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Mol. Cell. Biol., 06 1995, 3171-3178, Vol 15, No. 6
EN Neumeister, Y Zhu, S Richard, C Terhorst, AC Chan and AS Shaw
ZAP-70 is a protein tyrosine kinase thought to play a critical role in
T-cell receptor (TCR) signal transduction. During T-cell activation, ZAP-70
binds to a conserved signalling motif known as the immune receptor tyrosine
activating motif (ITAM) and becomes tyrosine phosphorylated. To determine
whether binding of ZAP-70 to the phosphorylated ITAM was able to activate
its kinase activity, we measured the kinase activity of ZAP-70 both when it
was bound and when it was unbound to phosphorylated TCR subunits. The
ability of ZAP-70 to phosphorylate itself, but not exogenous substrates,
was enhanced when it was bound to the tyrosine-phosphorylated TCR zeta and
eta chains or to a construct that contained duplicated epsilon ITAMs. No
enhanced ZAP- 70 autophosphorylation was noted when it was bound to
tyrosine- phosphorylated CD3 gamma or epsilon. In addition,
autophosphorylation of ZAP-70 when bound to zeta or eta resulted in the
generation of multiple distinct ZAP-70 phosphorylated tyrosine residues
which had the capacity to bind the SH2 domains of fyn, lck, GAP, and abl.
As the effect was noted only when ZAP-70 was bound to TCR subunits
containing multiple ITAMs, we propose that one of the roles of the tandem
ITAMs is to facilitate the autophosphorylation of ZAP-70. Tyrosine-
phosphorylated ZAP-70 then mediates downstream signalling by recruiting SH2
domain-containing signalling proteins.
Copyright © 1995, American Society for Microbiology
Binding of ZAP-70 to phosphorylated T-cell receptor zeta and eta enhances its autophosphorylation and generates specific binding sites for SH2 domain-containing proteins
Center for Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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