TNNT2: Difference between revisions
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{{ | '''Cardiac muscle troponin T''' (cTnT), is a [[protein]] which in humans is encoded by the ''TNNT2'' [[gene]].<ref name = "Townsend_1998"/><ref name = "Gerull_1998"/> Cardiac TnT is the [[tropomyosin]]-binding subunit of the [[troponin]] complex, which is located on the thin filament of striated muscles and regulates muscle contraction in response to alterations in intracellular calcium ion concentration. | ||
| | |||
| | The TNNT2 gene is located at 1q32 in the human chromosomal genome, encoding the cardiac muscle isoform of troponin T (cTnT). Human cTnT is an ~36-kDa protein consisting of 297 amino acids including the first methionine with an isoelectric point (pI) of 4.88. It is the tropomyosin- binding and thin filament anchoring subunit of the troponin complex in cardiac muscle cells.<ref name = "Perry_1998"/><ref name = "Jin_2008"/><ref name = "Wei_2011"/> TNNT2 gene is expressed in vertebrate cardiac muscles and embryonic skeletal muscles.<ref name = "Jin_2008"/><ref name = "Wei_2011"/><ref name = "Sheng_2014"/> | ||
| | |||
| | == Structure == | ||
| | |||
Cardiac TnT is a 35.9 kDa protein composed of 298 amino acids.<ref name = "COPa_Knowledgebase">{{cite web | title = Troponin T, cardiac muscle | work = Cardiac Organellar Protein Atlas Database | url = http://www.heartproteome.org/copa/ProteinInfo.aspx?QType=Protein%20ID&QValue=P45379 }}</ref><ref name = "Zong_2013"/> Cardiac TnT is the largest of the three troponin subunits (cTnT, [[TNNI3|troponin I]] (TnI), [[TNNC1|troponin C]] (TnC)) on the [[ACTC1|actin]] thin filament of cardiac muscle. The structure of TnT is asymmetric; the globular C-terminal domain interacts with [[TPM1|tropomyosin]] (Tm), [[TNNI3|TnI]] and [[TNNC1|TnC]], and the N-terminal tether which strongly binds [[TPM1|Tm]]. The N-terminal region of TnT is alternatively spliced, accounting for multiple isoforms observed in cardiac muscle.<ref name = "Anderson_1991"/> | |||
== Function == | |||
As part of the Troponin complex, the function of cTnT is to regulate muscle contraction. The N-terminal region of TnT that strongly binds [[ACTC1|actin]] most likely moves with [[TPM1|Tm]] and [[ACTC1|actin]] during strong [[MYH7|myosin]] crossbridge binding and force generation. This region is likely involved in the transduction of [[cooperative binding|cooperativity]] down the thin filament.<ref name = "Kobayashi_2005"/> The C-terminal region of TnT constitutes part of the globular troponin complex domain, and participates in employing the calcium sensitivity of strong [[MYH7|myosin]] crossbridge binding to the thin filament.<ref name = "Kobayashi_2008"/> | |||
== Clinical significance == | |||
Mutations in this gene have been associated with familial [[hypertrophic cardiomyopathy]] as well as with [[restrictive cardiomyopathy|restrictive]]<ref name = "Revera_2007"/> and [[dilated cardiomyopathy]]. Transcripts for this gene undergo [[alternative splicing]] that results in many tissue-specific isoforms, however, the full-length nature of some of these variants has not yet been determined.<ref name = "Entrez">{{cite web | title = Entrez Gene: TNNT2 troponin T type 2 (cardiac)| url = https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7139 }}</ref> Mutations of this gene may be associated with mild or absent [[hypertrophy]] and predominant restrictive disease, with a high risk of [[sudden cardiac death]].<ref name = "Revera_2007"/> Advancement to dilated cardiomyopathy may be more rapid in patients with TNNT2 mutations than in those with [[myosin heavy chain]] mutations.<ref name = "Fujino_2001"/><ref name = "Fujino_2002"/> | |||
== Evolution == | |||
[[File:TnT TnI gene pairs.jpg|thumb]] | |||
Three homologous genes have evolved in vertebrates encoding three muscle type- specific isoforms of TnT.<ref name = "Wei_2011"/> Each of the TnT isoform genes is linked in chromosomal DNA to a troponin I (TnI) isoform gene encoding the inhibitory subunit of the troponin complex to form three gene pairs: The fast skeletal muscle TnI (fsTnI)-fsTnT, slow skeletal muscle TnI (ssTnI)-cTnT, and cTnI-ssTnT pairs. Sequence and epitope conservation studies suggested that genes encoding the muscle type-specific TnT and TnI isoforms have originated from a TnI-like ancestor gene and duplicated and diversified from a fsTnI-like-fsTnT-like gene pair.<ref name = "Chong_2009"/> | |||
[[File:TNNT2 gene phylogenic tree.jpg|thumb]] | |||
The apparently scrambled linkage between ssTnI-cTnT and cTnI-ssTnT genes actually reflects original functional linkages as that TNNT2 gene is expressed together with ssTnI gene in embryonic cardiac muscle.<ref name = "Jin_1996"/> Protein sequence alignment demonstrated that TNNT2 gene is conserved in vertebrate species (Fig. 2) in the middle and C-terminal regions, while the three muscle type isoforms are significantly diverged.<ref name = "Jin_2008"/><ref name = "Wei_2011"/> | |||
== Alternative splicing == | |||
