Scorpion venom glands produce a large variety of bioactive peptides. This communication reports the identification of venom components obtained by sequencing clones isolated from a cDNA library prepared with venomous glands of the Brazilian scorpion Opisthacanthus cayaporum (Ischnuridae). Two main types of components were identified: peptides with toxin-like sequences and proteins involved in cellular processes. Using the expressed sequence tag (EST) strategy 118 clones were identified, from which 61 code for unique sequences (17 contigs and 44 singlets) with an average length of 531 base-pairs (bp). These results were compared with those previously obtained by the proteomic analysis of the same venom, showing a considerable degree of similarity in terms of the molecular masses expected and DNA sequences found. About 36% of the ESTs correspond to toxin-like peptides and proteins with identifiable open reading frames (ORFs). The cDNA sequencing results also show the presence of sequences whose putative products correspond to a scorpine-like component; three short antimicrobial peptides; three K(+)-channel blockers; and an additional peptide containing 78 amino acid residues, whose sequence resembles peptide La1 from another Ischnuridae scorpion Liocheles australiasiae, thus far with unknown function.

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The kappa-KTx family of peptides, which is the newest K⁺-channel blocker family from scorpion venom, is present in scorpions from the families Scorpionidae and Liochelidae. Differently from the other scorpion KTx families, the three-dimensional structure of the known kappa-KTxs toxins is formed by two parallel α-helices linked by two disulfide bridges. Here, the characterization of a new kappa-KTx peptide, designated kappa-KTx 2.5, derived from the Liochelidae scorpion Opisthacanthus cayaporum, is described. This peptide was purified by HPLC and found to be identical to OcyC8, a predicted mature sequence precursor (UniProtKB C5J89) previously described by our group. The peptide was chemically synthesized and the circular dichroism (CD) spectra of both, native and synthetic, conducted at different temperatures in water and water/trifluoroethanol (TFE), showed a predominance of α-helices. The kappa-KTx 2.5 is heat stable and was shown to be a blocker of K⁺-currents on hKv1.1, and hKv1.4, with higher affinity for Kv1.4 channels (IC₅₀= 71 μM). Similarly to the other kappa-KTxs, the blockade of K⁺-channels occurred at micromolar concentrations, leading to uncertainness about their proper molecular target, and consequently their pharmacologic effect. In order to test other targets, kappa-KTx2.5 was tested on other K⁺-channels, on Na⁺-channels, on bacterial growth and on smooth muscle tissue, a known assay to identify possible bradykinin-potentiating peptides, due to the presence of two contiguous prolines at the C-terminal sequence. It has no effect on the targets used except on hKv1.1, and hKv1.4 expressed in Chinese hamster ovary cells. Since the only plausible function found for kappa-KTx2.5 seems to be the blockade of K⁺-channels, a discussion regarding the analysis of structure-function relationships is included in this communication, based on sequence alignments of members of the kappa-KTx toxin family, and on computational simulation of a structural model of the kappa-KTx2.5-Kv1.2 complex.

Arthropods are the most diverse animal group on the planet, and occupy almost all ecological niches. Venomous arthropods are a rich source of bioactive compounds evolved for prey capture and defense against predators and/or microorganisms. These highly potent chemical arsenals represent an available source for new insecticidal compounds as they act selectively on their molecular targets. These toxins affect the invertebrate nervous system and, until the moment, several insecticidal compounds belonging to the class of peptides or polyamine-like compounds have been purified and characterized from the venom of arachnids and hymenopterans. This review focuses on invertebrate-specific peptide neurotoxins that have been isolated from the venom ofspiders, scorpions, centipedes, ants, and wasps, discussing their potential in pest control and as invaluable tools in neuropharmacology.

