Grb7 is an adapter protein aberrantly overexpressed, along with the erbB-2 receptor in breast and other cancers. Normally recruited to focal adhesions with a role in cell migration, in cancer cells it is associated with erbB-2 and found to exacerbate the cancer progression via stimulation of cell migration, and proliferation. The G7-18NATE peptide (sequence: WFEGYDNTFPC cyclised via a thioether bond) is a non-phosphorylated peptide that was developed for the specific inhibition of Grb7 by blocking its SH2 domain. Cell permeable versions of G7-18NATE are effective in the reduction of migration and proliferation in Grb7 overexpressing cells. It thus represents a promising starting point for the development of a therapeutic against Grb7. Here we report the crystal structure of the G7-18NATE peptide in complex with the Grb7-SH2 domain, revealing the structural basis for its interaction. We also report further rounds of phage display that have
identified G7-18NATE analogues with micromolar affinity for Grb7-SH2. These peptides all retained amino acids F2, G4 and F9, as well as the YDN motif that the structural biology study showed to be the main residues in contact with the Grb7-SH2 domain. ITC measurements reveal similar and better binding affinity of these peptides compared with G7-18NATE. Together this study facilitates the optimization of second-generation inhibitors of Grb7.