Crystallization and preliminary X-ray analysis of glucose dehydrogenase from Haloferax mediterranei

Glucose dehydrogenase (E.C 1.1.1.47; GlcDH) from Haloferax mediterranei has been overexpressed in Escherichia coli, solubilized by the addition of 8 M urea and refolded by rapid dilution. The protein has been purified by conventional techniques and crystallized by the hanging-drop vapour-diffusion method using sodium citrate as the precipitant. Two crystal forms representing the free enzyme and the binary complex with NADP⁺ grow under these conditions. Crystals of form I diffract to beyond 3.5 Å resolution and belong to the hexagonal space group P622, with unit-cell parameters a = b = 89.1, c = 214.6 Å, α = β = 90, γ = 120°. Crystals of form II diffract to greater than 2.0 Å and belong to the orthorhombic space group I222 or I2₁2₁2₁, with unit-cell parameters a = 61.8, b = 110.9, c = 151.7 Å, α = β = γ = 90°. Calculated values for V_M and consideration of the packing for both crystal forms suggests that the asymmetric units in both crystal forms contain a monomer.