Characterising A/E pathogens’ Type III secretion system effector proteins

Abstract

The human diarrhoeal pathogens enteropathogenic Escherichia coli, enterohaemorrhagic E. coli and their murine analogue Citrobacter rodentium are a family of enteric bacteria that cause characteristic attaching and effacing lesions at the site of intestinal colonisation. Lesion formation and successful infection depends on a Type III Secretion System and its cognate effector proteins. Once translocated into the host cytosol, effectors subvert several mammalian cell processes to create and maintain an infectious niche. With the advent of high-throughput screening techniques, the rate of effector discovery has surpassed their biochemical investigation. This work therefore explores the function of seven effectors, three uncharacterised and four previously described. Through machine learning algorithms, two completely novel C. rodentium effectors were identified and designated NleN and NleO. While nleN encodes a truncation of a conserved effector, NleO disrupts the host cytoskeleton by binding and cleaving the Rho GTPase Rac1 at a unique scission site. A third C. rodentium effector, EspS, which has previously demonstrated to modulate intestinal pathology, binds the host mitochondrial protein TRIAP1 and contributes to the remodelling of host lipids during infection of C57Bl/6 mice. Finally, the contribution of EspZ, TccP, EspT and NleG to the recently described pyroptotic cell death pathway in human macrophages is explored. The findings presented herein contribute to the ever-growing repertoire of effector protein knowledge and underscore the importance of studying effector synergy during infection.