Prediction and analysis of SH2 domain-phosphopeptide interactions

Src homology 2 (SH2) domains are small protein modules of approximately 100 amino acids that are found in many proteins involved in intracellular signal transduction. They mediate protein-protein interactions and modulate enzyme activity by their ability to bind to specific sequence patterns that contain a phosphorylated tyrosine. As the three-dimensional structures of the phosphatidylinositol (PI) 3-kinase, Lck, Src and Abl SH2 domains have been shown to be similar, we have modelled other SH2 domains that show distinct sequence specificity to allow comparative analysis of SH2-phosphopeptide interactions. The SH2 domains of PLC gamma-Nterm., Nck, Grb2, GAP and Abl have been model-built with high-affinity phosphopeptides fitted into the putative binding sites. For each SH2 domain a detailed analysis of the peptide-protein interaction was performed. It is apparent that specificity is mainly conferred by three to five residues downstream from the phosphotyrosine residue (Y*), especially, although not exclusively, peptide position Y* + 3. The SH2 pocket that binds the Y* + 3 residue is mainly composed of three sections: part of strand beta E going into loop EF, part of alpha B and loop BG. The residues that constitute the Y* + 3 binding pocket show variability that seems to determine which amino acid binds preferentially. Residue position beta E4 seems to play a vital role in the SH2 specificity. This study shows that the development of modelling protocols for SH2 domains whose structure has not been determined can prove very useful in predicting which residues are involved in conferring the affinity and binding specificity of these domains towards distinct phosphotyrosine-containing sequences.