Crawford Michael J, Thomsen-Zieger Nadine, Ray Manisha, Schachtner Joachim, Roos David S, Seeber Frank
Department of Biology, University of Pennsylvania, Philadelphia, USA.
EMBO J. 2006 Jul 12;25(13):3214-22. doi: 10.1038/sj.emboj.7601189. Epub 2006 Jun 15.
In contrast to other eukaryotes, which manufacture lipoic acid, an essential cofactor for several vital dehydrogenase complexes, within the mitochondrion, we show that the plastid (apicoplast) of the obligate intracellular protozoan parasite Toxoplasma gondii is the only site of de novo lipoate synthesis. However, antibodies specific for protein-attached lipoate reveal the presence of lipoylated proteins in both, the apicoplast and the mitochondrion of T. gondii. Cultivation of T. gondii-infected cells in lipoate-deficient medium results in substantially reduced lipoylation of mitochondrial (but not apicoplast) proteins. Addition of exogenous lipoate to the medium can rescue this effect, showing that the parasite scavenges this cofactor from the host. Exposure of T. gondii to lipoate analogues in lipoate-deficient medium leads to growth inhibition, suggesting that T. gondii might be auxotrophic for this cofactor. Phylogenetic analyses reveal the secondary loss of the mitochondrial lipoate synthase gene after the acquisition of the plastid. Our studies thus reveal an unexpected metabolic deficiency in T. gondii and raise the question whether the close interaction of host mitochondria with the parasitophorous vacuole is connected to lipoate supply by the host.
与其他真核生物不同，其他真核生物在线粒体内制造硫辛酸（几种重要脱氢酶复合物的必需辅因子），而我们发现专性细胞内原生动物寄生虫刚地弓形虫的质体（顶质体）是从头合成硫辛酸的唯一场所。然而，针对与蛋白质结合的硫辛酸的特异性抗体显示，在刚地弓形虫的顶质体和线粒体中均存在硫辛酰化蛋白。在硫辛酸缺乏的培养基中培养刚地弓形虫感染的细胞，会导致线粒体（而非顶质体）蛋白的硫辛酰化显著减少。向培养基中添加外源性硫辛酸可以挽救这种效应，表明该寄生虫从宿主中获取这种辅因子。在硫辛酸缺乏的培养基中，让刚地弓形虫接触硫辛酸类似物会导致生长抑制，这表明刚地弓形虫可能对这种辅因子营养缺陷。系统发育分析揭示了在获得质体后线粒体硫辛酸合酶基因的二次丢失。因此，我们的研究揭示了刚地弓形虫中一种意想不到的代谢缺陷，并提出了宿主线粒体与寄生泡的紧密相互作用是否与宿主提供硫辛酸有关的问题。
