Application of the Spot method to the identification of peptides and amino acids from the antibody paratope that contribute to antigen binding

Development and evaluation of a recombinant multi-epitopic protein (TsMEP) as an antigen candidate for Tityus serrulatus antivenom production

Scorpionism is Brazil's most prevalent envenomation. Treatment typically involves the use of heterologous antivenoms derived from the immunization of horses with crude T. serrulatus venom (TsV). Due to the high toxicity of this immunogen, as well as the particular challenges associated with the use of venoms as antigens, there is interest in exploring new alternatives for reducing their use in antivenom production. In this study, ten linear B-cell epitopes from hyaluronidase and voltage-gated sodium channel toxins, previously identified using the SPOT-synthesis method, were selected to construct a recombinant chimeric MultiEpitopic Protein from T. serrulatus scorpion venom (TsMEP). We demonstrated that TsMEP is non-toxic, and antibodies elicited in rabbits against this antigen exhibited reactivity in ELISA with Brazilian T. serrulatus, T. bahiensis, T. obscurus, and T. stigmurus venoms, as well as with Peruvian Hadruroides lunatus and North African Androctonus australis hector scorpion venoms. In vivo and in vitro neutralization assays revealed that rabbit anti-TsMEP antibodies partially neutralize the hyaluronidase activity of T. serrulatus venom and its lethality. Data presented here suggests that this multiepitopic protein could be a promising candidate in experimental immunization approaches for antivenom production for clinical use against Tityus spp. venoms.

Mapping possible interaction sites for crotoxin in CNF, a gamma PLA2 inhibitor from Crotalus durissus terrificus rattle snake, using SPOT synthesis

Phospholipases A2 (PLA2s) are main components of snake venoms. Several snake species possess endogenous PLA2 inhibitors in their circulating blood, which are generally known as sbPLIs (an acronym for snake blood phospholipase A2inhibitors). The sbPLIs are categorized in three classes (alpha, beta or gamma) depending on the existence of distinguishing protein domains in their structure. The Crotalus durrissus terrificus venom has a highly neurotoxic PLA2 - crotoxin (CTX) - in its composition and the self-protection of the snake is mainly ensured by a sbγPLI named CNF (standing for Crotalusneutralizing factor). In an attempt to find smaller molecules able to inhibit the catalytic activity of CTX, in the present study we used linear peptide arrays to identify CNF segments possibly involved in the interaction with the toxin. Five reacting segments were identified as possible interacting regions. The target peptides were synthesized and located in the in silico CNF structure. Although all of them are exposed to the solvent, high concentrations were needed to inhibit the PLA2 activity of the whole venom or CTX. Limitations of the methodology employed and particular characteristics of CTX inhibition by CNF are discussed.

Toxic and antigenic characterization of Peruvian Micrurus surinamensis coral snake venom

Micrurus surinamensis is a semi-aquatic coral snake found in primary forest region and can cause relevant human accidents. In this work we investigated the toxic and antigenic activities of the Peruvian Micrurus surinamensis venom (MsV). We found that MsV show hyaluronidase activity but lack LAAO and PLA₂ enzymatic activities. Interestingly, MsV induce edematogenic responses but cannot cause nociceptive effects. Furthermore, MsV can reduce in vitro cell viability in MGSO-3 cell line derived from human breast cancer tissue. To evaluate its antigenic potential, rabbits were immunized with MsV, which proved to be immunogenic. ELISA, immunobloting and in vivo neutralization assays demonstrated that the specific rabbit anti-MsV antivenom is more efficient than the therapeutic Brazilian antivenom in recognizing and neutralizing the lethal activity of MsV. MsV differs in protein profile and biological activities from M. frontalis venom (MfV), used as control, which impairs its recognition and neutralization by Brazilian therapeutic anti-elapidic antivenom. We performed a SPOT immunoassay for the identification of B-cell linear epitopes in the main toxins described for MsV targeted by the elicited neutralizing antibodies previously produced. A membrane containing 15-mer peptides representing the sequences of five 3TFxs and five PLA₂s was produced and probed with anti- MsV antibodies. Results revealed important regions in 3FTx toxins for venom neutralization. Identifying the main MsV components and its biological activities can be helpful in guiding the production of antivenoms and in the optimization of treatment for coral snake envenomation in Brazil.

Structural Basis for the IgE-Binding Cross-Reacting Epitopic Peptides of Cup s 3, a PR-5 Thaumatin-like Protein Allergen from Common Cypress (Cupressus sempervirens) Pollen

The present work was aimed at identifying the IgE-binding epitopic regions on the surface of the Cup s 3 allergen from the common cypress Cupressus sempervirens, that are possibly involved in the IgE-binding cross-reactivity reported between Cupressaceae species. Three main IgE-binding epitopic regions were mapped on the molecular surface of Cup s 3, the PR-5 thaumatin-like allergen of common cypress Cupressus sempervirens. They correspond to exposed areas containing either electropositive (R, K) or electronegative (D, E) residues. A coalescence occurs between epitopes #1 and #2, that creates an extended IgE-binding regions on the surface of the allergen. Epitope #3 contains a putative N-glycosylation site which is actually glycosylated and could therefore comprise a glycotope. However, most of the allergenic potency of Cup s 3 depends on non-glycosylated epitopic peptides. The corresponding regions of thaumatin-like allergens from other closely related Cupressaceae (Cryptomeria, Juniperus, Thuja) exhibit a very similar conformation that should account for the IgE-binding cross-reactivity observed among the Cupressaceae allergens.

Identification of Potential IgE-Binding Epitopes Contributing to the Cross-Reactivity of the Major Cupressaceae Pectate-Lyase Pollen Allergens (Group 1)

Pectate-lyase allergens, the group 1 of allergens from Cupressaceae pollen, consist of glycoproteins exhibiting an extremely well-conserved three-dimensional structure and sequential IgE-binding epitopes. Up to 10 IgE-binding epitopic regions were identified on the molecular surface, which essentially cluster at both extremities of the long, curved β-prism-shaped allergens. Most of these IgE-binding epitopes possess very similar conformations that provide insight into the IgE-binding cross-reactivity and cross-allergenicity commonly observed among Cupressaceae pollen allergens. Some of these epitopic regions coincide with putative N-glycosylation sites that most probably consist of glycotopes or cross-reactive carbohydrate determinants, recognized by the corresponding IgE antibodies from allergic patients. Pectate-lyase allergens of Cupressaceae pollen offer a nice example of structurally conserved allergens that are widely distributed in closely-related plants (Chamæcyparis, Cryptomeria, Cupressus, Hesperocyparis, Juniperus, Thuja) and responsible for frequent cross-allergenicity.

