Solution structure of Cn5, a crustacean toxin found in the venom of the scorpions Centruroides noxius and Centruroides suffusus suffusus

Cn29, a novel orphan peptide found in the venom of the scorpion Centruroides noxius: Structure and function

A peptide (Cn29) from the venom of the scorpion Centruroides noxius (about 2% of the soluble venom) was purified and its primary and three-dimensional structures were determined. The peptide contains 27 amino acids with primary sequence: LCLSCRGGDYDCRVKGTCENGKCVCGS. The peptide is tightly packed by three disulfide linkages formed between C2-C23, C5-C18 and C12-C25. Since the native peptide was obtained in limited amounts, the full synthetic peptide was prepared using the standard F-moc-based solid phase synthesis method of Merrifield. The native and synthetic peptides were shown to be identical by sequencing, HPLC separation and mass spectrometry. The solution structure of the peptide solved from NMR data shows that it consists of a well-defined N-terminal region without regular secondary structure extending from Leu 1 to Asp 9, followed by a short helical fragment from Tyr10 to Val14 and two short β strands (Thr17-Glu19 and Lys22-Val24). The primary and tertiary structures of Cn29 are different from all other scorpion peptides described in the literature. Transcriptome analysis of RNA obtained from C. noxius confirmed the expression of a gene coding for Cn29 in its venom gland. Initial experiments were conducted to identify its possible function: lethality tests in mice and insects as well as ion-channel binding using in vitro electrophysiological assays. None of the physiological or biological tests displayed any activity for this peptide, which at present is considered to be another orphan peptide found in scorpion venoms. The peptide is thus the first example of a novel structural component present in scorpion venoms.

Mass fingerprinting and electrophysiological analysis of the venom from the scorpion Centruroides hirsutipalpus (Scorpiones: Buthidae)

Background

Centruroides hirsutipalpus, of the family Buthidae, is a scorpion endemic to the Western Pacific region of Mexico. Although medically important, its venom has not yet been studied. Therefore, this communication aims to identify their venom components and possible functions.

Methods

Fingerprinting mass analysis of the soluble venom from this scorpion was achieved by high-performance liquid chromatography and electrospray mass spectrometry. Furthermore, the soluble venom and its toxic effects were evaluated extensively via electrophysiological assays in HEK cells expressing human voltage-gated Na⁺ channels (hNav 1.1 to Nav1.6), CHO cells expressing hNav 1.7, potassium channel hERG 1 (Ether-à-go-go-related-gene) and the human K⁺-channel hKv1.1.

Results

The separation of soluble venom produced 60 fractions from which 83 distinct components were identified. The molecular mass distribution of these components varies from 340 to 21,120 Da. Most of the peptides have a molecular weight between 7001 and 8000 Da (46% components), a range that usually corresponds to peptides known to affect Na⁺ channels. Peptides with molecular masses from 3000 to 5000 Da (28% of the components) were identified within the range corresponding to K⁺-channel blocking toxins. Two peptides were obtained in pure format and completely sequenced: one with 29 amino acids, showing sequence similarity to an “orphan peptide” of C. limpidus, and the other with 65 amino acid residues shown to be an arthropod toxin (lethal to crustaceans and toxic to crickets). The electrophysiological results of the whole soluble venom show a beta type modification of the currents of channels Nav1.1, Nav1.2 and Nav1.6. The main effect observed in channels hERG and hKv 1.1 was a reduction of the currents.

Conclusion

The venom contains more than 83 distinct components, among which are peptides that affect the function of human Na⁺-channels and K⁺-channels. Two new complete amino acid sequences were determined: one an arthropod toxin, the other a peptide of unknown function.

To4, the first Tityus obscurus β-toxin fully electrophysiologically characterized on human sodium channel isoforms

Many scorpion toxins that act on sodium channels (NaScTxs) have been characterized till date. These toxins may act modulating the inactivation or the activation of sodium channels and are named α- or β-types, respectively. Some venom toxins from Tityus obscurus (Buthidae), a scorpion widely distributed in the Brazilian Amazon, have been partially characterized in previous studies; however, little information about their electrophysiological role on sodium ion channels has been published. In the present study, we describe the purification, identification and electrophysiological characterization of a NaScTx, which was first described as Tc54 and further fully sequenced and renamed To4. This toxin shows a marked β-type effect on different sodium channel subtypes (hNa_v1.1-hNa_v1.7) at low concentrations, and has more pronounced activity on hNa_v1.1, hNa_v1.2 and hNa_v1.4. By comparing To4 primary structure with other Tityus β-toxins which have already been electrophysiologically tested, it is possible to establish some key amino acid residues for the sodium channel activity. Thus, To4 is the first toxin from T. obscurus fully electrophysiologically characterized on different human sodium channel isoforms.

