Grammotoxin is 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...

 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...

 of the tarantula

Tarantula

Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to...

 Grammostola spatulata. It is a protein toxin that inhibits P-, Q- and N-type voltage-gated calcium channels (Ca ²⁺ channels) in neurons. Grammotoxin is also known as omega-grammotoxin SIA

Omega-grammotoxin SIA

Omega-grammotoxin SIA is a protein toxin that inhibits P, Q and N voltage-gated calcium channels in neurons.- Source :The source of omega-grammotoxin SIA is the venom of a tarantula spider .- Chemistry :...

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Chemistry

Grammotoxin is a 36 Amino Acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 protein toxin, which has the following sequence:
Asp-Cys-Val-Arg-Phe-Trp-Gly-Lys-Cys-Ser-Gln-Thr-Ser-Asp-Cys-Cys-Pro-His-Leu-Ala-Cys-Lys-Ser-Lys-Trp-Pro-Arg-Asn-Ile-Cys-Val-Trp-Asp-Gly-Ser-Val (1)

Its chemical formula is: C₁₇₇H₂₆₈N₅₂O₅₀S₆

Grammotoxin can be purified from Grammostola spatulata venom by reverse phase high performance liquid chromatography

High performance liquid chromatography

High-performance liquid chromatography , HPLC, is a chromatographic technique that can separate a mixture of compounds and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.HPLC typically utilizes different types of stationary...

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Mode of action

The toxin binding site on the channels has high affinity for the toxins when they are closed and low affinity when channels are activated. As a result, the toxin preferentially binds to the closed channels. It binds at a region which contains the voltage-sensing domains. When bound, the toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

 makes it more difficult for channels to be opened by depolarization

Depolarization

In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...

, so much larger depolarization

Depolarization

In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...

s are required for channel activation. Grammotoxin also binds to potassium channels but with lower affinity than to the calcium channels.