The N-terminal half of a mitochondrial presequence peptide inserts into cardiolipin-containing membranes. Consequences for the action of a transmembrane potential.

The orientation of a mitochondrial-presequence peptide, associated with anionic lipid-containing model membranes, was investigated. The peptide inserts with its N-terminal alpha-helical part into cardiolipin (CL) monolayers so that the N-terminal 14 residues are protected from proteinase K. In phosphatidylglycerol (PG) monolayers the inserted peptide was fully accessible to the protease. A consequence of the different orientations of the peptide was that membrane potential-dependent protection from trypsin was much faster for the peptide bound to PG-containing vesicles compared to CL-containing membranes, suggesting that in the mitochondrial protein import process other components of the import apparatus are involved in the efficient potential-driven translocation of presequences across the inner mitochondrial membranes.