title: Broad distribution of TPI-GAPDH fusion proteins among eukaryotes: evidence for glycolytic reactions in the mitochondrion?
abstract: Glycolysis is a central metabolic pathway in eukaryotic and prokaryotic cells. In eukaryotes, the textbook view is that glycolysis occurs in the cytosol. However, fusion proteins comprised of two glycolytic enzymes, triosephosphate isomerase (TPI) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were found in members of the stramenopiles (diatoms and oomycetes) and shown to possess amino-terminal mitochondrial targeting signals. Here we show that mitochondrial TPI-GAPDH fusion protein genes are widely spread across the known diversity of stramenopiles, including non-photosynthetic species (Bicosoeca sp. and Blastocystis hominis). We also show that TPI-GAPDH fusion genes exist in three cercozoan taxa (Paulinella chromatophora, Thaumatomastix sp. and Mataza hastifera) and an apusozoan protist, Thecamonas trahens. Interestingly, subcellular localization predictions for other glycolytic enzymes in stramenopiles and a cercozoan show that a significant fraction of the glycolytic enzymes in these species have mitochondrial-targeted isoforms. These results suggest that part of the glycolytic pathway occurs inside mitochondria in these organisms, broadening our knowledge of the diversity of mitochondrial metabolism of protists.
authors.affiliation: Department of Biochemistry & Molecular Biology, Canadian Institute for Advanced Research, Program in Integrated Microbial Biodiversity, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Takuro
authors.initials: T
authors.lastname: Nakayama
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Ishida
authors.forename: John M
authors.initials: JM
authors.lastname: Archibald
mesh_terms: D016844:Blastocystis / Q000378:metabolism; D056907:Cercozoa / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics / Q000378:metabolism*; D006019:Glycolysis / Q000235:genetics / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D032126:Paullinia / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D014305:Triose-Phosphate Isomerase / Q000235:genetics / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D014305:Triose-Phosphate Isomerase