The Biogenesis and Homeostasis of the Shigella flexneri Cell Envelope

Shigella flexneri is a significant cause of gastroenteric disease in the developing world, predominantly devastating the paediatric age group. This bacterial pathogen synthesises a plethora of polysaccharide-based complexes on its cell surface, such as lipopolysaccharide (LPS), that facilitate host cell adhesion, and influence key immunomodulatory responses. LPS is comprised of three distinct domains including the lipid A endotoxin, a core oligosaccharide, and a highly variable distal polysaccharide termed the O antigen (Oag). Importantly, S. flexneri expresses two distinct variants of the Oag polysaccharide: short-Oag (S-Oag; 10-17 repeat units) and very long-Oag (VL-Oag; > 90 repeat units) through the Wzx/Wzy-dependent pathway. However, the protein interactions required for the biogenesis of these Oag variants, and their relative roles during disease, remain poorly characterised. In this study, we implemented a combination of protein labelling, mutagenesis, and in silico analyses to decipher the molecular interactions between the main protein candidates of the Oag biosynthetic pathway. Specifically, we identified a key disulphide bond within a critical protein-protein interaction domain, and described a new model for VL-Oag LPS synthesis. Furthermore, using a tissue infection model in combination with biochemical analyses we identified that Oag length directly influences the ability of this pathogen to interact with key molecules within its infectious niche. This includes exogenous bile salts and host dietary fatty acids that dramatically affect the cell’s lipid homeostasis, surface glycan decoration, gene expression, morphology and viability. Collectively, this work has provided novel insights in the synthesis of Oag polysaccharides and has established a new role for LPS in Shigella lipid homeostasis. In addition to identifying putative druggable targets, these findings also lay a foundation for dietary lipid intervention strategies to protect susceptible children against this debilitating and potentially lethal pathogen.

Author dc:creator

• Ascari, Alice

Advisors dc:contributor.advisor

• Morona, Renato
• Eijkelkamp, Bart (Flinders University)
• Wilson, Danny

• Shigella flexneri
• Lipopolysaccharide
• O antigen Wzy Polymerase
• Wzz Co-Polymerase
• Lipid Homeostasis
• Fatty Acids
• Bacterial Cell Envelope
• Lipid Droplets

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2440/140565

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/140565