Olfactory receptor 665470 222920006 2008-07-01T19:13:09Z DOI bot 6652755 Citation maintenance. Removed redundant parameters. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. '''Olfactory receptors''' expressed in the [[cell membrane]]s of [[olfactory receptor neuron]]s are responsible for the detection of [[odor]] molecules. Activated olfactory receptors are the initial player in a [[signal transduction]] cascade which ultimately produces a [[nerve impulse]] which is transmitted to the brain. These receptors are members of the [[rhodopsin-like receptors|class A rhodopsin-like]] family of [[G protein-coupled receptor]]s.<ref name="pmid14999405">{{cite journal | author = Gaillard I, Rouquier S, Giorgi D | title = Olfactory receptors | journal = Cell. Mol. Life Sci. | volume = 61 | issue = 4 | pages = 456–69 | year = 2004 | pmid = 14999405 | doi = 10.1007/s00018-003-3273-7 }}</ref> ==Expression== In [[vertebrate]]s, the olfactory receptors are located in the cilia of the olfactory sensory neurons.<ref name="pmid17603536">{{cite journal | author = Rinaldi A | title = The scent of life. The exquisite complexity of the sense of smell in animals and humans | journal = EMBO Rep. | volume = 8 | issue = 7 | pages = 629–33 | year = 2007 | pmid = 17603536 | doi = 10.1038/sj.embor.7401029 }}</ref> In [[insect]]s, olfactory receptors are located on the [[antenna (biology)|antennae]].<ref name="pmid16332206">{{cite journal | author = Hallem EA, Dahanukar A, Carlson JR | title = Insect odor and taste receptors | journal = Annu. Rev. Entomol. | volume = 51 | issue = | pages = 113–35 | year = 2006 | pmid = 16332206 | doi = 10.1146/annurev.ento.51.051705.113646 }}</ref> [[Sperm]] cells also express odor receptors, which are thought to be involved in [[chemotaxis]] to find the [[egg cell]].<ref name="pmid16413109">{{cite journal | author = Spehr M, Schwane K, Riffell JA, Zimmer RK, Hatt H | title = Odorant receptors and olfactory-like signaling mechanisms in mammalian sperm | journal = Mol. Cell. Endocrinol. | volume = 250 | issue = 1-2 | pages = 128–36 | year = 2006 | pmid = 16413109 | doi = 10.1016/j.mce.2005.12.035 }}</ref> ==Mechanism== Rather than binding specific ligands like most [[receptor_(biochemistry)|receptors]], olfactory receptors display affinity for a range of [[odor]] molecules and conversely a single odorant molecule may bind to a number of olfactory receptors with varying affinities.<ref name="pmid15630933">{{cite journal | author = Buck LB | title = Olfactory receptors and odor coding in mammals | journal = Nutr. Rev. | volume = 62 | issue = 11 Pt 2 | pages = S184–8; discussion S224–41 | year = 2004 | pmid = 15630933 | doi = 10.1301/nr.2004.nov.S184-S188 }}</ref> Once the odorant has bound to the odor receptor, the receptor undergoes structural changes and it binds and activates the olfactory-type [[G protein]] on the inside of the olfactory receptor neuron. The [[heterotrimeric G protein|G protein]] ([[GNAL|G<sub>olf</sub>]] and/or [[GNAS1|G<sub>s</sub>]])<ref name="pmid2499043">{{cite journal | author = Jones DT, Reed RR | title = Golf: an olfactory neuron specific-G protein involved in odorant signal transduction | journal = Science | volume = 244 | issue = 4906 | pages = 790–5 | year = 1989 | pmid = 2499043 | doi = 10.1126/science.2499043 }}</ref> in turn activates the lyase - [[adenylate cyclase]] - which converts [[adenosine triphosphate|ATP]] into [[cyclic AMP]] (cAMP). The cAMP opens [[cyclic nucleotide-gated ion channel]]s which allow [[calcium]] and [[sodium]] [[ion]]s to enter into the cell, depolarizing the olfactory receptor neuron and beginning an [[action potential]] which carries the information to the [[brain]]. ==Diversity== There are a wide range of different odor receptors, with as many as 1,000 in the mammalian [[genome]] which represents approximately 3% of the genes in the genome. However not all of these potential odor receptor genes are expressed and are functional. According to an analysis of data derived from the [[human genome project]], humans have approximately 400 functional [[gene]]s coding for olfactory receptors and the remaining 600 candidates are [[pseudogene]]s.<ref name="pmid12644552">{{cite journal | author = Gilad Y, Lancet D | title = Population differences in the human functional olfactory repertoire | journal = Mol. Biol. Evol. | volume = 20 | issue = 3 | pages = 307–14 | year = 2003 | pmid = 12644552 | doi = 10.1093/molbev/msg013 }}</ref> The reason for the large number of different odor receptors is to provide a system for discriminating between as many different odors as possible. Even so, each odor receptor does not detect a single odor. Rather each individual odor receptor is broadly tuned to be activated by a number of similar odorant structures.