title: Multiple interactions of components mediating preprotein translocation across the inner mitochondrial membrane.
abstract: The protein transport machinery of the inner mitochondrial membrane contains three essential Tim proteins. Tim17 and Tim23 are thought to build a preprotein translocation channel, while Tim44 transiently interacts with the matrix heat shock protein Hsp70 to form an ATP-driven import motor. For this report we characterized the biogenesis and interactions of Tim proteins. (i) Import of the precursor of Tim44 into the inner membrane requires mtHsp70, whereas import and inner membrane integration of the precursors of Tim17 and Tim23 are independent of functional mtHsp70. (ii) Tim17 efficiently associates with Tim23 and mtHsp70, but only weakly with Tim44. (iii) Depletion of Tim44 does not affect the co-precipitation of Tim17 with antibodies directed against mtHsp70. (iv) Tim23 associates with both Tim44 and Tim17, suggesting the presence of two Tim23 pools in the inner membrane, a Tim44-Tim23-containing sub-complex and a Tim23-Tim17-containing sub-complex. (v) The association of mtHsp70 with the Tim23-Tim17 sub-complex is ATP sensitive and can be distinguished from the mtHsp70-Tim44 interaction by the differential influence of an amino acid substitution in mtHsp70. (vi) Genetic evidence, suppression of the protein import defect of a tim17 yeast mutant by overexpression of mtHsp70 and synthetic lethality of conditional mutants in the genes of Tim17 and mtHsp70, supports a functional interaction of mtHsp70 with Tim17. We conclude that the protein transport machinery of the mitochondrial inner membrane consists of dynamically interacting sub-complexes, each of which transiently binds mtHsp70.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Bömer
authors.forename: M
authors.initials: M
authors.lastname: Meijer
authors.forename: A C
authors.initials: AC
authors.lastname: Maarse
authors.forename: A
authors.initials: A
authors.lastname: Hönlinger
authors.forename: P J
authors.initials: PJ
authors.lastname: Dekker
authors.forename: N
authors.initials: N
authors.lastname: Pfanner
authors.forename: J
authors.initials: J
authors.lastname: Rassow
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001692:Biological Transport; D000252:Calcium-Transporting ATPases; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D011233:Precipitin Tests; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism; D012097:Repressor Proteins; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D012097:Repressor Proteins; C101767:SSC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C091191:TIM17 protein, S cerevisiae; C083081:TIM23 protein, S cerevisiae; C077016:TIM44 protein, S cerevisiae; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases