Comparison of the conformation and GTP hydrolysing ability of N-terminal ras p21 protein segments.

Conformational, GTP binding, and GTP hydrolytic studies are carried out with synthetically prepared N-terminal 34 residue segments (residues 2-35) of p21 ras oncogenic (12-Val) and non-oncogenic (12-Gly) proteins. It was found that these N-terminal regions bind nucleotides through their phosphate groups, and that substitution of valine for glycine produces a more pronounced alpha-helical structure and decreases the conformational flexibility. The glycine containing peptide, when compared to the valine containing analog, catalyses the hydrolysis of GTP 6 times more efficiently. Results suggest that restriction of conformational adaptation may contribute to the transforming capacity of the Val-12 p21 protein.