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Catalytic domain of the Serine/Threonine Kinase, B-Raf (Rapidly Accelerated Fibrosarcoma) kinase STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. B-Raf activates ERK with the strongest magnitude, compared with other Raf kinases. Mice embryos deficient in B-Raf die around midgestation due to vascular hemorrhage caused by apoptotic endothelial cells. Mutations in B-Raf have been implicated in initiating tumorigenesis and tumor progression, and are found in malignant cutaneous melanoma, papillary thyroid cancer, as well as in ovarian and colorectal carcinomas. Most oncogenic B-Raf mutations are located at the activation loop of the kinase and surrounding regions; the V600E mutation accounts for around 90% of oncogenic mutations. The V600E mutant constitutively activates MEK, resulting in sustained activation of ERK. B-Raf is a mitogen-activated protein kinase kinase kinase (MAP3K, MKKK, MAPKKK), which phosphorylates and activates MAPK kinases (MAPKKs or MKKs or MAP2Ks), which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals. They function in the linear Ras-Raf-MEK-ERK pathway that regulates many cellular processes including cycle regulation, proliferation, differentiation, survival, and apoptosis. The B-Raf 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",