title: A mutant form of mitochondrial GrpE suppresses the sorting defect caused by an alteration in the presequence of cytochrome b2.
abstract: Transport of preproteins across the inner mitochondrial membrane requires the action of the matrix heat shock protein Hsp70. Together with its co-chaperone mitochondrial GrpE (Mge1), mtHsp70 transiently binds to the inner membrane translocase subunit Tim44 in a nucleotide-regulated manner, forming an ATP-dependent import driving machinery. We report that a mutant form of Mge1 (Mge1-100) is completely absent in mtHsp70-Tim44 complexes, although its ability to interact with soluble mtHsp70 is only partially reduced. While this mge1-100 mutation only partially retards preprotein translocation into the matrix, it exerts a selective effect on sorting of cytochrome b2 to the intermembrane space. A cytochrome b2 with an altered sorting signal, which is only processed to the intermediate stage and mistargeted to the matrix of wild-type mitochondria, is processed to the mature form and correctly targeted to the intermembrane space of mge1-100 mitochondria. These results suggest that (1) Mge1-100 discriminates between soluble and membrane-bound mtHsp70 and (2) the membrane-bound mtHsp70-Mge1 driving system competes with the sorting machinery for translocation of preproteins like cytochrome b2.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Merlin
authors.forename: O
authors.initials: O
authors.lastname: von Ahsen
authors.forename: E A
authors.initials: EA
authors.lastname: Craig
authors.forename: K
authors.initials: K
authors.lastname: Dietmeier
authors.forename: N
authors.initials: N
authors.lastname: Pfanner
mesh_terms: D015153:Blotting, Western; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D042844:L-Lactate Dehydrogenase (Cytochrome); D008565:Membrane Proteins / Q000032:analysis / 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; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D011233:Precipitin Tests; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics
chemical_list: D002352:Carrier Proteins; 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; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae; C077016:TIM44 protein, S cerevisiae; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome); D013762:Tetrahydrofolate Dehydrogenase