The Type III secretion system 'translocation stop' activity of EspZ

Lead Research Organisation: University of Edinburgh
Department Name: The Roslin Institute


Escherichia coli is a bacterium that often inhabits the intestines of warm-blooded animals. Subsets of E. coli have evolved the ability to cause disease. One such group are enterohaemorrhagic E. coli (EHEC), which can cause bloody diarrhoea in humans. Infections can involve life-threatening complications affecting the kidneys and are frequently acquired via the food chain and farm environment from ruminants. Cattle are a major reservoir of EHEC, including the O157:H7 form that has caused serious outbreaks in recent years. Enteropathogenic E. coli (EPEC) are a related subset of bacteria that cause acute watery diarrhoea in infants in the developing world. Both types of E. coli rely on a 'molecular syringe' to colonise the intestines and produce disease. This syringe, encoded by a cluster of genes called the locus of enterocyte effacement (LEE), serves to inject a set of bacterial proteins termed effectors into cells lining the intestines. This process, known as Type III secretion, enables the bacteria to take control of processes inside host cells for their own benefit. Our research has shown that Type III secretion is vital for adherence of EHEC and EPEC to the gut lining and to interfere with the induction of host responses that might otherwise resolve the infection.

To orchestrate host cell pathways, the bacteria must deliver Type III secreted effectors in the required order and amounts. Moreover, it is necessary to control the timing of delivery, and the duration of action and location of effectors inside host cells. Our recent research has indicated that the effector protein EspZ plays an important role in controlling the flow of effector proteins into host cells. It appears to do this only once injected, and host cells that have been engineered to express EspZ are resistant to injection of effectors. Bacteria that lack EspZ cause excessive damage to host cells, likely because they inject effectors at elevated levels. These data suggest that EspZ is a novel natural inhibitor of Type III secretion that may arrest the injection process once it has been delivered into host cells. Our pilot data suggest that EspZ may interact with other LEE-encoded proteins to close the pore created by the syringe, and that it may be modified once it enters host cells. The nature and consequences of interactions between EspZ and other proteins, and of modification of EspZ, are not known. We therefore propose to:

1. Define when EspZ is injected into host cells, and whether targeting of the protein to the host cell membrane coincides with arrest of Type III secretion.
2. Identify proteins that interact with EspZ and determine how such interactions arrest Type III secretion.
3. Define the nature and consequences of modification of EspZ inside host cells.
4. Determine the role of EspZ in bacterial persistence and disease in animal models.

An understanding of how EspZ modulates Type III secretion will aid the rational design of strategies to control EHEC and EPEC infections and carriage by farm animals. Inhibitors of the process may be used to treat infections in humans or reservoir hosts. Moreover, we will explore the possibility of creating transgenic animals that are refractory to infection as a consequence of expression of EspZ in intestinal cells.

Technical Summary

'Attaching & effacing' (AE) E. coli exert a substantial burden on human and animal health and use Type III secretion to colonise intestinal epithelia and induce pathology. The locus of enterocyte effacement (LEE)-encoded Type III secretion system of such pathogens mediates injection of tens of bacterial effectors into enterocytes. These orchestrate cellular pathways in a manner requiring exquisite temporal and spatial control. Our data indicate that the LEE-encoded effector EspZ is modified upon entry into host cells and is integrated into the host cell plasma membrane where it functions as an inhibitor of further effector translocation. Ectopic expression of EspZ in eukaryotic cells renders them refractory to infection, and cells infected with AE pathogens are resistant to super-infection in an EspZ-dependent manner. Bacteria lacking EspZ cause cell damage, likely owing to accumulation of effectors to toxic levels. Our yeast-2-hybrid analysis has indicated that EspZ may interact with a constituent of the translocation pore (EspD), however the molecular mechanism by which it arrests Type III secretion is not known. We propose to define the kinetics of EspZ translocation, its insertion into the host cell plasma membrane and the onset of 'translocation-stop' activity. We will map the protein-protein interaction sites of EspZ and its partner proteins, and determine the role of the partner proteins and interacting residues in its 'translocation-stop' activity. The electrophoretic mobility of EspZ shifts on entry into cells and we propose to define the nature and consequences of post-translational modification. We will also evaluate the impact of mutation and over-espression of espZ on intestinal persistence of enterohaemorrhagic E. coli in calves and Citrobacter rodentium in mice. Unravelling the mode of action of EspZ will have major implications for the design of novel strategies to control infections by pathogenic E. coli.

Planned Impact

Please see Impact Summary and Pathway to Impact submitted by lead applicant (joint ref. M1517309).


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Description This was a joint project with Imperial College London to explore the role of the E. coli O157:H7 type III secreted protein EspZ. The Roslin Institute component (lasting 4 months of the 36 at Imperial College) was completed in 2015. The magnitude and duration of faecal excretion of an espZ mutant of E. coli O157:H7 was compared to the parent strain and a complemented derivative following oral inoculation of calves (n=4 per strain). The results indicated modest but statistically significant attenuation of the espZ mutant in cattle, consistent with a role for EspZ in colonisation of the bovine host. Data will be included in a future publication.

Prof. Frankel and I co-authored a comprehensive review on Type III secretion and effector proteins for the second edition of a respected text on E. coli O157 and other Shiga toxin-producing E. coli (reprinted in Microbiology Spectrum).
Exploitation Route Too early to say.
Sectors Agriculture, Food and Drink,Pharmaceuticals and Medical Biotechnology
Description Collaboration with Professor Gad Frankel, Imperial College London. 
Organisation Imperial College London (ICL)
Department Department of Bioengineering
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution This was a joint project, where Prof. Frankel was the lead Principal Investigator. Our component was to evaluate the phenotype of an espZ mutant of E. coli O157 in cattle relative to the isogenic parent strain.
Collaborator Contribution Provision of strains for testing in cattle.
Impact We anticipate that the data arising from our in vivo studies with the E. coli O157 espZ mutant will be included in a future publication.
Start Year 2011