Taicatoxin
Encyclopedia
Taicatoxin is a snake toxin
that blocks voltage-dependent L-type calcium channel
s and small conductance Ca2+-activated K+ channels
. The name taicatoxin (TAIpan + CAlcium + TOXIN) is derived from its natural source, the taipan
snake, the site of its action, calcium channel
s, and from its function as a toxin
. Taicatoxin was isolated from the venom of Australian taipan snake, Oxyuranus scutellatus scutellatus. TCX is a secreted protein
, produced in the venom
gland of the snake.
analysis, TCX was determined to be a complex held together by non-covalent forces
of the following three polypeptides in a stoichiometry
of 1:1:4 respectively:
The active complex was isolated by ion exchange chromatography
through DE-Cellulose and two steps of Cm-Cellulose chromatography at pH = 4.7 and pH = 6.0, respectively. It migrates in beta-alanine-acetate-urea gel electrophoresis
as a single compound. The phospholipase activity can be separated by affinity chromatography, using a phospholipid analog (PC-Sepharose). The alpha-neurotoxin-like peptide can be separated from the protease inhibitor, Sephadex
G-50 gel filtration chromatography can be used, in the presence of high salt (1M NaCl) and alkaline conditions (pH = 8.2). The amino sequence of the protease inhibitor was determined by using the automatic Edman degradation
method.
It has a high affinity for the 125I-apamin
acceptor-binding sites of the rat synaptosomal membranes (Ki = 1.45±0.22 nM) and blocks affinity-labeling of a 33-kDa 125I-apamin-binding polypeptide. Other neurotoxins that act on the calcium channels are calcicludine
, calciseptine, ω-conotoxin
, ω-agatoxin
.
, decreasing the duration and the concentration parameters in the heart muscle cells. It has been seen that the 16-kDa subunit exhibits phospholipase activity, inducing a release of acyl CoA and acyl carnitine, fact which has a negative effect on cell’s integrity and function. TCX is involved in the outer hair cell motility
too, by blocking the calcium traffic and preventing the cell shortening and elongation. Taicatoxin has an inhibitory effect by reducing the affinity of 125I-apamin for its acceptor and not by alteration of the acceptor binding site density.
Pretreatment with taicatoxin (0.19 μM) on the outer hair cells of guinea pig
prevented the cell shortening induced by high K+ (50 mM) and the cell elongation induced by ionomycine (10 μM). This is because taicatoxin blocks the calcium influx through the calcium channels in the cell’s membrane.
50 nM of taicatoxin blocks the apamin-sensitive after-hyperpolarizing slow tail K+ currents in rat chromaffin cells, but not immediately; instead, 5 μM of this toxin immediately blocks the ISK(Ca) tail current.
It has been shown that taicatoxin blocks the calcium currents in heart cells with IC50 between 10-500 nM. Also was seen to evoke severe arrhythmias and prolonged changes in the intercellular electrical coupling.
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
that blocks voltage-dependent L-type calcium channel
L-type calcium channel
The L-type calcium channel is a type of voltage-dependent calcium channel. "L" stands for long-lasting referring to the length of activation. Like the others of this class, the α1 subunit is the one that determines most of the channel's properties....
s and small conductance Ca2+-activated K+ channels
SK channel
SK channels are a subfamily of Ca2+-activated K+ channels. They are so called because of their small single channel conductance, ~10 pS. SK channels are a type of ion channel allowing potassium cations to cross the cell membrane and are activated by an increase in the concentration of...
. The name taicatoxin (TAIpan + CAlcium + TOXIN) is derived from its natural source, the taipan
Taipan
The taipans are a genus of large, fast, highly venomous Australasian snakes of the elapid family.-Overview:The taipan was named by Donald Thomson after the word used by the Wik-Mungkan Aboriginal people of central Cape York Peninsula, Queensland, Australia.There are three known species: the coastal...
snake, the site of its action, calcium channel
Calcium channel
A Calcium channel is an ion channel which displays selective permeability to calcium ions. It is sometimes synonymous as voltage-dependent calcium channel, although there are also ligand-gated calcium channels.-Comparison tables:...
s, and from its function as a toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
. Taicatoxin was isolated from the venom of Australian taipan snake, Oxyuranus scutellatus scutellatus. TCX is a secreted protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
, produced in the venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
gland of the snake.
Chemistry
Through SDS-PAGESDS-PAGE
SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis, describes a collection of related techniques widely used in biochemistry, forensics, genetics and molecular biology to separate proteins according to their electrophoretic mobility...
analysis, TCX was determined to be a complex held together by non-covalent forces
Noncovalent bonding
A noncovalent bond is a type of chemical bond, typically between macromolecules, that does not involve the sharing of pairs of electrons, but rather involves more dispersed variations of electromagnetic interactions. The noncovalent bond is the dominant type of bond between supermolecules in...
of the following three polypeptides in a stoichiometry
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
of 1:1:4 respectively:
- a α-neurotoxinNeurotoxinA neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
-like peptidePeptidePeptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
(8 kDa), - a neurotoxic phospholipasePhospholipaseA phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. There are four major classes, termed A, B, C and D, distinguished by the type of reaction which they catalyze:*Phospholipase A...
