Characterisation of autotransporter genes carried on the she pathogenicity island of Shigella flexneri

Research output: ThesisDoctoral Thesis

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Abstract

[Truncated abstract] This work aimed to study two distinct autotransporter proteins encoded on the she pathogenicity island in S. flexneri 2a, designated SigA and Sap respectively. The first aim was to investigate the structure-function relationship of SigA, an autotransporter protease capable of degrading casein and α-fodrin, and which is cytotoxic to HEp-2 epithelial cells (Al-Hasani et al., 2000; Al-Hasani et al., 2009). Bioinformatic analysis suggested that the secreted α domain of SigA may be further derived into two subdomains, termed α1 and α2. It was hypothesised that the α1-subdomain is a proteolytic domain as it contains a putative serine protease motif (G256DSGSGS) (Al-Hasani et al., 2000). The hypothetical α2-subdomain, in contrast, shares low but significant sequence similarity to pertactin, suggesting that it may act as a cell-binding domain that targets SigA to the epithelial cell surface. Consistent with these hypotheses, we have successfully demonstrated that α1, when isolated from α2, was capable of degrading casein and that α2 protein bound specifically to HEp-2 epithelial cells, showing that SigA consists of two functionally distinct domains specifying cytotoxic protease (α1) and epithelial cell binding (α2) activities. The second aim of this study was to characterise the functional properties of Sap, which displays a high level of sequence similarity and identity to the Ag43 autotransporter of E. coli K12 and a family of sequence variants found in both commensal and pathogenic strains of E. coli. Members of the Ag43 family variously mediate biofilm formation, bacterial autoaggregation and bacterial adherence to epithelial cells. Like Ag43, Sap mediates biofilm formation in S. flexneri, but no other functions have been attributed to it. Experiments were therefore performed to investigate the ability of Sap to mediate bacterial autoaggregation and adherence to colonic epithelial cells.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2011

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