Expression Pattern, Molecular Docking and Dynamics Simulation Analysis of CSP4 from Sirex nitobei Provides Molecular Basis of CSP Bound to Scent Molecules

Insects stimulate specific behaviors by correctly recognizing scent molecules in the external environment. Sirex nitobei, a wood-boring wasp species native to Asia with a distribution area that includes the Palaearctic and Oriental regions, is a significant pest of conifers. Focusing on the molecular mechanism of protein-ligand binding, this study resolved the tissue expression profile of CSP4 from S. nitobei (SnitCSP4) and probed its binding properties with target ligands using molecular docking and dynamics simulations to verify the odor recognition function of this protein. The open reading frame (ORF) of SnitCSP4 was 396 bp, encoding 131 amino acids. Tissue expression analysis revealed that SnitCSP4 was significantly expressed in female antennae and docking showed that all ligands were bound in hydrophobic cavities and close to many hydrophobic amino acid residues. GLN68 and LEU49 were important amino acid residues for SnitCSP4 to bind various odors, and THR9 was the key ligand-binding site in identifying (-)-globulol in the SnitCSP4. Molecular dynamics verified the docking results, confirming that SnitCSP4 bound well to two sex pheromone molecules, three host plant volatiles, and three symbiotic fungal volatiles, with (Z)-7-heptacosene, (Z)-9-nonacosene, and (-)-globulol binding being the most highly stable. These results mean that SnitCSP4 is critical for insects recognizing scent molecules, providing a favorable molecular basis for regulating the behavioral interactions between S. nitobei and the environment, and offering the possibility of developing new strategies for more environmentally friendly and effective control.