Isolation and characterization of the insecticidal, two-domain toxin LaIT3 from the scorpion venom.

A novel insecticidal peptide (LaIT3) was isolated from the venom. The primary structure of LaIT3 was determined by a combination of Edman degradation and MS/MS de novo sequencing analysis. Discrimination between Leu and Ile in MS/MS analysis was achieved based on the difference in side chain fragmentation assisted by chemical derivatization. LaIT3 was determined to be an 84-residue peptide with three intrachain disulfide bonds. The sequence similarity search revealed that LaIT3 belongs to the scorpine-like peptides consisting of two structural domains: an N-terminal α-helical domain and a C-terminal cystine-stabilized domain. As observed for most of the scorpine-like peptides, LaIT3 showed significant antibacterial activity against , which is likely to be caused by its membrane-disrupting property.