FIGURE 6.

Evidence for Mn²⁺ bound in the active site of SUMO-BDP. A, anomalous signal due to Mn²⁺ ions. SUMO-BDP expressed in culture media supplemented with 1 mm MnCl₂ was crystallized in a Tris buffer containing 0.2 m MgCl₂ and 0.3 MnCl₂. The crystal was soaked with 0.3 mm MnCl₂ in the crystallization buffer for 18–24 h, followed by the collection of long-wavelength x-ray diffraction data. Superimposed on the final refined model, which has been transformed to the coordinate system of a Mn²⁺-only-containing crystal, is an anomalous difference Fourier map (black mesh) contoured at the 4-σ level. The representation and coloration are as in Fig. 5.