title: Mitochondrial import of the ADP/ATP carrier: the essential TIM complex of the intermembrane space is required for precursor release from the TOM complex.
abstract: The mitochondrial intermembrane space contains a protein complex essential for cell viability, the Tim9-Tim10 complex. This complex is required for the import of hydrophobic membrane proteins, such as the ADP/ATP carrier (AAC), into the inner membrane. Different views exist about the role played by the Tim9-Tim10 complex in translocation of the AAC precursor across the outer membrane. For this report we have generated a new tim10 yeast mutant that leads to a strong defect in AAC import into mitochondria. Thereby, for the first time, authentic AAC is stably arrested in the translocase complex of the outer membrane (TOM), as shown by antibody shift blue native electrophoresis. Surprisingly, AAC is still associated with the receptors Tom70 and Tom20 when the function of Tim10 is impaired. The nonessential Tim8-Tim13 complex of the intermembrane space is not involved in the transfer of AAC across the outer membrane. These results define a two-step mechanism for translocation of AAC across the outer membrane. The initial insertion of AAC into the import channel is independent of the function of Tim9-Tim10; however, completion of translocation across the outer membrane, including release from the TOM complex, requires a functional Tim9-Tim10 complex.
authors.affiliation: Institut für Biochemie und Molekularbiologie. Fakultät für Biologie, Universität Freiburg, D-79104 Freiburg, Germany.
authors.forename: Kaye N
authors.initials: KN
authors.lastname: Truscott
authors.forename: Nils
authors.initials: N
authors.lastname: Wiedemann
authors.forename: Peter
authors.initials: P
authors.lastname: Rehling
authors.forename: Hanne
authors.initials: H
authors.lastname: Müller
authors.forename: Chris
authors.initials: C
authors.lastname: Meisinger
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
mesh_terms: D007425:Intracellular Membranes / Q000378:metabolism; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases / Q000235:genetics / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009154:Mutation; D021381:Protein Transport / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; C107250:TIM10 protein, S cerevisiae; C116366:Tim9 protein, S cerevisiae; D000226:Mitochondrial ADP, ATP Translocases