Crystallization

The Ni- and Co- bound proteins were crystallized using the vapor diffusion method with previously reported crystallization condition (19.0% (w/v) polyethylene glycol (PEG) - 4000, 19.0% (w/v) isopropanol, 5.0% glycerol, and 0.095 M Na-citrate pH 4.2 (final pH 5.6)).¹⁵ The ligand 2-keto-4-(methylthio)-butyric acid (KMTB) was soaked to a 10 molar excess into already formed Ni and Co-MmARD crystals. The ligands valeric acid (VA) and D-lactic acid (DLA) were soaked to a 10 molar excess into only Ni-MmARD crystals.