Binding to SH2 domain

Figure 11-13 (A) A simplified version of the mitogen-activated kinase (MAPK) signaling cascade. At left is shown a hormone receptor, e.g., that for the epidermal growth factor (EGF). The receptor tyrosine kinase undergoes autophosphorylation on numerous tyrosines. The resulting phosphotyrosyl (Y-P) groups bind to SH2 domains of adapters such as Grb2 and She.

Figure 3. The EBV protein LMP2A binds the SH2 domains of the Lyn and Syk B cell tyrosine kinases, and the WW domains of the AIP4 E3 protein-ubiquitin ligase. The protein-protein interactions elicited by the viral protein lead to the ubiquitination and destabilization of Lyn (and potentially other B cell proteins), which may contribute to the inhibition of BCR signaling in latently infected cells.

The PI3 kinase (PI3-K) is translocated to the membrane by interaction of the SH2 domain of its p85 subunit with phosphotyrosine residues of the activated receptor. There it converts PtdIns(3,4)P2.into PtdIns(3,4,5)P3 which binds to PH domains of various effector molecules and recruits them into the signaling chain. The effector molecules can stimulate cell division or can induce the programmed cell death. The tumor suppressor PTEN hydrolyses phosphates from PtdIns(3,4,5)P3 and thus inhibits the growth promoting effect of the PI3 kinase signaling. An important effector of PI3 kinase is the protein kinase Akt which is also termed protein kinase B (PKB). GF growth factor GFR growth factor receptor. 

Kavanaugh, W. M. and Williams, L. T. An alternative to SH2 domains for binding tyrosine-phosphorylated proteins. Science, 266,1862-1865, 1994. 

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

Ras is known to be involved in the regulation of cellular proliferation and terminal differentiation [7,40]. In mammals, ras is activated by growth-factor-receptor tyrosine kinases and other tyrosine kinases. Some of these kinases phosphorylate the She protein and phosphorylated She plus autophosphorylated receptor proteins bind the SH2 domain... 

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. 

Nearly all SH2 domains require tyrosine phosphorylation of their targets for recognition (for the exception, see Section V). This has been established from numerous studies which have compared the binding of phosphorylated and dephosphorylated peptides to SH2 domains (Bibbins et al., 1993 Domchek et al., 1992 Gilmer et al., 1994 Lemmon and Ladbury, 1994 Mayer et al., 1992 Piccione et al., 1993). These binding experiments have established that high-affinity tyrosyl... 

Investigations which have probed the binding of just the amino acid pTyr (or close variants thereof) to SH2 domains have underscored the dominant role played by just this single amino acid in SH2 domain binding. It was initially qualitatively observed that pTyr weakly associates with SH2 domains (Lemmon and Ladbury, 1994 Mayer et al., 1992). Competition binding experiments then revealed that pTyr-like mimetics have measurable affinity for the Src and N-p85 SH2 domains at a Kd of 1 mM (Burke et al., 1995). These findings have been confirmed by direct calorimetric titrations to measure binding of pTyr alone to the Src SH2 domain, which indicated that pTyr binds with an affinity of 333 pM at 25°C (Bradshaw et al., 1999). 

SH2 domains bind to phosphotyrosine-containing regions of target molecules... 

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