title: Hsp60-independent protein folding in the matrix of yeast mitochondria.
abstract: Proteins that are imported from the cytosol into mitochondria cross the mitochondrial membranes in an unfolded conformation and then fold in the matrix. Some of these proteins require the chaperonin hsp60 for folding. To test whether hsp60 is required for the folding of all imported matrix proteins, we monitored the folding of four monomeric proteins after import into mitochondria from wild-type yeast or from a mutant strain in which hsp60 had been inactivated. The four precursors included two authentic matrix proteins (rhodanese and the mitochondrial cyclophilin Cpr3p) and two artificial precursors (matrix-targeted variants of dihydrofolate reductase and barnase). Only rhodanese formed a tight complex with hsp60 and required hsp60 for folding. The three other proteins folded efficiently without, and showed no detectable binding to, hsp60. Thus, the mitochondrial chaperonin system is not essential for the folding of all matrix proteins. These data agree well with earlier in vitro studies, which had demonstrated that only a subset of proteins require chaperones for efficient folding.
authors.affiliation: Department of Biochemistry, Biozentrum der Universitat Basel, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Rospert
authors.forename: R
authors.initials: R
authors.lastname: Looser
authors.forename: Y
authors.initials: Y
authors.lastname: Dubaquie
authors.forename: A
authors.initials: A
authors.lastname: Matouschek
authors.forename: B S
authors.initials: BS
authors.lastname: Glick
authors.forename: G
authors.initials: G
authors.lastname: Schatz
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000591:Amino Acid Isomerases / Q000378:metabolism; D001426:Bacterial Proteins; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002474:Cell-Free System; D018834:Chaperonin 60 / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase; D011485:Protein Binding; D017510:Protein Folding; D012260:Ribonucleases / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D013884:Thiosulfate Sulfurtransferase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D018834:Chaperonin 60; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D000255:Adenosine Triphosphate; D013762:Tetrahydrofolate Dehydrogenase; D013884:Thiosulfate Sulfurtransferase; D012260:Ribonucleases; C019760:Bacillus amyloliquefaciens ribonuclease; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase