Understanding the mode of action of BtEcR/USP-LBD with benzpyrimoxan in combination with high throughput SPR screening and molecular simulation approaches

Abstract

Bemisia tabaci (B. tabaci) is a major agricultural pest that infests over 500 plant species, posing a significant threat to agricultural production due to its polyphagy, adaptability, and ability to transmit plant viruses. Excessive and improper insecticide use has caused resistance to pyrethroids, organophosphates, and neonicotinoids, creating an urgent need for new insecticides with novel structures and mechanisms of action. In this study, we developed an in vitro test platform targeting B. tabaci ecdysteroid receptor (BtEcR/USP-LBD) using Surface Plasmon Resonance (SPR) and investigated the novel insect growth regulator benzpyrimoxan through SPR, molecular docking, and molecular dynamics (MD) simulations. Benzpyrimoxan specifically bound to BtEcR/USP-LBD with a kinetic K_D of 14.19 μM, but its binding strength was lower than that of PonA (K_D = 0.21 μM). SPR and MD analyses showed that benzpyrimoxan had a slower binding rate and weaker interactions with Cys394 and Asn390 in the ligand binding domain of BtEcR (BtEcR-LBD), compared to PonA. Met389, Asn390, Thr393 and Cys394 have been shown to establish a specific hydrogen-bonding network in BtEcR-LBD, which exhibits significant variations in HvEcR-LBD. Molecular docking and MD simulations showed that benzpyrimoxan forms hydrogen bonds with this network but requires greater stability to enhance binding. This study identifies the potential mode of action of benzpyrimoxan and offers a strategy for discovering novel ecdysteroid analogues for controlling B. tabaci.