UK Tec family kinases

TP K

SH2 domain: binds phosphotyrosine

SH3 domain: binds praline-rich peptides

PH domain: binds inositol phospholipids

U: unique domain T: Tec homology domain K: kinase domain P: proline peptide

FIGURE 7-3 The modular structure of tyrosine kinases that influence lymphocyte activation. Modules include SH2 domains that bind specific phosphotyrosine-containing polypeptides, SH3 domains that recognize proline-rich stretches in polypeptides, PH domains that recognize PIP3 or other phosphatidylinositol-derived lipids, and Tec homology domains found in tyrosine kinases of the Tec family. Tyrosine kinase families depicted are the Src family kinases, which include c-Src, Lyn, Fyn, and Lck; the Syk family kinases, which include Syk and ZAP-70; and the Tec family kinases, which include Tec, Btk, and Itk.

contains a catalytic tyrosine kinase domain and an N-terminal lipid addition domain that facilitates the cova-lent addition of a myristic acid molecule to the protein. The myristate helps target Src family kinases to the plasma membrane. The modular structures of three families of tyrosine kinases that are important in the immune system are depicted in Figure 7-3.

SH2 domains are composed of about 100 amino acids folded into a particular conformation, and they recognize specific phosphotyrosine-containing peptides. In antigen receptor signaling, Src family kinases phosphorylate tyro-sine residues present in particular motifs in the cytoplas-mic tails of proteins that are part of the receptor complex (described later). These phosphotyrosine motifs in the antigen receptor complex are then recognized by SH2 domains present in tyrosine kinases of the Syk family, such as Syk and ZAP-70 (see Fig. 7-3). The recruitment

SH3 domain: binds praline-rich peptides

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