BASIC PEPTIDES CAN BE IMPORTED INTO YEAST MITOCHONDRIA BY 2 DISTINCT TARGETING PATHWAYS - INVOLVEMENT OF THE PEPTIDE-SENSITIVE CHANNEL OF THE OUTER-MEMBRANE

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 positiv e 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 o f cytochrome c oxidase subunit IV, e.g. pCyt OX IV (1-12) Y; and pepti des of class II unrelated to the mitochondria, such as dynorphin B (1- 13). Class I peptides inhibited the translocation of a chimeric protei n, cytochrome b(2)- DHFR, into the mitochondrial matrix, whereas pepti des of class II failed to inhibit-this import. Experiments with iodina ted pCyt OX TV (1-12) Y and dynorphin B (1-13) showed, however, that b oth types of peptides were imported into yeast mitochondria in vitro a nd subsequently degraded. At 30 degrees C, two import mechanisms could be distinguished; the mitochondrial presequences (class I) were trans located into the matrix in a temperature- and potential-sensitive mann er, probably along the general import pathway, while class II dynorphi n B (1-13) was imported into the intermembrane space by a process that was neither temperature- nor potential-sensitive. At 0 degrees C, bot h peptides were imported in a class II manner. The class II characteri stics suggested the existence of a direct pathway into the intermembra ne space, which may be associated with the peptide-sensitive channel. This hypothesis is substantiated by the competition for the import int o 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 cla ss I, IV whereas, at 0 degrees C, this import was also inhibited by pe ptides of class II. Import of peptides of the latter class was inhibit ed by peptides of the two classes both at 0 degrees C and 30 degrees C .