Key Amino Acid Residues Involved in Binding Interactions between Bactrocera minax Odorant-Binding Protein 3 (BminOBP3) and Undecanol

SIMPLE SUMMARY: Odorant-binding proteins (OBPs) play a crucial role in insect olfaction perception in which OBPs are believed to discriminate, capture, and ferry odors to olfactory receptors, and thus, OBP-based behavioral interference is thought to be a potential novel pest management measure. Our previous study demonstrated that Bactrocera minax OBP3 (BminOBP3) exhibited strong binding affinity only with undecanol, which is believed to be a main B. minax sex pheromone, among 13 ligands tested. Here, homology modeling and molecular docking were carried out to explore the interaction mechanism between BminOBP3 and undecanol. The results suggested that the C-terminus (I116-P122), especially the last three amino acids of the C-terminus (V120-P122), play an essential role in the ligand binding for BminOBP3, and this was further proven by mutagenesis studies and fluorescence binding assays. These findings have provided important insights into the molecular mechanism by which BminOBP3 interacts with undecanol. Moreover, this study could serve as a significant reference for developing potentially useful technology to control pests, although disturbing their olfaction judgments. ABSTRACT: Insect odorant-binding proteins (OBPs) are significant in binding and transporting odorants to specific receptors. Our previous study demonstrated that BminOBP3 exhibited a strong affinity with undecanol. However, the binding mechanism between them remains unknown. Here, using homology modeling and molecular docking, we found that the C-terminus (I116-P122), especially the hydrogenbonds formed by the last three amino acid residues (V120, F121, and P122) of the C-terminus, is essential for BminOBP3′s ligand binding. Mutant binding assays showed that the mutant T-OBP3 that lacks C-terminus (I116-P122) displayed a significant decrease in affinity to undecanol (K(i) = 19.57 ± 0.45) compared with that of the wild-type protein BminOBP3 (K(i) = 11.59 ± 0.51). In the mutant 3D2a that lacks F121 and P122 and the mutant V120A in which V120 was replaced by alanine, the bindings to undecanol were completely abolished. In conclusion, the C-terminus plays a crucial role in the binding interactions between BminOBP3 and undecanol. Based on the results, we discussed the ligand-binding process of BminOBP3.