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Orexin Edit Wikipedia article
|This article relies on references to primary sources. (March 2012)|
|orexin (hypocretin) neuropeptide precursor|
Solution phase NMR structure of orexin B based on the PDB coordinates .
|Alt. symbols||PPOX, OX|
|Locus||Chr. 17 q21|
Orexin, also called hypocretin, is a neurotransmitter that regulates arousal, wakefulness, and appetite. The most common form of narcolepsy, in which the sufferer briefly loses muscle tone (cataplexy), is caused by a lack of orexin in the brain due to destruction of the cells that produce it.
The brain contains very few cells that produce orexin; in a human brain, about 10,000 to 20,000 neurons in the hypothalamus. However, the axons from these neurons extend throughout the entire brain and spinal cord, where there are also receptors for orexin.
Orexin was discovered in 1998 almost simultaneously by two independent groups of rat-brain researchers. One group named it orexin, from orexis, meaning "appetite" in Greek; the other group named it hypocretin, because it is produced in the hypothalamus and bears a weak resemblance to secretin, a hormone found in the gut. The scientific community has not yet settled on a consensus for which word to use.
There are two types of orexin: orexin-A and -B (hypocretin-1 and -2). They are excitatory neuropeptide hormones with approximately 50% sequence identity, are produced by cleavage of a single precursor protein. Orexin-A is 33 amino acid residues long and has two intrachain disulfide bonds; orexin-B is a linear 28 amino acid residue peptide. Studies suggest that orexin-A may be of greater biological importance than orexin-B. Although these peptides are produced by a very small population of cells in the lateral and posterior hypothalamus, they send projections throughout the brain. The orexin peptides bind to the two G-protein coupled orexin receptors, OX1 and OX2, with orexin-A binding to both OX1 and OX2 with approximately equal affinity while orexin-B binds mainly to OX2 and is 5 times less potent as OX1.
The orexins are strongly conserved peptides, found in all major classes of vertebrates.
The orexin system was initially suggested to be primarily involved in the stimulation of food intake, based on the finding that central administration of orexin-A and -B increased food intake. In addition, it stimulates wakefulness and energy expenditure.
Brown fat activation
Obesity in orexin knockout mice is a result of inability of brown preadipocytes to differentiate into brown adipose tissue (BAT), which in turn reduces BAT thermogenesis. BAT differentiation can be restored in these knockout mice through injections of orexin. Deficiency in orexin has also been linked to narcolepsy, a sleep disorder. Furthermore narcoleptic people are more likely to be obese. Hence obesity in narcoleptic patients may be due to orexin deficiency leading to impaired thermogenesis and energy expenditure.
Orexin seems to promote wakefulness. Recent studies indicate that a major role of the orexin system is to integrate metabolic, circadian and sleep debt influences to determine whether an animal should be asleep or awake and active. Orexin neurons strongly excite various brain nuclei with important roles in wakefulness including the dopamine, norepinephrine, histamine and acetylcholine systems and appear to play an important role in stabilizing wakefulness and sleep.
The discovery that an orexin receptor mutation causes the sleep disorder canine narcolepsy in Doberman Pinschers subsequently indicated a major role for this system in sleep regulation. Genetic knockout mice lacking the gene for orexin were also reported to exhibit narcolepsy. Transitioning frequently and rapidly between sleep and wakefulness, these mice display many of the symptoms of narcolepsy. Researchers are using this animal model of narcolepsy to study the disease. Narcolepsy results in excessive daytime sleepiness, inability to consolidate wakefulness in the day (and sleep at night), and cataplexy, which is the loss of muscle tone in response to strong, usually positive, emotions. Dogs that lack a functional receptor for orexin have narcolepsy, while animals and people lacking the orexin neuropeptide itself also have narcolepsy.
Central administration of orexin-A strongly promotes wakefulness, increases body temperature, locomotion and elicits a strong increase in energy expenditure. Sleep deprivation also increases orexin-A transmission. The orexin system may thus be more important in the regulation of energy expenditure than food intake. In fact, orexin-deficient narcoleptic patients have increased obesity rather than decreased BMI, as would be expected if orexin were primarily an appetite stimulating peptide. Another indication that deficits of orexin cause narcolepsy is that depriving monkeys of sleep for 30–36 hours and then injecting them with the neurochemical alleviates the cognitive deficiencies normally seen with such amount of sleep loss.
