Odotope theory
Odotope theory, also known as weak shape theory,[1] is a theory of how olfactory receptors bind to odor molecules. The theory proposes that a combination of shape factors determine the coupling, which utilizes the commonly accepted mechanism of combinatorial receptor codes.[2] In the mechanism, each odorant may activate multiple receptors, and each receptor may respond to multiple odorants. The word itself is an analogy to epitopes.
It falls under the field of structure-odor relations (SOR),[3] and is not to be confused with the docking theory of olfaction, which describes an earlier model of olfaction where one odor molecule would selectively bind to one olfactory receptor.[4]
Mechanism
[edit]An odotope describes each molecular and topological feature of an odorant molecule, each of which may be bind to an olfactory receptor(s) that may recognize the particular spatial arrangement.[5] Therefore, an olfactory system would 'deconstruct' odors into its odotopes, and then the pattern of odotopes detected would yield a particular smell.
These receptors are often G-protein-coupled receptors (GPCRs) in mammals. After an odorant dissolves in the nasal mucus, it will bind to the olfactory receptors, which are present on olfactory sensroy neurons. This triggers the activation of olfactory G-protein, stimulating adenylate cyclase and producing cAMP. This in turn opens a cAMP-gated channel for an influx of sodium and calcium ions. As a result, the olfactory sensory neuron gets depolarized, triggering an action potential. This neuronal signal then travels from the olfactory bulb to the olfactory cortex.[5]
In insects, their odorant receptors are known as OrX proteins. These will form heteromeric ligand-gated ion channels with a co-receptor, Orco. Upon odorant binding to the OrX/Orco complex, a non-selective cation channel opens, resulting in calcium, potassium, and sodium passage into the olfactory sensory neuron, triggering depolarization.[6]
See also
[edit]References
[edit]- ^ "The scent of life. The exquisite complexity of the sense of smell in animals and humans". EMBO Rep. 8 (7): 629–33. July 2007. doi:10.1038/sj.embor.7401029. PMC 1905909. PMID 17603536.
- ^ Zarzo, Manuel (5 March 1999). "The sense of smell: molecular basis of odorant recognition". Cell Press. 82 (3): 455–479. doi:10.1111/j.1469-185X.2007.00019.x. ISSN 1464-7931.
- ^ Yoshii, Fumiko (January 2003). "Structure-odor relations: A modern perspective". Handbook of Olfaction and Gustation – via ResearchGate.
- ^ Horsfield, A. P.; Haase, A.; Turin, L. (2017-05-04). "Molecular recognition in olfaction". Advances in Physics: X. 2 (3): 937–977. doi:10.1080/23746149.2017.1378594. hdl:11572/187885.
- ^ a b Park, Seok-Won (2014). "Understanding the Human Sensory Conduction of Smell". Hanyang Medical Reviews. 34 (3): 100. doi:10.7599/hmr.2014.34.3.100. ISSN 1738-429X.
- ^ Wicher, Dieter; Miazzi, Fabio (27 Jan 2021). "Functional properties of insect olfactory receptors: ionotropic receptors and odorant receptors". Cell and Tissue Research. 383 (1): 7–19. doi:10.1007/s00441-020-03363-x. ISSN 0302-766X. PMC 7873100. PMID 33502604.
- Mori, K. and Shepherd, GM. (1994). Emerging principles of molecular signal processing by mitral/tufted cells in the olfactory bulb. Semin Cell Biol 5-1:65-74.
- Burr, Chandler. The Emperor of Scent: A true story of perfume and obsession. Random House, New York: 2002.
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