Molecular cloning of a novel putative potassium channel-blocking neurotoxin from the venom of the North African scorpion, Androctonus amoreuxi

Venoms of Iranian Scorpions (Arachnida, Scorpiones) and Their Potential for Drug Discovery

Scorpions, a characteristic group of arthropods, are among the earliest diverging arachnids, dating back almost 440 million years. One of the many interesting aspects of scorpions is that they have venom arsenals for capturing prey and defending against predators, which may play a critical role in their evolutionary success. Unfortunately, however, scorpion envenomation represents a serious health problem in several countries, including Iran. Iran is acknowledged as an area with a high richness of scorpion species and families. The diversity of the scorpion fauna in Iran is the subject of this review, in which we report a total of 78 species and subspecies in 19 genera and four families. We also list some of the toxins or genes studied from five species, including Androctonus crassicauda, Hottentotta zagrosensis, Mesobuthus phillipsi, Odontobuthus doriae, and Hemiscorpius lepturus, in the Buthidae and Hemiscorpiidae families. Lastly, we review the diverse functions of typical toxins from the Iranian scorpion species, including their medical applications.

Proteome of fraction from Tityus serrulatus venom reveals new enzymes and toxins

Background

Tityus serrulatus venom (Ts venom) is a complex mixture of several compounds with biotechnological and therapeutical potentials, which highlights the importance of the identification and characterization of these components. Although a considerable number of studies have been dedicated to the characterization of this complex cocktail, there is still a limitation of knowledge concerning its venom composition. Most of Ts venom studies aim to isolate and characterize their neurotoxins, which are small, basic proteins and are eluted with high buffer concentrations on cation exchange chromatography. The first and largest fraction from carboxymethyl cellulose-52 (CMC-52) chromatography of Ts venom, named fraction I (Fr I), is a mixture of proteins of high and low molecular masses, which do not interact with the cation exchange resin, being therefore a probable source of components still unknown of this venom. Thus, the present study aimed to perform the proteome study of Fraction I from Ts venom, by high resolution mass spectrometry, and its biochemical characterization, by the determination of several enzymatic activities.

Methods

Fraction I was obtained by a cation exchange chromatography using 50 mg of crude venom. This fraction was subjected to a biochemical characterization, including determination of L-amino acid oxidase, phospholipase, hyaluronidase, proteases activities and inhibition of angiotensin converting enzyme (ACE) activity. Fraction I was submitted to reduction, alkylation and digestion processes, and the tryptic digested peptides obtained were analyzed in a Q-Exactive Orbitrap mass spectrometer. Data analysis was performed by PEAKS 8.5 software against NCBI database.

Results

Fraction I exhibits proteolytic activity and it was able to inhibit ACE activity. Its proteome analysis identified 8 different classes of venom components, among them: neurotoxins (48%), metalloproteinases (21%), hypotensive peptides (11%), cysteine-rich venom protein (9%), antimicrobial peptides (AMP), phospholipases and other enzymes (chymotrypsin and lysozymes) (3%) and phosphodiesterases (2%).

Conclusions

The combination of a proteomic and biochemical characterization strategies leads us to identify new components in the T. serrulatus scorpion venom. The proteome of venom´s fraction can provide valuable direction in the obtainment of components in their native forms in order to perform a preliminary characterization and, consequently, to promote advances in biological discoveries in toxinology.

Purificación parcial de péptidos y actividad citotóxica del veneno T. macrochirus

