Investigating the role of N-linked glycosylation system in bacteria

Glycosylation is the most abundant protein post-translational modification found in nature. The attachment of glycans to proteins has been shown to play a central role in modulating protein folding, stability, and signalling. In recent years, it has become evident that glycosylation systems are found in all domains of life. Advances in genomics and mass spectrometry have revealed several types of glycosylation systems in bacteria. However, how and why bacterial proteins are modified remains poorly defined. The aim of this study is to a) investigate the role of general N-linked glycosylation in a major food poisoning bacterium; Campylobacter jejuni b) functionally analyse other N-linked glycosylation systems in deep-sea vent bacteria c) Interrogate the role of other forms of N-linked glycosylation systems in bacteria. This study evaluates the differential protein expression in glycosylation deficient C. jejuni compared to its wildtype counterpart. Thus, enriching our understanding of the role of general N-linked glycans and the pleotropic effects caused by knocking out this post-translational modification. Isobaric labelling mass spectrometry results indicate that protein quality control machineries are more abundant in glycosylation deficient C. jejuni. Also, the major multidrug efflux pump; CmeABC and nitrate reduction assembly; NapAB were shown to be impaired in N-linked glycosylation null C. jejuni. Furthermore, examination of the role of Nlinked glycans in stabilising CmeABC indicated that N-linked glycans modulate protein folding, reduce protein unfolding rate and enhance protein-protein interaction. Computational and functional analysis confirmed the presence and the activity of the oligosaccharyltransferase PglB, of N-linked glycosylation system from deep-sea vent bacteria. Investigating other forms of N-linked glycosylation in the pig pathogen bacterium; Actinobacillus pleuropneumoniae, showed its importance in cell adhesion and pathogenesis. This study provides deeper insights into the roles of N-glycans at the molecular level and enriches our understanding of microbial glycoproteome.