Array ( [0] => {{Short description|Largest-known protein in human muscles}} [1] => {{distinguish|Titan (disambiguation){{!}}Titan|Tintin (disambiguation){{!}}Tintin|Titian}} [2] => [7] => {{Infobox_gene}} [8] => [9] => [[File:Cardiac sarcomere structure.png|thumb|330x330px|[[Cardiac#Microanatomy|Cardiac sarcomere]] structure, featuring titin]] [10] => [[File:Mammalian Titin Structure from the relaxed thick filament.tif|thumb|Reconstruction of the thin (green) and thick filament from mammalian cardiac tissue. Myosin is in blue, MyBP-C is in yellow, and titin is in two shades of red (dark red for titin-alpha and light red for titin-beta).]] [11] => '''Titin''' {{IPAc-en|ˈ|t|aɪ|t|ɪ|n}} (contraction for Titan protein) (also called '''connectin''') is a [[protein]] that in humans is encoded by the ''TTN'' [[gene]].{{cite web |date=April 2018 |title=TTN, the human gene for Titin |url=https://www.ncbi.nlm.nih.gov/gene?Db=gene&Cmd=ShowDetailView&TermToSearch=7273 |url-status=live |access-date= |website=[[National Library of Medicine]]; [[National Center for Biotechnology Information]] |archive-date=2010-03-07 |archive-url=https://web.archive.org/web/20100307070431/http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7273}}{{cite journal | vauthors = Labeit S, Barlow DP, Gautel M, Gibson T, Holt J, Hsieh CL, Francke U, Leonard K, Wardale J, Whiting A | display-authors = 6 | title = A regular pattern of two types of 100-residue motif in the sequence of titin | journal = Nature | volume = 345 | issue = 6272 | pages = 273–276 | date = May 1990 | pmid = 2129545 | doi = 10.1038/345273a0 | url = https://ui.adsabs.harvard.edu/abs/1990Natur.345..273L/abstract | access-date = 8 May 2022 | url-status = live | s2cid = 4240433 | bibcode = 1990Natur.345..273L | archive-url = https://web.archive.org/web/20211022223626/https://ui.adsabs.harvard.edu/abs/1990Natur.345..273L/abstract | archive-date = 22 October 2021 }} Titin is a protein, over 1 [[Micrometre|µm]] in length,{{cite web | vauthors = Lee EH |url=http://www.ks.uiuc.edu/Research/z1z2/ |title=The Chain-like Elasticity of Titin |publisher=Theoretical and Computational Biophysics Group, University of Illinois |access-date=25 September 2014 |archive-date=13 February 2021 |archive-url=https://web.archive.org/web/20210213032405/http://www.ks.uiuc.edu/Research/z1z2/ |url-status=live}} that functions as a molecular [[Spring (device)|spring]] that is responsible for the passive elasticity of [[muscle]]. It comprises 244 individually folded [[protein domain]]s connected by unstructured [[peptide]] sequences.{{cite journal | vauthors = Labeit S, Kolmerer B | title = Titins: giant proteins in charge of muscle ultrastructure and elasticity | journal = Science | volume = 270 | issue = 5234 | pages = 293–296 | date = October 1995 | pmid = 7569978 | doi = 10.1126/science.270.5234.293 | url = https://ui.adsabs.harvard.edu/abs/1995Sci...270..293L/abstract | access-date = 8 May 2022 | url-status = live | s2cid = 20470843 | bibcode = 1995Sci...270..293L | archive-url = https://web.archive.org/web/20210302130853/https://ui.adsabs.harvard.edu/abs/1995Sci...270..293L/abstract | archive-date = 2 March 2021 }} These domains [[denaturation (biochemistry)|unfold]] when the protein is stretched and [[protein folding|refold]] when the tension is removed.{{cite journal | vauthors = Minajeva A, Kulke M, Fernandez JM, Linke WA | title = Unfolding of titin domains explains the viscoelastic behavior of skeletal myofibrils | journal = Biophysical Journal | volume = 80 | issue = 3 | pages = 1442–1451 | date = March 2001 | pmid = 11222304 | pmc = 1301335 | doi = 10.1016/S0006-3495(01)76116-4 | bibcode = 2001BpJ....80.1442M | author-link2 = Matthew Kulke }} [12] => [13] => Titin is important in the contraction of [[striated muscle tissue]]s. It connects the [[Myofibril#Appearance|Z disc]] to the [[Myofibril#Appearance|M line]] in the [[sarcomere]]. The protein contributes to force transmission at the Z disc and resting tension in the [[Myofibril#Appearance|I band]] region.{{cite journal | vauthors = Itoh-Satoh M, Hayashi T, Nishi H, Koga Y, Arimura T, Koyanagi T, Takahashi M, Hohda S, Ueda K, Nouchi T, Hiroe M, Marumo F, Imaizumi T, Yasunami M, Kimura A | display-authors = 6 | title = Titin mutations as the molecular basis for dilated cardiomyopathy | journal = Biochemical and Biophysical Research Communications | volume = 291 | issue = 2 | pages = 385–393 | date = February 2002 | pmid = 11846417 | doi = 10.1006/bbrc.2002.6448 }} It limits the range of motion of the sarcomere in tension, thus contributing to the passive stiffness of muscle. Variations in the sequence of titin between different types of striated muscle ([[Cardiac muscle|cardiac]] or [[Skeletal muscle|skeletal]]) have been correlated with differences in the mechanical properties of these muscles.{{OMIM|188840}} [14] => [15] => Titin is the third most abundant protein in muscle (after [[myosin]] and [[actin]]), and an adult human contains approximately 0.5 kg of titin.{{cite journal | vauthors = Labeit S, Kolmerer B, Linke WA | title = The giant protein titin. Emerging roles in physiology and pathophysiology | journal = Circulation Research | volume = 80 | issue = 2 | pages = 290–294 | date = February 1997 | pmid = 9012751 | doi = 10.1161/01.RES.80.2.290 }} With its length of ~27,000 to ~35,000 [[amino acid]]s (depending on the [[Alternative splicing|splice isoform]]), titin is the largest known [[protein]].