The origin of dihydroorotate dehydrogenase genes of kinetoplastids, with special reference to their biological significance and adaptation to anaerobic, parasitic conditions
The origin of dihydroorotate dehydrogenase genes of kinetoplastids, with special reference to their biological significance and adaptation to anaerobic, parasitic conditions
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DOI：
10.1007/s00239-004-0078-8
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发表时间：
2005-01-01
影响因子：
3.9
通讯作者：
Aoki, T
中科院分区：
文献类型：
--
作者：
Annoura, T;Nara, T;Aoki, T
克氏锥虫二氢乳清酸脱氢酶（DHOD）是从头嘧啶生物合成途径的第四种酶，定位于胞质溶胶中并利用延胡索酸作为电子受体（延胡索酸还原酶活性），而来自其他各种真核生物的酶是线粒体膜连接的。在这里，我们报告，DHOD敲除T。Cruzi不表达酶蛋白，并且即使在嘧啶核苷（潜在活性补救途径的底物）存在下也不能存活，这表明富马酸还原酶活性在调节细胞氧化还原平衡中的重要作用。对裸藻DHOD基因的克隆和系统发育分析表明，纤细裸藻（Euglena gracilis）具有线粒体DHOD基因，而动质体内锥虫的姐妹群双鞭毛体虫（biflagellated bodonids）具有胞质DHOD基因。此外，Bodo saliens（一种bodonid）具有ACT/DHOD基因融合体，其编码天冬氨酸氨基甲酰基转移酶（ACT）（从头嘧啶途径的第二种酶）和DHOD。这是首次报道这种新的基因结构。这些结果与真核动物门的一个共同祖先具有线粒体DHOD，其后代存在于真核动物门的推测相一致。gracilis的共同祖先的动质体（bodonids和锥虫）随后获得了细胞质DHOD水平基因转移。因此获得的胞质DHOD基因可能有助于适应厌氧的动质体谱系，并进一步促进了随后建立的寄生在锥虫祖先。动质体和裸藻在嘧啶生物合成中厌氧适应的不同分子策略。讨论了ACT/DHOD基因融合的进化意义进行了讨论。
Trypanosoma cruzi dihydroorotate dehydrogenase (DHOD), the fourth enzyme of the de novo pyrimidine biosynthetic pathway, is localized in the cytosol and utilizes fumarate as electron acceptor (fumarate reductase activity), while the enzyme from other various eukaryotes is mitochondrial membrane-linked. Here we report that DHOD-knockout T. cruzi did not express the enzyme protein and could not survive even in the presence of pyrimidine nucleosides, substrates for the potentially active salvage pathway, suggesting a vital role of fumarate reductase activity in the regulation of cellular redox balance. Cloning and phylogenetic analysis of euglenozoan DHOD genes showed that the euglenoid Euglena gracilis had a mitochondrial DHOD and that biflagellated bodonids, a sister group of trypanosomatids within kinetoplastids, harbor the cytosolic DHOD. Further, Bodo saliens, a bodonid, had an ACT/DHOD gene fusion encoding aspartate carbamoyltransferase (ACT), the second enzyme of the de novo pyrimidine pathway, and DHOD. This is the first report of this novel gene structure. These results are consistent with suggestions that an ancient common ancestor of Euqlenozoa had a mitochondrial DHOD whose descendant exists in E. gracilis and that a common ancestor of kinetoplastids (bodonids and trypanosomatids) subsequently acquired a cytosolic DHOD by horizontal gene transfer. The cytosolic DHOD gene thus acquired may have contributed to adaptation to anaerobiosis in the kinetoplastid lineage and further contributed to the subsequent establishment of parasitism in a trypanosomatid ancestor. Different molecular strategies for anaerobic adaptation in pyrimidine biosynthesis, used by kinetoplastids and by euglenoids. are discussed. Evolutionary implications of the ACT/DHOD gene fusion are also discussed.