Structure of D-lactate dehydrogenase from Aquifex aeolicus complexed with NAD⁺ and lactic acid (or pyruvate)

The crystal structure of D-lactate dehydrogenase from Aquifex aeolicus (aq_727) was determined to 2.12 Å resolution in space group P2₁2₁2₁, with unit-cell parameters a = 90.94, b = 94.43, c = 188.85 Å. The structure was solved by molecular replacement using the coenzyme-binding domain of Lactobacillus helveticus D-lactate dehydrogenase and contained two homodimers in the asymmetric unit. Each subunit of the homodimer was found to be in a `closed' conformation with the NADH cofactor bound to the coenzyme-binding domain and with a lactate (or pyruvate) molecule bound at the interdomain active-site cleft.