Expression profile and ligand-binding characterization of odorant-binding protein 2 from Batocera horsfieldi ( Hope).

Odorant-binding proteins ( OBPs) are important components in insect olfactory systems that transport semiochemicals through the aqueous sensillum lymph to surface of olfactory receptor neurons. In this study, we cloned the c DNA of odorant-binding protein 2 ( Bhor OBP2) in Batocera horsfieldi ( Hope) and measured the level of the Bhor OBP2 m RNA in a variety of tissues using quantitative reverse transcription and real-time polymerase chain reaction. We found that the Bhor OBP2 m RNA was primarily expressed in the antennae, the level of Bhor OBP2 m RNA was higher in males than in females, and correlated with age and mating status. The Bhor OBP2 m RNA was also expressed in the labial palps at relatively high level, suggesting that it might have a role in gestation as well. To better understand the functions of the Bhor OBP2 protein in odorant reception, recombinant Bhor OBP2 was expressed in Escherichia coli, and the binding specificity of the protein for 18 volatile developmentally relevant chemicals and host-plant-related metabolites were assessed using N-phenyl-1-naphthylamine as a fluorescent probe. Competitive fluorescence binding assays showed that Bhor OBP2 bound a broad range of host-plant-related odorants, including ( E)-2-hexenal, 2-methyl-butanal, salicylaldehyde, (1 S)-(-)-verbenone, ( Z)-3-hexen-1-ol, ( E)-2-hexen-1-ol, β-pinene and ethyl acetate. Our results imply that Bhor OBP2 might play an important role in the selectivity and specificity of odorant reception. [ABSTRACT FROM AUTHOR]