Syk, activated by cross-linking the B-cell antigen receptor, localizes to the cytosol where it interacts with and phosphorylates alpha-tubulin on tyrosine

J Biol Chem. 1996 Mar 1;271(9):4755-62. doi: 10.1074/jbc.271.9.4755.


Syk (p72syk) is a 72-kDa, nonreceptor, protein-tyrosine kinase that becomes tyrosine-phosphorylated and activated in B lymphocytes following aggregation of the B-cell antigen receptor. To explore the subcellular location of activated Syk, anti-IgM-activated B-cells were fractionated into soluble and particulate fractions by ultracentrifugation. Activated and tyrosine-phosphorylated Syk was found predominantly in the soluble fraction and was not associated with components of the antigen receptor. Similarly, the activated forms of Syk and its homolog, ZAP-70, were found in soluble fractions prepared from pervanadate-treated Jurkat T-cells. A 54-kDa protein that co-immunoprecipitated with Syk from the soluble fraction of activated B-cells was identified by peptide mapping as alpha-tubulin. alpha-Tubulin was an excellent in vitro substrate for Syk and was phosphorylated on a single tyrosine present within an acidic stretch of amino acids located near the carboxyl terminus. alpha-Tubulin was phosphorylated on tyrosine in intact cells following aggregation of the B-cell antigen receptor in a reaction that was inhibited by the Syk-selective inhibitor, piceatannol. Thus, once activated, Syk releases from the aggregated antigen receptor complex and is free to associate with and phosphorylate soluble proteins including alpha-tubulin.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • B-Lymphocytes / drug effects
  • B-Lymphocytes / immunology
  • B-Lymphocytes / metabolism*
  • Cytosol / enzymology
  • Enzyme Activation
  • Enzyme Precursors / isolation & purification
  • Enzyme Precursors / metabolism*
  • Glutathione Transferase / metabolism
  • Humans
  • Immunoglobulin M / pharmacology
  • Intracellular Signaling Peptides and Proteins
  • Kinetics
  • Mice
  • Molecular Sequence Data
  • Phosphorylation
  • Phosphotyrosine / metabolism*
  • Protein-Tyrosine Kinases / isolation & purification
  • Protein-Tyrosine Kinases / metabolism*
  • Receptors, Antigen, B-Cell / metabolism*
  • Recombinant Fusion Proteins / metabolism
  • Substrate Specificity
  • Syk Kinase
  • Tubulin / metabolism*


  • Enzyme Precursors
  • Immunoglobulin M
  • Intracellular Signaling Peptides and Proteins
  • Receptors, Antigen, B-Cell
  • Recombinant Fusion Proteins
  • Tubulin
  • Phosphotyrosine
  • Glutathione Transferase
  • Protein-Tyrosine Kinases
  • SYK protein, human
  • Syk Kinase
  • Syk protein, mouse