Mammalian TNNT2 gene contains 14 constitutive exons and 3 alternatively spliced exons.<ref name = "Jin_1992"/> Exons 4 and 5 encoding the N-terminal variable region and exon 13 between the middle and C-terminal regions are alternatively spliced.<ref name = "Farza_1998"/> Exon 5 encodes a 9 or 10 amino acid segment that is highly acidic and negatively charged at physiological pH.<ref name = "Jin_2008"/> Exon 5 is expressed in embryonic heart, down-regulated and ceases express during postnatal development.<ref name = "Jin_1989"/> | |||
Embryonic cTnT with more negative charge at the N-terminal region exerts higher calcium sensitivity of actomyosin ATPase activity and myofilament force production, compared with the adult cardiac TnT, as well as a higher tolerance to acidosis.<ref name = "Solaro_1998"/> | |||
TNNT2 gene is transiently expressed in embryonic and neonatal skeletal muscles in both avian and mammalian organisms.<ref name = "Jin_1996"/><ref name = "Toyota_1983"/><ref name = "Cooper_1985"/> When TNNT2 is expressed in neonatal skeletal muscle, the alternative splicing of exon 5 exhibits a synchronized regulation to that in the heart in a species-specific manner.<ref name = "Jin_1996"/> This phenomenon indicates that alternative splicing of TNNT2 pre-mRNA is under the control of a genetically built- in systemic biological clock. | |||
== Posttranslational modifications == | |||
=== Phosphorylation === | |||
Ser2 of cTnT at the N terminus is constitutively phosphorylated by unknown mechanisms.<ref name = "Perry_1998"/> cTnT has been found to be phosphorylated by PKC at Thr197, Ser201, Thr206, Ser208 and Thr287 in the C-terminal region. Phosphorylation of Thr206 alone was sufficient to reduce myofilament calcium sensitivity and force production.<ref name = "Nolan_1992"/><ref name = "Sumandea_2003"/><ref name = "Jideama_2006"/><ref name = "Dubois_Deruy_2015"/> cTnT is also phosphorylated at Thr194 and Ser198 under stress conditions,<ref name = "He_2003"/> leading to attenuated cardiomyocyte contractility. Phosphorylation of cTnT at Ser278 and Thr287 by ROCK-II was shown to decrease myosin ATPase activity and myofilament force development in skinned cardiac muscle.<ref name = "Vahebi_2005"/> Table 1 summarizes the phosphorylation modifications of cTnT and possible functions. | |||
=== O-linked GlcNAcylation === | |||
cTnT is increasingly modified at Ser190 by O-GlcNAcylation during the development of heart failure in rat, accompanied by decreased phosphorylation of Ser208.<ref name = "Dubois_Deruy_2015"/> | |||
=== Proteolytic modification === | |||
In apoptotic cardiomyocytes, cTnT was cleaved by caspase 3 to generate a 25-kDa N-terminal truncated fragment.<ref name = "Communal_2002"/> This destructive fragmentation removes a part of the middle region tropomyosin binding site 1,<ref name = "Chong_2009"/> leading to attenuation of the myofilament force production by decreasing the myosin ATPase activity.<ref name = "Communal_2002"/> | |||
In cardiac muscle under stress conditions, cardiac TnT is cleaved by calpain I, restrictively removing the entire N-terminal variable region.<ref name = "Geesink_2006"/><ref name = "Zhang_2006"/> This proteolytic modification of cTnT occurs in cardiac muscle in acute ischemia-reperfusion or pressure overload.<ref name = "Feng_2008"/> | |||
The restrictively N-terminal truncated cTnT remains functional in the myofilaments and leads to reduced contractile velocity of the ventricular muscle, which extends the rapid ejection phase and results in an increase in stroke volume, especially under increased afterload.<ref name = "Feng_2008"/> In vitro studies showed that N-terminal truncated cTnT preserved the overall cardiac myofilament calcium sensitivity and cooperativity, but altered TnT’s binding affinities for tropomyosin, TnI and TnC proteins,<ref name = "Pan_1991"/><ref name = "Biesiadecki_2007"/> and lead to slightly decreased maximum myosin ATPase activity and myofilament force production, which forms the basis of the selective decrease in contractile velocity of ventricular muscle to increase stroke volume without significant increase in energy expenditure.<ref name = "Feng_2008"/> | |||
With the relatively short half life of cTnT in cardiomyocytes (3–4 days),<ref name = "Martin_1981"/> the N-terminal truncated cTnT would be replaced by newly synthesized intact cTnT in several days. Therefore, this mechanism provides a reversible posttranslational regulation to modulate cardiac function in adaptation to stress conditions. | |||
{| class="wikitable" | |||
|+ '''Phosphorylation sites in cTnT in comparison with ssTnT and fsTnT''' | |||
|- | |||
! colspan="3" | Phosphorylation site !! rowspan="2" | Kinase !! rowspan="2" | Function !! rowspan="2" | Reference | |||
|- | |||
! cTnT !! ssTnT !! fsTnT | |||
|- | |||
| Ser<sub>2</sub> || c || c || PKC || Unknown || <ref name = "Villar_Palasi_1981"/><ref name = "Gusev_1983"/><ref name = "Zhang_2011"/> | |||
|- | |||
| Thr<sub>197</sub> || n || N || PKC || No functional effect || <ref name = "Sumandea_2003"/><ref name = "Jideama_1996"/> | |||
|- | |||
| Ser<sub>201</sub> || n || n || PKC || No functional effect || <ref name = "Sumandea_2003"/><ref name = "Jideama_1996"/> | |||
