Taicatoxin (TCX) is a snake
toxinA toxin is a poisonous substance produced by living cells or organisms ....
that blocks voltage-dependent
L-type calcium channelThe L-type calcium channel is a type of voltage-dependent calcium channel. 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+ channelsSK channels are a subfamily of Ca2+-activated K+ channels. 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 intracellular calcium...
. The name taicatoxin (TAIpan + CAlcium + TOXIN) is derived from its natural source, the
taipanThe taipans are a genus of large, fast, highly venomous Australasian snakes.-Overview:There are three known species: the coastal taipan , the inland taipan and a recently discovered third species, the Central Ranges taipan...
snake, the site of its action,
calcium channelA Calcium channel is an ion channel which displays selective permeabiltiy 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
toxinA toxin is a poisonous substance produced by living cells or organisms ....
. Taicatoxin was isolated from the venom of Australian taipan snake,
Oxyuranus scutellatus scutellatus. TCX is a secreted
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
, produced in the
venomVenom is any of a variety of toxins used by certain types of animals. Generally, venom is injected by such means as a bite or a sting.-The distinction between venom and poison:...
gland of the snake.
Through
SDS-PAGESDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis, is a technique 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 forcesA 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
stoichiometryStoichiometry is the calculation of quantitative relationships of the reactants and products in a balanced chemical reaction...
of 1:1:4 respectively:
- a α-neurotoxin
A 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 peptidePeptides are short polymers formed from the linking, in a defined order, of α-amino acids. The link between one amino acid residue and the next is called an amide bond or a peptide bond....
(8 kDa),
- a neurotoxic phospholipase
A 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 what type of reaction they catalyze:* Phospholipase A...
(16 kDa; ), and
- a serine protease inhibitor (7 kDa; ).
The active complex was isolated by ion exchange
chromatographyChromatography 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.
Taicatoxin (TCX) is a snake
toxinA toxin is a poisonous substance produced by living cells or organisms ....
that blocks voltage-dependent
L-type calcium channelThe L-type calcium channel is a type of voltage-dependent calcium channel. 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+ channelsSK channels are a subfamily of Ca2+-activated K+ channels. 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 intracellular calcium...
. The name taicatoxin (TAIpan + CAlcium + TOXIN) is derived from its natural source, the
taipanThe taipans are a genus of large, fast, highly venomous Australasian snakes.-Overview:There are three known species: the coastal taipan , the inland taipan and a recently discovered third species, the Central Ranges taipan...
snake, the site of its action,
calcium channelA Calcium channel is an ion channel which displays selective permeabiltiy 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
toxinA toxin is a poisonous substance produced by living cells or organisms ....
. Taicatoxin was isolated from the venom of Australian taipan snake,
Oxyuranus scutellatus scutellatus. TCX is a secreted
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
, produced in the
venomVenom is any of a variety of toxins used by certain types of animals. Generally, venom is injected by such means as a bite or a sting.-The distinction between venom and poison:...
gland of the snake.
Chemistry
Through
SDS-PAGESDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis, is a technique 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 forcesA 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
stoichiometryStoichiometry is the calculation of quantitative relationships of the reactants and products in a balanced chemical reaction...
of 1:1:4 respectively:
- a α-neurotoxin
A 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 peptidePeptides are short polymers formed from the linking, in a defined order, of α-amino acids. The link between one amino acid residue and the next is called an amide bond or a peptide bond....
(8 kDa),
- a neurotoxic phospholipase
A 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 what type of reaction they catalyze:* Phospholipase A...
(16 kDa; ), and
- a serine protease inhibitor (7 kDa; ).
The active complex was isolated by ion exchange
chromatographyChromatography 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 electrophoresisGel electrophoresis is a technique used for the separation of deoxyribonucleic acid , ribonucleic acid , or protein molecules using an electric field applied to a gel matrix...
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,
SephadexSephadex 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 an anagram of 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 degradationEdman 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 Ca
2+-activated K
+ channels in the chromaffin cells and in the brain.
It has a high affinity for the
125I-
apaminApamin is a neurotoxin which selectively blocks SK channels, a type of Ca2+-activated K+ channels expressed in the central nervous system. The final 18 amino acid polypeptide is a component of apitoxin...
acceptor-binding sites of the rat synaptosomal membranes (K
i = 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
calcicludineCalcicludine 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 ....
,
calciseptineclass="infobox bordered" cellpadding="2" cellspacing="0" | | colspan="2" align=center bgcolor="#cccccc" | Calciseptine |- |Molecular weight || 7036 |- | colspan=2 align=center |
|}...
, ω-
conotoxinA 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-
agatoxinAgatoxins 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 potentialAn action potential is a transient alteration of the transmembrane voltage across an excitable membrane generated by the activity of voltage-gated ion channels embedded in the membrane. Action potentials play multiple roles in several types of excitable cells such as neurons, myocytes, 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
motilityMotility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. It can apply to either single-celled or multicellular organisms. Motile marine animals are commonly called free-swimming...
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 pigThe guinea pig , also commonly 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 pigs, nor do they come 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 I
SK(Ca) tail current.
It has been shown that taicatoxin blocks the calcium currents in heart cells with IC
50 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