Heme biosynthesis by the malarial parasite - Import of delta-aminolevulinate dehydrase from the host red cell
Heme biosynthesis by the malarial parasite - Import of delta-aminolevulinate dehydrase from the host red cell
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DOI：
10.1074/jbc.272.35.21839
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发表时间：
1997-08-29
影响因子：
4.8
通讯作者：
Padmanaban, G
中科院分区：
文献类型：
--
作者：
Bonday, ZQ;Taketani, S;Padmanaban, G
小鼠和人类疟原虫伯氏疟原虫（Plasmodium berghei）和恶性疟原虫（Plasmodium falciparum）分别按照在动物中观察到的标准途径重新合成血红素，尽管红细胞血红蛋白中有大量的血红素，这些血红素以血红素色素的形式储存。伯氏疟原虫感染的小鼠红细胞中，δ -氨基乙酰酸脱氢酶（ALAD）、同比例卟啉原氧化酶和铁螯合酶的含量惊人地高。分离的寄生虫具有低水平的ALAD，数据清楚地表明它是红细胞起源。从未感染的红细胞中纯化的酶制剂和寄生虫在动力学性质、亚基分子量、与人酶抗体的交叉反应和n端氨基酸序列上是相同的。感染培养物的免疫金电镜显示，该酶存在于寄生虫体内，因此不是一种污染物。寄生虫从宿主体内获得功能性的ALAD，该酶在体外特异性地与分离的寄生虫膜结合，这表明ALAD在其转运到寄生虫体内时参与了一种受体。在sds -聚丙烯酰胺凝胶电泳上，来自寄生虫的铁螯合酶与未感染的红细胞上清具有相同的亚基分子量，并与人酶抗体发生免疫学交叉反应，Western分析显示，该途径的第一个酶，即δ氨基乙酰酸合成酶（ALAS），与红细胞宿主不同，不与人酶抗体发生交叉反应。寄生虫的ALAS酶活性高于被感染的红细胞上清。因此，我们得出结论，寄生虫在制造自己的ALAS的同时，从宿主进口ALAD和可能是该途径的大多数其他酶来重新合成血红素，这将使其能够从红细胞血红蛋白降解产生的血红素中分离出这种血红素，寄生虫的ALAS和参与宿主酶转运到寄生虫中的受体将是独特的药物靶点。
The mouse and human malarial parasites, Plasmodium berghei and Plasmodium falciparum, respectively, synthesize heme de novo following the standard pathway observed in animals despite the availability of large amounts of heme, derived from red cell hemoglobin, which is stored as hemozoin pigment, The enzymes, delta-aminolevulinate dehydrase (ALAD), coproporphyrinogen oxidase, and ferrochelatase are present at strikingly high levels in the P, berghei infected mouse red cell in vivo, The isolated parasite has low levels of ALAD and the data clearly indicate it to be of red cell origin. The purified enzyme preparations from the uninfected red cell and the parasite are identical in kinetic properties, subunit molecular weight, cross-reaction with antibodies to the human enzyme, and N-terminal amino acid sequence. Immunogold electron microscopy of the infected culture indicates that the enzyme is present inside the parasite and, therefore, is not a contaminant, The parasite derives functional ALAD from the host and the enzyme binds specifically to isolated parasite membrane in vitro, suggestive of the involvement of a receptor in its translocation into the parasite, While, ALAD, coproporphyrinogen oxidase, and ferrochelatase from the parasite and the uninfected red cell supernatant have identical subunit molecular weights on SDS-polyacrylamide gel electrophoresis and show immunological cross-reaction with antibodies to the human enzymes, as revealed by Western analysis, the first enzyme of the pathway, namely, delta-aminolevulinate synthase (ALAS) in the parasite, unlike that of the red cell host, does not cross-react with antibodies to the human enzyme, However, ALAS enzyme activity in the parasite is higher than that of the infected red cell supernatant. We therefore conclude that the parasite, while making its own ALAS, imports ALAD and perhaps most of the other enzymes of the pathway from the host to synthesize heme de novo, and this would enable it to segregate this heme from the heme derived from red cell hemoglobin degradation, ALAS of the parasite and the receptor(s) involved in the translocation of the host enzymes into the parasite would be unique drug targets.