Biosynthesis of the N-linked glycan in Campylobacter jejuni and addition onto protein through block transfer

In eukaryotes, N-linked protein glycosylation is a universal modification involving addition of preformed oligosaccharides to select Asn-Xaa-Ser/Thr motifs and influencing multiple biological events. We recently demonstrated that Campylobacter jejuni is the first member of the Bacteria to possess an N-linked glycan pathway. In this study, high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) was applied to probe and quantitate C. jejuni N-glycan biosynthesis in vivo. To confirm HR-MAS NMR findings, glycosylation mutants were screened for chicken colonization potential, and glycoproteins were examined by mass spectrometry and lectin blotting. Consistent with the mechanism in eukaryotes, the combined data indicate that bacterial glycans are assembled en bloc, emphasizing the evolutionary conservation of protein N glycosylation. We also show that under the conditions examined, PglG plays no role in glycan biosynthesis, PglI is the glucosyltransferase and the putative ABC transporter, and WlaB (renamed PglK) is required for glycan assembly. These studies underpin the mechanism of N-linked protein glycosylation in Bacteria and provide a simple model system for investigating protein glycosylation and for exploitation in glycoengineering.