Figure 1.

Neutron diffraction crystal structure of Ras with protonated γ-GppNHp. Observed deuterons of the triphosphate groups are depicted as white spheres (PDB ID: 4RSG). Tyr-32 of a neighboring symmetry cell is bound to γ-GppNHp and is depicted as blue sticks. The Mg²⁺ atom is depicted as a green sphere. Labels of α-,β-, and γ-oxygens were retained hereafter. Protonation at γ2 (asterisk) corresponds to experimental observation of γ-protonation.