G7-18NATE is a nonphosphorylated,
cyclic peptide that specifically inhibits the Grb7 adapter
protein implicated in several pathways critical to cell proliferation and migration. It has been shown that
G7-18NATE is able to compete with natural
ligands for the Grb7 SH2
phosphotyrosine binding site, and to attenuate cell migration in a
pancreatic cancer cell line. It is thus an important lead in the development of a selective inhibitor of Grb7 and potential novel anticancer
therapeutics. The current study reports the
solution properties of G7- 18NATE determined using NMR spectroscopy, in both water (pH 2-3) and
phosphate buffer (pH 6.0), with 100 mM NaCl. The spectra reveal that
G7-18NATE exists in two distinguishable conformational states on the NMR timescale, most likely due to cis-trans
proline isomerization. In addition, the chemical shift data are consistent with a tendency of
G7-18NATE to form a turn about the YDN motif, known to be important for binding, and suggest that this turn is stabilized in low
salt and low pH conditions. Low NH temperature coefficients of Tyr-5 and Asn-7
amide protons may reflect their involvement in the formation of hydrogen bonds that stabilize such a turn. Overall, however, the
peptide does not form a rigid structure, but exists in a highly flexible state in
solution. Averaged 3JNH-H coupling constants and a lack of interresidue NOEs are characteristic of such
peptide solution behavior. This suggests that there is scope for increasing the rigidity of the
peptide that may enhance its binding affinity and specificity for Grb7.