Amino acid sequence of a presynaptic neurotoxin from the venom of Notechis scutatus scutatus (Australian tiger snake)

Further observations on the pathological responses of rat skeletal muscle to toxins isolated from the venom of the Australian tiger snake, Notechis scutatus scutatus

1. Some aspects of the response of mammalian skeletal muscle following the injection of purified toxins from the venom of the Australian tiger snake, Notechis scutatus scutatus, are described. 2. The toxins used were notexin, notechis II-5, notechis II-1 and a modified form of notexin (PBP-notexin). They were injected into the dorso-lateral aspect of one himd limb so that the soleus muscle would be exposed to the toxins. 3. Within 1 h after the injection of notexin, the soleus muscles were oedematous and by 3--6 h, polymorphonuclear leucocytes had entered the interstitial spaces. The invasion of necrotic muscle fibers was extensive by this time. Muscle spindles appeared relatively unaffected by the toxin. 4. The muscle regenerated via myoblasts at 2--3 days to myotubes at 3--5 days, immature muscle fibers at 7--14 days and fully differentiated muscle fibers by 21--28 days. Even after 6 months, however, the nuclei of many muscle fibres remained in a central position. 5. A second component of Australian tiger snake venom was also found to be myotoxic. It was slightly less potent than notexin, but caused qualitatively similar damage to that caused by notexin. It was identified as notechis II-5. A third fraction, notechis II-1, was found to be inactive. 6. Notexin could be neutralized by incubation with tiger snake antivenene; the simultaneous injection of antivenene with notexin did not afford complete protection against muscle damage.

Some biochemical responses of rat skeletal muscle to a single subcutaneous injection of a toxin (notexin) isolated from the venom of the Australian tiger snake Notechis scutatus scutatus

1. Some biochemical responses of mammalian skeletal muscle to a single subcutaneous injection of a purified toxin from the venom of the Australian tiger snake, Notechis scutatus scutatus, have been investigated to determine the role of changes in peptide hydrolase enzymes in the muscle wasting caused by notexin administration. 2. Within 6 h of injection, serum creatine kinase activity was increased by five- to ten-fold, and remained elevated for at least 24 h. 3. There was an initial inflammatory response in the muscle adjacent to the site of injection; by 12 h after injection, muscle wet weight increased by 60%. 4. After the initial increase, wet weight fell to about 50% of normal at 7 days. Normal wet weight was achieved by 20 days after the injection. Over the period 1-20 days after the injection of the toxin, the changes in wet weight were mirrored by changes in non-collagen protein content. 5. The activities of cathepsin B and acid proteinase were increased following the injection of the toxin. By 2 days after injection, there was a ten-fold increase in the activity of cathepsin B, and a seven-fold increase in the activity of acid proteinase. The activity of both enzymes become normal by 20 days. 6. Experiments utilizing a variety of cytotoxic drugs suggested that the acid proteinase and cathespin B are primarily located within invading phagocytic cells. 7. The results are discussed with reference to the previously described pathology of toxin-damaged skeletal muscle.

The primary structure of bovine pancreatic phospholipase A2

The complete amino acid sequence of bovine phospholipase A2 (EC 3.1.1.4) was determined. This enzyme has a molecular weight of 13 782 and consists of a single polypeptide chain of 123 amino acids cross-linked by seven disulfide bridges. The main fragmentation of the polypeptide chain was accomplished by digesting the reduced and thialaminated derivative of the protein with trypsin, staphylococcal protease and cyanogen bromide. A number of chymotryptic peptides were used for alignment and to obtain overlaps of at least two residues. The sequence of the peptides was determined by Edman degradation by means of direct phenylthiohydantoin identification in combination with identification as dansyl amino acids. Although 71% of all residues of phospholipase A2 from bovine, porcine and equine sources are conserved, bovine phospholipase A2 differs from the others by the total number of residues and by substitutions at 20 (porcine) and 33 (equine) positions.

