Mohamed El Ayeb

A new fold in the scorpion toxin family, associated with an activity on a ryanodine-sensitive calcium channel.

We determined the structure in solution by 1H two‐dimensional NMR of Maurocalcine from the venom of Scorpio maurus. This toxin has been demonstrated to be a potent effector of ryanodyne‐sensitive calcium channel from skeletal muscles. This is the first description of a scorpion toxin which folds following the Inhibitor Cystine Knot fold (ICK) already described for numerous toxic and inhibitory peptides, as well as for various protease inhibitors. Its three dimensional structure consists of a compact disulfide‐bonded core from which emerge loops and the N‐terminus. A double‐stranded antiparallel β‐sheet comprises residues 20–23 and 30–33. A third extended strand (residues 9–11) is perpendicular to the β‐sheet. Maurocalcine structure mimics the activating segment of the dihydropyridine receptor II‐III loop and is therefore potentially useful for dihydropyridine receptor/ryanodine receptor interaction studies. Proteins 2000;40:436–442.

A bispecific nanobody to provide full protection against lethal scorpion envenoming

Envenoming following scorpion sting is a common emergency in many parts of the world. Our aim was to ameliorate the current 100‐kDa horse plasma antivenom serum (PAS)‐derived Fab′2 to more quickly reach the highly diffusible scorpion toxins (7 kDa). We immunized dromedaries with toxins from Androctonus australis hector (Aah) scorpions and cloned the single‐domain antibody fragments or nanobodies (15 kDa) from their B cells. Nanobodies against AahI′ toxin (with AahII the most toxic compound of the venom) were retrieved from the libraries, and their AahI′ ‐toxin neutralization was monitored in mice. Remarkably, the NbAahI′ F12 fully protected mice against 100 LD50 of AahI′ administered intracerebroventricularly. Moreover, where PAS failed completely to neutralize 2 LD50 of crude venom injected subcutaneously, the designed bispecific NbF12‐10 against AahI′/AahII toxins succeeded in neutralizing 5 LD50. Finally, in a challenge assay in which mice were subcutaneously injected with a lethal dose of scorpion venom, the subsequent intravenous injection of 85 μg of NbF12‐10 protected all mice, even if the whole procedure was repeated 3 times. Furthermore, the NbF12‐10 remained fully protective when mice with severe signs of envenoming were treated a few minutes before the untreated mice died.—Hmila, I., Saerens, D., Ben Abderrazek, R., Vincke, C., Abidi, N., Benlasfar, Z., Govaert, J., El Ayeb, M., Bouhaouala‐Zahar, B., Muyldermans, S. A bispecific nanobody to provide full protection against lethal scorpion envenoming. FASEB J. 24, 3479–3489 (2010). www.fasebj.org

Hemicalcin, a new toxin from the Iranian scorpion Hemiscorpius lepturus which is active on ryanodine-sensitive Ca2+ channels.

In the present work, we purified and characterized a novel toxin named hemicalcin from the venom of the Iranian chactoid scorpion Hemiscorpius lepturus where it represents 0.6% of the total protein content. It is a 33-mer basic peptide reticulated by three disulfide bridges, and that shares between 85 and 91% sequence identity with four other toxins, all known or supposed to be active on ryanodine-sensitive calcium channels. Hemicalcin differs from these other toxins by seven amino acids at positions 9 (leucine/arginine), 12 (alanine/glutamic acid), 13 (aspartic acid/asparagine), 14 (lysine/asparagine), 18 (serine/glycine), 26 (threonine/alanine) and 28 (proline/isoleucine/alanine). In spite of these differences, hemicalcin remains active on ryanodine-sensitive Ca2+ channels, since it increases [3H]ryanodine binding on RyR1 (ryanodine receptor type 1) and triggers Ca2+ release from sarcoplasmic vesicles. Bilayer lipid membrane experiments, in which the RyR1 channel is reconstituted and its gating properties are analysed, indicate that hemicalcin promotes an increase in the opening probability at intermediate concentration and induces a long-lasting subconductance level of 38% of the original amplitude at higher concentrations. Mice intracerebroventricular inoculation of 300 ng of hemicalcin induces neurotoxic symptoms in vivo, followed by death. Overall, these data identify a new biologically active toxin that belongs to a family of peptides active on the ryanodine-sensitive channel.

