New toxins from the venom of the common tiger snake (Notechis scutatus scutatus)

The Cardiovascular, Coagulation and Haematological Effects of Tiger Snake (Notechis scutatus) Prothrombin Activator and Investigation of Release of Vasoactive Substances

The cardiovascular, coagulation and haematological effects of prothrombin activator from Tiger Snake (Notechis scutatus) venom were investigated in anaesthetized mechanically ventilated dogs. Infusion caused dose-related systemic hypotension, marked decreases in cardiac output and stroke volume, marked increases in pulmonary artery pressure, pulmonary artery occlusion pressure and pulmonary vascular resistance. Effects occurred within several minutes but abated over 30 to 40 minutes. Evidence of procoagulation included prolongation of prothrombin and partial thromboplastin times and depletion of serum fibrinogen. Thrombocytopenia and leucopenia occurred. All effects were prevented by prior administration of heparin but none by inhaled nitric oxide. Oesophageal echocardiography during infusion identified thrombi within the heart, right ventricular dilatation and dyskinesia. Electrocardiography suggested myocardial ischaemia. Pulmonary thromboemboli were identified histologically post mortem. Cardiovascular effects of the activator were not due to a variety of endogenous substances as indicated by use of antagonists to platelet activating factor and thromboxane A2, indomethacin, dexamethasone, serotonin, ketanserin, histamine, promethazine and ondansetron. Tiger Snake prothrombin activator causes bilateral ventricular failure by thrombotic obstruction of the pulmonary vasculature and possibly by coronary ischaemia.

Catch a tiger snake by its tail: Differential toxicity, co-factor dependence and antivenom efficacy in a procoagulant clade of Australian venomous snakes

A paradigm of venom research is adaptive evolution of toxins as part of a predator-prey chemical arms race. This study examined differential co-factor dependence, variations relative to dietary preference, and the impact upon relative neutralisation by antivenom of the procoagulant toxins in the venoms of a clade of Australian snakes. All genera were characterised by venoms rich in factor Xa which act upon endogenous prothrombin. Examination of toxin sequences revealed an extraordinary level of conservation, which indicates that adaptive evolution is not a feature of this toxin type. Consistent with this, the venoms did not display differences on the plasma of different taxa. Examination of the prothrombin target revealed endogenous blood proteins are under extreme negative selection pressure for diversification, this in turn puts a strong negative selection pressure upon the toxins as sequence diversification could result in a drift away from the target. Thus this study reveals that adaptive evolution is not a consistent feature in toxin evolution in cases where the target is under negative selection pressure for diversification. Consistent with this high level of toxin conservation, the antivenom showed extremely high-levels of cross-reactivity. There was however a strong statistical correlation between relative degree of phospholipid-dependence and clotting time, with the least dependent venoms producing faster clotting times than the other venoms even in the presence of phospholipid. The results of this study are not only of interest to evolutionary and ecological disciplines, but also have implications for clinical toxinology.

Ophthalmoplegia in tiger snake envenomation

Herein, we present the case of a 67-year-old grazier who was bitten by a tiger snake and developed coagulopathy and respiratory distress. The patient required intubation and ventilation in intensive care. There was delayed detection of snake envenomation and administration of antivenom. On extubation several days later, gross external ocular paresis was noted. Clinical testing indicated that the ocular pathology was secondary to neurotoxin-mediated presynaptic blockade. The paresis was partially resolved by the time of discharge one week later. The present case report discusses the possible mechanisms for the delayed development of ophthalmoplegia.

Comparison of the in vitro neuromuscular activity of venom from three Australian snakes (Hoplocephalus stephensi, Austrelaps superbus and Notechis scutatus): efficacy of tiger snake antivenom