In humans, narcolepsy is associated with a specific variant of the human leukocyte antigen (HLA) complex. Furthermore, genome-wide analysis shows that, in addition to the HLA variant, narcoleptic humans also exhibit a specific genetic mutation in the T-cell receptor alpha locus. In conjunction, these genetic anomalies cause the immune system to attack and kill the critical orexin neurons. Hence the absence of orexin-producing neurons in narcoleptic humans may be the result of an autoimmune disorder.
Orexin increases the craving for food, and correlates with the function of the substances that promote its production.
Leptin is a hormone produced by fat cells and acts as a long-term internal measure of energy state. Ghrelin is a short-term factor secreted by the stomach just before an expected meal, and strongly promotes food intake.
Orexin-producing cells have recently been shown to be inhibited by leptin (through the leptin receptor pathway), but are activated by ghrelin and hypoglycemia (glucose inhibits orexin production). Orexin, as of 2007, is claimed to be a very important link between metabolism and sleep regulation. Such a relationship has been long suspected, based on the observation that long-term sleep deprivation in rodents dramatically increases food intake and energy metabolism, i.e., catabolism, with lethal consequences on a long-term basis. Sleep deprivation then leads to a lack of energy. In order to make up for this lack of energy, many people use high-carbohydrate and high-fat foods that ultimately can lead to poor health and weight gain. Other dietary nutrients, amino acids, also can activate orexin neurons, and they can suppress the glucose response of orexin neurons at physiological concentration, causing the energy balance that orexin maintains to be thrown off its normal cycle.
The research on orexin mimics is still in an early phase, although many scientists believe that orexin-based drugs could help narcoleptics and increase alertness in the brain without the side effects of amphetamines.
Merck reported at the Sleep 2012 conference that insomniacs taking an orexin blocker, suvorexant, fell asleep faster and slept an hour longer. Suvorexant was tested for three months on over a thousand patients in a phase III trial. Survorexant has undergone three phase III trials and will be available in late 2014 or early 2015 as "Belsomra".
Preliminary research has been conducted that shows potential for orexin blockers in the treatment of alcoholism. Lab rats given drugs which targeted the orexin system lost interest in alcohol despite being given free access in experiments.
A study has reported that transplantation of orexin neurons into the pontine reticular formation in rats is feasible, indicating the development of alternative therapeutic strategies in addition to pharmacological interventions to treat narcolepsy.
Because orexin-A receptors have been shown to regulate relapse to cocaine seeking, a new study investigated its relation to nicotine by studying rats. By blocking the orexin-A receptor with low doses of the selective antagonist SB-334,867, nicotine self-administration decreased and also the motivation to seek and obtain the drug. The study showed that blocking of receptors in the insula decreased self-administration, but not blocking of receptors in the adjacent somatosensory cortex. The greatest decrease in self-administration was found when blocking all orexin-A receptors in the brain as a whole. A rationale for this study was the fact that the insula has been implicated in regulating feelings of craving. The insula contains orexin-A receptors. It has been reported that smokers who sustained damage to the insula lost the desire to smoke.
Orexin-A (OXA) has been recently demonstrated to have direct effect on a part of the lipid metabolism. OXA stimulates glucose uptake in 3T3-L1 adipocytes and that increased energy uptake is stored as lipids (triacylglycerol). OXA thus increases lipogenesis. It also inhibits lipolysis and stimulates the secretion of adiponectin. These effects are thought to be mostly conferred via the PI3K pathway because this pathway inhibitor (LY294002) completely blocks OXA effects in adipocytes. The link between OXA and the lipid metabolism is new and currently under more research.
High levels of orexin-A have been associated with happiness in human subjects, while low levels have been associated with sadness. The finding suggests that boosting levels of orexin-A could elevate mood in humans, being thus a possible future treatment for disorders like depression. Likewise, it helps explain the incidence of depression associated with narcolepsy.