|- | |||
| Thr<sub>204</sub> || n || n || PKC || Reduce Myosin ATPase activity, myofilament force production and Ca<sup>2+</sup> sensitivity || <ref name = "Jideama_1996"/><ref name = "Noland_1989"/><ref name = "Montgomery_2001"/> | |||
|- | |||
| Thr<sub>204</sub> || n || n || CaMK II || Unknown || <ref name = "Jaquet_1995"/> | |||
|- | |||
| Thr<sub>204</sub> || n || n || ASK I || Reduce cardiomyocyte contractility || <ref name = "He_2003"/> | |||
|- | |||
| Thr<sub>206</sub> || || || PKC || Reduce Ca<sup>2+</sup> sensitivity, actomyosin ATPase activity and tension development || <ref name = "Sumandea_2003"/> | |||
|- | |||
| Ser<sub>208</sub> || n || n || PKC || Reduce Myosin ATPase activity, alter myofilament Ca<sup>2+</sup> sensitivity || <ref name = "Jideama_1996"/><ref name = "Montgomery_2001"/><ref name = "Sumandea_2009"/> | |||
|- | |||
| Ser<sub>208</sub> || n || n || ASK I || Reduce cardiomyocyte contractility || <ref name = "He_2003"/> | |||
|- | |||
| Thr<sub>213</sub> || ''c'' || ''c'' || PKC || Reduce Myosin ATPase activity, myofilament force production and Ca<sup>2+</sup> sensitivity || <ref name = "Streng_2013"/> | |||
|- | |||
| Thr<sub>213</sub> || c || c || Raf-1 || Unknown || <ref name = "Pfleiderer_2009"/> | |||
|- | |||
| Ser<sub>285</sub> || n || c || PKC || Reduce Myosin ATPase activity, myofilament force production and Ca<sup>2+</sup> sensitivity || <ref name = "Sumandea_2009"/> | |||
|- | |||
| Ser<sub>285</sub> || n || c || ROCK-II || Reduce myofilament force development, Myosin ATPase activity and Ca<sup>2+</sup> sensitivity || <ref name = "Vahebi_2005"/> | |||
|- | |||
| Thr<sub>294</sub> || ''n'' || n || PKC || Reduce Myosin ATPase activity, myofilament force production and Ca<sup>2+</sup> sensitivity || <ref name = "Jideama_1996"/><ref name = "Noland_1989"/><ref name = "Montgomery_2001"/><ref name = "Sumandea_2009"/> | |||
|- | |||
| Thr<sub>294</sub> || ''n'' || n || ROCK-II || Reduce myofilament force development, myosin ATPase activity and Ca<sup>2+</sup> sensitivity || <ref name = "Vahebi_2005"/> | |||
|} | |||
The residues in cardiac TnT with phosphorylation regulations are summarized. The residue numbers for phosphorylatable serine and threonine are that in human cardiac TnT with the first methionine included. The phosphorylation of cardiac TnT at these residues is compared with the counterparts in fast TnT and slow TnT. C, conserved; N, non-conserved. Kinases responsible for each phosphorylation, functional effects, and references are also listed. | |||
== Mutations in cardiomyopathies == | |||
Point mutations in TNNT2 gene cause various types of cardiomyopathies, including hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) and restrictive cardiomyopathy (RCM). The table below summarizes representative TNNT2 mutations and abnormal splicings found in human and animal cardiomyopathies. | |||
{| class="wikitable" style="width: 600px;" | |||
|+ '''Representative TNNT2 mutations and abnormal splicings that cause cardiomyopathy''' | |||
|- | |||
! Mutation !! Diagnosis !! Reference | |||
|- | |||
| Ile79Asn || HCM || <ref name = "Thierfelder_1994"/><ref name = "Lin_1996"/><ref name = "Palm_2001"/> | |||
|- | |||
| Arg92Gln || HCM || <ref name = "Thierfelder_1994"/><ref name = "Marian_1997"/> | |||
|- | |||
| Intron 16G1→A (D14 and D28+7) || HCM || <ref name = "Thierfelder_1994"/> | |||
|- | |||
| Arg92Leu || HCM || <ref name = "Palm_2001"/><ref name = "Forissier_1996"/> | |||
|- | |||
| Arg92Trp || HCM || <ref name = "Fujino_2001"/><ref name = "Moolman_1997"/><ref name = "Shimizu_2003"/> | |||
|- | |||
| Arg94Leu || HCM || <ref name = "Palm_2001"/><ref name = "Varnava_1999"/> | |||
|- | |||
| Arg94Cys || HCM || <ref name = "D'Cruz_2000"/> | |||
|- | |||
| ΔE96 || RCM || <ref name = "Peddy_2006"/><ref name = "Pinto_2008"/> | |||
|- | |||
| Ala104Val || HCM || <ref name = "Nakajima-Taniguchi_1997"/> | |||
|- | |||
| Phe110Ile || DCM || <ref name = "Watkins_1995"/><ref name = "Nakaura_1999"/> | |||
|- | |||
| Arg130Cys || HCM || <ref name = "Koga_1996"/> | |||
|- | |||
| Arg131Trp || DCM || <ref name = "Mogensen_2004"/><ref name = "Mirza_2005"/> | |||
|- | |||
| E136K || RCM || <ref name = "Kaski_2008"/> | |||
|- | |||
| Arg141Trp || DCM || <ref name = "Li_2001"/><ref name = "Lu_2003"/> | |||
|- | |||
| DGlu160 || HCM || <ref name = "Harada_2000"/> | |||
|- | |||
| Glu163Arg || HCM || <ref name = "Koga_1996"/> | |||
|- | |||
| Glu163Lys || HCM || <ref name = "Watkins_1995"/> | |||
|- | |||
| Ser179Phe || HCM || <ref name = "Van_Driest_2002"/> | |||
|- | |||
| Arg205Leu || DCM || <ref name = "Mogensen_2004"/> | |||
|- | |||
| DLys210 || DCM || <ref name = "Kamisago_2000"/><ref name = "Hanson_2002"/><ref name = "Hershberger_2009"/> | |||
|- | |||
| Glu244Asp || HCM || <ref name = "Watkins_1995"/> | |||
|- | |||
| Asp270Asn || DCM || <ref name = "Kamisago_2000"/> | |||
|- | |||
| Lys273Glu || DCM || <ref name = "Fujino_2002"/> | |||
|- | |||
| Arg278Cys ||HCM || <ref name = "Watkins_1995"/><ref name = "Morimoto_1999"/> | |||
|} | |||