Introducción. Los venenos de escorpiones poseen péptidos con actividad neurotóxica, que actúan principalmente en canales iónicos del sistema nervioso de insectos y mamíferos. También se ha determinado acción citolítica y anticancerígena, características biológicas que aún no se han reportado sobre el veneno del escorpión Tityus macrochirus.Objetivo. Evaluar si tanto el veneno total de T. macrochirus, como la fracción de péptidos parcialmente purificados disminuyen el porcentaje de viabilidad de diferentes líneas celulares provenientes de tumores.Materiales y métodos. A partir del veneno de T. macrochirus, obtenido por estimulación eléctrica, se utilizaron métodos cromatográficos, electroforéticos y de centrifugación con Amicon, para la identificación y purificación parcial de sus péptidos. Los ensayos de actividad citotóxica del veneno y de la fracción de péptidos, se realizaron sobre líneas celulares provenientes de tumores, por el método colorimétrico de MTT.Resultados. El veneno de T. macrochirus, posee péptidos con pesos moleculares entre 3 a 10kDa, que fueron parcialmente purificados por medio de ultrafiltración y evaluados por RP¬HPLC. Los ensayos de citotoxicidad con el veneno total T. macrochirus, mostraron mayor disminución de viabilidad en la línea celular PC3, con respecto a las demás líneas celulares evaluadas y la fracción parcialmente purificada de péptidos, logró disminuir la viabilidad en la línea celular HeLa.Conclusión. En el veneno de T. macrochirus se encuentran péptidos que presentaron actividad citotóxica sobre algunas líneas celulares provenientes de tumores, observándose algún tipo de selectividad frente a las diferentes líneas celulares evaluadas.

Discovery of three toxin peptides with Kv1.3 channel and IL-2 cytokine-inhibiting activities from Non-Buthidae scorpions, Chaerilus tricostatus and Chaerilus tryznai

Non-Buthidae venomous scorpions are huge natural sources of toxin peptides; however, only a few studies have been done to understand their toxin peptides. Herein, we describe three new potential immunomodulating toxin peptides, Ctri18, Ctry68 and Ctry2908, from two non-Buthidae scorpions, Chaerilus tricostatus and Chaerilus tryznai. Sequence alignment analyses showed that Ctri18, Ctry68 and Ctry2908 are three new members of the scorpion toxin α-KTx15 subfamily. Electrophysiological experiments showed that Ctri18, Ctry68 and Ctry2908 blocked the Kv1.3 channel at micromole to nanomole levels, but had weak effects on potassium channel KCNQ1 and sodium channel Nav1.4, which indicated that Ctri18, Ctry68 and Ctry2908 might have specific inhibiting effects on the Kv1.3 channel. ELISA experiments showed that Ctri18, Ctry68 and Ctry2908 inhibited IL-2 cytokine secretions of activated T lymphocyte in human PBMCs. Excitingly, consistent with the good Kv1.3 channel inhibitory activity, Ctry2908 inhibited cytokine IL-2 secretion in nanomole level, which indicated that Ctry2908 might be a new lead drug template toward Kv1.3 channels. Together, these studies discovered three new toxin peptides, Ctri18, Ctry68 and Ctry2908, with Kv1.3 channel and IL-2 cytokine-inhibiting activities from two scorpions, C. tricostatus and C. tryznai, and highlighted that non-Buthidae venomous scorpions are new natural toxin peptide sources.

Characterizing the biological and biochemical profile of six different scorpion venoms from the Buthidae and Scorpionidae family

The objective of this study was to characterize six different scorpion venoms using biological and biochemical methods, including a preliminary MS/MS and a post-translational modifications analysis. Despite the diversity of scorpion species of medical importance in Africa and Colombia, the venoms of these arachnids have been poorly studied in these two regions. We report the biochemical, electrophoretic, chromatographic profile, internal peptide sequences with a post-translational modification report, and a preliminary antitumor activity of five different scorpions of the Buthidae family, Androctonus amoreuxi, Babycurus jacksoni, Grosphus grandidieri, Hottentotta gentili and Tityus fuhrmanni, and one of the Scorpionidae family Pandinus imperator. No L-amino oxidase activity was detected in the evaluated venoms. Proteolytic activity using azocasein was detected only in G. grandidieri and P. imperator, indicating the possible presence of metalloproteinases in these two venoms. Proteolytic activity using NOBA was detected in all venoms indicating the possible presence of serine-proteinases. Phospholipase A₂ activity was detected in the venoms of P. imperator, G. grandidieri, H. gentili and A. amoreuxi, with P. imperator venom being the most active. All venoms analyzed contained defensin-like proteins, alpha toxins, metalloproteinases, neuropeptides, DBP affecting ion channels, DBP with antimicrobial activity, among others. Venoms from P. imperator, G. grandidieri and T. fuhrmanni showed a dose-dependent cytotoxic activity over MCF-7 cells. Only two isolated RP-HPLC fractions from P. imperator and T. fuhrmanni showed cytotoxic activity over MCF-7. No cytotoxic activity was found in the venoms from A. amoreuxi, B. jacksoni, and H. gentili.

