(a) The hydrogen-bonding network in the active site of a representative structure of KRasGDP·PiS2 from clustering analysis. The GDP, Pi, Mg2+ and the key residues in the hydrogen-bonding network are shown in stick models and hydrogen-bonds are indicated with dotted lines. (b) The probability of hydrogen-bond interactions between Pi with the atoms of Q61, T35, GDP and K16. (c) The distribution of the Mg-CAQ61-CBQ61-OE1Q61 dihedral angle in KRasGDP·PiS2. The stable hydrogen-bonding conformations are highlighted on the right, which correspond to the probability peaks with the dihedrals of θ=1, 141, 77 and 133 degrees in panel (c), respectively.