Pharmacokinetics of gallium maltolate in Lawsonia intracellularis-infected and uninfected rabbits

Oral gallium maltolate (GaM) pharmacokinetics (PK) and intestinal tissue (IT) concentrations of elemental gallium ([Ga]) and iron ([Fe]) were investigated in a rabbit model of equine proliferative enteropathy (EPE). New Zealand white does (uninfected controls and EPE-infected, n = 6/group) were given a single oral GaM dose (50 mg/kg). Serial blood samples were collected from 0 to 216 h post-treatment (PT) and IT samples after euthanasia. Serology, qPCR, and immunohistochemistry confirmed, or excluded, EPE. Blood and IT [Ga] and [Fe] were determined using inductively coupled plasma-mass spectrometry. PK parameters were estimated through noncompartmental approaches. For all statistical comparisons on [Ga] and [Fe] α = 5%. The Ga log-linear terminal phase rate constant was lower in EPE rabbits vs. uninfected controls [0.0116 ± 0.004 (SD) vs. 0.0171 ± 0.0028 per hour; P = 0.03]; but half-life (59.4 ± 24.0 vs. 39.4 ± 10.8 h; P = 0.12); Cmax (0.50 ± 0.21 vs. 0.59 ± 0.42 μg/mL; P = 0.45); tmax (1.75 ± 0.41 vs. 0.9 ± 0.37 h; P = 0.20); and oral clearance (6.743 ± 1.887 vs. 7.208 ± 2.565 L/h; P = 0.74) were not. IT's [Ga] and [Fe] were higher (P < 0.0001) in controls. In conclusion, although infection reduces IT [Ga] and [Fe], a 48 h GaM dosing interval is appropriate for multidose studies in EPE rabbits.

Species-specificity of equine and porcine Lawsonia intracellularis isolates in laboratory animals

Lawsonia intracellularis infection causes proliferative enteropathy (PE) in many mammalian species, with porcine and equine proliferative enteropathy (PPE and EPE) known worldwide. Hamsters are a well-published animal model for PPE infection studies in pigs. There is no laboratory animal model for EPE infection studies and it is not known whether there is species-specificity for equine or porcine isolates of L. intracellularis in animal models. The objective of this study was to determine whether it is possible to generate typical EPE lesions in hamsters after inoculation with an equine strain of L. intracellularis (EPE strain) and whether it is comparatively possible to generate PPE lesions in rabbits after inoculation with a porcine strain of L. intracellularis (PPE strain). In 2 separate trials, 4-week-old and 3-week-old weanling golden Syrian hamsters were challenged with EPE strains and compared to uninfected (both trials) and PPE-infected controls (Trial 2 only). Concurrently, 6 female New Zealand white juvenile rabbits were infected with PPE strain and observed concomitantly to 8 similar rabbits infected with EPE strain for a different experiment. Hamsters and rabbits were observed for 21 to 24 days post-infection (DPI), depending on the experiment. Neither infected species developed clinical signs. The presence of disease was assessed with diagnostic techniques classically used for pigs and horses: immune-peroxidase monolayer assay on sera; quantitative polymerase chain reaction (qPCR) detection of molecular DNA in feces; and hematoxylin and eosin (H&E) stain and immunohistochemistry (IHC) on intestinal tissues. Our results showed that EPE-challenged hamsters do not develop infection when compared with PPE controls (IHC, P = 0.009; qPCR, P = 0.0003). Conversely, PPE-challenged rabbits do not develop typical intestinal lesions in comparison to EPE-challenged rabbits, with serological response at 14 DPI being significantly lower (P = 0.0023). In conclusion, PPE and EPE strains appear to have different host-specificities for hamsters and rabbits, respectively.