History and nomenclature
In 1996, Gautvik, de Lecea, and colleagues reported the discovery of several genes in the rat brain, including one they dubbed "clone 35." Their work showed that clone 35 expression was limited to the lateral hypothalamus.
Masashi Yanagisawa and colleagues at the University of Texas Southwestern Medical Center at Dallas, coined the term orexin to reflect the orexigenic (appetite-stimulating) activity of these hormones. In their 1998 paper (with authorship attributed to Sakurai and colleagues) describing these neuropeptides, they also reported discovery of two orexin receptors, dubbed OX1R and OX2R.
In 1998, Luis de Lecea, Thomas Kilduff, and colleagues also reported discovery of these same peptides, dubbing them hypocretins to indicate that they are synthesized in the hypothalamus and to reflect their structural similarity to the hormone secretin (i.e., hypothalamic secretin). This is the same group that first identified clone 35 two years earlier. De Lecea and colleagues were originally in search of novel genes expressed in the hypothalamus. To do this, they extracted selective DNA found in the lateral hypothalamus. They cloned this DNA and studied it under electron microscopy. Neurotransmitters found in this area were oddly similar to the gut hormone, secretin, so de Lecea decided to name the two forms of peptides hypocretin-1 and hypocretin-2. These cells were first thought to reside and work only within the lateral hypothalamus area, but immunocytochemmistry tactics revealed the various projections this area truly had to other parts of the brain. A majority of these projections reached the limbic system and structures associated with it (including the amygdala, septum, and basal forebrain area).
The name of this family of peptides is currently an unsettled issue. The name "orexin" has been rejected by some due to evidence that the orexigenic effects of these peptides may be incidental or trivial (i.e., orexin induced subjects eat more because they are awake more), though this issue is also unsettled, while other groups maintain that the name "hypocretin" is awkward, pointing out that many neuropeptides have names that are unrelated to their most important functions, and that waking is one of the important factors that supports feeding behavior. Both "orexin" and "hypocretin" will likely continue to appear in published works until a preferred name has been accepted by the scientific community.
Several drugs acting on the orexin system are under development, either orexin agonists for the treatment of conditions such as narcolepsy, or orexin antagonists for insomnia. No non-peptide agonists are yet available, although synthetic Orexin-A polypeptide has been made available as a nasal spray and tested on monkeys. Several non-peptide antagonists are in development however; SB-649,868 is under development by GlaxoSmithKline for sleep disorders and is a non-selective orexin receptor antagonist. Another OX1 and OX2 receptor antagonist (ACT-078573, almorexant) is a similar compound under development for primary insomnia by Actelion. A third entry is Merck's MK-4305.
Most ligands acting on the orexin system so far are polypeptides modified from the endogenous agonists Orexin-A and Orexin-B, however there are some subtype-selective non-peptide antagonists available for research purposes.
- SB-334,867 – selective OX1 antagonist
- SB-408,124 – selective OX1 antagonist
- TCS-OX2-29 – selective OX2 antagonist
- EMPA(drug) (N-Ethyl-2-[(6-methoxy-pyridin-3-yl)-(toluene-2-sulfonyl)-amino]-N-pyridin-3-ylmethyl-acetamide) – selective OX2 antagonist
Interaction with other neurotransmitter systems
||This section may be too technical for most readers to understand. (October 2013)|
Orexinergic neurons have been shown to be sensitive to inputs from Group III metabotropic glutamate receptors, adenosine A1 receptors, muscarinic M3 receptors, serotonin 5-HT1A receptors, neuropeptide Y receptors, cholecystokinin A receptors, and catecholamines, as well as to ghrelin, leptin, and glucose. Orexinergic neurons themselves regulate release of acetylcholine, serotonin and noradrenaline, so despite the relatively small number of orexinergic neurons compared to other neurotransmitter systems in the brain, this system plays a key regulatory role and extensive research will be required to unravel the details. Orexins act on Gq-protein-coupled receptors signaling through phospholipase C (PLC) and calcium-dependent as well as calcium-independent transduction pathways. These include activation of electrogenic sodium-calcium exchangers (NCX) and a non-specific cationic conductance, likely channels of the transient receptor potential canonical-(TRPC) type activation of L-type voltage-dependent calcium channels, closure of G-protein-activated inward rectifier potassium channels (GIRK), and activation of protein kinases, including protein kinase C (PKC), protein kinase A (PKA), and mitogen-associated protein kinase, also called mitogen-activated protein kinase (MAPK). Postsynaptic actions of orexins on their numerous neuronal targets throughout the CNS are almost entirely excitatory.
