No abstract

We demonstrate the ability of a peptide corresponding to the presequence of the cytochrome c oxidase subunit IV to induce lipid mixing between large unilameilar liposomes. This lipid mixing requires the presence of CL or PE, lipids able to form non-bilayer structures, and is not observed with other negatively charged lipids. However, the fact that this mixing occurs without mixing of the liposome aqueous phases and without destabilizing the lipid orgauisation is unusual and has not been observed for other amphiphilic peptides. This observation supports the idea that the presequence could play a role in the formation of translocation contact sites between the two mitochondrial membranes and facilitate the structural rearrangements of the outer and inner membrane proteins involved in the two import machineries in a way to permit the formation of a continuous import channel through the two mitochondrial membranes without mixing the cytoplasmic and mitochondrial aqueous contents.

branes with the help of mitochondrial import machineries (for Abstract The orientation of a mitochondrial presequence peptide, associated with anionic lipid-containing model memreviews, see [1,2]). Translocation of the presequence across the branes, was investigated. The peptide inserts with its N-terminal inner mitochondrial membrane requires a membrane potential a-helical part into cardiolipin (CL) monolayers so that the N-(A~) across that membrane [3,4]. terminal 14 residues are protected from proteinase K. In Although the amount of information about the import prophosphatidylglycerol (PG) monolayers the inserted peptide was cess and components involved is still growing, the molecular fully accessible to the protease. A consequence of the different mechanism of the protein translocation process is largely unorientations of the peptide was that membrane potentialknown. This applies in particular to the molecular interactions dependent protection from trypsin was much faster for the the presequence is involved in. The presequence is assumed to peptide bound to PG-eontaining vesicles compared to CLinteract with different proteinaceous components of the imcontaining membranes, suggesting that in the mitochondrial protein import process other components of the import apparatus port apparatus, as well as with membrane lipids (cf. [5,6]). Of are involved in the efficient potential-driven translocation of special interest is cardiolipin (CL), a phospholipid with a unpresequences across the inner mitochondrial membrane, ique chemical structure, which in the eukaryotic cell is only synthesized [7] and found in mitochondria [8,9]. Several ob-