Crystallization and preliminary X-ray diffraction studies of the lipopolysaccharide core biosynthetic enzyme ADP-L-glycero-D-mannoheptose 6-­epimerase from Escherichia coli K-12

ADP-L-glycero-D-mannoheptose 6-epimerase is a 240 kDa NAD-dependent nucleotide diphosphosugar epimerase from Escherichia coli K12 which catalyzes the interconversion of ADP-D-glycero-D-mannoheptose and ADP-L-glycero-D-mannoheptose. ADP-L-glycero-D-mannoheptose is a required intermediate for lipopolysaccharide inner-core and outer-membrane biosynthesis in several genera of pathogenic and non-pathogenic Gram-negative bacteria. ADP-L-glycero-D-mannoheptose 6-epimerase was overexpressed in E. coli and purified to apparent homogeneity by chromatographic methods. Three crystal forms of the epimerase were obtained by a hanging-drop vapor-diffusion method. A native data set for crystal form III was collected in-house on a Rigaku R-AXIS-IIC image plate at 3.0 Å resolution. The form III crystals belong to the monoclinic space group P2₁. The unit-cell parameters are a = 98.94, b = 110.53, c = 180.68 Å and β = 90.94°. Our recent results show that these crystals diffract to 2.0 Å resolution at the Cornell High Energy Synchrotron Source. The crystal probably contains six 40 kDa monomers per asymmetric unit, with a corresponding volume per protein mass (V_m) of 4.11 ų Da⁻¹ and a solvent fraction of 70%.