Mammalian odorant receptors: functional evolution and variation

- Mammalian ORs undergo rapid evolution at the primary sequence and functional levels.
- Functional differences are more frequently observed among OR paralogs than orthologs.
- OR orthologs show conserved ligand selectivity, yet can be different in their sensitivity and/or efficacy.
- Human OR repertoire displays high degrees of polymorphisms which translate into functional changes.
- Functional variation of ORs partly explains differences in odor perception in humans.

In mammals, the perception of smell starts with the activation of odorant receptors (ORs) by volatile molecules in the environment. The mammalian OR repertoire has been subject to rapid evolution, and is highly diverse within the human population. Recent advances in the functional expression and ligand identification of ORs allow for functional analysis of OR evolution, and reveal that changes in OR protein sequences translate into high degrees of functional variations. Moreover, in several cases the functional variation of a single OR affects the perception of its cognate odor ligand, providing clues as to how an odor is coded at the receptor level.