1. Tiger snake antivenom, raised against Notechis scutatus venom, is indicated not only for the treatment of envenomation by this snake, but also that of the copperhead (Austrelaps superbus) and Stephen's banded snake (Hoplocephalus stephensi). The present study compared the neuromuscular pharmacology of venom from these snakes and the in vitro efficacy of tiger snake antivenom. 2. In chick biventer cervicis muscle and mouse phrenic nerve diaphragm preparations, all venoms (3-10 microg/mL) produced inhibition of indirect twitches. In the biventer muscle, venoms (10 micro g/mL) inhibited responses to acetylcholine (1 mmol/L) and carbachol (20 micromol/L), but not KCl (40 mmol/L). The prior (10 min) administration of 1 unit/mL antivenom markedly attenuated the neurotoxic effects of A. superbus and N. scutatus venoms (10 microg/mL), but was less effective against H. stephensi venom (10 microg/mL); 5 units/mL antivenom attenuated the neurotoxic activity of all venoms. 3. Administration of 5 units/mL antivenom at t90 partially reversed, over a period of 3 h, the inhibition of twitches produced by N. scutatus (10 microg/mL; 41% recovery), A. superbus (10 microg/mL; 25% recovery) and H. stephensi (10 microg/mL; 50% recovery) venoms. All venoms (10-100 microg/mL) also displayed signs of in vitro myotoxicity. 4. The results of the present study indicate that all three venoms contain neurotoxic activity that is effectively attenuated by tiger snake antivenom.

Structure-function properties of venom components from Australian elapids

A comprehensive review of venom components isolated thus far from Australian elapids. Illustrated is that a tremendous structural homology exists among the components but this homology is not representative of the functional diversity. Further, the review illuminates the overlooked species and areas of research.

The cardiovascular, coagulation and haematological effects of tiger snake (Notechis scutatus) venom

The cardiovascular, coagulation and haematological effects of Tiger Snake (Notechis scutatus) venom were investigated in anaesthetized, mechanically ventilated dogs. Intravenous infusion of venom caused dose-related systemic hypotension, low cardiac output, pulmonary hypertension and raised pulmonary artery occlusion pressure. These effects occurred within several minutes of venom administration but recovered over 30 to 40 minutes. They were accompanied by prolongation of prothrombin and activated partial thromboplastin times and by depletion of serum fibrinogen. Fibrin degradation products were not detected. Thrombocytopenia and leucopenia were observed within minutes of venom administration but recovered over 30 to 40 minutes. The mechanism of systemic hypotension is probably pulmonary vascular obstruction and coronary ischaemia caused by disseminated intravascular coagulation, although the existence of a myocardial depressant in venom or release of vasoactive substances by venom cannot be excluded.

Toxins isolated from the venom of the Brazilian coral snake (Micrurus frontalis frontalis) include hemorrhagic type phospholipases A2 and postsynaptic neurotoxins

Toxins isolated from the venom of the Brazilian coral snake (Micrurus frontalis frontalis) include hemorrhagic type phospholipases A2 and postsynaptic neurotoxins. Toxicon 35, 1193-1203, 1997.-Two sets of proteins have been purified from the venom of the Brazilian coral snake, Micrurus frontalis frontalis. One set has mol. wts, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), in the 8000-13,000 range and includes some proteins which are toxic to mice and others which are not. These proteins appear to be isoforms of postsynaptic toxins. The other set shows phospholipase A2 (PLA2) activity and the toxic members of this set promote hemorrhage in mice in a manner closely resembling that produced by PLA2s isolated from the venom of the Australian tiger snake (Notechis scutatus scutatus). These PLA2s migrate on SDS-PAGE with apparent mol. wts in the 18,000-22,000 range which is characteristic of PLA2s that have an alpha-helix D similar to pancreatic PLA2s. Elapid venom PLA2s of the type which typically migrate on SDS-PAGE with mol. wts in the 13,000-16,000 range and do not have alpha-helix D have not been detected in M. f. frontalis venom.

Bovine granulocyte chemotactic protein-2 is secreted by the endometrium in response to interferon-tau (IFN-τ)

Interferon-tau (IFN-τ) is secreted by the bovine conceptus and may regulate synthesis of uterine endometrial cytokines to provide an environment that is conducive to embryo development and implantation. Interferon-τ stimulates secretion of an 8-kDa uterine protein (P8) in the cow. P8 was purified, digested to yield internal peptides, and partially sequenced to determine identity. Two internal peptides had 100% (13-mer) and 92% (12-mer) amino acid sequence identity with bovine granulocyte chemotactic protein-2 (bGCP-2). Bovine GCP-2 is an α-chemokine that acts primarily as a potent chemoattractant for granulocyte cells of the immune system. A peptide was synthesized based on a region of bGCP-2 that overlapped with a P8 peptide amino acid sequence, coupled to keyhole limpet hemocyanin, and used to generate high titer polyclonal antiserum in sheep. Western blots revealed that bGCP-2 was not released by endometrium from day 14 nonpregnant cows, but was released in response to 25 nM IFN-τ (p<0.05). Uterine GCP-2 exhibited high affinity to heparin agarose, a characteristic shared by all α chemokines. This is the first report describing presence of GCP-2 in the uterine endometrium and regulation by IFN-τ. The regulation of bGCP-2 by IFN-τ may have important implications for cytokine networking in the uterus during pregnancy. Also, the regulation of inflammation and angiogenesis by bGCP-2 working together with other cytokines may be integral to establishing early pregnancy and implantation in the cow.