{{cite journal | vauthors = Opitz CA, Kulke M, Leake MC, Neagoe C, Hinssen H, Hajjar RJ, Linke WA | title = Damped elastic recoil of the titin spring in myofibrils of human myocardium | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 100 | issue = 22 | pages = 12688–12693 | date = October 2003 | pmid = 14563922 | pmc = 240679 | doi = 10.1073/pnas.2133733100 | bibcode = 2003PNAS..10012688O | doi-access = free }} Furthermore, the gene for titin contains the largest number of [[exon]]s (363) discovered in any single gene,{{cite journal | vauthors = Bang ML, Centner T, Fornoff F, Geach AJ, Gotthardt M, McNabb M, Witt CC, Labeit D, Gregorio CC, Granzier H, Labeit S | display-authors = 6 | title = The complete gene sequence of titin, expression of an unusual approximately 700-kDa titin isoform, and its interaction with obscurin identify a novel Z-disc to I-band Linking system | journal = Circulation Research | volume = 89 | issue = 11 | pages = 1065–1072 | date = November 2001 | pmid = 11717165 | doi = 10.1161/hh2301.100981 | doi-access = free }} as well as the longest single exon (17,106 [[Base pair|bp]]). [16] => [17] => == Discovery == [18] => [19] => In 1954, Reiji Natori proposed the existence of an elastic structure in muscle fiber to account for the return to the resting state when muscles are stretched and then released.{{cite journal |vauthors=Natori R |title=Skinned Fibres of Skeletal Muscle and the Mechanism of Muscle Contraction－A Chronological Account of the Author's Investigations into Muscle Physiology |journal=Jikeikai Medical Journal |year=1954 |volume=54 |issue=1 |url=http://ir.jikei.ac.jp/bitstream/10328/3410/1/54-1-51.pdf |access-date=2014-09-09 |archive-date=2016-06-03 |archive-url=https://web.archive.org/web/20160603072338/http://ir.jikei.ac.jp/bitstream/10328/3410/1/54-1-51.pdf |url-status=dead [20] => |hdl=10328/3410}} In 1977, Koscak Maruyama and coworkers isolated an elastic protein from muscle fiber that they called connectin.{{cite journal | vauthors = Maruyama K, Matsubara S, Natori R, Nonomura Y, Kimura S | title = Connectin, an elastic protein of muscle. Characterization and Function | journal = Journal of Biochemistry | volume = 82 | issue = 2 | pages = 317–337 | date = August 1977 | pmid = 914784 }} Two years later, [[Kuan Wang]] and coworkers identified a doublet band on [[gel electrophoresis|electrophoresis gel]] corresponding to a high molecular weight, elastic protein that they named titin.{{cite journal | vauthors = Wang K, McClure J, Tu A | title = Titin: major myofibrillar components of striated muscle | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 76 | issue = 8 | pages = 3698–3702 | date = August 1979 | pmid = 291034 | pmc = 383900 | doi = 10.1073/pnas.76.8.3698 | doi-access = free | bibcode = 1979PNAS...76.3698W }}{{cite journal | vauthors = Maruyama K | title = Connectin, an elastic protein of striated muscle | journal = Biophysical Chemistry | volume = 50 | issue = 1–2 | pages = 73–85 | date = May 1994 | pmid = 8011942 | doi = 10.1016/0301-4622(94)85021-6 }} [21] => [22] => In 1990, Siegfried Labeit isolated a partial [[cDNA]] clone of titin. Five years later, Labeit and Bernhard Kolmerer determined the cDNA sequence of human cardiac titin. In 2001, Labeit and colleagues determined the complete sequence of the human titin gene.{{OMIM|188840|Titin}} [23] => [24] => == Genetics == [25] => [26] => The human gene encoding for titin is located on the long arm of chromosome 2 and contains 363 exons, which together code for 38,138 [[amino acid]] [[Residue (chemistry)#Biochemistry|residues]] (4200 kDa). Within the gene are found a large number of PEVK (proline-glutamate-valine-lysine -abundant [[structural motif]]s) exons 84 to 99 nucleotides in length, which code for conserved 28- to 33-residue motifs that may represent structural units of the titin PEVK spring. The number of PEVK motifs in the titin gene appears to have increased during evolution, apparently modifying the genomic region responsible for titin's spring properties.{{cite journal | vauthors = Freiburg A, Trombitas K, Hell W, Cazorla O, Fougerousse F, Centner T, Kolmerer B, Witt C, Beckmann JS, Gregorio CC, Granzier H, Labeit S | display-authors = 6 | title = Series of exon-skipping events in the elastic spring region of titin as the structural basis for myofibrillar elastic diversity | journal = Circulation Research | volume = 86 | issue = 11 | pages = 1114–1121 | date = June 2000 | pmid = 10850961 | doi = 10.1161/01.res.86.11.1114 | doi-access = free }} [27] => [28] => == Isoforms == [29] => [30] => A number of titin [[protein isoform|isoform]]s are produced in different striated muscle tissues as a result of [[alternative splicing]]. All but one of these isoforms are in the range of ~27,000 to ~36,000 amino acid residues in length. The exception is the small cardiac novex-3 isoform, which is only 5,604 amino acid residues in length. The following table lists the known titin isoforms: [31] => [32] => {| class="wikitable" [33] => |- [34] => ! Isoform !! Alias/description !! Length !! Molecular weight [35] => |- [36] => | Q8WZ42-1 || The "canonical" sequence || 34,350 || 3,816,030 [37] => |- [38] => | Q8WZ42-2 || || 34,258 || 3,805,708 [39] => |- [40] => | Q8WZ42-3 || Small cardiac N2-B || 26,926 || 2,992,939 [41] => |- [42] => | Q8WZ42-4 || Soleus || 33,445 || 3,716,027 [43] => |- [44] => | Q8WZ42-5 || || 32,900 || 3,653,085 [45] => |- [46] => | Q8WZ42-6 || Small cardiac novex-3 || 5,604 || 631,567 [47] => |- [48] => | Q8WZ42-7 || Cardiac novex-2 || 33,615 || 3,734,648 [49] => |- [50] => | Q8WZ42-8 || Cardiac novex-1 || 34,475 || 3,829,846 [51] => |- [52] => | Q8WZ42-9 || || 27,118 || 3,013,957 [53] => |- [54] => | Q8WZ42-10 || || 27,051 || 3,006,755 [55] => |- [56] => | Q8WZ42-11 || || 33,423 || 3,713,600 [57] => |- [58] => | Q8WZ42-12 || || 35,991 || 3,994,625 [59] => |- [60] => | Q8WZ42-13 || || 34,484 || 3,831,069 [61] => |} [62] => [63] => == Structure == [64] => [65] => Titin is the largest known protein; its human variant consists of 34,350 [[amino acid]]s, with the [[molecular weight]] of the mature "canonical" isoform of the protein being approximately 3,816,030.05 [[atomic mass unit|Da]]. Its mouse homologue is even larger, comprising 35,213 amino acids with a molecular weight of 3,906,487.6 [[atomic mass unit|Da]].