Comparison and characterization of the venoms of three Parabuthus scorpion species occurring in southern Africa

Comparative Proteomic Analysis of the Venoms from the Most Dangerous Scorpions in Morocco: Androctonus mauritanicus and Buthus occitanus

Morocco is known to harbor two of the world's most dangerous scorpion species: the black Androctonus mauritanicus (Am) and the yellow Buthus occitanus (Bo), responsible for 83% and 14% of severe envenomation cases, respectively. Scorpion venom is a mixture of biological molecules of variable structures and activities, most of which are proteins of low molecular weights referred to as toxins. In addition to toxins, scorpion venoms also contain biogenic amines, polyamines, and enzymes. With the aim of investigating the composition of the Am and Bo venoms, we conducted an analysis of the venoms by mass spectrometry (ESI-MS) after separation by reversed-phase HPLC chromatography. Results from a total of 19 fractions obtained for the Am venom versus 22 fractions for the Bo venom allowed the identification of approximately 410 and 252 molecular masses, respectively. In both venoms, the most abundant toxins were found to range between 2-5 kDa and 6-8 kDa. This proteomic analysis not only allowed the drawing of an extensive mass fingerprint of the Androctonus mauritanicus and Buthus occitanus venoms but also provided a better insight into the nature of their toxins.

Investigating the chemical profile of regenerated scorpion (Parabuthus transvaalicus) venom in relation to metabolic cost and toxicity

We investigated the biochemical profile of regenerated venom of the scorpion Parabuthus transvaalicus in relation to its metabolic cost and toxicity. Using a closed-system respirometer, we compared oxygen consumption between milked and unmilked scorpions to determine the metabolic costs associated with the first 192 h of subsequent venom synthesis. Milked scorpions had a substantially (21%) higher mean metabolic rate than unmilked scorpions, with the largest increases in oxygen consumption occurring at approximately 120 h, 162 h, and 186 h post-milking. Lethality tests in crickets indicated that toxicity of the regenerated venom returned to normal levels within 4 d after milking. However, the chemical profile of the regenerated venom, as evaluated by FPLC and MALDI-TOF mass spectrometry, suggested that regeneration of different venom components was asynchronous. Some peptides regenerated quickly, particularly those associated with the scorpion's "prevenom," whereas others required much or all of this time period for regeneration. This asynchrony could explain the different spikes detected in oxygen consumption of milked scorpions as various peptides and other venom components were resynthesized. These observations confirm the relatively high metabolic cost of venom regeneration and suggest that greater venom complexity can be associated with higher costs of venom production.

Peptide fingerprinting of snake venoms by direct infusion nano-electrospray ionization mass spectrometry: potential use in venom identification and taxonomy

Fingerprinting by mass spectrometry has been increasingly used to study venom variations and for taxonomic analyses based on venom components. Most of these studies have concentrated on components heavier than 3 kDa, but Bothrops snake venoms contain many biologically active peptides, principally C-type natriuretic peptides and bradykinin-potentiating peptides (BPPs). In this work, we have examined the peptide profile of Bothrops venoms (B. alternatus, B. erythromelas, B. insularis, B. jararaca, B. jararacussu, B. leucurus and B. moojeni) using direct infusion nano-electrospray ionization mass spectrometry (nano-ESI-MS) subjecting the data further to principal components analysis (PCA) to assess whether the peptide distributions are reliable in distinguishing the venoms. ESI-MS of a low molar mass fraction obtained by ultrafiltration of each venom (5 kDa nominal cutoff filters) revealed that the venoms have a variety of peptides in common but that each venom also contains taxonomic marker peptides not shared with other venoms. One BPP peptide, QGGWPRPGPEIPP, was found to be common to the seven Bothrops species examined. This peptide may represent a specific marker for this genus since it was not found in the venom of the South American rattlesnake, Crotalus durissus terrificus. PCA on the ESI-MS data reveals a close relationship between B. jararaca, B. jararacussu and B. moojeni venoms, with B. leucurus and B. erythromelas being more distant from these three; B. alternatus and B. insularis were also located distant from these five species, as was C. d. terrificus. These results agree partially with established phylogenetic relationships among these species and suggest that ESI-MS peptide fingerprinting of snake venoms coupled with PCA is a useful tool for identifying venoms and for taxonomic analyses.

