title: A broad distribution of the alternative oxidase in microsporidian parasites.
abstract: Microsporidia are a group of obligate intracellular parasitic eukaryotes that were considered to be amitochondriate until the recent discovery of highly reduced mitochondrial organelles called mitosomes. Analysis of the complete genome of Encephalitozoon cuniculi revealed a highly reduced set of proteins in the organelle, mostly related to the assembly of iron-sulphur clusters. Oxidative phosphorylation and the Krebs cycle proteins were absent, in keeping with the notion that the microsporidia and their mitosomes are anaerobic, as is the case for other mitosome bearing eukaryotes, such as Giardia. Here we provide evidence opening the possibility that mitosomes in a number of microsporidian lineages are not completely anaerobic. Specifically, we have identified and characterized a gene encoding the alternative oxidase (AOX), a typically mitochondrial terminal oxidase in eukaryotes, in the genomes of several distantly related microsporidian species, even though this gene is absent from the complete genome of E. cuniculi. In order to confirm that these genes encode functional proteins, AOX genes from both A. locustae and T. hominis were over-expressed in E. coli and AOX activity measured spectrophotometrically using ubiquinol-1 (UQ-1) as substrate. Both A. locustae and T. hominis AOX proteins reduced UQ-1 in a cyanide and antimycin-resistant manner that was sensitive to ascofuranone, a potent inhibitor of the trypanosomal AOX. The physiological role of AOX microsporidia may be to reoxidise reducing equivalents produced by glycolysis, in a manner comparable to that observed in trypanosomes.
authors.affiliation: School of Biosciences, Geoffrey Pope Building, University of Exeter, Exeter, Devon, United Kingdom.
authors.forename: Bryony A P
authors.initials: BA
authors.lastname: Williams
authors.forename: Catherine
authors.initials: C
authors.lastname: Elliot
authors.forename: Lena
authors.initials: L
authors.lastname: Burri
authors.forename: Yasutoshi
authors.initials: Y
authors.lastname: Kido
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kita
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Moore
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Keeling
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D005800:Genes, Fungal; D016814:Microsporidia / Q000201:enzymology* / Q000235:genetics*; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D010088:Oxidoreductases; D010802:Phylogeny; D010940:Plant Proteins; D016133:Polymerase Chain Reaction; D000099188:Alternative Oxidase
chemical_list: D005656:Fungal Proteins; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase