Sugarcoating it: Enterococcal polysaccharides as key modulators of host–pathogen interactions
Fig 2
Comparison of predicted epa-like loci among enterococcal strains.
In Enterococcus faecalis V583 and OG1RF, EPA biosynthesis is encoded by a cluster of genes organized in 2 genetic loci: first, a conserved region, consisting of 18 genes, from epaA to epaR, which participate in the rhamnan backbone biosynthesis (core region), and, second, a downstream cluster of approximately 10–20 genes exhibiting genetic variability among strains, which has been proposed to account for the major differences on EPA decoration among E. faecalis isolates (variable region) [10,14,32,105]. The core region of Enterococcus faecium is differentially organized in comparison with the EPA core from E. faecalis. It does not have homologs of epaI, epaJ, and epaK. Instead, it has the 2 genes, epaP and epaQ, located at that site [104,105,107]. E. faecium’s variable locus is proposed to be divided into 4 main variants based on sequence similarities [104,107]. The scheme depicts variants 2 and 4 for strains 1,141,733 and Aus0004, respectively. Arrow colors correspond to colored boxes (bottom) and indicate predicted open reading frame function according to genome annotations and BLASTP analysis. Blue shades connect homologs of different strains. The absence/variability of epa genes suggests that the EPA polysaccharides of the 2 species have different sugar compositions, and, in consequence, may confer diverse physiological functions. The epa loci were adapted from [10,20,32,54,104,105,107]. All genes are drawn to scale. EPA, enterococcal polysaccharide antigen; GTF, glycosyltransferase.