Protein snake neurotoxin

Another example of a quantal repeat—but with considerable variation in sequence—is seen in the keratin-associated proteins (KAPs). In sheep, these display pentapeptide and decapeptide consensus repeats of the form G—G—Q—P—S/T and C-C-Q/R—P—S/T—C/S/T—C—Q—P/T—S, respectively (Parry et al., 1979). Some of the positions, as indicated by the presence of a consensus sequence, contain residues that occur much more frequently than others, but the absolute conservation of a residue in any position is not observed. The decapeptide consists of a pair of five-residue repeats closely related, but different to that displayed by the pentapeptide. Although the repeats have an undetermined structure, the similarity of the repeat to a sequence in snake neurotoxin suggests that the pentapeptides will adopt a closed loop conformation stabilized by a disulphide bond between cysteine residues four apart (Fig. 5 Fraser et al., 1988 Parry et al, 1979). Relative freedom of rotation about the single bond connecting disulphide-bonded knots would give rise to the concept of a linear array of knots that can fold up to form a variety of tertiary structures. The KAPS display imperfect disulphide stabilization of knots and have interacting... 

Fig. 5. Predicted conformation of the pentapeptide repeat C-X-Y-Z-C in trichocyte keratin-associated proteins. Glutamine and arginine residues are found commonly in the X position, prolines in the Yposition, and serines and threonines in the Z position. The structure is based on the known conformation of a similar repeat in snake neurotoxin. The model shows a disulphide bond-stabilized /5-bend with a potential hydrogen bond (dotted). A string of these /5-bends, linked by bonds about which there is relatively free rotation, has been proposed as a model for this important family of matrix proteins in trichocyte keratin (Fraser et al, 1988). Figure from Fraser et al (1988) with permission from Elsevier.

One major protein, MW 40,000, is labeled labeling is blocked by reversible cholinergic ligands or snake neurotoxins... 

Almost aU publications on the metabolites of marine reptiles are devoted to snake venoms. Like their terrestrial homologs, these venoms are mixtures of proteins. The most studied are netirotoxins, particularly erabutoxins A and B, isolated from species of the genus Laticauda, the amino acid sequences of which have been determined (Gttinea, Tamiya, and Cogger, 1983 Tamiya et al., 1983). The toxic sites of snake neurotoxin molecules from marine and land snakes always include a number of invariant amino adds (Menez et al., 1986). 

Snake neurotoxins are the main toxic proteins of cobra, krait, tiger snake and sea snake venoms which block neuromuscular transmission and cause animals death of respiratory paralysis. Snake neurotoxins are classified into two distinct types, postsynaptic and presynaptic neurotoxins, in relation to the neuromuscular junction. Postsynaptic neurotoxins bind specifically to nicotinic acetylcholine receptor (AChR) at the motor endplate and produce a nondepolarizing block of neuromuscular transmission. Presynaptic neurotoxins block the release of acetylcholine from the presynaptic motor nerve terminals. 

Since predators of snakes (and humans) have to deal with snake venoms as defenses, they are included here, even though they serve in predation. Snake venoms are primarily enzymes (proteins), especially of the phospholipase A2 type, which breaks down cell membrane phospholipids hydrolytically. Other snake venoms such as cobrotoxin contain peptides with 60-70 amino acid residues. Pharmacologically, they have neurotoxic, cytotoxic, anticoagulant, and other effects. The neurotoxins, in turn, can have pre- or postsynaptic effects. Snake venoms with both neurotoxic and hemolytic effects on the heart are known as cardiotoxins. Cytotoxins attach to the cells of blood vessels and cause hemorrhage. Snake venom factors may stimulate or inhibit blood clotting. Finally, platelet-active factors can contribute to hemorrhage. 

Snakes Phospholipases A2 Proteins, peptides (cobrotoxin), amino acids Neurotoxins... 

Use of Toxin Binding to Purify a Channel Protein a-Bungarotoxin is a powerful neurotoxin found in the venom of a poisonous snake (Bungarus multicinctus). It binds with high specificity to the nicotinic acetylcholine receptor (AChR) protein and prevents the ion channel from opening. This interaction was used to purify AChR from the electric organ of torpedo fish. 

Black Widow spider venom contains several different protein fractions. The most significant component of the venom is the neurotoxin, a-latrotoxin. This neurotoxin acts at the presynaptic membrane of the neuronal and the neuromuscular junctions. The binding of the a-latrotoxin results in the opening of nonspecific cation channels, a massive influx of calcium, release of acetylcholine and norepinephrine and decreased uptake of the neurotransmitter. The neurotransmitter release is most likely responsible for hypertension, muscle fasciculations, and spasms frequently experienced by victims of a bite. Later, generalized muscle weakness and labored breathing may develop in severe cases. While the venom of the black widow spider has been characterized as being more potent than that of many poisonous snakes, the small amount of venom injected limits the degree of toxicity. 

Most venoms are mixtures of dozens of compounds, and the active toxic ingredients are proteins that wreak havoc on the recipient in a variety of ways. While the exact enzymes vary from species to species, and even geographically within a species, many snake venoms contain some sort of neurotoxins which block signals sent through your nervous system, leading to numbness or even paralysis. 

Most snake venom contains proteins, which act either as a neurotoxin or a cardiotoxin. They paralyse the muscular system and lead to cardiac arrest. Apart... 

One of the most favourable group of proteins for such study is the so-called short neurotoxins isolated from elapidae and hydrophidae snake venom(21). They consist of only 60-62 amino acid residues with four disulphide bridges, they possess higly stable conformations in solution(22) and have an abundant set of homologs(23)... 

CONTEXT The secondary structure of a protein is crucial to its biological activity, whether for good or ill. Snake venoms consist of saliva with a high proportion of toxic proteins. Cobra venom in particular acts on the victim by means of neurotoxins, proteins that attack the nervous system, in this case by blocking the acetylcholine receptors on the membranes of muscle cells. Normally, when acetylcholine... 

Venoms are usually protein molecules secreted by different animals from vertebrate and invertebrate species, including snakes, amphibians, bees, arthropods, fish, and gastropods. Under this definition are toxic products with different structures, most of them protein molecules with enzymatic effects, such as the snake-secreted toxins or ion channels modulators, the conotoxins produced by gastropods, while others are alkaloids with similar structure and effect as marine toxins, as is the case of batrachotoxin secreted by frogs. In this family of compounds is also included the tetrodotoxin (TTX) group, a potent neurotoxin found in puffer and tetraodontiforme fish and... 

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