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Catalytic domain of the Serine/Threonine Kinase, Myosin Light Chain Kinase 3 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. MLCK3 (or MYLK3) phosphorylates myosin regulatory light chain 2 and controls the contraction of cardiac muscles. It is expressed specifically in both the atrium and ventricle of the heart and its expression is regulated by the cardiac protein Nkx2-5. MLCK3 plays an important role in cardiogenesis by regulating the assembly of cardiac sarcomeres, the repeating contractile unit of striated muscle. MLCK3 contains a single kinase domain near the C-terminus and a unique N-terminal half, and unlike MLCK1/2, it does not appear to be regulated by Ca2+/calmodulin. The MLCK3 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.
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