Selected scorpion toxin exposures induce cytokine release in human peripheral blood mononuclear cells

A cytokine screening on human peripheral blood mononuclear cells (PBMCs) stimulated with selected scorpion toxins (ScTx's) was performed in order to evaluate their effect on human immune cells. The ScTx's chosen for this report were three typical buthid scorpion venom peptides, one with lethal effects on mammals Centruroides suffussus suffusus toxin II (CssII), another, with lethal effects on insects and crustaceans Centruroides noxius toxin 5 (Cn5), and one more without lethal effects Tityus discrepans toxin (Discrepin). A Luminex multiplex analysis was performed in order to determine the amounts chemokines and cytokines IL-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12-p40, IL-13, interferon alpha (IFN-α), interferon gamma (IFN-γ), tumor necrosis factor alpha TNF-α, and interferon-inducible protein-10 (IP-10) secreted from human PBMCs exposed to these toxins. Although, the ScTx Cn5 is not lethal for mammals, it was able to induce the secretion of cytokines IL-1β, IL-6, and TNF-α, IL-10 and IP-10 in comparison to the lethal CssII, which was able to induce only IP-10 secretion. Discrepin also was able to induce only IP-10. Interestingly, only low amounts of interferons α and β were induced in the presence of the ScTx's assayed. In a synergic experiment, the combination of Discrepin and Cn5 displayed considerable reverse effects on induction of IL-1β, IL-6, IL-10 and TNF-α, but they had a slight synergic effect on IP-10 cytokine production in comparison with the single effect obtained with the Cn5 alone. Thus, the results obtained suggest that the profile of secreted cytokines promoted by ScTx Cn5 is highly related with a cytokine storm event, and also it suggests that the mammalian lethal neurotoxins are not solely responsible of the scorpion envenomation symptomatology.

Molecular and bioinformatical characterization of a novel superfamily of cysteine-rich peptides from arthropods

The full-length cDNA sequences of two novel cysteine-rich peptides (referred to as HsVx1 and MmKTx1) were obtained from scorpions. The two peptides represent a novel class of cysteine-rich peptides with a unique cysteine pattern. The genomic sequence of HsVx1 is composed of three exons interrupted by two introns that are localized in the mature peptide encoding region and inserted in phase 1 and phase 2, respectively. Such a genomic organization markedly differs from those of other peptides from scorpions described previously. Genome-wide search for the orthologs of HsVx1 identified 59 novel cysteine-rich peptides from arthropods. These peptides share a consistent cysteine pattern with HsVx1. Genomic comparison revealed extensive intron length differences and intronic number and position polymorphisms among the genes of these peptides. Further analysis identified 30 cases of intron sliding, 1 case of intron gain and 22 cases of intron loss occurred with the genes of the HsVx1 and HsVx1-like peptides. It is interesting to see that three HsVx1-like peptides XP_001658928, XP_001658929 and XP_001658930 were derived from a single gene (XP gene): the former two were generated from alternative splicing; the third one was encoded by a DNA region in the reverse complementary strand of the third intron of the XP gene. These findings strongly suggest that the genes of these cysteine-rich peptides were evolved by intron sliding, intron gain/loss, gene recombination and alternative splicing events in response to selective forces without changing their cysteine pattern. The evolution of these genes is dominated by intron sliding and intron loss.

Isolation and molecular cloning of beta-neurotoxins from the venom of the scorpion Centruroides suffusus suffusus

This communication reports the identification and characterization of two new toxins from the venom of the scorpion Centruroides suffusus suffusus, named: CssVIII and CssIX, according to the original nomenclature of toxins previously described for this scorpion. The isolation was obtained by means of two chromatographic steps, and a cDNA library was used to fully identify their precursors. CssVIII and CssIX contain signal peptides of 19 and 17 amino acid residues, and mature peptides of 66 and 65 residues, respectively. Intracranial injections into mice of both purified toxins showed toxicity results similar to those found for toxins CssII and CssIV. Additionally, they compete with the parent toxin CssIV, in binding and displacement experiments, conducted with brain synaptosomes showing nanomolar affinities. These results strongly support the conclusion that they are new β-neurotoxins and certainly would be of the interest of researchers in the field of venomics for studying sodium channels.