Binding of the General Odorant Binding Protein of Bombyx mori BmorGOBP2 to the Moth Sex Pheromone Components

Insects use olfactory cues to locate hosts and mates. Pheromones and other semiochemicals are transported in the insect antenna by odorant-binding proteins (OBPs), which ferry the signals across the sensillum lymph to the olfactory receptors (ORs). In the silkworm, Bombyx mori (L.), two OBP subfamilies, the pheromone-binding proteins (PBPs) and the general odorant-binding proteins (GOBPs), are thought to be involved in both sensing and transporting the sex pheromone, bombykol [(10E,12Z)-hexadecadien-1-ol], and host volatiles, respectively. Quantitative examination of transcript levels showed that BmorPBP1 and BmorGOBP2 are expressed specifically at very high levels in the antennae, consistent with their involvement in olfaction. A partitioning binding assay, along with other established assays, showed that both BmorPBP1 and BmorGOBP2 bind to the main sex pheromone component, bombykol. BmorPBP1 also binds equally well to the other major pheromone component, bombykal [(10E,12Z)-hexadecadienal], whereas BmorGOBP2 discriminates between the two ligands. The pheromone analogs (10E,12Z)-hexadecadienyl acetate and (10E,12Z)-octadecadien-1-ol bind to both OBPs more strongly than does bombykol, suggesting that they could act as potential blockers of the response to sex pheromone by the male. These results are supported by further comparative studies of molecular docking, crystallographic structures, and EAG recording as a measure of biological response.