Fig. 4.

Interactions of Ras with the transition state analog, GDP·AlF₃, from the crystal structure of Ras·GDP·AlF₃·RasGAP (PDB ID 1WQ1). The functional groups of Ras that contribute to interactions with the pro-S β nonbridge oxygen include the main chain NH groups of Val-14, Gly-15, and Lys-16, as well as the Nζ of Lys-16. The main chain NH of Ser-17 and Mg²⁺ interact with pro-R oxygen. The amide hydrogen of Gly-13 forms a strong hydrogen bond with the β–γ bridge oxygen. Interactions between Ras and γ nonbridge oxygens include Mg²⁺, the main chain NH of Thr-35 and Gly-60, the side chain of Gln-61, and the side chain of Lys-16.