Successive translocation into and out of the mitochondrial matrix: targeting of proteins to the intermembrane space by a bipartite signal peptide.
We investigated the import and sorting pathways of cytochrome b2 and cytochrome c1, which are functionally located in the intermembrane space of mitochondria. Both proteins are synthesized on cytoplasmic ribosomes as larger precursors and are processed in mitochondria in two steps upon import. The precursors are first translocated across both mitochondrial membranes via contact sites into the matrix. Processing by the matrix peptidase leads to intermediate-sized forms, which are subsequently redirected across the inner membrane. The second proteolytic processing occurs in the intermembrane space. We conclude that the hydrophobic stretches in the presequences of the intermediate-sized forms do not stop transfer across the inner membrane, but rather act as transport signals to direct export from the matrix into the intermembrane space.
Hartl
F U
FU
Institut für Physiologische Chemie, München, Federal Republic of Germany.
Ostermann
J
J
Guiard
B
B
Neupert
W
W
D003574:Cytochrome c Group / Q000031:analogs & derivatives*; D003575:Cytochromes c1 / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D042844:L-Lactate Dehydrogenase (Cytochrome); D008928:Mitochondria / Q000378:metabolism*; D009491:Neurospora / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism
D003574:Cytochrome c Group; D011498:Protein Precursors; D021382:Protein Sorting Signals; D003575:Cytochromes c1; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome)