Olfactory receptors (ORs) have diverse protein sequences but can be assigned to subfamilies on the basis of sequence relationships. Odorants and pheromones bind to these seven transmembrane domain G-protein-coupled receptors that permit signal transduction. These receptors are encoded by large multigene families that evolved in mammal species in function of specific olfactory needs. Members of the same subfamily have related sequences and are likely to recognize structurally related odorants.
Of the 960 human OR genes and pseudogenes, there is experimental evidence which indicates that at least 437 actually are expressed in human olfactory epithelium; this includes 357 OR genes, and 80 OR pseudogenes (Zhang, 2007). These 357 olfactory-expressed OR genes are therefore expected to be functional in the Olfactory Signaling Pathway, and to interact directly with human G alpha olf in human olfactory cells.
(Note: A subset of 200 of these 357 OR genes are shown as components of OR-G Protein reaction. The others will be added to Reactome later.)