Transcriptome analysis of scorpion species belonging to the Vaejovis genus

Scorpions belonging to the Buthidae family have traditionally drawn much of the biochemist's attention due to the strong toxicity of their venoms. Scorpions not toxic to mammals, however, also have complex venoms. They have been shown to be an important source of bioactive peptides, some of them identified as potential drug candidates for the treatment of several emerging diseases and conditions. It is therefore important to characterize the large diversity of components found in the non-Buthidae venoms. As a contribution to this goal, this manuscript reports the construction and characterization of cDNA libraries from four scorpion species belonging to the Vaejovis genus of the Vaejovidae family: Vaejovis mexicanus, V. intrepidus, V. subcristatus and V. punctatus. Some sequences coding for channel-acting toxins were found, as expected, but the main transcribed genes in the glands actively producing venom were those coding for non disulfide-bridged peptides. The ESTs coding for putative channel-acting toxins, corresponded to sodium channel β toxins, to members of the potassium channel-acting α or κ families, and to calcium channel-acting toxins of the calcin family. Transcripts for scorpine-like peptides of two different lengths were found, with some of the species coding for the two kinds. One sequence coding for La1-like peptides, of yet unknown function, was found for each species. Finally, the most abundant transcripts corresponded to peptides belonging to the long chain multifunctional NDBP-2 family and to the short antimicrobials of the NDBP-4 family. This apparent venom composition is in correspondence with the data obtained to date for other non-Buthidae species. Our study constitutes the first approach to the characterization of the venom gland transcriptome for scorpion species belonging to the Vaejovidae family.

AaTX1, from Androctonus australis scorpion venom: purification, synthesis and characterization in dopaminergic neurons

We have purified the AaTX1 peptide from the Androctonus australis (Aa) scorpion venom, previously cloned and sequenced by Legros and collaborators in a venom gland cDNA library from Aa scorpion. AaTX1 belongs to the α-Ktx15 scorpion toxins family (αKTx15-4). Characterized members of this family share high sequence similarity and were found to block preferentially IA-type voltage-dependent K(+) currents in rat cerebellum granular cells in an irreversible way. In the current work, we studied the effects of native AaTX1 (nAaTX1) using whole-cell patch-clamp recordings of IA current in substantia nigra pars compacta dopaminergic neurons. At 250 nM, AaTX1 induces 90% decrease in IA current amplitude. Its activity was found to be comparable to that of rAmmTX3 (αKTx15-3), which differs by only one conserved (R/K) amino acid in the 19th position suggesting that the difference between R19 and K19 in AaTX1 and AmmTX3, respectively, may not be critical for the toxins' effects. Molecular docking of both toxins with Kv4.3 channel is in agreement with experimental data and suggests the implication of the functional dyade K27-Y36 in toxin-channel interactions. Since AaTX1 is not highly abundant in Aa venom, it was synthesized as well as AmmTX3. Synthetic peptides, native AaTX1 and rAmmTX3 peptides showed qualitatively the same pharmacological activity. Overall, these data identify a new biologically active toxin that belongs to a family of peptides active on Kv4.3 channel.

Scorpion venom peptides with no disulfide bridges: a review

Scorpion venoms are rich sources of biologically active peptides that are classified into disulfide-bridged peptides (DBPs) and non-disulfide-bridged peptides (NDBPs). DBPs are the main scorpion venom components responsible for the neurotoxic effects observed during scorpion envenomation as they usually target membrane bound ion channels of excitable and non-excitable cells. Several hundred DBPs have been identified and functionally characterized in the past two decades. The NDBPs represent a novel group of molecules that have gained great interest only recently due to their high diversity both in their primary structures and bioactivities. This review provides an overview of scorpion NDBPs focusing on their therapeutic applications, modes of discovery, mechanisms of NDBPs genetic diversity and structural properties. It also provides a simple classification for NDBPs that could be adopted and applied to other NDBPs identified in future studies.

