Heterologous expression of a gene that codes for Pg8, a scorpion toxin of Parabuthus granulatus, capable of generating protecting antibodies in mice.

A novel peptide named Pg8 was purified from the venom of the South African scorpion Parabuthus granulatus and its primary structure was determined. It contains 63 amino acid residues tightly folded by 4 disulfide bridges. The gene coding for this peptide was cloned from a cDNA library. By recursive PCR strategy a hybrid gene was constructed having a factor X recognition site for proteolysis and a modified sequence for preferential codon usage of E. coli. A pQE30 molecular vector already contained a His-tag was used for expression. This construction was expressed in BL21 and Origami strains. The fusion protein from inclusion bodies was separated by HPLC (yield approximately 5mg/L) and properly folded in vitro. Lethality tests showed that the recombinant peptide was toxic and was used to immunize mice. A volume of 0.25ml of the anti-serum produced was capable of protecting up to 3 LD(50) doses of pure toxin Pg8 but also, and more importantly, the entire soluble venom.

Evolutionary trace analysis of scorpion toxins specific for K-channels.

Scorpion alpha-K(+) channel toxins are a large family of polypeptides with a similar structure but diverse pharmacological activities. Despite many structural and functional data available at present, little progress has been made in understanding the toxin's molecular basis responsible for the functional diversification. In this paper, we report the first complete cDNA sequences of toxins belonging to subfamily 6 and identify five new members, called alpha-KTx 6.6-6.10. By analyzing the rates of mutations that occurred in the corresponding cDNAs, we suggest that accelerated evolution in toxin-coding regions may be associated with the functional diversification of this subfamily. To pinpoint sites probably involved in the functional diversity of alpha-KTx family, we analyzed this family of sequences using the evolutionary trace method. This analysis highlighted one channel-binding surface common for all the members. This surface is composed of one conserved lysine residue at position 29 assisted by other residues at positions 10, 26, 27, 32, 34, and 36. Of them, the positions 29, 32, and 34 have been reported to be the most major determinants of channel specificity. Interestingly, another contrary surface was also observed at a higher evolutionary time cut-off value, which may be involved in the binding of ERG (ether-a-go-go-related gene) channel-specific toxins. The good match between the trace residues and the functional epitopes of the toxins suggested that the evolutionary trace results reported here can be applied to predict channel-binding sites of the toxins. Because, the side-chain variation in the trace positions is strongly linked with the functional alteration and channel-binding surface transfer of alpha-KTx family, we conclude that our findings should also be important for the rational design of new toxins targeting a given potassium channel with high selectivity.

A subfamily of acidic alpha-K(+) toxins.

Three homologous acidic peptides have been isolated from the venom of three different Parabuthus scorpion species, P. transvaalicus, P. villosus, and P. granulatus. Analysis of the primary sequences reveals that they structurally belong to subfamily 11 of short chain alpha-K(+)-blocking peptides (Tytgat, J., Chandy, K. G., Garcia, M. L., Gutman, G. A., Martin-Eauclaire, M. F., van der Walt, J. J., and Possani, L. D. (1999) Trends Pharmacol. Sci. 20, 444-447). These toxins are 36-37 amino acids in length and have six aligned cysteine residues, but they differ substantially from the other alpha-K(+) toxins because of the absence of the critical Lys(27) and their total overall negative charge. Parabutoxin 1 (PBTx1), which has been expressed by recombinant methods, has been submitted to functional characterization. Despite the lack of the Lys(27), this toxin blocks several Kv1-type channels heterologously expressed in Xenopus oocytes but with low affinities (micromolar range). Because a relationship between the biological activity and the acidic residue substitutions may exist, we set out to elucidate the relative impact of the acidic character of the toxin and the lack of the critical Lys(27) on the weak activity of PBTx1 toward Kv1 channels. To achieve this, a specific mutant named rPBTx1 T24F/V26K was made recombinantly and fully characterized on Kv1-type channels heterologously expressed in Xenopus oocytes. Analysis of rPBTx1 T24F/V26K displaying an affinity toward Kv1.2 and Kv1.3 channels in the nanomolar range shows the importance of the functional dyad above the acidic character of this toxin.

Evolutionary origin of inhibitor cystine knot peptides.

The inhibitor cystine knot (ICK) fold is an evolutionarily conserved structural motif shared by a large group of polypeptides with diverse sequences and bioactivities. Although found in different phyla (animal, plant, and fungus), ICK peptides appear to be most prominent in venoms of cone snail and spider. Recently, two scorpion toxins activating a calcium release channel have been found to adopt an ICK fold. We have isolated and identified both cDNA and genomic clones for this family of ICK peptides from the scorpion Opistophthalmus carinatus. The gene characterized by three well-delineated exons respectively coding for three structural and functional domains in the toxin precursors illustrates the correlation between exon and module as suggested by the "exon theory of genes." Based on the analysis of precursor organization and gene structure combined with the 3-D fold and functional data, our results highlight a common evolutionary origin for ICK peptides from animals. In contrast, ICK peptides from plant and fungus might be independently evolved from another ancestor.

The structure and ion channel activity of 6-benzylamino-3-hydroxyhexa-cyclo[6.5.0.0(3,7).0(4,12).0(5,10).0(9,13]tridecane.

