title: A functional Tom70 in the human parasite Blastocystis sp.: implications for the evolution of the mitochondrial import apparatus.
abstract: Core proteins of mitochondrial protein import are found in all mitochondria, suggesting a common origin of this import machinery. Despite the presence of a universal core import mechanism, there are specific proteins found only in a few groups of organisms. One of these proteins is the translocase of outer membrane 70 (Tom70), a protein that is essential for the import of preproteins with internal targeting sequences into the mitochondrion. Until now, Tom70 has only been found in animals and Fungi. We have identified a tom70 gene in the human parasitic anaerobic stramenopile Blastocystis sp. that is neither an animal nor a fungus. Using a combination of bioinformatics, genetic complementation, and immunofluorescence microscopy analyses, we demonstrate that this protein functions as a typical Tom70 in Blastocystis mitochondrion-related organelles. Additionally, we identified putative tom70 genes in the genomes of other stramenopiles and a haptophyte, that, in phylogenies, form a monophyletic group distinct from the animal and the fungal homologues. The presence of Tom70 in these lineages significantly expands the evolutionary spectrum of eukaryotes that contain this protein and suggests that it may have been part of the core mitochondrial protein import apparatus of the last common ancestral eukaryote.
authors.affiliation: Department of Biochemistry and Molecular Biology, Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie University, Halifax, Canada. tsaousis.anastasios@gmail.com
authors.forename: Anastasios D
authors.initials: AD
authors.lastname: Tsaousis
authors.forename: Daniel
authors.initials: D
authors.lastname: Gaston
authors.forename: Alexandra
authors.initials: A
authors.lastname: Stechmann
authors.forename: Peter B
authors.initials: PB
authors.lastname: Walker
authors.forename: Trevor
authors.initials: T
authors.lastname: Lithgow
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Roger
mesh_terms: D005075:Biological Evolution; D016844:Blastocystis / Q000235:genetics* / Q000378:metabolism* / Q000648:ultrastructure; D055785:Gene Knockdown Techniques; D005816:Genetic Complementation Test; D006801:Humans; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008958:Models, Molecular; D010802:Phylogeny; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C489039:TOM70 protein, S cerevisiae