Current Research Projects
- Pathogenesis and Prevention of Pneumococcal DiseaseInvestigators: Prof. James Paton, Dr. David Ogunniyi, Dr. Claudia Trappetti, Dr. Austen Chen, Dr. Richard Harvey, Dr. Lauren McAllister
Streptococcus pneumoniae (the pneumococcus) is a major human respiratory pathogen, causing as many deaths in young children as all bacterial enteric pathogens combined. Global management of pneumococcal disease is complicated by an alarming increase in the prevalence of pneumococci resistant to multiple antibiotics, and the poor clinical efficacy of existing vaccines. This programme has the broad aim of gaining a complete understanding of the molecular mechanism whereby S. pneumoniae invades and damages body tissues, with a view to improving preventative and therapeutic strategies against pneumococcal disease. Experimental approaches include identification and characterization of candidate virulence factors, construction of derivatives of S. pneumoniae with defined mutations in the genes which encode them, and examining the impact on virulence in a mouse model. Other studies involve examination of in vivo alterations in expression of putative virulence factor genes. This information is being used to design and test novel pneumococcal vaccines based on combinations of virulence proteins. Such combination protein vaccines are likely to provide broader protection than the recently released serotype-specific polysaccharide-protein conjugate vaccines. Moreover, they will be vastly cheaper to produce, thereby enabling deployment in third world countries, where the need for effective pneumococcal vaccines is greatest.
- Shiga toxigenic Escherichia coli (STEC) and biology of AB5 toxinsInvestigators: Prof. Adrienne Paton, Prof. James Paton, Dr. Hui Wang
Shiga toxin-producing strains of E. coli (STEC) are known to cause serious gastrointestinal disease in humans, with potentially life-threatening complications such as haemolytic uraemic syndrome (HUS). Prof Adrienne Paton is directing an extensive STEC research program, involving characterisation of novel virulence factors to determine their precise contribution to the pathogenesis of disease.
A major achievement has been the discovery of Subtilase cytotoxin (SubAB), the prototype of a new AB5 cytotoxin family - the first in over 30 years. SubAB is produced by hyper-virulent STEC strains; it is 10-100 times more potent than Shiga toxin and is a potential bioterrorism agent. Its toxicity is due to subtilase-like serine protease activity of its A subunit (SubA). The extreme cytotoxicity of SubAB for eukaryotic cells is due to a specific single-site cleavage of the essential endoplasmic reticulum (ER) chaperone BiP. Structural analysis of SubA revealed an unusually deep active site cleft, accounting for this exquisite specificity. The extraordinary specificity of SubAB makes it a powerful cell biological tool, and numerous collaborations have been established to investigate its utility for probing the role of ER stress in diverse cellular processes and the potential of SubAB as an anti-tumour agent.
We have also shown that SubB targets glycans terminating in N-glycolylneuraminic acid (Neu5Gc). The crystal structures of SubB-Neu5Gc complexes revealed the basis for this specificity, and identified the glycan binding pocket, opening the way for development of small molecule inhibitors. Humans should be genetically resistant to the toxin, as they are deficient in Neu5Gc synthesis. However, assimilation of Neu5Gc from dietary sources enables expression of high-affinity receptors on the surface of human cells, thereby conferring susceptibility to the lethal effects of SubAB. Ironically, foods that are rich sources of Neu5Gc (red meat and dairy products) are also the commonest source of STEC contamination. This represents an unusual paradigm of bacterial pathogenesis, whereby humans directly contribute to disease through dietary choices, simultaneously exposing themselves to STEC and sensitising their tissues to a key virulence factor. Interestingly, Neu5Gc is known to be displayed on the surface of many human cancers and recent research has shown that SubB can be used to detect Neu5Gc in human serum, which is a highly specific marker for metastasis; SubB can also be used to delineate tumour margins in tissue sections, pointing to the potential for using appropriately tagged SubB for direct tumour imaging in vivo.
- Receptor Mimic TechnologyInvestigators: Prof. Adrienne Paton, Assoc. Prof. Renato Morona, Prof. James Paton
Receptor Mimic Technology involves development of a novel anti-infective strategy based on recombinant probiotics expressing mimics of host receptors for toxins, bacterial adhesins or viruses on their surface. These “designer probiotics” bind toxins or the pathogens themselves with high avidity, and have great potential for treatment of a wide range of gastrointestinal infections in humans and domestic animals. We have already developed probiotics capable of preventing STEC disease, travellers’ diarrhoea and cholera, and we are now directing our attention at other important enteric pathogens including rotavirus and Clostridium difficile.