Neurotoxins of Bungarus multicinctus vernom. Purification and partial characterization

The purification to homogeneity of nine neurotoxic components of the venom of Bungarus multicinctus is described. The purified components include alpha-bungarotoxin and two other alpha-type synaptic toxins and beta-bungarotoxin and five other beta-type synaptic toxins. The purified toxins have been characterized by electrophoresis, isoelectric focusing, amino acid analysis, and N-terminal amino acid determination. The alpha-type synaptic neurotoxins constitute a discrete class with molecular weights of 7000-8500, isoelectric points (pI) of 9.0-9.2, and N-terminal isoleucine or methionine. The beta-type synaptic neurotoxins constitute a second group with molecular weights of 20 000-22 000 and pI = 8.8-9.7. Fractions 10 through 13 exhibit a chain structure consisting of a 6000-7000 light chain and a 11 000-15 000 heavy chain apparently covalently stabilized by interchain disulfides. Fractions 9A and 14 were single chains of 11 000-14 000 which resemble the sequenced beta-type synaptic neurotoxin notexin (Halpert, J., and Eaker, D. (1975), J. Biol. Chem. 250, 6990). All of the beta-type synaptic toxins have a single tryptophan and N-terminal aspartic acid or asparagine.

The mode of action at the mouse neuromuscular junction of the phospholipase A-crotapotin complex isolated from venom of the South American rattlesnake

1 Phospholipase A(2)-crotapotin complex (P-C complex) isolated from the venom of Crotalus durissus terrificus induced an irreversible blockade of neuromuscular transmission when twitch tension was measured in the mouse phrenic nerve-hemidiaphragm preparation in vitro at 37 degrees C.2 A similar concentration of the phospholipase A(2) (10 mug/ml) alone did not affect neuromuscular transmission and no priming action was detected on later addition of crotapotin.3 The rate of neuromuscular blockade induced by P-C complex (15 mug/ml) was not altered by raising the frequency of nerve stimulation. Lower temperatures markedly increased the time of onset and reduced the rate of blockade (Q(10) (27-37 degrees C) of 4.4) whilst replacement of Ca by Sr in the medium prevented this activity. These latter results suggest that enzymatic activity is important in the neurotoxicity of the complex.4 A myotoxic action was shown by 30 mug/ml P-C complex and 30 mug/ml phospholipase A(2).5 P-C complex (150 mug) was injected into the tail vein of mice and the intoxicated hemidiaphragm preparation removed for intracellular recording at 25 degrees C.6 In fully intoxicated hemidiaphragms, resting membrane potentials were unaltered and endplate potentials (e.p.ps) varied in average amplitude from zero to less than 3 mV.7 Miniature endplate potential (m.e.p.p.) frequency was lower at fully poisoned endplates than at controls; the frequency rose during a 50 Hz tetanus but was unaffected by either raising external K or the application of the Ca-ionophore A23187.8 E.p.ps were recorded in partially intoxicated hemidiaphragms with (+)-tubocurarine (0.5-1.0 mug/ml) added to prevent contraction. Evoked release was abnormal as 50 Hz tetanus elicited e.p.ps of very variable amplitude, no facilitation of response was shown to paired stimuli, and tetraethylammonium (0.5 mM) failed to increase e.p.p. amplitudes.9 M.e.p.ps and e.p.ps were recorded at partially poisoned endplates in low Ca-high Mg solution. A reduction in the quantal content of evoked transmitter release was observed in comparison with controls.10 M.e.p.ps recorded at partially and at fully intoxicated endplates showed an altered amplitude distribution with a higher proportion of large potentials.11 It is concluded that P-C complex has a presynaptic site of action and may interfere with depolarization-secretion coupling at the motor nerve terminals.

Effects of Sr2+ and Mg2+ on the phospholipase A and the presynaptic neuromuscular blocking actions of beta-bungarotoxin, crotoxin and taipoxin