The rabbit as an infection model for equine proliferative enteropathy

The objective of this study was to demonstrate the susceptibility of rabbits to Lawsonia intracellularis obtained from a case of clinical equine proliferative enteropathy (EPE). This is a preliminary step toward developing a rabbit infection model for studying pathogenesis and therapy of EPE in horses. Nine does were equally assigned to 3 groups. Animals in 2 groups (Group 1 and Group 2) were orally inoculated with different doses of cell-cultured L. intracellularis. Controls (Group 3) were sham-inoculated. Feces and blood were collected before the rabbits were infected and at 7, 14, and 21 days post-infection (DPI). Serum immunoglobulin G (IgG) titers were measured using an immunoperoxidase monolayer assay (IPMA) and fecal samples were analyzed with quantitative polymerase chain reaction (qPCR). A doe from each group was euthanized at 7, 14, and 21 DPI for collection and evaluation of intestinal samples. Tissues were stained by routine hematoxylin and eosin (H&E) method and immunohistochemistry (IHC) with L. intracellularis-specific mouse monoclonal antibody. At 14 DPI, serologic responses were detected in both infected groups, which maintained high titers through to 21 DPI. Lawsonia intracellularis DNA was detected in the feces of Group 2 on 7 DPI and in both infected groups on 14 DPI. Gross lesions were apparent in Group 1 and Group 2 on 14 DPI. Immunohistochemistry confirmed L. intracellularis antigen within cells of rabbits in Group 1 and Group 2 on 7, 14, and 21 DPI. No lesions, serologic response, shedding, or IHC labeling were found in Group 3 rabbits. This study describes an EPE rabbit model that simulates natural infection, as typical lesions, immune response, and fecal shedding were present.

Effects of oral electrolyte supplementation on endurance horses competing in 80 km rides

REASONS FOR PERFORMING STUDY

There is no evidence that use of oral electrolyte pastes enhances performance in competing endurance horses.

OBJECTIVE

To ascertain whether oral administration of a high dose (HD) of sodium chloride (NaCl) and potassium chloride (KCl) to endurance horses would differentially increase water intake, attenuate bodyweight (bwt) loss and improve performance when compared to a low dose (LD).

METHODS

A randomised, blinded, crossover study was conducted on 8 horses participating in two 80 km rides (same course, 28 days apart). Thirty minutes before and at 40 km of the first ride 4, horses received orally 02 g NaCl/kg bwt and 0.07 g KCl/kg bwt. The other 4 received 0.07 g NaCl/kg bwt and 0.02 g KCl/kg bwt. Horses received the alternate treatment in the second ride. Data were analysed with 2-way ANOVA for repeated measures (P<0.05).

RESULTS

Estimated water intake was significantly greater with HD both at the 40 km mark and as total water intake; however, differences in bwt loss and speed between HD and LD were not found. Treatment significantly affected serum Na+, Cl-, HCO3, pH and water intake, but not serum K+ or bwt. Serum Na+ and Cl- were significantly higher at 80 km when horses received HD, but no differences were found in early recovery. Venous HCO3- and pH were significantly lower throughout the ride and in early recovery when horses received HD.

CONCLUSIONS AND POTENTIAL RELEVANCE

Other than enhancing water intake, supplementing endurance horses with high doses of NaCI and KCl did not provide any detectable competitive advantage in 80 km rides. Further, the elevated serum electrolyte concentrations induced with HD might not be appropriate for endurance horses.

[Chemical synthesis of lactococcin B and functional evaluation of the N-terminal domain using a truncated synthetic analogue]

The lactococcin B (LnB) is a hydrophobic, positively charged bacteriocin, produced by Lactococcus lactis ssp. cremoris 9B4. It consists of a peptidic chain made up of 47 amino acid residues, and inhibits Lactococcus exclusively. In order to study its biological activity a synthetic lactococcin B (LnBs) was obtained by solid-phase chemical synthesis using a Fmoc strategy. LnBs was shown to be indistinguishable from the natural peptide. In addition, a synthetic (7-47) LnBst analogue was obtained by withdrawal of peptidyl-resin after the 41 cycle of LnBs peptide chain assembly. The synthetic N-terminal truncated (7-47) LnBst analogue was found to be inactive on indicator strains. Our results strongly suggest that the first six N-terminal amino acid residues are involved in the bactericidal activity of LnB.

Clinical West Nile virus infection in 2 horses in western Canada

Two horses had a history of ataxia and weakness or recumbency. One recovered and was diagnosed with West Nile virus (WNV) infection by serologic testing. The other was euthanized; it had meningoencephalomyelitis, WNV was detected by polymerase chain reaction. West Nile virus infection is an emerging disease. Year 2002 is the first year in which cases have been seen in Saskatchewan.

