemorrhage, are primarily caused by snake venom metalloproteinases (SVMPs), which are not fully neutralized by conventional therapy. Here, we report the production of a neutralizing monoclonal antibody (mAb) against the hemorrhagic activity of B. atrox venom metalloproteinases. mAbs were produced by immunization of BALB/c mice using the B. atrox venom (BaV). The resulting hybridomas were screened by ELISA using BaV as antigen. The selected clone 4H4D11 (mAb-BaSVMP) showed cross-reactivity with other medically important species of Bothrops snakes in Brazil and Peru. Western blot assays revealed that the produced mAb binds to proteins with molecular masses of approximately 50 kDa and 20 kDa in BaV and recognizes native Atroxlysin-III and Atroxlysin-I by ELISA. mAb-BaSVMP did not bind to a cellulose membrane containing the primary sequence of a metalloproteinase, suggesting that it may recognize a conformational epitope. Additionally, mAb-BaSVMP neutralizes the in vivo hemorrhagic activity caused by BaV in mice. These results highlight the potential usefulness of mAb-BaSVMP for developing effective antivenoms for passive immunotherapy against bothropic envenomation.

Fuentes L, Pimenta A, Nagem RAP, Chávez-Olórtegui C, Schneider FS, Molina F, Sanchez EF, Suárez D, Ferreira RS. Assessing the Interactions between Snake Venom Metalloproteinases and Hydroxamate Inhibitors Using Kinetic and ITC Assays, Molecular Dynamics Simulations and MM/PBSA-Based Scoring Functions

Bothrops species are the main cause of snake bites in rural communities of tropical developing countries of Central and South America. Envenomation by Bothrops snakes is characterized by prominent local inflammation, hemorrhage and necrosis as well as systemic hemostatic disturbances. These pathological effects are mainly caused by the major toxins of the viperidae venoms, the snake venom metalloproteinases (SVMPs). Despite the antivenom therapy efficiency to block the main toxic effects on bite victims, this treatment shows limited efficacy to prevent tissue necrosis. Thus, drug-like inhibitors of these toxins have the potential to aid serum therapy of accidents inflicted by viper snakes. Broad-spectrum metalloprotease inhibitors bearing a hydroxamate zinc-binding group are potential candidates to improve snake bites therapy and could also be used to study toxin-ligand interactions. Therefore, in this work, we used both docking calculations and molecular dynamics simulations to assess the interactions between six hydroxamate inhibitors and two P-I SVMPs selected as models: Atroxlysin-I (hemorrhagic) from Bothrops atrox, and Leucurolysin-a (nonhemorrhagic) from Bothrops leucurus. We also employed a large variety of end-point free energy methods in combination with entropic terms to produce scoring functions of the relative affinities of the inhibitors for the toxins. Then we identified the scoring functions that best correlated with experimental data obtained from kinetic activity assays. In addition, to the characterization of these six molecules as inhibitors of the toxins, this study sheds light on the main enzyme-inhibitor interactions, explaining the broad-spectrum behavior of the inhibitors, and identifies the energetic and entropic terms that improve the performance of the scoring functions.

Bothrops atrox venom: Biochemical properties and cellular phenotypes of three highly toxic classes of toxins

Snake venoms have a complex mixture of compounds that are conserved across species and act synergistically, triggering severe local and systemic effects. Identification of the toxin classes that are most damaging to cell homeostasis would be a powerful approach to focus on the main activities that underpin envenomation. Here, we focus on the venom of Bothrops atrox, snake responsible for most of the accidents in Amazon region of South America. We identified the key cytotoxic toxin fractions from B. atrox venom and mapped their biochemical properties, protein composition and cell damage. Five fractions were obtained by mass exclusion chromatography and contained either a single class of enzymatic activity (i.e., L-amino acid oxidases or Hyaluronidases) or different activities co-distributed in two or more protein fractions (e.g., Metalloproteinases, Serine Proteases, or Phospholipases A2). Only three protein fractions reduced cell viability of primary human cells. Strikingly, such activity is accompanied by disruption of cell attachment to substratum and to neighbouring cells. Such strong perturbation of morphological cell features indicates likely defects in tissue integrity in vivo. Mass spectrometry identified the main classes of toxins that contribute to these phenotypes. We provide here a strategy for the selection of key cytotoxic proteins for targeted investigation of their mechanism of action and potential synergism during snakebite envenomation. Our data highlights putative toxins (or combinations of) that may be the focus of future therapeutic interference.

