A conserved sequence region of scorpion toxins rendered immunogenic induces broadly cross-reactive, neutralizing antibodies

Evaluation of the immunoprotective power of a multiple antigenic peptide against Aah II toxin of Androctonus australis hector scorpion

Scorpion envenoming (SE) is a public health problem in developing countries. In Algeria, the population exposed to the risk of SE was estimated at 86.45% in 2019. Thus, the development of a vaccine to protect the exposed population against scorpion toxins would be a major advance in the fight against this disease. This work aimed to evaluate the immunoprotective effect of a Multiple Antigenic Peptide against the Aah II toxin of Androctonus australis hector scorpion, the most dangerous scorpion species in Algeria. The immunogen MAP1Aah2 was designed and tested accordingly. This molecule contains a B epitope, derived from Aah II toxin, linked by a spacer to a universal T epitope, derived from the tetanus toxin. The results showed that MAP1Aah2 was non-toxic despite the fact that its sequence was derived from Aah II toxin. The immunoenzymatic assay revealed that the 3 immunization regimens tested generated specific anti-MAP1Aah2 antibodies and cross-reacted with the toxin. Mice immunized with this immunogen were partially protected against mortality caused by challenge doses of 2 and 3 LD50 of the toxin. The survival rate and developed symptoms varied depending on the adjuvant and the challenge dose used. In the in vitro neutralization test, the immune sera of mice having received the immunogen with incomplete Freund's adjuvant neutralized a challenge dose of 2 LD50. Hence, the concept of using peptide dendrimers, based on linear epitopes of scorpion toxins, as immunogens against the parent toxin was established. However, the protective properties of the tested immunogen require further optimizations.

Antigenic cross-reactivity between sixteen venoms from scorpions belonging to six genera

Venoms of 15 scorpion species from Venezuela and one from Brazil were compared in their antigenic cross-reactivity with specific F(ab')2 against Tityus discrepans (Td-antibodies), using the method of King and collaborators (1). Our results show that Tityus venoms cross-reactivity (shared epitopes) with the venoms of other species within the genus tended to be less for a greater distance between the habitat of the species. A nonparametric linear regression of free Td-antibody binding to T. discrepans venom immobilized to a solid phase in the presence of other Tityus venoms versus distance showed binding = a + b x log10 (distance) where: median (95% confidence interval) for a = 0.92 (7.43, 9.80) and b = 17.20 (4.15, 22.57) binding/log10(Km); Spearman rS = 0.783 with associated P = 0.006. Our results show that toxins from different Tityus species, targeting mammalian Na+ and K+ channels, are antigenically very similar. Venoms from species from other genera such as Centruroides, Broteas, Diplocentrus, Chactas, and Rhopalurus did not cross-react with Td-antibodies.

The neutralizing effect of a polyclonal antibody raised against the N-terminal eighteen-aminoacid residues of birtoxin towards the whole venom of Parabuthus transvaalicus

Scorpion venom is composed among other things of a large number of neurotoxic peptides affecting all major types of ion channels. The majority of the toxicity of the venom is attributed to the presence of these peptides. In our previous studies using a combination of HPLC and mass spectrometry, we showed that birtoxin like peptides are the major peptidic components of the venom of Parabuthus transvaalicus. These peptides are quite similar to each other differing by only few amino acid residues. In addition they all share a common N-terminus of eighteen amino acid residues. We hypothesize that neutralization of this domain will decrease the toxicity of the whole venom of P. transvaalicus. Polyclonal antibodies against the common N-terminal region of the peptides are generated. Here we show by bioassays that the polyclonal antibodies neutralize the venom of P. transvaalicus in a dose dependent manner and by mass spectrometry and western blotting that these peptides indeed react with the polyclonal antibodies. Previously antibodies generated against a single major toxic component of venom have proven to be an effective strategy for antivenin production. In the case of P. transvaalicus the generated antibody is against the majority of the peptidic fraction due to the presence of several highly similar and highly toxic components in this venom. We show that using the knowledge obtained through biochemical characterization studies it is possible to design very specific antibodies that will be useful for clinical applications against Parabuthus envenomation.

Molecular characterization of a neutralizing murine monoclonal antibody against Tityus serrulatus scorpion venom