Combined pituitary hormone deficiency due to the F135C human Pit-1 (pituitary-specific factor 1) gene mutation: functional and structural correlates

The pituitary-specific transcription factor Pit-1 (pituitary-specific factor 1) is known to play a key role in the differentiation of PRL-, GH-, and TSH-secreting cells, and in the regulation of expression of the corresponding genes. In recent years, 12 distinct mutations of the Pit-1 gene have been shown to be responsible for a phenotype of multiple congenital pituitary hormone deficiency involving PRL, GH, and TSH. We had previously identified, in four siblings with GH, PRL, and TSH deficiencies, a mutation (F135C) resulting in a single amino acid change within the POU-specific binding domain of the Pit-1 molecule. In the present report, we have explored the functional effect of the F135C mutation. In vitro activity tests performed by transfection in human HeLa cells showed decreased transactivation capacity on the PRL, GH, and Pit-1 genes. The DNA binding experiments performed by gel shift showed that the F135C mutation generated a protein capable of binding to DNA response elements. To analyze how the F135C mutation might affect functionality of the transcription factor despite a normal DNA binding, we used a structure modelization approach and also analyzed two other Pit-1 mutant proteins (F135A and F135Y). The loss of functionality in these two mutants was similar to that of F135C. This finding was in keeping with our molecular modeling studies. According to structural data derived from the crystallographic analysis of the DNA/Pit-1 POU domain complex, the conformation of the first helix of the F135C-mutated POU-specific domain could be perturbed to such an extent that any interaction with other transcription cofactors might be definitively prevented.

Purification, characterization and molecular modelling of two toxin-like proteins from the Androctonus australis Hector venom

Two toxin-like proteins (AahTL1 and AahTL3) were purified from the venom of the scorpion Androctonus australis Hector (Aah). AahTL1 and AahTL3 are the first non toxic proteins cross-reacting with AahI toxins group which indicates that these proteins can be used as a model of vaccins. In order to study structure-function relationships, their complete amino-acid sequences (66 residues) were determined, by automated Edman degradation. They show more than 50% of similarity with both AahI and AahIII antimammal toxins. Three-dimensional structural models of AahTL1 and AahTL3 constructed by homology suggest that the two proteins are structurally similar to antimammal scorpion alpha-toxins specific to voltage dependent Na+ channels. The models showed also that amino-acid changes between potent Aah toxins and both AahTL1 and AahTL3 disrupt the electrostatic potential gradient at their surface preventing their interaction with the receptor, which may explain their non toxicity.

Role of lysine and tryptophan residues in the biological activity of toxin VII (Ts gamma) from the scorpion Tityus serrulatus

Toxin VII (TsVII), also known as Ts gamma, is the most potent neurotoxin in the venom of the Brazilian scorpion Tityus serrulatus. It has been purified to homogeneity using a new fast and efficient method. Chemical modification of TsVII with the tryptophan-specific reagent o-nitrophenylsulfenyl chloride yielded three modified derivatives (residues Trp39, Trp50 and Trp54). Acetylation of TsVII mostly generated the monoacetylated Lys12 derivative. No side reactions were detected, as indicated by endoproteinase Lys-C peptide mapping, Edman degradation and electrospray mass spectrometry. Circular dichroism and fluorimetric measurements showed that none of the chemical modifications altered the overall structure of the derivatives. The acetylation of Lys12 or the sulfenylation of Trp39 or Trp54 led to a loss of both toxicity in mice and apparent binding affinity for rat brain and cockroach synaptosomal preparations. Sulfenylation of Trp50, however, moderately affected the toxicity of TsVII in mice and had almost no effect on its binding properties. A 3-dimensional model of TsVII was constructed by homology modeling. It suggests that the most reactive residues (Lys12 and Trp39 and Trp54) are all important in the functional disruption of neuronal sodium channels by TsVII, and are close to each other in the hydrophobic conserved region.