Multi-perspectives and challenges in identifying B-cell epitopes

The identification of B-cell epitopes (BCEs) in antigens is a crucial step in developing recombinant vaccines or immunotherapies for various diseases. Over the past four decades, numerous in silico methods have been developed for predicting BCEs. However, existing reviews have only covered specific aspects, such as the progress in predicting conformational or linear BCEs. Therefore, in this paper, we have undertaken a systematic approach to provide a comprehensive review covering all aspects associated with the identification of BCEs. First, we have covered the experimental techniques developed over the years for identifying linear and conformational epitopes, including the limitations and challenges associated with these techniques. Second, we have briefly described the historical perspectives and resources that maintain experimentally validated information on BCEs. Third, we have extensively reviewed the computational methods developed for predicting conformational BCEs from the structure of the antigen, as well as the methods for predicting conformational epitopes from the sequence. Fourth, we have systematically reviewed the in silico methods developed in the last four decades for predicting linear or continuous BCEs. Finally, we have discussed the overall challenge of identifying continuous or conformational BCEs. In this review, we only listed major computational resources; a complete list with the URL is available from the BCinfo website (https://webs.iiitd.edu.in/raghava/bcinfo/).

Venom biotechnology: casting light on nature's deadliest weapons using synthetic biology

Venoms are complex chemical arsenals that have evolved independently many times in the animal kingdom. Venoms have attracted the interest of researchers because they are an important innovation that has contributed greatly to the evolutionary success of many animals, and their medical relevance offers significant potential for drug discovery. During the last decade, venom research has been revolutionized by the application of systems biology, giving rise to a novel field known as venomics. More recently, biotechnology has also made an increasing impact in this field. Its methods provide the means to disentangle and study venom systems across all levels of biological organization and, given their tremendous impact on the life sciences, these pivotal tools greatly facilitate the coherent understanding of venom system organization, development, biochemistry, and therapeutic activity. Even so, we lack a comprehensive overview of major advances achieved by applying biotechnology to venom systems. This review therefore considers the methods, insights, and potential future developments of biotechnological applications in the field of venom research. We follow the levels of biological organization and structure, starting with the methods used to study the genomic blueprint and genetic machinery of venoms, followed gene products and their functional phenotypes. We argue that biotechnology can answer some of the most urgent questions in venom research, particularly when multiple approaches are combined together, and with other venomics technologies.

Antibodies as Snakebite Antivenoms: Past and Future

Snakebite envenomation is considered a neglected tropical disease, affecting tens of thousands of people each year. The recommended treatment is the use of antivenom, which is composed of immunoglobulins or immunoglobulin fragments obtained from the plasma of animals hyperimmunized with one (monospecific) or several (polyspecific) venoms. In this review, the efforts made in the improvement of the already available antivenoms and the development of new antivenoms, focusing on snakes of medical importance from sub-Saharan Africa and Latin America, are described. Some antivenoms currently used are composed of whole IgGs, whereas others use F(ab')2 fragments. The classic methods of attaining snake antivenoms are presented, in addition to new strategies to improve their effectiveness. Punctual changes in immunization protocols, in addition to the use of cross-reactivity between venoms from different snakes for the manufacture of more potent and widely used antivenoms, are presented. It is known that venoms are a complex mixture of components; however, advances in the field of antivenoms have shown that there are key toxins that, if effectively blocked, are capable of reversing the condition of in vivo envenomation. These studies provide an opportunity for the use of monoclonal antibodies in the development of new-generation antivenoms. Thus, monoclonal antibodies and their fragments are described as a possible alternative for the production of antivenoms, regardless of the venom. This review also highlights the challenges associated with their development.