Antimicrobial/cytolytic peptides from the venom of the North African scorpion, Androctonus amoreuxi: biochemical and functional characterization of natural peptides and a single site-substituted analog

The venoms of scorpions are complex cocktails of polypeptide toxins that fall into two structural categories: those that contain cysteinyl residues with associated disulfide bridges and those that do not. As the majority of lethal toxins acting upon ion channels fall into the first category, most research has been focused there. Here we report the identification and structural characterization of two novel 18-mer antimicrobial peptides from the venom of the North African scorpion, Androctonus amoreuxi. Named AamAP1 and AamAP2, both peptides are C-terminally amidated and differ in primary structure at just two sites: Leu-->Pro at position 2 and Phe-->Ile at position 17. Synthetic replicates of both peptides exhibited a broad-spectrum of antimicrobial activity against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli) and a yeast (Candida albicans), at concentrations ranging between 20 μM and 150 μM. In this concentration range, both peptides produced significant degrees of hemolysis. A synthetic replicate of AamAP1 containing a single substitution (His-->Lys) at position 8, generated a peptide (AamAP-S1) with enhanced antimicrobial potency (3-5 μM) against the three test organisms and within this concentration range, hemolytic effects were negligible. In addition, this His-->Lys variant exhibited potent growth inhibitory activity (ID(50) 25-40 μm) against several human cancer cell lines and endothelial cells that was absent in both natural peptides. Natural bioactive peptide libraries, such as those that occur in scorpion venoms, thus constitute a unique source of novel lead compounds with drug development potential whose biological properties can be readily manipulated by simple synthetic chemical means.

Potassium Channels Blockers from the Venom of Androctonus mauretanicus mauretanicus

K⁺ channels selectively transport K⁺ ions across cell membranes and play a key role in regulating the physiology of excitable and nonexcitable cells. Their activation allows the cell to repolarize after action potential firing and reduces excitability, whereas channel inhibition increases excitability. In eukaryotes, the pharmacology and pore topology of several structural classes of K⁺ channels have been well characterized in the past two decades. This information has come about through the extensive use of scorpion toxins. We have participated in the isolation and in the characterization of several structurally distinct families of scorpion toxin peptides exhibiting different K⁺ channel blocking functions. In particular, the venom from the Moroccan scorpion Androctonus mauretanicus mauretanicus provided several high-affinity blockers selective for diverse K⁺ channels  (SK_Ca,  K_v4.x, and  K_v1.x K⁺ channel families). In this paper, we summarize our work on these toxin/channel interactions.

Functional peptidomics of amphibian skin secretion: A novel Kunitz-type chymotrypsin inhibitor from the African hyperoliid frog, Kassina senegalensis

Amphibian skin secretions are, for the most part, complex peptidomes. While many peptide components have been biologically- and structurally-characterised into discrete "families", some of which are analogues of endogenous vertebrate regulatory peptides, a substantial number are of unique structure and unknown function. Among the components of these secretory peptidomes is an array of protease inhibitors. Inhibitors of trypsin are of widespread occurrence in different taxa and are representative of many established structural classes, including Kunitz, Kazal and Bowman-Birk. However, few protease inhibitors with activity against other specific proteases have been described from this source. Here we report for the first time, the isolation and structural characterisation of an inhibitor of chymotrypsin of Kunitz-type from the skin secretion of the African hyperoliid frog, Kassina senegalensis. To this end, we employed a functional peptidomic approach. This scheme involves fractionation of the peptidome, functional end-point screening, structural characterisation of resultant actives followed by molecular cloning of biosynthetic precursor-encoding cDNA(s). The novel mature and active polypeptide identified consisted of 62 amino acid residues (average molecular mass 6776.24 Da), of which 6 were positionally-conserved cysteines. The P(1) position within the active site was occupied by a phenylalanyl residue. Bioinformatic analysis of the sequence using BLAST, revealed a structural similarity to Kunitz-type chymotrypsin inhibitors from other organisms, ranging from silkworms to snakes.

