Polypeptides from snake venoms which act on nerve and muscle

Using Reduced Amino Acid Alphabet and Biological Properties to Analyze and Predict Animal Neurotoxin Protein

AIMS

Because of the high affinity of these animal neurotoxin proteins for some special target site, they were usually used as pharmacological tools and therapeutic agents in medicine to gain deep insights into the function of the nervous system.

BACKGROUND AND OBJECTIVE

The animal neurotoxin proteins are one of the most common functional groups among the animal toxin proteins. Thus, it was very important to characterize and predict the animal neurotoxin proteins.

METHODS

In this study, the differences between the animal neurotoxin proteins and non-toxin proteins were analyzed.

RESULT

Significant differences were found between them. In addition, the support vector machine was proposed to predict the animal neurotoxin proteins. The predictive results of our classifier achieved the overall accuracy of 96.46%. Furthermore, the random forest and k-nearest neighbors were applied to predict the animal neurotoxin proteins.

CONCLUSION

The compared results indicated that the predictive performances of our classifier were better than other two algorithms.

Prediction of presynaptic and postsynaptic neurotoxins by combining various Chou's pseudo components

Presynaptic and postsynaptic neurotoxins are two groups of neurotoxins. Identification of presynaptic and postsynaptic neurotoxins is an important work for numerous newly found toxins. It is both costly and time consuming to determine these two neurotoxins by experimental methods. As a complement, using computational methods for predicting presynaptic and postsynaptic neurotoxins could provide some useful information in a timely manner. In this study, we described four algorithms for predicting presynaptic and postsynaptic neurotoxins from sequence driven features by using Increment of Diversity (ID), Multinomial Naive Bayes Classifier (MNBC), Random Forest (RF), and K-nearest Neighbours Classifier (IBK). Each protein sequence was encoded by pseudo amino acid (PseAA) compositions and three biological motif features, including MEME, Prosite and InterPro motif features. The Maximum Relevance Minimum Redundancy (MRMR) feature selection method was used to rank the PseAA compositions and the 50 top ranked features were selected to improve the prediction accuracy. The PseAA compositions and three kinds of biological motif features were combined and 12 different parameters that defined as P1-P12 were selected as the input parameters of ID, MNBC, RF, and IBK. The prediction results obtained in this study were significantly better than those of previously developed methods.

Toxin insights into nicotinic acetylcholine receptors

Venomous species have evolved cocktails of bioactive peptides to facilitate prey capture. Given their often exquisite potency and target selectivity, venom peptides provide unique biochemical tools for probing the function of membrane proteins at the molecular level. In the field of the nicotinic acetylcholine receptors (nAChRs), the subtype specific snake alpha-neurotoxins and cone snail alpha-conotoxins have been widely used to probe receptor structure and function in native tissues and recombinant systems. However, only recently has it been possible to generate an accurate molecular view of these nAChR-toxin interactions. Crystal structures of AChBP, a homologue of the nAChR ligand binding domain, have now been solved in complex with alpha-cobratoxin, alpha-conotoxin PnIA and alpha-conotoxin ImI. The orientation of all three toxins in the ACh binding site confirms many of the predictions obtained from mutagenesis and docking simulations on homology models of mammalian nAChR. The precise understanding of the molecular determinants of these complexes is expected to contribute to the development of more selective nAChR modulators. In this commentary, we review the structural data on nAChR-toxin interactions and discuss their implications for the design of novel ligands acting at the nAChR.

Animal experimentation in snake venom research and in vitro alternatives

Current experimental techniques used in snake venom research (with and without the use of animals) are reviewed. The emphasis is on the reduction of the use of animals in the development of antivenoms for the clinical treatment of snakebite. Diagnostic and research techniques for the major pathologies of envenoming are described and those using animals are contrasted with non-sentient methods where possible. In particular, LD50 and ED50 assays using animals (in vivo) and fertilised eggs (in vivo, non-sentient) are compared as well as in vitro procedures (ELISA and haemolytic test) for ED50 estimations. The social context of antivenom production, supply and demand is outlined together with the consequent tension between the benefits derived and the increase in opposition to experiments on animals. Stringent regulations governing the use of animals, limited research funds and public pressure all focus the need for progress towards non-animal, or non-sentient, research methods. Some achievements are noted but success is hampered by lack of detailed knowledge of the many constituents of venom which have to be assessed as a whole rather than individually. The only way to evaluate the net pathological effect of venom is to use a living system, usually a rodent, and similarly, the efficacy of antivenoms is also measured in vivo. The pre-clinical testing of antivenoms in animals is therefore a legal requirement in many countries and is strictly monitored by government authorities. New technologies applied to the characterisation of individual venom proteins should enable novel in vitro assays to be designed thus reducing the number of animals required. In the meantime, the principles of Reduce, Refine and Replace relating to animals in research are increasingly endorsed by those working in the field and the many agencies regulating ethical and research policy.