A novel compound, 6-benzylamino-3-hydroxyhexacyclo [6.5.0.0(3, 7).0(4, 12).0(5, 10).0(9, 13)]-tridecane, was synthesized as part of an ongoing study to explore the ion channel activity of polycyclic cage amines. The known polycyclic calcium channel antagonist, 8-benzylamino-8, 11-oxapentacyclo [5.4.0.0(2, 6).0(3, 10).0(5, 9)]undecane (NGP 1-01) served as the lead compound and as a positive control for channel activity. The title compound inhibited calcium currents at test concentrations of 10 microM at depolarized membrane potentials (in the potential range where the L-type calcium channel inactivates). At the test concentrations modulating effects were also observed for sodium and the delayed rectifier potassium currents. Due to its activity at both Ca(2+) and Na(+) channels, this compound may offer utility as a cardiovascular and/or neuroprotecting agent.

Scorpion toxins that block T-type Ca2+ channels in spermatogenic cells inhibit the sperm acrosome reaction.

The acrosome reaction (AR) is a Ca(2+)-dependent event required for sperm to fertilize the egg. The activation of T-type voltage-gated Ca(2+) channels plays a key role in the induction of this process. This report describes the actions of two toxins from the scorpion Parabuthus granulatus named kurtoxin-like I and II (KLI and KLII, respectively) on sperm Ca(2+) channels. Both toxins decrease T-type Ca(2+) channel activity in mouse spermatogenic cells and inhibit the AR in mature sperm. Saturating concentrations of the toxins inhibited at most approximately 70% of the whole-cell Ca(2+) current, suggesting the presence of a toxin-resistant component. In addition, both toxins inhibited approximately 60% of the AR, which is consistent with the participation of T-type Ca(2+) channels in the sperm AR.

Two new scorpion toxins that target voltage-gated Ca2+ and Na+ channels.

This report describes the isolation, primary structure determination, and functional characterization of two similar toxins from the scorpion Parabuthus granulatus named kurtoxin-like I and II (KLI and KLII, respectively). KLII from P. granulatus is identical to kurtoxin from Parabuthus transvaalicus (a 63 amino-acid long toxin) whereas KLI is a new peptide containing 62 amino acid residues closely packed by four disulfide bridges with a molecular mass of 7244. Functional assays showed that both toxins, KLI and kurtoxin from P. granulatus, potently inhibit native voltage-gated T-type Ca(2+) channel activity in mouse male germ cells. In addition, KLI was shown to significantly affect the gating mechanisms of recombinant Na(+) channels and weakly block alpha(1)3.3Ca(V) channels expressed in Xenopus oocytes. KLI and kurtoxin from P. granulatus represent new probes to study the role of ion channels in germ cells, as well as in cardiac and neural tissue.

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.

The effect of the isomers of cyclo(Trp-Pro) on heart and ion-channel activity.

Cyclo(L-Trp-L-Pro) has shown potential for use in the treatment of cardiovascular dysfunction. The aim of the study was to determine the effects of the isomers of cyclo(Trp-Pro) - cyclo(L-Trp-L-Pro), cyclo(L-Trp-D-Pro), cyclo(D-Trp-L-Pro) and cyclo(D-Trp-D-Pro) - on heart and ion-channel activity. The effects on L-type Ca(2+)-channel, Na(+)-channel and inward rectifier K(+)-channel activity were determined by using the whole-cell patch-clamp technique on myocytes of guinea-pig origin. Dependence on the membrane potential in terms of Ca(2+)-channel activity was also investigated. A modified Langendorff method was used to determine the effects of the isomers on heart rate, coronary flow, duration of ventricular tachycardia and arrhythmia, time to sinus rhythm and QRS interval on the rat isolated heart. Cyclo(L-Trp-L-Pro), cyclo(L-Trp-D-Pro) and cyclo(D-Trp-D-Pro), 100 microM, showed agonism towards Ca(2+)-channel activity, while cyclo(D-Trp-L-Pro) caused a blockage of the current. The action of cyclo(D-Trp-L-Pro) was shown to be independent of membrane potential. No significant effect (P > 0.05) on the inward rectifier K(+) current was observed in the presence of cyclo(L-Trp-D-Pro) and cyclo(D-Trp-D-Pro), while antagonism was noted in the presence of cyclo(L-Trp-L-Pro) and cyclo(D-Trp-L-Pro). All isomers showed antagonist effects on the Na(+) channel. No adverse effects were noted on chronotropic effects in the presence of 200 microM cyclo(L-Trp-L-Pro) and cyclo(D-Trp-D-Pro) (P > 0.05), while cyclo(L-Trp-D-Pro) significantly increased the heart rate. Cyclo(D-Trp-L-Pro) significantly reduced the heart rate (P < 0.05). In addition, no significant effects were observed on the coronary flow rate in the presence of the isomers. All isomers significantly reduced the duration of ventricular tachycardia and arrhythmia, as well as the time to sinus rhythm. Furthermore, no change in the QRS intervals was noted in the presence of the isomers in comparison with the control, with a significant increase being noted for cyclo(D-Trp-D-Pro) (P < 0.05) in reference to the other isomers. The isomers thus show antiarrhythmic potential and may manifest as novel agents in the treatment of cardiovascular dysfunction, since a decrease in ventricular fibrillation may reduce the mortality rates in acute myocardial infarction.