- Davis JF, Choi DL, Benoit SC (2011). "24. Orexigenic Hypothalamic Peptides Behavior and Feeding - 24.5 Orexin". In Preedy VR, Watson RR, Martin CR. Handbook of Behavior, Food and Nutrition. Springer. pp. 361–2. ISBN 9780387922713.
- Stanford Center for Narcolepsy FAQ (retrieved 27-Mar-2012)
- Marcus JN, Elmquist JK (2006). "3. Orexin Projections and Localization of Orexin Receptors". In Nishino S, Sakurai T. The Orexin/Hypocretin System: Physiology and Pathophysiology. Springer. p. 195. ISBN 9781592599509.
- Sakurai T, Amemiya A, Ishii M, Matsuzaki I, Chemelli RM, Tanaka H, Williams SC, Richardson JA, Kozlowski GP, Wilson S, Arch JR, Buckingham RE, Haynes AC, Carr SA, Annan RS, McNulty DE, Liu WS, Terrett JA, Elshourbagy NA, Bergsma DJ, Yanagisawa M (1998). "Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior". Cell 92 (4): 573–85. doi:10.1016/S0092-8674(00)80949-6. PMID 9491897.
- de Lecea L, Kilduff TS, Peyron C, Gao X, Foye PE, Danielson PE, Fukuhara C, Battenberg EL, Gautvik VT, Bartlett FS, Frankel WN, van den Pol AN, Bloom FE, Gautvik KM, Sutcliffe JG (1998). "The hypocretins: Hypothalamus-specific peptides with neuroexcitatory activity". Proc. Natl. Acad. Sci. U.S.A. 95 (1): 322–7. doi:10.1073/pnas.95.1.322. PMC 18213. PMID 9419374.
- Langmead CJ, Jerman JC, Brough SJ, Scott C, Porter RA, Herdon HJ (January 2004). "Characterisation of the binding of 3H-SB-674042, a novel nonpeptide antagonist, to the human orexin-1 receptor". Br. J. Pharmacol. 141 (2): 340–6. doi:10.1038/sj.bjp.0705610. PMC 1574197. PMID 14691055.
- Sellayah D, Bharaj P, Sikder D (October 2011). "Orexin is required for brown adipose tissue development, differentiation, and function". Cell Metab. 14 (4): 478–90. doi:10.1016/j.cmet.2011.08.010. PMID 21982708. Lay summary – ScienceDaily.
- Sherin JE, Elmquist JK, Torrealba F, Saper CB (June 1998). "Innervation of histaminergic tuberomammillary neurons by GABAergic and galaninergic neurons in the ventrolateral preoptic nucleus of the rat". The Journal of Neuroscience 18 (12): 4705–21. PMID 9614245.
- Lu J, Bjorkum AA, Xu M, Gaus SE, Shiromani PJ, Saper CB (June 2002). "Selective activation of the extended ventrolateral preoptic nucleus during rapid eye movement sleep". J. Neurosci. 22 (11): 4568–76. PMID 12040064.
- Lin L, Faraco J, et al. (1999). "The sleep disorder canine narcolepsy is caused by a mutation in the hypocretin (orexin) receptor 2 gene". Cell 98 (3): 365–376. doi:10.1016/S0092-8674(00)81965-0. PMID 10458611.
- Chemelli RM, Willie JT, et al. (1999). "Narcolepsy in orexin knockout mice: molecular genetics of sleep regulation". Cell 98 (4): 437–451. doi:10.1016/S0092-8674(00)81973-X. PMID 10481909.
