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Mol. Cell. Biol., Jan 1995, 272-281, Vol 15, No. 1
L Shiue, J Green, OM Green, JL Karas, JP Morgenstern, MK Ram, MK Taylor, MJ Zoller, LD Zydowsky and JB Bolen
Activation of protein tyrosine kinases is one of the initial events
following aggregation of the high-affinity receptor for immunoglobulin E
(Fc epsilon RI) on RBL-2H3 cells, a model mast cell line. The protein
tyrosine kinase p72syk (Syk), which contains two Src homology 2 (SH2)
domains, is activated and associates with phosphorylated Fc epsilon RI
subunits after receptor aggregation. In this report, we used Syk SH2
domains, expressed in tandem or individually, as fusion proteins to
identify Syk-binding proteins in RBL-2H3 lysates. We show that the tandem
Syk SH2 domains selectively associate with tyrosine- phosphorylated forms
of the gamma and beta subunits of Fc epsilon RI. The isolated
carboxy-proximal SH2 domain exhibited a significantly higher affinity for
the Fc epsilon RI subunits than did the amino- proximal domain. When in
tandem, the Syk SH2 domains showed enhanced binding to phosphorylated gamma
and beta subunits. The conserved tyrosine-based activation motifs contained
in the cytoplasmic domains of the gamma and beta subunits, characterized by
two YXXL/I sequences in tandem, represent potential high-affinity binding
sites for the dual SH2 domains of Syk. Peptide competition studies
indicated that Syk exhibits a higher affinity for the phosphorylated
tyrosine activation motif of the gamma subunit than for that of the beta
subunit. In addition, we show that Syk is the major protein in RBL-2H3
cells that is affinity isolated with phosphorylated peptides corresponding
to the phosphorylated gamma subunit motif.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Interaction of p72syk with the gamma and beta subunits of the high- affinity receptor for immunoglobulin E, Fc epsilon RI
ARIAD Pharmaceuticals, Inc., Cambridge, Massachusetts 02139.
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