Production of a murine mAb against Bothrops alternatus and B. neuwiedi snake venoms and its use to isolate a thrombin-like serine protease fraction

Accidents with snakes from the genus Bothrops represent ~90 % of all snakebites in Brazil. Monoclonal antibodies (mAbs) targeting venom components can be important assets for treating envenoming syndromes, for developing diagnostic tests and for research purposes. Therefore, in this study, we aimed to generate murine mAbs against the antigenic mixture of Bothropic venoms traditionally used as immunogen to produce Bothropic antivenoms in Brazil. ELISA showed that one of the produced mAbs recognizes B. alternatus and B. neuwiedi venoms (mAb anti-Ba/Bn) specifically and Western Blot revealed that this mAb binds to a single protein band of molecular mass of ≈50 kDa. MAb anti-Ba/Bn inhibited the coagulant activity but was unable to neutralize hemorrhagic and phospholipase A2 activities caused by the B. neuwiedi venom. MAb anti-Ba/Bn was immobilized to Sepharose beads and used for immunoaffinity chromatography of B. neuwiedi venom. Proteolytic activity assays indicated that the immunoaffinity-purified fraction (BnF-Bothrops neuwiedi fraction) has a serine protease thrombin-like profile, which was supported by coagulability assays in mice. Bottom-up proteomic analysis confirmed the prevalence of serine proteases in BnF using label-free quantification. In conclusion, this work characterized a mAb with neutralizing properties against B. neuwiedi coagulant activity and demonstrates that immunoaffinity chromatography using mAbs can be a useful technique for purification of bioactive toxic proteins from Bothrops spp. snake venoms.

Biological and proteomic characterization of the venom from Peruvian Andes rattlesnake Crotalus durissus

The Peruvian rattlesnake Crotalus durissus is a venomous species that is restricted to the Peruvian Departments of Puno and Madre de Dios. Although clinically meaningful in this region, Crotalus durissus venom composition remains largely elusive. In this sense, this work aimed to provide a primary description of Peruvian C. durissus venom (PCdV). The enzymatic activities (SVMP, SVSP, LAAO, Hyaluronidase and PLA₂) of PCdV were analyzed and compared to Brazilian Crotalus durissus terrificus venom (BCdtV). PCdV showed higher PLA₂ activity when compared to the Brazilian venom. PCdV also showed cytotoxicity in VERO cells. For proteomic analysis, PCdV proteins were separated by HPLC, followed by SDS-PAGE. Gel bands were excised and tryptic digested for MALDI-TOF/TOF identification. Approximately 21 proteins were identified, belonging to 7 families. Phospholipases A₂ (PLA₂, 66.63%) were the most abundant proteins of the venom, followed by snake venom serine proteinases (SVSPs, 13.37%), C-type lectins (Snaclec, 8.98%) and snake venom metalloproteinases (SVMPs, 7.13%), crotamine (2.98%) and phosphodiesterase (PDE, 0.87%). Moreover, antivenom recognition assays indicated that both Brazilian and Peruvian antivenoms recognize PCdV, indicating the presence of antigenically related proteins in crotalic venoms. The results reported here, may impact in the venom selection for the production of effective Pan-American crotalic antivenom.

Exploring rotavirus proteome to identify potential B- and T-cell epitope using computational immunoinformatics

Rotavirus is the most common cause of acute gastroenteritis in infants and children worldwide. The functional correlation of B- and T-cells to long-lasting immunity against rotavirus infection in the literature is limited. In this work, a series of computational immuno-informatics approaches were applied and identified 28 linear B-cells, 26 conformational B-cell, 44 T_C cell and 40 T_H cell binding epitopes for structural and non-structural proteins of rotavirus. Further selection of putative B and T cell epitopes in the multi-epitope vaccine construct was carried out based on immunogenicity, conservancy, allergenicity and the helical content of predicted epitopes. An in-silico vaccine constructs was developed using an N-terminal adjuvant (RGD motif) followed by T_C and T_H cell epitopes and B-cell epitope with an appropriate linker. Multi-threading models of multi-epitope vaccine construct with B- and T-cell epitopes were generated and molecular dynamics simulation was performed to determine the stability of designed vaccine. Codon optimized multi-epitope vaccine antigens was expressed and affinity purified using the E. coli expression system. Further the T cell epitope presentation assay using the recombinant multi-epitope constructs and the T cell epitope predicted and identified in this study have not been investigated. Multi-epitope vaccine construct encompassing predicted B- and T-cell epitopes may help to generate long-term immune responses against rotavirus. The computational findings reported in this study may provide information in developing epitope-based vaccine and diagnostic assay for rotavirus-led diarrhea in children's.