We identified Tf2, the first β-scorpion toxin from the venom of the Brazilian scorpion Tityus fasciolatus. Tf2 is identical to Tb2-II found in Tityus bahiensis. We found that Tf2 selectively activates human (h)Nav1.3, a neuronal voltage-gated sodium (Nav) subtype implicated in epilepsy and nociception. Tf2 shifts hNav1.3 activation voltage to more negative values, thereby opening the channel at resting membrane potentials. Seven other tested mammalian Nav channels (Nav1.1-1.2; Nav1.4-1.8) expressed in Xenopus oocytes are insensitive upon application of 1 μM Tf2. Therefore, the identification of Tf2 represents a unique addition to the repertoire of animal toxins that can be used to investigate Nav channel function.

The venom of social wasps has been poorly studied so far, despite the high number of accidents in humans and assessment of the use of these wasps as a biological control of pests. The study of the pharmacological effects of the venom is of great importance since the poisoning is dangerous causing serious systemic effects, including death in the case of multiple attacks. In this study, the pharmacological activities of venom from the social wasp Synoeca cyanea were evaluated by the following assays: LD50 in mice, the behavioural effects and the hemorrhagic activity induced by the venom in mice, the oedematogenic activity in rat, the haemolysis in human blood, the stimulating effect on guinea-pig smooth muscle, and the antimicrobial activity. The aim was to determine the toxic effects of venom and to perform a comparative study with earlier work conducted with venom from other wasp species. Results showed that S. cyanea venom produced a potent dose-dependent oedema, as well as antibacterial and haemolytic activities, suggesting the presence of histamine, serotonin, kinins and other molecules related to increased vascular permeability and cytolytic activity in this venom. Despite previous studies with wasp venoms, S. cyanea venom presented a slight hemorrhagic effect. Data obtained in the smooth muscle assay also suggest the presence of BK or analogues in S. cyanea whole venom. The knowledge of symptoms and effects produced by S. cyanea venom is critical for health organizations, in order to improve clinical treatment in accidents caused by wasp stings.

Scorpion venoms are a complex mixture of components. Among them the most important are peptides, which presents the capacity to interact and modulate several ion channel subtypes, including voltage-gated sodium channels (NaV). Screening the activity of scorpion toxins on different subtypes of NaV reveals the scope of modulatory activity and, in most cases, low channel selectivity. Until now there are approximately 60 scorpion toxins experimentally assayed on NaV channels. However, the molecular bases of interaction between scorpion toxins and NaV channels are not fully elucidated. The activity description of new scorpion toxins is crucial to enhance the predictive strength of the structural–function correlations of these NaV modulatory molecules. In the present work a new scorpion toxin (Tf1a) was purified from Tityus fasciolatus venom by RP-HPLC, and characterized using electrophysiological experiments on different types of voltage-gated sodium channels. Tf1a was able to modify the normal function of NaV tested, showing to be a typical β-NaScTx. Tf1a also demonstrated an unusual capability to alter the kinetics of NaV1.5.

For decades, the study of venomous animals has focused on the isolation and biochemical characterization of specific venom components that have medical or biotechnological importance. Indeed, scorpions have been extensively studied under this optics, which has led to the identification of hundreds of different transcripts encoding toxic peptides. However, scorpions are interesting organisms not only because of their toxin diversity but also because they represent the most ancient terrestrial animals that fossil records have identified. About 2,000 species have been described around the world, which also implies that scorpions are extremely well-adapted arthropods that have managed to survive in different environmental conditions. Even though the divergence timing of scorpions places them as interesting model organisms for evolutionary inferences, little is known about the genomic organization, speciation events, and population dynamics of these arthropods.Different "omic" approaches have become a very powerful strategy for understanding the complexity of venomous animals. Transcriptomics, in particular, has been widely used to explore the transcriptional diversity of venom glands of several scorpion species. Recently, high-throughput sequencing platforms have substantially improved our capacity to describe biological features of scorpions but, most importantly, have outlined new directions toward a more complete understanding of the evolution of these arthropods.In this chapter, those transcriptomic strategies followed in the last two decades that went from cDNA cloning to next-generation sequencing methods will be described. Some biological and evolutionary questions about scorpion speciation and venom diversification will also be addressed. Finally, an attempt to raise some future directions in the field will be made.