Protein O-glycosyliation in Tannerella and pathogenicity

The anaerobic oral biofilm-forming pathogen Tannerella forsythia (Tf) is one of the main etiological agents of periodontitis. Because of the increasing frequencies with which bacterial glycosylation systems are seen in pathogenic species, they have come under enhanced scrutiny; especially the “sweet” cell envelope of pathogens contributes to their cross-talk with the hosts. Consequently, for the study of virulence mechanisms and the associated development of therapeutic strategies, a molecular understanding of the glycans displayed in the cell envelope of pathogens is necessary. Although a complete genome sequence is available for Tf, relatively little is known about the cell biology and glycobiology of this pathogen. Tf is the only Gram-negative bacterium known to possess a 2D crystalline glycoprotein layer (S-layer) as outermost cell envelope layer. The Tf S-layer is a virulence factor and contributes to delaying the host immune defense. It is evident that the uniqueness of the Tf cell envelope is defined by its glyco-biology (ongoing FWF-project). The S layer is unique in being formed by co-assembly of two different proteins, which are modified with a specific type of complex oligosaccharides a multiple sites. A novel type of rough lipopolysaccharide is predicted to anchor the S-layer glycoprotein assembly to the outer membrane, and the Tf outer membrane is dominated by additional antigenic, high molecular-mass glycoproteins. Some of these as well as the S-layer glycoproteins are up-regulated in the biofilm life-style of Tf. The present research proposal is designed to get insight into the Tf S layer O glycosylation system and its scope at the molecular level. We have evidence that several Tf proteins are modified with this specific S layer O glycan, pinpointing to a glycosylation scenario of general relevance. We hypothesize that the S-layer glycosylation system of Tf affects a wide number of different target proteins and, thus, is of high relevance for the bacterium. Considering the presence of a modified pseudaminic acid residue in the Tf S layer glycan, it is conceivable that this glycan does not only have a demonstrated impact on the bacterium’s life style and, hence, development of periodontal disease, but also is a mediator of pathogenicity. As a way to profile this O glycosylation system to assess its contribution to bacterial pathogenicity, our research goals are: A) molecular characterization of key modules of the Tf S layer protein glycosylation; B) assessment of the influence of cell envelope glycosylation on the immune response elicited against Tf; and C) investigation of the “glyco-impact” on the life style of Tf by analyzing biofilm formation of Tf mutants with defined defects in selected genes of the glycosylation system. Profiling of this general O glycosylation system of Tf at the molecular level and investigating how it affects the physiology of Tf may reveal novel pathogenic strategies in Gram-negative organisms. This, in the future, may constitute new targets for interfering with the pathogen’s ability to establish infection in periodontal disease and for developing of novel diagnostic tools.