Identification of potent nanobodies to neutralize the most poisonous polypeptide from scorpion venom

Scorpion venom, containing highly toxic, small polypeptides that diffuse rapidly within the patient, causes serious medical problems. Nanobodies, single-domain antigen-binding fragments derived from dromedary heavy-chain antibodies, have a size that closely matches that of scorpion toxins. Therefore these nanobodies might be developed into potent immunotherapeutics to treat scorpion envenoming. Multiple nanobodies of sub-nanomolar affinity to AahII, the most toxic polypeptide within the Androctonus australis hector venom, were isolated from a dromedary immunized with AahII. These nanobodies neutralize the lethal effect of AahII to various extents without clear correlation with the kinetic rate constants kon or koff, or the equilibrium dissociation constant, KD. One particular nanobody, referred to as NbAahII10, which targets a unique epitope on AahII, neutralizes 7 LD50 of this toxin in mice, corresponding to a neutralizing capacity of approx. 37000 LD50 of AahII/mg of nanobody. Such high neutralizing potency has never been reached before by any other monoclonal antibody fragment.

Evaluation of antivenom therapy in children severely envenomed by Androctonus australis garzonii (Aag) and Buthus occitanus tunetanus (Bot) scorpions.

One hundred and forty-seven cases of envenomed children under 15 years old presenting local and general symptoms without failure in vital functions (clinical grade II) or presenting serious general symptoms with failure in vital functions (clinical grade III) were collected during the summer seasons of 1993-1997. They were classified in six groups according to the use or not of antivenom, the route and the frequency of antivenom administration. The determination, by a sensitive ELISA, of blood venom concentration before and until 6 h after antivenom therapy, allowed the establishment of the venom toxicokinetic curve for each group. The intramuscular administration of antivenom did not show significant effects on venom toxicokinetic curves and on patients recovery time. However, the same amount of antivenom administered by intravenous route clear rapidly the blood free venom toxins. Also, the patient recovery time was significantly shortened. These data are in favor of intravenous application of an adequate dose of an efficient antivenom in order to treat successfully severe scorpion envenoming cases.

Lebectin, a Macrovipera lebetina venom‐derived C‐type lectin, inhibits angiogenesis both in vitro and in vivo

Integrins play an essential role in endothelial cell motility processes during angiogenesis and thus present interesting targets for the development of new anti‐angiogenic agents. Snake venoms naturally contain a variety of proteins that can affect integrin–ligand interactions. Recently, the C‐type lectin proteins (CLPs) have been characterized as efficient modulators of integrin functions. In this study, we investigated the anti‐angiogenic activity of lebectin, a newly discovered CLP from Macrovipera lebetina venom. Human brain microvascular endothelial cells (HBMEC), used as an in vitro model, express αvβ3, αvβ5, and α5β1 integrins, as well as the α2, α3, α6, and β4 subunits. Our data show that lebectin acts as a very potent inhibitor (IC50 ≈ 0.5 nM) of HBMEC adhesion and migration on fibronectin by blocking the adhesive functions of both the α5β1 and αV integrins. In addition, lebectin strongly inhibits both HBMEC in vitro tubulogenesis on Matrigel™ (IC50 = 0.4 nM) and proliferation. Finally, using both a chicken CAM assay and a Matrigel™ Plug assay in nude mice, our results show that lebectin displays potent anti‐angiogenic activity in vivo. Lebectin thus represents a new C‐type lectin with anti‐angiogenic properties with great potential for the treatment of angiogenesis‐related diseases. J. Cell. Physiol. 211: 307–315, 2007.

Cobatoxin 1 from Centruroides noxius scorpion venom: chemical synthesis, three-dimensional structure in solution, pharmacology and docking on K+ channels

CoTX1 (cobatoxin 1) is a 32-residue toxin with three disulphide bridges that has been isolated from the venom of the Mexican scorpion Centruroides noxius Hoffmann. Here we report the chemical synthesis, disulphide bridge organization, 3-D (three-dimensional) solution structure determination, pharmacology on K+ channel subtypes (voltage-gated and Ca2+-activated) and docking-simulation experiments. An enzyme-based cleavage of the synthetic folded/oxidized CoTX1 indicated half-cystine pairs between Cys3-Cys22, Cys8-Cys27 and Cys12-Cys29. The 3-D structure of CoTX1 (solved by 1H-NMR) showed that it folds according to the common alpha/beta scaffold of scorpion toxins. In vivo, CoTX1 was lethal after intracerebroventricular injection to mice (LD50 value of 0.5 microg/mouse). In vitro, CoTX1 tested on cells expressing various voltage-gated or Ca2+-activated (IKCa1) K+ channels showed potent inhibition of currents from rat K(v)1.2 ( K(d) value of 27 nM). CoTX1 also weakly competed with 125I-labelled apamin for binding to SKCa channels (small-conductance Ca2+-activated K+ channels) on rat brain synaptosomes (IC50 value of 7.2 microM). The 3-D structure of CoTX1 was used in docking experiments which suggests a key role of Arg6 or Lys10, Arg14, Arg18, Lys21 (dyad), Ile23, Asn24, Lys28 and Tyr30 (dyad) residues of CoTX1 in its interaction with the rat K(v)1.2 channel. In addition, a [Pro7,Gln9]-CoTX1 analogue (ACoTX1) was synthesized. The two residue replacements were selected aiming to restore the RPCQ motif in order to increase peptide affinity towards SKCa channels, and to alter the CoTX1 dipole moment such that it is expected to decrease peptide activity on K(v) channels. Unexpectedly, ACoTX1 exhibited an activity similar to that of CoTX1 towards SKCa channels, while it was markedly more potent on IKCa1 and several voltage-gated K+ channels.

