Helicobacter pylori infects more than half of the global population and causes gastric disorders. The increasing development of antibiotic resistance by the bacterium continues to limit treatment options. The identification and characterisation of novel therapeutic targets are necessary for successful future treatment of the infection. One potential target for therapeutic intervention is the gpt gene encoded by hp0735 (jhp0672) in H. pylori strain 26695 (J99). This gene produces a putative xanthine-guanine phosphoribosyltransferase (XGPRTase), an enzyme of the purine salvage synthesis pathway. This project employed theoretical, molecular and biochemical approaches to investigate features of H. pylori gpt and XGPRTase that will serve to ascertain their therapeutic potential. The production of a functional XGPRTase by H. pylori was investigated in cell-free extracts, and the kinetic parameters of this activity were compared to those of purified rXGPRTase enzyme. The three 6-oxopurine substrates were recognised by rXGPRTase and allosteric kinetics were observed for some substrates of the enzyme in cell-free extracts and for purified enzyme. These observations indicate complex regulation and an influence of cellular interactions on activity. Bioinformatics were employed to analyse XGPRTase phylogeny, and threading techniques used to build a structural model of XGPRTase. The enzyme is significantly divergent from the equivalent mammalian enzyme, and modelling identified specific features of the enzyme. Molecular approaches were utilised to analyse the essential role of gpt in H. pylori survival. These included insertional inactivation of the gpt in wild-type H. pylori strains and in mutants possessing a complementing copy of the gene present at the rdxA locus. No mutants were recovered with inactivated gpt possibly as a result of pleiotropic effects. Plasmid-mediated complementation was attempted employing IPTG-inducible shuttle vectors and did not yield any mutants. Further characterisation of H. pylori XGPRTase was performed by determining the effects of nucleotide monophosphates and purine analogues on enzyme activity. Inhibition by GMP was observed in all cases, however differences in the inhibition by other nucleotide monophosphates were found between cell-free extracts and the recombinant enzyme. Inhibition of rXGPRTase activity was observed by the purine analogue 6-mercaptopurine ribose, a compound that previously has been shown to inhibit H. pylori growth in culture.
| Identifer | oai:union.ndltd.org:ADTP/257819 |
| Date | January 2008 |
| Creators | Duckworth, Megan Jane, Medical Sciences, Faculty of Medicine, UNSW |
| Publisher | Publisher:University of New South Wales. Medical Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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