Ligand-binding properties and 3D model of odorant binding protein 1 of the lucerne plant bug, Adelphocoris lineolatus (Goeze)

Evidences showed that odorant binding proteins (OBPs) are widely and robustly expressed in insect olfactory organs and play a key role in chemsensing and transporting hydrophobic odorants to the olfactory receptor. In present study, a novel OBP (AlinOBP1) in the lucerne plant bug, Adelphocoris lineolatus was identified, cloned and expressed in laboratory. The expression pattern of AlinOBP1 evaluated by Real-time PCR indicated that the expression level of AlinOBP1 gene was different along the each developmental stage. Moreover, AlinOBP1 gene was dominantly expressed in the antennae of adults. The binding properties of AlinOBP1 with 114 odorants were measured by fluorescence competitive binding method. The results revealed that AlinOBP1 exhibits high binding abilities with two major putative pheromones, Ethyl butyrate and Trans-2-Hexenyl butyrate. In addition, it was observed that six volatiles released from cotton, Octanal, Nonanal, Decanal, 2-Ethyl-1-hexanol, â-caryophyllene and â-ionone can also significantly bind with AlinOBP1. We suggest that AlinOBP1 may have a dual-function in the perception of pheromone and plant volatiles. To predict the 3D model of AlinOBP1, the FUGUE fold recognition method was employed to identify structural homologues. BmorPBP1 with bound bombykol was finally chosen as template. The 3D model of AlinOBP1 reveals a large binding pocket. Most of the proposed binding residues of AlinOBP1 are hydrophobic, including Val26, Met63, Leu67, Met72, Leu73, Ala87, Ala101, Val105, Ala109, Ala124, Met127, Ala128, and Ala131, which may be responsible for the hydrophobic interactions with the hydrocarbon part of the ligands. However, some hydrophilic residues, including Asp19, Thr22, Asn23, Glu79 and Lys102, are also present in the binding pocket, which may be responsible for a hydrogen bond with the functional group of the ligand. They are likely to be involved in the formation of hydrogen bonds with the functional group of the ligand and play a key role in the initial ligand recognition.