Carbohydrate metabolism in the Toxoplasma gondii apicoplast:: Localization of three glycolytic isoenzymes, the single pyruvate dehydrogenase complex, and a plastid phosphate translocator
Carbohydrate metabolism in the Toxoplasma gondii apicoplast:: Localization of three glycolytic isoenzymes, the single pyruvate dehydrogenase complex, and a plastid phosphate translocator
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DOI：
10.1128/ec.00061-07
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发表时间：
2007-06-01
期刊：
影响因子：
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通讯作者：
Bohne, Wolfgang
中科院分区：
文献类型：
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作者：
Fleige, Tobias;Fischer, Karsten;Bohne, Wolfgang
许多顶复门寄生虫，例如弓形虫和疟原虫物种，都具有非光合质体，称为顶质体，它对于寄生虫的生存能力至关重要，并表现出与植物中非绿色质体相似的特征。在这项研究中，我们通过工程改造表达表位标记融合蛋白的寄生虫，将弓形虫碳水化合物代谢的几种关键酶定位到顶质体或细胞质。胞质溶胶含有一整套糖酵解酶，这将使寄生虫能够将输入的葡萄糖代谢为丙酮酸。所有糖酵解酶，从磷酸果糖激酶到丙酮酸激酶，都存在于弓形虫基因组中，因为磷酸丙糖异构酶、磷酸甘油酸激酶和丙酮酸激酶的重复物和亚型被发现定位于顶质体。比较速殖子和缓殖子所有糖酵解产物基因的mRNA表达水平；然而，仅针对烯醇化酶 I 观察到严格的缓殖子特异性表达模式。弓形虫基因组编码单个丙酮酸脱氢酶复合物，该复合物位于顶质体中，而在线粒体中不存在，如表位标记融合蛋白的靶向和天然丙酮酸脱氢酶复合物的免疫定位所示。细胞质和顶质体之间代谢物的交换可能是由定位于顶质体的磷酸盐易位蛋白介导的。基于这些定位研究，提出了一个模型来解释顶质体的 ATP 供应和还原能力，以及细胞质和顶质体之间代谢物的交换。
Many apicomplexan parasites, such as Toxoplasma gondii and Plasmodium species, possess a nonphotosynthetic plastid, referred to as the apicoplast, which is essential for the parasites' viability and displays characteristics similar to those of nongreen 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 the 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 levels of all genes with glycolytic products were compared between tachyzoites and bradyzoites; however, a strict bradyzoite-specific expression pattern was observed only 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. The 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 the reduction power, as well as the exchange of metabolites between the cytosol and the apicoplast.