Sense of Smell: Structural, Functional, Mechanistic Advancements and Challenges in Human Olfactory Research

摘要

Olfaction, the sense of smell detects and discriminate odors as well as social cues whichinfluence our innate responses. The olfactory system in human beings is found to be weak as com-pared to other animals; however, it seems to be very precise. It can detect and discriminate millionsof chemical moieties (odorants) even in minuscule quantities. The process initiates with the bindingof odorants to specialized olfactory receptors, encoded by a large family of Olfactory Receptor(OR) genes belonging to the G-protein-coupled receptor superfamily. Stimulation of ORs convertsthe chemical information encoded in the odorants, into respective neuronal action-potentials whichcauses depolarization of olfactory sensory neurons. The olfactory bulb relays this signal to differentparts of the brain for processing. Odors are encrypted using a combinatorial approach to detect avariety of chemicals and encode their unique identity. The discovery of functional OR genes andproteins provided an important information to decipher the genomic, structural and functional basisof olfaction. ORs constitute 17 gene families, out of which 4 families were reported to contain morethan hundred members each. The olfactory machinery is not limited to GPCRs; a number of non-GPCRs is also employed to detect chemosensory stimuli. The article provides detailed informationabout such olfaction machinery, structures, transduction mechanism, theories of odor perception,and challenges in the olfaction research. It covers the structural, functional and computational stud-ies carried out in the olfaction research in the recent past.