Agitoxin
Agitoxin is a toxin found in the venom of the scorpion Leiurus quinquestriatus herbraeus (yellow scorpion).
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 (Kd < 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): 68346839.CS1 maint: Explicit use of et al. (link) .mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em} 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): 146154.CS1 maint: Explicit use of et al. (link)  doi: 10.1002/prot.10341