Catalytic domain of the dual-specificity Protein Kinase, Mitogen-activated protein Kinase Kinase 5
PKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine (ST) or tyrosine residues on protein substrates. MKK5 (also called MEK5) is a dual-specificity PK that phosphorylates its downstream target, extracellular signal-regulated kinase 5 (ERK5), on specific threonine and tyrosine residues. MKK5 is activated by MEKK2 and MEKK3 in response to mitogenic and stress stimuli. The ERK5 cascade promotes cell proliferation, differentiation, neuronal survival, and neuroprotection. This cascade plays an essential role in heart development. Mice deficient in either ERK5 or MKK5 die around embryonic day 10 due to cardiovascular defects including underdevelopment of the myocardium. In addition, MKK5 is associated with metastasis and unfavorable prognosis in prostate cancer. The MKK5 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.