1.beta-Bungarotoxin, crotoxin and taipoxin, presynaptic neurotoxins of snake venom origin, have about the same phospholipid-splitting activities as a much less toxic cobra phospholipase A2 in the presence of Ca2+ and deoxycholate. 2. Sr2+ was a much less effective activator of the enzymes than is Ca2+, the activation by Sr2+ being only 3-6% for beta-bungarotoxin and crotoxin and 12% for taipoxin. 3. Sr2+ also inhibited the Ca2+ -activated enzymes by 80% in the cases of beta-bungarotoxin and crotoxin, but only 16% in the case of taipoxin. 4. Mg2" had no significant effect on beta-bungarotoxin or crotoxin, but activated taipoxin in the presence or absence of Ca2". 5. In Sr2+ -Tyrode lacking Ca2+ all three toxins exhibited the same immediate depression followed by facilitation in the rat and mouse diaphragms, but the final blocking activity was only 3-10% with beta-bungarotoxin and crotoxin and was 30% with taipoxin. 6. In Sr2+ -Tyrode, increasing in the rate of nerve stimulation had less accelerating effect on the development of neuromuscular block than in Ca2+ -Tyrode for any of the toxins. 7. Removal of Mg2+ from Sr2+ -Tyrode did not diminish the potency of taipoxin in blocking neuromuscular transmission, suggesting that enzyme activity at the outer surface of the axolemma does not contribute to the neuromuscular blocking action. 8. All of the results indicate that there are close correlations between the presynaptic activities of these toxins and their phospholipid-splitting activities in the cationic environment prevailing in the axoplasm. Apparently the final blocking effect of these toxins is due to phospholipase A action within the nerve terminal.

Homology of functionally diverse proteins

Disulphide-rich proteins of widely differing functions were aligned with the aid of their half-cystinyl residues. This led to the grouping of ribonuclease, phospholipase A, lysozyme, snake venom toxins, bee and scorpion venom peptides, and the plant proteins potatoe carboxypeptidase inhibitor, ragweed pollen allergen, mistletoe toxins and pineapple sulfhydryl protease inhibitor into one super-family of proteins. Very few deletions/insertions were needed to effect alignment and probabilities were calculated for random occurrence of the matches that were found.

Naja mossambica mossambica venom. Purification, some properties and the amino acid sequences of three phospholipases A (CM-I, CM-II and CM-III)

Three phospholipases A, CM-I, CM-II and CM-III, were purified from Naja mossambica mossambica venom by gel filtration on Sephadex G-50 followed by ion-exchange chromatography on CM-cellulose. They comprise each 118 amino acid residues and are close-linked by seven intrachain disulphide bridges. The complete primary structure of the three phospholipases A have been elucidated. The sequences and the invariant amino acid residues of CM-I, CM-II and CM-III resemble those of phospholipases A from other snake venoms and also from porcine pancreas. However, the letality (LD50 values) of the three phospholipases A from Naja mossambica mossambica venom, differ among themselves, and are also much higher than the LD100 value encountered for notexin from Notechis scutatus scutatus venom.

Histidine and lysine residues and the activity of phospholipase A2 from the venom of Bitis gabonica

Chemical modification of phospholipase A2 (phosphatide 2-acyl-hydrolase, EC 3.1.1.4) from the venom of gaboon adder (Bitis gabonica) showed that histidine and lysine residues are essential for enzyme activity. Treatment with p-bromophenacyl bromide or pyridoxal 5'-phosphate resulted in the specific covalent modification of one histidine or a total of one lysine residue per molecule of enzyme, respectively, with a concomitant loss of enzyme activity. Competitive protection against modification and inactivation was afforded by the presence of Ca2+ and/or micellar concentrations of substrate analogue, lysophosphatidylcholine. Neither modification caused any significant conformational change, as judged from circular dichroic properties. Amino acid analyses and the alignment of peptides from cyanogen bromide and proteolytic cleavage of modified enzyme preparations delineated His-45 as the only residue modified by p-bromophenacyl bromide. However, pyridoxal 5'-phosphate was shown to have reacted not with a single lysine but with four different ones (residues 11, 33, 58 and 111) in such a manner that an overall stoichiometry of one modified lysine residue/molecule enzyme resulted. Apparently, the essential function of lysine could be fulfilled by any one out of these four residues.

The primary structure of phospholipase A2 from porcine pancreas. A reinvestigation

The primary structure of porcine pancreatic phospholipase A2 (EC 3.1.1.4) has been reinvestigated. A number of modifications have been introduced including the addition of a 7th disulfide bridge. The structure which is presented here shows a high degree of homology with the amino acid sequence of snake venom and horse pancreas phospholipase A2.