Conformational analysis of a toxic peptide from Trimeresurus wagleri which blocks the nicotinic acetylcholine receptor

The 22-residue toxic peptide (WTX1) from the venom of the Southeast Asian snake Trimeresurus wagleri has multiple sites of action, but its lethal effect has been attributed to blocking the postsynaptic acetylcholine receptor at the neuromuscular junction. The 3-dimensional structure of WTX1 was studied using 2-dimensional nuclear magnetic resonance spectroscopy, circular dichroism, and computer simulations. In aqueous solution, WTX1 was shown to have extended and flexible "tails" defined by a short, rigid disulfide-bonded loop. The flexible regions can undergo structural rearrangement when moved from an aqueous to a less polar environment and may contribute to its effectiveness at different receptor sites. By substituting Gly or Phe for His at position 10, significant effects on the disulfide bond formation and, thereby, the activity of the peptide were observed. These results suggest that even subtle differences in single residues can have profound effects on the dynamics of folding, disulfide bond formation, and activity of this toxic peptide.

Specificity and binding affinity of an anti-crotoxin combinatorial antibody selected from a phage-displayed library

A crotoxin-specific, monoclonal, high-affinity, single-chain antibody variable region (scFv) was generated by combinatorial methods using Pharmacia's Recombinant Phage Antibody System. A high-affinity clone, designated A10G, was selected, and its DNA sequence was determined. Protein A10G showed high reaction specificity, with only the closely related rattlesnake neurotoxins, concolor toxin and Mojave toxin, showing cross-reactivity out of eleven group II phospholipase A2s (PLA2s) screened. No group I PLA2s cross-reacted in enzyme-linked immunosorbent assays. The gene coding for A10G was subcloned into an expression vector, and the resulting expressed nonfusion protein, designated A10GPE, was renatured and purified to apparent homogeneity. Dissociation constants of A10G with intact crotoxin and crotoxin basic subunit were determined to be 7 x 10(-10) and 6.8 x 10(-9) M, respectively. When A10GPE was preincubated with either the basic subunit or intact crotoxin at molar ratios of up to 5:1, no inhibition of phospholipase activity was observed. Expressed protein, however, could partially neutralize the lethality of Mojave toxin, a crotoxin homolog, in mice.

Anions and the anomalous gel filtration behavior of notexin and scutoxin

Based on their mol. wts, notexin and scutoxin elute later than expected from gel filtration columns in multiple peaks [Francis et al. (1991) Toxicon 29, 85-96]. Notexins present in these peaks have identical amino acid sequences and unmodified amino acid side-chains. Scutoxin is an isoform of notexin which contains arginine at position 16 and glutamate at position 82. Like notexin, it also elutes in different fractions on a gel filtration column, yet the fractions show identical amino acid sequence. This perplexing chromatographic behavior appears to be caused by the association of these proteins with different anions, since dissolving notexin in buffers containing different anions produces up to a 30% change in elution volume. Certain anions promote an apparent reduction in the interaction of notexin with gel filtration matrix, hence earlier elution. These anions include citrate, 3-phosphoglycerate and 2-phosphoglycerate, which also inhibit the PLA2 activity of notexin. However, even under conditions which minimize protein-matrix interaction the toxins elute later than expected based on their mol. wt.

