Doctor of Philosophy
Microbiology and Immunology
Dr. Carole Creuzenet
Campylobacter jejuni and Helicobacter pylori are phylogenetically related human gastro-intestinal pathogens. C. jejuni colonizes the intestine and is the leading cause of bacterial gastroenteritis worldwide. H. pylori colonizes the stomach of half the world’s population, causing gastritis, gastric ulcers and gastric cancer. Both pathogens express glycoproteins and glycolipids (capsule, lipooligosaccharide or lipopolysaccharide (LPS)) that are important in pathogenesis. Sugar units from capsule or LPS can modify proteins in several bacteria. We reasoned that this may occur in C. jejuni and H. pylori as means to diversify their surface glycosylation and aid in colonization, immune evasion and virulence.
The putative sugar nucleotide dehydratase of C. jejuni NCTC 11168, Cj1319, has predicted roles in initiating the pathway for capsular heptose modification or participating in legionaminic acid synthesis for flagellin glycosylation. Alternatively, we propose that Cj1319 may use the GDP-manno-heptose precursor normally used for capsular heptose modification in a novel protein glycosylation pathway. We determined through enzymatic reactions with GDP-manno-heptose and compositional analysis of capsule from a cj1319 knockout mutant that Cj1319 does not use GDP-manno-heptose and does not affect capsule. Furthermore, our comprehensive mass spectrometry (MS) analysis of flagellin glycopeptides showed that flagellin glycosylation is highly heterogeneous and includes modification by legionaminic acid. We determined that the cj1319 mutant glycosylates flagellins with more legionaminic acid than WT, thus excluding the direct involvement of Cj1319 in legionaminic acid synthesis. This increase in legionaminic acid correlated with higher colonization of chickens but with lower virulence in Galleria mellonella larvae.
H. pylori NCTC 11637 expresses Lewis Y (Ley) blood group mimics in the O-antigen of LPS which is important in immune evasion. We determined that the outer membrane protein HopE is glycosylated with Ley through a comprehensive MS analysis of outer membrane peptides. This novel level of host mimicry is likely important for colonization and pathogenicity.
Zebian, Najwa, "At the interface of glycolipids and glycoproteins in the two gastro-intestinal pathogens Campylobacter jejuni and Helicobacter pylori" (2016). Electronic Thesis and Dissertation Repository. 3710.