The role of Hsp70 in conferring unidirectionality on protein translocation into mitochondria.
The entry of segments of preproteins of defined lengths into the matrix space of mitochondria was studied. The mitochondrial chaperone Hsp70 (mtHsp70) interacted with proteins emerging from the protein import channel and stabilized translocation intermediates across the membranes in an adenosine triphosphate-dependent fashion. The chaperone bound to the presequence and mature parts of preproteins. In the absence of mtHsp70 binding, preproteins with less than 30 to 40 residues in the matrix diffused out of mitochondria. Thus, protein translocation was reversible up to a late stage. The import channels in both mitochondrial membranes constitute a passive pore that interacts weakly with polypeptide chains entering the matrix.
Institut für Physiologische Chemie, Universität München, Germany.
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Ungermann
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Neupert
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D000255:Adenosine Triphosphate / Q000378:metabolism; D001692:Biological Transport; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D008564:Membrane Potentials; D008666:Metalloendopeptidases / Q000378:metabolism; D008727:Methotrexate / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism*; D009492:Neurospora crassa; D011498:Protein Precursors / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D000096122:Mitochondrial Processing Peptidase
D000255:Adenosine Triphosphate; D018840:HSP70 Heat-Shock Proteins; D008666:Metalloendopeptidases; D008727:Methotrexate; D011498:Protein Precursors; D006180:Proton-Translocating ATPases; D011993:Recombinant Fusion Proteins; D013762:Tetrahydrofolate Dehydrogenase; D000096122:Mitochondrial Processing Peptidase