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Agitoxin

Agitoxin is a toxin found in the venom of the scorpion Leiurus quinquestriatus herbraeus (yellow scorpion).

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Agitoxin binds to the Shaker K⁺ channel in Drosophila as well as to its mammalian homologue. It blocks this channel by binding with high affinity (K_d < 1 nmol/L) to its external vestibule.

Agitoxin can be purified using HPLC techniques. Its structure consists of a triple-stranded antiparallel beta-sheet and a single helix covering one face of the beta-sheet. The cysteine side chains connect the beta-sheet and the helix form to the core of the molecule. The fold of agitoxin is homologous to the previously determined folds of scorpion venom toxins.

Three types of agitoxin can be distinguished; all 3 agitoxins have been identified as 38 amino acid toxins (cystine bonds not shown):

Agitoxin-1 Gly-Val-Pro-Ile-Asn-Val-Lys-Cys-Thr-Gly-Ser-Pro-Gln-Cys-Leu-Lys-Pro-Cys-Lys-Asp-Ala-Gly-Met-Arg-Phe-Gly-Lys-Cys-Ile-Asn-Gly-Lys-Cys-His-Cys-Thr-Pro-Lys (molecular weight = 4014.87 Da, molecular formula = C₁₆₉H₂₇₈N₅₂O₄₇S₇)

Agitoxin-2 Gly-Val-Pro-Ile-Asn-Val-Ser-Cys-Thr-Gly-Ser-Pro-Gln-Cys-Ile-Lys-Pro-Cys-Lys-Asp-Ala-Gly-Met-Arg-Phe-Gly-Lys-Cys-Met-Asn-Arg-Lys-Cys-His-Cys-Thr-Pro-Lys (molecular weight = 4090.95 Da, molecular formula = C₁₆₉H₂₇₈N₅₄O₄₈S₈)

Agitoxin-3 Gly-Val-Pro-Ile-Asn-Val-Pro-Cys-Thr-Gly-Ser-Pro-Gln-Cys-Ile-Lys-Pro-Cys-Lys-Asp-Ala-Gly-Met-Arg-Phe-Gly-Lys-Cys-Met-Asn-Arg-Lys-Cys-His-Cys-Thr-Pro-Lys (molecular weight = 4100.98 Da, molecular formula = C₁₇₁H₂₈₀N₅₄O₄₇S₈, CAS Number 155646-23-4)

References:

Garcia ML et al. (1994). "Purification and characterization of three inhibitors of voltage-dependent K⁺ channels from Leiurus quinquestriatus var. hebraeus venom". Biochemistry 33 (22): 6834-6839. doi: 10.1021/bi00188a012
Gao YD et al. (2003). "Interaction of agitoxin2, charybdotoxin, and iberiotoxin with potassium channels: selectivity between voltage-gated and Maxi-K channels". Proteins 52 (2): 146–154. doi: 10.1002/prot.10341