Odor detection and signal transduction occur in cilia where they are initiated by the interaction of odorant molecules with G-protein coupled olfactory receptors. Olfactory receptors comprise a large multigene family;in humans there are an estimated 400 functional genes found in many different chromosomal locations. A great deal of information has been gathered regarding both the second messenger excitation cascade in olfactory transduction and signal termination over the past years. Nonetheless, there is a paucity of knowledge about the first step in the process, namely, the interaction of an odorant molecule with the receptor, itself. This is primarily due to the lack of experimental data on the biochemical properties and structure of olfactory receptors. The long-term goal of our research program is to determine the structure of olfactory receptors at the atomic level using three-dimensional (3D) X-ray crystallographic techniques to understand how odorants interact with these specialized receptors. Having even one structure in hand would open up many possibilities to study other odorant receptors using homology modeling. Consequently, the objectives of this R21 application are to: (1) use an inducible heterologous over-expression system to produce milligram quantities of selected olfactory receptors and (2) begin assaying these proteins for crystallization in house and using the facility at Hauptman-Woodward Medical Research Institute at the University of Buffalo. The proposed research is significant because the exploratory data expected from this work would open the way to determine the atomic structure of a prototypical OR. Achieving this goal would have a major impact on the Chemical Senses field by providing for the first time the structural basis of odorant molecule/receptor interactions. This would provide an opportunity to understand and interpret at the molecular level the results from mutagenesis experiments, both published and future, that are using functional assays. Moreover, an atomic structure would allow the creation of more accurate homology models, improving the ability to predict an olfactory receptor's odorant binding properties. This information could be used to design molecules to bind more tightly or to inhibit binding of natural odorants. It could help understand variation in olfactory sensation between individual people potentially arising from olfactory receptor amino acid sequence polymorphisms. Finally, an olfactory receptor structure would have significant impact for all disciplines that involve G-protein coupled receptor superfamily, since at present there is only one known structure (i.e. rhodopsin).
There is a growing demand to understand the structural basis for the selective binding of molecules like hormones or odorants to their membrane protein receptors. This is particularly important for rational drug design and producing molecular detectors. This grant is aimed at elucidating the three dimensional structure of olfactory receptors, a large family of proteins that detect a wide variety of molecules with diverse molecular structures.
