title: In the absence of the first membrane-spanning segment of subunit 4(b), the yeast ATP synthase is functional but does not dimerize or oligomerize.
abstract: The N-terminal portion of the mitochondrial b-subunit is anchored in the inner mitochondrial membrane by two hydrophobic segments. We investigated the role of the first membrane-spanning segment, which is absent in prokaryotic and chloroplastic enzymes. In the absence of the first membrane-spanning segment of the yeast subunit (subunit 4), a strong decrease in the amount of subunit g was found. The mutant ATP synthase did not dimerize or oligomerize, and mutant cells displayed anomalous mitochondrial morphologies with onion-like structures. This phenotype is similar to that of the null mutant in the ATP20 gene that encodes subunit g, a component involved in the dimerization/oligomerization of ATP synthase. Our data indicate that the first membrane-spanning segment of the mitochondrial b-subunit is not essential for the function of the enzyme since its removal did not directly alter the oxidative phosphorylation. It is proposed that the unique membrane-spanning segment of subunit g and the first membrane-spanning segment of subunit 4 interact, as shown by cross-linking experiments. We hypothesize that in eukaryotic cells the b-subunit has evolved to accommodate the interaction with the g-subunit, an associated ATP synthase component only present in the mitochondrial enzyme.
authors.affiliation: Institut de Biochimie et Génétique Cellulaires du CNRS, Université Victor Segalen, Bordeaux 2, 1, rue Camille Saint Saëns, 33077 Bordeaux cedex, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Soubannier
authors.forename: Jacques
authors.initials: J
authors.lastname: Vaillier
authors.forename: Patrick
authors.initials: P
authors.lastname: Paumard
authors.forename: Benedicte
authors.initials: B
authors.lastname: Coulary
authors.forename: Jacques
authors.initials: J
authors.lastname: Schaeffer
authors.forename: Jean
authors.initials: J
authors.lastname: Velours
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D025261:Mitochondrial Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020112:Rhodamine 123 / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
chemical_list: D003432:Cross-Linking Reagents; D020112:Rhodamine 123; D000251:Adenosine Triphosphatases; D025261:Mitochondrial Proton-Translocating ATPases; D010100:Oxygen