Correlation between dynamics and high affinity binding in an SH2 domain interaction

Protein-protein interfaces can consist of interactions between large numbers of residues of each molecule; some of these interactions are critical in determining binding affinity and conferring specificity, while others appear to play only a marginal role. Src-homology-2 (SH2) domains bind to proteins containing phosphorylated tyrosines, with additional specificity provided by interactions with residues C-terminal to the phosphotyrosine (pTyr) residue. While the C-terminal SH2 domain of phospholipase C-gamma 1 (PLCC SH2) interacts with eight residues of a pTyr-containing peptide from its high affinity binding site on the beta-platelet-derived growth factor receptor, it can still bind tightly to a phosphopeptide containing only three residues. Novel deuterium (H-2) based nuclear magnetic resonance (NMR) spin relaxation experiments which probe the nanosecond-picosecond time scale dynamics of methyl containing side chain residues have established that certain regions of the PLCC SH2 domain contacting the residues C-terminal to the pTyr have a high degree of mobility in both the free and peptide complexed states. In contrast, there is significant restriction of motion in the pTyr binding site. These results suggest a correlation between the dynamic behavior of certain groups in the PLCC SH2 complex and their contribution to high affinity binding and binding specificity.