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Catalytic domain of the Serine/Threonine Kinase, Mitogen-activated protein kinase kinase kinase kinase 5 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. MAP4K5, also called germinal center kinase-related enzyme (GCKR), has been shown to activate the MAPK c-Jun N-terminal kinase (JNK). MAP4K5 also facilitates Wnt signaling in B cells, and may therefore be implicated in the control of cell fate, proliferation, and polarity. MAP4Ks are involved in some MAPK signaling pathways by activating a MAPK kinase kinase. Each MAPK cascade is activated either by a small GTP-binding protein or by an adaptor protein, which transmits the signal either directly to a MAP3K to start the triple kinase core cascade or indirectly through a mediator kinase, a MAP4K. Members of this subfamily contain an N-terminal catalytic domain and a C-terminal citron homology (CNH) regulatory domain. The MAP4K5 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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