Agitoxin (AgTX)

Agitoxin is a toxin found in the venom of the scorpion Leiurus quinquestriatus hebraeus (yellow scorpion). Agitoxin consists of a triple-stranded antiparallel beta-sheet in which the C-terminal strand sits in the centre of the sheet, and a single alpha-helix covering one face of the beta-sheet. The cysteine side chains connect the beta-sheet and the helix via disulphide bonds to form the core of the molecule. The fold of agitoxin is homologous to the previously determined folds of scorpion venom toxins, classified as 'Scorpion short toxins' by Pfam. This fold, and the location of the disulphide bonds, are a shared element between toxins stemming from arthropods. The structure of agitoxin-2, has been determined by NMR. 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 to its external vestibule.