Catalytic activity:ATP + a [protein]-L-tyrosine = ADP + a [protein]-L-tyrosine phosphate. ,Function:Positive effector of BCR-stimulated responses. Couples the B-cell antigen receptor (BCR) to the mobilization of calcium ion either through a phosphoinositide 3-kinase-dependent pathway , when not phosphorylated on tyrosines of the linker region , or through a phospholipase C-gamma-dependent pathway , when phosphorylated on Tyr-348 and Tyr-352. Thus the differential phosphorylation of Syk can determine the pathway by which BCR is coupled to the regulation of intracellular calcium ion. ,PTM:Autophosphorylated. ,PTM:Phosphorylation on Tyr-323 creates a binding site for c-Cbl , an adapter protein that serves as a negative regulator of BCR-stimulated calcium ion signaling. ,PTM:Phosphorylation on Tyr-348 and Tyr-352 enhances the phosphorylation and activation of phospholipase C-gamma and the early phase of calcium ion mobilization via a phosphoinositide 3-kinase-independent pathway. ,PTM:Ubiquitinated by CBLB after BCR activation; which promotes proteasomal degradation. ,similarity:Belongs to the protein kinase superfamily. Tyr protein kinase family. ,similarity:Belongs to the protein kinase superfamily. Tyr protein kinase family. SYK/ZAP-70 subfamily. ,similarity:Contains 1 protein kinase domain. ,similarity:Contains 2 SH2 domains. ,subunit:Interacts with CBL and SLA when it is phosphorylated. The interaction with SLA may link it to CBL , leading to its destruction. Interacts with phosphorylated NFAM1 (By similarity) . Interacts with Epstein-Barr virus LMP2A. Interacts through its SH2 domains with the phosphorylated ITAM domain of CD79A which stimulates SYK autophosphorylation and activation. Interacts with FCRL3. ,
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