A mutant form of mitochondrial GrpE suppresses the sorting defect caused by an alteration in the presequence of cytochrome b2.
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.
Merlin
A
A
Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
von Ahsen
O
O
Craig
E A
EA
Dietmeier
K
K
Pfanner
N
N
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
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