The structure of the UDP-Glc/GlcNAc 4-epimerase from the human pathogen Campylobacter jejuni

Worldwide, the food-born pathogen Campylobacter jejuni is the leading bacterial source of human gastroenteritis. C. jejuni produces a variety of diverse cell-surface carbohydrates that are essential for pathogenicity. A critical component of these oligo- and polysaccharides is the sugar N-acetylgalactosamine (GalNAc). The sole source of this sugar is the epimerization of UDP-N-acetylglucosamine (GlcNAc), a reaction catalyzed by the enzyme UDP-GlcNAc 4-epimerase (Gne). This enzyme is unique among known bacterial epimerases in that it also catalyzes the equivalent reaction with the non-N-acetylated sugars. Understanding how CjGne catalyzes these various interconversions is critical to designing novel inhibitors of this enzyme. Here, to further the mechanistic understanding we present a 2.0[A] structure of CjGne with its NAD+ co-factor bound. Based on novel features found in the structure we perform a variety of biochemical studies to probe the mechanism and compare these results to another bifunctional epimerase, human GalE. We further show that ebselen, previously identified for inhibition of HsGalE, is active against CjGne, suggesting a route for antibiotic development.