Amino Acid residues of mutations were numbered as in human cardiac TnT with the first methionine included. Mutations of cardiac TnT that caused cardiomyopathies were mostly found in the conserved middle and C-terminal regions. | |||
==Notes== | |||
{{Academic-written review | |||
| wikidate = 2015 | |||
| journal = [[Gene (journal)|Gene]] | |||
| title = {{#property:P1476|from=Q37666010}} | |||
| authors = {{#property:P2093|from=Q37666010}} | |||
| date = {{#property:P577|from=Q37666010}} | |||
| volume = {{#property:P478|from=Q37666010}} | |||
| issue = {{#property:P433|from=Q37666010}} | |||
| pages = {{#property:P304|from=Q37666010}} | |||
| doi = {{#property:P356|from=Q37666010}} | |||
| pmid = {{#property:P698|from=Q37666010}} | |||
| pmc = {{#property:P932|from=Q37666010}} | |||
}} | }} | ||
< | == References == | ||
{{ | {{Reflist|33em|refs = | ||
| | <ref name = "Anderson_1991">{{cite journal | vauthors = Anderson PA, Malouf NN, Oakeley AE, Pagani ED, Allen PD | title = Troponin T isoform expression in humans. A comparison among normal and failing adult heart, fetal heart, and adult and fetal skeletal muscle | journal = Circulation Research | volume = 69 | issue = 5 | pages = 1226–33 | date = Nov 1991 | pmid = 1934353 | doi=10.1161/01.res.69.5.1226}}</ref> | ||
| | <ref name = "Biesiadecki_2007">{{cite journal | vauthors = Biesiadecki BJ, Chong SM, Nosek TM, Jin JP | title = Troponin T core structure and the regulatory NH2-terminal variable region | journal = Biochemistry | volume = 46 | issue = 5 | pages = 1368–79 | date = Feb 2007 | pmid = 17260966 | pmc = 1794682 | doi = 10.1021/bi061949m }}</ref> | ||
| | |||
<ref name = "Chong_2009">{{cite journal | vauthors = Chong SM, Jin JP | title = To investigate protein evolution by detecting suppressed epitope structures | journal = Journal of Molecular Evolution | volume = 68 | issue = 5 | pages = 448–60 | date = May 2009 | pmid = 19365646 | pmc = 2752406 | doi = 10.1007/s00239-009-9202-0 }}</ref> | |||
<ref name = "Communal_2002">{{cite journal | vauthors = Communal C, Sumandea M, de Tombe P, Narula J, Solaro RJ, Hajjar RJ | title = Functional consequences of caspase activation in cardiac myocytes | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 99 | issue = 9 | pages = 6252–6 | date = Apr 2002 | pmid = 11972044 | pmc = 122935 | doi = 10.1073/pnas.092022999 | bibcode = 2002PNAS...99.6252C }}</ref> | |||
<ref name = "Cooper_1985">{{cite journal | vauthors = Cooper TA, Ordahl CP | title = A single cardiac troponin T gene generates embryonic and adult isoforms via developmentally regulated alternate splicing | journal = The Journal of Biological Chemistry | volume = 260 | issue = 20 | pages = 11140–8 | date = Sep 1985 | pmid = 2993302 }}</ref> | |||
<ref name = "COPa_Knowledgebase">{{cite web | title = Troponin T, cardiac muscle | work = Cardiac Organellar Protein Atlas Database | url = http://www.heartproteome.org/copa/ProteinInfo.aspx?QType=Protein%20ID&QValue=P45379 }}</ref> | |||
| | |||
| | <ref name = "D'Cruz_2000">{{cite journal | vauthors = D'Cruz LG, Baboonian C, Phillimore HE, Taylor R, Elliott PM, Varnava A, Davison F, McKenna WJ, Carter ND | title = Cytosine methylation confers instability on the cardiac troponin T gene in hypertrophic cardiomyopathy | journal = Journal of Medical Genetics | volume = 37 | issue = 9 | pages = E18 | date = Sep 2000 | pmid = 10978365 | pmc = 1734704 | doi = 10.1136/jmg.37.9.e18}}</ref> | ||
| | |||
| | <ref name = "Dubois_Deruy_2015">{{cite journal | vauthors = Dubois-Deruy E, Belliard A, Mulder P, Bouvet M, Smet-Nocca C, Janel S, Lafont F, Beseme O, Amouyel P, Richard V, Pinet F | title = Interplay between troponin T phosphorylation and O-N-acetylglucosaminylation in ischaemic heart failure | journal = Cardiovascular Research | volume = 107 | issue = 1 | pages = 56–65 | date = Jul 2015 | pmid = 25916824 | doi = 10.1093/cvr/cvv136 }}</ref> | ||
<ref name = "Entrez">{{cite web | title = Entrez Gene: TNNT2 troponin T type 2 (cardiac)| url = https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7139 }}</ref> | |||
<ref name = "Farza_1998">{{cite journal | vauthors = Farza H, Townsend PJ, Carrier L, Barton PJ, Mesnard L, Bährend E, Forissier JF, Fiszman M, Yacoub MH, Schwartz K | title = Genomic organisation, alternative splicing and polymorphisms of the human cardiac troponin T gene | journal = Journal of Molecular and Cellular Cardiology | volume = 30 | issue = 6 | pages = 1247–53 | date = Jun 1998 | pmid = 9689598 | doi = 10.1006/jmcc.1998.0698 }}</ref> | |||
<ref name = "Feng_2008">{{cite journal | vauthors = Feng HZ, Biesiadecki BJ, Yu ZB, Hossain MM, Jin JP | title = Restricted N-terminal truncation of cardiac troponin T: a novel mechanism for functional adaptation to energetic crisis | journal = The Journal of Physiology | volume = 586 | issue = 14 | pages = 3537–50 | date = Jul 2008 | pmid = 18556368 | pmc = 2538805 | doi = 10.1113/jphysiol.2008.153577 }}</ref> | |||
