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Titin adalah protein terbesar yang diketahui; varian manusianya terdiri dari 34.350 [[asam amino]], dengan berat molekul isoform "kanonik" dewasa dari protein sekitar 3.816.188,13 [[unit massa atom|Da]].<ref name="urlExPASy_human"/> Homolog protein ini pada tikus bahkan lebih besar lagi, terdiri dari 35.213 asam amino dengan MW 3.906.487,6 [[unit massa atom|Da]].<ref name="urlExPASy_mouse">{{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 |accessdate=2010-05-06}}</ref> Protein ini memiliki [[titik isoelektrik]] teoritis 6,01.<ref name="urlExPASy_human"/> [[Rumus kimia]] empiris proteinnya adalah C<sub>169,719</sub>H<sub>270,464</sub>N<sub>45,688</sub>O<sub>52,237</sub>S<sub>911</sub>.<ref name="urlExPASy_human">{{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 |accessdate=2011-07-25}}</ref> Ini memiliki teori [[indeks ketidakstabilan]] (II) 42,41, dan karena itu diklasifikasikan sebagai protein tidak stabil.<ref name="urlExPASy_human"/> [[Paruh waktu]] protein [[in vivo]], waktu yang dibutuhkan setengah dari jumlah protein dalam sel untuk dipecah setelah sintesisnya di dalam sel, diperkirakan sekitar 30 jam (pada [[reticulocyte]] [[mamalia]]).<ref name="url_UniProt_Q8WZ42)">{{cite web|url= http://www.uniprot.org/uniprot/Q8WZ42 |title= Titin - Homo sapiens (Human) | work = Universal Protein Resource | publisher = UniProt Consortium | date=2010-10-05 |accessdate=2010-10-15}}</ref>
Protein titin terletak di antara filamen tebal [[myosin]] dan cakram Z.<ref name="Wang_1991">{{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 = 7101–5 | date = August 1991 | pmid = 1714586 | pmc = 52241 | doi = 10.1073/pnas.88.16.7101 }}</ref> Titin terdiri dari rangkaian linear dua jenis modul (juga disebut sebagai [[domain protein]]; 244 total salinan): tipe I ([[domain fibronektin tipe III]]; 132 salinan) dan tipe II ([[domain imunoglobulin]]; 112 salinan).<ref name="pmid7569978"/> ThisArray linearlinier arrayini isselanjutnya furtherdisusun organizedmenjadi intodua two regionswilayah:
* [[N-terminus|N-terminal]] I-band: actsbertindak assebagai thebagian elasticelastis partdari ofmolekul thedan moleculesebagian andbesar isterdiri composeddari mainlymodul of typetipe II modules. Lebih Morekhusus specifically thelagi, I-band containsberisi twodua regionswilayah ofdomain imunoglobulin tandem typetipe II immunoglobulindi domainskedua on either side ofsisi awilayah PEVK regionyang thatkaya isakan rich in prolineprolin, glutamateglutamat, valinevalin anddan lysine.lisin<ref name="Wang_1991"/> Elastisitas PVK elasticity hasmemiliki bothsifat entropicentropik anddan enthalpic originsyang characterizabledapat bydikarakterisasi aoleh polymerpanjang persistenceketekunan lengthpolimer anddan amodulus stretch modulusregangan.<ref>{{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 = 8052–7 | date = July 1998 | pmid = 9653138 | doi=10.1073/pnas.95.14.8052 | pmc=20927}}</ref> AtPada lowelastisitas to moderate extensionsekstensi PEVK elasticityyang canrendah besampai modeledsedang withdapat adimodelkan standarddengan wormlikemodel chainelastisitas (WLC)entropik modeltipe ofwormlike entropic(rantai elasticitycacing). AtPada high extensionsekstensi PEVK stretchingyang cantinggi bedapat modeleddimodelkan withdengan a modifiedmodel WLC modelyang thatdimodifikasi incorporatesyang menggabungkan elastisitas enthalpic elasticity. ThePerbedaan differenceantara betweenelastisitas low-andelastisitas high-rendah stretchdan elasticitytinggi isadalah duekarena topenguatan electrostatickaku stiffeningdan andefek hydrophobichidrofobik effectselektrostatik.
* [[C-terminus|C-terminal]] A-band: isdianggap thoughtbertindak tosebagai actpenguasa asprotein a protein-rulerdan andmemiliki possessesaktivitas [[kinase]] activity. The A-band isterdiri composeddari ofmodul alternating typetipe I anddan II modulesbergantian withdengan segmen pengulang-super-repeat segments. TheseHal haveini beentelah shownditunjukkan tountuk alignmenyelaraskan topengulangan themiosin aksial berketebalan 43 nm axial repeats of myosin thick filamentsdengan withdomain immunoglobulinimunoglobulin domainsyang correlatingberkorelasi todengan myosinmahkota crownsmiosin.<ref name="pmid8683592">{{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 }}</ref>
== FunctionFugsi ==
[[File:Sarcomere.svg|thumb|370px|SlidingModel filamentfilamen modelgeser ofkontraksi muscle contractionotot. (Titin labeledberlabel atdi upperkanan rightatas.)]]
Titin isadalah aprotein largeotot abundantlurik proteinyang ofmelimpah. striatedFungsi muscle.utama Titin's primaryadalah functionsmenstabilkan arefilamen to stabilize the thick filamenttebal, center itmemusatkannya betweendi theantara thinfilamen filamentstipis, preventmencegah overstretchingperenggangan ofsarkomer theyang sarcomereberlebihan, anddan tountuk recoilmelepaskan thesarkomer sarcomereseperti likepegas asetelah spring after it is stretcheddiregangkan.<ref>{{cite book | last1 = Saladin | first1 = Kenneth | name-list-format = vanc | title = Anatomy & Physiology | date = 2015 | publisher = McGraw Hill | page = 401 | edition = 7 | accessdate=14 November 2016 }}</ref> AnDaerah ''N-terminal'' ''Z-disc'' regiondan and adaerah ''C-terminal M-line'' regionmasing-masing bindterikat to theke ''Z-line'' anddan ''M-line of the'' [[sarcomeresarkomer]], respectively,sehingga sosatu that a singlemolekul titin molecule spans half themembentang lengthsetengah ofpanjang asarkomer sarcomere. Titin alsojuga containsmengandung bindingsitus sitespengikat foruntuk muscle-associatedprotein proteinsyang soberhubungan itdengan servesotot assehingga anberfungsi adhesionsebagai templatetemplat forpenempel theuntuk assemblyperakitan ofmesin contractilekontraktil machinerypada insel muscle cellsotot. ItIni hasjuga alsotelah beendiidentifikasi identifiedsebagai asprotein a structural proteinstruktural foruntuk [[chromosomekromosom]]s.<ref name="Machado_1998"/><ref name = "Machado_2000">{{cite journal | vauthors = Machado C, Andrew DJ | title = Titin as a chromosomal protein | journal = Advances in Experimental Medicine and Biology | volume = 481 | issue = | pages = 221–32; discussion 232–6 | year = 2000 | pmid = 10987075 | doi = 10.1007/978-1-4615-4267-4_13 }}</ref> 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.<ref name= "Entrez_ 7273"/><ref name="pmid2129545" />
Titin interacts with many [[sarcomere|sarcomeric]] proteins including:<ref name="pmid11717165"/>
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