The structure of the LPS O-chain of Fusobacterium nucleatum strain 25586 containing two novel monosaccharides, 2-acetamido-2,6-dideoxy-L-altrose and a 5-acetimidoylamino-3,5,9-trideoxy-gluconon-2-ulosonic acid

Fusobacterium nucleatum is an anaerobic bacterium found in the human mouth where it causes periodontitis. Recently, it has been gaining attention as a potential causative agent for colorectal cancer and is strongly linked with pregnancy complications including pre- term and still births. Little is known about the virulence factors of this organism, and thus we have initiated studies to examine the bacterium's surface glycochemistry. We isolated lipopolysaccharide ( LPS) from F. nucleatum strain 25586 and purified and performed structural analysis on the O- antigen polysaccharide. The polysaccharide contained two novel sugars, 2- acetamido- 2,6- dideoxy-(L)- altrose ( (L)- 6dAltNAc) and a 5- acetimidoylamino- 3,5,9- trideoxygluco- non- 2- ulosonic acid ( Non5Am), which was tentatively assigned the L- glycero- (L)- gluco configuration. The polysaccharide was found to have a trisaccharide repeating unit, which is phosphorylated with phosphocholine ( PCho), and the following structure was established: -[-4-beta- Nonp5Am- 4-alpha-(L)- 6dAltpNAc3PCho-3-b-(D)-QuipNAc-]-We propose the trivial name 'fusaminic acid' for the novel nonulosonic acid. It is the first occurrence of a 9-deoxynonulosonic acid with a hydroxyl group at C-7, which is occupied by an amino group in all monosaccharides of this class described so far. (C) 2017 Elsevier Ltd. All rights reserved.