Terpenoid inhibition of DsbA : a periplasmic protein from the dysentery-causing bacterium, Shigella sonnei

  • Thaer Abdullah Hasan Hasan

Student thesis: Doctoral Thesis

Abstract

A major challenge faced by modern medicine is antimicrobial resistance that has become a major problem in recent year. As such, there is a requirement for the introduction of alternative approaches to treat infections of multi-resistant strains of bacillary dysentery-caused by Shigella sonnei. DsbA is a disulphide bond oxidoreductase enzyme and is a major contributor to virulence in S. sonnei. It is a periplasmic protein required for Shigella survival in the host cell cytosol. DsbA is found in all Gram-negative and some Gram-positive bacteria, therefore, targeting DsbA is a logical strategy to treat dysentery-causing Shigella. Here we show that terpenoids, natural substances present in the essential oils of plants, can reduce S.sonnei proliferation inside host cells. Terpenoids exert little cytotoxicity on the cell lines and protected Galleria mellonella larvae from killing by S. sonnei. Geraniol was the most potent compound from the twelve terpenoids tested in this study. In addition, the study confirmed that DsbA is vital for S. sonnei to survive and proliferate in a reducing environment. Geraniol was able to reduce the activity of purified DsbA protein on reduction of Di-E-GSSG in an in vitro assay. Importantly, this study also showed that S. sonnei could catalyse E-GSH conversion to Di-E-GSSG through DsbA activity. This finding explained for the first time a novel mechanism used by S. sonneiin recycling non-functional reduced DsbA to its functional oxidised form. Moreover, geraniol was also able to inhibit the catalysis of E-GSH to around half of the wild type DsbA activity in S. sonnei. Geraniol became completely inactive when its interaction sites were substituted on DsbA, and it was unable to protect Galleria mellonella from killing by S. sonnei dsbA mutants. These findings suggest that geraniol holds a great therapeutic potential against Shigella infection.
Date of Award19 Sep 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorPaul Herron (Supervisor) & Veronique Seidel (Supervisor)

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