Figure 4.

NMR and infrared spectra for deprotonated and protonated GTP. A and D, geometries of (A) deprotonated and (D) γ-protonated GTP. Shown are the crystal structures of (A) Ras·GTP (1QRA.pdb) and (D) Ras·GppNHp (4RSG.pdb) in color and the dynamics of the substrate in the QM/MM optimized snapshots (gray sticks). The γ-GTP proton sampled the crystal structure (black asterisk), an O–Pγ–O–H torsion angle of 0° (orange asterisk) and 180° (cyan asterisk). B, calculated ³¹P NMR spectra match the experimental spectra for deprotonated GTP, with Pβ being most shielded, followed by Pα and Pγ, respectively. E, this was not the case for protonated GTP. C and F, the same applies for infrared spectra of deprotonated (C) and protonated (F) GTP. Therefore, GTP was most likely deprotonated in the experiments. Error bars depict the mean ± S.E. from each 15 independent calculations.