The role of the GrpE homologue, Mge1p, in mediating protein import and protein folding in mitochondria.
Mge1p, a mitochondrial GrpE homologue, has recently been identified in the yeast Saccharomyces cerevisiae and a role for this protein in precursor import has been reported. To dissect the molecular mechanism of Mge1p function, conditional mge1 mutants were constructed. Cells harbouring mutant mge1 accumulated precursor proteins at restrictive temperature. Both kinetics and efficiency of import were reduced in mitochondria isolated from strains possessing mutant mge1. Binding of mitochondrial-Hsp70 (mt-Hsp70) to incoming precursor proteins was abolished at restrictive temperature. Nucleotide-dependent dissociation of mt-Hsp70 from the import component MIM44 was reduced in mitochondria from mutant mge1 strains. Furthermore, at restrictive temperature an increase of incompletely folded, newly imported protein and enhanced protein aggregation was observed in mitochondria isolated from the mutant strains. We conclude that Mge1p exerts an essential function in import and folding of proteins by controlling the nucleotide-dependent binding of mt-Hsp70 to substrate proteins and the association of mt-Hsp70 with MIM44.
Westermann
B
B
Institut für Physiologische Chemie der Universität München, Germany.
Prip-Buus
C
C
Neupert
W
W
Schwarz
E
E
D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D017931:DNA Primers; D005656:Fungal Proteins / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D008565:Membrane Proteins / 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; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009711:Nucleotides / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D011498:Protein Precursors / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature
D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D005656:Fungal Proteins; C068113:GrpE protein, Bacteria; 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; D009711:Nucleotides; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; C077016:TIM44 protein, S cerevisiae