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N-terminal catalytic domain of the Serine/Threonine Kinase, Mitogen and stress-activated kinase 2 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. MSK2 and MSK1 play nonredundant roles in activating histone H3 kinases, which play pivotal roles in compaction of the chromatin fiber. MSK2 is the required H3 kinase in response to stress stimuli and activation of the p38 MAPK pathway. MSK2 also plays a role in the pathogenesis of psoriasis. MSKs contain an N-terminal kinase domain (NTD) from the AGC family and a C-terminal kinase domain (CTD) from the CAMK family, similar to 90 kDa ribosomal protein S6 kinases (RSKs). MSKs are activated by two major signaling cascades, the Ras-MAPK and p38 stress kinase pathways, which trigger phosphorylation in the activation loop (A-loop) of the CTD of MSK. The active CTD phosphorylates the hydrophobic motif (HM) of NTD, which facilitates the phosphorylation of the A-loop and activates the NTD, which in turn phosphorylates downstream targets. The MSK2 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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