cDNA cloning of ecdysone receptor (EcR) and ultraspiracle (USP) from Harmonia axyridis and Epilachna vigintioctopunctata and the evaluation of the binding affinity of ecdysone agonists to the in vitro translated EcR/USP heterodimers

cDNAs for ecdysone receptor (EcR) and ultraspiracle (USP) genes were cloned from the Asian lady beetle Harmonia axyridis and the phytophagous ladybird beetle Epilachna vigintioctopunctata. The ligand binding affinity of ponasterone A (PonA) to EcRs was determined by measuring the inhibition of the binding of PHIPonA to the in vitro translated EcR/USP heterodimers for H. axyridis and E. vigintioctopunctata. The IC50 values of PonA to EcR/USP were determined to be 5.6 nM against H. axyridis and 4.0 nM against E. vigintioctopunctata. RH-5849 and tebufenozide significantly inhibited the [H-3]PonA binding to the H. axyridis but was inactive against E. vigintioctopunctata. The IC50 values of RH-5849 and tebufenozide against H. axyridis were determined to be 10.5 mu M and 11.0 mu M, respectively. The tertiary structures of ligand binding domains (LBDs) of both EcRs were modeled from the crystal structure of EcR-LBD of the tobacco budworm Heliothis virescens, and the ligand-receptor interaction was studied in in silico ligand-receptor docking. (C) Pesticide Science Society of Japan