title: Import of carrier proteins into the mitochondrial inner membrane mediated by Tim22.
abstract: Translocation of mitochondrial preproteins across the inner membrane is facilitated by the TIM machinery. Tim23 binds to matrix targeting signals and initiates membrane potential-dependent import. Tim23 and Tim17 are constituents of a translocation channel across the inner membrane. Tim44 is associated with this channel at the matrix side, and Tim44 recruits mitochondrial Hsp70 and its co-chaperone Mgel, which drive protein translocation into the matrix using ATP as an energy source. Tim22 is a new component of the import machinery of mitochondria, which shares sequence similarity with both Tim23 and Tim17. Here we report that Tim22 is required for the import of proteins of the mitochondrial ADP/ATP carrier (AAC) family into the inner membrane. Members of the yeast AAC family are synthesized without matrix targeting signals. Tim22 is in an assembly of high relative molecular mass that is distinct from the Tim23-Tim17 complex. Import of proteins of the AAC family is independent of Tim23, and import of matrix targeting signals containing preproteins is independent of Tim22.
authors.affiliation: Institut für Physiologische Chemie der Universität München, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Sirrenberg
authors.forename: M F
authors.initials: MF
authors.lastname: Bauer
authors.forename: B
authors.initials: B
authors.lastname: Guiard
authors.forename: W
authors.initials: W
authors.lastname: Neupert
authors.forename: M
authors.initials: M
authors.lastname: Brunner
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D003470:Culture Media; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins; D007425:Intracellular Membranes / Q000378:metabolism*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D028044:Phosphate-Binding Proteins; D011498:Protein Precursors / Q000378:metabolism; D012097:Repressor Proteins; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D002352:Carrier Proteins; D003470:Culture Media; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C086039:MGE1 protein, S cerevisiae; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones; D028044:Phosphate-Binding Proteins; D011498:Protein Precursors; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C091191:TIM17 protein, S cerevisiae; C102549:TIM22 protein, S cerevisiae; C083081:TIM23 protein, S cerevisiae; C077016:TIM44 protein, S cerevisiae; D000226:Mitochondrial ADP, ATP Translocases