AepG is a glucuronosyltransferase involved in acidic exopolysaccharide synthesis and contributes to environmental adaptation of Haloarcula hispanica

The attachment of a sugar to a hydrophobic lipid carrier is the first step in the biosynthesis of many glycoconjugates. In the halophilic archaeon Haloarcula hispanica, HAH_1206, renamed AepG, is a predicted glycosyltransferase belonging to the CAZy Group 2 family that shares a conserved amino acid sequence with dolichol phosphate mannose synthases. In this study, the function of AepG was investigated by genetic and biochemical approaches. We found that aepG deletion led to the disappearance of dolichol phosphate-glucuronic acid. Our biochemical assays revealed that recombinant cellulose-binding, domain-tagged AepG could catalyze the formation of dolichol phosphate-glucuronic acid in time- and dose-dependent manners. Based on the in vivo and in vitro analyses, AepG was confirmed to be a dolichol phosphate glucuronosyltransferase involved in the synthesis of the acidic exopolysaccharide produced by H. hispanica. Furthermore, lack of aepG resulted in hindered growth and cell aggregation in high salt medium, indicating that AepG is vital for the adaptation of H. hispanica to a high salt environment. In conclusion, AepG is the first dolichol phosphate glucuronosyltransferase identified in any of the three domains of life and, moreover, offers a starting point for further investigation into the diverse pathways used for extracellular polysaccharide biosynthesis in archaea.