Functional expression and characterization of odorant receptors using the Semliki Forest virus system

The human olfactory system can recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants starts with the binding of an odorant ligand to a specific receptor protein on the olfactory neuron cell surface. To address the problem of olfactory perception at a molecular level, we have expressed and characterized different olfactory receptors with several expression systems. Here we provide the first documentation of functional expression of odorant receptors using the Semliki Forest virus system. The human odorant OR 17-40 receptor and the rat 17 receptor were functionally expressed in vertebrate kidney cells (HEK293) using recombinant Semliki Forest viruses. Receptors were expressed as a fusion protein with the N-terminal membrane import sequence of the guinea pig serotonin receptor. Experiments employing the Ca2+-sensitive dye fura-2 revealed a fast, transient increase in the [Ca2+]i after application of the specific agonists helional and octanal to HEK293 cells infected with viruses containing RNA for the human odorant OR 17-40 receptor and the rat 17 receptor, respectively.