Titin

Titin[5] /ˈtaɪtɪn/ (contraction for Titan protein) (also called connectin) is a protein that in humans is encoded by the TTN gene.[6][7] Titin is a giant protein, greater than 1 µm in length,[8] that functions as a molecular spring that is responsible for the passive elasticity of muscle. It comprises 244 individually folded protein domains connected by unstructured peptide sequences.[9] These domains unfold when the protein is stretched and refold when the tension is removed.[10]

TTN
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 4UOW, 1BPV, 1G1C, 1NCT, 1NCU, 1TIT, 1TIU, 1TKI, 1TNM, 1TNN, 1WAA, 1YA5, 2A38, 2BK8, 2F8V, 2ILL, 2J8H, 2J8O, 2NZI, 2RQ8, 2WP3, 2WWK, 2WWM, 2Y9R, 3KNB, 3LCY, 3LPW, 3PUC, 3Q5O, 3QP3, 4C4K, 4JNW, 4O00, 4QEG, 5BS0
Identifiers
Aliases	TTN, CMD1G, CMH9, CMPD4, EOMFC, HMERF, LGMD2J, MYLK5, TMD, titin, SALMY, LGMDR10
External IDs	OMIM: 188840 MGI: 98864 HomoloGene: 130650 GeneCards: TTN
EC number	2.7.11.1
Gene location (Human) Chr. Chromosome 2 (human)[1] Band 2q31.2 Start 178,525,989 bp[1] End 178,830,802 bp[1]
Gene location (Mouse) Chr. Chromosome 2 (mouse)[2] Band 2 C3|2 45.13 cM Start 76,703,980 bp[2] End 76,982,547 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in triceps brachii muscle right ventricle thoracic diaphragm body of tongue vastus lateralis muscle deltoid muscle tibialis anterior muscle vena cava gastrocnemius muscle sural nerve Top expressed in vastus lateralis muscle digastric muscle triceps brachii muscle sternocleidomastoid muscle knee joint body of femur temporal muscle atrium intercostal muscle ankle More reference expression data BioGPS More reference expression data
Gene ontology Molecular function transferase activity nucleotide binding calcium ion binding protein kinase activity actinin binding muscle alpha-actinin binding structural molecule activity conferring elasticity metal ion binding telethonin binding protease binding protein self-association actin filament binding protein serine/threonine kinase activity kinase activity protein binding identical protein binding enzyme binding protein tyrosine kinase activity structural constituent of muscle ATP binding protein kinase binding calmodulin binding Cellular component cytoplasm cytosol I band striated muscle thin filament condensed nuclear chromosome extracellular region Z disc muscle myosin complex extracellular exosome nucleus M band sarcomere Biological process sarcomerogenesis muscle contraction mitotic chromosome condensation cardiac muscle contraction phosphorylation cardiac muscle hypertrophy platelet degranulation cardiac muscle tissue morphogenesis skeletal muscle thin filament assembly detection of muscle stretch response to calcium ion cardiac myofibril assembly protein phosphorylation muscle filament sliding regulation of protein kinase activity regulation of catalytic activity sarcomere organization skeletal muscle myosin thick filament assembly striated muscle contraction peptidyl-tyrosine phosphorylation positive regulation of gene expression protein kinase A signaling positive regulation of protein secretion Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 7273 22138 Ensembl ENSG00000155657 ENSMUSG00000051747 UniProt Q8WZ42 A2ASS6 RefSeq (mRNA) NM_001256850 NM_001267550 NM_003319 NM_133378 NM_133379 NM_133432 NM_133437 NM_011652 NM_028004 RefSeq (protein) NP_001243779 NP_001254479 NP_003310 NP_596869 NP_596870 NP_597676 NP_597681 NP_035782 NP_082280 NP_001372637 Location (UCSC) Chr 2: 178.53 – 178.83 Mb Chr 2: 76.7 – 76.98 Mb PubMed search [3] [4]
Wikidata
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Titin is important in the contraction of striated muscle tissues. It connects the Z line to the M line in the sarcomere. The protein contributes to force transmission at the Z line and resting tension in the I band region.[11] 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 or skeletal) have been correlated with differences in the mechanical properties of these muscles.[6][12]

Titin is the third most abundant protein in muscle (after myosin and actin), and an adult human contains approximately 0.5 kg of titin.[13] With its length of ~27,000 to ~35,000 amino acids (depending on the splice isoform), titin is the largest known protein.[14] Furthermore, the gene for titin contains the largest number of exons (363) discovered in any single gene,[15] as well as the longest single exon (17,106 bp).