Solution structure and dynamics of G1TE, a nonphosphorylated cyclic peptide inhibitor for the Grb2 SH2 domain

The solution structure and dynamics of G1TE, a nonphosphorylated cyclic pep tide inhibitor for the Grb2 SH2 domain, was determined using two-dimensiona l NMR and simulated annealing methods. G1TE consists of 10 amino acids and a C-terminal Cys cyclized through its side-chain sulfur atom by a thioether linkage to its N terminus. The results indicate that G1TE assumes a circle -like shape in solution in which all the side chains are protruding outside , and none of the residues are involved in intramolecular hydrogen bonding. The average root-mean-square deviations were found to be 0.41 +/- 0.11 Ang strom for the backbone heavy atoms C, C alpha, and N, and 1.03 +/- 0.14 Ang strom for all heavy atoms in a family of 10 structures. N-15 relaxation mea surements indicate that G1TE has rather restricted dynamics in the fast tim e scale within its backbone. However, residues Tyr3, Val6, and Gly7 may be involved in a possible conformational exchange. The structural comparison b etween G1TE in solution and the BCR-Abl phosphopeptide bound to Grb2 SH2 do main revealed that G1TE may form a larger circle-like binding surface than the BCR-Abl phosphopeptide in the bound form. Also, the restricted backbone dynamics of G1TE may result in a reduced loss of entropy and can compensat e for the absence of a phosphate group at the Tyr3 position. These structur al and dynamic properties of G1TE may provide a molecular basis for underst anding its interactions with the Grb2 SH2 domain. (C) 1999 Academic Press.