title: Highly divergent mitochondrial ATP synthase complexes in Tetrahymena thermophila.
abstract: The F-type ATP synthase complex is a rotary nano-motor driven by proton motive force to synthesize ATP. Its F(1) sector catalyzes ATP synthesis, whereas the F(o) sector conducts the protons and provides a stator for the rotary action of the complex. Components of both F(1) and F(o) sectors are highly conserved across prokaryotes and eukaryotes. Therefore, it was a surprise that genes encoding the a and b subunits as well as other components of the F(o) sector were undetectable in the sequenced genomes of a variety of apicomplexan parasites. While the parasitic existence of these organisms could explain the apparent incomplete nature of ATP synthase in Apicomplexa, genes for these essential components were absent even in Tetrahymena thermophila, a free-living ciliate belonging to a sister clade of Apicomplexa, which demonstrates robust oxidative phosphorylation. This observation raises the possibility that the entire clade of Alveolata may have invented novel means to operate ATP synthase complexes. To assess this remarkable possibility, we have carried out an investigation of the ATP synthase from T. thermophila. Blue native polyacrylamide gel electrophoresis (BN-PAGE) revealed the ATP synthase to be present as a large complex. Structural study based on single particle electron microscopy analysis suggested the complex to be a dimer with several unique structures including an unusually large domain on the intermembrane side of the ATP synthase and novel domains flanking the c subunit rings. The two monomers were in a parallel configuration rather than the angled configuration previously observed in other organisms. Proteomic analyses of well-resolved ATP synthase complexes from 2-D BN/BN-PAGE identified orthologs of seven canonical ATP synthase subunits, and at least 13 novel proteins that constitute subunits apparently limited to the ciliate lineage. A mitochondrially encoded protein, Ymf66, with predicted eight transmembrane domains could be a substitute for the subunit a of the F(o) sector. The absence of genes encoding orthologs of the novel subunits even in apicomplexans suggests that the Tetrahymena ATP synthase, despite core similarities, is a unique enzyme exhibiting dramatic differences compared to the conventional complexes found in metazoan, fungal, and plant mitochondria, as well as in prokaryotes. These findings have significant implications for the origins and evolution of a central player in bioenergetics.
authors.affiliation: Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America.
authors.forename: Praveen
authors.initials: P
authors.lastname: Balabaskaran Nina
authors.forename: Natalya V
authors.initials: NV
authors.lastname: Dudkina
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Kane
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: van Eyk
authors.forename: Egbert J
authors.initials: EJ
authors.lastname: Boekema
authors.forename: Michael W
authors.initials: MW
authors.lastname: Mather
authors.forename: Akhil B
authors.initials: AB
authors.lastname: Vaidya
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D002853:Chromatography, Liquid; D017124:Conserved Sequence; D019143:Evolution, Molecular; D014644:Genetic Variation / Q000187:drug effects; D013058:Mass Spectrometry; D025261:Mitochondrial Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics*; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010802:Phylogeny; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D016808:Tetrahymena thermophila / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*
chemical_list: D009097:Multienzyme Complexes; D021122:Protein Subunits; D000244:Adenosine Diphosphate; D025261:Mitochondrial Proton-Translocating ATPases