cd05583: STKc_MSK_N (this model, PSSM-Id:173674 is obsolete and has been replaced by 270735)
N-terminal catalytic domain of the Protein Serine/Threonine Kinase, Mitogen and stress-activated kinase
Serine/Threonine Kinases (STKs), Mitogen and stress-activated kinase (MSK) subfamily, N-terminal catalytic (c) domain. STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. The MSK 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. 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, in response to various stimuli such as growth factors, hormones, neurotransmitters, cellular stress, and pro-inflammatory cytokines. This triggers phosphorylation in the activation loop (A-loop) of the CTD of MSK. The active CTD phosphorylates the hydrophobic motif (HM) in the C-terminal extension of NTD, which facilitates the phosphorylation of the A-loop and activates the NTD, which in turn phosphorylates downstream targets. MSKs are predominantly nuclear proteins. They are widely expressed in many tissues including heart, brain, lung, liver, kidney, and pancreas. There are two isoforms of MSK, called MSK1 and MSK2.