Immunological characterization of a non-toxic peptide conferring protection against the toxic fraction (AahG50) of the Androctonus australis hector venom

KAaH1 and KAaH2 are non-toxic peptides, isolated from the venom of the Androctonus australis hector (Aah) scorpion. In a previous study, we showed these peptides to be the most abundant (approximately 10% each) in the toxic fraction (AahG50) of the Aah venom. KAaH1 and KAaH2 showed high sequence identities (approximately 60%) with birtoxin-like peptides, which likewise are the major peptidic components of Parabuthus transvaalicus scorpion venom. Here, we report the immunological characterization of KAaH1 and KAaH2. These peptides were found to be specifically recognized by polyclonal antibodies raised against AahII, the most toxic peptide of Aah venom, and represents the second antigenic group, including toxins from different scorpion species in the world. Moreover, KAaH1 partially inhibits AahII binding to its specific antibody, suggesting some common epitopes between these two peptides. The identification of possible key antigenic residues in KAaH1 was deduced from comparison of its 3-D model with the experimental structure of AahII. Two clusters of putative antigenically important residues were found at the exposed surface; one could be constituted of V3 and D53, the other of D10, T15 and Y16. Polyclonal antibodies raised against KAaH1 in mice were found to cross-react with both AahII and AahG50, and neutralizing 5LD(50)/ml of the toxic fraction. Mice vaccinated with KAaH1 were protected against a challenge of 2LD(50) of AahG50 fraction. All these data suggest that KAaH1 has clear advantages over the use of the whole or part of the venom. KAaH1 is not toxic and could produce sera-neutralizing scorpion toxins, not only from Aah venom, but also toxins of other venoms from Buthus, Leiurus, or Parabuthus scorpion species presenting antigenically related toxins.

Cost of venom regeneration in Parabuthus transvaalicus (Arachnida: Buthidae)

Scorpion venom has many components, but is mainly made up of water, salts, small molecules, peptides, and proteins. One can reasonably assume that the production and storage of this complex secretion is an expensive metabolic investment. However, to date, no study has addressed the costs associated with the regeneration of venom by scorpions. Using a closed-system respirometer, we examined the difference in oxygen consumption between milked and unmilked scorpions to determine the metabolic costs associated with the first 72 h of subsequent venom synthesis. During this time period, milked scorpions had a significantly higher (39%) metabolic rate than unmilked scorpions. The regenerated venom from a second milking had significantly lower (74%) protein concentration, suggesting that venom regeneration was incomplete after 72 h. The protein content in the regenerated venom was not correlated with oxygen consumption. The significant increase in oxygen consumption after milking supports existing hypotheses about the metabolic cost associated with venom regeneration and provides further insight on why scorpions appear to be judicious in their stinger use.

Mass fingerprinting of toxic fractions from the venom of the Indian red scorpion, Mesobuthus tamulus: biotope-specific variation in the expression of venom peptides

The red scorpion, Mesobuthus tamulus, is found in two distinct biotopes within the Indian state of Maharastra-a tropical, sea-level biotope and a semi-arid biotope, up to 600 m. Scorpions from these two geographical areas show marked differences in toxicity. Using mass spectrometry, we have shown biotope-specific variation in the expression of peptides from scorpions collected from these two distinct areas. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) and reversed-phase liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI-MS) were assessed as techniques for obtaining mass fingerprint data. On line LC/ESI-MS was judged to be the method of choice and unique biotope-specific mass fingerprints, with key diagnostic markers, were obtained.

