Purification, crystallization and preliminary structural studies of dTDP-6-deoxy-D-xylo-4-hexulose 3,5-epimerase (RmlC), the third enzyme of the dTDP-L-rhamnose synthesis pathway, from Salmonella enterica serovar Typhimurium

L-Rhamnose is an essential component of the cell wall of many pathogenic ba cteria. Its precusor, dTDP-L-rhamnose, is synthesized from alpha-D-glucose- 1-phosphate and dTTP via a pathway requiring four distinct enzymes: RmlA, R mlB, RmlC and RmlD. RmlC was overexpressed in Escherichia coli. The recombi nant protein was purified by a two-step protocol involving anion-exchange a nd hydrophobic chromatography. Dynamic light-scattering experiments indicat ed that the recombinant protein is monodisperse. Crystals were obtained usi ng the sitting-drop vapour-diffusion method with ammonium sulfate as precip itant. Diffraction data were collected on a frozen crystal to a resolution of 2.17 Angstrom. The crystal belongs to either space group P3(1)21 or P3(2 )21, with unit-cell parameters a = b = 71.56, c = 183.53 Angstrom and alpha = beta = 90, gamma = 120 degrees.