Titin,also called connectin, is a protein that is encoded by the TTN gene.



 Titin is a large  protein, greater than 1 µm in length.



Titin is a large abundant protein of striated muscle. 



It functions as a molecular spring which that accounts for the passive elasticity of muscle in addition to keeping myosin molecules in place. 



Titin is comprises 244 folded protein domains connected by peptide sequences.



These domains unfold when the protein is stretched and refold when the tension is removed.



It is important in the contraction of striated muscle tissues, connecting 


 the Z line to the M k


Titin contributes to force transmission at the Z line and resting tension in the I band region.



Titin limits the range of motion of the sarcomere in tension.



It  contributes to the passive stiffness of muscle. 



Titin is the third most abundant protein in muscle, after myosin and actin.



An adult contains approximately 0.5 kg of titin.



With its length of ~27,000 to ~35,000 amino acids it is the largest known protein.



The gene for titin contains the largest number of exons (363) in any single gene



Totin has the  longest single exon (17,106 bp).



The gene encoding for titin is located on the long arm of chromosome 2 and contains 363 exons.



The  protein is unstable.



Its primary function is  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.



A single titin molecule spans half the length of a sarcomere. 



Titin also serves as an adhesion template for the assembly of contractile machinery in muscle cells. 



Titin mutations are associated with: hereditary myopathy with early respiratory failure, early-onset myopathy with fatal cardiomyopathy, core myopathy with heart disease, centronuclear myopathy, limb-girdle muscular dystrophy, familial dilated cardiomyopathy hypertrophic cardiomyopathy and tibial muscular dystrophy.



Autoantibodies to titin are produced in patients with the autoimmune disease scleroderma.



As the largest known protein, titin also has the longest name of a protein, and contains 189,819 letters and is sometimes stated to be the longest word in the English language.




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