Monoclonal antibodies (mAbs) against Tityus serrulatus venom were obtained by the fusion of SP2/0 murine myeloma cells and spleen cells from BALB/c mice immunized with a toxic fraction (TstFG50) of the Tityus venom (this G50 chromatography fraction represents most of the toxicity of the crude venom) conjugated to bovine serum albumin (BSA) with glutaraldehyde. From the initial screening of over 200 hybridoma fusion wells, a panel of 9 anti-TstFG50 secreting hybridomas was established. The capacity of mAbs to neutralize the TstFG50 toxic fraction toxic was determined by in vitro neutralization assays and by inhibition of the binding of 125I-TsVII to its site on rat brain synaptosomes. Only mAbTs1 neutralized 50% of the toxic effects produced by scorpion venom and showed 35% inhibition of the binding of 125I-TsVII at 10(-7) M. To map the epitope recognized by the protective mAbTs1, we prepared a comprehensive series of overlapping 15-mer synthetic peptides covering the amino acid sequences of the four Tityus proteins. MAbTs1 reacted with peptide 26 of TsIV (KKSKDKKADSGYSYW), peptide 30 of TsVII (KKGSSGYSAWPASYS) and peptide 31 of TsNTxP (KKGSSGYSAWPASYS). MAbTs1 was not reactive with any peptide from TsII. The N-terminal lysine residue from the epitope was found to be critical for mAbTs1 binding. The epitope was positioned on the available three-dimensional structure of TsVII together with the recently identified residues from the pharmacophore of beta-scorpion toxins. The neutralizing properties of mAbTs1 might be explained by spatial vicinity of epitope residues with pharmacophore residues.

Analysis of the immune response induced by a scorpion venom sub-fraction, a pure peptide and a recombinant peptide, against toxin Cn2 of Centruroides noxius Hoffmann

Three different immunogens from the venom of the Mexican scorpion Centruroides noxius Hoffmann were used to study protective antibody response in mice and rabbits, challenged with toxin Cn2, one of the most abundant toxic peptide of this venom. The immunogens were: Cn5, a crustacean specific toxin; a recombinant protein containing the peptide Cn5 linked to the maltose transporter and a sub-fraction (F.II.5) containing 25 distinct peptides, among which is Cn5. Mice immunized with these three preparations, when directly challenged with Cn2 presented no apparent protection, whereas anti-sera produced in rabbits with these three immunogens were capable of partially neutralizing the effect of Cn2, when injected into naive mice. Cn5 rabbit anti-serum showed a better protective effect on mice, than the rabbit sera obtained against the two other antigens. The subcutaneous route of challenging mice was shown to be better than intraperitoneal injections. Comparative structural analysis of Cn5 with other toxins of this venom showed that our results are important to be taken into consideration, when choosing appropriate immunogens aimed at the production of better anti-venoms or for the rational design of possible vaccines.

Molecular basis for the cross-reactivity of antibodies elicited by a natural anatoxin with alpha- and beta-toxins from the venom of Tityus serrulatus scorpion

A non-toxic protein (TsNTxP) isolated from the venom of the noxious scorpion Tityus serrulatus (Ts) induces polyclonal antibodies cross-reactive with several toxins from the venom, in sharp contrast to anti-toxin antibodies which are toxin specific. To try to uncover the molecular basis for these unusual properties, peptide scanning experiments were performed and indicated that the N- and C-terminal parts of TsNTxP enclose continuous epitopes (residues 1-15 and 47-61). Antibodies raised against peptides corresponding to these two regions were found to have neutralizing properties against a mixture of all toxic proteins from the T. serrulatus venom, indicating that residues 1-15 and 47-61 correspond to neutralizing epitopes. The identification of key antigenic residues within these two epitopes revealed that several of them are well conserved in the amino-acid sequences of the three main toxins (Ts II, Ts IV and Ts VII) from the venom: Glu 3, Tyr 5, Asp 8, Asp 50, Trp 55 and Lys 61. A single key-residue (Glu 58) is unique to TsNTxP. By using homology modeling, a model of the three-dimensional structure of TsNTxP was obtained. The antigenically important residues from TsNTxP were found to be surface exposed, with five of them clustered on the facet of the protein reported to enclose the active site of toxins. Residues equivalent to the seven key-residues of the anatoxin were also found to be exposed in the active toxins from T. serrulatus venom. These results show that antibodies elicited by the non-toxic protein TsNTxP recognized, within the N- and C-terminal parts of toxins of T. serrulatus, conserved and surface exposed residues which might also be involved in the toxic action of the proteins.

Monoclonal antibodies neutralizing the toxin II from Androctonus australis hector scorpion venom: usefulness of a synthetic, non-toxic analog

Scorpion venom contains toxins that act on ion channels. Some are responsible for the noxious effects observed when people are stung by scorpions. The study of the neutralization of these molecules and the production of monoclonal antibodies (mAbs) should prove valuable. Toxin II from Androctonus australis hector scorpion (AahII) is one of the most potent toxins and has been well-characterized and studied. Producing mAbs against such molecules is often difficult due to their toxicity. We used a synthetic, non-toxic analog, (Abu)8-AahII, to obtain mAbs which recognize and neutralize the native toxin AahII. Sets of peptides spanning the entire sequence of AahII were assayed to identify the binding sites of the mAbs. The various mAbs recognized only the largest peptides (12-17 residues). They recognized peptides corresponding to different parts of the AahII sequence, suggesting that several regions of the (Abu)8-AahII sequence mimic AahII epitopes and then elicit mAbs directed against toxin.