The pleiotropic odorant binding protein CaspOBP12 involved in perception of Ceutorhynchus asper for plant volatiles and pesticides.

The olfactory system of insects plays a vital role in their survival by enabling them to detect chemical cues and adapt to changing environments. The rape stem weevil, Ceutorhynchus asper, is a significant pest posing a challenge for rapeseed production due to its destructive feeding habit and increasing resistance to insecticides. So far, there's still limited knowledge about structure and function of odorant binding proteins (OBPs) in beetles like C. asper. In this study, we identified and expressed CaspOBP12, a highly expressed OBP in antennae of C. asper with female-biased expression. Phylogenetic analyses of OBPs from Curculionidae showed that CaspOBP12 and its homologs fell into a distinct and conservative clade, likely involved in the evolutionary radiation of the Curculionidae. CaspOBP12 exhibited a broad-spectrum binding pattern. CaspOBP12 demonstrated good binding affinities for host plant volatiles, such as benzyl isothiocyanate (ITC) (Ki = 10.44 μM) and decanal (Ki = 9.94 μM), and the pesticide λ-cyhalothrin (Ki = 7.41 μM), suggesting its multiple roles in perception of host volatiles and insecticides. The beetle exhibited strong electrophysiological responses to benzyl ITC and decanal, and further behavioral experiments demonstrated that both volatiles were strongly attractive to C. asper. Molecular docking and dynamics simulations identified candidate key residues (i.e., VAL42, VAL83 and PHE104) in ligand binding of CaspOBP12. Site-directed mutagenesis experiments targeting these residues significantly reduced the mutant proteins' binding affinities, with no binding with λ-cyhalothrin or decanal observed for the mutant protein at PHE104. Our study highlight interactions of the conserved CaspOBP12 and its homologs with variable plant volatiles and insecticides, suggesting their multiple functional roles in chemical senses and insecticide resistance development. This study can also enhance our understanding of the olfactory mechanisms of C. asper, and provide a basis for the development of novel environment-friendly control techniques.