Aah VI, a novel, N-glycosylated anti-insect toxin from Androctonus australis hector scorpion venom: isolation, characterisation, and glycan structure determination

Aah VI was isolated from the venom of the North African scorpion, Androctonus australis hector. It is the first glycosylated neurotoxin from scorpion venom to be described. It was not toxic to mice, when injected intracerebroventricularly at a dose of 1.2 microg per animal. However, it had typical activity in Blatella germanica cockroaches resulting in gradual paralysis and very low toxicity (LD50 = 8.5 microg/g of animal). It consists of 66 amino acid residues and is heterogeneously N-glycosylated at a single site, on asparagine 9, of the Asn-Gly-Thr sequence. The potential N-glycosylation site was deduced from automatic Edman degradation and amino acid analysis, and glycan heterogeneity was evidenced by ESMS. Determination of the N-glycan structures (dHex, Hex and HexNAc) was assessed by nanoESMS/MS with picomolar amounts of sample. Current knowledge of N-glycan structure and composition suggests that the glycan structures are derived from a common core.

Maurotoxin, a four disulfide bridges scorpion toxin acting on K+ channels

Maurotoxin, a toxin from the venom of the Tunisian chactoid scorpion Scorpio maurus, has been purified to homogeneity by gel filtration/reversed-phase HPLC, and characterized. It is a basic and C-terminal amidated 34-residue polypeptide cross-linked by four disulfide bridges. From Edman sequencing results, only six different pairings between the first six half-cystines were retained whereas a disulfide bridge was predicted between the two half-cystines in positions 31 and 34. Modelling based on the structure of charybdotoxin favored two different pairings, one of which possessed two disulfides in common with the general motif of scorpion toxins. The solid-phase technique was used to obtain synthetic maurotoxin, sMTX. The half-cystine pairings of sMTX were determined by enzymatic cleavage and were found to be Cys3 Cys24, Cys9-Cys29, Cys13-Cys19, and Cys31-34, in agreement with experimental data obtained with natural maurotoxin. Both natural and synthetic maurotoxins were lethal to mice following intracerebroventricular injection (LD50, 80 ng/mouse). They blocked the Kv1.1, Kv1.2, and Kv1.3 channels expressed in Xenopus oocytes with almost identical half-effects (IC50) in the range of 40, 0.8 and 150 nM, respectively. They also competed with 125I-apamin (SKca channel blocker) and 125I-kaliotoxin (Kv channel blocker) for binding to rat brain synaptosomes with IC50 of about 5 and 0.03 nM. As the natural and synthetic maurotoxins exhibit indistinguishable physicochemical and pharmacological properties, they are likely to adopt the same half-cystine pairing pattern which is unique among known scorpion toxins. However, this disulfide organization is different from those reported for Pandinus imperator and Heterometrus spinnifer toxins 1 (Pi1 and HsTx1), two novel four-disulfide bridged K+ channel-acting scorpion toxin sharing about 50-70% sequence identity with maurotoxin.

Adenosine and the nervous system: pharmacological data and therapeutic perspectives

1. Adenosine acts on a family of G-protein-coupled receptors called purinoreceptors. 2. Four subtypes have been cloned and pharmacologically characterized. 3. The principal pharmacological data and structure-function relations for agonist interactions with P1 receptors are presented. 4. We conclude that the potent role of adenosine in the nervous system may be interesting for the development of drugs targeted at purines and their receptors.

Adenosine and migraine

BACKGROUND

Adenosine is a powerful natural vasodilator that participates in the control of cerebral and meningeal blood flow. In this context, it could be involved in the pathophysiology of migraine, since it was previously reported that intravenous adenosine can precipitate crises in migraine patients.

METHODS

We have investigated circulating adenosine levels in 12 patients suffering from migraine without aura, during crises and in crisis-free periods, and have compared the levels noted to those of a population of 10 controls. To determine if there are interactions between adenosine and serotonin, we examined the effect of adenosine and antagonists on the uptake and the release of (14C) serotonin by platelets.

