Scyllatoxin


Scyllatoxin is a toxin, from the scorpion Leiurus quinquestriatus hebraeus, which blocks small-conductance Ca2+-activated K+ channels.

Chemistry

Leiurotoxin I is a 31-residue peptide, with a helix and a short antiparallel β-sheet. This toxin is stabilized by disulfide bonds: Cys8-Cys26 and Cys12-Cys28 is bound to the β-sheet, Cys3-Cys21 is bound to an N-terminal segment preceding the helix. Leiurotoxin adopts the ά/β motif. Especially the positively charged residues are important for the expression of toxin biological activities and for its receptor affinity.

Target

Scyllatoxin is a blocker of small-conductance Ca2+– activated K+ channels at 10−13–10−11 M concentrations in various cell types.
This toxin shows similarity in its physiological activity and binding specificity to apamin, but both toxins show no structural similarity.

Mode of action

Scyllatoxin blocks the slow after-hyperpolarization that follows an action potential in some nerve cells.

Toxicity

Scyllatoxin induces spontaneous contractions in guinea pig taenia coli muscle cells that have
been relaxed with epinephrine.