Proteomic and toxinological characterization of Peruvian pitviper Bothrops brazili ("jergón shushupe"), venom

Bothrops brazili is a pitviper from Amazonian region, responsible for many accidents in Peru. Despite its relevance, its venom has not been extensively characterized. In the present work, Bothrops brazili venom (BbV) components were analyzed by RP-HPLC, SDS-PAGE and MALDI-TOF/TOF. Approximately 37 proteins were identified, belonging to 7 families. Snake venom metalloproteinases (SVMPs) were the most abundant proteins of the venom (33.05%), followed by snake venom serine proteinases (SVSPs, 26.11%), phospholipases A₂ (PLA₂, 25.57%), snake C-type lectins (CTLs, 9.61%), L-aminoacid oxidase (LAAO, 3.80%), cystein-rich secretory proteins (CRISP, 1.67%) and Bradykinin-potentiating peptide (BPP, 0.20%). In vitro enzymatic activities of BbV showed high levels of SVMP activity and reduced Hyal activity in comparison with other bothropic venoms. Furthermore, BbV reduced VERO cells viability. ELISA and Western Blotting showed that both Peruvian and Brazilian bothropic antivenoms were able to recognize BbV components. This work provides an overview of BbV venom content and indicates a potential efficiency of Peruvian and Brazilian antivenoms to treat accidents with this species.

Prediction of Epitope-Based Peptide Vaccine Against the Chikungunya Virus by Immuno-informatics Approach

BACKGROUND

Chikungunya is an arthropod-borne viral disease characterized by abrupt onset of fever frequently accompanied by joint pain, which has been identified in over 60 countries in Africa, the Americas, Asia, and Europe.

METHODS

Regardless of the availability of molecular knowledge of this virus, no definite vaccine or other remedial agents have been developed yet. In the present study, a combination of B-cell and T-cell epitope predictions, followed by molecular docking simulation approach has been carried out to design a potential epitope-based peptide vaccine, which can trigger a critical immune response against the viral infections.

RESULTS

A total of 52 sequences of E1 glycoprotein from the previously reported isolates of Chikungunya outbreaks were retrieved and examined through in silico methods to identify a potential B-cell and T-cell epitope. From the two separate epitope prediction servers, five potential B-cell epitopes were selected, among them "NTQLSEAHVEKS" was found highly conserved across strains and manifests high antigenicity with surface accessibility, flexibility, and hydrophilicity. Similarly, two highly conserved, non-allergenic, non-cytotoxic putative T-cell epitopes having maximum population coverage were screened to bind with the HLA-C 12*03 molecule. Molecular docking simulation revealed potential T-cell based epitope "KTEFASAYR" as a vaccine candidate for this virus.

CONCLUSION

A combination of these B-cell and T-cell epitope-based vaccine can open up a new skyline with broader therapeutic application against Chikungunya virus with further experimental and clinical investigation.

Pathogenesis of local necrosis induced by Naja atra venom: Assessment of the neutralization ability of Taiwanese freeze-dried neurotoxic antivenom in animal models

Naja atra envenomation is one of the most significant clinical snakebite concerns in Taiwan. Taiwanese freeze-dried neurotoxic antivenom (FNAV) is currently used clinically for the treatment of cobra snakebite, and has been shown to limit the mortality of cobra envenomation to less than 1%. However, more than half of victims (60%) require surgery because of local tissue necrosis, a major problem in patients with cobra envenomation. Although the importance of evaluating the neutralizing effect of FNAV on this pathology is recognized, whether FNAV is able to prevent the local necrosis extension induced by N. atra venom has not been investigated in detail. Cytotoxins (CTXs) are considered as the major components of N. atra venom that cause necrosis. In the current study, we isolated CTXs from whole cobra venom and used both whole venom and purified CTXs to develop animal models for assessing the neutralization potential of FNAV against venom necrotizing activity. Local necrotic lesions were successfully produced in mice using CTXs in place of whole N. atra venom. FNAV was able to rescue mice from a subcutaneously injected lethal dose of cobra venom; however, it was unable to prevent CTX-induced dermo-necrosis. Furthermore, using the minimal necrosis dose (MND) of CTXs and venom proteome data, we found a dose of whole N. atra venom suitable for FNAV and developed a workable protocol for inducing local necrosis in rodent models that successfully imitated the clinical circumstance of cobra envenoming. This information provides a more comprehensive understanding of the pathophysiology of N. atra envenomation, and serves as a guide for improving current antivenom strategies and advancing clinical snakebite management in Taiwan.