RESULTS AND CONCLUSION

We have reached a dual conclusion: 1) during migraine headaches there is an increase (mean 68%) in circulating adenosine levels and this increase may participate in cephalalgia; 2) activation of A2 receptors by adenosine causes a dose-dependent serotonin uptake by platelets. This inhibition of uptake could participate in the rapid elimination of serotonin in migraine sufferers. As a result of this, the use of adenosine antagonists could be an effective complementary treatment for migraine.

Influence of a NH2-terminal extension on the activity of KTX2, a K+ channel blocker purified from Androctonus australis scorpion venom

A cDNA encoding a short polypeptide blocker of K+ channels, kaliotoxin 2 (KTX2), from the venom of the North African scorpion Androctonus australis was expressed in the periplasmic space of Escherichia coli. KTX2 was produced as a fusion protein with the maltose binding protein followed by the recognition site for factor Xa or enterokinase preceding the first amino acid residue of the toxin. The fully refolded recombinant KTX2 (rKTX2) was obtained (0.15-0.30 mg/l of culture) and was indistinguishable from the native toxin according to chemical and biological criteria. An N-extended analogue of KTX2 exhibiting three additional residues was also expressed. This analogue had 1000-fold less affinity for the 125I-kaliotoxin binding site on rat brain synaptosomes than KTX2. Conformational models of KTX2 and its mutant were designed by amino acid replacement using the structure of agitoxin 2 from Leiurus quinquestriatus as template, to try to understand the decrease in affinity for the receptor.

1H-NMR-derived secondary structure and overall fold of a natural anatoxin from the scorpion Androctonus australis hector

The venom of the scorpion Androctonus australis hector contains several protein neurotoxins of which structure and structure/activity relationships have been extensively studied. It also contains polypeptides such as Aah STR1, which are not toxic, while having highly similar sequences to fully active toxins. We have determined the solution structure of Aah STR1 by use of conventional two-dimensional NMR techniques followed by distance-geometry and energy minimization. We have demonstrated that, despite its lack of toxicity, Aah STR1 is structurally highly related to anti-mammal scorpion toxins specific for Na+ channels. The calculated structure is composed of a short alpha-helix (residues 26-33) connected by a tight turn to a three-stranded antiparallel beta-sheet (sequences 3-6, 38-41 and 44-48). This beta-sheet is right-handed twisted as usual for such secondary structures. The beta-turn connecting the strands 38-41 and 44-48 belongs to type II'. The overall fold of Aah STR1 is typical of beta-type scorpion toxins. This is, however, the first example of such a fold in Old World scorpion toxins. Either the absence of a basic residue in position 63 or the high mobility of loops, compared to active beta-type neurotoxins, may explain the lack of activity of this protein.

Maurotoxin, a four disulfide bridge toxin from Scorpio maurus venom: purification, structure and action on potassium channels

A new toxin acting on K+ channels, maurotoxin (MTX), has been purified to homogeneity from the venom of the chactoid scorpion Scorpio maurus. MTX is a basic single chain 34 amino acid residue polypeptide, amidated at its C terminal, and crosslinked by four disulfide bridges. It shows 29-68% sequence identity with other K+ channel toxins, and presents an original disulfide pattern, the last two half-cystine residues (31-34) being connected. Although the first three disulfide bonds have not been defined experimentally, modelling based on the structure of charybdotoxin favored two combinations out of six, one of which has two bridges (3-24 and 9-29) in common with the general motif of scorpion toxins. The last bridge would connect residues 13 and 19. MTX inhibits the binding to rat brain synaptosomal membranes of both [125I]apamin, a SK(Ca) channel blocker (IC50 5 nM), and [125I]kaliotoxin, a Kv channel blocker (IC50 30 pM). MTX blocks the Kv1.1, Kv1.2 and Kv1.3 currents expressed in Xenopus oocytes with IC50 of 45, 0.8 and 180 nM, respectively. MTX represents a member of a new class of short toxins with 4 disulfide bridges, active on voltage-dependent K+ channel and also competing with apamin for binding to its receptor.