Antibodies having markedly different effects on enzymatic activity and induction of acetylcholine release by two presynaptically-acting phospholipase A2 neurotoxins

The enzymatic and acetylcholine-releasing activities of two presynaptically-acting phospholipase A2 neurotoxins (pseudexin B and scutoxin) were studied in a synaptosomal fraction. Scutoxin (100 nM) induced greater [14C]acetylcholine release than did pseudexin B (100 nM). Both toxins caused fatty acid production in the synaptosomal fraction, although pseudexin B was more active than scutoxin. One monoclonal antibody raised against pseudexin B (#4) had no effect on the enzymatic activity of either pseudexin B or scutoxin. Two other monoclonal antibodies (#3 and #7), also raised against pseudexin B, antagonized the enzymatic activity of pseudexin B and scutoxin. Monoclonal antibody #3 was more effective than #7 in reducing the amount of acetylcholine released by the toxins, whereas #7 was more effective than #3 in reducing fatty acid production. Although antibody #3 caused complete inhibition of phospholipase A2 activity of pseudexin B on purified substrates, it only reduced phospholipase A2 activity by 35% in synaptosomes. These findings support the hypothesis that gross phospholipase A2 activity does not play a role in stimulation of acetylcholine release by the presynaptically-acting phospholipase A2 neurotoxins.

Proteins isolated from the venom of the common tiger snake (Notechis scutatus scutatus) promote hypotension and hemorrhage

Notechis scutatus scutatus venom contains several toxic acidic proteins called HTa-i which promote hypotension and hemorrhage in mice. They have apparent mol. wts in the 18,000-21,000 range, i.v. LD50 values between 0.5 and 1.5 micrograms/g, and no detectable phospholipase, arginine esterase, proteolytic or hemolytic activities. A polyclonal antibody raised against HTg binds to other purified proteins, suggesting that they are isoforms of the same protein. Many other elapid crude venoms contain proteins which recognize the polyclonal antibody raised against HTg. Crotalid and viperid crude venoms do not recognize this antibody, although some of their component proteins are known to exhibit hypotensive and hemorrhagic activities. A combination of gel-filtration on Sephacryl S-200, cation-exchange and anion-exchange chromatography allows isolation of the N. s. scutatus proteins in high purity. They are the first hypotension-inducing proteins to be purified from an Australian elapid.

Identification of the site at which phospholipase A2 neurotoxins localize to produce their neuromuscular blocking effects

Experiments were conducted on mouse hemidiaphragm preparations using five phospholipase A2 neurotoxins of differing chain structures and antigenicities [notexin (one chain); crotoxin (two chains not covalently bound), beta-bungarotoxin (two chains covalently bound); taipoxin (three chains), and textilotoxin (five chains; one copy each of three chains and two copies of a fourth chain)]. Three clostridial neurotoxins (botulinum neurotoxin types A and B, and tetanus toxin) were used in comparison experiments. Phospholipase A2 neurotoxins produced concentration-dependent blockade of neuromuscular transmission. There was no obvious relationship between chain structure and potency, but there was an indication of a relationship between chain structure and binding. The binding of notexin was substantially reversible, the binding of crotoxin was slightly reversible, and the binding of beta-bungarotoxin, taipoxin and textilotoxin was poorly reversible. Experiments with neutralizing antibodies indicated that phospholipase A2 neurotoxins became associated with binding sites on or near the cell surface. This binding did not produce neuromuscular blockade. When exposed to physiological temperatures and nerve stimulation, bound toxin disappeared from accessibility to neutralizing antibody. This finding suggests that there was some form of molecular rearrangement. The two most likely possibilities are: (1) there was a change in the conformation of the toxin molecule, or (2) there was a change in the relationship between the toxin and the membrane. The molecular rearrangement step did not produce neuromuscular blockade. At a later time there was onset of paralysis; the amount of time necessary for onset of blockade was a function of toxin concentration. Phospholipase A2 neurotoxins were not antagonized by drugs that inhibit receptor-mediated endocytosis. In addition, phospholipase A2 neurotoxins did not display the pH-induced conformational changes that are typical of other endocytosed proteins, such as clostridial neurotoxins. However, phospholipase A2 neurotoxins were antagonized by strontium, and this antagonism was expressed against toxins that were free in solution and toxins that were bound to the cell surface. Limited antagonism was expressed after toxins had undergone molecular rearrangement, and no antagonism was expressed after toxin-induced neuromuscular blockade. The cumulative data suggest that phospholipase A2 neurotoxins are not internalized to produce their poisoning effects. These toxins appear to act on the plasma membrane, and this is the site at which they initiate the events that culminate in neuromuscular blockade.

