Structural details of the Polyelectrolytic Exopolysaccharide (APE), the stabilizing component of the Acinetobacter venetianus RAG-1 emulsan complex

Emulsan is a polysaccharide complex, secreted from Acinetobacter venetianus RAG-1, that has been studied extensively for its ability to effectively stabilize oil-in-water emulsions. In previous research, the active emulsion stabilizing component of the emulsan complex was isolated and termed Acinetobacter Polyelectrolytic Exopolysaccharide (APE). In the research presented here, both native and O-deacetylated APE were studied by 1H and 13C NMR spectroscopy, including 1D 1H and 13C and 2D ge-DQF COSY, TOCSY, NOESY, and ge-HSQC experiments. The native polysaccharide was found to contain 6-O-acetyl-2-acetamido-2-deoxy-α-d-galactopyranose, 2-acetamido-2-deoxy-α-d-galactopyranosyluronic acid, and 2-acetamido-4-(3-hydroxybutyramido)-2,4,6-trideoxy-α-d-glucopyranose residues. The sequence of the linear trisaccharide repeating unit of the polysaccharide APE was determined to be →4)-α-d-GalpNAc-6-OAc-(1 → 4)-α-d-GalpNAcA-(1 → 3)-α-d-QuipNAc4NHb-(1→.

► The structure of an oil emulsifying polysaccharide is presented.
► A 1- and 2-D NMR based repeat structure for the emulsan exopolysaccharide.
► The polymer has a trisaccharide repeat with N and O linked acetates.
► Emulsan contains a 4-(3-hydroxybutyramido)-2,4,6-trideoxy-α-d-glucopyranose residue.