Chemical Synthesis and Biological Evaluation of the Insecticidal Peptide AaIT5 Identified From the Androctonus australis Venom.

Scorpion venom contains various bioactive peptides. Voltage-gated sodium channel toxins (NaTxs) have been the primary focus of scorpion venom research because of their significant potency and high selectivity. A variety of NaTxs have been identified in the venom of Androctonus australis, six of which exhibit insecticidal activity. Among these, the biological activity of AaIT5 remains poorly characterized because of its low abundance in the venom. In this study, AaIT5 was chemically synthesized via native chemical ligation (NCL), suppressing side reactions associated with aspartimide formation using specialized Fmoc-protected amino acids, followed by oxidative folding. Subsequent LC/MS/(MS) analyses of the enzymatic digests confirmed that the synthetic peptide adopted the disulfide bond pattern predicted from the related NaTxs. Synthetic AaIT5 exhibited insecticidal activity against both Spodoptera litura and Acheta domesticus, although it was less potent than related insecticidal NaTxs such as LqhIT2. Sequence alignment and molecular modeling suggested that the reduced activity results from the substitution of a highly conserved tryptophan residue with valine, thereby abolishing a potential cation-π interaction with insect sodium channels. The successful chemical synthesis and functional characterization of AaIT5 provide a robust platform for the preparation of toxin analogs and further studies on the structure-activity relationships of insecticidal NaTxs.