Tachykinin family | |||||||||
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Identifiers | |||||||||
Symbol | Tachykinin | ||||||||
Pfam | PF02202 | ||||||||
InterPro | IPR002040 | ||||||||
SMART | TK | ||||||||
PROSITE | PDOC00240 | ||||||||
SCOP2 | 1myu / SCOPe / SUPFAM | ||||||||
OPM superfamily | 143 | ||||||||
OPM protein | 1myu | ||||||||
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Tachykinin peptides are one of the largest families of neuropeptides, found from amphibians to mammals. They were so named due to their ability to rapidly induce contraction of gut tissue. [2] The tachykinin family is characterized by a common C-terminal sequence, Phe-X-Gly-Leu-Met-NH2, where X is either an Aromatic or an Aliphatic amino acid. The genes that produce tachykinins encode precursor proteins called preprotachykinins , which are chopped apart into smaller peptides by posttranslational proteolytic processing. The genes also code for multiple splice forms that are made up of different sets of peptides.
Tachykinins [3] [4] [5] excite neurons, evoke behavioral responses, are potent vasodilators, and contract (directly or indirectly) many smooth muscles. Tachykinins are from ten to twelve residues long.
The two human tachykinin genes are called TAC1 and TAC3 for historical reasons, and are equivalent to Tac1 and Tac2 of the mouse, respectively. TAC1 encodes neurokinin A (formerly known as substance K), neuropeptide K (which has also been called neurokinin K [6] ), neuropeptide gamma, and Substance P. [7] Alpha, beta, and gamma splice forms are produced; the alpha form lacks exon 6 and the gamma form lacks exon 4. All three splice forms of TAC1 produce substance P, but only the beta and gamma forms produce the other three peptides. Neuropeptide K and neuropeptide gamma are N-terminally longer versions of neurokinin A that appear to be final peptide products in some tissues. [2]
TAC3 encodes neurokinin B. [8]
The best known tachykinin is Substance P.
There are three known mammalian tachykinin receptors termed NK1, NK2 and NK3. All are members of the 7 transmembrane g protein-coupled family of receptors and induce the activation of phospholipase C, producing inositol triphosphate. NK1, NK2 and NK3 selectively bind to substance P, neurokinin A, and neurokinin B, respectively. Whilst the receptors are not specific to any individual tachykinin, they do have differing affinity for the tachykinins:
Antagonists of neurokinin-1 (NK1) receptors (NK1 receptor antagonists), through which substance P acts, have been proposed to belong to a new class of antidepressants, [9] [10] while NK2 antagonists have been proposed as anxiolytics [11] [12] and NK3 antagonists have been proposed as antipsychotics. [13] [14]
Tachykinin peptides are also involved in inflammation, and tachykinin receptor antagonists have been researched for use in treating inflammatory conditions such as asthma and irritable bowel syndrome. [15] [16] [17] The main use for which these antagonist drugs have been applied so far, however, is as antiemetics, in both human and veterinary medicine. [18] [19]
Examples of tachykinin antagonists include: [20]
Substance P (SP) is an undecapeptide and a type of neuropeptide, belonging to the tachykinin family of neuropeptides. It acts as a neurotransmitter and a neuromodulator. Substance P and the closely related neurokinin A (NKA) are produced from a polyprotein precursor after alternative splicing of the preprotachykinin A gene. The deduced amino acid sequence of substance P is as follows:
Physalaemin is a tachykinin peptide obtained from the Physalaemus frog, closely related to substance P. Its structure was first elucidated in 1964.
There are three known mammalian tachykinin receptors termed NK1, NK2 and NK3. All are members of the 7 transmembrane G-protein coupled receptor family and induce the activation of phospholipase C, producing inositol triphosphate (so called Gq-coupled).
Kassinin is a peptide derived from the Kassina frog. It belongs to tachykinin family of neuropeptides. It is secreted as a defense response, and is involved in neuropeptide signalling.
