FIGURE 4.

Coordination of the Mg²⁺ ion. The Mg²⁺ ion is tightly coordinated by oxygen atoms of the β- and γ-phosphate, Ser²³³ of switch I, Thr¹¹² of the P-loop, and two water molecules. The ion location is quite similar to that seen in the Eg5·ADP structure (18), in which the Mg²⁺ ion is coordinated by Thr¹¹², a β-phosphate oxygen atom, and four water molecules.