Discussion

Clostridium difficile is the most common cause of antibiotic-associated intestinal infections in humans and a significant cause of morbidity and mortality worldwide. C. difficile infection (CDI) results from gut dysbiosis, typically caused by antibiotic therapy and clinical symptoms are largely attributed to the well studied toxins. Other aspects of the unique C. difficile pathobiology, such as sporulation and colonisation of the gut, are still poorly understood and we aim at elucidating them at the atomic level, with a focus on surface and spore formation proteins. C. difficile possess a paracrystalline proteinaceous surface layer (S-layer) that has been implicated in adherence to host tissues and activation of innate, inflammatory responses in vitro and is therefore a unique therapeutic target. Structure determination of SlpA, the main S-layer protein, is ongoing. Type IV Pili (TFP) are associated with cell-surface adhesion, motility and biofilm formation, providing another therapeutic avenue. In order to further understand TFP in C. difficile, we have been dissecting the atomic structure of the major and minor pilins and the interactions that allow the assembly of the pilus. Spores are the primary infective agent and represent an attractive target for intervention. One of the critical stages of sporulation is engulfment, during which the mother cell membrane envelops the newly formed forespore. Our work has focused on characterising two key complexes required for effective engulfment - the SpoIIQ:SpoIIIAH putative channel and the SpoIID/M/P machinery - and their potential activity as peptidoglycan remodelling enzymes. A brief overview of our research, which combines structural biology, biochemical/biophysical characterisation and microbiology to provide a detailed understanding of these potential therapeutic targets, will be presented.