Investigations into aspects of central metabolism in the human malaria parasite Plasmodium falciparum.

UoM administered thesis: Phd

Abstract

AbstractThe University of ManchesterMartin Read Doctor of PhilosophyInvestigations into aspects of central metabolism in the human malaria parasite Plasmodium falciparum. 2011. This thesis combines four published research papers and a book chapter investigating aspects of central metabolism in the human malaria parasite Plasmodium falciparum. The publications are preceded by a statement which explores features of the research not fully described in the published texts, incorporates a review of the development over time and the present state of relevant scientific knowledge, and discusses the place of the individual papers and book chapter within malaria research. An assessment of the impact of each publication on its field of study is also included. A general discussion of the combination of papers as representative of the progress of research into the metabolism of malaria parasites concludes the statement section. The first publication is a chapter from a book, which describes detailed methods for the in vitro cultivation of P. falciparum. Such methodology, both robust and reliable, is a prerequisite for any investigation of parasite metabolism. The following publications are all primary research papers. The second publication describes the isolation and characterisation of the gene encoding the glycolytic pathway enzyme enolase from P. falciparum. The inferred amino acid sequence included peptide insertions found only in the enolases of higher plants and other photosynthetic organisms. This raised implications concerning the deep evolutionary history of the malaria parasite and related species. The third is concerned with the elucidation of the molecular basis of resistance to the antimalarial drug sulfadoxine. Resistance was found to result from point mutations within the dihydropteroate synthetase domain of the bifunctional protein hydroxymethylpterin pyrophosphokinase-dihydroptero¬ate synthetase, an enzyme of the parasite folate pathway. Additionally, it was discovered that the presence of exogenous folate has an antagonistic effect on sulfadoxine in some parasites of a defined genotype. This highlighted the importance of folate salvage in parasite metabolism. Fourth is a paper representing the discovery of a novel metabolism in both P. falciparum and the related apicomplexan parasite Toxoplasma gondii. The use of parasite genes in rescuing an Escherichia coli tyrosine auxotroph resulted in a proof of function of the products of these genes as pterin-4a-carbinolaminedehydratases. Pterin recycling, hitherto undetected in apicomplexans, was therefore added to the known metabolic processes of these organisms. The final paper describes an investigation into the subcellular distribution of the folate pathway enzyme serine hydroxymethyltransferase (SHMT) within P. falciparum erythrocytic stage parasites. The use of confocal laser scanning microscopy and immunofluorescent techniques showed that SHMTc, the sole enzymatically active parasite SHMT protein, was found in the cytoplasm but also showed a stage-specific localisation to both the mitochondrion and apicoplast organelles. The otherwise enigmatic, enzymatically inert, SHMTm paralogue revealed a possible function, when in complex, in allowing targeted localisation of SHMTc to the mitochondrion. The spatial distribution of SHMTm also suggested a possible role in the morphogenesis of elongating apicoplasts during schizogony.

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Original languageEnglish
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    Award date1 Aug 2012