<ref name = "Forissier_1996">{{cite journal | vauthors = Forissier JF, Carrier L, Farza H, Bonne G, Bercovici J, Richard P, Hainque B, Townsend PJ, Yacoub MH, Fauré S, Dubourg O, Millaire A, Hagège AA, Desnos M, Komajda M, Schwartz K | title = Codon 102 of the cardiac troponin T gene is a putative hot spot for mutations in familial hypertrophic cardiomyopathy | journal = Circulation | volume = 94 | issue = 12 | pages = 3069–73 | date = Dec 1996 | pmid = 8989109 | doi = 10.1161/01.cir.94.12.3069}}</ref> | |||
<ref name = "Fujino_2001">{{cite journal | vauthors = Fujino N, Shimizu M, Ino H, Okeie K, Yamaguchi M, Yasuda T, Kokado H, Mabuchi H | title = Cardiac troponin T Arg92Trp mutation and progression from hypertrophic to dilated cardiomyopathy | journal = Clinical Cardiology | volume = 24 | issue = 5 | pages = 397–402 | date = May 2001 | pmid = 11346248 | doi = 10.1002/clc.4960240510 }}</ref> | |||
<ref name = "Fujino_2002">{{cite journal | vauthors = Fujino N, Shimizu M, Ino H, Yamaguchi M, Yasuda T, Nagata M, Konno T, Mabuchi H | title = A novel mutation Lys273Glu in the cardiac troponin T gene shows high degree of penetrance and transition from hypertrophic to dilated cardiomyopathy | journal = The American Journal of Cardiology | volume = 89 | issue = 1 | pages = 29–33 | date = Jan 2002 | pmid = 11779518 | doi = 10.1016/S0002-9149(01)02158-0 }}</ref> | |||
<ref name = "Geesink_2006">{{cite journal | vauthors = Geesink GH, Kuchay S, Chishti AH, Koohmaraie M | title = Micro-calpain is essential for postmortem proteolysis of muscle proteins | journal = Journal of Animal Science | volume = 84 | issue = 10 | pages = 2834–40 | date = Oct 2006 | pmid = 16971586 | doi = 10.2527/jas.2006-122 }}</ref> | |||
<ref name = "Gerull_1998">{{cite journal | vauthors = Gerull B, Osterziel KJ, Witt C, Dietz R, Thierfelder L | title = A rapid protocol for cardiac troponin T gene mutation detection in familial hypertrophic cardiomyopathy | journal = Human Mutation | volume = 11 | issue = 2 | pages = 179–82 | year = 1998 | pmid = 9482583 | doi = 10.1002/(SICI)1098-1004(1998)11:2<179::AID-HUMU12>3.0.CO;2-W }}</ref> | |||
<ref name = "Gusev_1983">{{cite journal | vauthors = Gusev NB, Barskaya NV, Verin AD, Duzhenkova IV, Khuchua ZA, Zheltova AO | title = Some properties of cardiac troponin T structure | journal = The Biochemical Journal | volume = 213 | issue = 1 | pages = 123–9 | date = Jul 1983 | pmid = 6615417 | pmc = 1152098 | doi = 10.1042/bj2130123}}</ref> | |||
}} | <ref name = "Hanson_2002">{{cite journal | vauthors = Hanson EL, Jakobs PM, Keegan H, Coates K, Bousman S, Dienel NH, Litt M, Hershberger RE | title = Cardiac troponin T lysine 210 deletion in a family with dilated cardiomyopathy | journal = Journal of Cardiac Failure | volume = 8 | issue = 1 | pages = 28–32 | date = Feb 2002 | pmid = 11862580 | doi = 10.1054/jcaf.2002.31157}}</ref> | ||
<ref name = "Harada_2000">{{cite journal | vauthors = Harada K, Takahashi-Yanaga F, Minakami R, Morimoto S, Ohtsuki I | title = Functional consequences of the deletion mutation deltaGlu160 in human cardiac troponin T | journal = Journal of Biochemistry | volume = 127 | issue = 2 | pages = 263–8 | date = Feb 2000 | pmid = 10731693 | doi = 10.1093/oxfordjournals.jbchem.a022603}}</ref> | |||
<ref name = "He_2003">{{cite journal | vauthors = He X, Liu Y, Sharma V, Dirksen RT, Waugh R, Sheu SS, Min W | title = ASK1 associates with troponin T and induces troponin T phosphorylation and contractile dysfunction in cardiomyocytes | journal = The American Journal of Pathology | volume = 163 | issue = 1 | pages = 243–51 | date = Jul 2003 | pmid = 12819028 | pmc = 1868161 | doi = 10.1016/S0002-9440(10)63647-4 }}</ref> | |||
<ref name = "Hershberger_2009">{{cite journal | vauthors = Hershberger RE, Pinto JR, Parks SB, Kushner JD, Li D, Ludwigsen S, Cowan J, Morales A, Parvatiyar MS, Potter JD | title = Clinical and functional characterization of TNNT2 mutations identified in patients with dilated cardiomyopathy | journal = Circulation: Cardiovascular Genetics | volume = 2 | issue = 4 | pages = 306–13 | date = Aug 2009 | pmid = 20031601 | pmc = 2900844 | doi = 10.1161/CIRCGENETICS.108.846733 }}</ref> | |||
<ref name = "Jaquet_1995">{{cite journal | vauthors = Jaquet K, Fukunaga K, Miyamoto E, Meyer HE | title = A site phosphorylated in bovine cardiac troponin T by cardiac CaM kinase II | journal = Biochimica et Biophysica Acta | volume = 1248 | issue = 2 | pages = 193–5 | date = Apr 1995 | pmid = 7748902 | doi = 10.1016/0167-4838(95)00028-s}}</ref> | |||
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<ref name = "Jideama_2006">{{cite journal | vauthors = Jideama NM, Crawford BH, Hussain AK, Raynor RL | title = Dephosphorylation specificities of protein phosphatase for cardiac troponin I, troponin T, and sites within troponin T | journal = International Journal of Biological Sciences | volume = 2 | issue = 1 | pages = 1–9 | pmid = 16585947 | pmc = 1415850 | year = 2006 }}</ref> | |||
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<ref name = "Palm_2001">{{cite journal | vauthors = Palm T, Graboski S, Hitchcock-DeGregori SE, Greenfield NJ | title = Disease-causing mutations in cardiac troponin T: identification of a critical tropomyosin-binding region | journal = Biophysical Journal | volume = 81 | issue = 5 | pages = 2827–37 | date = Nov 2001 | pmid = 11606294 | pmc = 1301748 | doi = 10.1016/S0006-3495(01)75924-3 | bibcode = 2001BpJ....81.2827P }}</ref> | |||
