Figure 4. Position and coordination of a metal ion.

Left, the putative Mg²⁺ ion (blue sphere) is shown solvated in its first atomic shell by six water molecules (red spheres). The corresponding 2Fo-Fc electron density map (contoured 1σ) with a cross shape is shown in purple. Residues of Nsp16 involved in coordination of Mg²⁺ ion via water molecules are labeled. Right, a global view of the bound metal ion in its electron density on the opposite side from the SAH molecule (red sticks). Nsp16 is shown as green ribbons, nsp10 as yellow ribbons with its two bound Zn²⁺ as grey spheres as in Fig. 1.