title: Protein Import by the Mitochondrial Presequence Translocase in the Absence of a Membrane Potential.
abstract: The highly organized mitochondrial inner membrane harbors enzymes that produce the bulk of cellular ATP via oxidative phosphorylation. The majority of inner membrane protein precursors are synthesized in the cytosol. Precursors with a cleavable presequence are imported by the presequence translocase (TIM23 complex), while other precursors containing internal targeting signals are imported by the carrier translocase (TIM22 complex). Both TIM23 and TIM22 are activated by the transmembrane electrochemical potential. Many small inner membrane proteins, however, do not resemble canonical TIM23 or TIM22 substrates and their mechanism of import is unknown. We report that subunit e of the F1Fo-ATP synthase, a small single-spanning inner membrane protein that is critical for inner membrane organization, is imported by TIM23 in a process that does not require activation by the membrane potential. Absence of positively charged residues at the matrix-facing amino-terminus of subunit e facilitates membrane potential-independent import. Instead, engineered positive charges establish a dependence of the import reaction on the electrochemical potential. Our results have two major implications. First, they reveal an unprecedented pathway of protein import into the mitochondrial inner membrane, which is mediated by TIM23. Second, they directly demonstrate the role of the membrane potential in driving the electrophoretic transport of positively charged protein segments across the inner membrane.
authors.affiliation: Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Spemann Graduate School for Biology and Medicine, University of Freiburg, 79104 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Uma
authors.initials: U
authors.lastname: Turakhiya
authors.affiliation: Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Karina
authors.initials: K
authors.lastname: von der Malsburg
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.
authors.forename: Vicki A M
authors.initials: VAM
authors.lastname: Gold
authors.affiliation: Centre de Génétique Moléculaire, Centre National de la Recherche Scientifique, 91190 Gif-sur-Yvette, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.affiliation: International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Chacinska
authors.affiliation: Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany; Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: van der Laan
authors.affiliation: Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de la Recherche Scientifique, Université Paul Sabatier, 31077 Toulouse, France. Electronic address: raffaele.ieva@ibcg.biotoul.fr.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Ieva
mesh_terms: D004252:DNA Mutational Analysis; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism* / Q000502:physiology*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D025261:Mitochondrial Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae; D025261:Mitochondrial Proton-Translocating ATPases; C102550:TIM11 protein, S cerevisiae
keywords: ATP synthase; TIM23 complex; membrane potential; mitochondrial biogenesis; protein import