{{cite web |url=http://www.expasy.org/cgi-bin/protparam1?A2ASS6@noft@ |title=ProtParam for mouse titin |work=ExPASy Proteomics Server |publisher=Swiss Institute of Bioinformatics |access-date=2010-05-06}} It has a theoretical [[isoelectric point]] of 6.02. The protein's [[empirical formula|empirical]] [[chemical formula]] is C169,719H270,466N45,688O52,238S911.{{cite web |url=http://web.expasy.org/cgi-bin/protparam/protparam1?Q8WZ42@1-34350@ |title=ProtParam for human titin |work=ExPASy Proteomics Server |publisher=Swiss Institute of Bioinformatics |access-date=2011-07-25 |archive-date=2019-09-18 |archive-url=https://web.archive.org/web/20190918231125/https://web.expasy.org/cgi-bin/protparam/protparam1?Q8WZ42@1-34350@ |url-status=live}} It has a theoretical [[instability index]] (II) of 42.38, classifying the protein as unstable. The protein's [[in vivo]] [[half-life]], the time it takes for half of the amount of protein in a cell to break down after its synthesis in the cell, is predicted to be approximately 30 hours (in [[mammalian]] [[reticulocyte]]s).{{cite web |url=https://www.uniprot.org/uniprot/Q8WZ42 |title=Titin - Homo sapiens (Human) |work=Universal Protein Resource |publisher=UniProt Consortium |date=2010-10-05 |access-date=2010-10-15 |archive-date=2021-02-13 |archive-url=https://web.archive.org/web/20210213032327/https://www.uniprot.org/uniprot/Q8WZ42 |url-status=live}} [66] => [67] => [[File:Titin_IG_Domains.jpg|thumb|256x256px|Titin Ig domains. a) Schematic of part of a sarcomere b) Structure of Ig domains c) Topology of Ig domains.{{cite journal | vauthors = Giganti D, Yan K, Badilla CL, Fernandez JM, Alegre-Cebollada J | title = Disulfide isomerization reactions in titin immunoglobulin domains enable a mode of protein elasticity | journal = Nature Communications | volume = 9 | issue = 1 | pages = 185 | date = January 2018 | pmid = 29330363 | pmc = 5766482 | doi = 10.1038/s41467-017-02528-7 | bibcode = 2018NatCo...9..185G }}|alt=]] [68] => [69] => The Titin protein is located between the [[myosin]] thick filament and the Z disk.{{cite journal | vauthors = Wang K, McCarter R, Wright J, Beverly J, Ramirez-Mitchell R | title = Regulation of skeletal muscle stiffness and elasticity by titin isoforms: a test of the segmental extension model of resting tension | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 88 | issue = 16 | pages = 7101–7105 | date = August 1991 | pmid = 1714586 | pmc = 52241 | doi = 10.1073/pnas.88.16.7101 | doi-access = free | bibcode = 1991PNAS...88.7101W }} Titin consists primarily of a linear array of two types of modules, also referred to as [[protein domain]]s (244 copies in total): type I [[fibronectin type III domain]] (132 copies) and type II [[immunoglobulin domain]] (112 copies). However, the exact number of these domains is different in different species. This linear array is further organized into two regions: [70] => [71] => * [[N-terminus|N-terminal]] I-band: acts as the elastic part of the molecule and is composed mainly of type II modules. More specifically the I-band contains two regions of tandem type II immunoglobulin domains on either side of a ''PEVK region'' that is rich in [[proline]] (P), [[Glutamic acid|glutamate]] (E), [[valine]] (V) and [[lysine]] (K). [72] => * [[C-terminus|C-terminal]] A-band: is thought to act as a protein-ruler and is composed of alternating type I (Fn3) and II (Ig) modules with super-repeat segments. These have been shown to align to the 43 nm axial repeats of myosin thick filaments with immunoglobulin domains correlating to myosin crowns.{{cite journal | vauthors = Bennett PM, Gautel M | title = Titin domain patterns correlate with the axial disposition of myosin at the end of the thick filament | journal = Journal of Molecular Biology | volume = 259 | issue = 5 | pages = 896–903 | date = June 1996 | pmid = 8683592 | doi = 10.1006/jmbi.1996.0367 }} [73] => [74] => The C-terminal region also contains a serine [[kinase]] domain{{cite journal | vauthors = Higgins DG, Labeit S, Gautel M, Gibson TJ | title = The evolution of titin and related giant muscle proteins | journal = Journal of Molecular Evolution | volume = 38 | issue = 4 | pages = 395–404 | date = April 1994 | pmid = 8007007 | doi = 10.1007/BF00163156 | s2cid = 35756951 | bibcode = 1994JMolE..38..395H }} that is primarily known for adapting the muscle to mechanical strain.{{cite journal | vauthors = Puchner EM, Alexandrovich A, Kho AL, Hensen U, Schäfer LV, Brandmeier B, Gräter F, Grubmüller H, Gaub HE, Gautel M | display-authors = 6 | title = Mechanoenzymatics of titin kinase | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 36 | pages = 13385–13390 | date = September 2008 | pmid = 18765796 | pmc = 2527993 | doi = 10.1073/pnas.0805034105 | doi-access = free | bibcode = 2008PNAS..10513385P }} It is “stretch-sensitive” and helps repair overstretching of the sarcomere.