Eukaryotic Cell doi:10.1128/EC.00061-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Carbohydrate metabolism in the Toxoplasma gondii apicoplast: localization of three glycolytic isoenzymes, the single pyruvate dehydrogenase complex and a plastid phosphate translocator
Tobias Fleige,
Karsten Fischer,
David J.P. Ferguson,
Uwe Gross,
and
Wolfgang Bohne*
Institute of Medical Microbiology, University of Göttingen, Kreuzbergring 57, Göttingen D-37075; GERMANY; Institute for Biology, University of Tromsø, 9037 Tromsø, NORWAY; Nuffield Department of Pathology, University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU; ENGLAND
* To whom correspondence should be addressed. Email:
wbohne{at}gwdg.de.
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Abstract |
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Many apicomplexan parasites such as Toxoplasma gondii and Plasmodium species possess a non-photosynthetic plastid, referred to as the apicoplast, which is essential for parasite viability and displays characteristics similar to those of non-green plastids in plants. In this study, we localized several key enzymes of the carbohydrate metabolism of T. gondii to either the apicoplast or the cytosol by engineering parasites which express epitope tagged fusion proteins. The cytosol contains a complete set of enzymes for glycolysis, which should enable the parasite to metabolize imported glucose into pyruvate. All glycolytic enzymes from phosphofructokinase up to pyruvate kinase are present in the T. gondii genome as duplicates and isoforms of triose phosphate isomerase, phosphoglycerate kinase and pyruvate kinase were found to localize to the apicoplast. The mRNA expression level of all glycolytic genes was compared between tachyzoites and bradyzoites, however, a strict bradyzoite specific expression pattern was only observed for enolase-I. The T. gondii genome encodes a single pyruvate dehydrogenase complex which was located in the apicoplast and absent in the mitochondrion, as shown by targeting of epitope tagged fusion proteins and by immunolocalization of the native pyruvate dehydrogenase complex. Exchange of metabolites between the cytosol and the apicoplast is likely to be mediated by a phosphate translocator which was localized to the apicoplast. Based on these localization studies, a model is proposed that explains the supply of the apicoplast with ATP and reduction power as well as the exchange of metabolites between the cytosol and the apicoplast.
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