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Title: Diversity in the protein N-glycosylation pathways among campylobacter species

item NOTHAFT, HARALD - University Of Alberta
item SCOTT, NICHOLLAS - University Of Sydney
item VINGRADOV, EVGENY - National Research Council - Canada
item LIU, XIN - National Research Council - Canada
item HU, RUI - National Research Council - Canada
item LI, JIANJUN - National Research Council - Canada
item BEADLE, BERNADETTE - University Of Alberta
item FODOR, CHRISTOPHER - University Of Alberta
item Miller, William - Bill
item CORDWELL, STUART - Macquarie University
item SZYMANSKI, CHRISTINE - University Of Alberta

Submitted to: Molecular and Cellular Proteomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2012
Publication Date: 8/2/2012
Citation: Nothaft, H., Scott, N.E., Vingradov, E., Liu, X., Hu, R., Li, J., Beadle, B., Fodor, C., Miller, W.G., Cordwell, S.J., Szymanski, C.M. 2012. Diversity in the protein N-glycosylation pathways among campylobacter species. Molecular and Cellular Proteomics. doi:10.1074/mcp.m112.021519.

Interpretive Summary: Campylobacter strains decorate their outer surface in part through the addition of sugar molecules onto proteins that span the outer membrane. These sugars are synthesized and added as polysaccharides to proteins via the protein glycosylation pathway. Genome analysis of Campylobacter indicated that all campylobacters contain complete protein glycosylation pathways. However, some in some species, the sugars added are heptasaccharides (7 sugar molecules linked) and in other species, two different types of hexasaccharides (6 sugar molecules linked) are added. Two groups of Campylobacter have been identified: campylobacters that grow primarily at the temperature similar to the body temperature of birds (thermotolerant) and those that grow at a temperature similar to the body temperature of humans (non-thermotolerant). The sugars produced by the thermotolerant strains are very similar, whereas those produced by the non-thermotolerant species show a great deal of variety. A byproduct of the protein glycosylation pathway is the release of free polysaccharides into the bacterial periplasm. Antibodies obtained after immunization with these free polysaccharides were able to recognize the protein-sugar conjugates on the bacterial outer surface. Such antibodies could be tentatively used as potential diagnostic tools or vaccines.

Technical Abstract: The foodborne bacterial pathogen, Campylobacter jejuni, possesses an N-linked protein glycosylation (pgl) pathway involved in adding conserved heptasaccharides to asparaginecontaining motifs of >60 proteins, and releasing the same glycan into its periplasm as free oligosaccharides. In this study, comparative genomics of 29 fully sequenced Campylobacter taxa revealed conserved pgl gene clusters in all, but one species. Structural, phylogenetic and immunological studies showed that the N-glycosylation systems could be divided into two major groups. Group I includes all thermotolerant taxa, which typically reside in birds, and produce the C. jejuni-like glycans. Within group I, the niche-adapted C. lari subgroup contains the smallest genome among the epsilonproteobacteria, and have all lost the ability to glucosylate their pgl pathway glycans reminiscent of the glucosyltransferase regression observed in the O-glycosylation system of Neisseria species. The non-thermotolerant campylobacters, which inhabit a variety of hosts and niches, comprise group II and produce an unexpected diversity of N-glycan structures varying in length and composition. This includes the human gut commensal, C. hominis, which is capable of producing at least 3 different N-glycan structures, akin to the surface carbohydrate diversity observed in the well-studied commensal, Bacteroides. Both group I and II glycans are immunogenic and cell surface exposed, making these structures attractive targets for vaccine design and diagnostics. Since the terminal non-reducing sugar residues are the determinants for adaptive and innate immune recognition, we propose that the pressures influencing N-glycan diversity in this genus are related to the natural hosts and niches that each Campylobacter species inhabits.