Analyses of structural dynamics revealed flexible binding mechanism for the Agrilus mali odorant binding protein 8 towards plant volatiles

BACKGROUND: Volatiles from host plants are an important source of insect pest attractants and repellents. Insect odorant binding proteins (OBPs) have been widely characterized, but the molecular binding dynamics and underlying mechanisms are still not well understood. Thus, we characterized binding characteristics of AmalOBP8 from the apple buprestid beetle (Agrilus mali Matsumura), an unprecedented serious threat to rare apple germplasm resources and local ecosystems. RESULTS: Fluorescence studies demonstrated that the quenching mechanism was clearly static. AmalOBP8 was found to bind with both volatiles at single independent sites. Negative thermodynamic parameters suggested that binding interactions between AmalOBP8 and both volatiles could occur spontaneously. Hydrogen bonding was the key force in AmalOBP8's binding to geranyl formate, for which the amino acid residue Trp106 played a critical role in the binding pocket. Multiple Leu residues in AmalOBP8 created a strong hydrophobic environment, and formed the binding pocket for (Z)-3-hexenyl hexanoate. Compared to classic OBPs, in addition to lack of one disulfide bridge, AmalOBP8 had a small α-helix (α7) at the C-terminus, resulting in greater flexibility and adaptability for this protein to bind with different compound molecules. CONCLUSION: Key residues of AmalOBP8 in binding interactions with plant volatiles were clarified. AmalOPB8 had a large ligand binding spectrum and great flexibility in binding with plant volatiles, providing good molecular targets for screening insect attractants and repellents. Our results can promote understanding of insects' perception of various odorants, and establish a foundation for discovery of new pest control agents. © 2020 Society of Chemical Industry.