A kinetic model of glucose catabolism in Plasmodium falciparum

[摘要] ENGLISH ABSTRACT: Malaria infects over 200 million individuals and leads to the death of over 600000 people annually. Currently artemisinin combination therapy treatmentsare effective in treating the disease, but resistance has started to emerge inCambodia and it is suspected in parts of Vietnam. To maintain the drive toeradicate malaria globally, a great deal of research is aimed at identifying novelprevention strategies, vaccines and antimalarial compounds.Plasmodium falciparum, the most deadly of the malaria parasites, is entirelydependent on glycolysis for ATP. Several of the enzymes within this pathwayhave been proposed as drug targets and studied in isolation, but the pathwayas a whole has not been considered. In this study we employ a bottom upapproach for drug target identification in P. falciparum glycolysis. In this thesis we present the biochemical characterisation each of the glycolyticenzymes in P. falciparum trophozoites. The kinetic rate equations, which describedthe kinetic behaviour of the individual enzymes, were incorporatedinto a kinetic model. The unfitted model was validated in its ability to predictexperimentally measured steady state metabolite concentrations and fluxes aswell as the experimental inhibition of the glucose transporter.The validated model provided a tool for drug target identification in P. falciparumglycolysis. Metabolic control analysis and differential control analysisidentified the glucose transporter, PfHT1, as a drug target based on its highcontrol of glycolytic flux in the parasite, but low control of flux in the hosterythrocyte. This differential control makes the transporter an attractive drugtarget, as even if both the erythrocyte and parasite glucose transporters areinhibited to the same degree, it is expected that the parasite glycolytic fluxwould be inhibited to a much greater degree.To demonstrate the differential control of the glucose transporter on the fluxand provide further evidence that PfHT1 is an attractive drug target, we investigatedthe inhibition of the glucose transporter in isolated trophozoites bycytochalasin B. We also measured the inhibition of lactate production flux bycytochalasin B in both isolated P. falciparum trophozoites as well as in erythrocytes.Our findings demonstrated that differential control analysis can beused as a tool for drug target identification and that PfHT1 is an attractivedrug target.In this study the fields of biochemistry and systems biology were merged tocreate a detailed kinetic model of asexual P. falciparum glycolysis and identifyseveral drug targets in the pathway. The model prediction and experimentalevidence of differential flux control of the glucose transporter in the host andparasite, has highlighted PfHT1 as a drug target and also demonstrates thestrength of differential control analysis in identifying drug targets within asystem. The kinetic model is a valuable tool for furthering our understandingof P. falciparum glycolysis and it provides a good foundation for expansion toidentify drug targets in the entire central carbon metabolism of P. falciparum.

[发布机构] Stellenbosch University