Naja atra envenomation is an important public health issue in Taiwan. Although the mortality rate of cobra snakebite is controlled using antivenom, more than half of victims develop symptoms of local necrosis and require surgical intervention. Whether the Taiwanese freeze-dried neurotoxic antivenom (FNAV) currently in clinical use is able to prevent the local necrosis extension induced by N. atra venom is still unclear. In this study, we developed a dermo-necrosis animal model using purified cytotoxins (CTXs), the major necrosis-related proteins from N. atra venom. We found that FNAV was able to neutralize the lethality of whole cobra venom, but was unable to neutralize the necrosis induced by CTXs in vivo. This finding introduced an example that supplementary quality control assays may be necessary to determine the effectiveness of antivenoms in neutralizing specific pathology induced by the venom; only evaluating the rodent lethality prevention is insufficient. Our results provide insights that should help improve current antivenoms and advance cobra snakebite management in Taiwan.

Computational B-cell epitope identification and production of neutralizing murine antibodies against Atroxlysin-I

Epitope identification is essential for developing effective antibodies that can detect and neutralize bioactive proteins. Computational prediction is a valuable and time-saving alternative for experimental identification. Current computational methods for epitope prediction are underused and undervalued due to their high false positive rate. In this work, we targeted common properties of linear B-cell epitopes identified in an individual protein class (metalloendopeptidases) and introduced an alternative method to reduce the false positive rate and increase accuracy, proposing to restrict predictive models to a single specific protein class. For this purpose, curated epitope sequences from metalloendopeptidases were transformed into frame-shifted Kmers (3 to 15 amino acid residues long). These Kmers were decomposed into a matrix of biochemical attributes and used to train a decision tree classifier. The resulting prediction model showed a lower false positive rate and greater area under the curve when compared to state-of-the-art methods. Our predictions were used for synthesizing peptides mimicking the predicted epitopes for immunization of mice. A predicted linear epitope that was previously undetected by an experimental immunoassay was able to induce neutralizing-antibody production in mice. Therefore, we present an improved prediction alternative and show that computationally identified epitopes can go undetected during experimental mapping.

Development of a Simple Permeability Assay Method for Snake Venom-induced Vascular Damage

We have developed a novel bioassay method for the detection of snake venom based on the permeability of endothelial cell monolayers cultured in Transwell cell culture inserts. This assay relies on the proteolytic degradation of capillary basement membrane proteins, a pathophysiological event that occurs due to snakebites in vivo. Transwell permeability assays with fluorescence measurements are advantageous with regard to ethical considerations for the use of animals. The assay time was reduced from 24 h for animal tests to 2 h, and many samples could be assayed easily.

Proteomic profile, biological activities and antigenic analysis of the venom from Bothriopsis bilineata smaragdina ("loro machaco"), a pitviper snake from Peru

In order to determine Bothriopsis bilineata smaragdina venom (BbsV) composition, proteomic approaches were performed. Venom components were analyzed by RP-HPLC, SDS- PAGE and nano LC on line with LTQ Orbitrap XL. Results showed a total of 189 identified proteins, grouped into 11 different subgroups, which include snake venom metalloproteinases (SVMPs, 54.67%), snake C-type lectins (Snaclecs, 15.78%), snake venom serine proteinases (SVSPs, 14.69%), cystein-rich secretory proteins (CRISP, 2.61%), phospholipases A₂ (PLA₂, 1.14%), phosphodiesterase (PDE, 1.17%), venom endothelial growth factor (VEGF, 1.06%) 5'nucleotidases (0.33%), L-amino acid oxidases (LAAOs, 0.28%) and other proteins. In vitro enzymatic activities (SVMP, SVSP, LAAO, Hyal and PLA₂) of BbsV were also analyzed. BbsV showed high SVSP activity but low PLA₂ activity, when compared to other Bothrops venoms. In vivo, BbsV induced hemorrhage and edema in mice and showed intraperitoneal median lethal dose (LD₅₀) of 92.74 (± 0.15) μg/20 g of mice. Furthermore, BbsV reduced cell viability when incubated with VERO cells. Peruvian and Brazilian bothropic antivenoms recognize BbsV proteins, as detected by ELISA and Western Blotting. Both antivenoms were able to neutralize in vivo edema and hemorrhage.