Downsizing antibodies: Towards complementarity-determining region (CDR)-based peptide mimetics

Monoclonal antibodies emerged as an important therapeutic drug class with remarkable specificity and binding affinity. Nonetheless, these heterotetrameric immunoglobulin proteins come with high manufacturing and therapeutic costs which can take extraordinary proportions, besides other limitations such as their limited in cellulo access imposed by their molecular size (ca. 150 kDa). These drawbacks stimulated the development of downsized functional antibody fragments (ca. 15-50 kDa), together with smaller synthetic peptides (ca. 1-3 kDa) derived from the antibodies' crucial complementarity-determining regions (CDR). Despite the general lack of success in the literal translation of CDR loops in peptide mimetics, rational structure-based and computational approaches have shown their potential for obtaining functional CDR-based peptide mimetics. In this review, we describe the efforts made in the development of antibody and nanobody paratope-derived peptide mimetics with particular focus on the used design strategies, in addition to highlighting the challenges associated with their development.

A prokaryote system optimization for rMEPLox expression: A promising non-toxic antigen for Loxosceles antivenom production

Loxoscelism is the most dangerous araneism form in Brazil and antivenom therapy is the recommended treatment. Antivenom is produced by horse immunization with Loxosceles spider venom, which is toxic for the producer animal. Moreover, due to the high amount of venom required for horse hyperimmunization, new strategies for antigens obtention have been proposed. In this sense, our research group has previously produced a non-toxic recombinant multiepitopic protein derived from Loxosceles toxins (rMEPLox). rMEPLox was a successful immunogen, being able to induce the production of neutralizing antibodies, which could be used in the Loxoscelism treatment. However, rMEPLox obtention procedure requires optimization, as its production needs to be scaled up to suit antivenom manufacture. Therefore, an effective protocol development for rMEPlox production would be advantageous. To achieve this objective, we evaluated the influence of different cultivation conditions for rMEPLox optimum expression. The optimum conditions to obtain large amounts of rMEPlox were defined as the use of C43(DE3)pLysS as a host strain, 2xTY medium, 0.6 mM IPTG, biomass pre induction of OD600nm = 0.4 and incubation at 30 °C for 16 h. Following the optimized protocol, 39.84 mg/L of soluble rMEPLox was obtained and tested as immunogen. The results show that the obtained rMEPLox preserved the previously described immunogenicity, and it was able to generate antibodies that recognize different epitopes of the main Loxosceles venom toxins, which makes it a promising candidate for the antivenom production for loxoscelism treatment.

Determination of the Rituximab Binding Site to the CD20 Epitope Using SPOT Synthesis and Surface Plasmon Resonance Analyses

Antibodies not only play a major role in clinical diagnostics and biopharmaceutical analysis but also are a class of drugs that are regularly used to treat numerous diseases. The identification of antibody-epitope binding sites is then of great interest to many emerging medical and bioanalytical applications, particularly to design monoclonal antibodies (mAb) mimics taking advantage of amino acid residues involved in the binding. Among relevant antibodies, the monoclonal antibody rituximab has received significant attention as it is exploited to treat several cancers including non-Hodgkin's lymphoma and chronic lymphocytic leukemia, as well as some autoimmune disorders such as rheumatoid arthritis. The binding of rituximab to the targeted cells occurs via the recognition of the CD20 epitope. A crystallographic study has shown that the binding area, named paratope, is located at the surface of rituximab. Combining the SPOT method and the complementary surface plasmon resonance technique allowed us to detect an extended recognition domain buried in the pocket of the rituximab Fab formed by four β-sheets. More generally, the present study offers a comprehensive approach to identify antibody-epitope binding sites.

IgE-Binding Epitopes of Pis v 1, Pis v 2 and Pis v 3, the Pistachio (Pistacia vera) Seed Allergens

Sequential IgE-binding epitopes were identified on the molecular surface of the Pis v 1 (2S albumin), Pis v 2 (11S globulin/legumin) and Pis v 3 (7S globulin/vicilin)—major allergens from pistachio (Pistacia vera) seeds—using the Spot technique. They essentially consist of hydrophilic and electropositively charged residues well exposed on the surface of the allergens. Most of the epitopic regions identified on Pis v 1 and Pis v 3 do not coincide with the putative N-glycosylation sites and thus are not considered as glycotopes. Surface analysis of these epitopic regions indicates a high degree of conformational similarity with the previously identified epitopic regions of the corresponding allergens Ana o 1 (vicilin), Ana o 2 (legumin) and Ana o 3 (2S albumin) from the cashew (Anacardium occidentale) nut. These results offer a molecular basis for the IgE-binding cross-reactivity often observed between pistachio and cashew nut. They support the recommendation for prescribing pistachio avoidance in cashew allergic patients. Other conformational similarities were identified with the corresponding allergens Ses i 1 (2S albumin), Ses i 3 (vicilin) and Ses i 6 (legumin) from sesame (Sesamum indicum), and Jug r 1 (2S albumin), Jug r 2 (vicilin) and Jug r 4 (legumin) from walnut (Juglans regia). Conversely, conformation of most of the epitopic regions of the pistachio allergens often differs from that of epitopes occurring on the molecular surface of the corresponding Ara h 1 (vicilin), Ara h 2 (2S albumin) and Ara h 3 (legumin) allergens from peanut (Arachis hypogaea).

Molecular cloning and functional characterization of recombinant Loxtox from Loxosceles similis venom

Loxoscelism is a recognized public health problem in Brazil, but the venom from Loxosceles similis, which is widespread in Brazil due to its adaptability to the urban environment, remains poorly characterized. Loxtox is a family of phospholipase D enzymes (PLDs), which are the major components of Loxosceles venom and are responsible for the clinical effects of loxoscelism. Loxtox toxins correspond to 15% of L. similis venom gland transcripts, but the Loxtox family of L. similis has yet to be fully described. In this study, we cloned and functionally characterized recLoxtox s1A and recLoxtox s11A. These recombinant toxins exhibited different in vitro activities depending on pH, and recLoxtox s1A had more intense effects on rabbit skin than did recLoxtox s11A in vivo. Both recombinant toxins were used in immunization protocols, and mapping of their epitopes revealed different immunological reactions for the produced immune serums. Additionally, polyclonal antibodies raised against recLoxtox s1A had greater capacity to significantly reduce the in vitro and in vivo effects of L. similis venom. In summary, we obtained and characterized two novel Loxtox isoforms from L. similis venom, which may be valuable biotechnological and immunological tools against loxoscelism.

Engineered antigen containing epitopes from Loxosceles spp. spider toxins induces a monoclonal antibody (Lox-mAb3) against astacin-like metalloproteases

Loxoscelism pose a health issue in the South America. The treatment for these accidents is based on the administration of antivenom produced in animals immunized with Loxosceles venom. In this work, a previously produced non-toxic multiepitopic chimeric protein (rMEPlox), composed of epitopes derived from the main toxins families (sphyngomielinase-D, metalloproteases, and hyaluronidases) of Loxosceles spider venoms, was used as antigen to produce monoclonal antibodies (mAbs). A selected anti-rMEPlox mAb (Lox-mAb3) reacted with metalloprotease from L. intermedia venom and showed cross-reactivity with metalloproteses from Brazilian and Peruvian Loxosceles laeta and Loxosceles gaucho venoms in immunoassays. The sequence recognized by Lox-mAb3 (₁₈₄ENNTRTIGPFDYDSIMLYGAY₂₀₅) corresponds to the C-terminal region of Astacin-like metalloprotease 1 and the amino acid sequence IGPFDYDSI, conserved among the homologs metalloproteases sequences, is important for antibody recognition. Lox-mAb3 neutralizes the fibrinogenolytic activity caused by metalloprotease from L. intermedia spider venom in vitro, which may lead to a decrease in hemorrhagic disturbances caused by Loxosceles envenomation. Our results show, for the first time, the use of a non-toxic multiepitopic protein for the production of a neutralizing monoclonal antibody against a metalloprotease of medically important Loxosceles venoms. These results contribute for the production improvement of therapeutic antivenom against loxoscelism.