(16 kDa; UniProtUniProtUniProt is a comprehensive, high-quality and freely accessible database of protein sequence and functional information, many of which are derived from genome sequencing projects...
), and - a serine protease inhibitor (7 kDa; UniProtUniProtUniProt is a comprehensive, high-quality and freely accessible database of protein sequence and functional information, many of which are derived from genome sequencing projects...
).
The active complex was isolated by ion exchange chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
through DE-Cellulose and two steps of Cm-Cellulose chromatography at pH = 4.7 and pH = 6.0, respectively. It migrates in beta-alanine-acetate-urea gel electrophoresis
Gel electrophoresis
Gel electrophoresis is a method used in clinical chemistry to separate proteins by charge and or size and in biochemistry and molecular biology to separate a mixed population of DNA and RNA fragments by length, to estimate the size of DNA and RNA fragments or to separate proteins by charge...
as a single compound. The phospholipase activity can be separated by affinity chromatography, using a phospholipid analog (PC-Sepharose). The alpha-neurotoxin-like peptide can be separated from the protease inhibitor, Sephadex
Sephadex
Sephadex is a trademark for cross-linked dextran gel used for gel filtration. It was launched by Pharmacia in 1959, after development work by Jerker Porath and Per Flodin. The name is derived from separation Pharmacia dextran. It is normally manufactured in a bead form and most commonly used for...
G-50 gel filtration chromatography can be used, in the presence of high salt (1M NaCl) and alkaline conditions (pH = 8.2). The amino sequence of the protease inhibitor was determined by using the automatic Edman degradation
Edman degradation
Edman degradation, developed by Pehr Edman, is a method of sequencing amino acids in a peptide. In this method, the amino-terminal residue is labeled and cleaved from the peptide without disrupting the peptide bonds between other amino acid residues....
method.
Target
Taicatoxin acts on the voltage-dependent L-type calcium channels from the heart, and on the small conductance Ca2+-activated K+ channels in the chromaffin cells and in the brain.It has a high affinity for the 125I-apamin
Apamin
Apamin is an 18 amino acid peptide neurotoxin found in apitoxin . It selectively blocks SK channels, a type of Ca2+-activated K+ channel expressed in the central nervous system and smooth muscle...
acceptor-binding sites of the rat synaptosomal membranes (Ki = 1.45±0.22 nM) and blocks affinity-labeling of a 33-kDa 125I-apamin-binding polypeptide. Other neurotoxins that act on the calcium channels are calcicludine
Calcicludine
Calcicludine is a protein toxin from the venom of the green mamba that inhibits high-voltage-activated calcium channels, especially L-type calcium channels.- Source :Calcicludine is a toxin in the venom of the green mamba ....
, calciseptine, ω-conotoxin
Conotoxin
A conotoxin is one of a group of neurotoxic peptides isolated from the venom of the marine cone snail, genus Conus.Conotoxins, which are peptides consisting of 10 to 30 amino acid residues, typically have one or more disulfide bonds. Conotoxins have a variety of mechanisms of actions, most of...
, ω-agatoxin
Agatoxin
Agatoxins are a class of chemically diverse polyamine and peptide toxins which are isolated from the venom of various spiders. Their mechanism of action includes blockade of glutamate-gated ion channels, voltage-gated sodium channels, or voltage-dependent calcium channels...
.
Mode of action
It lowers the plateau of the action potentialAction potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
, decreasing the duration and the concentration parameters in the heart muscle cells. It has been seen that the 16-kDa subunit exhibits phospholipase activity, inducing a release of acyl CoA and acyl carnitine, fact which has a negative effect on cell’s integrity and function. TCX is involved in the outer hair cell motility
Motility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...
too, by blocking the calcium traffic and preventing the cell shortening and elongation. Taicatoxin has an inhibitory effect by reducing the affinity of 125I-apamin for its acceptor and not by alteration of the acceptor binding site density.
Toxicity
A dose of 1 to 2 μg of taicatoxin can kill a mouse of 20 g in 2 hours.Pretreatment with taicatoxin (0.19 μM) on the outer hair cells of guinea pig
Guinea pig
The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...
prevented the cell shortening induced by high K+ (50 mM) and the cell elongation induced by ionomycine (10 μM). This is because taicatoxin blocks the calcium influx through the calcium channels in the cell’s membrane.
50 nM of taicatoxin blocks the apamin-sensitive after-hyperpolarizing slow tail K+ currents in rat chromaffin cells, but not immediately; instead, 5 μM of this toxin immediately blocks the ISK(Ca) tail current.
It has been shown that taicatoxin blocks the calcium currents in heart cells with IC50 between 10-500 nM. Also was seen to evoke severe arrhythmias and prolonged changes in the intercellular electrical coupling.
External links
- http://www.uniprot.org/entry/Q7LZE4
- http://www.uniprot.org/entry/Q7LZG2