5-aminoindole restrained larval growth and chitin biosynthesis via depressing TPS activity in Hyphantria cunea

Trehalose-6-phosphate synthase (TPS) is a key enzyme responsible for catalyzing the biosynthesis of trehalose in insects, and its multiple functions related to trehalose metabolism have been well established. In contrast, research on insect TPS inhibitors has received less attention. Previously 5-aminoindole had been reported to possess a potent inhibition on the TPS of Mycobacterium tuberculosis, but it is not clear whether it has an inhibitory effect on insect TPS. Here, we focused on the role of 5-aminoindole in inhibiting TPS activity of Hyphantria cunea larvae, a polyphagous pest in agriculture and forestry. In parallel, the HcTPS was identified from the pest, and the influences of 5-aminoindole on larval growth and development, trehalose metabolism, especially chitin synthesis were evaluated. Bioinformatics analysis indicated that HcTPS encoded a protein of 401 amino acids residues, which contained a GT20_TPS domain (18-377), belonging to glycosyltransferase family 20. The bioassay indicated that 5-aminoindole significantly suppressed in vivo TPS activity and reduced carbohydrate levels in H. cunea larvae, resulted in growth arrest and a high lethality. Meanwhile, 5-aminoindole significantly downregulated the expression of key genes in the chitin biosynthesis pathway (HcG6PI, HcGFAT, HcGNA, HcPAGM, HcUAP, and HcCHSA), and disrupted chitin biosynthesis in epidermis of H. cunea larvae. Homologous modeling and molecular docking revealed that 5-aminoindole had a potent binding affinity (BE = -4.31 kcal/mol) with HcTPS protein via forming a hydrogen bond with residue S23, R25 and D176, and hydrophobic interactions with the residue N24, L48 and D176. In addition, 5-aminoindole also had a strong binding affinity with the TPS proteins of other four insect species, including Helicoverpa armigera, Drosophila melanogaster, Anoplophora glabripennis, and Vespula germanica. These findings provided a new insight into potential application of indole derivatives as insect TPS inhibitor for pest control.