Immunotherapy of ovarian cancer with a monoclonal antibody specific for the extracellular domain of anti-Müllerian hormone receptor II

Epithelial ovarian carcinoma (EOC) is the most prevalent and lethal form of ovarian cancer. The low five-year overall survival after EOC diagnosis indicates an urgent need for more effective ways to control this disease. Anti-Müllerian hormone receptor 2 (AMHR2) is an ovarian protein overexpressed in the majority of human EOCs. We have previously found that vaccination against the ovarian-specific extracellular domain of AMHR2 (AMHR2-ED) significantly inhibits growth of murine EOCs through an IgG-mediated mechanism that agonizes receptor signaling of a Bax/caspase-3 dependent proapoptotic cascade. To determine if a single monoclonal antibody (mAb) could inhibit growth of human EOC, we generated a panel of mAbs specific for recombinant human AMHR2-ED and characterized a candidate mAb for humanization and use in clinical trials. We found that our candidate 4D12G1 mAb is an IgG₁ that shows high affinity antigen-specific binding to the 7-mer ²⁰KTLGELL²⁶ sequence of AMHR2-ED that facilitates induction of programmed cell death in EOC cells. Most importantly, the 4D12G1 mAb significantly inhibits growth of primary human EOCs in patient-derived xenografts (PDXs) by inducing direct apoptosis of EOC tumors. Our results support the view that a humanized 4D12G1 mAb may be a much needed and effective reagent for passive immunotherapy of human EOC.

Engineered protein containing crotoxin epitopes induces neutralizing antibodies in immunized rabbits

Crotoxin (Ctx) is the main lethal component of Crotalus durissus terrificus venom. It is a neurotoxin, composed of two subunits associated by noncovalent interactions, the non-toxic acid subunit (CA), named Crotapotin, and the basic subunit (CB), with phospholipase A₂ (PLA₂) activity. Employing the SPOT synthesis technique, we determined two epitopes located in the C-terminal of each Ctx subunit. In addition, 3 other epitopes were mapped in different regions of Ctx using subcutaneous spot implants surgically inserted in mice. All epitopes mapped here were expressed together as recombinant multi-epitopic protein (rMEPCtx), which was used to immunize New Zealand rabbits. Anti-rMEPCtx rabbit serum cross-reacted with Ctx and crude venoms from C. d. terrificus, Crotalus durissus ruruima, Peruvian C. durissus and Bothrops jararaca (with lower intensity). Furthermore, anti-rMEPCtx serum was able to neutralize Ctx lethal activity. As the recombinant multiepitopic protein is not toxic, it can be administered in larger doses without causing adverse effects on the immunized animals health. Therefore, our work evidences the identification of neutralizing epitopes of Ctx and support the use of recombinant multiepitopic proteins as an innovation to immunotherapeutics production.

PEPOP 2.0: new approaches to mimic non-continuous epitopes

BACKGROUND

Bioinformatics methods are helpful to identify new molecules for diagnostic or therapeutic applications. For example, the use of peptides capable of mimicking binding sites has several benefits in replacing a protein which is difficult to produce, or toxic. Using peptides is less expensive. Peptides are easier to manipulate, and can be used as drugs. Continuous epitopes predicted by bioinformatics tools are commonly used and these sequential epitopes are used as is in further experiments. Numerous discontinuous epitope predictors have been developed but only two bioinformatics tools have been proposed so far to predict peptide sequences: Superficial and PEPOP 2.0. PEPOP 2.0 can generate series of peptide sequences that can replace continuous or discontinuous epitopes in their interaction with their cognate antibody.

RESULTS

We have developed an improved version of PEPOP (PEPOP 2.0) dedicated to answer to experimentalists' need for a tool able to handle proteins and to turn them into peptides. The PEPOP 2.0 web site has been reorganized by peptide prediction category and is therefore better formulated to experimental designs. Since the first version of PEPOP, 32 new methods of peptide design were developed. In total, PEPOP 2.0 proposes 35 methods in which 34 deal specifically with discontinuous epitopes, the most represented epitope type in nature.

CONCLUSION

Through the presentation of its user-friendly, well-structured new web site conceived in close proximity to experimentalists, we report original methods that show how PEPOP 2.0 can assist biologists in dealing with discontinuous epitopes.

Recombinant mutagenic 3ABC protein and monoclonal antibody for quality-control testing in foot-and-mouth disease vaccines

To achieve the goal of performing quality control on vaccines for foot-and-mouth disease several steps were performed in this study. First, the gene that encodes the 3ABC region of the A24 Cruzeiro strain (which is used in vaccine production) was amplified. Second, to improve protein stability, the 3ABC protein was mutated at the 3C^pro catalytic site and cloned the amplification products in the pET-SUMO expression vector. In the third step, the resulting recombinant protein was tested, which the polyclonal antibody recognized, with the semi-purified viral 3ABC protein using an immunoassay test. Fourth, the muted recombinant protein was used to produce a monoclonal antibody. Of the 217 clones obtained, two of them that were particularly stable (mAb2D3 and mAb3D12) were selected to work with. One showed better results, as characterized by immunoassay (ELISA), Western blotting, spot synthesis, and sequencing methodologies; it also showed high reactivity against the 3ABC protein. This kind of monoclonal antibodies, which was considered as immunochemical inputs, have been used in industrial processes as part of quality-control procedures, to evaluate the elimination of the 3ABC protein so as to ensure regulatory approval of the vaccine. They have also been used in immunological tests to distinguish infected from vaccinated animals.

