Dual targeting of antioxidant and metabolic enzymes to the mitochondrion and the apicoplast of Toxoplasma gondii.
Dual targeting of antioxidant and metabolic enzymes to the mitochondrion and the apicoplast of Toxoplasma gondii.
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DOI：
10.1371/journal.ppat.0030115
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发表时间：
2007-08-31
期刊：
影响因子：
6.7
通讯作者：
Soldati-Favre, Dominique
中科院分区：
文献类型：
--
作者：
Pino, Paco;Foth, Bernardo Javier;Kwok, Lai-Yu;Sheiner, Lilach;Schepers, Rebecca;Soldati, Thierry;Soldati-Favre, Dominique
刚地弓形虫是一种需氧原生动物寄生虫，具有线粒体抗氧化酶，可以安全地处理细胞呼吸和代谢产生的氧自由基。与大多数顶复体一样，它也有一个叶绿体样的细胞器，顶质体，它承载着各种生物合成途径，需要抗氧化保护。大多数顶质体驻留蛋白在核基因组中编码，并通过两部分n端靶向序列靶向细胞器。我们在这里展示了两种抗氧化酶——一种超氧化物歧化酶（TgSOD2）和一种硫氧还蛋白依赖过氧化物酶（TgTPX1/2）——以及一种乌头化酶，它们可以双重靶向弓形虫的顶质体和线粒体。在TgSOD2的案例中，我们的研究结果表明，由于细胞器蛋白的假定信号肽内的不显著变化，单个基因产物是双峰靶向的，这显著改变了其亚细胞定位。在顶复合体中，蛋白质的双细胞器靶向可能经常发生，具有重要的生物功能，如抗氧化保护和碳代谢。刚地弓形虫是顶复虫大类群中人畜致病菌的代表。除了管状线粒体外，这一门的大多数成员还含有第二种内共生细胞器，称为顶质体，这是寄生虫生存所必不可少的。这种非光合质体是几种合成代谢途径的位点，包括脂肪酸、类异戊二烯、铁硫簇和血红素的生物合成。几乎所有在顶质体内活跃的酶都是由核基因组编码的，并通过内质网通过两部分氨基末端识别序列靶向细胞器。顶质体的代谢活动对抗氧化保护提出了很高的要求。我们在这里表明，弓形虫具有一个超氧化物歧化酶和一个过氧化物酶，通过一种不寻常的双峰靶向机制在两个细胞器之间共享，即信号肽的性质影响蛋白质到达两个细胞器的目的地。双重靶向也扩展到其他经典代谢酶，如乌头酸酶，揭示了在这些细胞器中发生的意想不到的代谢途径。因此，在缺乏实验证实的情况下，基于n端序列特征的可塑性或线粒体靶向的生物信息学预测是不够的。
Toxoplasma gondii is an aerobic protozoan parasite that possesses mitochondrial antioxidant enzymes to safely dispose of oxygen radicals generated by cellular respiration and metabolism. As with most Apicomplexans, it also harbors a chloroplast-like organelle, the apicoplast, which hosts various biosynthetic pathways and requires antioxidant protection. Most apicoplast-resident proteins are encoded in the nuclear genome and are targeted to the organelle via a bipartite N-terminal targeting sequence. We show here that two antioxidant enzymes—a superoxide dismutase (TgSOD2) and a thioredoxin-dependent peroxidase (TgTPX1/2)—and an aconitase are dually targeted to both the apicoplast and the mitochondrion of T. gondii. In the case of TgSOD2, our results indicate that a single gene product is bimodally targeted due to an inconspicuous variation within the putative signal peptide of the organellar protein, which significantly alters its subcellular localization. Dual organellar targeting of proteins might occur frequently in Apicomplexans to serve important biological functions such as antioxidant protection and carbon metabolism. Toxoplasma gondii is a human and animal pathogen representative of the large group of Apicomplexa. Most members of this phylum contain, in addition to a tubular mitochondrion, a second endosymbiotic organelle indispensable for parasite survival, called the apicoplast. This non-photosynthetic plastid is the site of several anabolic pathways, including the biosynthesis of fatty acids, isoprenoids, iron-sulphur cluster, and heme. Virtually all enzymes active inside the apicoplast are encoded by the nuclear genome and targeted to the organelle via the endoplasmic reticulum courtesy of a bipartite amino terminal recognition sequence. The metabolic activities of the apicoplast impose a high demand for antioxidant protection. We show here that T. gondii possesses a superoxide dismutase and a peroxidase that are shared between the two organelles by an unusual mechanism of bimodal targeting whereby the nature of the signal peptide influences the destination of the protein to both organelles. Dual targeting also extends to other classical metabolic enzymes such as aconitase, uncovering unexpected metabolic pathways occurring in these organelles. In consequence, the bioinformatic predictions for plastidic or mitochondrial targeting on the basis of the characteristics of N-terminal presequences are insufficient in the absence of an experimental confirmation.