Evidence for the existence of insect defensin-like peptide in scorpion venom

Insect defensin refers to a group of antibacterial peptides derived from a variety of insect species as well as from scorpion and possessing a three-d imensional structure highly similar to that of scorpion toxins. A full-leng th cDNA encoding an insect defensin-like peptide was isolated from the veno m gland cDNA library of the Chinese scorpion Buthus martensii Karsch, The p recursor, the overall organization of which is similar to that of insect de fensins, consists of 61 amino acid residues with a putative signal peptide of 15 residues, a propeptide of 7 residues, and a mature peptide of 39 resi dues (named BmTXKS2), The positions of six cysteines and a conserved glycin e in mature BmTXKS2 are the same as those in LqDef, the first defensin foun d in scorpions, which suggests these peptides should present a similar cyst eine-stabilized alpha beta motif. Phylogenetic analysis further shows that the structure of BmTXKS2 is closer to that of ancient defensins (e.g., LqDe f and AaDef, two insect defensins present in the scorpion hemolymph) than t o scorpion toxins.