Dual-targeted natural product inhibitors of Ostrinia furnacalis chitinases and inhibitory mechanisms

Multiple chitinases are required for effective hydrolysis of insect epidermal chitin and play an indispensable role in insect molting. As chitin is absent in plants and mammals, these enzymes can be potential targets for the design of green insecticides. In this paper, three dual-target inhibitors against the Asian corn borer (Ostrinia furnacalis)-derived chitinases OfChtI and OfChi-h, anacardic acid, di(2-ethylhexyl) phthalate (DEHP), and shionone, were obtained through high-throughput screening of 1680 natural products. The respective K_i values for OfChtI are 0.57, 0.53 and 3.95 μmol/L, and are 0.48, 1.42 and 27.33 μmol/L for OfChi-h. The molecular docking results showed that all three inhibitors were bound to the substrate-binding sites of the target enzymes through hydrophobic stacking interaction. In addition, the 1-carboxyl oxygen atom of anacardic acid, as a hydrogen bond acceptor, formed hydrogen bonds with guanidine hydrogen atoms of Arg274 side chain in OfChtI and Arg439 side chain in OfChi-h, respectively. The carbonyl and etheryl oxygen atoms of DEHP, as hydrogen bond receptors, formed hydrogen bonds with hydrogen atoms of Arg274 guanidine group side chain in OfChtI; the etheryl oxygen atom of DEHP, as a hydrogen bond acceptor, formed hydrogen bond with guanidine hydrogen atom of Arg439 side chain in OfChi-h. The insecticidal activity was determined to be 33.3% for anacardic acid and DEHP at 2 mmol/L, while shionone showed no obvious insecticidal activity. This study may provide a clue for the development of novel green pesticides targeting multiple chitinases simultaneously.