Immunology of scorpion toxins and perspectives for generation of anti-venom vaccines

Scorpions and other venomous animals contain concentrates of biologically active substances developed to block vital physiological and biochemical functions of the victims. These have contrasting human health concerns, provide important pharmacological raw material and pose a serious threat to human life and health in tropical and subtropical regions. Because only occasional and minor quantities of venom are introduced into the human organism with a scorpion sting and their mortal effect is an acute phenomenon these substances are unknown to the immune defense system and thus no immunity has appeared against them during evolution. Antidotes prepared from animal anti-sera are effective against some species of scorpions but depend on the manufacturer and the availability of product to the medical community. Although significant progress has been made in immunological studies of certain groups of toxins, few centers are dedicated to this research. Information is still insufficient to generate a comprehensive picture of the subject and to propose vaccines against venoms. A novel approach based on mimotopes selected from phage-displayed random peptide libraries show potential to impel further progress of toxin immunological studies and to provide putative vaccine resources. In this report we revise the "state of the art" in the field.

Life-threatening stings, bites, infestations, and parasitic diseases

Bites, stings and infestations can be fatal. Anaphylaxis to vespids and bees can be prevented with immunotherapy. Patients should be referred to an allergist. The acute care and prevention of arthropod injury is discussed below.

Purification, characterization and biosynthesis of parabutoxin 3, a component of Parabuthus transvaalicus venom

A novel peptidyl inhibitor of voltage-gated K+ channels, named parabutoxin 3 (PBTx3), has been purified to homogeneity from the venom of Parabuthus transvaalicus. This scorpion toxin contains 37 residues, has a mass of 4274 Da and displays 41% identity with charybdotoxin (ChTx, also called 'alpha-KTx1.1'). PBTx3 is the tenth member (called 'alpha-KTx1.10') of subfamily 1 of K+ channel-blocking peptides known thus far. Electrophysiological experiments using Xenopus laevis oocytes indicate that PBTx3 is an inhibitor of Kv1 channels (Kv1.1, Kv1.2, Kv1.3), but has no detectable effects on Kir-type and ERG-type channels. The dissociation constants (Kd) for Kv1.1, Kv1.2 and Kv1.3 channels are, respectively, 79 microm, 547 nm and 492 nm. A synthetic gene encoding a PBTx3 homologue was designed and expressed as a fusion protein with the maltose-binding protein (MBP) in Escherichia coli. The recombinant protein was purified from the bacterial periplasm compartment using an amylose affinity resin column, followed by a gel filtration purification step and cleavage by factor Xa (fXa) to release the recombinant toxin peptide (rPBTx3). After final purification and refolding, rPBTx3 was shown to be identical to the native PBTx3 with respect to HPLC retention time, mass spectrometric analysis and functional properties. The three-dimensional structure of PBTx3 is proposed by homology modelling to contain a double-stranded antiparallel beta sheet and a single alpha-helix, connected by three disulfide bridges. The scaffold of PBTx3 is homologous to most other alpha-KTx scorpion toxins.

Determination of species-specific components in the venom of Parabuthus scorpions from southern Africa using matrix-assisted laser desorption time-of-flight mass spectrometry

The aim of the present study was to analyze mass spectra of scorpions belonging to the genus Parabuthus (Pocock 1890) by means of matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOFMS) and to construct a species-specific venom code for species identification. The venom compositions of sixteen Parabuthus species, occurring in southern Africa, were characterized using representative peaks in the molecular mass range of 6400-8400 Da. This mass range is characteristic for the typical long-chain neurotoxins influencing sodium channels. Only a few of these peptides have been sequenced up to now. The impetus for development of these species-specific profiles was the observation of unique, highly reproducible mass spectral peaks within a specific species. An identification label for all the different species could be found using a minimum number of peaks. MALDI-TOFMS is therefore proposed as a complementary method to morphological and behavioural characteristics for species and ultimately subspecies discrimination.

