Deorphanizing vertebrate olfactory receptors: recent advances in odorant-response assays.
Olfactory receptors (ORs) comprise the largest multigene G protein-coupled receptor families in organisms from fish to primates, and play a critical role in recognizing thousands of odorant molecules. Recent achievement of functional OR expression in heterologous cells led to identification of ligands for some ORs, revealing a combinatorial receptor coding scheme in the olfactory sensory system. Using the functional assay, the odorant-binding site in ORs has been elucidated, showing that a binding pocket constructed by transmembrane helices provides the molecular basis for agonist and antagonist specificity. To retrospectively identify ORs that recognize a particular odorant of interest, two functional cloning strategies have been developed: one is a strategy wherein OR genes are amplified from single olfactory neurons that show odorant responsiveness in Ca(2+) imaging, and another is an approach based on glomerular activity by combining in vivo bulbar Ca(2+) imaging and retrograde dye labeling of innervating olfactory neurons. The conventional ligand-screening approach and the functional cloning strategies in an odorant-directed manner have allowed us to match ORs to the cognate odorants both in vitro and in vivo.
Touhara
Kazushige
K
Department of Integrated Biosciences, University of Tokyo, Chiba 277-8562, Japan. touhara@k.u-tokyo.ac.jp
D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D019143:Evolution, Molecular; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D008024:Ligands; D008967:Molecular Biology / Q000379:methods; D009812:Odorants; D017434:Protein Structure, Tertiary / Q000502:physiology; D018035:Receptors, Odorant / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D012903:Smell / Q000187:drug effects / Q000235:genetics*; D014714:Vertebrates / Q000235:genetics* / Q000378:metabolism*
D008024:Ligands; D018035:Receptors, Odorant; D002118:Calcium