Phosphotyrosine binding

Figure 13.30 Ribbon diagram of the structure of Src tyrosine kinase. The structure is divided in three units starting from the N-terminus an SH3 domain (green), an SH2 domain (blue), and a tyrosine kinase (orange) that is divided into two domains and has the same fold as the cyclin dependent kinase described in Chapter 6 (see Figure 6.16a). The linker region (red) between SH2 and the kinase is bound to SH3 in a polyproline helical conformation. A tyrosine residue in the carboxy tail of the kinase is phosphorylated and bound to SH2 in its phosphotyrosine-binding site. A disordered part of the activation segment in the kinase is dashed. (Adapted from W. Xu et al.. Nature 385 595-602, 1997.)...

Noncatalytic phosphotyrosine binding (PTB) domains are 100-150 residue modules, which bind Asn-Pro-X-Tyr motifs. PTB-domain binding specificity is determined by residues at the amino-terminal side of the phosphotyrosine. In most cases, the tyrosine residue must be phosphorylated in order to mediate binding. PTB domain containing proteins are often found in signal transduction pathways. 

Phosphotyrosine-Binding (PTB) Domain Molecular Modeling Tyrosine Kinases... 

Benes CH, Wu N, Elia AE, Dharia T, Cantley LC, Soltoff SP. The C2 domain of protein kinase C-delta is a phosphotyrosine binding domain. Cell 2005 121 (2) 271-280. 

TABLE 24-1 Specificity and affinity of SH2, phosphotyrosine binding (PTB) and SH3 domains... 

PACAP pituitary adenylyl cyclase-activating peptide PTB phosphotyrosine binding domain... 

PTB Phosphotyrosine-binding domain, phosphotyrosine-interaction (PI) domain E(M) 0(0) 11(11) 1AQC... 

Yankee, T. M., L. M. Keshvara, S. Sawasdikosol, M. L. Harrison, and R. L. Geahlen. Inhibition of signaling through the B cell antigen receptor by the protooncogene product, c-Cbl, requires Syk tyrosine 317 and the c-Cbl phosphotyrosine-binding domain. J Immunol. 163 5827-35.1999. 

Fig. 6 Proteins with GPR motifs. (RBD Ras binding domain, PTB phosphotyrosine binding domain, RGS regulator of G-protein signaling domain, PDZ PSD95/DLG/ZO-1 domain, cc coiled-coil domain). This figure is adapted from the thesis of Dr. Yuri Peterson...

Fig. 8.3. Ligand-induced autophosphorylation and substrate phosphorylation of receptor tyrosine kinases. The tyrosine kinase domain of the receptor tyrosine kinase is activated by ligand binding. Consequently, autophosphorylation and/or phosphorylation of substrate proteins takes place. The substrate proteins possess specific phosphotyrosine binding domains (SH2 in the figure or FTP domains, see 8.2), which bind to phosphate residues formed in the process of autophosphorylation.

Fig. 8.6. Functions of autophosphorylation of receptor tyrosine kinases. Autophosphorylation of receptor tyrosine kinases takes place in trans, i.e., between neighboring protomers of the receptor. The catalytic domain of the receptor is shown as a shaded segment. As a consequence of autophosphorylation, the intrinsic tyrosine kinase activity of the receptor is stimulated. Effector proteins can also bind to the activated receptor. Binding takes place with specific phosphotyrosine binding domains (SH2 or PTB domains) at phosphotyrosine residues of the activated receptor. A critical factor for further signal transduction is the membrane association of the effector proteins that enter into binding with the activated receptor. Details of the effector proteins can be found as follows phospholipase Cy 5.6.2 Src kinase 8.3.2 pl20 GAP 9.4 Grb2, She, IRS 8.5 PI3-kinase 6.6.1 Syp tyrosine phosphatase 8.4.

The phosphotyrosine residues of the activated receptors are attachment points for effector proteins that possess a phosphotyrosine binding domain, such as the SH2... 

Songyang and Cantely, 1995). Furthermore, another phosphotyrosine binding motif was foimd, known as the phosphotyrosine binding domain (PTB) (review Van Geer and Pawson, 1995, Sudol, 1998). In the following, the principles of the SH2-phosphoty-rosine interaction will be described, based on the SH2 domains of class lA and class 3. 

Fig. 8.20. Modular composition of adaptor proteins. Adaptor proteins do not show any enzyme activity of their own, but rather they contain protein modules which help to bind signal proteins into signal pathways. IRS-1 insulin receptor substrate 1 PTB phosphotyrosine binding domain PH pleckstrin homology domain P phosphotyrosine-containing binding site for SH2 or PTB domains HLH helrx-loop-hehx DNA binding motif...

The insulin receptor substrate IRS couples the insulin receptor to sequential effector molecules (review Ogawa et al., 1998). On binding of insulin to the insulin receptor, the tyrosine kinase activity of the receptor is stimulated. The IRS protein is phosphory-lated at several Tyr residues, which then serve as attachment points for sequential effector molecules as e.g. the Grb2-mSos complex, the P13-kinase and the protein tyrosine phosphatase SHP-2. The IRS protein also has a phosphotyrosine binding domain and a PH domain. Both modules are required for signal transduction in vivo. It is assumed that the PTB domain binds to autophosphorylation sites of the insulin receptor and that the PH domain is involved in membrane association of IRS. 

In the other pathway, an additional adaptor protein, the She protein (see 8.5), is involved in the signal transduction. The She protein has a phosphotyrosine binding domain (PTB domain) and specifically binds via this domain to autophosphorylated receptors such as the PDGF receptor and the EGF receptor. The She protein is phos-phorylated itself in the process. The phosphotyrosine residues may also serve as attachment points for the SH2 domain of Grb2 protein, whereby the Grb2-Sos complex is attached to the membrane. 

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