Recombinant Protein Containing B-Cell Epitopes of Different Loxosceles Spider Toxins Generates Neutralizing Antibodies in Immunized Rabbits

Loxoscelism is the most important form of araneism in South America. The treatment of these accidents uses heterologous antivenoms obtained from immunization of production animals with crude loxoscelic venom. Due to the scarcity of this immunogen, new alternatives for its substitution in antivenom production are of medical interest. In the present work, three linear epitopes for Loxosceles astacin-like protease 1 (LALP-1) (SLGRGCTDFGTILHE, ENNTRTIGPFDYDSIMLYGAY, and KLYKCPPVNPYPGGIRPYVNV) and two for hyaluronidase (LiHYAL) (NGGIPQLGDLKAHLEKSAVDI and ILDKSATGLRIIDWEAWR) from Loxosceles intermedia spider venom were identified by SPOT-synthesis technique. One formerly characterized linear epitope (DFSGPYLPSLPTLDA) of sphingomyelinase D (SMase D) SMase-I from Loxosceles laeta was also chosen to constitute a new recombinant multiepitopic protein. These epitopes were combined with a previously produced chimeric multiepitopic protein (rCpLi) composed by linear and conformational B-cell epitopes from SMase D from L. intermedia venom, generating a new recombinant multiepitopic protein derived from loxoscelic toxins (rMEPLox). We demonstrated that rMEPLox is non-toxic and antibodies elicited in rabbits against this antigen present reactivity in ELISA and immunoblot assays with Brazilian L. intermedia, L. laeta, L. gaucho, and L. similis spider venoms. In vivo and in vitro neutralization assays showed that anti-rMEPLox antibodies can efficiently neutralize the sphingomyelinase, hyaluronidase, and metalloproteinase activity of L. intermedia venom. This study suggests that this multiepitopic protein can be a suitable candidate for experimental vaccination approaches or for antivenom production against Loxosceles spp. venoms.

Epitope mapping of recombinant Leishmania donovani virulence factor A2 (recLdVFA2) and canine leishmaniasis diagnosis using a derived synthetic bi-epitope

Background

Leishmaniasis is one of the most important zoonotic diseases spread in Latin America. Since many species are involved in dog infection with different clinical manifestations, the development of specific diagnostic tests is mandatory for more accurate disease control and vaccine strategies.

Methodology/Principal findings

Seventy-five 15-mer peptides covering the sequence of recombinant Leishmania donovani virulence factor A2 (recLdVFA2) protein were prepared by Spot synthesis. Membrane-bound peptides immunoreactivity with sera from dogs immunized with recLdVFA2 and with a specific anti-recLdVFA2 monoclonal antibody allowed mapping of continuous B-cell epitopes. Five epitopes corresponding to the N-terminal region of recLdVFA2 (MKIRSVRPLVVLLVC, RSVRPLVVLLVCVAA, RPLVVLLVCVAAVLA, VVLLVCVAAVLALSA and LVCVAAVLALSASAE, region 1–28) and one located within the repetitive units (PLSVGPQAVGLSVG, regions 67–81 and 122–135) were identified. A 34-mer recLdVFA2-derived bi-epitope containing the sequence MKIRSVRPLVVLLVC linked to PLSVGPQAVGLSVG by a Gly-Gly spacer was chemically synthesized in its soluble form. The synthetic bi-epitope was used as antigen to coat ELISA plates and assayed with dog sera for in vitro diagnosis of canine visceral leishmaniasis (CVL). The assay proved to be highly sensitive (98%) and specific (99%).

Conclusions/Significance

Our work suggests that synthetic peptide-based ELISA strategy may be useful for the development of a sensitive and highly specific serodiagnosis for CVL or other parasitic diseases.

Leishmaniasis is a neglected tropical disease being among the six endemic prioritized diseases in the world. Visceral leishmaniasis (VL) is caused by Leishmania infantum and represents a serious public health problem in Brazil. Dogs are the main source of infection in the urban area and, in Brazil, the main strategies of the Visceral Leishmaniasis Control Program are directed to control the canine reservoir (serological survey and euthanasia of dogs which present reactive serum). In general, diagnosis of canine visceral leishmaniasis (CVL) has been presented as a problem for Brazilian public health services. The issue should be attributed mainly to the following factors: 1- range of similar clinical signs observed in other infectious diseases that affect dogs; 2- large percentage of asymptomatic or oligosymptomatic dogs; 3- nonspecific histopathological changes; 4- nonexistence of a diagnostic test 100% specific and sensitive. In this work, we developed a synthetic bi-epitope peptide as an antigen for immunodiagnostic ELISA to detect CVL. The biepitope used for ELISA assay accurately distinguish (98% sensitivity and 99% specificity) CVL dogs sera from non-infected dogs sera.

Tissue-type plasminogen activator controls neuronal death by raising surface dynamics of extrasynaptic NMDA receptors

N-methyl-d-aspartate receptors (NMDARs) are ion channels whose synaptic versus extrasynaptic localization critically influences their functions. This distribution of NMDARs is highly dependent on their lateral diffusion at the cell membrane. Each obligatory subunit of NMDARs (GluN1 and GluN2) contains two extracellular clamshell-like domains with an agonist-binding domain and a distal N-terminal domain (NTD). To date, the roles and dynamics of the NTD of the GluN1 subunit in NMDAR allosteric signaling remain poorly understood. Using single nanoparticle tracking in mouse neurons, we demonstrate that the extracellular neuronal protease tissue-type plasminogen activator (tPA), well known to have a role in the synaptic plasticity and neuronal survival, leads to a selective increase of the surface dynamics and subsequent diffusion of extrasynaptic NMDARs. This process explains the previously reported ability of tPA to promote NMDAR-mediated calcium influx. In parallel, we developed a monoclonal antibody capable of specifically blocking the interaction of tPA with the NTD of the GluN1 subunit of NMDAR. Using this original approach, we demonstrate that the tPA binds the NTD of the GluN1 subunit at a lysine in position 178. Accordingly, when applied to mouse neurons, our selected antibody (named Glunomab) leads to a selective reduction of the tPA-mediated surface dynamics of extrasynaptic NMDARs, subsequent signaling and neurotoxicity, both in vitro and in vivo. Altogether, we demonstrate that the tPA is a ligand of the NTD of the obligatory GluN1 subunit of NMDAR acting as a modulator of their dynamic distribution at the neuronal surface and subsequent signaling.

Rendomab B4, a monoclonal antibody that discriminates the human endothelin B receptor of melanoma cells and inhibits their migration

Metastatic melanoma is an aggressive cancer with a poor prognostic, and the design of new targeted drugs to treat melanoma is a therapeutic challenge. A promising approach is to produce monoclonal antibodies (mAbs) against the endothelin B receptor (ETB), which is known to be overexpressed in melanoma and to contribute to proliferation, migration and vasculogenic mimicry associated with invasiveness of this cancer. We previously described rendomab-B1, a mAb produced by DNA immunization. It is endowed with remarkable characteristics in term of affinity, specificity and antagonist properties against human ETB expressed by the endothelial cells, but, surprisingly, had poor affinity for ETB expressed by melanoma cells. This characteristic strongly suggested the existence of a tumor-specific ETB form. In the study reported here, we identified a new mAb, rendomab-B4, which, in contrast to rendomab-B1, binds ETB expressed on UACC-257, WM-266-4 and SLM8 melanoma cells. Moreover, after binding to UACC-257 cells, rendomab-B4 is internalized and colocalizes with the endosomal protein EEA-1. Interestingly, rendomab-B4, despite its inability to compete with endothelin binding, is able to inhibit phospholipase C pathway and migration induced by endothelin. By contrast, rendomab-B4 fails to decrease ERK1/2 phosphorylation induced by endothelin, suggesting a biased effect on ETB. These particular properties make rendomab-B4 an interesting tool to analyze ETB-structure/function and a promising starting point for the development of new immunological tools in the field of melanoma therapeutics.

