Heteronuclear NMR Studies of the Combined Src Homology Domains 2 and 3 of pp60 c-Src:  Effects of Phosphopeptide Binding^†

The results of heteronuclear NMR studies on the combined Src homology domains 2 and 3 (SH3-SH2) of pp60 c-Src are presented. Resonance assignments were obtained using heteronuclear triple-resonance experiments in conjunction with ¹⁵N-separated nuclear Overhauser effect spectroscopy (NOESY) data. A modified three-dimensional ¹³CO−¹⁵N−¹H spectral correlation experiment [(HACA)CO(CA)NH] with improved sensitivity is presented that provided additional sequential information and resolved several ambiguities. Chemical shifts and sequential- and medium-range NOE cross peaks indicate that the structures of both the SH3 and SH2 portions of the polypeptide are very similar to those of the isolated SH3 and SH2 domains. Binding of a high-affinity phosphopeptide, EPQpYEEIPIYL, induces large chemical shift changes at several locations in the SH2 domain. Comparison with known results for peptide binding to SH2 domains shows that the residues displaying the largest effects are all involved in peptide binding or undergo significant conformational changes upon binding. However, subtle changes of both ¹H and ¹⁵N chemical shifts are observed for residues within the SH3 domain and the connecting linker region, indicating possible cross-domain communication.