- Mochizuki T, Crocker A, McCormack S, Yanagisawa M, Sakurai T, Scammell TE (July 2004). "Behavioral state instability in orexin knock-out mice". J. Neurosci. 24 (28): 6291–300. doi:10.1523/JNEUROSCI.0586-04.2004. PMID 15254084.
- Alexis Madrigal (2007-12-28). "Snorting a Brain Chemical Could Replace Sleep". Wired News, Condé Nast. Retrieved 2008-02-05.
- Deadwyler SA, Porrino L, Siegel JM, Hampson RE (2007). "Systemic and nasal delivery of orexin-A (Hypocretin-1) reduces the effects of sleep deprivation on cognitive performance in nonhuman primates". J. Neurosci. 27 (52): 14239–47. doi:10.1523/JNEUROSCI.3878-07.2007. PMID 18160631.
- Klein J, Sato A (September 2000). "The HLA system. Second of two parts". N. Engl. J. Med. 343 (11): 782–6. doi:10.1056/NEJM200009143431106. PMID 10984567.
- Hallmayer J, Faraco J, Lin L, et al. (June 2009). "Narcolepsy is strongly associated with the TCR alpha locus". Nat. Genet. 41 (6): 708–11. doi:10.1038/ng.372. PMC 2803042. PMID 19412176.
- "Narcolepsy is an autoimmune disorder, Stanford researcher says". EurekAlert. American Association for the Advancement of Science. 2009-05-03. Retrieved 2009-05-31.
- Helen Puttick (2006-12-26). "Hope in fight against alcoholism". The Herald.
- Lawrence AJ, Cowen MS, Yang HJ, Chen F, Oldfield B (2006). "The orexin system regulates alcohol-seeking in rats". Br. J. Pharmacol. 148 (6): 752–9. doi:10.1038/sj.bjp.0706789. PMC 1617074. PMID 16751790.
- Arias-Carrión O, Murillo-Rodriguez E, Xu M, Blanco-Centurion C, Drucker-Colín R, Shiromani PJ (2004). "Transplantation of Hypocretin Neurons into the Pontine Reticular Formation: Preliminary Results". Sleep 27 (8): 1465–70. PMC 1201562. PMID 15683135.
- "Blocking A Neuropeptide Receptor Decreases Nicotine Addiction". ScienceDaily LLC. 2008-12-01. Retrieved 2009-02-11.
- Skrzypski M, Le TT, Kaczmarek P, Pruszynska-Oszmalek E, Pietrzak P, Szczepankiewicz D, Kolodziejski PA, Sassek M, Arafat A, Wiedenmann B, Nowak KW, Strowski MZ (July 2011). "Orexin A stimulates glucose uptake, lipid accumulation and adiponectin secretion from 3T3-L1 adipocytes and isolated primary rat adipocytes". Diabetologia 5 (47): 1841–52. doi:10.1007/s00125-011-2152-2. PMID 21505958.
- Blouin AM, Fried I, Wilson CL, Staba RJ, Behnke EJ, Lam HA, Maidment NT, Karlsson KÆ, Lapierre JL, Siegel JM (2013). "Human hypocretin and melanin-concentrating hormone levels are linked to emotion and social interaction". Nature Communications 4: 1547. doi:10.1038/ncomms2461. PMC 3595130. PMID 23462990. Lay summary – Science Daily.
- Gautvik KM, de Lecea L, et al. (1996). "Overview of the most prevalent hypothalamus-specific mRNAs, as identified by directional tag PCR subtraction". PNAS 93 (16): 8733–8738. doi:10.1073/pnas.93.16.8733. PMC 38742. PMID 8710940.
- Heifetz A, Morris GB, Biggin PC, Barker O, Fryatt T, Bentley J, Hallett D, Manikowski DP, Pal S, Reifegerste R, Slack M, Law R (2012). "Study of Human Orexin-1 and -2 G-Protein-Coupled Receptors with Novel and Published Antagonists by Modeling, Molecular Dynamics Simulations, and Site-Directed Mutagenesis". Biochemistry 51 (15): 3178–3197. doi:10.1021/bi300136h.
