Abstract: Insect olfactory receptors are important proteins which are required for the insect olfactory identification process. As a receptor strikingly different from all other insect olfactory receptors, Orco is highly conserved in insect species and widely expressed. Orco plays a critical role in insect olfaction. Insects show severe olfaction defects when Orco is silenced by gene targeting or RNA interference. Orco can form heteromeric complexes by binding the conventional olfactory receptors rather than binding odorant ligands to facilitate the localization and stability of the conventional olfactory receptors in the olfactory sensory neurons (OSNs) dendrites and improve efficient odor response of conventional olfactory receptors. The structure of insect olfactory receptors is similar to the G protein-coupled receptors (GPCRs) of vertebrates with seven transmembrane regions. However, they adopt a membrane topology distinct from that of GPCRs, with their N-termini located intracellularly and C-termini located extracellularly. Orco interacts with the conventional olfactory receptors forming the Or-Orco complexes by the conserved C-terminal region wihch is a new ligandgated ion channel. Clarifying the functional mechanism of Orco in insect olfaction recognition may provide the basis for developing a new pest control measures based on insect olfactory behavior interference.

Key words: Insect, olfactory receptor, Orco, expression characterization, function, structure