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Catalytic domain of the Giant Serine/Threonine Kinase Titin STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Titin, also called connectin, is a muscle-specific elastic protein and is the largest known protein to date. It contains multiple immunoglobulin (Ig)-like and fibronectin type III (FN3) domains, and a single kinase domain near the C-terminus. It spans half of the sarcomere, the repeating contractile unit of striated muscle, and performs mechanical and catalytic functions. Titin contributes to the passive force generated when muscle is stretched during relaxation. Its kinase domain phosphorylates and regulates the muscle protein telethonin, which is required for sarcomere formation in differentiating myocytes. In addition, titin binds many sarcomere proteins and acts as a molecular scaffold for filament formation during myofibrillogenesis. The Titin subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",