SH2 domains provide fundamental
recognition sites in
tyrosine kinase-mediated
signaling pathways which, when aberrant, give rise to disease states such as cancer,
diabetes, and
immune deficiency. Designing specific inhibitors that target the SH2 domain-binding site, however, have presented a major challenge. Despite well over a decade of intensive research, clinically useful
SH2 domain inhibitors have yet to become available. A better understanding of the structural, dynamic, and thermodynamic contributions to
ligand binding of individual
SH2 domains will provide some insight as to whether inhibitor development is possible. We report the first
high resolution solution structure of the apo-v-Src
SH2 domain. This is accompanied by the analysis of backbone dynamics and pK(a) values within the apo- and peptide-bound states. Our results indicate that the
phosphotyrosine (pY) pocket is tightly structured and hence not adaptable to exogenous ligands. On the other
hand, the pocket which accommodates residues
proximal and
C-terminal of the pY (pY + 3) or so-called specificity determining region, is a large dynamic-binding surface. This appears to allow a high level of promiscuity in binding. Binding of a series of synthetic, phosphotyrosyl, peptidomimetic compounds designed to explore interactions in the pY + 3 pocket further demonstrates the ability of the
SH2 domain to accommodate diverse ligands. The thermodynamic parameters of these interactions show dramatic enthalpy/
entropy compensation. These data suggest that the v-Src
SH2 domain does not have a highly specific secondary-binding site, which clearly presents a major hurdle to design
selective inhibitors. Proteins 2008. (c) 2008 Wiley-Liss, Inc.
