Figure 2: Determination of the metal sites replaced and/or occupied by Co²⁺ in the PfTET3 active site by anomalous x-ray scattering.

Crystals of PfTET3 were grown in the presence of 2 Co²⁺ equivalents. Blue spheres are cobalt ions (M1 and M3), red sphere is zinc ion (M2). (A) Schematic representation of the PfTET3 active site. M1 is coordinated by Asp177, Glu208 and His314 and M2 is coordinated by His63, Asp177 and Asp230. Both sites are represented as grey spheres. (B) Anomalous Fourier map (red) of the PfTET3 catalytic site (contour 8σ) at Zn²⁺ absorption edge (both Zn²⁺and Co²⁺ display anomalous signal). M2 is highlighted by the anomalous Fourier map with an extra density for the M1 site. (C) Anomalous Fourier map (blue) of the PfTET3 catalytic site (contour 9σ) at Co²⁺ absorption edge (only Co²⁺ display anomalous signal). M1 and an additional metal site (M3) coordinated by Thr232, Asp254 and Glu281 are highlighted by the anomalous Fourier map. (D) Anomalous Fourier map (red and yellow) of the PfTET3 catalytic site (contour 4.5σ) at 40ev below Co²⁺ absorption edge. At this wavelength the anomalous signal from Co²⁺ is lower than that of Zn²⁺ or sulphur. Only the M2 site is highlighted by the anomalous Fourier map. The yellow map indicates the sulphur anomalous signal while the red map highlights the anomalous contribution from the zinc ion.