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==Crystal structure of the titin domain Fn3-49==
<StructureSection load='8osd' size='340' side='right'caption='[[8osd]], [[Resolution|resolution]] 1.70&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[8osd]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=8OSD OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=8OSD FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 1.7&#8491;</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=8osd FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=8osd OCA], [https://pdbe.org/8osd PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=8osd RCSB], [https://www.ebi.ac.uk/pdbsum/8osd PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=8osd ProSAT]</span></td></tr>
</table>
== Disease ==
[https://www.uniprot.org/uniprot/TITIN_HUMAN TITIN_HUMAN] Defects in TTN are the cause of hereditary myopathy with early respiratory failure (HMERF) [MIM:[https://omim.org/entry/603689 603689]; also known as Edstrom myopathy. HMERF is an autosomal dominant, adult-onset myopathy with early respiratory muscle involvement.<ref>PMID:15802564</ref>   Defects in TTN are the cause of familial hypertrophic cardiomyopathy type 9 (CMH9) [MIM:[https://omim.org/entry/613765 613765]. Familial hypertrophic cardiomyopathy is a hereditary heart disorder characterized by ventricular hypertrophy, which is usually asymmetric and often involves the interventricular septum. The symptoms include dyspnea, syncope, collapse, palpitations, and chest pain. They can be readily provoked by exercise. The disorder has inter- and intrafamilial variability ranging from benign to malignant forms with high risk of cardiac failure and sudden cardiac death.<ref>PMID:10462489</ref>   Defects in TTN are the cause of cardiomyopathy dilated type 1G (CMD1G) [MIM:[https://omim.org/entry/604145 604145]. Dilated cardiomyopathy is a disorder characterized by ventricular dilation and impaired systolic function, resulting in congestive heart failure and arrhythmia. Patients are at risk of premature death.<ref>PMID:11846417</ref> <ref>PMID:11788824</ref> <ref>PMID:16465475</ref>   Defects in TTN are the cause of tardive tibial muscular dystrophy (TMD) [MIM:[https://omim.org/entry/600334 600334]; also known as Udd myopathy. TMD is an autosomal dominant, late-onset distal myopathy. Muscle weakness and atrophy are usually confined to the anterior compartment of the lower leg, in particular the tibialis anterior muscle. Clinical symptoms usually occur at age 35-45 years or much later.<ref>PMID:12145747</ref> <ref>PMID:12891679</ref>   Defects in TTN are the cause of limb-girdle muscular dystrophy type 2J (LGMD2J) [MIM:[https://omim.org/entry/608807 608807]. LGMD2J is an autosomal recessive degenerative myopathy characterized by progressive weakness of the pelvic and shoulder girdle muscles. Severe disability is observed within 20 years of onset.  Defects in TTN are the cause of early-onset myopathy with fatal cardiomyopathy (EOMFC) [MIM:[https://omim.org/entry/611705 611705]. Early-onset myopathies are inherited muscle disorders that manifest typically from birth or infancy with hypotonia, muscle weakness, and delayed motor development. EOMFC is a titinopathy that, in contrast with the previously described examples, involves both heart and skeletal muscle, has a congenital onset, and is purely recessive. This phenotype is due to homozygous out-of-frame TTN deletions, which lead to a total absence of titin's C-terminal end from striated muscles and to secondary CAPN3 depletion.<ref>PMID:17444505</ref> 
== Function ==
[https://www.uniprot.org/uniprot/TITIN_HUMAN TITIN_HUMAN] Key component in the assembly and functioning of vertebrate striated muscles. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. The size and extensibility of the cross-links are the main determinants of sarcomere extensibility properties of muscle. In non-muscle cells, seems to play a role in chromosome condensation and chromosome segregation during mitosis. Might link the lamina network to chromatin or nuclear actin, or both during interphase.<ref>PMID:9804419</ref> 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
Titin is the largest protein found in nature and spans half a sarcomere in vertebrate striated muscle. The protein has multiple functions, including in the organisation of the thick filament and acting as a molecular spring during the muscle contraction cycle. Missense variants in titin have been linked to both cardiac and skeletal myopathies. Titin is primarily composed of tandem repeats of immunoglobulin and fibronectin type III (Fn3) domains in a variety of repeat patterns; however, the vast majority of these domains have not had their high-resolution structure determined experimentally. Here, we present the crystal structures of seven wild type titin Fn3 domains and two harbouring rare missense variants reported in hypertrophic cardiomyopathy (HCM) patients. All domains present the typical Fn3 fold, with the domains harbouring variants reported in HCM patients retaining the wild-type conformation. The effect on domain folding and stability were assessed for five rare missense variants found in HCM patients: four caused thermal destabilization of between 7 and 13 degrees C and one prevented the folding of its domain. The structures also allowed us to locate the positions of residues whose mutations have been linked to congenital myopathies and rationalise how they convey their deleterious effects. We find no evidence of physiological homodimer formation, excluding one hypothesised mechanism as to how titin variants could exert pathological effects.

Structure determination and analysis of titin A-band fibronectin type III domains provides insights for disease-linked variants and protein oligomerisation.,Rees M, Nikoopour R, Alexandrovich A, Pfuhl M, Lopes LR, Akhtar MM, Syrris P, Elliott P, Carr-White G, Gautel M J Struct Biol. 2023 Aug 5;215(3):108009. doi: 10.1016/j.jsb.2023.108009. PMID:37549721<ref>PMID:37549721</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 8osd" style="background-color:#fffaf0;"></div>
== References ==
<references/>
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</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Gautel M]]
[[Category: Nikoopour R]]
[[Category: Rees M]]