title: Mitochondrial protein import: biochemical and genetic evidence for interaction of matrix hsp70 and the inner membrane protein MIM44.
abstract: The import of preproteins into mitochondria involves translocation of the polypeptide chains through putative channels in the outer and inner membranes. Preprotein-binding proteins are needed to drive the unidirectional translocation of the precursor polypeptides. Two of these preprotein-binding proteins are the peripheral inner membrane protein MIM44 and the matrix heat shock protein hsp70. We report here that MIM44 is mainly exposed on the matrix side, and a fraction of mt-hsp70 is reversibly bound to the inner membrane. Mt-hsp70 binds to MIM44 in a 1:1 ratio, suggesting that mt-hsp70 is localizing to the membrane via its interaction with MIM44. Formation of the complex requires a functional ATPase domain of mt-hsp70. Addition of Mg-ATP leads to dissociation of the complex. Overexpression of mt-hsp70 rescues the protein import defect of mutants in MIM44; conversely, overexpression of MIM44 rescues protein import defects of mt-hsp70 mutants. In addition, yeast strains with conditional mutations in both MIM44 and mt-hsp70 are barely viable, showing a synthetic growth defect compared to strains carrying single mutations. We propose that MIM44 and mt-hsp70 cooperate in translocation of preproteins. By binding to MIM44, mt-hsp70 is recruited at the protein import sites of the inner membrane, and preproteins arriving at MIM44 may be directly handed over to mt-hsp70.
authors.affiliation: Biochemisches Institut, Universität Freiburg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Rassow
authors.forename: A C
authors.initials: AC
authors.lastname: Maarse
authors.forename: E
authors.initials: E
authors.lastname: Krainer
authors.forename: M
authors.initials: M
authors.lastname: Kübrich
authors.forename: H
authors.initials: H
authors.lastname: Müller
authors.forename: M
authors.initials: M
authors.lastname: Meijer
authors.forename: E A
authors.initials: EA
authors.lastname: Craig
authors.forename: N
authors.initials: N
authors.lastname: Pfanner
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002451:Cell Compartmentation; D003432:Cross-Linking Reagents; D005656:Fungal Proteins / Q000235:genetics; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding / Q000187:drug effects; D011498:Protein Precursors / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013489:Suppression, Genetic
chemical_list: D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011498:Protein Precursors; C074215:SEC63 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C077016:TIM44 protein, S cerevisiae; D000255:Adenosine Triphosphate