SH2 domain-binding peptides

Protein kinase substrate/inhibitor (Csk, 3 bp2, Fps Fes, Grb-2, Hep, She, Syk, Vav, Zap-70) Fpitope mapping for monoclonal antibodies SH2 domain-binding peptides and kinase domains of protein tyrosine kinases... 

The Src SH2 domain typifies a large number of those characterized to date. The pTyr fits into a pocket on the opposite side of the central sheet to the pY-r3 pocket (Figure 13.27a). All known SH2 domains bind pTyr in essentially the same way, but some have a different pattern of contacts for the residues that follow. For example, in the Grb2 SH2 domain, a tryptophan side chain from the small sheet fills the pY-r3 pocket, and the bound peptide takes a different course, with important interactions to an asparagine at pY-r2. Screens of peptide libraries have detected the importance of this asparagine. The SH2 domain from PFC-yl contacts five mainly hydrophobic residues that follow pTyr. 

For this review we have selected the cyclic modified peptides mentioned above, i.e. vancomycin, nisin, cyclosporin, and cyclotheonamide, as well as two examples, i.e. RGD-containing cyclic peptides and SH2 domain binding cyclic peptides, which were inspired by proteins. 

SH2 domains recognize peptide sequences bearing phos-photyrosine (pTyr) residues. They bind to compatible phosphopeptides with an affinity in the 10-100 nM range and bind to phosphopeptides of random sequence with a 1000-fbld lower affinity. They have practically no affinity for unphosphorylated peptides. xhe topography of a tyrosyl-binding SH2 domain is well known, thanks to structural studies (Plate 2).21.22... 

Cell surface ligands (integrins, adhesion molecules or surface receptors, vasculature, tumor lymphatics, normal organs/cells/body fluids) B-cell epitope mapping (gpl20, neolactotetraosylceramide) MHC class II molecule binding peptides peptide substrate for tPA peptide substrates for HIV-1 protease and SH2 and SH3 domain-binding peptides. 

Scheme 3.2-11 Tyrosine residues equipped with various caging groups rendered peptides inactive with respect to SH2-domain binding.

Information about the specificity of SH2 domain binding came initially from the structures of the Src and Lck SH2 domains in complex with tyrosyl phosphopeptides with the sequence Glu, Glu, He (EEI) C-ter-minal to the pTyr (pY) (Eck et al., 1993 Waksman et al., 1993). This pYEEI sequence had previously been identified to be specific for the Src family of SH2 domains, which includes Lck (see Section III). The Src and Lck structures are very similar to one another. Although the peptides employed in both studies contained residues outside the pYEEI motif, the structures indicate that only these four residues contact the SH2 domain. The peptide binds the SH2 domains perpendicular to the central p-sheet in an extended conformation (Fig. 2A). The pTyr makes contacts very similar to those observed for the structure of the Src SH2 domain in complex with low-affinity tyrosyl phosphopeptides (see above). However, in addition, the EEI motif makes specific contact with other residues of the protein. 

Binding studies using other Src family member SH2 domains have revealed that these domains have binding properties similar to those of the Src SH2 domain. For instance, several different investigations have determined that Src family SH2 domains bind selectively to the pYEEI peptide, but the level of specificity is modest (1) competition binding assays using both the Lck and Src SH2 domains and radioactive peptides... 

Met of a high-affinity pYMDM peptide decreased N-p85 SH2 domain binding hy about 1000-fold (Gunther et al., 1996). 

The crystal structure of the tandem SH2 domain of the Syk kinase has also been solved in complex with a dpITAM peptide (Fiitterer et al., 1998). This structure is similar to that of Zap-70 (1) the peptide binding sites of each SH2 domain are spatially colinear so that a single dpITAM peptide bridges the two SH2 domains (2) an a-helical coiled coil links the two SH2 domains (3) the peptide and tandem SH2 domains bind... 

SH2 domains bind to peptides or sections of proteins that contain phosphotyrosine residues in particular sequence contexts. The formation of phosphorylated tyrosine residues in a receptor often results from hormone activation of the receptor. The phosphorylated tyrosine-containing peptides in the receptor can be recognized and bound by other proteins that have SH2 domains. The SH2 domain allows different proteins to respond to and be affected by the phosphorylated tyrosines that arise in proteins as a result of a signal transduction event. 

Figure 13.26 Schematic diagram of the SH2 domain from the Src tyrosine kinase with bound peptide. The SH2 domain (blue) comprises a central p sheet surrounded by two a helices. Three positively charged residues (green) are involved in binding the phosphotyrosine moiety of the bound peptide (red). (Adapted from G. Waksman et al.. Cell 72 779-790, 1993.)...

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