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  • Title: Syk protein-tyrosine kinase is regulated by tyrosine-phosphorylated Ig alpha/Ig beta immunoreceptor tyrosine activation motif binding and autophosphorylation.
    Author: Rowley RB, Burkhardt AL, Chao HG, Matsueda GR, Bolen JB.
    Journal: J Biol Chem; 1995 May 12; 270(19):11590-4. PubMed ID: 7538118.
    Abstract:
    Syk is a cytoplasmic protein-tyrosine kinase containing two amino-terminal Src homology 2 domains that is activated following ligation of the B cell antigen receptor. Syk activation in B cells correlates with Syk tyrosine phosphorylation as well as with Syk SH2-mediated association with the tyrosine-phosphorylated Ig alpha and Ig beta B cell antigen receptor subunits. Tyrosine-phosphorylated peptide 20-mers representing Ig alpha and Ig beta immunoreceptor tyrosine activation motifs were synthesized and found to stimulate the specific activity of Syk by as much as 10-fold in vitro. Maximal phosphopeptide-induced Syk activation required both Syk SH2 domains and phosphorylation of both tyrosine residues present in the immunoreceptor tyrosine activation motif. The biochemical mechanism responsible for the phosphopeptide-induced Syk enzyme activation appears to be a function of Syk autophosphorylation. Our observations suggest the association of Syk tandem SH2 domains with the tyrosine-phosphorylated Ig alpha and/or Ig beta immunoreceptor tyrosine activation motifs in B cells stimulates Syk autophosphorylation leading to Syk enzyme activation.
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