Downstream of tyrosine kinase 1, 2, and 3 proteins phosphotyrosine-binding domain (PTBi)
The Dok family adapters are phosphorylated by different protein tyrosine kinases. Dok proteins are involved in processes such as modulation of cell differentiation and proliferation, as well as in control of the cell spreading and migration The Dok protein contains an N-terminal pleckstrin homology (PH) domain followed by a central phosphotyrosine binding (PTB) domain, which has a PH-like fold, and a proline- and tyrosine-rich C-terminal tail. The PH domain is binds to acidic phospholids and localizes proteins to the plasma membrane, while the PTB domain mediates protein-protein interactions by binding to phosphotyrosine-containing motifs. The C-terminal part of Dok contains multiple tyrosine phosphorylation sites that serve as potential docking sites for Src homology 2-containing proteins such as ras GTPase-activating protein and Nck, leading to inhibition of ras signaling pathway activation and the c-Jun N-terminal kinase (JNK) and c-Jun activation, respectively. There are 7 mammalian Dok members: Dok-1 to Dok-7. Dok-1 and Dok-2 act as negative regulators of the Ras-Erk pathway downstream of many immunoreceptor-mediated signaling systems, and it is believed that recruitment of p120 rasGAP by Dok-1 and Dok-2 is critical to their negative regulation. Dok-3 is a negative regulator of the activation of JNK and mobilization of Ca2+ in B-cell receptor-mediated signaling, interacting with SHIP-1 and Grb2. Dok-4- 6 play roles in protein tyrosine kinase(PTK)-mediated signaling in neural cells and Dok-7 is the key cytoplasmic activator of MuSK (Muscle-Specific Protein Tyrosine Kinase). PTB domains have a common PH-like fold and are found in various eukaryotic signaling molecules. This domain was initially shown to binds peptides with a NPXY motif with differing requirements for phosphorylation of the tyrosine, although more recent studies have found that some types of PTB domains can bind to peptides lack tyrosine residues altogether. In contrast to SH2 domains, which recognize phosphotyrosine and adjacent carboxy-terminal residues, PTB-domain binding specificity is conferred by residues amino-terminal to the phosphotyrosine. PTB domains are classified into three groups: phosphotyrosine-dependent Shc-like, phosphotyrosine-dependent IRS-like, and phosphotyrosine-independent Dab-like PTB domains. This cd is part of the IRS-like subgroup.
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