Characterization of RP 333, a gene encoding CapD of Rickettsia prowazekii with UDP-glucose 4-epimerase activity

The genetic mechanism of membrane assembly in Rickettsia prowazekii, the causative agent of epidemic typhus, is unknown. Recent progress in genomics of this small intracellular bacterium prompted us to explore membrane biogenesis as it pertains to identification and characterization of gene products that are of importance in polysaccharide biosynthesis. We chose to define the function of the R. prowazekii capD gene (RP 333) product designated as a putative epimerase. We detected a capD transcript in yolk sacs infected with R. prowazekii at ten days post-infection. The capD gene was PCR amplified and cloned into the entry vector pENTR/SD/D-TOPO and transferred to a low copy arabinose-inducible pBAD/Myc-HisA expression plasmid constructed in our laboratory. The corresponding recombinant protein (CapD) was expressed in PL2, a galE28 mutant of Escherichia coli, and has been shown to epimerize UDP-galactose to UDP-glucose without the addition of NAD+. CapD characterization is important for defense strategies targeted towards design of an R. prowazekii vaccine, generation of new antibiotics, and opening the way for research in membrane biogenesis with respect to the parasitic lifestyle of Rickettsia.