Neuromuscular effects of candoxin, a novel toxin from the venom of the Malayan krait (Bungarus candidus)

1 Candoxin (MW 7334.6), a novel toxin isolated from the venom of the Malayan krait Bungarus candidus, belongs to the poorly characterized subfamily of nonconventional three-finger toxins present in Elapid venoms. The current study details the pharmacological effects of candoxin at the neuromuscular junction. 2 Candoxin produces a novel pattern of neuromuscular blockade in isolated nerve-muscle preparations and the tibialis anterior muscle of anaesthetized rats. In contrast to the virtually irreversible postsynaptic neuromuscular blockade produced by curaremimetic alpha-neurotoxins, the neuromuscular blockade produced by candoxin was rapidly and completely reversed by washing or by the addition of the anticholinesterase neostigmine. 3 Candoxin also produced significant train-of-four fade during the onset of and recovery from neuromuscular blockade, both, in vitro and in vivo. The fade phenomenon has been attributed to a blockade of putative presynaptic nicotinic acetylcholine receptors (nAChRs) that mediate a positive feedback mechanism and maintain adequate transmitter release during rapid repetitive stimulation. In this respect, candoxin closely resembles the neuromuscular blocking effects of d-tubocurarine, and differs markedly from curaremimetic alpha-neurotoxins that produce little or no fade. 4 Electrophysiological experiments confirmed that candoxin produced a readily reversible blockade (IC(50) approximately 10 nM) of oocyte-expressed muscle (alphabetagammadelta) nAChRs. Like alpha-conotoxin MI, well known for its preferential binding to the alpha/delta interface of the muscle (alphabetagammadelta) nAChR, candoxin also demonstrated a biphasic concentration-response inhibition curve with a high- (IC(50) approximately 2.2 nM) and a low- (IC(50) approximately 98 nM) affinity component, suggesting that it may exhibit differential affinities for the two binding sites on the muscle (alphabetagammadelta) receptor. In contrast, curaremimetic alpha-neurotoxins have been reported to antagonize both binding sites with equal affinity.

What does beta-bungarotoxin do at the neuromuscular junction?

beta-Bungarotoxin from the Taiwan banded krait, Bungarus multicinctus is a basic protein (pI=9.5), with a molecular weight of 21,800 consisting of two different polypeptide subunits. A phospholipase A(2) subunit named the A-chain and a non-phospholipase A(2) subunit named the B-chain, which is homologous to Kunitz protease inhibitors. The A-chain and the B-chain are covalently linked by one disulphide bridge. On mouse hemi-diaphragm nerve-muscle preparations, partially paralysed by lowering the external Ca(2+) concentration, beta-bungarotoxin classically produces triphasic changes in the contraction responses to indirect nerve stimulation. The initial transient inhibition of twitches (phase 1) is followed by a prolonged facilitatory phase (phase 2) and finally a blocking phase (phase 3). These changes in twitch tension are mimicked, to some extent, by similar changes to end plate potential amplitude and miniature end plate potential frequency. The first and second phases are phospholipase-independent and are thought to be due to the B-chain (a dendrotoxin mimetic) binding to or near to voltage-dependent potassium channels. The last phase (phase 3) is phospholipase dependent and is probably due to phospholipase A(2)-mediated destruction of membrane phospholipids in motor nerve terminals.

Successful treatment of neurotoxic king cobra envenomation in Myrtle Beach, South Carolina

The growing trend toward the collection of exotic snakes by private collectors increases the likelihood that emergency physicians will face the challenge of treating an exotic envenomation. We report a case involving a professional reptile handler who sustained an extremity bite from a king cobra (Ophiophagus hannah ). Rapid, progressive neurotoxicity developed as manifested clinically by bulbar and respiratory paralysis requiring endotracheal intubation and mechanical support. After infusion of Thai Red Cross Society monospecific king cobra antivenin, all neurologic sequelae rapidly resolved within 7 hours after the bite. In treating an exotic envenomation, the emergency physician should contact personnel at the regional poison control center or local zoo. Both are prepared to assist the physician by facilitating the timely acquisition of exotic antivenins and by arranging consultation with experts experienced in the management and treatment of exotic envenomations.

