Functional Characterization of Chemosensory Proteins in the Scarab Beetle, Holotrichia oblita Faldermann (Coleoptera: Scarabaeida)

Chemosensory proteins (CSPs) play important roles in chemical communication by insects, as they recognize and transport environmental chemical signals to receptors within sensilla. In this study, we identified Hobl CSP1 and Hobl CSP2 from a cDNA library of Holotrichia oblita antennae, successfully expressed them in E. coli and purified them by Ni ion affinity chromatography. We then measured the ligand-binding specificities of Hobl CSP1 and Hobl CSP2 to 50 selected ligands in a competitive binding assay. These results demonstrated that Hobl CSP1 and Hobl CSP2 have similar ligand-binding spectra. Both proteins displayed the highest affinity for β-ionone, α-ionone and cinnamaldehyde, indicating that they prefer binding to odorants other than sex pheromones. Additionally, immuno-localization revealed that Hobl CSP1 is highly concentrated in sensilla basiconica, while Hobl CSP2 is specifically localized to sensilla placodea. In conclusion, Hobl CSP1 and Hobl CSP2 are responsible for binding to general odorants with slightly different specificities due to their different in vivo environments.