A Heterologous Multiepitope DNA Prime/Recombinant Protein Boost Immunisation Strategy for the Development of an Antiserum against Micrurus corallinus (Coral Snake) Venom

Background

Envenoming by coral snakes (Elapidae: Micrurus), although not abundant, represent a serious health threat in the Americas, especially because antivenoms are scarce. The development of adequate amounts of antielapidic serum for the treatment of accidents caused by snakes like Micrurus corallinus is a challenging task due to characteristics such as low venom yield, fossorial habit, relatively small sizes and ophiophagous diet. These features make it difficult to capture and keep these snakes in captivity for venom collection. Furthermore, there are reports of antivenom scarcity in USA, leading to an increase in morbidity and mortality, with patients needing to be intubated and ventilated while the toxin wears off. The development of an alternative method for the production of an antielapidic serum, with no need for snake collection and maintenance in captivity, would be a plausible solution for the antielapidic serum shortage.

Methods and Findings

In this work we describe the mapping, by the SPOT-synthesis technique, of potential B-cell epitopes from five putative toxins from M. corallinus, which were used to design two multiepitope DNA strings for the genetic immunisation of female BALB/c mice. Results demonstrate that sera obtained from animals that were genetically immunised with these multiepitope constructs, followed by booster doses of recombinant proteins lead to a 60% survival in a lethal dose neutralisation assay.

Conclusion

Here we describe that the genetic immunisation with a synthetic multiepitope gene followed by booster doses with recombinant protein is a promising approach to develop an alternative antielapidic serum against M. corallinus venom without the need of collection and the very challenging maintenance of these snakes in captivity.

Coral snakes are a group of deadly venomous snakes that exhibit a characteristic red, yellow/white, and black coloured banding pattern. Accidents involving these snakes tend to be very severe or even lethal, causing peripheral nervous system depression with muscle paralysis and vasomotor instability. The only acceptable medical treatment for snakebite accidents is the administration of an antivenom, generally produced by immunising horses with the snake venom. Nonetheless, for what concerns the antielapidic serum production in Brazil, the total amount of venom available for horse immunisations is insufficient. This is mainly due to the small size of coral snake glands, their underground life style, combined with its very low survival rates in captivity. Moreover, cases of patients being intubated and ventilated as a consequence of antivenom shortage in USA have also been registered. In this work, we present an alternative method for the development of antielapidic serum, which does not rely upon snake capture. This serum was produced by a heterologous DNA prime—with a multiepitope DNA string coding for the most reactive epitopes from the most abundant toxins of M. corallinus, a coral snake which occupy highly populated areas in Brazil—followed by recombinant multiepitope protein boost immunisation of mice.

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.

General characterization of Tityus fasciolatus scorpion venom. Molecular identification of toxins and localization of linear B-cell epitopes

This communication describes the general characteristics of the venom from the Brazilian scorpion Tityus fasciolatus, which is an endemic species found in the central Brazil (States of Goiás and Minas Gerais), being responsible for sting accidents in this area. The soluble venom obtained from this scorpion is toxic to mice being the LD50 is 2.984 mg/kg (subcutaneally). SDS-PAGE of the soluble venom resulted in 10 fractions ranged in size from 6 to 10-80 kDa. Sheep were employed for anti-T. fasciolatus venom serum production. Western blotting analysis showed that most of these venom proteins are immunogenic. T. fasciolatus anti-venom revealed consistent cross-reactivity with venom antigens from Tityus serrulatus. Using known primers for T. serrulatus toxins, we have identified three toxins sequences from T. fasciolatus venom. Linear epitopes of these toxins were localized and fifty-five overlapping pentadecapeptides covering complete amino acid sequence of the three toxins were synthesized in cellulose membrane (spot-synthesis technique). The epitopes were located on the 3D structures and some important residues for structure/function were identified.

Use of Phage Display technology in development of canine visceral leishmaniasis vaccine using synthetic peptide trapped in sphingomyelin/cholesterol liposomes

Background

Leishmania parasites can cause visceral or cutaneous disease and are found in subtropical and tropical regions of the Old and New World. The pathology of the infection is determined by both host immune factors and species/strain differences of the parasite. Dogs represent the major reservoir of Leishmania infantum (syn. L. chagasi) and vaccines are considered the most cost-effective control tools for canine disease.

Methods

Selection of immunodominant peptides was performed by Phage Display to identify sequences recognized by L. infantum naturally infected animals. Sera from Leishmania infected animals were used in the biopanning to selection of specific peptides. Serum samples from T. cruzi infected and healthy animals were used as control. After selection, synthetic peptides were produced in membrane (spot-synthesis) in soluble form and blotting and ELISA were performed for validation of serum reactivity. Selected peptide was formulated with aluminum hydroxide and liposomes and immunization was performed in BALB/c mice. Protection was determined by qPCR after challenge infection with virulent L. infantum.

Results

We reported the selection of Peptide 5 through Phage Display technique and demonstrate its ability to promote a state of immunity against L. infantum infection in murine model after immunization using liposomes as vaccine carrier. Our results demonstrate that immunization with Peptide 5 when formulated with aluminum hydroxide and liposomes is immunogenic and elicited significant protection associated with the induction of mixed Th1/Th2 immune response against L. infantum infection.

Conclusion

Peptide 5 is a promising vaccine candidate and the findings obtained in the present study encourage canine trials to confirm the effectiveness of a vaccine against CVL.

Computer-predicted peptides that mimic discontinuous epitopes on the A2 domain of factor VIII

Development of antibodies (Abs) against factor VIII (FVIII) is a severe complication of haemophilia A treatment. Recent publications suggest that domain specificity of anti-FVIII antibodies, particularly during immune tolerance induction (ITI), might be related to the outcome of the treatment. Obtaining suitable tools for a fine mapping of discontinuous epitopes could thus be helpful. The aim of this study was to map discontinuous epitopes on FVIII A2 domain using a new epitope prediction functionality of the PEPOP bioinformatics tool and a peptide inhibition assay based on the Luminex technology. We predicted, selected and synthesized 40 peptides mimicking discontinuous epitopes on the A2 domain of FVIII. A new inhibition assays using Luminex technology was performed to identify peptides able to inhibit the binding of anti-A2 Abs to A2 domain. We identified two peptides (IFKKLYHVWTKEVG and LYSRRLPKGVKHFD) able to block the binding of anti-A2 allo-antibodies to this domain. The three-dimensional representation of these two peptides on the A2 domain revealed that they are localized on a limited region of A2. We also confirmed that residues 484-508 of the A2 domain define an antigenic site. We suggest that dissection of the antibody response during ITI using synthetic peptide epitopes could provide important information for the management of patients with inhibitors.

