Fig. 6.
Hydrolysis of GTP by Gα. (A) Transition state of the Gα based on the Gαi1•GDP•AlF4 structure superimposed onto the structure of Gαi1•GTP. The highly conserved Gln204 in the swII region coordinates an attacking water molecule, leading to the nucleophilic attack of the γ-phosphate of GTP (PDB: 1GFI). (B) Switch II can also be further stabilized to promote better geometry for the Gln204 through an interaction with RGS4, a GTPase accelerating protein (PDB: 1AGR). (C) Hydrolysis results in the subtle relaxation of the swII region (PDB: 1GIT). (D) Pi release results in the complete disordering of swII (PDB: 1GDD).