Molecular cloning of disintegrins from Cerastes vipera and Macrovipera lebetina transmediterranea venom gland cDNA libraries: insight into the evolution of the snake venom integrin-inhibition system

We report the cloning and sequence analysis of Cerastes vipera and Macrovipera lebetina transmediterranea cDNAs coding for short non-RGD (Arg-Gly-Asp) disintegrins and for dimeric disintegrin subunits. The mRNAs belong to the short-coding class, suggesting that these disintegrin mRNAs may be more widely distributed than previously thought. Our data also argue for a common ancestry of the mRNAs of short disintegrins and those coding for precursors of dimeric disintegrin chains. The Macrovipera lebetina transmediterranea dimeric disintegrin reported to inhibit the laminin-binding integrins alpha3beta1, alpha6beta1 and alpha7beta1 was analysed using a proteomic approach and was shown to bear MLD (Met-Leu-Asp) and VGD (Val-Gly-Asp) motifs. The results highlight the fact that disintegrins have evolved a restricted panel of integrin-blocking sequences that segregate with defined branches of the phylogenetic tree of the integrin alpha-chains, providing novel insights into the evolutionary adaptation of the snake venom antagonists to the ligand-binding sites of their target integrin receptors.

Effects of antivenom on Buthus occitanus tunetanus (Bot) scorpion venom pharmacokinetics: towards an optimization of antivenom immunotherapy in a rabbit model

The pharmacokinetic parameters of Bot venom were determined in a rabbit model using a specific sandwich type ELISA. After intravenous injection, Bot venom seems to follow a three-compartment pharmacokinetic open model. However, after subcutaneous injection, the distribution and elimination kinetics of Bot venom are best characterized by a bi-compartment pharmacokinetic open model. Bot venom is completely absorbed from its SC injection site, since the absolute bioavailability is higher than 95%; the maximum plasma venom concentration is reached between 30 and 60 min after venom injection. Bot venom diffuses rapidly to tissues and is distributed in a high body volume. The total body clearance of Bot venom is relatively high in agreement with a low mean residence time. Antivenom immunotherapy experiments were carried out in the rabbit model, in order to select the most appropriate strategy for the adequate use of this treatment. The effects of the route, the dose and the delay of antivenom injection on Bot venom pharmacokinetic parameters and on the antivenom immunotherapy efficacy were then studied. These studies indicated in particular that: (1) the injection of a minimal neutralizing antivenom dose is required for a complete and permanent neutralization of circulating venom antigens; this dose is named minimal (threshold) efficacious antivenom dose; (2) the intramuscular route is not the most appropriate way for antivenom injection; and (3) a delayed antivenom immunotherapy remains efficacious especially on the neutralization of the remaining circulating venom. In short, these experimental studies show that early intravenous injection of an appropriate antivenom dose (at least the threshold efficacious dose) is the indicated way for a rapid and permanent neutralization of circulating scorpion venom toxins.

Immunochemistry of scorpion α-toxins: Antigenic homologies checked with radioimmunoassays (RIA)

Three toxins, i.e. toxins II and III of Androctonus australis Hector and toxin I of Buthus occitanus tunetanus, were labeled with 125I. High specific radioactivities were obtained (490–1100 Ci/mmole) that allowed the setting up to three radioimmunoassays. We were able to quantify the amount of toxin in 0.1 ml of 10−9–10−10 M solutions and to test antigenic homologies between toxins belonging to different structural groups. Three possibilities exist: (1) no cross-reactivity when sequence difference is greater than 25%; (2) full-cross-reactivity when this difference is lower than 25%; (3) partial cross-reactivity, which is interpreted as a loss of some common antigenic sites.