Structure, Binding Characteristics, and 3D Model Prediction of a Newly Identified Odorant-Binding Protein from the Cotton Bollworm, Helicoverpa armigera (Hübner)

The full-length sequence of the odorant binding protein 5 gene, HarmOBP5, was obtained from an antennae cDNA library of cotton bollworm, Helicoverpa armigera (Hübner). The cDNA contains a 444 bp open reading frame, encoding a protein with 147 amino acids, namely HarmOBP5. HarmOBP5 was expressed in Escherichia coli and the recombinant protein was purified by affinity chromatography. SDS-PAGE and Western blot analysis demonstrated that the purified protein can be used for further investigation of its binding characteristics. Competitive binding assays with 113 odorant chemicals indicated that HarmOBP5 has strong affinity to some special plant volatiles, including (E)-ß-farnesene, ethyl butyrate, ethyl heptanoate, and acetic acid 2-methylbutyl ester. Based on three-dimensional (3D) model of AaegOBP1 from Aedes aegypti, a 3D model of HarmOBP5 was predicted. The model revealed that some key binding residues in HarmOBP5 may play important roles in odorant perception of H. armigera. This study provides clues for better understanding physiological functions of OBPs in H. armigera and other insects.