title: Mitochondrial GrpE is present in a complex with hsp70 and preproteins in transit across membranes.
abstract: We characterized a 24-kDa protein associated with matrix hsp70 (mt-hsp70) of Neurospora crassa and Saccharomyces cerevisiae mitochondria. By using specific antibodies, the protein was identified as MGE, a mitochondrial homolog of the prokaryotic heat shock protein GrpE. MGE extracted from mitochondria was quantitatively bound to hsp70. It was efficiently released from hsp70 by the addition of Mg-ATP but not by nonhydrolyzable ATP analogs or high salt. A mutant mt-hsp70, which was impaired in release of bound precursor proteins, released MGE in an ATP-dependent manner, indicating that precursor proteins and MGE bind to different sites of hsp70. A preprotein accumulated in transit across the mitochondrial membranes was specifically coprecipitated by either antibodies directed against MGE or antibodies directed against mt-hsp70. The preprotein accumulated at the outer membrane was not coprecipitated by either antibody preparation. After being imported into the matrix, the preprotein could be coprecipitated only by antibodies against mt-hsp70. We propose that mt-hsp70 and MGE cooperate in membrane translocation of preproteins.
authors.affiliation: Biochemisches Institut, Universität Freiburg, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Voos
authors.forename: B D
authors.initials: BD
authors.lastname: Gambill
authors.forename: S
authors.initials: S
authors.lastname: Laloraya
authors.forename: D
authors.initials: D
authors.lastname: Ang
authors.forename: E A
authors.initials: EA
authors.lastname: Craig
authors.forename: N
authors.initials: N
authors.lastname: Pfanner
mesh_terms: D001203:Ascomycota / Q000378:metabolism*; D001692:Biological Transport; D002451:Cell Compartmentation; D005656:Fungal Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D018832:Molecular Chaperones; D009492:Neurospora crassa / Q000378:metabolism; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D005656:Fungal Proteins; D006360:Heat-Shock Proteins; C086039:MGE1 protein, S cerevisiae; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D018832:Molecular Chaperones; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins