Grammotoxin

Grammotoxin 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.

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Source

The source of grammotoxin is the venom of a tarantula spider (Grammostola spatulate).

Chemistry

Grammotoxin is a 36 Amino Acid 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 (1)

Grammotoxin can be purified from Grammostola spatulata venom by reverse phase high performance liquid chromatography.(2)

Target

Grammotoxin is a 36 amino acid residue protein toxin from spider venom that inhibits P-, Q- and N-type voltage-gated calcium channels in neurons.

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. (4) 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 makes it more difficult for channels to be opened by depolarization, so much larger depolarizations are required for channel activation. (4) Grammotoxin also binds to potassium channels but with lower affinity than to the calcium channels.(3)

References

(1) ω-Grammotoxin SIA from Grammostola spatulata venom, ≥98% (HPLC)

(2) Lampe R.A. et al. Isolation and pharmacological characterization of omega-grammotoxin SIA, a novel peptide inhibitor of neuronal voltage-sensitive calcium channel responses. Mol Pharmacol. 1993 Aug;44(2):451-60

(3) Takeuchi K. et al. Solution Structure of v-Grammotoxin SIA, A Gating Modifier of P/Q and N-type Ca21 Channel. J. Mol. Biol. 2002, 321: 517–526

(4) Stefan I. McDonough et al. Voltage-Dependent Inhibition of N- and P-Type Calcium Channels by the Peptide Toxin v-Grammotoxin-SIA. Molucular pharmacology, 1997 52:1095–1104.