PD-sauvagine: a novel sauvagine/corticotropin releasing factor analogue from the skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor

Sauvagine is a potent and broad-spectrum biologically active peptide of 40 amino acid residues originally isolated from the skin of the South American frog, Phyllomedusa sauvagei. Since its discovery, no additional sauvagine structures have been reported. Following the discovery of sauvagine, peptides with similar primary structures/activities were identified in mammalian brain [corticotropin-releasing factor (CRF) and urocortin]. Here, we report the identification of a second sauvagine from the Mexican giant leaf frog, Pachymedusa dacnicolor, which displays primary structural features of both sauvagine and CRF. A cDNA encoding the peptide precursor was "shotgun" cloned from a cDNA library constructed from lyophilised skin secretion by 3'- and 5'-RACE reactions. From this, the primary structure of a 38-mer peptide was deduced and this was located in reverse phase HPLC fractions of skin secretion and both its mass and structure were confirmed by mass spectrometry. The biological activities of synthetic replicates of PD-sauvagine and sauvagine were compared using two different mammalian smooth muscle preparations and the novel peptide was found to be more potent in both. Bioinformatic analyses of PD-sauvagine revealed that it shared different regional sequence identities with both sauvagine and CRF.

Elements of the granular gland peptidome and transcriptome persist in air-dried skin of the South American orange-legged leaf frog, Phyllomedusa hypocondrialis

The defensive strategy of amphibians against predator attack relies heavily on the secretion of noxious/toxic chemical cocktails from specialized skin granular glands. Bioactive peptides constitute a major component of secretions in many species and the most complex are produced by neotropical leaf frogs of the sub-family Phyllomedusinae. We recently reported that these skin secretions contain elements of both the granular gland peptidome and transcriptome and that polyadenylated mRNAs constituting the latter are protected from degradation by interactions with endogenous amphipathic peptides. This thus permits parallel amino acid sequencing of peptides and nucleic acid sequencing of cloned precursor transcripts from single lyophilized samples of secretion. Here we report that the protection afforded is sufficiently robust to permit transcriptome studies by cloning of full-length polyadenylated peptide precursor encoding mRNAs from libraries constructed using ambient temperature air-dried skin from recently deceased specimens as source material. The technique was sufficiently sensitive to permit the identification of cDNAs encoding antimicrobial peptides constituted by six different isoforms of phylloseptin and two dermaseptins. Also, for the first time, establishment of the nucleic acid and amino acid sequence of the precursor encoding the phyllomedusine frog skin bradykinin-related peptide, phyllokinin, from cloned cDNA, was achieved. These data unequivocally demonstrate that the granular gland transcriptome persists in air-dried amphibian skin--a finding that may have fundamental implications in the study of archived materials but also in the wider field of molecular biology.

Molecular dissection of venom from Chinese scorpion Mesobuthus martensii: identification and characterization of four novel disulfide-bridged venom peptides

Scorpion venom is composed of a large repertoire of biologically active polypeptides. However, most of these peptides remain to be identified and characterized. In this paper, we report the identification and characterization of four novel disulfide-bridged venom peptides (named BmKBTx, BmKITx, BmKKx1 and BmKKx2, respectively) from the Chinese scorpion, Mesobuthus martensii (also named Buthus martensii Karsch). BmKBTx is composed of 58 amino acid residues and cross-linked by three disulfide bridges. The sequence of BmKBTx shows some similarities to that of the toxin, birtoxin, and its analogs. It is likely that BmKBTx is a beta-toxin active on Na+ channels, which is toxic to either insects or mammals. BmKITx is composed of 71 amino acid residues with four disulfide bridges. It is the longest venom peptide identified from M. martensii so far. BmKITx shows little sequence identity with scorpion alpha-toxins toxic to insects. It is likely that BmKITx is a new type of Na+ -channel specific toxin active on both insects and mammals. BmKKx1 contains 38 amino acid residues cross-linked by three disulfide bridges and shows 84% sequence identity with BmTx3, an inhibitor of A-type K+ channel and HERG currents. BmKKx1 has been classified as alpha-KTx-15.8. BmKKx2 is composed of 36 residues and stabilized by three disulfide bridges. BmKKx2 is a new member of the gamma-K+ -channel toxin subfamily (classified as gamma-KTx 2.2). The venoms of scorpions thus continue to provide novel toxins with potential novel actions on targets.