Molecular characterization of sex pheromone binding proteins from Holotrichia oblita (Coleoptera: Scarabaeida)

Pheromone binding proteins (PBPs), a subfamily of the odorant binding proteins (OBPs), capture and transfer sex pheromones across the sensillum lymph to pheromone receptors and initiate insect courtship and mating. In this study, we functionally characterized ten OBPs from the black chafer, Holotrichia oblita (HoblOBPs), among which six HoblOBPs (HoblOBP2, 4, 5, 8, 9 and 24) were shown to recognize sex pheromones using electroantennography assays (EAG) and in vitro fluorescence competitive binding assays. Insect tropism to sex pheromones was significantly reduced after those genes were knocked down in vivo, e.g. HoblOBP24 RNAi reduced the tropism of H. oblita to methyl glycinate by 34%. Furthermore, molecular docking revealed key residues for the binding of the six HoblOBPs with sex pheromones. And hydrogen bonds and hydrophobic forces were shown to be the main forces in the binding of the six HoblOBPs and their sex pheromone ligands. Our study characterized six H. oblita PBPs and their binding abilities to sex pheromone ligands. The results will improve our understanding on the olfactory mechanisms that H. oblita utilizes to recognize sex pheromones, and will promote the development of novel strategies for controlling H. oblita and other insect pests.