{{cite journal | vauthors = Myhre JL, Pilgrim D | title = A Titan but not necessarily a ruler: assessing the role of titin during thick filament patterning and assembly | journal = Anatomical Record | volume = 297 | issue = 9 | pages = 1604–1614 | date = September 2014 | pmid = 25125174 | doi = 10.1002/ar.22987 | s2cid = 32840140 | doi-access = free }} The N-terminal (the Z-disc end) contains a "Z repeat" that recognizes [[Actinin alpha 2]].{{cite web |title=Titin, Z repeat (IPR015129) < InterPro < EMBL-EBI |url=http://www.ebi.ac.uk/interpro/entry/IPR015129 |access-date=13 March 2019 |archive-date=13 February 2021 |archive-url=https://web.archive.org/web/20210213032409/http://www.ebi.ac.uk/interpro/entry/IPR015129 |url-status=live }} [75] => [76] => The elasticity of the PEVK region has both [[entropic]] and [[enthalpic]] contributions and is characterized by a polymer [[persistence length]] and a [[Young's modulus|stretch modulus]].{{cite journal | vauthors = Linke WA, Ivemeyer M, Mundel P, Stockmeier MR, Kolmerer B | title = Nature of PEVK-titin elasticity in skeletal muscle | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 14 | pages = 8052–8057 | date = July 1998 | pmid = 9653138 | pmc = 20927 | doi = 10.1073/pnas.95.14.8052 | doi-access = free | bibcode = 1998PNAS...95.8052L }} At low to moderate extensions PEVK elasticity can be modeled with a standard [[worm-like chain]] (WLC) model of [[entropic elasticity of an ideal chain|entropic elasticity]]. At high extensions PEVK stretching can be modeled with a modified WLC model that incorporates enthalpic elasticity. The difference between low-and high- stretch elasticity is due to electrostatic stiffening and [[hydrophobic effect]]s. [77] => [78] => Embedded between the PEVK and Ig residues are N2A domains.{{cite journal | vauthors = Buck D, Smith JE, Chung CS, Ono Y, Sorimachi H, Labeit S, Granzier HL | title = Removal of immunoglobulin-like domains from titin's spring segment alters titin splicing in mouse skeletal muscle and causes myopathy | journal = The Journal of General Physiology | volume = 143 | issue = 2 | pages = 215–230 | date = February 2014 | pmid = 24470489 | pmc = 4001778 | doi = 10.1085/jgp.201311129 }} [79] => [80] => == Evolution == [81] => The titin domains have evolved from a common ancestor through many gene duplication events.{{cite journal | vauthors = Tskhovrebova L, Trinick J | title = Properties of titin immunoglobulin and fibronectin-3 domains | journal = The Journal of Biological Chemistry | volume = 279 | issue = 45 | pages = 46351–46354 | date = November 2004 | pmid = 15322090 | doi = 10.1074/jbc.r400023200 | url = http://www.jbc.org/content/279/45/46351 | access-date = 2018-12-16 | url-status = live | doi-access = free | archive-url = https://web.archive.org/web/20180603172142/http://www.jbc.org/content/279/45/46351 | archive-date = 2018-06-03 }} Domain duplication was facilitated by the fact that most domains are encoded by single exons. Other giant sarcomeric proteins made out of Fn3/Ig repeats include [[obscurin]] and [[MYOM1|myomesin]]. Throughout evolution, titin mechanical strength appears to decrease through the loss of disulfide bonds as the organism becomes heavier.{{cite journal | vauthors = Manteca A, Schönfelder J, Alonso-Caballero A, Fertin MJ, Barruetabeña N, Faria BF, Herrero-Galán E, Alegre-Cebollada J, De Sancho D, Perez-Jimenez R | display-authors = 6 | title = Mechanochemical evolution of the giant muscle protein titin as inferred from resurrected proteins | journal = Nature Structural & Molecular Biology | volume = 24 | issue = 8 | pages = 652–657 | date = August 2017 | pmid = 28671667 | doi = 10.1038/nsmb.3426 | s2cid = 54482436 | hdl = 20.500.12105/9931 | hdl-access = free }} [82] => [83] => Titin A-band has homologs in invertebrates, such as twitchin (unc-22) and projectin, which also contain Ig and FNIII repeats and a protein kinase domain. The gene duplication events took place independently but were from the same ancestral Ig and FNIII domains. It is said that the protein titin was the first to diverge out of the family. ''Drosophila'' projectin, officially known as bent (''bt''), is associated with lethality by failing to escape the egg in some mutations as well as dominant changes in wing angles.{{cite journal | vauthors = Fyrberg CC, Labeit S, Bullard B, Leonard K, Fyrberg E | title = Drosophila projectin: relatedness to titin and twitchin and correlation with lethal(4) 102 CDa and bent-dominant mutants | journal = Proceedings. Biological Sciences | volume = 249 | issue = 1324 | pages = 33–40 | date = July 1992 | pmid = 1359548 | doi = 10.1098/rspb.1992.0080 | s2cid = 34408190 | bibcode = 1992RSPSB.249...33F }}{{cite web |title=bent phenotype |url=http://cgslab.com/cgs1/phenotypes.cgi?n=17 |website=Classical Genetics Simulator |access-date=13 March 2019 |archive-date=11 February 2019 |archive-url=https://web.archive.org/web/20190211134649/http://www.cgslab.com/cgs1/phenotypes.cgi?n=17 |url-status=live}}{{cite web |title=FlyBase Gene Report: Dmel\bt |url=https://flybase.org/reports/FBgn0005666 |website=flybase.org |access-date=13 March 2019 |archive-date=13 March 2019 |archive-url=https://web.archive.org/web/20190313224757/http://flybase.org/reports/FBgn0005666 |url-status=live}} [84] => [85] => {{Pfam box|Pfam=PF06582|Name=Titin repeat|Symbol=Titin_Ig-rpts|InterPro=IPR010939}} [86] => ''Drosophila'' Titin, also known as Kettin or [[wikt:sallimus|sallimus]] (''sls''), is kinase-free. It has roles in the elasticity of both muscle and chromosomes. It is homologous to vertebrate titin I-band and contains Ig PEVK domains, the many repeats being a hot target for splicing.