<ref name="pmid10089886">{{cite journal | author = Malnic B, Hirono J, Sato T, Buck LB | title = Combinatorial receptor codes for odors | journal = Cell | volume = 96 | issue = 5 | pages = 713–23 | year = 1999 | pmid = 10089886 | doi = 10.1016/S0092-8674(00)80581-4 }}</ref><ref name="pmid14724183">{{cite journal | author = Araneda RC, Peterlin Z, Zhang X, Chesler A, Firestein S | title = A pharmacological profile of the aldehyde receptor repertoire in rat olfactory epithelium | journal = J. Physiol. (Lond.) | volume = 555 | issue = Pt 3 | pages = 743–56 | year = 2004 | pmid = 14724183 | doi = 10.1113/jphysiol.2003.058040 }}</ref> Analogous to the [[immune system]], the diversity that exists within the olfactory receptor family allows molecules that have never been encountered before to be characterized. Furthermore most odors activate more than one type of odor receptor. Since the number of [[combinatorics|combinations and permutations]] of olfactory receptors is almost limitless, the olfactory receptor system is capable of detecting and distinguishing between a practically infinite number of odorant molecules. ==Families== A [[gene nomenclature|nomenclature]] system has been devised for the olfactory receptor family<ref name="pmid11063259">{{cite journal | author = Glusman G, Bahar A, Sharon D, Pilpel Y, White J, Lancet D | title = The olfactory receptor gene superfamily: data mining, classification, and nomenclature | journal = Mamm. Genome | volume = 11 | issue = 11 | pages = 1016–23 | year = 2000 | pmid = 11063259 | doi = 10.1007/s003350010196 }}</ref> and is the basis for the official Human Genome Project ([[HUGO]]) symbols for the [[gene]]s that encode these receptors. The names of individual olfactory receptor family members are in the format "ORnXm" where: * OR is the root name ('''O'''lfactory '''R'''eceptor superfamily) * n = an integer representing a family (e.g., 1-56) whose members have greater than 40% sequence identity, * X = a single letter (A, B, C, ...) denoting a subfamily (>60% sequence identity), and * m = an integer representing an individual family member ([[protein isoform|isoform]]). For example {{gene|OR1A1}} is the first isoform of subfamily A of olfactory receptor family 1. Members belonging to the same subfamily of olfactory receptors (>60% sequence identity) are likely to recognize structurally similar odorant molecules.<ref name="pmid14983052">{{cite journal | author = Malnic B, Godfrey PA, Buck LB | title = The human olfactory receptor gene family | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 101 | issue = 8 | pages = 2584–9 | year = 2004 | pmid = 14983052 | doi = 10.1073/pnas.0307882100 }}</ref> Two major classes of olfactory receptors have been identified in humans:<ref name="pmid11337468">{{cite journal | author = Glusman G, Yanai I, Rubin I, Lancet D | title = The complete human olfactory subgenome | journal = Genome Res. | volume = 11 | issue = 5 | pages = 685–702 | year = 2001 | pmid = 11337468 | doi = 10.1101/gr.171001 }}</ref> * class I (fish-like receptors) OR families 51-56 * class II ([[tetrapod]] specific receptors) OR families 1-13 ==Discovery== In [[2004]] [[Linda B. Buck]] and [[Richard Axel]] won the [[Nobel Prize in Physiology or Medicine]] for their work on olfactory receptors.<ref name="pmid1840504">{{cite journal | author = Buck L, Axel R | title = A novel multigene family may encode odorant receptors: a molecular basis for odor recognition | journal = Cell | volume = 65 | issue = 1 | pages = 175–87 | year = 1991 | pmid = 1840504 | doi = 10.1016/0092-8674(91)90418-X }}</ref><ref>{{cite web |url=http://nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html |title=Press Release: The 2004 Nobel Prize in Physiology or Medicine |accessdate=2007-06-06 |format= |work=}}</ref> In 2006 it was shown that another class of odorant receptors exist for volatile [[amine]]s.<ref name="pmid16878137">{{cite journal | author = Liberles SD, Buck LB | title = A second class of chemosensory receptors in the olfactory epithelium | journal = Nature | volume = 442 | issue = 7103 | pages = 645–50 | year = 2006 | pmid = 16878137 | doi = 10.1038/nature05066 }}</ref> This class of receptors consists of the [[trace amine-associated receptor]]s (TAAR) with the exception of TAAR1 which is a receptor for [[thyronamine]]s. Unfortunately, there is still a lack of experimental structures at atomic level for [[olfactory receptors]] and structural information is based on [[homology modeling]] methods.<ref name="pmid17120078">{{cite journal | author = Khafizov K, Anselmi C, Menini A, Carloni P | title = Ligand specificity of odorant receptors | journal = J Mol Model | volume = 13 | issue = 3 | pages = 401–9 | year = 2007 | pmid = 17120078 | doi = 10.1007/s00894-006-0160-9 }}</ref> == See also == * [[Receptor (biochemistry) | Receptor]] * [[Trace amine-associated receptor]] * [[Aroma compound | Odorant]] == References == {{Reflist|2}} ==External links== * [http://senselab.med.yale.edu/senselab/ORDB/ Olfactory Receptor Database] * [http://bioportal.weizmann.ac.il/HORDE/ Human Olfactory Receptor Data Exploratorium (HORDE)] * {{MeshName|Olfactory+Receptor+Protein}} {{Olfactory_system}} {{Olfactory receptors}} {{G protein-coupled receptors}} {{Transmembrane receptors}} [[Category:G protein coupled receptors]] [[Category:Sensory receptors]] [[Category:olfactory system]] [[Category:Neurophysiology]] [[Category:Integral membrane proteins]] [[de:Geruchsrezeptor (Protein)]] [[fr:Récepteurs olfactifs]] [[ja:嗅覚受容体]] [[zh:嗅覺受器]]