Abstract 2165 Investigating a Novel Carbohydrate Deacetylase Involved in Bacteroides Capsular Polysaccharide Biosynthesis

Gut microbes Bacteroides have several demonstrated beneficial properties to their host, such as the suppression of intestinal inflammation. Like many bacteria, Bacteroides have a polysaccharide capsule which is linked to their survival and can modulate these positive immune effects. However, the capsular polysaccharides (CPS) can also play a role in virulence. Here we present characterization of a novel putative polysaccharide deacetylase from Bacteroides ovatus (BoPDA), encoded in a likely CPS biosynthesis loci. We found that this enzyme is highly conserved in the majority of Bacteroides species. Sequence and structural analysis indicates BoPDA contains a NodB homology domain common to the carbohydrate esterase 4 (CE4) superfamily, attached to a flanking carbohydrate binding domain. Interestingly, CE4 family members typically have a His-His-Asp metal binding site that BoPDA lacks. We solved multiple high resolution crystal structures (1.4 Å – 1.8 Å) of the enzyme bound to divalent cations Ni2+, Co2+, Cu2+ or Zn2+ that reveal its metal binding strategy. BoPDA deacetylase activity assays show that its catalysis is specific to Zn2+ despite the metal binding promiscuity seen in the crystal structures. Our findings provide insight into a novel, conserved polysaccharide deacetylase that may play a role in Bacteroides CPS biosynthesis. Financial support for this research comes from Cottrell Scholar Award #28277 sponsored by Research Corporation for Science Advancement.