Glycosylation of the Aeromonas caviae polar flagellum

The bacterial flagellum is an important appendage at the bacterial cell surface, not only for motility, but for adherence to host cells, and therefore has an extensive role in bacterial colonisation and virulence. A number of pathogenic bacteria modify their flagellins with nonulosonic acids, such as Aeromonas, Campylobacter and Helicobacter species, via an O-linked glycosylation process. This modification is essential for their ability to form flagella, thus having implications in pathogen virulence. However, the role of flagellin glycosylation is currently undetermined.
The mesophilic aeromonad, Aeromonas caviae, forms a constitutively expressed polar flagellum necessary for motility in liquid environments. It is thought to be a good model for glycosylation as it decorates its flagellins solely with pseudaminic acid, and contains a genetically simple system for this process to occur. The work in this thesis has explored the pathway, and role of flagellin glycosylation in this microorganism.
The function of a putative deglycosylation enzyme (AHA0618) and its possible role in the fine tuning of flagellin glycosylation was examined, where it was concluded that this protein is likely to be involved in peptidoglycan crosslinking at the cell wall, and not the flagellin glycosylation pathway. This demonstrates that subtle changes to bacterial cellular morphology are able to affect bacterial behaviour.
Additionally, investigations into the sites of flagellin glycosylation via mass spectrometric methods concluded that the sites of modification on A. caviae flagellins can vary. However, certain residues were found to be predominantly glycosylated, suggesting partial selectivity to the glycosylation process via the putative glycosyltransferase, Maf1.
Finally, protein interaction studies have provided evidence that glycosylation is likely to occur in the cytoplasm before binding of the flagellin-specific chaperone and flagellin export. Moreover, Maf specificity investigations, together with these interaction studies have suggested that the Maf proteins may be recognising and docking to the N-terminal region of the flagellins.