Adenosine and neuropathic pain

Recent studies have reported the possibilities of relieving neuropathic pain by administering adenosine or its analogs. In order to determine if there exists a metabolic anomaly of this nucleoside in patients with neuropathic pain, circulating adenosine levels were compared in three patient groups. The first was composed of individuals suffering from neuropathic pain, the second of patients with nervous system lesions in the absence of pain, and the third was composed of patients suffering from pain resulting from excessive nociception. The adenosine blood levels of these patients were compared to those of a control group. Finally, adenosine in the cerebrospinal fluid (CSF) of some patients was also assayed. The results show that there are reduced levels of blood and CSF adenosine in patients with neuropathic pain. This adenosine deficiency could explain the potential therapeutic effects of administering adenosine or its analogs.

Adenosine and the nervous system: clinical implications

After a review of the metabolism and pharmacology of adenosine, this work will examine the various therapeutic possibilities involving the use of agonists or antagonists of adenosine A1 or A2 receptors in neurological disorders. Promising preclinical results have been obtained with epilepsy, cerebral ischemia, alcoholism, and pain.

Tetrodotoxin reverses brevetoxin allosteric inhibition of scorpion alpha-toxin binding on rat brain sodium channels

Voltage-sensitive sodium channels are responsible for the initiation of action potentials in many excitable cells. Several neurotoxins bind to distinct receptor sites on sodium channels and reveal strong allosteric interactions among them. Scorpion alpha toxins, which inhibit sodium channel inactivation by binding to receptor site 3, have been very important tools to study sodium channel structure and function. Recently, we have shown that brevetoxin induce a strong negative allosteric modulation on scorpion alpha-toxin binding on rat brain sodium channels, in contrast to previously published studies. In this report we have examined the reasons for this discrepancy and found new, unexpected allosteric interactions between the tetrodotoxin and brevetoxin receptor sites, using scorpion alpha-toxin as sensitive probe for subtle conformational changes on sodium channels. Tetrodotoxin reverses the negative modulation induced by brevetoxin on scorpion alpha-toxin binding, revealing new dynamic interactions in sodium channel structure.

Use of dantrolene in experimental scorpion envenomation by Androctonus australis hector

Hyperthermia and profuse perspiration are rarely absent in severe cases of scorpion envenomation. Based on these observations, the aim of this study was to determine the therapeutic effects of dantrolene, on experimental poisoning by the venom of Androctonus australis hector. Dantrolene is a directly acting muscle relaxant which lowers the body temperature in malignant hyperthermia. The results indicate that the early use of this drug raises the LD50 in experimentally poisoned mice. If these results are transposable to humans, dantrolene could be a useful therapeutic adjuvant.

The use of HPLC to evaluate the variations of blood coronary adenosine levels during percutaneous transluminal angioplasty

Although it is well established that adenosine is released during acute ischemia, little is known of the behaviour of adenosine levels following treatment of coronary lesion by percutaneous transluminal coronary angioplasty (PTCA). Using high performance liquid chromatography, we measured intracoronary adenosine levels before and 5 min after PTCA in ten patients with one-vessel disease and a significant (> 70%) coronary stenosis. Adenosine levels decrease in all patients after PTCA. Nevertheless, more studies are now necessary to evaluate the possible predictive value (with regard to restenosis) of coronary adenosine levels after PTCA.

Positively charged amino acid residues located similarly in sea anemone and scorpion toxins

Specific groups of sea anemone and scorpion toxins compete on the same pharmacological site, on the voltage-gated sodium channel of mammal excitable membranes. However, these scorpion and sea anemone toxins are two distinct protein families. Here we purified and sequenced a new sea anemone toxin, Bg II, highly toxic to mammals and also a less toxic mutant, Bg III. Two Bg II models were determined from sequence homologies with two sea anemone toxin two-dimensional NMR structures. Only one model conformed to circular dichroism data obtained from Bg II and was compared with an x-ray structure of a scorpion toxin. The comparison of the two structures shows that 5 amino acid residues are located similarly in the sea anemone toxin and the scorpion toxin. From these 5 residues, 4 are basic residues, constituting two distinct positively charged poles on the surface of these toxins. In the sea anemone mutant isolated, a negative charge beside one of the positive poles decreases the toxicity. These results show that positively charged amino acid residues could be essential for the activity of these toxins and outline the role of electrostatic bonds in the interaction of sea anemone and scorpion toxins with their receptor.