<ref name = "Pan_1991">{{cite journal | vauthors = Pan BS, Gordon AM, Potter JD | title = Deletion of the first 45 NH2-terminal residues of rabbit skeletal troponin T strengthens binding of troponin to immobilized tropomyosin | journal = The Journal of Biological Chemistry | volume = 266 | issue = 19 | pages = 12432–8 | date = Jul 1991 | pmid = 1829457 }}</ref> | |||
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<ref name = "Perry_1998">{{cite journal | vauthors = Perry SV | title = Troponin T: genetics, properties and function | journal = Journal of Muscle Research and Cell Motility | volume = 19 | issue = 6 | pages = 575–602 | date = Aug 1998 | pmid = 9742444 | doi=10.1023/a:1005397501968}}</ref> | |||
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<ref name = "Pinto_2008">{{cite journal | vauthors = Pinto JR, Parvatiyar MS, Jones MA, Liang J, Potter JD | title = A troponin T mutation that causes infantile restrictive cardiomyopathy increases Ca<sup>2+</sup> sensitivity of force development and impairs the inhibitory properties of troponin | journal = The Journal of Biological Chemistry | volume = 283 | issue = 4 | pages = 2156–66 | date = Jan 2008 | pmid = 18032382 | doi = 10.1074/jbc.M707066200 }}</ref> | |||
<ref name = "Revera_2007">{{cite journal | vauthors = Revera M, Van der Merwe L, Heradien M, Goosen A, Corfield VA, Brink PA, Moolman-Smook JC | title = Long-term follow-up of R403WMYH7 and R92WTNNT2 HCM families: mutations determine left ventricular dimensions but not wall thickness during disease progression | journal = Cardiovascular Journal of Africa | volume = 18 | issue = 3 | pages = 146–53 | year = 2007 | pmid = 17612745 | pmc = 4213759 | doi = | url = http://blues.sabinet.co.za/WebZ/Authorize?sessionid=0:autho=pubmed:password=pubmed2004&/AdvancedQuery?&format=F&next=images/ejour/cardio1/cardio1_v18_n3_a4.pdf }}</ref> | |||
<ref name = "Sheng_2014">{{cite journal | vauthors = Sheng JJ, Jin JP | title = Gene regulation, alternative splicing, and posttranslational modification of troponin subunits in cardiac development and adaptation: a focused review | journal = Frontiers in Physiology | volume = 5 | issue = | pages = 165 | year = 2014 | pmid = 24817852 | pmc = 4012202 | doi = 10.3389/fphys.2014.00165 }}</ref> | |||
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<ref name = "Streng_2013">{{cite journal | vauthors = Streng AS, de Boer D, van der Velden J, van Dieijen-Visser MP, Wodzig WK | title = Posttranslational modifications of cardiac troponin T: an overview | journal = Journal of Molecular and Cellular Cardiology | volume = 63 | issue = | pages = 47–56 | date = Oct 2013 | pmid = 23871791 | doi = 10.1016/j.yjmcc.2013.07.004 }}</ref> | |||
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<ref name = "Sumandea_2009">{{cite journal | vauthors = Sumandea MP, Vahebi S, Sumandea CA, Garcia-Cazarin ML, Staidle J, Homsher E | title = Impact of cardiac troponin T N-terminal deletion and phosphorylation on myofilament function | journal = Biochemistry | volume = 48 | issue = 32 | pages = 7722–31 | date = Aug 2009 | pmid = 19586048 | doi = 10.1021/bi900516n }}</ref> | |||
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<ref name = "Townsend_1998">{{cite journal | vauthors = Townsend PJ, Farza H, MacGeoch C, Spurr NK, Wade R, Gahlmann R, Yacoub MH, Barton PJ | title = Human cardiac troponin T: identification of fetal isoforms and assignment of the TNNT2 locus to chromosome 1q | journal = Genomics | volume = 21 | issue = 2 | pages = 311–6 | date = May 1994 | pmid = 8088824 | doi = 10.1006/geno.1994.1271 }}</ref> | |||
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<ref name = "Vahebi_2005">{{cite journal | vauthors = Vahebi S, Kobayashi T, Warren CM, de Tombe PP, Solaro RJ | title = Functional effects of rho-kinase-dependent phosphorylation of specific sites on cardiac troponin | journal = Circulation Research | volume = 96 | issue = 7 | pages = 740–7 | date = Apr 2005 | pmid = 15774859 | doi = 10.1161/01.RES.0000162457.56568.7d }}</ref> | |||
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}} | }} | ||
== | == External links == | ||
* [http://www.heartproteome.org/copa/ProteinInfo.aspx?QType=Protein%20ID&QValue=P45379 Mass spectrometry characterization of human TNNT2 at COPaKB] | |||
* [https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=hyper-card GeneReviews/NIH/NCBI/UW entry on Familial Hypertrophic Cardiomyopathy Overview] | |||
* | |||
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{{ | {{PDB Gallery|geneid=7139}} | ||
{{ | {{Cytoskeletal Proteins}} |
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Cardiac muscle troponin T (cTnT), is a protein which in humans is encoded by the TNNT2 gene.[1][2] Cardiac TnT is the tropomyosin-binding subunit of the troponin complex, which is located on the thin filament of striated muscles and regulates muscle contraction in response to alterations in intracellular calcium ion concentration.