Notechis 11'2, a non-toxic phospholipase A2 from the venom of Notechis scutatus scutatus

Previously, we deduced the amino acid sequence of a novel phospholipase-A2-like protein (PLA2) from the nucleotide sequence of a cDNA isolated from a library prepared from the venom gland of the Australian elapid Notechis scutatus scutatus. The corresponding protein has now been identified, purified from the venom and named Notechis 11'2. Its complete amino acid sequence has been determined by automated Edman degradation of both the whole protein and peptides generated by Staphylococcus aureus protease digestion and chemical cleavage at a tryptophan residue. As predicted from its sequence which contains all the residues putatively required for PLA2 activity, Notechis 11'2 exhibits an esterase activity, preferentially against neutral phospholipids. However, despite its sequence homology with other highly toxic PLA2 present in the venom of Notechis scutatus scutatus, notechis 11'2 has no lethal activity. This observation further supports the view that the lethal activity of PLA2 from Notechis scutatus scutatus is not due to the esterasic activity only.

Comparative chromatography of Brazilian coral snake (Micrurus) venoms

1. Elution profiles of 11 coral snake venoms, including those of Micrurus albicinctus, M. corallinus, M. frontalis altirostris, M. f. brasiliensis, M. f. frontalis, M. fulvius fulvius, M. ibiboboca, M. lemniscatus ssp., M. rondonianus, M. spixii spixii and M. surinamensis surinamensis, were compared using high performance gel filtration and reverse phase media. 2. Micrurus venom profiles were compared with those of "outgroup" taxa Bothrops moojeni, Naja naja kaouthia and Bungarus multicinctus. 3. Purified elapid venom constituents were also chromatographed under identical conditions in order to suggest possible identities of Micrurus venom constituents. 4. Masses of various components were confirmed by mass spectrometry. 5. Phospholipase constituents in three venoms were positively identified based on their reverse phase chromatograms. 6. Venoms of M. rondonianus and M. s. surinamensis are shown to be significantly different in their peptide composition from other Micrurus venoms.

Specific binding of crotoxin to brain synaptosomes and synaptosomal membranes

Crotoxin, the presynaptic neurotoxin from Crotalus durissus terrificus, was iodinated and used to demonstrate high affinity, specific binding to guinea-pig (Cavia porcellus) brain synaptosomes and synaptosomal membrane fragments. 125I-crotoxin binding to the membrane fragments displays two binding plateaus, (Kd1 = 4 nM and Kd2 = 87 nM, Bmax1 = 2 and Bmax2 = 4 pmoles/mg membrane protein), but binding to whole synaptosomes revealed only one plateau (Kd = 2 nM and Bmax = 5 pmoles/mg membrane protein). Rosenthal analyses of Scatchard plots yielded similar binding constants in the presence or absence of 0.025% Triton X-100. In addition to equilibrium analyses, kinetic analyses of 125I-crotoxin binding to synaptosomal membrane fragments gave a Kd-value of 3 nM. The Kd value was not significantly changed by the exclusion of added calcium, but the binding site number was lowered. Crotoxin binding was inhibited by the acidic subunit of crotoxin and several presynaptic neurotoxins, which were classified according to their inhibitory properties as, strong (acidic subunit of crotoxin, Mojave toxin, concolor toxin, taipoxin and pseudexin), moderate (ammodytoxin A and textilotoxin), weak (notexin and scutoxin A), very weak (notechis II-5) and non-inhibitory (basic subunit of crotoxin, beta-bungarotoxin, Crotalus atrox and porcine pancreatic phospholipases A2, dendrotoxin, and notechis III-4). Purified acidic subunit of crotoxin, the most potent competitor of crotoxin binding, was somewhat more competitive than intact crotoxin and the other strong inhibitors on a molar basis. Strong, moderate and weak inhibitor groups each differed from the preceding group by requiring about a ten fold increase in concentration to effect a 50% inhibition of crotoxin binding. The weak group was therefore at least two-orders of magnitude less effective than the strong inhibition shown by the acidic subunit of crotoxin. Treatment of synaptosomal membranes with protease K lowered 125I-crotoxin binding, whereas treatment with trypsin did not. Iodinated, phospholipase A2 from C. atrox venom showed no specific binding to whole synaptosomes. Our results demonstrate the presence and describe some of the properties of high affinity, specific binding sites in brain tissue for crotoxin and related presynaptic neurotoxins.