Importance of residues carboxyl terminal relative to the cleavage site in substrates of mitochondrial processing peptidase for their specific recognition and cleavage

We previously identified distal and proximal arginine residues in the N-terminal portion and an aromatic amino acid at position 1 (P₁' site³) relative to the cleavage site as important recognition signals in substrates of mitochondrial processing peptidase. To further elucidate the elements required for the specific recognition and cleavage by the enzyme, we synthesized synthetic peptides that possessed only the distal and proximal arginine residues and phenylalanine at the P₁' site in a poly alanine sequence, and analyzed the processing reaction toward them. They were not cleaved by the peptidase although they inhibited the peptidase activity. However, when serine was introduced into the C-terminal portions of the sequence, processing was observed. The efficiency of the resultant peptides improved as the number of serine residues was increased. A peptide with serine or histidine at P₂' and threonine at P₃' was processed most efficiently. These results indicate that the processing reaction catalyzed by the peptidase depends not only on the N-terminal portion but also on the C-terminal portion from the cleavage site in the substrates.