Neurokinin 1 (NK1) antagonists (-pitants) are a novel class of medications that possesses unique antidepressant, anxiolytic, and antiemetic properties. NK-1 antagonists boost the efficacy of 5-HT3 antagonists to prevent nausea and vomiting. The discovery of neurokinin 1 (NK1) receptor antagonists was a turning point in the prevention of nausea and vomiting associated with cancer chemotherapy.
Neurokinin A (NKA), formerly known as Substance K, is a neurologically active peptide translated from the pre-protachykinin gene. Neurokinin A has many excitatory effects on mammalian nervous systems and is also influential on the mammalian inflammatory and pain responses.
The galanin receptor is a G protein-coupled receptor, or metabotropic receptor which binds galanin.
Neurokinin B (NKB) belongs in the family of tachykinin peptides. Neurokinin B is implicated in a variety of human functions and pathways such as the secretion of gonadotropin-releasing hormone. Additionally, NKB is associated with pregnancy in females and maturation in young adults. Reproductive function is highly dependent on levels of both neurokinin B and also the G-protein coupled receptor ligand kisspeptin. The first NKB studies done attempted to resolve why high levels of the peptide may be implicated in pre-eclampsia during pregnancy. NKB, kisspeptin, and dynorphin together are found in the arcuate nucleus (ARC) known as the KNDy subpopulation. This subpopulation is targeted by many steroid hormones and works to form a network that feeds back to GnRH pulse generator.
The tachykinin receptor 1 (TACR1) also known as neurokinin 1 receptor (NK1R) or substance P receptor (SPR) is a G protein coupled receptor found in the central nervous system and peripheral nervous system. The endogenous ligand for this receptor is Substance P, although it has some affinity for other tachykinins. The protein is the product of the TACR1 gene.
Substance-K receptor is a protein that in humans is encoded by the TACR2 gene.
Tachykinin receptor 3, also known as TACR3, is a protein which in humans is encoded by the TACR3 gene.
Eledoisin is an undecapeptide of mollusk origin, belonging to the tachykinin family of neuropeptides.
Tachykinin-3 is a protein that in humans is encoded by the TAC3 gene.
Osanetant (developmental code name SR-142,801) is a neurokinin 3 receptor antagonist which was developed by Sanofi-Synthélabo and was being researched for the treatment of schizophrenia but was discontinued. It was the first non-peptide NK3 antagonist developed in the mid-1990s.
GR-159897 is a potent and selective NK2 receptor antagonist drug. It has anxiolytic effects in animal models, and also inhibits bronchoconstriction of the airways, which may potentially make it useful in the treatment of asthma.
L-733,060 is a drug developed by Merck which acts as an orally active, non-peptide, selective antagonist for the NK1 receptor, binding with a Ki of 0.08 nM. Only one enantiomer is active which has made it the subject of several asymmetric synthesis efforts.
Ezlopitant (INN, code name CJ-11,974) is an NK1 receptor antagonist. It has antiemetic and antinociceptive effects. Pfizer was developing ezlopitant for the treatment of irritable bowel syndrome but it appears to have been discontinued.
Netupitant is an antiemetic medication. In the United States, the combinations of netupitant/palonosetron and the prodrug fosnetupitant/palonosetron are approved by the Food and Drug Administration for the prevention of acute and delayed chemotherapy-induced nausea and vomiting, including highly emetogenic chemotherapy such as with cisplatin. In the European Union, the combinations are approved by the European Medicines Agency (EMA) for the same indication.
Vofopitant (GR205171) is a drug which acts as an NK1 receptor antagonist. It has antiemetic effects as with other NK1 antagonists, and also shows anxiolytic actions in animals. It was studied for applications such as the treatment of social phobia and post-traumatic stress disorder, but did not prove sufficiently effective to be marketed.
Neuropeptide K, is a protein encoded by the TAC1 gene. It is an elongated derivative of the N-terminus of neurokinin A as the final post-translational processing product of beta-preprotachykinin.
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