Primary structure of scorpion anti-insect toxins isolated from the venom of Leiurus quinquestriatus quinquestriatus

Abstract

The amino acid sequences of insect-selective scorpion toxins, purified from the venom of Leiurus quinquestriatus quinquestriatus, have been determined by automatic phenyl isothiocyanate degradation of the S-carboxymethylated proteins and derived proteolytic peptides. The excitatory toxin Lqq IT 1 and Lqq IT 1' (70 residues) show the shift of one half-cystine from an external position, which is characteristic of anti-mammal toxins, to an internal sequence position. Lqq IT 2, (61 residues) displays the half-cystine residue in position 12, common to the sequence of all known antimammal toxins; it induces flaccid paralysis on insects but is non-toxic for the mouse. Lqq IT 2, structurally defines a new type of anti-insect toxins from scorpion venoms. CD spectra and immunological data are in agreement with this finding.