East-Asian Helicobacter pylori strains synthesize heptan-deficient lipopolysaccharide

The lipopolysaccharide O-antigen structure expressed by the European Helicobacter pylori model strain G27 encompasses a trisaccharide, an intervening glucan-heptan and distal Lewis antigens that promote immune escape. However, several gaps still remain in the corresponding biosynthetic pathway. Here, systematic mutagenesis of glycosyltransferase genes in G27 combined with lipopolysaccharide structural analysis, uncovered HP0102 as the trisaccharide fucosyltransferase, HP1283 as the heptan transferase, and HP1578 as the GlcNAc transferase that initiates the synthesis of Lewis antigens onto the heptan motif. Comparative genomic analysis of G27 lipopolysaccharide biosynthetic genes in strains of different ethnic origin revealed that East-Asian strains lack the HP1283/HP1578 genes but contain an additional copy of HP1105 and JHP0562. Further correlation of different lipopolysaccharide structures with corresponding gene contents led us to propose that the second copy of HP1105 and the JHP0562 may function as the GlcNAc and Gal transferase, respectively, to initiate synthesis of the Lewis antigen onto the Glc-Trio-Core in East-Asian strains lacking the HP1283/HP1578 genes. In view of the high gastric cancer rate in East Asia, the absence of the HP1283/HP1578 genes in East-Asian H. pylori strains warrants future studies addressing the role of the lipopolysaccharide heptan in pathogenesis. Author summary The human gastric pathogen Helicobacter pylori is the most important aetiological factor for gastric cancer. H. pylori lipopolysaccharide, a major bacterial surface molecule, plays essential roles in host-pathogen interactions. Due to the scattered organisation of the lipopolysaccharide genes in its genome, several key enzymes involved in H. pylori lipopolysaccharide biosynthesis remain to be identified. Here, through systematic mutagenesis of glycosyltransferase genes in the model strain G27 combined with lipopolysaccharide structural analysis, we identified novel glycosyltransferases and established the first complete lipopolysaccharide biosynthetic pathway in G27. Furthermore, we analysed the conservation of the lipopolysaccharide genes across a large panel of H. pylori strains and demonstrated that many of the lipopolysaccharide genes are highly conserved, whereas the genes involved in lipopolysaccharide heptan incorporation are lacking in East-Asian strains. Finally, based on the correlation of lipopolysaccharide structure and gene contents in specific strains, we proposed a lipopolysaccharide biosynthetic model of how East-Asian strains, missing the heptan moiety, attach Lewis antigens onto the conserved Glc-Trio-Core. Future studies are needed to address whether the lack of heptan in lipopolysaccharide of East-Asian H. pylori strains is related to the high gastric cancer rate in East Asia, accounting for almost half of the worldwide gastric cancer cases.