{{cite journal | vauthors = Machado C, Andrew DJ | title = D-Titin: a giant protein with dual roles in chromosomes and muscles | journal = The Journal of Cell Biology | volume = 151 | issue = 3 | pages = 639–652 | date = October 2000 | pmid = 11062264 | pmc = 2185597 | doi = 10.1083/jcb.151.3.639 | url = http://jcb.rupress.org/content/jcb/151/3/639.full.pdf | access-date = 2019-09-04 | url-status = live | archive-url = https://web.archive.org/web/20190904063833/http://jcb.rupress.org/content/jcb/151/3/639.full.pdf | archive-date = 2019-09-04 }} There also exists a titin homologue, ''ttn-1'', in ''[[C. elegans]]''.{{cite web |title=ttn-1 (gene) |url=https://wormbase.org/species/c_elegans/gene/WBGene00006436 |website=WormBase: Nematode Information Resource |access-date=13 March 2019 |archive-date=27 March 2018 |archive-url=https://web.archive.org/web/20180327031428/http://www.wormbase.org/species/c_elegans/gene/WBGene00006436 |url-status=live }} It has a kinase domain, some Ig/Fn3 repeats, and PEVT repeats that are similarly elastic.{{cite journal | vauthors = Forbes JG, Flaherty DB, Ma K, Qadota H, Benian GM, Wang K | title = Extensive and modular intrinsically disordered segments in C. elegans TTN-1 and implications in filament binding, elasticity and oblique striation | journal = Journal of Molecular Biology | volume = 398 | issue = 5 | pages = 672–689 | date = May 2010 | pmid = 20346955 | pmc = 2908218 | doi = 10.1016/j.jmb.2010.03.032 }} [87] => [88] => == Function == [89] => [[File:Sarcomere.svg|thumb|200px|Sliding filament model of muscle contraction. (Titin labeled at upper right.)]] [90] => Titin is a large abundant protein of striated muscle. Titin's primary functions are to stabilize the thick filament, center it between the thin filaments, prevent overstretching of the sarcomere, and to recoil the sarcomere like a spring after it is stretched.{{cite book |vauthors=Saladin K |title=Anatomy & Physiology |date=2015 |edition=7th |publisher=McGraw Hill |page=401 |isbn=978-0-07-340371-7}} An N-terminal Z-disc region and a C-terminal M-line region bind to the Z-line and M-line of the [[sarcomere]], respectively, so that a single titin molecule spans half the length of a sarcomere. Titin also contains binding sites for muscle-associated proteins so it serves as an adhesion template for the assembly of contractile machinery in muscle cells. It has also been identified as a structural protein for [[chromosome]]s.{{cite journal | vauthors = Machado C, Sunkel CE, Andrew DJ | title = Human autoantibodies reveal titin as a chromosomal protein | journal = The Journal of Cell Biology | volume = 141 | issue = 2 | pages = 321–333 | date = April 1998 | pmid = 9548712 | pmc = 2148454 | doi = 10.1083/jcb.141.2.321 }}{{cite book |vauthors=Machado C, Andrew DJ |chapter=Titin as a Chromosomal Protein |series=Advances in Experimental Medicine and Biology |title=Elastic Filaments of the Cell |volume=481 |pages=221–32; discussion 232–6 |year=2000 |pmid=10987075 |doi=10.1007/978-1-4615-4267-4_13 |isbn=978-1-4613-6916-5}} Considerable variability exists in the I-band, the M-line and the Z-disc regions of titin. Variability in the I-band region contributes to the differences in elasticity of different titin isoforms and, therefore, to the differences in elasticity of different muscle types. Of the many titin variants identified, five are described with complete transcript information available. [91] => [92] => [[Dominance (genetics)|Dominant]] mutation in TTN causes predisposition to [[hernia]]s.{{cite journal | vauthors = Mihailov E, Nikopensius T, Reigo A, Nikkolo C, Kals M, Aruaas K, Milani L, Seepter H, Metspalu A | display-authors = 6 | title = Whole-exome sequencing identifies a potential TTN mutation in a multiplex family with inguinal hernia | journal = Hernia | volume = 21 | issue = 1 | pages = 95–100 | date = February 2017 | pmid = 27115767 | pmc = 5281683 | doi = 10.1007/s10029-016-1491-9 }} [93] => [94] => Titin interacts with many [[sarcomere|sarcomeric]] proteins including: [95] => * Z line region: [[TCAP (gene)|telethonin]] and [[ACTN1|alpha-actinin]] [96] => * I band region: [[CAPN3|calpain-3]] and [[OBSCN|obscurin]] [97] => * M line region: [[MYBPC3|myosin-binding protein C]], [[calmodulin 1]], [[CAPN3]], and [[TRIM63|MURF1]] [98] => [99] => == Clinical relevance == [100] => [101] => [[Mutation]]s anywhere within the unusually long sequence of this gene can cause [[premature stop codon]]s or other defects. Titin mutations are associated with hereditary [[myopathy]] with early respiratory failure,{{cite journal | vauthors = Pfeffer G, Elliott HR, Griffin H, Barresi R, Miller J, Marsh J, Evilä A, Vihola A, Hackman P, Straub V, Dick DJ, Horvath R, Santibanez-Koref M, Udd B, Chinnery PF | display-authors = 6 | title = Titin mutation segregates with hereditary myopathy with early respiratory failure | journal = Brain | volume = 135 | issue = Pt 6 | pages = 1695–1713 | date = June 2012 | pmid = 22577215 | pmc = 3359754 | doi = 10.1093/brain/aws102 }}{{cite journal | vauthors = Ohlsson M, Hedberg C, Brådvik B, Lindberg C, Tajsharghi H, Danielsson O, Melberg A, Udd B, Martinsson T, Oldfors A | display-authors = 6 | title = Hereditary myopathy with early respiratory failure associated with a mutation in A-band titin | journal = Brain | volume = 135 | issue = Pt 6 | pages = 1682–1694 | date = June 2012 | pmid = 22577218 | doi = 10.1093/brain/aws103 | url = https://lup.lub.lu.se/search/ws/files/1591356/3900864.pdf | access-date = 2021-09-11 | url-status = live | archive-url = https://web.archive.org/web/20210911003000/https://lup.lub.lu.se/search/ws/files/1591356/3900864.pdf | archive-date = 2021-09-11 }} early-onset myopathy with fatal [[cardiomyopathy]],{{cite journal | vauthors = Carmignac V, Salih MA, Quijano-Roy S, Marchand S, Al Rayess MM, Mukhtar MM, Urtizberea JA, Labeit S, Guicheney P, Leturcq F, Gautel M, Fardeau M, Campbell KP, Richard I, Estournet B, Ferreiro A | display-authors = 6 | title = C-terminal titin deletions cause a novel early-onset myopathy with fatal cardiomyopathy | journal = Annals of Neurology | volume = 61 | issue = 4 | pages = 340–351 | date = April 2007 | pmid = 17444505 | doi = 10.1002/ana.21089 | s2cid = 6042810 }} core myopathy with heart disease, [[centronuclear myopathy]], [[limb-girdle muscular dystrophy]] type 2J, [[family|familial]] [[dilated cardiomyopathy]] 9,{{cite journal | vauthors = Siu BL, Niimura H, Osborne JA, Fatkin D, MacRae C, Solomon S, Benson DW, Seidman JG, Seidman CE | display-authors = 6 | title = Familial dilated cardiomyopathy locus maps to chromosome 2q31 | journal = Circulation | volume = 99 | issue = 8 | pages = 1022–1026 | date = March 1999 | pmid = 10051295 | doi = 10.1161/01.cir.99.8.1022 | doi-access = free }} [[hypertrophic cardiomyopathy]] and [[distal muscular dystrophy|tibial muscular dystrophy]].{{cite journal | vauthors = Hackman P, Vihola A, Haravuori H, Marchand S, Sarparanta J, De Seze J, Labeit S, Witt C, Peltonen L, Richard I, Udd B | display-authors = 6 | title = Tibial muscular dystrophy is a titinopathy caused by mutations in TTN, the gene encoding the giant skeletal-muscle protein titin | journal = American Journal of Human Genetics | volume = 71 | issue = 3 | pages = 492–500 | date = September 2002 | pmid = 12145747 | pmc = 379188 | doi = 10.1086/342380 }} Further research also suggests that no genetically linked form of any [[dystrophy]] or myopathy can be safely excluded from being caused by a mutation on the TTN gene.{{cite journal | vauthors = Udd B, Vihola A, Sarparanta J, Richard I, Hackman P | title = Titinopathies and extension of the M-line mutation phenotype beyond distal myopathy and LGMD2J | journal = Neurology | volume = 64 | issue = 4 | pages = 636–642 | date = February 2005 | pmid = 15728284 | doi = 10.1212/01.WNL.0000151853.50144.82 | s2cid = 28801620 }} Truncating mutations in dilated cardiomyopathy patients are most commonly found in the A region; although truncations in the upstream I region might be expected to prevent translation of the A region entirely, [[alternative splicing]] creates some transcripts that do not encounter the premature stop codon, ameliorating its effect.{{cite journal | vauthors = Hinson JT, Chopra A, Nafissi N, Polacheck WJ, Benson CC, Swist S, Gorham J, Yang L, Schafer S, Sheng CC, Haghighi A, Homsy J, Hubner N, Church G, Cook SA, Linke WA, Chen CS, Seidman JG, Seidman CE | display-authors = 6 | title = HEART DISEASE. Titin mutations in iPS cells define sarcomere insufficiency as a cause of dilated cardiomyopathy | journal = Science | volume = 349 | issue = 6251 | pages = 982–986 | date = August 2015 | pmid = 26315439 | pmc = 4618316 | doi = 10.1126/science.aaa5458 }} [[Splicing (genetics)|mRNA splicing factors]] such as RBM20 and [[KHDRBS3|SLM2]] ([[KHDRBS3]]) were shown to mediated alternative mRNA splicing of titin mRNA contributing to the development of [[heart failure]] due to [[Cardiomyopathy|cardiomyopathies]].{{cite journal | vauthors = Li S, Guo W, Dewey CN, Greaser ML | title = Rbm20 regulates titin alternative splicing as a splicing repressor | journal = Nucleic Acids Research | volume = 41 | issue = 4 | pages = 2659–2672 | date = February 2013 | pmid = 23307558 | pmc = 3575840 | doi = 10.1093/nar/gks1362 }}{{cite journal | vauthors = Boeckel JN, Möbius-Winkler M, Müller M, Rebs S, Eger N, Schoppe L, Tappu R, Kokot KE, Kneuer JM, Gaul S, Bordalo DM, Lai A, Haas J, Ghanbari M, Drewe-Boss P, Liss M, Katus HA, Ohler U, Gotthardt M, Laufs U, Streckfuss-Bömeke K, Meder B | display-authors = 6 | title = SLM2 Is A Novel Cardiac Splicing Factor Involved in Heart Failure due to Dilated Cardiomyopathy | journal = Genomics, Proteomics & Bioinformatics | volume = 20 | issue = 1 | pages = 129–146 | date = February 2022 | pmid = 34273561 | pmc = 9510876 | doi = 10.1016/j.gpb.2021.01.006 | doi-access = free }} [102] => [103] => Autoantibodies to titin are produced in patients with the autoimmune disease [[Myasthenia gravis]].{{cite journal | vauthors = Skeie GO, Aarli JA, Gilhus NE | title = Titin and ryanodine receptor antibodies in myasthenia gravis | journal = Acta Neurologica Scandinavica. Supplementum | volume = 183 | issue = | pages = 19–23 | date = 2006 | pmid = 16637922 | doi = 10.1111/j.1600-0404.2006.00608.x | s2cid = 24972330 }} [104] => [105] => == Interactions == [106] => [107] => Titin has been shown to [[Protein-protein interaction|interact]] with: [108] => {{div col|colwidth=20em}} [109] => * [[ANK1]],{{cite journal | vauthors = Kontrogianni-Konstantopoulos A, Bloch RJ | title = The hydrophilic domain of small ankyrin-1 interacts with the two N-terminal immunoglobulin domains of titin | journal = The Journal of Biological Chemistry | volume = 278 | issue = 6 | pages = 3985–3991 | date = February 2003 | pmid = 12444090 | doi = 10.1074/jbc.M209012200 | doi-access = free }} [110] => * [[ANKRD1]],{{cite journal | vauthors = Miller MK, Bang ML, Witt CC, Labeit D, Trombitas C, Watanabe K, Granzier H, McElhinny AS, Gregorio CC, Labeit S | display-authors = 6 | title = The muscle ankyrin repeat proteins: CARP, ankrd2/Arpp and DARP as a family of titin filament-based stress response molecules | journal = Journal of Molecular Biology | volume = 333 | issue = 5 | pages = 951–964 | date = November 