The TNNT2 gene is located at 1q32 in the human chromosomal genome, encoding the cardiac muscle isoform of troponin T (cTnT). Human cTnT is an ~36-kDa protein consisting of 297 amino acids including the first methionine with an isoelectric point (pI) of 4.88. It is the tropomyosin- binding and thin filament anchoring subunit of the troponin complex in cardiac muscle cells.[3][4][5] TNNT2 gene is expressed in vertebrate cardiac muscles and embryonic skeletal muscles.[4][5][6]
Structure
Cardiac TnT is a 35.9 kDa protein composed of 298 amino acids.[7][8] Cardiac TnT is the largest of the three troponin subunits (cTnT, troponin I (TnI), troponin C (TnC)) on the actin thin filament of cardiac muscle. The structure of TnT is asymmetric; the globular C-terminal domain interacts with tropomyosin (Tm), TnI and TnC, and the N-terminal tether which strongly binds Tm. The N-terminal region of TnT is alternatively spliced, accounting for multiple isoforms observed in cardiac muscle.[9]
Function
As part of the Troponin complex, the function of cTnT is to regulate muscle contraction. The N-terminal region of TnT that strongly binds actin most likely moves with Tm and actin during strong myosin crossbridge binding and force generation. This region is likely involved in the transduction of cooperativity down the thin filament.[10] The C-terminal region of TnT constitutes part of the globular troponin complex domain, and participates in employing the calcium sensitivity of strong myosin crossbridge binding to the thin filament.[11]
Clinical significance
Mutations in this gene have been associated with familial hypertrophic cardiomyopathy as well as with restrictive[12] and dilated cardiomyopathy. Transcripts for this gene undergo alternative splicing that results in many tissue-specific isoforms, however, the full-length nature of some of these variants has not yet been determined.[13] Mutations of this gene may be associated with mild or absent hypertrophy and predominant restrictive disease, with a high risk of sudden cardiac death.[12] Advancement to dilated cardiomyopathy may be more rapid in patients with TNNT2 mutations than in those with myosin heavy chain mutations.[14][15]
Evolution
Three homologous genes have evolved in vertebrates encoding three muscle type- specific isoforms of TnT.[5] Each of the TnT isoform genes is linked in chromosomal DNA to a troponin I (TnI) isoform gene encoding the inhibitory subunit of the troponin complex to form three gene pairs: The fast skeletal muscle TnI (fsTnI)-fsTnT, slow skeletal muscle TnI (ssTnI)-cTnT, and cTnI-ssTnT pairs. Sequence and epitope conservation studies suggested that genes encoding the muscle type-specific TnT and TnI isoforms have originated from a TnI-like ancestor gene and duplicated and diversified from a fsTnI-like-fsTnT-like gene pair.[16]
The apparently scrambled linkage between ssTnI-cTnT and cTnI-ssTnT genes actually reflects original functional linkages as that TNNT2 gene is expressed together with ssTnI gene in embryonic cardiac muscle.[17] Protein sequence alignment demonstrated that TNNT2 gene is conserved in vertebrate species (Fig. 2) in the middle and C-terminal regions, while the three muscle type isoforms are significantly diverged.[4][5]
Alternative splicing
Mammalian TNNT2 gene contains 14 constitutive exons and 3 alternatively spliced exons.[18] Exons 4 and 5 encoding the N-terminal variable region and exon 13 between the middle and C-terminal regions are alternatively spliced.[19] Exon 5 encodes a 9 or 10 amino acid segment that is highly acidic and negatively charged at physiological pH.[4] Exon 5 is expressed in embryonic heart, down-regulated and ceases express during postnatal development.[20]
Embryonic cTnT with more negative charge at the N-terminal region exerts higher calcium sensitivity of actomyosin ATPase activity and myofilament force production, compared with the adult cardiac TnT, as well as a higher tolerance to acidosis.[21]
TNNT2 gene is transiently expressed in embryonic and neonatal skeletal muscles in both avian and mammalian organisms.[17][22][23] When TNNT2 is expressed in neonatal skeletal muscle, the alternative splicing of exon 5 exhibits a synchronized regulation to that in the heart in a species-specific manner.[17] This phenomenon indicates that alternative splicing of TNNT2 pre-mRNA is under the control of a genetically built- in systemic biological clock.
Posttranslational modifications
Phosphorylation
Ser2 of cTnT at the N terminus is constitutively phosphorylated by unknown mechanisms.[3] cTnT has been found to be phosphorylated by PKC at Thr197, Ser201, Thr206, Ser208 and Thr287 in the C-terminal region. Phosphorylation of Thr206 alone was sufficient to reduce myofilament calcium sensitivity and force production.[24][25][26][27] cTnT is also phosphorylated at Thr194 and Ser198 under stress conditions,[28] leading to attenuated cardiomyocyte contractility. Phosphorylation of cTnT at Ser278 and Thr287 by ROCK-II was shown to decrease myosin ATPase activity and myofilament force development in skinned cardiac muscle.[29] Table 1 summarizes the phosphorylation modifications of cTnT and possible functions.
O-linked GlcNAcylation
cTnT is increasingly modified at Ser190 by O-GlcNAcylation during the development of heart failure in rat, accompanied by decreased phosphorylation of Ser208.[27]
Proteolytic modification
In apoptotic cardiomyocytes, cTnT was cleaved by caspase 3 to generate a 25-kDa N-terminal truncated fragment.[30] This destructive fragmentation removes a part of the middle region tropomyosin binding site 1,[16] leading to attenuation of the myofilament force production by decreasing the myosin ATPase activity.[30]
In cardiac muscle under stress conditions, cardiac TnT is cleaved by calpain I, restrictively removing the entire N-terminal variable region.[31][32] This proteolytic modification of cTnT occurs in cardiac muscle in acute ischemia-reperfusion or pressure overload.[33]
The restrictively N-terminal truncated cTnT remains functional in the myofilaments and leads to reduced contractile velocity of the ventricular muscle, which extends the rapid ejection phase and results in an increase in stroke volume, especially under increased afterload.[33] In vitro studies showed that N-terminal truncated cTnT preserved the overall cardiac myofilament calcium sensitivity and cooperativity, but altered TnT’s binding affinities for tropomyosin, TnI and TnC proteins,[34][35] and lead to slightly decreased maximum myosin ATPase activity and myofilament force production, which forms the basis of the selective decrease in contractile velocity of ventricular muscle to increase stroke volume without significant increase in energy expenditure.[33]
With the relatively short half life of cTnT in cardiomyocytes (3–4 days),[36] the N-terminal truncated cTnT would be replaced by newly synthesized intact cTnT in several days. Therefore, this mechanism provides a reversible posttranslational regulation to modulate cardiac function in adaptation to stress conditions.
