Titin

Titin[5] /ˈttɪn/ (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
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesTTN, CMD1G, CMH9, CMPD4, EOMFC, HMERF, LGMD2J, MYLK5, TMD, titin, SALMY, LGMDR10
External IDsOMIM: 188840 MGI: 98864 HomoloGene: 130650 GeneCards: TTN
EC number2.7.11.1
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_011652
NM_028004

RefSeq (protein)

NP_035782
NP_082280
NP_001372637

Location (UCSC)Chr 2: 178.53 – 178.83 MbChr 2: 76.7 – 76.98 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse
Cardiac sarcomere structure, featuring titin

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).


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