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Title: Histidine and Lysine amino acid biosyntheis as antimicrobial targets in Acanthamoeba species
Author: Rice, Christopher Aaron
Awarding Body: University of the West of Scotland
Current Institution: University of the West of Scotland
Date of Award: 2013
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Acanthamoeba species have been found to be facultative, opportunistic, protozoan, parasites. They are found ubiquitously in the environment. Acanthamoeba species are emerging pathogens causing a severe corneal infection called Acanthamoeba keratitis (AK) in immunocompetent individuals normally associated with contact lens wearers, which may result in blindness. Many drugs used to treat Acanthamoeba infections are poorly effective because they can induce encystation and/or fail to eliminate cysts, so more reliable and effective therapies are required. To this end, the studies described herein demonstrate the ability of Acanthamoeba unlike its mammalian host to synthesise histidine and lysine. Thus growth of Acanthamoeba spp. was restricted by 3-amino-1, 2, 4-triazole (3AT) (IC50 125μM), an inhibitor of imidazoleglycerol-phosphate dehydratase (IGPD) (EC a key enzyme for de novo histidine biosynthesis. The addition of histidine was able to ablate the effects of 3AT in a dose dependent manner when added to cultures, indicating that 3AT was specifically acting on histidine biosynthesis. 3AT had minimal cytotoxicity to a prostate cancer cell line (PC3-luc) at concentrations that restrict the growth of Acanthamoeba. Bioinformatic analysis demonstrated that Acanthamoeba has the full complement of enzymes necessary for histidine biosynthesis. The complete coding sequence for a novel multifunctional gene, histidinol dehydrogenase (EC and IGPD (EC have both been amplified from A. castellanii and A. polyphaga cDNA, both have been cloned and sequenced. The gene encoding histidinol dehydrogenase from Acanthamoeba has been found to encode several enzymes including imidazoleglycerol phosphate synthase, phosphoribosyl-formimino-5-amino-1-imidazole-carboxyamide ribotide isomerase, phosphoribosyl-AMP cyclohydrolase, phosphoribosyl-ATP pyrophosphatase, histidinol dehydrogenase and ATP Phosphoribosyltransferase. An experimental compound (C348) previously demonstrated to inhibit IGPD of plant species was found to restrict the growth of Acanthamoeba (IC50 305nM). This inhibition was also ablated with the addition of exogenous histidine when added to the medium. C348 showed no cytotoxicity effects to the PC3-luc at concentrations restricting the growth of Acanthamoeba species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available