Sequence and structure analysis for chemosensory proteins and odorant-binding proteins in Nilaparvata lugens...

Chemosensation is crucial for insect behavior and physiology, involving several molecules. Chemosensory proteins (CSPs) and odorant-binding proteins (OBPs) transport volatile and lipophilic semiochemicals to activate the chemosensory system. Nilaparvata lugens Stål, is a monophagous pest of rice plants, causing significant economic losses worldwide. To date, 15 CSPs and 13 OBPs have been characterized, but their functions have not been fully investigated especially regarding their binding affinity with various ligands. This study compares the commonalities and differences between the 15 CSPs and 13 OBPs regarding sequence similarity, phylogeny, structural identity, and binding affinity with 3 different ligands. As expected, all 15 CSPs contain 4 conserved cysteine residues and 6 α-helical domains, whereas 13 OBPs have at least 6 cysteine residues and 6 α-helical domains. CSP1, 2, 8, and 14 cluster together in the phylogenetic tree, showing high structural similarity and similar binding affinity to the 3 ligands. OBP9 and 10 form a clade with high structural conservation; however, molecular docking indicates OBP9 exhibits a high binding affinity for the insecticide thiamethoxam. Three OBPs, OBP56d, OBPunknown1, and OBPunknown2 have been characterized and they display no significant preference for the 3 ligands. Overall, our integrated sequence and structural analysis reveals both functional redundancy and specific ligand preferences within the N. lugens chemosensory system. These findings provide a critical foundation for understanding the molecular basis of chemoreception in N. lugens and may inform the development of novel behavioral interference strategies.