A cell-penetrating antibody fragment against HIV-1 Rev has high antiviral activity: characterization of the paratope

The HIV-1 protein Rev oligomerizes on viral transcripts and directs their nuclear export. Previously, a Fab against Rev generated by phage display was used to crystallize and solve the structure of the Rev oligomerization domain. Here we have investigated the capability of this Fab to block Rev oligomerization and inhibit HIV-1 replication. The Fab itself did not have antiviral activity, but when a Tat-derived cell-penetrating peptide was appended, the resulting molecule (FabRev1-Tat) was strongly inhibitory of three different CCR5-tropic HIV-1 isolates (IC50 = 0.09-0.44 μg/ml), as assessed by suppression of reverse transcriptase activity in infected peripheral blood mononuclear cells, and had low cell toxicity (TC50 > 100 μg/ml). FabRev1-Tat was taken up by both peripheral blood mononuclear and HEK293T cells, appearing in both the cytoplasm and nucleus, as shown by immunofluorescence confocal laser scanning microscopy. Computational alanine scanning was used to identify key residues in the complementarity-determining regions to guide mutagenesis experiments. Residues in the light chain CDR3 (LCDR3) were assessed to be important. Residues in LCDR3 were mutated, and LCDR3-Tyr(92) was found to be critical for binding to Rev, as judged by surface plasmon resonance and electron microscopy. Peptides corresponding to all six CDR regions were synthesized and tested for Rev binding. None of the linear peptides had significant affinity for Rev, but four of the amide-cyclic forms did. Especially cyclic-LCDR3 (LGGYPAASYRTA) had high affinity for Rev and was able to effectively depolymerize Rev filaments, as shown by both surface plasmon resonance and electron microscopy.

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

Background

The snake Bothrops atrox is responsible for the majority of envenomings in the northern region of South America. Severe local effects, including hemorrhage, which are mainly caused by snake venom metalloproteinases (SVMPs), are not fully neutralized by conventional serum therapy. Little is known about the immunochemistry of the P-I SVMPs since few monoclonal antibodies (mAbs) against these molecules have been obtained. In addition, producing toxin-neutralizing mAbs remains very challenging.

Methodology/Principal Findings

Here, we report on the set-up of a functional screening based on a synthetic peptide used as a biosensor to select neutralizing mAbs against SVMPs and the successful production of neutralizing mAbs against Atroxlysin-I (Atr-I), a P-I SVMP from B. atrox. Hybridomas producing supernatants with inhibitory effect against the proteolytic activity of Atr-I towards the FRET peptide Abz-LVEALYQ-EDDnp were selected. Six IgG1 Mabs were obtained (named mAbatr1 to mAbatr6) and also two IgM. mAbatrs1, 2, 3 and 6 were purified. All showed a high specific reactivity, recognizing only Atr-I and B. atrox venom in ELISA and a high affinity, showing equilibrium constants in the nM range for Atr-I. These mAbatrs were not able to bind to Atr-I overlapping peptides, suggesting that they recognize conformational epitopes.

Conclusions/Significance

For the first time a functional screening based on a synthetic biosensor was successfully used for the selection of neutralizing mAbs against SVMPs.

In this work, we propose a new screening strategy to produce monoclonal antibodies against Atr-I, a P-I class SVMP from Bothrops atrox, which is the snake responsible for the majority of the accidents in South America. SVMPs are the main toxic factors in Bothrops venom causing systemic and local hemorrhage, which may evolve to inflammation and/or necrosis. Since the toxic effects of SVMPs are related to their proteolytic activity, we have produced a peptide which was used as a biosensor for Atr-I hydrolysis. Hydrolysis of this substrate was monitored and the clones possessing inhibitory activity against the proteolytic activity of Atr-I upon the peptide were selected. Using our new approach, we have obtained four monoclonal antibodies highly specific and with neutralizing capacity against the hemorrhagic activity of either Atr-I alone or Bothrops atrox whole venom. To the best of the authors' knowledge, this is the first time where a functional screening is used for the selection of neutralizing mAbs against SVMPs. It is also the first description of mAbs anti-Atr-I, with inhibitory potential against its toxic activities which may be useful for diagnosis and treatment in the future.

Molecular, immunological, and biological characterization of Tityus serrulatus venom hyaluronidase: new insights into its role in envenomation

Background

Scorpionism is a public health problem in Brazil, and Tityus serrulatus (Ts) is primarily responsible for severe accidents. The main toxic components of Ts venom are low-molecular-weight neurotoxins; however, the venom also contains poorly characterized high-molecular-weight enzymes. Hyaluronidase is one such enzyme that has been poorly characterized.

Methods and principal findings

We examined clones from a cDNA library of the Ts venom gland and described two novel isoforms of hyaluronidase, TsHyal-1 and TsHyal-2. The isoforms are 83% identical, and alignment of their predicted amino acid sequences with other hyaluronidases showed conserved residues between evolutionarily distant organisms. We performed gel filtration followed by reversed-phase chromatography to purify native hyaluronidase from Ts venom. Purified native Ts hyaluronidase was used to produce anti-hyaluronidase serum in rabbits. As little as 0.94 µl of anti-hyaluronidase serum neutralized 1 LD₅₀ (13.2 µg) of Ts venom hyaluronidase activity in vitro. In vivo neutralization assays showed that 121.6 µl of anti-hyaluronidase serum inhibited mouse death 100%, whereas 60.8 µl and 15.2 µl of serum delayed mouse death. Inhibition of death was also achieved by using the hyaluronidase pharmacological inhibitor aristolochic acid. Addition of native Ts hyaluronidase (0.418 µg) to pre-neutralized Ts venom (13.2 µg venom+0.94 µl anti-hyaluronidase serum) reversed mouse survival. We used the SPOT method to map TsHyal-1 and TsHyal-2 epitopes. More peptides were recognized by anti-hyaluronidase serum in TsHyal-1 than in TsHyal-2. Epitopes common to both isoforms included active site residues.

Conclusions

Hyaluronidase inhibition and immunoneutralization reduced the toxic effects of Ts venom. Our results have implications in scorpionism therapy and challenge the notion that only neurotoxins are important to the envenoming process.

In Brazil, accidents with scorpion stings have been a serious public health problem, and Tityus serrulatus (Ts) is primarily responsible for severe accidents. Therefore, efforts have been made to understand the characteristics of the molecules present in scorpion venoms. These venoms are complex mixtures, in which neurotoxins are the main toxic components. Ts venom also contains enzymes, such as hyaluronidase, that have not been well characterized. In this study, we described for the first time two sequences of Ts hyaluronidase isoforms: TsHyal-1 and TsHyal-2. We purified native hyaluronidase from Ts venom and produced anti-hyaluronidase serum in rabbits. This serum neutralized hyaluronidase activity present in Ts venom. In vivo neutralization assays showed that anti-hyaluronidase serum inhibited and delayed mouse death after injection of a lethal dose (50% lethal dose, LD₅₀) of Ts venom. This work confirms the influence of hyaluronidase in Ts venom lethality and paves the way for the development of new strategies for scorpionism therapy.

