Glycobiology of the oral pathogen Porphyromonas gingivalis and related species

• Porphyromonas gingivalis has two types of lipopolysaccharide (O-LPS and A-LPS).
• Type IX secretion substrate proteins bind to anionic O polysaccharide of A-LPS.
• A final product of Wbp pathway may be involved in anionic O polysaccharide of A-LPS.
• Many genes contributing to LPS synthesis have been characterized in P. gingivalis.

Until recently, glycoproteins had only been described in eukaryotes. However, advances in detection methods and genome analyses have allowed the discovery of N-linked or O-linked glycoproteins, similar to those found in eukaryotes, in some bacterial species. These prokaryotic glycoproteins play roles in adhesion, solubility, formation of protein complexes, protection from protein degradation, and changes in antigenicity. Periodontal pathogen Porphyromonas gingivalis secretes virulence proteins via the type IX secretion system, some of which localize on the cell surface by binding to lipopolysaccharide (LPS). These virulence proteins have a conserved C-terminal domain (CTD) region, which is used as a secretion signal. However, it is still uncertain how the secreted proteins on the cell surface bind to LPS. In this review, we discuss the synthesis of P. gingivalis O polysaccharide, which plays a role in anchoring the CTD protein on the cell surface, and recent discoveries of glycoproteins in P. gingivalis as well as other species in the phylum Bacteroidetes.