Glycoengineering of host mimicking type‐2 LacNAc polymers and L ewis X antigens on bacterial cell surfaces

Bacterial carbohydrate structures play a central role in mediating a variety of host–pathogen interactions. Glycans can either elicit protective immune response or lead to escape of immune surveillance by mimicking host structures. Lipopolysaccharide ( LPS ), a major component on the surface of G ram‐negative bacteria, is composed of a lipid A ‐core and the O ‐antigen polysaccharide. Pathogens like N eisseria meningitidis expose a lipooligosaccharide ( LOS ), which outermost glycans mimick mammalian epitopes to avoid immune recognition. L ewis X ( G alβ1–4( F ucα1–3) GlcNAc ) antigens of H elicobacter pylori or of the helminth S chistosoma mansoni modulate the immune response by interacting with receptors on human dendritic cells. In a glycoengineering approach we generate human carbohydrate structures on the surface of recombinant G ram‐negative bacteria, such as E scherichia coli and S almonella enterica sv. T yphimurium that lack O ‐antigen. A ubiquitous building block in mammalian N ‐linked protein glycans is G alβ1‐4 GlcNAc , referred to as a type‐2 N ‐acetyllactosamine, LacNAc , sequence. Strains displaying polymeric LacNAc were generated by introducing a combination of glycosyltransferases that act on modified lipid A ‐cores, resulting in efficient expression of the carbohydrate epitope on bacterial cell surfaces. The poly‐ LacNAc scaffold was used as an acceptor for fucosylation leading to polymers of L ewis X antigens. We analysed the distribution of the carbohydrate epitopes by FACS , microscopy and ELISA and confirmed engineered LOS containing LacNAc and L ewis X repeats by MALDI‐TOF and NMR analysis. Glycoengineered LOS induced pro‐inflammatory response in murine dendritic cells. These bacterial strains can thus serve as tools to analyse the role of defined carbohydrate structures in different biological processes.