Schlüsselwörter
(Englisch)
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Apicomplexa; Coccidia; Toxoplasma gondii; methylcitrate cycle; propionyl-CoA
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Forschungsprogramme
(Englisch)
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COST-Action 857 - Apicomplexian Biology in the Post-Genomic Era
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Kurzbeschreibung
(Englisch)
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Comparative analyses of apicomplexan genomes show that coccidian parasites harbour genes encoding a metabolic pathway otherwise only known to occur in bacteria and fungi, the methylcitrate cycle (MCC). The described research project aims to investigate the expression and localisation of MCC enzymes in the human parasite Toxoplasma gondii, to functionally characterise them, and to assess the potential of the MCC pathway as a novel therapeutic drug target.
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Weitere Hinweise und Angaben
(Englisch)
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Full name of research-institution/enterprise: Université de Genève Faculté de médecine Département de microbiologie et de médecine moléculaire
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Partner und Internationale Organisationen
(Englisch)
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AT, CH, CZ, DE, DK, ES, FR, GR, IT, NL, NO, PT, SE, UK
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Abstract
(Englisch)
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Toxoplasma gondii is an obligate intracellular protozoan parasite, which actively enters host cells and thereby leading to the formation of a unique non-phagosomal parasitophorous vacuole (PV). Fast intracellular multiplication of the parasite critically depends on its access to energy and carbon sources, in particular for the extremely high demand on lipids. T. gondii harbours the two types of fatty acid synthesis (FAS) pathways. While glucose converted into phosphoenol pyruvate by the glycolysis is anticipated to serve as carbon source for type II fatty acid biosynthesis (hosted by the apicoplast, a non-photosynthetic plastid organelle), it is unclear what constitutes the source of carbon fuelling the cytosolic FAS I pathway. We hypothesized that host amino acids can be taken up by the parasites and converted into acetyl-CoA and thus serve as carbon source for FAS I and TCA cycle. Consistent with this model we have shown that T. gondii and other members of the coccidi-ans possess the branched-chain amino acid degradation pathway leading to the production of acetyl-CoA in the mitochondrion and an ATP citrate lyase (ACL), capable of converting the citrate produced by the TCA-cycle into acetyl-CoA in the cytosol. Concommitently to the production of acetyl-CoA, the degradation of branched-chain amino acids aslo generates propionyl-CoA, a toxic compound, which inhibits cell growth. To circumvent this problem, the coccidians have retained the 2-methylcitrate cycle (2MC-cycle), a pathway present in fungi and in bacteria and capable of detoxifying propionyl-CoA into pyruvate. We have localized the enzymes of the 2MC-cycle between the mitochondrion and cytosol and obtained biochemical evidence that this pathway is active in the parasite. All attempts to disrupt the enzymes of this pathway were unsuccessful, suggesting that MCC could be essential for parasite survival. We are currently undertaking a conditional approach to disrupt TgPrpD gene to resolve this issue. In a collaborative effort with the group of Dr. N Gupta, we have investigated the importance of sugar transporters for the uptake of carbon and energy sources in T. gondii. Unexpectedly, the glucose transporter TgGT1 is not vital for the parasite, indicating that other transporters such a hexose phosphate transporters (HPT) is likely to fuel glycolysis. However, thus far no HPT has been localized to the parasite surface. In contrast and most intriguingly, T. gondii and the other coccidians possess a very unusual transporter known as INDY (I am not dead yet) previously described in Drosophila melanogaster and corresponding to a cation-independent, electroneutral transporter for tricarboxylic acid-cycle intermediates. Given that TgINDY localizes to the parasite surface, it leads to the provocative hypothesis that the parasite could directly mobilizes the host TCA intermediates as carbon sources for its own benefits during its intracellular replication.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C05.0142
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