Omega-grammotoxin SIA is a protein toxin

Toxin

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

 that inhibits P, Q and N voltage-gated calcium channels (Ca²⁺ channels) in neurons.

Source

The source of omega-grammotoxin SIA is 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 a 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...

  spider

Spider

Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...

 (Grammostola rosea).

Chemistry

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...

 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

Molecular Formula: C₁₇₇H₂₆₈N₅₂O₅₀S₆

Omega-grammotoxin SIA can be purified from Grammostola rosea 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...

.

Target

Omega-Grammotoxin SIA is a 36 amino acid residue protein toxin from spider venom that inhibits P, Q and N-type voltage-gated calcium channels in neurons. It binds to the channels with high affinity (if closed). It also binds to potassium channels but with lower affinity than to the calcium channels.
The toxin binding site has high affinity when channels are in closed states and low affinity when channels are activated. (4)

Mode of action

It is believed that omega-grammotoxin SIA inhibits channel function by binding with high affinity to closed, resting states of the channel and that bound toxin 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.