Bilayer-penetrating properties enable apocytochrome c to follow a special import pathway into mitochondria.
In this study, we have investigated the protein/lipid interactions of two mitochondrial precursor proteins, apocytochrome c and pCOX IV-DHFR, which exhibit mitochondrial import pathways with different characteristics. In-vitro-synthesized apocytochrome c was found to bind efficiently and specifically to liposomes composed of negatively charged phospholipids and showed a (at least partial) translocation across a lipid bilayer, as reported previously for the chemically prepared precursor protein [Rietveld, A. & de Kruijff, B. (1984) J. Biol. Chem. 259, 6704-6707; Dumont, M. E. & Richards, F. M. (1984) J. Biol. Chem. 259, 4147-4156]. Negatively charged liposomes were shown to efficiently compete with mitochondria for import of in-vitro-synthesized apocytochrome c into the organelle, suggesting an important role for negatively charged phospholipids in the initial binding of apocytochrome c to mitochondria. In contrast, the purified and in-vitro-synthesized precursor fusion protein pCOX IV-DHFR, consisting of the presequence of yeast cytochrome oxidase subunit IV fused to mouse dihydrofolate reductase was unable to translocate across a pure lipid bilayer. The data indicate that the ability of apocytochrome c to spontaneously translocate across the bilayer is not shared by all mitochondrial precursor proteins. The implications of the special protein/lipid interaction of apocytochrome c for import into mitochondria will be discussed.
Jordi
W
W
Centre for Biomembranes and Lipid Enzymology, Department of Biochemistry of Membranes, University of Utrecht, The Netherlands.
Hergersberg
C
C
de Kruijff
B
B
D000818:Animals; D001059:Apoproteins / Q000235:genetics / Q000378:metabolism*; D001345:Autoradiography; D001665:Binding Sites; D001692:Biological Transport; D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c; D004591:Electrophoresis, Polyacrylamide Gel; D008051:Lipid Bilayers; D008081:Liposomes; D008929:Mitochondria, Heart / Q000201:enzymology* / Q000378:metabolism; D009492:Neurospora crassa / Q000201:enzymology; D014176:Protein Biosynthesis; D014158:Transcription, Genetic
D001059:Apoproteins; D003574:Cytochrome c Group; D008051:Lipid Bilayers; D008081:Liposomes; D045304:Cytochromes c