Ligand-binding specificities of four odorant-binding proteins in Conogethes punctiferalis

Odorant-binding proteins (OBPs) play essential roles in lepidopteran insects' perception of host volatiles by binding and transporting hydrophobic ligands. The yellow peach moth (YPM), Conogethes punctiferalis (Guenée), is a serious agricultural pest, with broad host range and cryptic feeding habits. However, few studies about YPM perceiving pheromones and host plant odorants have been reported. In this study, four OBP genes (CpunOBP8, CpunOBP9, CpunABP, and CpunGOBP2) were cloned from the antennae of YPM. The recombinant proteins were expressed and purified by prokaryotic expression system, with their binding affinities to 26 ligands being tested. Four CpunOBPs all had six conserved cysteine residues, which were typical structural characteristics of classical OBPs. The fluorescence competitive binding assay indicated that CpunOBP8 and CpunABP could not only exhibit high binding affinities to female sex pheromones, but also to host plant odorants. For example, CpunOBP8 bound strongly with cis-10-hexadecenal, hexadecanal, and so forth, whereas CpunABP bound with cis-10-hexadecenal, camphene, and 3-carene. Comparatively, CpunOBP9 and CpunGOBP2 could only bind with host plant odorants, with CpunOBP9 binding strongly to 3-methyl-1-butanol, hexyl acetate, and so forth, while CpunGOBP2 displaying the widest binding spectra and correlating with 3-carene, pentyl acetate, and so forth. The results indicated that on the one hand, each of the four CpunOBPs had its specific binding spectra when binding and transporting olfactory ligands; on the other hand, the same ligand might be bound to more than one CpunOBPs, which would provide information for the potential application of semiochemicals in controlling YPM.