Towards an identification of odorant receptors

The molecular nature and diversity of receptive sites for odorous molecules is a central unanswered issue in olfaction. Based on the enormous resolving power of the olfactory system, which enables the stereospecific discrimination of numerous compounds at low concentrations specific receptor proteins have been proposed. Due to the central role of G-proteins in olfactory signalling it has been predicted that odorant receptors might be members of the superfamily of receptor proteins with seven transmembrane domains. Upon application of degenerated oligonucleotides and the PCR-technology a number of putative odorant receptors have been cloned and sequenced. In situ hybridisation studies using receptor-specific probes have been performed and olfactory neurons specifically expressing a particular receptor subtype are topologically identified in the nasal epithelium of rats. Clones of interest are now being expressed in heterologous systems in order to demonstrate functional activity of these putative receptor proteins and to match defined odorants to identified receptors.