- Baxter CA, Cleator ED, Karel MJ, Edwards JS, Reamer RA, Sheen FJ, Stewart GW, Strotman NA, Wallace DJ (2011). "The First Large-Scale Synthesis of MK-4305: A Dual Orexin Receptor Antagonist for the Treatment of Sleep Disorder". Organic Process Research & Development 15 (2): 367–375. doi:10.1021/op1002853.
- Acuna-Goycolea C, Li Y, Van Den Pol AN (March 2004). "Group III metabotropic glutamate receptors maintain tonic inhibition of excitatory synaptic input to hypocretin/orexin neurons". J. Neurosci. 24 (12): 3013–22. doi:10.1523/JNEUROSCI.5416-03.2004. PMID 15044540.
- Liu ZW, Gao XB (January 2007). "Adenosine inhibits activity of hypocretin/orexin neurons via A1 receptor in the lateral hypothalamus: a possible sleep-promoting effect". J. Neurophysiol. 97 (1): 837–48. doi:10.1152/jn.00873.2006. PMC 1783688. PMID 17093123.
- Ohno K, Hondo M, Sakurai T (March 2008). "Cholinergic regulation of orexin/hypocretin neurons through M(3) muscarinic receptor in mice". J. Pharmacol. Sci. 106 (3): 485–91. doi:10.1254/jphs.FP0071986. PMID 18344611.[dead link]
- Muraki Y, Yamanaka A, Tsujino N, Kilduff TS, Goto K, Sakurai T (August 2004). "Serotonergic regulation of the orexin/hypocretin neurons through the 5-HT1A receptor". J. Neurosci. 24 (32): 7159–66. doi:10.1523/JNEUROSCI.1027-04.2004. PMID 15306649.
- Fu LY, Acuna-Goycolea C, van den Pol AN (October 2004). "Neuropeptide Y inhibits hypocretin/orexin neurons by multiple presynaptic and postsynaptic mechanisms: tonic depression of the hypothalamic arousal system". J. Neurosci. 24 (40): 8741–51. doi:10.1523/JNEUROSCI.2268-04.2004. PMID 15470140.
- Tsujino N, Yamanaka A, Ichiki K, Muraki Y, Kilduff TS, Yagami K, Takahashi S, Goto K, Sakurai T (August 2005). "Cholecystokinin activates orexin/hypocretin neurons through the cholecystokinin A receptor". J. Neurosci. 25 (32): 7459–69. doi:10.1523/JNEUROSCI.1193-05.2005. PMID 16093397.
- Li Y, van den Pol AN (January 2005). "Direct and indirect inhibition by catecholamines of hypocretin/orexin neurons". J. Neurosci. 25 (1): 173–83. doi:10.1523/JNEUROSCI.4015-04.2005. PMID 15634779.
- Yamanaka A, Muraki Y, Ichiki K, Tsujino N, Kilduff TS, Goto K, Sakurai T (July 2006). "Orexin neurons are directly and indirectly regulated by catecholamines in a complex manner". J. Neurophysiol. 96 (1): 284–98. doi:10.1152/jn.01361.2005. PMID 16611835.
- Ohno K, Sakurai T (January 2008). "Orexin neuronal circuitry: role in the regulation of sleep and wakefulness". Front Neuroendocrinol 29 (1): 70–87. doi:10.1016/j.yfrne.2007.08.001. PMID 17910982.
- Bernard R, Lydic R, Baghdoyan HA (October 2003). "Hypocretin-1 causes G protein activation and increases ACh release in rat pons". Eur. J. Neurosci. 18 (7): 1775–85. doi:10.1046/j.1460-9568.2003.02905.x. PMID 14622212.
- Frederick-Duus D, Guyton MF, Fadel J (November 2007). "Food-elicited increases in cortical acetylcholine release require orexin transmission". Neuroscience 149 (3): 499–507. doi:10.1016/j.neuroscience.2007.07.061. PMID 17928158.