2003 | pmid = 14583192 | doi = 10.1016/j.jmb.2003.09.012 }} [111] => * [[ANKRD23]] [112] => * [[CAPN3]],{{cite journal | vauthors = Ono Y, Shimada H, Sorimachi H, Richard I, Saido TC, Beckmann JS, Ishiura S, Suzuki K | display-authors = 6 | title = Functional defects of a muscle-specific calpain, p94, caused by mutations associated with limb-girdle muscular dystrophy type 2A | journal = The Journal of Biological Chemistry | volume = 273 | issue = 27 | pages = 17073–17078 | date = July 1998 | pmid = 9642272 | doi = 10.1074/jbc.273.27.17073 | doi-access = free }}{{cite journal | vauthors = Sorimachi H, Kinbara K, Kimura S, Takahashi M, Ishiura S, Sasagawa N, Sorimachi N, Shimada H, Tagawa K, Maruyama K | display-authors = 6 | title = Muscle-specific calpain, p94, responsible for limb girdle muscular dystrophy type 2A, associates with connectin through IS2, a p94-specific sequence | journal = The Journal of Biological Chemistry | volume = 270 | issue = 52 | pages = 31158–31162 | date = December 1995 | pmid = 8537379 | doi = 10.1074/jbc.270.52.31158 | doi-access = free }} [113] => * [[FHL2]],{{cite journal | vauthors = Lange S, Auerbach D, McLoughlin P, Perriard E, Schäfer BW, Perriard JC, Ehler E | title = Subcellular targeting of metabolic enzymes to titin in heart muscle may be mediated by DRAL/FHL-2 | journal = Journal of Cell Science | volume = 115 | issue = Pt 24 | pages = 4925–4936 | date = December 2002 | pmid = 12432079 | doi = 10.1242/jcs.00181 | doi-access = free }} [114] => * [[OBSCN]],{{cite journal | vauthors = Young P, Ehler E, Gautel M | title = Obscurin, a giant sarcomeric Rho guanine nucleotide exchange factor protein involved in sarcomere assembly | journal = The Journal of Cell Biology | volume = 154 | issue = 1 | pages = 123–136 | date = July 2001 | pmid = 11448995 | pmc = 2196875 | doi = 10.1083/jcb.200102110 }} [115] => * [[Telethonin|TCAP]],{{cite journal | vauthors = Gregorio CC, Trombitás K, Centner T, Kolmerer B, Stier G, Kunke K, Suzuki K, Obermayr F, Herrmann B, Granzier H, Sorimachi H, Labeit S | display-authors = 6 | title = The NH2 terminus of titin spans the Z-disc: its interaction with a novel 19-kD ligand (T-cap) is required for sarcomeric integrity | journal = The Journal of Cell Biology | volume = 143 | issue = 4 | pages = 1013–1027 | date = November 1998 | pmid = 9817758 | pmc = 2132961 | doi = 10.1083/jcb.143.4.1013 }}{{cite journal | vauthors = Mayans O, van der Ven PF, Wilm M, Mues A, Young P, Fürst DO, Wilmanns M, Gautel M | display-authors = 6 | title = Structural basis for activation of the titin kinase domain during myofibrillogenesis | journal = Nature | volume = 395 | issue = 6705 | pages = 863–869 | date = October 1998 | pmid = 9804419 | doi = 10.1038/27603 | s2cid = 4426977 | bibcode = 1998Natur.395..863M }}{{cite journal | vauthors = Zou P, Gautel M, Geerlof A, Wilmanns M, Koch MH, Svergun DI | title = Solution scattering suggests cross-linking function of telethonin in the complex with titin | journal = The Journal of Biological Chemistry | volume = 278 | issue = 4 | pages = 2636–2644 | date = January 2003 | pmid = 12446666 | doi = 10.1074/jbc.M210217200 | doi-access = free }}{{cite journal | vauthors = Mues A, van der Ven PF, Young P, Fürst DO, Gautel M | title = Two immunoglobulin-like domains of the Z-disc portion of titin interact in a conformation-dependent way with telethonin | journal = FEBS Letters | volume = 428 | issue = 1–2 | pages = 111–114 | date = May 1998 | pmid = 9645487 | doi = 10.1016/S0014-5793(98)00501-8 | s2cid = 11786578 | doi-access = free }} and [116] => * [[TRIM63]].{{cite journal | vauthors = Centner T, Yano J, Kimura E, McElhinny AS, Pelin K, Witt CC, Bang ML, Trombitas K, Granzier H, Gregorio CC, Sorimachi H, Labeit S | display-authors = 6 | title = Identification of muscle specific ring finger proteins as potential regulators of the titin kinase domain | journal = Journal of Molecular Biology | volume = 306 | issue = 4 | pages = 717–726 | date = March 2001 | pmid = 11243782 | doi = 10.1006/jmbi.2001.4448 }} [117] => {{Div col end}} [118] => [119] => == Linguistic significance == [120] => [124] => The name titin is derived from the Greek [[Titan (mythology)|Titan]] (a giant deity, anything of great size). [125] => [126] => As the largest known protein, titin also has the longest [[IUPAC nomenclature of organic chemistry|IUPAC name]] of a protein. [[wikt:Appendix:List of protologisms/Long words/Titin|The full chemical name]] of the human canonical form of titin, which starts ''[[Methionine|methionyl]]...'' and ends ''...[[isoleucine]]'', contains 189,819 letters and is sometimes stated to be the [[Longest word in English|longest word in the English language]], or [[longest words|of any language]].{{cite web | url = http://www.sarahmcculloch.com/luminary-uprise/2009/longest-word/ | title = Longest word in English | vauthors = McCulloch S | work = Sarah McCulloch.com | date = December 2009 |archive-url=https://web.archive.org/web/20100114221953/http://www.sarahmcculloch.com/luminaryuprise/longest-word.html |archive-date=2010-01-14 | access-date = 2016-10-12 }} However, [[List of lexicographers|lexicographers]] regard generic names of [[chemical compound]]s as ''verbal [[Chemical formula|formulae]]'' rather than English words.