Relationship between the neurotoxicity and phospholipase A activity of beta-bungarotoxin

beta-Bungarotoxin is a protein neurotoxin that exhibits phospholipase A activity. The neurotoxin and phospholipase A activities were similarly affected by several agents that modify proteins in various ways. Both activities were very thermostable and resistant to treatment with proteases, 6 M urea, phenylmethylsulfonyl fluoride, and N-acetylimidazole. Both activities were sensitive to beta-mercaptoethanol, and to N-bromosuccinimide and ethoxyformic anhydride, which previously had been shown to inactivate rattlesnake venom phospholipase A by modifying selective amino acids. Dihexanoyllecithin, which acts as a substrate for the beta-bungarotoxin phospholipase A, and Ca2+ protect the phospholipase A activity against inactivation by ethoxyformic anhydride but not the neurotoxicity. Treatment of intact membranes with proteases reduces hydrolysis of the membranes lipids by the toxin phospholipase A.

Taipoxin, an extremely potent presynaptic neurotoxin from the venom of the australian snake taipan (Oxyuranus s. scutellatus). Isolation, characterization, quaternary structure and pharmacological properties

Taipoxin (taipan toxin), purified from the venom of the Australian taipan (Oxyuranus s. scutellatus) by gel filtration on Sephadex G-75 followed by column zone electrophoresis, is the most lethal neurotoxin yet isolated from any snake venom. The LD50 is 2 mug/kg in the mouse. The main physiological effect is a gradual reduction to complete stop of evoked and spontaneous release of acetylcholine from motor nerve terminals. Intoxicated animals die of asphyxia caused by neuromuscular blockage of the respiratory muscles. Taipoxin is a moderately acidic sialo-glycoprotein (pI 5) with a molecular weight of 45 600 as calculated from composition data or 46 800 as determined by meniscus depletion sedimentation equilibrium. Taipoxin is a 1:1:1 ternary complex of subunits designated alpha, beta and gamma which dissociate completely at low pH and high ionic strength or in 6 M guanidine hydrochloride. The dissociation by guanidine at neutral pH is reversible, while the acid-induced dissociation is not . The alpha and beta components consist of 120 amino acid residues cross-linked by seven disulfide bridges, whereas the gamma component has 135 residues and eight disulfides. The very basic (pI Greater than 10) alpha component contains 13 residues of arginine and is the only subunit displaying lethal neurotoxicity (mouse LD50 approximately 300 mug/kg). The neutral beta fraction was separated by ion-exchange chromatography into two iso-component, beta 1 and beta2, which differ slightly in amino acid composition. The very acidic gamma component contains all of the carbohydrate, which includes 4-5 residues of sialic aid. The three subunits are homologous in sequence although the gamma component is eight residues longer on the N-terminus and must also contain extra amino acids elsewhere.

The effects of taipoxin and notexin on the function and fine structure of the murine neuromuscular junction

The isolated neurotoxins taipoxin and notexin from the venoms of the Elapidae, Oxyuranus scutellatus and Notechis scutatus scutatus respectively cause a neuromuscular block when administered to the mouse in vivo or to the phrenic nerve-hemidiaphragm preparation in vitro. The block is preceded by a latency period during which the toxins bind irreversibly to the nerve. The period is shortened by nerve activity. The frequency of the miniature end-plate potentials is gradually reduced, almost to zero, and their amplitude distribution is altered; small and very large miniature endplate potentials appearing. Ultrastructurally the endplates are altered in the presynaptic portion but not in the postsynaptic part. In an early stage of poisoning the axolemma has an increased number of omega-shaped indentations similar in size to synaptic vesicles. At a later stage, when the animals die of respiratory paralysis, the axolemmal indentations are more numerous and the synaptic vesicles greatly reduced in number, the remaining vesicles having a variable and frequently larger than normal size. When impulse activity in the phrenic nerve is stopped by cutting the nerve before the administration of toxin there is no reduction in the number of synaptic vesicles, only the appearance of an increased number of axolemmal indentations. It is suggested that taipoxin and notexin irreversibly interfere with the formation of synaptic vesicles by arresting vesicle membrane recycling at the level of the axolemma. When the pre-existing store of vesicles is depleted, by nerve activity, a neuromuscular block results.