Interaction of peptides corresponding to mitochondrial presequences with membranes

The transport of the F1-ATPase beta-subunit precursor into mitochondria is dependent upon a presequence at its amino terminus. Within the mitochondrial membrane translocation site the potential amphiphilic character of the presequence region may be necessary to stabilize binding to the mitochondrial inner membrane. To better understand its role in protein import, the interaction of the F1 beta-presequence with lipid membranes was measured using circular dichroism and surface tensiometry. These studies reveal that a 20-residue peptide containing the F1 beta-presequence binds to phospholipid vesicles (Kd = 4.5-6.0 x 10(-8)M and adopts a predominantly alpha-helical structure. Although the presequence peptide binds avidly to lipids, it does not appear to penetrate deeply into the bilayer to perturb a reporter probe in the membrane interior. Compared with the effect of the peptides with demonstrated membrane insertion and lytic properties, the F1-beta-presequence appears to displace phospholipid head groups but not insert deeply into the bilayer. High concentrations (greater than 50 microM) of presequence peptides are required to noticibly perturb import of the full length F1 alpha- or F1 beta-subunit precursors. Thus, the F1 beta-presequence alone is not sufficient to efficiently compete for import but may require a protein context or a minimal length to assist insertion into the transport site. These observations are discussed in light of the different requirements for import of various presequence containing precursors into mitochondria.