New discoveries in bacterial N-glycosylation to expand the synthetic biology toolbox.

Historically, protein glycosylation was believed to be restricted to eukaryotes, but now is abundantly represented in all three domains of life. The first bacterial N-linked glycosylation system was discovered in the Gram-negative pathogen, Campylobacter jejuni, and subsequently transferred into the heterologous Escherichia coli host beginning a new era of synthetic bacterial glycoengineering. Since then, additional N-glycosylation pathways have been characterized resembling the classical C. jejuni system and unconventional new approaches for N-glycosylation have been uncovered. These include cytoplasmic protein modification, direct glycan transfer to proteins, and use of alternate amino acid acceptors, deepening our understanding of the vast mechanisms bacteria possess for protein modification and providing opportunities to expand the glycoengineering toolbox for designing novel vaccine formulations and protein therapeutics.