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Biochem Biophys Res Commun. 2007 Dec 7;364(1):111-7. Epub 2007 Oct 2.

Interdomain A is crucial for ITAM-dependent and -independent regulation of Syk.

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Laboratory of Immunology, Biomedical Science, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.


Non-receptor type protein tyrosine kinase (PTK) Syk is essential for the signaling via the B cell antigen receptor (BCR). Upon BCR crosslinking, Syk is recruited via its tandem SH2 domains to tyrosine-phosphorylated Ig-alpha/Ig-beta constituting components of BCR, and is then activated. The interdomain A lying between the two SH2 domains is highly conserved among different species of Syk and between Syk and ZAP-70. The mutant Syk carrying a deletion in the interdomain A (Delta140-159) became phosphorylated regardless of BCR ligation and did not induce Ca2+ mobilization upon crosslinking of BCR. Furthermore, in vitro binding assay revealed that deletion of a part of the interdomain A abolished its binding activity to phosphorylated Ig-alpha/Ig-beta. These results indicate that the interdomain A of Syk is required for activation of Syk by binding to the phosphorylated Ig-alpha/Ig-beta upon BCR ligation and inhibition of spontaneous activation at the resting state.

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