Synthetic peptides for in vitro evaluation of the neutralizing potency of Loxosceles antivenoms

An important step in the development of therapeutic antivenoms is the pre-clinical testing using in vivo methods to assess their neutralizing potency. For spider antivenoms (Loxosceles species), horse serum potency against the necrotizing activities of Loxosceles intermedia crude venom is currently tested in rabbits. These procedures are time consuming and involve a large number of animals. The aim of this study was to develop an in vitro method to assess the neutralizing potency of anti-Loxosceles sera. We first demonstrated that it was not possible to establish a correlation between the ELISA antibody reactivity of horse anti-Loxosceles serum and their neutralizing potency. We then showed that the antivenoms recognized several peptide epitopes from different regions of SMase-D proteins, which are toxic antigens from Loxosceles venoms. The recognition of some peptides was observed only when high neutralizing potency sera was used. Based on these results, three peptides (peptide 1, DNRRPIWNLAHMVNA and peptide 3, DFSGPYLPSLPTLDA corresponding to residues 2-16 and 164-178, respectively, of SMase-1 protein from Loxosceles laeta, and peptide 2, EFVNLGANSIETDVS corresponding to residues 22-36 of A1H - LoxGa protein from Loxosceles gaucho and LiD1 protein from L. intermedia) were selected. The peptides were synthesized, coupled to bovine serum albumin (BSA), and used as antigens in indirect ELISA to test their reactivity with horse anti-Loxosceles serum of varying neutralizing potencies. We found certain assay conditions that discriminated between the high and low neutralizing potency sera. This study introduced an in vitro and peptide-based neutralization assay for anti-Loxosceles antivenoms.

Generation and characterization of rendomab-B1, a monoclonal antibody displaying potent and specific antagonism of the human endothelin B receptor

Endothelin B receptor (ETBR) is a G protein-coupled receptor able to bind equally to the three identified human endothelin peptides. It is expressed primarily on vascular endothelial cells and involved in various physiological processes including vascular tone homeostasis, enteric nervous system development, melanogenesis and angiogenesis. Furthermore, overactivation or overexpression of ETBR have been associated with the development of various diseases such as cardiovascular disorders and cancers. Therefore, ETBR appears to be relevant target for the therapy or diagnosis of highly prevalent human diseases. In this study, we report the in vitro characterization of rendomab-B1, a monoclonal antibody (mAb) obtained by genetic immunization, which selectively recognizes the native form of human ETBR (hETBR). Rendomab-B1 is the first-reported mAb that behaves as a potent antagonist of hETBR. It recognizes an original extracellular conformational epitope on the receptor, distinct from the endothelin-1 (ET-1) binding site. Rendomab-B1 not only blocks ET-1-induced calcium signaling pathway and triggers rapid receptor internalization on recombinant hETBR-expressing cells, but also exerts pharmacological activities on human vascular endothelial cells, reducing both cell viability and ET-1-induced hETBR synthesis. In addition, binding experiments using rendomab-B1 on different melanoma cell lines reveal the structural and functional heterogeneity of hETBR expressed at the surface of these cancer cells, strongly suggesting the existence of tumor-specific receptors. Collectively, our results underscore the value of rendomab-B1 for research, therapeutic and diagnostic applications dealing with hETBR.

Discontinuous epitopes on the C2 domain of coagulation Factor VIII mapped by computer-designed synthetic peptides

The occurrence of alloantibodies against Factor VIII (FVIII) is the main iatrogenic complication in haemophilia A (HA). Anti-FVIII autoantibodies may also spontaneously appear in non-HA patients, leading to acquired haemophilia A. In both contexts, the antibody response against FVIII is complex and difficult to analyse due to the lack of suitable tools. Our purpose was to comprehensively map, at the amino acid level, discontinuous epitopes of the C2 domain of FVIII targeted by patients' antibodies. We synthesized 33 synthetic peptides, which were predicted by the bioinformatic algorithm PEPOP to mimic C2 domain discontinuous epitopes. Using an inhibition assay based on the x-MAP technology, we evaluated their ability to block the binding to the C2 domain of anti-C2 domain antibodies from pooled plasma samples. Nine peptides were thus selected and tested again in individual plasma samples. Our results support the view that C2 domain epitopes are organized as an epitopic mosaic distributed around the molecule, showed that each patient displayed a specific anti-C2 epitopic profile, and confirmed the complexity and variability of the immune response against the C2 domain of FVIII. This ability to finely map epitopes could be further used to follow the antibody specificity modifications over time.

Protection against the toxic effects of Loxosceles intermedia spider venom elicited by mimotope peptides

The venom of Loxosceles intermedia (Li) spiders is responsible for cutaneous lesions and other clinical manifestations. We previously reported that the monoclonal antibody LimAb7 can neutralize the dermonecrotic activity of crude Li venom. In this study, we observed that this antibody recognizes several proteins from the venom dermonecrotic fraction (DNF), including LiD1. Identifying the epitope of such a neutralizing antibody could help designing immunogens for producing therapeutic sera or vaccination approaches. To this aim, two sets of 25- and 15-mer overlapping peptides that cover the complete amino acid sequence of LiD1 were synthesized using the SPOT technique. None of them was recognized by LimAb7, suggesting that the epitope is discontinuous. Then, the screening of four peptide phage-display libraries yielded four possible epitope mimics that, however, did not show any obvious similarity with the LiD1 sequence. These mimotopes, together with a 3D model of LiD1, were used to predict with the MIMOP bioinformatic tool the putative epitope region (residues C197, Y224, W225, T226, D228, K229, R230, T232 and Y248 of LiD1) recognized by LimAb7. This analysis and the results of alanine-scanning experiments highlighted a few residues (such as W225 and D228) that are found in the active site of different SMases D and that may be important for LiD1 enzymatic activity. Finally, the only mimotope NCNKNDHLFACW that interacts with LimAb7 by SPOT and its analog NSNKNDHLFASW were used as immunogens in rabbits. The resulting antibodies could neutralize some of the biological effects induced by crude Li venom, demonstrating a mimotope-induced protection against L. intermedia venom.

Mimotopes of mutalysin-II from Lachesis muta snake venom induce hemorrhage inhibitory antibodies upon vaccination of rabbits

Mutalysin-II (mut-II) from Lachesis muta snake venom is an endopeptidase with hemorrhagic activity. A mAb against mutalysin-II that neutralized the hemorrhagic effect was produced previously. To identify the mAb epitopes, sets of 15-mer overlapping peptides covering the mut-II amino acid sequence were synthesized using the SPOT method and tested but failed to react with the mAb. Using a phage-display approach seventeen clones reactive with mAb were identified. Additional immunoassays with the peptides and mAb identified the QCTMDQGRLRCR, TCATDQGRLRCT, HCFHDQGRVRCA, HCTMDQGRLRCR and SCMLDQGRSRCR sequences as possible epitopes. Immunization of rabbits with these peptides induced antibodies that recognize mut-II and protected against the hemorrhagic effects of Lachesis venom.

