Structure of the lipopolysaccharide O-antigens from Fusobacterium nucleatum strains HM-994, HM-995, HM-997

Fusobacterium nucleatum is an anaerobic bacterium found in the human mouth where it causes periodontitis. It was also found in colorectal cancer tissues and is linked with pregnancy complications, including pre-term and stillbirths. Cell surface structures of the bacterium could be implicated in pathogenesis. Here we report the structure of the lipopolysaccharide O-chain (OPS) of three strains of F. nucleatum HM-994, HM-995, and HM-997, isolated from cancerous tissues: -3-β-D-ManNAc4Lac-4-β-D-Glc6OAc-3-β-D-FucNAc4N- HM-994. -4-α-L-GalNHBuA-3-α-D-QuiNAc4NHBu-3-α-L-Rha-6-α-D-GalN- HM-995. -3-[α-L-GulNAcA-4-]-β-D-Glc-4-β-D-ManNAcAN-3-β-D-FucNAc4N-3- HM-997. where HBu is 3-hydroxybutyryl, ManNAc4Lac is 4-O-(1-carboxyethyl)-2-acetamido-2-deoxy-mannose. All monosaccharides are in the pyranose form. The structures were determined using standard NMR (2D homo- and hetero-nuclear techniques), MS and chemical methods following gtypical LPS isolation and purification methods. In some cases polymeric material was further degraded in order to produce compounds that gave improved NMR spectra that were easier to be fully interpreted. Structure of the OPS from strain HM-994 was identical to the OPS from F. nucleatum strain MJR 7757 B. Structures of the OPS from HM-995 and HM-997 are novel and to our knowledge have not been previously reported and include the often observed 6-deoxy- sugars found in several F. nucleatum strains and butyrate rather than acetate modifications in the HM-995 strain. This structural knowledge adds to the ever increasing variation found in LPS O-antigen structures from F. nucleatum strain from both oral and cancerous origin and suggests that there may be a multitude of different LPS O-antigen structures elaborated by this organism that may present challenges to any serotyping efforts.