Effect of Copper Ions on the Crystal Packing and Conformation of Thiocyanate Dehydrogenase in the Crystal Structure

The copper-containing enzyme thiocyanate dehydrogenase (TcDH) catalyzes the oxidation of thiocyanate to cyanate and elemental sulfur. The three-dimensional structures of two bacterial TcDH (tpTcDH and pmTcDH) are currently known. Both enzymes are dimers and contain a trinuclear copper center in the active site. An important difference between these enzymes is that the subunits of the tpTcDH dimer have identical conformations in the crystal, whereas the subunits of the pmTcDH dimer have different conformations (open and closed). To elucidate the role of copper ions in changing the conformation of TcDH, the structure of the apo form of pmTcDH was established. In the apo form, both subunits of the dimer have a closed conformation. The soaking of apo-form crystals with copper led to the restoration of the trinuclear center and conformational rearrangements of the subunits.