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PMID:8798454
| Citation |
Latour, S, Chow, LM and Veillette, A (1996) Differential intrinsic enzymatic activity of Syk and Zap-70 protein-tyrosine kinases. J. Biol. Chem. 271:22782-90 |
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| Abstract |
Syk and Zap-70 are related protein-tyrosine kinases implicated in antigen and Fc receptor signaling. While Zap-70 is restricted to T-cells and natural killer cells, Syk accumulates in B-cells, mast cells, platelets, and immature T-cells. In addition, we found that an isoform of Syk (SykB), which carries a 23-amino acid deletion in the "linker" region, is prominently expressed in bone marrow. To better understand the relative impact of Syk, SykB, and Zap-70 on signal transduction, we compared their intrinsic enzymatic properties in transiently transfected COS-1 cells and in hemopoietic cells. Using modified versions of these enzymes bearing a common Myc epitope at the amino terminus, we determined that the ability of Syk and SykB to undergo autophosphorylation and to phosphorylate erythrocyte band 3 in immune complex kinase reactions was at least 100-fold greater than that of Zap-70. Similarly, Syk and SykB, but not Zap-70, caused prominent tyrosine phosphorylation of p120(c-)cbl in COS-1 cells. A similar pattern of activity was also noted for endogenous Syk and Zap-70 from hemopoietic cells. To understand the structural basis for these characteristics, we also created and analyzed a series of chimeras between Syk and Zap-70. These studies indicated that the catalytic domain of Syk and Zap-70, but not their SH2 domains, linker region or carboxyl-terminal tail, was responsible for their respective activity. Taken together, these data demonstrated that the intrinsic enzymatic activity of Syk and SykB is superior to that of Zap-70 and that such a distinction relates to structural variations in the catalytic domain. |
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| Keywords |
Amino Acid Sequence; Animals; Base Sequence; Bone Marrow/enzymology; Cell Line; Enzyme Precursors/metabolism; Hematopoietic Stem Cells/enzymology; Intracellular Signaling Peptides and Proteins; Isoenzymes/metabolism; Mice; Molecular Sequence Data; Protein-Tyrosine Kinases/metabolism; Recombinant Fusion Proteins/metabolism; ZAP-70 Protein-Tyrosine Kinase |
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Significance
Annotations
| Gene product | Qualifier | GO ID | GO term name | Evidence Code | with/from | Aspect | Notes | Status |
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