SIGNIFICANCE

In Peru, snakebite is a public health problem, especially in the rain forest, as a result of progressive colonization of this geographical area. This country is the second in Latin America, after Brazil, to exhibit the largest variety of venomous snakes. B. atrox and B. b. smaragdina snakes are sympatric species in Peruvian Amazon region and are responsible for approximately 95% of the envenomings reported in this region. B. b. smaragdina may cause a smaller share (3 to 38%) of those accidents, due to its arboreal habits, that make human encounters with these snakes less likely to happen. Despite B. b. smaragdina recognized medical importance, its venom composition and biological activities have been poorly studied. Furthermore, BbsV is not a component of the antigenic pool used to produce the corresponding Peruvian bothropic antivenom (P-BAV). Our results not only provide new insights on BbsV composition and biological activity, but also demonstrate that both P-BAV and B-BAV polyvalent antivenoms have a considerable recognition of proteins from BbsV and, more importantly, neutralized hemorrhage and edema, the main local effects of bothropic envenomation.

Identification of B cell recognized linear epitopes in a snake venom serine proteinase from the central American bushmaster Lachesis stenophrys

Snake venom serine proteinases are toxins that perturb hemostasis acting on proteins from the blood coagulation cascade, the fibrinolytic or the kallikrein-kinin system. Despite the relevance of these enzymes in envenomations by viper bites, the characterization of the antibody response to these toxins at the molecular level has not been previously addressed. In this work surface-located B cell recognized linear epitopes from a Lachesis stenophrys venom serine proteinase (UniProt accession number Q072L7) were predicted using an artificial neuronal network at the ABCpred server, the corresponding peptides were synthesized and their immunoreactivity was analyzed against a panel of experimental and therapeutic antivenoms. A molecular model of the L. stenophrys enzyme was built using as a template the structure of the D. acutus Dav-PA serine proteinase (Q9I8X1), which displays the highest degree of sequence similarity to the L. stenophrys enzyme among proteins of known 3D structure, and the surface-located epitopes were identified in the protein model using iCn3D. A total of 13 peptides corresponding to the surface exposed predicted epitopes from L. stenophrys serine proteinase were synthesized and, their reactivity with a rabbit antiserum against the recombinant enzyme and a panel of antivenoms was evaluated by a capture ELISA. Some of the epitopes recognized by monospecific and polyspecific antivenoms comprise sequences overlapping motifs conserved in viper venom serine proteinases. The identification and characterization of relevant epitopes recognized by B cells in snake venom toxins may provide valuable information for the preparation of immunogens that help in the production of improved therapeutic antivenoms.

Identification of protective B-cell epitopes of Atroxlysin-I: A metalloproteinase from Bothrops atrox snake venom

Atroxlysin-I (Atr-I) is a hemorrhagic snake venom metalloproteinase (SVMP) from Bothrops atrox venom, the snake responsible for the majority of bites in the north region of South America. SVMPs like Atr-I produce toxic effects in victims including hemorrhage, inflammation, necrosis and blood coagulation deficiency. Mapping of B-cell epitopes in SVMPs might result in the identification of non-toxic molecules capable of inducing neutralizing antibodies and improving the anti-venom therapy. Here, using the SPOT-synthesis technique we identified two epitopes located in the N-ter region of Atr-I (AtrEp1-(22)YNGNSDKIRRRIHQM(36); and AtrEp2-(55)GVEIWSNKDLINVQ(68)). Based on the sequence of AtrEp1 and AtrEp2 a third peptide named Atr-I biepitope (AtrBiEp) was designed and synthesized ((23)NGNSDKIRRRIH(34)GG(55)GVEIWSNKDLINVQ(68)). AtrBiEp was used to immunize BALB/c mice. Anti-AtrBiEp serum cross-reacted against Atr-I in western blot and was able to fully neutralize the hemorrhagic activity of Atr-I. Our results provide a rational basis for the identification of neutralizing epitopes on Atr-I snake venom toxin and show that the use of synthetic peptides could improve the generation of immuno-therapeutics.