title: In situ structure of trypanosomal ATP synthase dimer reveals a unique arrangement of catalytic subunits.
abstract: We used electron cryotomography and subtomogram averaging to determine the in situ structures of mitochondrial ATP synthase dimers from two organisms belonging to the phylum euglenozoa: Trypanosoma brucei, a lethal human parasite, and Euglena gracilis, a photosynthetic protist. At a resolution of 32.5 Å and 27.5 Å, respectively, the two structures clearly exhibit a noncanonical F1head, in which the catalytic (αβ)3assembly forms a triangular pyramid rather than the pseudo-sixfold ring arrangement typical of all other ATP synthases investigated so far. Fitting of known X-ray structures reveals that this unusual geometry results from a phylum-specific cleavage of the α subunit, in which the C-terminal αCfragments are displaced by ∼20 Å and rotated by ∼30° from their expected positions. In this location, the αCfragment is unable to form the conserved catalytic interface that was thought to be essential for ATP synthesis, and cannot convert γ-subunit rotation into the conformational changes implicit in rotary catalysis. The new arrangement of catalytic subunits suggests that the mechanism of ATP generation by rotary ATPases is less strictly conserved than has been generally assumed. The ATP synthases of these organisms present a unique model system for discerning the individual contributions of the α and β subunits to the fundamental process of ATP synthesis.
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Mühleip
authors.affiliation: Institute of Immunology and Infection Research and Centre for Immunity, Infection, and Evolution, University of Edinburgh, Edinburgh EH9 3FL, United Kingdom.
authors.forename: Caroline E
authors.initials: CE
authors.lastname: Dewar
authors.affiliation: Institute of Immunology and Infection Research and Centre for Immunity, Infection, and Evolution, University of Edinburgh, Edinburgh EH9 3FL, United Kingdom.
authors.forename: Achim
authors.initials: A
authors.lastname: Schnaufer
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany werner.kuehlbrandt@biophys.mpg.de KMDavies@lbl.gov.
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany werner.kuehlbrandt@biophys.mpg.de KMDavies@lbl.gov.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Davies
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D020134:Catalytic Domain; D016384:Consensus Sequence; D019281:Dimerization; D005056:Euglena gracilis / Q000201:enzymology*; D008928:Mitochondria / Q000201:enzymology; D008958:Models, Molecular; D011487:Protein Conformation; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism; D012399:Rotation; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014346:Trypanosoma brucei brucei / Q000201:enzymology*
chemical_list: D015800:Protozoan Proteins; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases
keywords: electron cryotomography; mitochondrial ATP synthase; rotary catalysis; subtomogram averaging; trypanosome