Basic peptides can be imported into yeast mitochondria by two distinct targeting pathways. Involvement of the...

The interaction of several basic peptides with yeast mitochondria has been analyzed. The peptides were selected for their ability to block a cationic channel of the outer membrane, the peptide-sensitive channel. These peptides possess common characteristics, such as a net positive charge superior to 2 and the capacity to form amphiphilic structures. They can be divided into two classes as follows: peptides of class I derived from mitochondrial signal peptides, such as the presequence of cytochrome c oxidase subunit IV, e.g. pCyt OX IV (1-12) Y; and peptides of class II unrelated to the mitochondria, such as dynorphin B (1-13). Class I peptides inhibited the translocation of a chimeric protein, cytochrome b2-DHFR, into the mitochondrial matrix, whereas peptides of class II failed to inhibit this import. Experiments with iodinated pCyt OX IV (1-12) Y and dynorphin B (1-13) showed, however, that both types of peptides were imported into yeast mitochondria in vitro and subsequently degraded. At 30 degrees C, two import mechanisms could be distinguished; the mitochondrial presequences (class I) were translocated into the matrix in a temperature- and potential-sensitive manner, probably along the general import pathway, while class II dynorphin B (1-13) was imported into the intermembrane space by a process that was neither temperature- nor potential-sensitive. At 0 degree C, both peptides were imported in a class II manner. The class II characteristics suggested the existence of a direct pathway into the intermembrane space, which may be associated with the peptide-sensitive channel. This hypothesis is substantiated by the competition for the import into the mitochondria between peptides of the two classes. The import of pCyt OX (1-12) Y was inhibited at 30 degrees C only by peptides of class I, IV whereas, at 0 degree C, this import was also inhibited by peptides of class II. Import of peptides of the latter class was inhibited by peptides of the two classes both at 0 degree C and 30 degrees C.