{{cite web | author = Oxford Word and Language Service team | title = Ask the experts - What is the longest English word? | publisher = AskOxford.com / [[Oxford University Press]] | url = http://www.askoxford.com/asktheexperts/faq/aboutwords/longestword | access-date = 2008-01-13 | archive-url = https://web.archive.org/web/20080913173417/http://www.askoxford.com/asktheexperts/faq/aboutwords/longestword | archive-date = 2008-09-13 | url-status = dead}} [127] => [128] => == References == [129] => {{Reflist|32em}} [130] => {{reflist|group=Titin}} [131] => [132] => == Further reading == [133] => {{refbegin|32em}} [134] => * {{cite journal | vauthors = Tskhovrebova L, Trinick J | title = Titin: properties and family relationships | journal = Nature Reviews. Molecular Cell Biology | volume = 4 | issue = 9 | pages = 679–689 | date = September 2003 | pmid = 14506471 | doi = 10.1038/nrm1198 | s2cid = 12293932 }} [135] => * {{cite journal | vauthors = Kinbara K, Sorimachi H, Ishiura S, Suzuki K | title = Skeletal muscle-specific calpain, p49: structure and physiological function | journal = Biochemical Pharmacology | volume = 56 | issue = 4 | pages = 415–420 | date = August 1998 | pmid = 9763216 | doi = 10.1016/S0006-2952(98)00095-1 }} [136] => * {{cite journal | vauthors = Kolmerer B, Witt CC, Freiburg A, Millevoi S, Stier G, Sorimachi H, Pelin K, Carrier L, Schwartz K, Labeit D, Gregorio CC, Linke WA, Labeit S | display-authors = 6 | title = The titin cDNA sequence and partial genomic sequences: insights into the molecular genetics, cell biology and physiology of the titin filament system | journal = Reviews of Physiology, Biochemistry and Pharmacology | volume = 138 | pages = 19–55 | year = 1999 | pmid = 10396137 | doi = 10.1007/BF02346659 }} [137] => * {{cite journal | vauthors = Trinick J, Tskhovrebova L | title = Titin: a molecular control freak | journal = Trends in Cell Biology | volume = 9 | issue = 10 | pages = 377–380 | date = October 1999 | pmid = 10481174 | doi = 10.1016/S0962-8924(99)01641-4 }} [138] => * {{cite book | vauthors = Sorimachi H, Ono Y, Suzuki K | chapter = Skeletal Muscle-Specific Calpain, p94, and Connectin/Titin: Their Physiological Functions and Relationship to Limb-Girdle Muscular Dystrophy Type 2A | series = Advances in Experimental Medicine and Biology | title = Elastic Filaments of the Cell | volume = 481 | pages = 383–95; discussion 395–7 | year = 2000 | pmid = 10987085 | doi = 10.1007/978-1-4615-4267-4_23 | isbn = 978-1-4613-6916-5 }} [139] => * {{cite journal | vauthors = Tskhovrebova L, Trinick J | title = Role of titin in vertebrate striated muscle | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 357 | issue = 1418 | pages = 199–206 | date = February 2002 | pmid = 11911777 | pmc = 1692937 | doi = 10.1098/rstb.2001.1028 }} [140] => * {{cite journal | vauthors = Sela BA | title = [Titin: some aspects of the largest protein in the body] | journal = Harefuah | volume = 141 | issue = 7 | pages = 631–5, 665 | date = July 2002 | pmid = 12187564 }} [141] => * {{cite journal | vauthors = Tskhovrebova L, Trinick J | title = Properties of titin immunoglobulin and fibronectin-3 domains | journal = The Journal of Biological Chemistry | volume = 279 | issue = 45 | pages = 46351–46354 | date = November 2004 | pmid = 15322090 | doi = 10.1074/jbc.R400023200 | doi-access = free }} [142] => * {{cite journal | vauthors = Wu Y, Labeit S, Lewinter MM, Granzier H | title = Titin: an endosarcomeric protein that modulates myocardial stiffness in DCM | journal = Journal of Cardiac Failure | volume = 8 | issue = 6 Suppl | pages = S276–S286 | date = December 2002 | pmid = 12555133 | doi = 10.1054/jcaf.2002.129278 }} [143] => {{refend}} [144] => [145] => == External links == [146] => {{Wiktionary pipe|Appendix:List of protologisms/Long words/Titin|the full chemical name of titin}} [147] => * [https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=hyper-card GeneReviews/NIH/NCBI/UW entry on Familial Hypertrophic Cardiomyopathy Overview] [148] => * [https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=udd GeneReviews/NCBI/NIH/UW entry on Udd Distal Myopathy, Tibial Muscular Dystrophy, Udd Myopathy] [149] => * [https://www.ncbi.nlm.nih.gov/books/NBK83297/ GeneReviews/NIH/NCBI/UW entry on Salih Myopathy or Early-Onset Myopathy with Fatal Cardiomyopathy] [150] => * [https://www.ebi.ac.uk/interpro/protein/Q8WZ42 InterPro domain organization of titin] [151] => [152] => {{PDB Gallery|geneid=7273}} [153] => {{Cytoskeletal proteins}} [154] => {{Muscle tissue}} [155] => {{Serine/threonine-specific protein kinases}} [156] => {{Enzymes}} [157] => {{Portal bar|Biology|border=no}} [158] => [159] => {{NLM content}} [160] => [161] => [[Category:Structural proteins]] [162] => [[Category:Genes on human chromosome 2]] [163] => [[Category:EC 2.7.11]] [164] => [[Category:Muscular system]] [165] => [[Category:Long words]] [] => )
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Titin

Titin is a protein found in muscle tissues that plays an essential role in muscle contraction and elasticity. It is the largest known protein, consisting of about 244 individually folded protein domains.

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It is the largest known protein, consisting of about 244 individually folded protein domains. Titin serves as a molecular spring, providing the muscle with the ability to stretch and recoil during contraction. Its size and complexity have made it a subject of interest and research in the fields of genetics, biophysics, and physiology. This Wikipedia page provides a comprehensive overview of titin, including its structure, function, genetic characteristics, and associated medical conditions. It also covers the latest advancements in studying titin and its implications in muscle diseases and potential therapeutic targets. whether annotation and verification.

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