Crystallization of D-lactate dehydrogenase from Lactobacillus bulgaricus

The D-lactate dehydrogenase (D-LDH) from Lactobacillus bulgaricus has been purified and co-crystallized with its cofactor NAD+. Crystals suitable for X-ray diffraction experiments have been obtained from an ammonium sulfate solution by the hanging-drop method. The crystals belong to the orthorhombic space group C222 (or C222(1)) with cell dimensions a = 76.5 A, b = 93.3 A, c = 118.4 A and one monomer of 37,000 daltons per asymmetric unit. They diffract beyond 3.0 A resolution. Sequence comparison suggests that D-LDHs have no evolutionary relationship to L-LDHs and belong instead to the family of the D-2-hydroxyacid dehydrogenases. The X-ray crystallographic structure of the D-LDH from Lactobacillus bulgaricus will be a decisive test of this hypothesis.