Electroporation-aided DNA immunization generates polyclonal antibodies against the native conformation of human endothelin B receptor

Endothelin B receptor (ET(B)R) is a G protein-coupled receptor (GPCR) specific for endothelin peptides (including endothelin-1, ET1), which mediates a variety of key physiological functions in normal tissues, such as modulation of vasomotor tone, tissue differentiation, or cell proliferation. Moreover, ET(B)R, overexpressed in various cancer cells including melanoma, has been implicated in the growth and progression of tumors, as well as in controlling T cell homing to tumors. To gather information on receptor structure and function, antibodies are generally considered choice molecular probes, but generation of such reagents against the native conformation of GPCRs is a real technical challenge. Here, we show that electroporation-aided genetic immunization, coupled to cardiotoxin pretreatment, is a simple and very efficient method to raise large amounts of polyclonal antibodies highly specific for native human ET(B)R (hET(B)R), as assessed by both flow cytometry analysis of different stably transfected cell lines and a new and rapid cell-based enzyme-linked immunosorbent assay that we also describe. The antibodies recognized two major epitopes on hET(B)R, mapped within the N-terminal extracellular domain. They were used to reveal hET(B)R on membranes of three different human melanoma cell lines, by flow cytometry and confocal microscopy, a method that we show is more relevant than mRNA polymerase chain reaction in assessing receptor expression. In addition, ET-1 partially competed with antibodies for receptor binding. The strategy described here, thus, efficiently generated new immunological tools to further analyze the role of ET(B)R under both normal and pathological conditions, including cancers. Above all, it can now be used to raise monoclonal antibodies against hET(B)R and, more generally, against GPCRs that constitute, by far, the largest reservoir of potential pharmacological targets.

In vivo protection against Tityus serrulatus scorpion venom by antibodies raised against a discontinuous synthetic epitope

Scorpion stings cause human fatalities in numerous countries. Serotherapy is the only specific means to try to circumvent the noxious effects of venom toxins. TsNTxP is a natural anatoxin from the venom of the scorpion Tityus serrulatus that may be useful to raise therapeutic anti-venom sera. Linear epitopes recognized by anti-TsNTxP antibodies have previously been mapped. Here, we attempted to identify discontinuous epitopes in TsNTxP since neutralizing epitopes are often associated with such complex entities. One hundred and fifty-three octadecapeptides with the general formula (P1)-(Gly-Gly)-(P2) were synthesized by the Spot method on cellulose membranes. P1 and P2 were octapeptides from the TsNTxP N-terminal and C-terminal sections, respectively. Each sequence of eight amino acids was frameshifted in turn by three residues, in order to cover TsNTxP entire sequence. Binding of neutralizing anti-TsNTxP rabbit antibodies to spotted peptides revealed GREGYPADGGGLPDSVKI as the more reactive peptide sequence. This epitope was made from the first eight residues of the protein (GREGYPAD) and from residues 47 to 54 (GLPDSVKI) of the C-terminal part of TsNTxP. BALB/c mice were immunized with synthetic GREGYPADGGGLPDSVKI peptide conjugated to ovalbumin. One week after the last immunization, in vivo protection assays showed that immunized mice could resist a challenge by an amount of T.serrulatus whole venom equivalent to 1.75 LD(100), a dose that killed all control non-immune mice. Based on molecular models of TsNTxP and related Tityus toxins, we found that the above peptide matches with a discontinuous epitope, well exposed at the toxin molecular surface which contains residues known to be important for the bioactivity of toxins.

Expression of Jug r 1, the 2S albumin allergen from walnut (Juglans regia), as a correctly folded and functional recombinant protein

Jug r 1, the 2S albumin allergen from walnut, was isolated from ripe nuts as a native allergen and expressed in Escherichia coli using the Gateway technology as a recombinant allergen. The recombinant Jug r 1 (15 kDa) differs from the native allergen by the absence of cleavage of the polypeptide chain in two covalently associated light (3.5 kDa) and heavy (8 kDa) chains. Recombinant rJug r 1 adopts the canonical alpha-helical fold of plant 2S albumins as checked on CD spectra. Four IgE-binding epitopic stretches were identified along the amino acid sequence of Jug r 1 and localized on the molecular surface of the modeled allergen. Both native and recombinant allergens exhibit similar IgE-binding activity and similarly trigger the degranulation of a FcepsilonRI-expressing rat basophilic leukaemia cell line previously treated by IgE-containing sera. Native Jug r 1 resists to heat denaturation and to the proteolytic attack of trypsin and chymotrypsin but is readily hydrolyzed in the presence of pepsin at acidic pH after 1 h of incubation at 37 degrees C in vitro. Recombinant Jug r 1 could be used for a component-resolved diagnosis of food-allergy.

IgE-binding epitopic peptide mapping on a three-dimensional model built for the 13S globulin allergen of buckwheat (Fagopyrum esculentum)

The three-dimensional model built for the 13S globulin allergen of buckwheat (Fagopyrum esculentum) consists of three protomers exhibiting the cupin motif, arranged in a homotrimer around a three-fold symmetry axis. Using the SPOT technique, 11 continuous IgE-binding epitopic peptides were characterized on the molecular surface of the 13S globulin allergen of buckwheat. Except for one of them, they all correspond to well exposed regions containing electropositiveley and/or electronegatively charged residues, which cover up to 40% of the molecular surface of the allergen. Some of these epitopes come in close contact to probably create more extended discontinuous epitopes, especially those located on the edge of the 13S globulin homotrimer. Half of the identified epitope peptides remain unaltered in a core structure protected against hydrolysis by digestive proteases and are thus assumed to promote the allergenicity of the 13S globulin. In addition, a few of these epitopes coincide with sequential IgE-binding epitopes previously characterized in soybean 11S globulins, that could account for the IgE-binding cross-reactions observed between soybean and buckwheat in Western blot experiments.

An in vivo protective response against toxic effects of the dermonecrotic protein from Loxosceles intermedia spider venom elicited by synthetic epitopes

Loxoscelism is a necrotic-hemolytic syndrome caused by bites of brown spiders belonging to the genus Loxosceles. Many approaches for the treatment of Loxosceles poisoning have already been proposed, among which administration of specific antivenom is thought to be the more specific. We have evaluated the use of peptides as immunogen to raise in rabbits an antibody response that could protect animals from a challenge by the Loxtox isoform LiD1, one of the main toxic component of Loxosceles intermedia venom. Six antigenic regions of LiD1 were mapped by using the SPOT method. The corresponding peptides were further chemically synthesized, mixed, and used as immunogens in rabbits. Control animal received recombinant LiD1 alone or together with peptides. We found that the rabbit antibody response to peptides was cross-reactive with LiD1, although only one peptide from the mix of six was immunogenic. The dermonecrotic, hemorrhagic and oedema forming activities induced by LiD1 in naïve rabbits were inhibited by 82%, 35% and 35% respectively, by preincubation of LiD1 with anti-peptide antibodies prepared from immunized rabbits. Animals that were immunized with peptides or LiD1r, were found to be protected from the dermonecrotic, hemorrhagic and oedema forming activities induced by a challenge with LiD1. The protection conferred by peptides was, however, lower than that provided by the peptide protein combination or by the full-length protein. These results encourage us in the utilization of synthetic peptides for therapeutic serum development or vaccination approaches.