title: The origin of dihydroorotate dehydrogenase genes of kinetoplastids, with special reference to their biological significance and adaptation to anaerobic, parasitic conditions.
abstract: 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 Euglenozoa 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.
authors.affiliation: Department of Molecular and Cellular Parasitology, Juntendo University School of Medicine, Hongo 2-1-1, Tokyo 113-8421, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Annoura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nara
authors.forename: Takashi
authors.initials: T
authors.lastname: Makiuchi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Hashimoto
authors.forename: Takashi
authors.initials: T
authors.lastname: Aoki
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D000818:Animals; D001221:Aspartate Carbamoyltransferase / Q000235:genetics; D015153:Blotting, Western; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D000090722:Dihydroorotate Dehydrogenase; D005056:Euglena gracilis / Q000201:enzymology / Q000235:genetics; D019143:Evolution, Molecular; D016830:Kinetoplastida / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D008969:Molecular Sequence Data; D009154:Mutation; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014170:Transformation, Genetic; D014349:Trypanosoma cruzi / Q000201:enzymology / Q000235:genetics
chemical_list: D018076:DNA, Complementary; D000090722:Dihydroorotate Dehydrogenase; D044925:Oxidoreductases Acting on CH-CH Group Donors; D001221:Aspartate Carbamoyltransferase