Comparison of the effects of four dendrotoxin peptides, 4-aminopyridine and tetraethylammonium on the electrically evoked [3H]noradrenaline release from rat hippocampus

We have examined the effects of four dendrotoxin (DaTX) peptides, alpha-, beta-, gamma- and delta-DaTX, separated from the venom of the green mamba (Dendroaspis angusticeps), on field stimulation-evoked [3H]noradrenaline (NA) release from rat hippocampus and compared their effects with those of two other inhibitors of K+ channels, 4-aminopyridine (4-AP) and tetraethylammonium (TEA). 4-AP (10-300 microM) and TEA (0.1-5 mM) facilitated the evoked [3H]NA release in a concentration-dependent manner. The evoked [3H]NA release was reduced to about half by alpha 2-adrenoceptor stimulation (UK 14,304; 100 nM) and this reduction was antagonized by 4-AP (10-100 microM), whereas TEA even at 5 mM was a poor inhibitor of alpha 2-effects. alpha-DaTX (10-200 nM) mimicked 4-AP in increasing the electrically evoked [3H]NA release and diminishing the inhibitory effects of UK 14,304 in a concentration-dependent manner. delta-DaTX did not itself alter the electrically evoked [3H]NA release, but at 200 nM, it reduced the effects of alpha 2-receptor stimulation. beta- and gamma-DaTX (up to 200 nM) had no significant effects. 4-AP, 3,4-diaminopyridine (3,4-DAP), TEA and the four dendrotoxins displaced the binding of [3H]p-aminoclonidine ([3H]PAC) from alpha 2-receptors. The IC50 values were 6.6 x 10(-4), 1.42 x 10(-3), 5.6 x 10(-2) for 4-AP, 3,4-DAP and TEA, respectively, and 3.19 x 10(-6) M for alpha-DaTX. Thus, their potency as inhibitors of alpha 2-receptors is apparently too low to account alone for the antagonism by K+ channel inhibitors of alpha 2-effects on NA release.(ABSTRACT TRUNCATED AT 250 WORDS)

Myotoxic components of snake venoms: their biochemical and biological activities

Necrosis of skeletal muscle is produced by two types of snake venom components: single chain peptides consisting of 42-44 amino acid residues and phospholipases A2 representing either single chain proteins or existing as complexes of several enzyme subunits or combined with other nonenzymatic proteins. Vacuolation, lysis and necrosis of skeletal muscle cells are the major pathological effects of these myotoxins. Although the exact mode of action of these toxins is not clear, interactions with the plasma membrane leading to permeability changes for ions and to their complete destruction is evident. The high specificities of some venom phospholipases A2 for skeletal muscle cells suggest a specific binding to certain membrane receptors; however, an enzymatic action on membranes may also be involved.

Potassium channel blocking actions of beta-bungarotoxin and related toxins on mouse and frog motor nerve terminals

1. beta-Bungarotoxin and other snake toxins with phospholipase activity augment acetylcholine release evoked from mouse motor nerve terminals before they produce blockade. This action of the toxins is independent of their phospholipase A2 activity, but the underlying mechanism for the facilitation of release is unclear. To determine whether the toxins affect ionic currents at motor nerve terminals, extracellular recordings were made from perineural sheaths of motor nerves innervating mouse triangularis sterni muscles. 2. Perineural waveforms had a characteristic shape, with two major negative deflections, the first being associated with nodal Na+ currents and the second with terminal K+ currents. Block of the K+ currents revealed a Ca2+-dependent component. 3. During the facilitatory phase of its action, beta-bungarotoxin (150 nM) reduced the second negative component of the perineural waveform by 30-50%. 4. The reduction could be a consequence of a decreased K+ ion contribution or of an increase in the current carried by Ca2+. As beta-bungarotoxin had similar effects in solutions which contained no added Ca2+, it is unlikely to be acting on the Ca2+ current. Also, it is unlikely to be blocking the Ca2+-activated K+ current, which is suppressed in zero Ca2+ conditions. 5. Other prejunctionally active snake toxins (taipoxin, notexin and crotoxin) had similar effects to those of beta-bungarotoxin, but a similar basic phospholipase of low toxicity from cobra venom had no effect. 6. Thus, beta-bungarotoxin and related toxins block a fraction of the K+ current in the motor nerve terminals of mouse preparations. Such an effect could explain the facilitation of acetylcholine release caused by these toxins before the onset of presynaptic blockade. 7. In frog cutaneous pectoris preparations, f-bungarotoxin reduced endplate potential amplitude but had little effect on perineural waveforms. Therefore, the consequences of toxin binding must be different in frog terminals.