Energy requirements for unfolding and membrane translocation of precursor proteins during import into mitochondria.
ATP is involved in conferring transport competence to numerous mitochondrial precursor proteins in the cytosol. Unfolded precursor proteins were found not to require ATP for import into mitochondria, suggesting a role of ATP in the unfolding of precursors. Here we report the unexpected finding that a hybrid protein containing the tightly folded passenger protein dihydrofolate reductase becomes unfolded and specifically translocated across the mitochondrial membranes independently of added ATP. Moreover, interaction of the precursor with the mitochondrial receptor components does not require ATP. The results suggest that ATP is not involved in the actual process of unfolding during membrane translocation of precursors. ATP rather appears to be necessary for preventing the formation of improper structures of precursors in the cytosol and for folding of imported polypeptides on (and release from) chaperone-like molecules in the mitochondrial matrix.
Pfanner
N
N
Institut für Physiologische Chemie, Universität Müchen, Federal Republic of Germany.
Rassow
J
J
Guiard
B
B
Söllner
T
T
Hartl
F U
FU
Neupert
W
W
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001081:Apyrase / Q000378:metabolism; D004734:Energy Metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D042844:L-Lactate Dehydrogenase (Cytochrome); D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D009491:Neurospora / Q000378:metabolism*; D009492:Neurospora crassa / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism
D011498:Protein Precursors; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome); D013762:Tetrahydrofolate Dehydrogenase; D001081:Apyrase