Synthesis and characterization of kaliotoxin. Is the 26-32 sequence essential for potassium channel recognition?

Kaliotoxin (KTX), a scorpion toxin characterized as a 37-residue inhibitor of the neuronal high conductance Ca(2+)-activated K+ channels (KCa channels), has been chemically synthetized. Differences were observed between natural toxin and the two peptides, KTX(1-37) and KTX(1-37)-amide. Re-examination of the KTX sequence showed that an extra lysine residue was present at the C-terminal end. The 38-residue synthetic peptide was found identical with natural toxin. All three peptides had comparable activities, with LD50 values of 6-9 pmol/mouse after intracerebroventricular injection, and Kd = 2-8 nM for blockage of the whole cell and unitary molluscan KCa currents. Pairing of the disulfide bonds in synthetic KTX corresponded to that in charybdotoxin and iberiotoxin. A competition assay between 125I-KTX(1-37) and different toxins (KTX, dendrotoxin, charybdotoxin, MCD peptide, and iberiotoxin) for binding to rat brain synaptosomal membranes suggested that KTX interacts also with voltage-gated K+ channels. Shorter peptides, KTX(25-35)-amide and KTX(26-32)-amide, expressed no KTX activity, but were able to compete in binding. They were further shown to antagonize KTX in both its toxicity and blocking activity. The (26-32) sequence of KTX, which is a highly conserved region, may contain a low affinity binding subsite essential for potassium channel recognition.

An anti-insect toxin purified from the scorpion Androctonus australis Hector also acts on the alpha- and beta-sites of the mammalian sodium channel: sequence and circular dichroism study

A new anti-insect neurotoxin, AaH IT4, has been isolated from the venom of the North African scorpion Androctonus australis Hector. This polypeptide has a toxic effect on insects and mammals and is capable of competing with anti-insect scorpion toxins for binding to the sodium channel of insects; it also modulates the binding of alpha-type and beta-type anti-mammal scorpion toxins to the mammal sodium channel. This is the first report of a scorpion toxin able to exhibit these three kinds of activity. The molecule is composed of 65 amino acid residues and lacks methionine and, more unexpectedly, proline, which until now has been considered to play a role in the folded structure of all scorpion neurotoxins. The primary structure showed a poor homology with the sequences of other scorpion toxins; however, it had features in common with beta-type toxins. In fact, radioimmunoassays using antibodies directed to scorpion toxins representative of the main structural groups showed that there is a recognition of AaH IT4 via anti-beta-type toxin antibodies only. A circular dichroism study revealed a low content of regular secondary structures, particularly in beta-sheet structures, when compared to other scorpion toxins. This protein might be the first member of a new class of toxins to have ancestral structural features and a wide toxic range.

Primary structure of scorpion anti-insect toxins isolated from the venom of Leiurus quinquestriatus quinquestriatus

The amino acid sequences of insect-selective scorpion toxins, purified from the venom of Leiurus quinquestriatus quinquestriatus, have been determined by automatic phenyl isothiocyanate degradation of the S-carboxymethylated proteins and derived proteolytic peptides. The excitatory toxin Lqq IT1 and Lqq IT1' (70 residues) show the shift of one half-cystine from an external position, which is characteristic of anti-mammal toxins, to an internal sequence position. Lqq IT2 (61 residues) displays the half-cystine residue in position 12, common to the sequence of all known anti-mammal toxins; it induces flaccid paralysis on insects but is non-toxic for the mouse. Lqq IT2 structurally defines a new type of anti-insect toxins from scorpion venoms. CD spectra and immunological data are in agreement with this finding.

Conformational flexibility of a scorpion toxin active on mammals and insects: a circular dichroism study

Three scorpion toxins have been analyzed by circular dichroism in water and in 2,2,2-trifluoroethanol (TFE) solutions. These toxins were chosen because they are representative of three kinds of pharmacological activities: (1) toxin AaH IT2, an antiinsect toxin purified from the venom of Androctonus australis Hector, which is able to bind to insect nervous system preparation, (2) toxin Css II, from the venom of Centruroides suffusus suffusus, which is a beta-type antimammal toxin capable of binding to mammal nervous system preparation, and (3) the toxin Ts VII from the venom of Tityus serrulatus, which is able to bind to both types of nervous systems. In order to minimize bias, CD data were analyzed by a predictive algorithm to assess secondary structure content. Among the three molecules, Ts VII presented the most unordered secondary structure in water, but it gained in ordered forms when solubilized in TFE. These results indicated that the Ts VII backbone is the most flexible, which might result in a more pronounced tendency for this toxin molecule to undergo conformational changes. This is consistent with the fact that it competes with both antiinsect and beta-type antimammal toxins for the binding to the sodium channel.

Amino acid sequence of toxin XI of the scorpion Buthus occitanus tunetanus. Evidence of a mutation having an important effect upon neurotoxic activity

The complete amino acid sequence of toxin XI of the North African scorpion Buthus occitanus tunetanus has been elucidated by automatic sequencing of the reduced and alkylated toxin and of the peptides obtained after tryptic cleavage restricted to arginyl bonds. This toxin is structurally homologous to toxin II of Androctonus australis Hector, the most active among the alpha-toxins, but is far less potent, both in vivo and in vitro. This work points out 12 mutations, many of which are conservative. Nevertheless, the most striking difference is the replacement of the lysine residue at position 58, known to be important in the activity of AaH toxin II, by a valine residue. Thus, it seems that the presence of a positive charge at this location facilitates the interactions between the receptor on the sodium channel and the alpha-type toxins.

Amino acid sequence of toxin VII, a beta-toxin from the venom of the scorpion Tityus serrulatus

The sequence of the 61 amino acids of toxin VII, a beta-toxin from the venom of the South American scorpion Tityus serrulatus, has been determined by automatic sequencing of the reduced and S-[14C] carboxymethylated protein and of tryptic peptides obtained before or after citraconylation of this protein. This toxin, the most active beta-toxin from this venom, is the first Tityus toxin to be fully sequenced. The results clearly show that toxin VII belongs to the structural group of scorpion toxins originating from Central and North America.

Structure-function relationships in scorpion neurotoxins. Identification of the supperreactive lysine residue in toxin I of Androctonus australis Hector

In a previous article (Habersetzer-Rochat, C. and Sampieri, R. (1976) Biochemistry 15, 2254--2261) it was demonstrated that the toxin I of the North African Scorpion Androctonus australis Hector was inactivated after reaction with iodoacetate; the toxicity loss in mice was correlated with the carboxymethylation of one superreactive residue. In the present work, alkylation of toxin I was performed with iodo[14C]-acetate. Hence, it was possible, after reduction, S-methylation and chymotryptic hydrolysis of this toxin, to isolate the peptide containing the labelled lysine residue. By automatic Edman degradation, this residue was identified as being the penultimate lysine at position 56 in the primary sequence. Comparison of three primary structures of scorpion neurotoxins and comparison in different kinds of activity seem to indicate that this lysine residue is mainly important for toxicity in mice.

Structure-function relationships of scorpion neurotoxins

Chemical modification of some trifunctional amino acid residues in toxins I, II, and III of the scorpion Androctonus australis Hector have been performed. The results indicate: (1) Reduction and methylation of one disulfide bridge destroy toxic activity of toxin II. (2) The only tryptophan residue of toxin II (position 38) is not included in the active site of the molecule. (3) Modification of five carboxylates out of the seven contained in toxin II suppresses the toxic activity. (4) Acetylation of the lysine and tyrosine residues in toxin II leads to the loss of both toxic and antigenic activity. Treatment of the acetylated toxin by hydroxylamine restores partially the antigenic activity. In the case of toxin I, total acetylation abolishes only the toxic activity. It is concluded that at least one tyrosine residue must be involved in an antigenic site of toxin II. (5) Citraconylation of toxins II and III leads to complete loss of toxicity; decitraconylation restores full activity. (6) Guanidination of toxin II does not affect its toxicity significantly. (7) Alkylation of toxin II by iodoacetic acid affects both amino groups and histidine residues. The loss of toxicity is mainly due to the modification of the lysine residues. In the case of toxin I, the kinetics of toxicity loss closely parallel the covalent modification of one lysine residue.