Structural characterization of the O-antigenic polysaccharide chain of Porphyromonas circumdentaria NCTC 12469

Structural studies were carried out on an O-antigenic polysaccharide moiety derived from Porphyromonas circumdentaria NCTC 12469, a reference strain of Porphyromonas species. The polysaccharide chain was composed of D-glucose, D-galactose, N-acetyl-D-glucosamine, and N-acetyl-D-galactosamine in a molar ratio of 1:2:1:1. On the basis of results from ¹H- and ¹³C-NMR spectroscopic analyses including COSY, TOCSY, and HMQC experiments together with results of Smith degradation, methylation analysis, and partial acid hydrolysis, it is concluded that the polysaccharide chain has a pentasaccharide repeating unit of →6)-β-D-Glcp-(1→6)-β-D-Galp-(1→6-β -D-Galp-(1→3)-β-D-GlcpNAc-(1→3)-β-D-GalpNAc-(1→. The immunoreaction between P. circumdentaria LPS and the corresponding antiserum was strongly inhibited by the pentasaccharide fragment (Glc-Gal-Gal-GlcNAc-GalNAc) isolated from partial acid hydrolysis of the above polysaccharide, suggestive of O-antigen specific antibodies in the used antiserum.