The sense of smell plays an important role in vertebrate behavior. In man it is crucial for the assessment of food quality and for avoiding of harmful substances. Olfaction also underlies many aspects of human social interactions. the understanding of molecular components in the olfactory mechanism constitutes a major challenge for sensory research. Previously, we have studied functional membrane proteins in olfactory cilia, namely olfactory GTP-binding protein (G-protein), odorant-sensitive adenylyl cyclase, as well as olfactory-specific membrane glycoproteins. In the last three years period we have identified by molecular cloning three novel olfactory-specific proteins: two olfactory biotransformation enzymes (cytochrome P-450olf1 and olfactory UDP glucuronosyl transferase, UGTolf), and the olfactory cyclic AMP gated channel. We propose here to continue our studies related to the identification, isolation and molecular cloning of olfactory proteins. Particular emphasis will be placed on components related to the regulation and termination of olfactory signals, a hitherto unexplored area. The proposed research includes: A) A plan to clone and express new olfactory receptor candidates (based on recently published sequences) followed by a novel optimization strategy for discovering receptors with known odorant specificity. This will establish the candidate receptors' function, and provide tools for subsequent research. B) studies of olfactory receptor phosphorylation and its possible role in sensory desensitization or adaptation. Native and cloned receptors, as well as model peptides will be used to try to identify the responsible protein kinase(s). C) Molecular studies of the olfactory ion channel related to its possible desensitization. D) Studies of odorant biotransformation by the well-documented enzyme UDPolf, as well as by the newly identified olfactory-enriched glutathione S-transferase. Proof for their role as olfactory signal termination devices will be sought. The study of olfactory signal termination is important for understanding how multitudes of odorants are perceived: without termination, current odorants would interfere with new incoming ones. Understanding olfactory biotransformation (detoxification) enzymes is also relevant to the ways by which the olfactory neuroepithelium (and possibly the overlying brain) are protected from exposure to potentially neurotoxic odorants.
