Panel A, the active site of the Y90F mutant of GalrD-II in the presence of Mg2+ and galactarate (PDB Code 3HPF). Panel B, the docking pose of galactarate obtained using the apo structure (PDB Code 2OQY). Panel C, the docking pose of galactarate obtained using the “wild type” holo structure (with Tyr 90) constructed from the coordinates of the Y90F•Mg2+•galactarate complex (PDB Code 3HPF). The Mg2+ ions are highlighted in green; galactarate is highlighted in yellow. Arg 385, missing in the apo structure (panel B), provides a hydrogen-bonding interaction to the substrate (panel C).