Isolation and characterization of a novel type of neurotoxic peptide from the venom of the South African scorpion Parabuthus transvaalicus (Buthidae)

The venom of the South African scorpion Parabuthus transvaalicus was characterized using a combination of mass spectrometry and RP-HPLC separation and bioassays. The crude venom was initially separated into 10 fractions. A novel, moderately toxic but very high abundance peptide (birtoxin) of 58 amino-acid residues was isolated, identified and characterized. Each purification step was followed by bioassays and mass spectroscopy. First a C4 RP-HPLC column was used, then a C18 RP Microbore column purification resulted in > 95% purity in the case of birtoxin from a starting material of 230 microg of crude venom. About 12-14% of the D214 absorbance of the total venom as observed after the first chromatography step was composed of birtoxin. This peptide was lethal to mice at low microgram quantities and it induced serious symptoms including tremors, which lasted up to 24 h post injection, at submicrogram amounts. At least seven other fractions that showed different activities including one fraction with specificity against blowfly larvae were identified. Identification of potent components is an important step in designing and obtaining effective anti-venom. Antibodies raised against the critical toxic components have the potential to block the toxic effects and reduce the pain associated with the scorpion envenomation. The discovery of birtoxin, a bioactive long chain neurotoxin peptide with only three disulfide bridges, offers new insight into understanding the role of conserved disulfide bridges with respect to scorpion toxin structure and function.

Scorpion toxins specific for Na+-channels

Na+-channel specific scorpion toxins are peptides of 60-76 amino acid residues in length, tightly bound by four disulfide bridges. The complete amino acid sequence of 85 distinct peptides are presently known. For some toxins, the three-dimensional structure has been solved by X-ray diffraction and NMR spectroscopy. A constant structural motif has been found in all of them, consisting of one or two short segments of alpha-helix plus a triple-stranded beta-sheet, connected by variable regions forming loops (turns). Physiological experiments have shown that these toxins are modifiers of the gating mechanism of the Na+-channel function, affecting either the inactivation (alpha-toxins) or the activation (beta-toxins) kinetics of the channels. Many functional variations of these peptides have been demonstrated, which include not only the classical alpha- and beta-types, but also the species specificity of their action. There are peptides that bind or affect the function of Na+-channels from different species (mammals, insects or crustaceans) or are toxic to more than one group of animals. Based on functional and structural features of the known toxins, a classification containing 10 different groups of toxins is proposed in this review. Attempts have been made to correlate the presence of certain amino acid residues or 'active sites' of these peptides with Na+-channel functions. Segments containing positively charged residues in special locations, such as the five-residue turn, the turn between the second and the third beta-strands, the C-terminal residues and a segment of the N-terminal region from residues 2-11, seems to be implicated in the activity of these toxins. However, the uncertainty, and the limited success obtained in the search for the site through which these peptides bind to the channels, are mainly due to the lack of an easy method for expression of cloned genes to produce a well-folded, active peptide. Many scorpion toxin coding genes have been obtained from cDNA libraries and from polymerase chain reactions using fragments of scorpion DNAs, as templates. The presence of an intron at the DNA level, situated in the middle of the signal peptide, has been demonstrated.

Purification and partial characterization of a 'short' insectotoxin-like peptide from the venom of the scorpion Parabuthus schlechteri

A disulfide-rich, low-molecular-mass toxin-like peptide has been isolated from Parabuthus schlechteri venom using gel filtration, ion exchange, and reversed phase chromatography. Partial characterization of this peptide reveals a relationship with four-disulfide bridge proteins belonging to the family of 'short' insectotoxins (44% residue identity). In recognition hereof, the peptide was named PBITx1 (sITx10). Our work also reports on the deduced sequences of two other 'short' insectotoxins from Buthus eupeus, I3 and I4, and it provides a consensus sequence and nomenclature for all known 'short' insectotoxins. Finally, sequence similarities with K+ channel blockers (charybdotoxin, kappa-conotoxin), and a Cl- channel blocker (chlorotoxin) are highlighted.