- Soffin EM, Gill CH, Brough SJ, Jerman JC, Davies CH (June 2004). "Pharmacological characterisation of the orexin receptor subtype mediating postsynaptic excitation in the rat dorsal raphe nucleus". Neuropharmacology 46 (8): 1168–76. doi:10.1016/j.neuropharm.2004.02.014. PMID 15111023.
- Selbach O, Haas HL (2006). "Hypocretins: the timing of sleep and waking". Chronobiology International 23 (1–2): 63–70. doi:10.1080/07420520500545961. PMID 16687280.
- orexins at the US National Library of Medicine Medical Subject Headings (MeSH)
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Prepro-orexin Provide feedback
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This tab holds annotation information from the InterPro database.
InterPro entry IPR001704
Orexins (also known as hypocretins) are recently identified neuropeptides that are specifically localised to the hypothalamus. They are thought to interact with autonomic, neurendocrine and neuroregulatory systems, and play an important role in the regulation of feeding behaviour [PUBMED:9892705, PUBMED:9419374]. When applied to hypothalamic neurones, these peptides are neuroexcitatory, which action is probably mediated by their binding to a new family of G-protein-coupled receptors (orexin receptors 1 and 2), which were previously orphan [PUBMED:9491897].
To date, two orexins have been characterised (orexin-A and -B), both encoded by a single mRNA transcript (prepro-orexin): orexin-A is a 33-residue peptide with two intramolecular disulphide bonds in the N-terminal region; and orexin-B is a linear 28-residue peptide. These peptides have 46% identity at the amino acid sequence level, and show some similarity to the glucagon/vasoactive intestinal polypeptide/secretin peptide family.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Biological process||feeding behavior (GO:0007631)|
|neuropeptide signaling pathway (GO:0007218)|
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- a Java applet developed at the University of Dundee. You will need Java installed before running jalview
- an HTML page showing the whole alignment.Please note: full Pfam alignments can be very large. These HTML views are extremely large and often cause problems for browsers. Please use either jalview or the Pfam viewer if you have trouble viewing the HTML version
- an HTML-based representation of the alignment, coloured according to the posterior-probability (PP) values from the HMM. As for the standard HTML view, heatmap alignments can also be very large and slow to render.
- Pfam viewer
- an HTML-based viewer that uses DAS to retrieve alignment fragments on request
You can download (or view in your browser) a text representation of a Pfam alignment in various formats:
You can also change the order in which sequences are listed in the alignment, change how insertions are represented, alter the characters that are used to represent gaps in sequences and, finally, choose whether to download the alignment or to view it in your browser directly.
You may find that large alignments cause problems for the viewers and the reformatting tool, so we also provide all alignments in Stockholm format. You can download either the plain text alignment, or a gzipped version of it.
We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.
1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
Format an alignment
We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.
You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.
MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.
HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...
If you find these logos useful in your own work, please consider citing the following article:
This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.
Note: You can also download the data file for the tree.
Curation and family details
This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.
|Author:||Mian N, Bateman A|
|Number in seed:||3|
|Number in full:||54|
|Average length of the domain:||111.00 aa|
|Average identity of full alignment:||55 %|
|Average coverage of the sequence by the domain:||75.78 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||10|
|Download:||download the raw HMM for this family|
Weight segments by...
Change the size of the sunburst
selected sequences to HMM
a FASTA-format file
- 0 sequences
- 0 species
This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.
How the sunburst is generated
The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.
In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:
Colouring and labels
Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.
As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.
Anomalies in the taxonomy tree
There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
Missing taxonomic levels
Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.
Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".
Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
Too many species/sequences
For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.
The tree shows the occurrence of this domain across different species. More...
We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.
Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.
If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.
For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.
Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
You can use the tree controls to manipulate how the interactive tree is displayed:
- show/hide the summary boxes
- highlight species that are represented in the seed alignment
- expand/collapse the tree or expand it to a given depth
- select a sub-tree or a set of species within the tree and view them graphically or as an alignment
- save a plain text representation of the tree
Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Orexin domain has been found. There are 4 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
Loading structure mapping...