Early steps in mitochondrial protein import: receptor functions can be substituted by the membrane insertion activity of apocytochrome c.
The process of insertion of precursor proteins into mitochondrial membranes was investigated using a hybrid protein (pSc1-c) that contains dual targeting information and, at the same time, membrane insertion activity. pSc1-c is composed of the matrix-targeting domain of the cytochrome c1 presequence joined to the amino terminus of apocytochrome c. It can be selectively imported along either a cytochrome c1 route into the mitochondrial matrix or via the cytochrome c route into the intermembrane space. In contrast to cytochrome c1, pSc1-c does not require the receptor system/GIP for entry into the matrix. The apocytochrome c in the pSc1-c fusion protein appears to exert its membrane insertion activity in such a manner that the matrix-targeting sequence gains direct access to the membrane potential-dependent step. These results attribute an essential function to the receptor system in facilitating the initial insertion of precursors into the mitochondrial membranes.
Stuart
R A
RA
Institut für Physiologische Chemie der Universität München, Federal Republic of Germany.
Nicholson
D W
DW
Neupert
W
W
D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001059:Apoproteins / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport; D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c; D003575:Cytochromes c1 / Q000235:genetics / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D019286:Endopeptidase K; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009491:Neurospora / Q000378:metabolism*; D009492:Neurospora crassa / Q000378:metabolism*; D010957:Plasmids; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000494:pharmacology; D013367:Submitochondrial Particles / Q000187:drug effects / Q000378:metabolism*
D001059:Apoproteins; D003574:Cytochrome c Group; D011993:Recombinant Fusion Proteins; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D003575:Cytochromes c1; D012697:Serine Endopeptidases; D019286:Endopeptidase K; D004072:Digitonin