Wrenger Carsten, Müller Sylke
Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, University of Dundee, WTB/MSI Complex, Dundee DD1 5EH, UK.
Mol Microbiol. 2004 Jul;53(1):103-13. doi: 10.1111/j.1365-2958.2004.04112.x.
Lipoic acid is an essential cofactor of alpha-keto acid dehydrogenase complexes (KADHCs). This study shows that Plasmodium falciparum possesses two distinct lipoylation pathways that are found in separate subcellular localizations. Lipoic acid synthesis comprising lipoic acid synthase and lipoyl-ACP:protein N-lipoyl transferase is present in the parasite's apicoplast, whereas the second pathway consisting of lipoic acid protein ligase is located in the parasite's mitochondrion. The two localizations were established by overexpressing green fluorescent protein fusions of the N-terminal sequences of lipoic acid synthase and lipoic acid protein ligase in intraerythrocytic stages of P. falciparum. Northern and Western blot analyses revealed that the genes/proteins encoding lipoic acid synthase, lipoyl-ACP:protein N-lipoyl transferase and lipoic acid protein ligase are expressed maximally in the early and late stages of P. falciparum erythrocytic development. The functionality of the three proteins was proven by complementation of bacteria deficient in lipA and lipB. Our results show that P. falciparum possesses two independent pathways, with different locations, responsible for the post-translational modification of KADHCs. Both pathways fundamentally differ from those in the human host. As KADHCs provide metabolites that are required for essential biosynthetic processes such as fatty acid biosynthesis and haem biosynthesis, the two lipoylation pathways of P. falciparum might be attractive therapeutic targets against malaria.
硫辛酸是α-酮酸脱氢酶复合体（KADHCs）的必需辅因子。本研究表明，恶性疟原虫拥有两条不同的硫辛酸化途径，它们存在于不同的亚细胞定位中。由硫辛酸合酶和脂酰-ACP：蛋白质N-脂酰转移酶组成的硫辛酸合成途径存在于疟原虫的顶质体中，而由硫辛酸蛋白连接酶组成的第二条途径位于疟原虫的线粒体中。通过在恶性疟原虫红细胞内阶段过表达硫辛酸合酶和硫辛酸蛋白连接酶N端序列的绿色荧光蛋白融合体，确定了这两种定位。Northern和Western印迹分析表明，编码硫辛酸合酶、脂酰-ACP：蛋白质N-脂酰转移酶和硫辛酸蛋白连接酶的基因/蛋白在恶性疟原虫红细胞发育的早期和晚期表达最高。通过对lipA和lipB缺陷细菌的互补作用，证明了这三种蛋白质的功能。我们的结果表明，恶性疟原虫拥有两条独立的、位于不同位置的途径，负责KADHCs的翻译后修饰。这两条途径与人类宿主中的途径根本不同。由于KADHCs提供脂肪酸生物合成和血红素生物合成等基本生物合成过程所需的代谢物，恶性疟原虫的两条硫辛酸化途径可能是抗疟疾的有吸引力的治疗靶点。
