Catalytic domain of an Uncharacterized subfamily of Mitogen-Activated Protein (MAP)/Extracellular signal-Regulated Kinase (ERK) Kinase Kinase 3-like Serine/Threonine Kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. This subfamily is composed of uncharacterized proteins with similarity to MEKK3, MEKK2, and related proteins; they contain an N-terminal PB1 domain, which mediates oligomerization, and a C-terminal catalytic domain. MEKK2 and MEKK3 are MAPK kinase kinases (MAPKKKs or MKKKs), proteins that phosphorylate and activate MAPK kinases (MAPKKs or MKKs), which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals. MEKK2 and MEKK3 activate MEK5 (also called MKK5), which activates ERK5. The ERK5 cascade plays roles in promoting cell proliferation, differentiation, neuronal survival, and neuroprotection. MEKK3 plays an essential role in embryonic angiogenesis and early heart development. MEKK2 and MEKK3 can also activate the MAPKs, c-Jun N-terminal kinase (JNK) and p38, through their respective MAPKKs. The MEKK3-like subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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