Phosphorylation site | Kinase | Function | Reference | ||
---|---|---|---|---|---|
cTnT | ssTnT | fsTnT | |||
Ser2 | c | c | PKC | Unknown | [37][38][39] |
Thr197 | n | N | PKC | No functional effect | [25][40] |
Ser201 | n | n | PKC | No functional effect | [25][40] |
Thr204 | n | n | PKC | Reduce Myosin ATPase activity, myofilament force production and Ca2+ sensitivity | [40][41][42] |
Thr204 | n | n | CaMK II | Unknown | [43] |
Thr204 | n | n | ASK I | Reduce cardiomyocyte contractility | [28] |
Thr206 | PKC | Reduce Ca2+ sensitivity, actomyosin ATPase activity and tension development | [25] | ||
Ser208 | n | n | PKC | Reduce Myosin ATPase activity, alter myofilament Ca2+ sensitivity | [40][42][44] |
Ser208 | n | n | ASK I | Reduce cardiomyocyte contractility | [28] |
Thr213 | c | c | PKC | Reduce Myosin ATPase activity, myofilament force production and Ca2+ sensitivity | [45] |
Thr213 | c | c | Raf-1 | Unknown | [46] |
Ser285 | n | c | PKC | Reduce Myosin ATPase activity, myofilament force production and Ca2+ sensitivity | [44] |
Ser285 | n | c | ROCK-II | Reduce myofilament force development, Myosin ATPase activity and Ca2+ sensitivity | [29] |
Thr294 | n | n | PKC | Reduce Myosin ATPase activity, myofilament force production and Ca2+ sensitivity | [40][41][42][44] |
Thr294 | n | n | ROCK-II | Reduce myofilament force development, myosin ATPase activity and Ca2+ sensitivity | [29] |
The residues in cardiac TnT with phosphorylation regulations are summarized. The residue numbers for phosphorylatable serine and threonine are that in human cardiac TnT with the first methionine included. The phosphorylation of cardiac TnT at these residues is compared with the counterparts in fast TnT and slow TnT. C, conserved; N, non-conserved. Kinases responsible for each phosphorylation, functional effects, and references are also listed.
Mutations in cardiomyopathies
Point mutations in TNNT2 gene cause various types of cardiomyopathies, including hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) and restrictive cardiomyopathy (RCM). The table below summarizes representative TNNT2 mutations and abnormal splicings found in human and animal cardiomyopathies.
Mutation | Diagnosis | Reference |
---|---|---|
Ile79Asn | HCM | [47][48][49] |
Arg92Gln | HCM | [47][50] |
Intron 16G1→A (D14 and D28+7) | HCM | [47] |
Arg92Leu | HCM | [49][51] |
Arg92Trp | HCM | [14][52][53] |
Arg94Leu | HCM | [49][54] |
Arg94Cys | HCM | [55] |
ΔE96 | RCM | [56][57] |
Ala104Val | HCM | [58] |
Phe110Ile | DCM | [59][60] |
Arg130Cys | HCM | [61] |
Arg131Trp | DCM | [62][63] |
E136K | RCM | [64] |
Arg141Trp | DCM | [65][66] |
DGlu160 | HCM | [67] |
Glu163Arg | HCM | [61] |
Glu163Lys | HCM | [59] |
Ser179Phe | HCM | [68] |
Arg205Leu | DCM | [62] |
DLys210 | DCM | [69][70][71] |
Glu244Asp | HCM | [59] |
Asp270Asn | DCM | [69] |
Lys273Glu | DCM | [15] |
Arg278Cys | HCM | [59][72] |
Amino Acid residues of mutations were numbered as in human cardiac TnT with the first methionine included. Mutations of cardiac TnT that caused cardiomyopathies were mostly found in the conserved middle and C-terminal regions.
Notes
The 2015 version of this article was updated by an external expert under a dual publication model. The corresponding academic peer reviewed article was published in Gene and can be cited as: {{#property:P2093|from=Q37666010}} ({{#property:P577|from=Q37666010}}). "{{#property:P1476|from=Q37666010}}". Gene. {{#property:P478|from=Q37666010}} ({{#property:P433|from=Q37666010}}): {{#property:P304|from=Q37666010}}. doi:{{#property:P356|from=Q37666010}} Check |doi= value (help). PMC {{#property:P932|from=Q37666010}} Check |pmc= value (help). PMID {{#property:P698|from=Q37666010}} Check |pmid= value (help). Check date values in: |date= (help) |
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- ↑ Moolman JC, Corfield VA, Posen B, Ngumbela K, Seidman C, Brink PA, Watkins H (Mar 1997). "Sudden death due to troponin T mutations". Journal of the American College of Cardiology. 29 (3): 549–55. doi:10.1016/s0735-1097(96)00530-x. PMID 9060892.
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- ↑ Lu QW, Morimoto S, Harada K, Du CK, Takahashi-Yanaga F, Miwa Y, Sasaguri T, Ohtsuki I (Dec 2003). "Cardiac troponin T mutation R141W found in dilated cardiomyopathy stabilizes the troponin T-tropomyosin interaction and causes a Ca2+ desensitization". Journal of Molecular and Cellular Cardiology. 35 (12): 1421–7. doi:10.1016/j.yjmcc.2003.09.003. PMID 14654368.
- ↑ Harada K, Takahashi-Yanaga F, Minakami R, Morimoto S, Ohtsuki I (Feb 2000). "Functional consequences of the deletion mutation deltaGlu160 in human cardiac troponin T". Journal of Biochemistry. 127 (2): 263–8. doi:10.1093/oxfordjournals.jbchem.a022603. PMID 10731693.
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- ↑ Hanson EL, Jakobs PM, Keegan H, Coates K, Bousman S, Dienel NH, Litt M, Hershberger RE (Feb 2002). "Cardiac troponin T lysine 210 deletion in a family with dilated cardiomyopathy". Journal of Cardiac Failure. 8 (1): 28–32. doi:10.1054/jcaf.2002.31157. PMID 11862580.
- ↑ Hershberger RE, Pinto JR, Parks SB, Kushner JD, Li D, Ludwigsen S, Cowan J, Morales A, Parvatiyar MS, Potter JD (Aug 2009). "Clinical and functional characterization of TNNT2 mutations identified in patients with dilated cardiomyopathy". Circulation: Cardiovascular Genetics. 2 (4): 306–13. doi:10.1161/CIRCGENETICS.108.846733. PMC 2900844. PMID 20031601.
- ↑ Morimoto S, Nakaura H, Yanaga F, Ohtsuki I (Jul 1999). "Functional consequences of a carboxyl terminal missense mutation Arg278Cys in human cardiac troponin T". Biochemical and Biophysical Research Communications. 261 (1): 79–82. doi:10.1006/bbrc.1999.1000. PMID 10405326.