More than just a ticket canceller: the mitochondrial processing peptidase tailors complex precursor proteins at internal cleavage sites

Abstract

Most mitochondrial proteins are synthesized as precursors that carry N-terminal presequences. After import into mitochondria, these targeting signals are cleaved off by the mitochondrial processing peptidase MPP. Using the mitochondrial tandem protein Arg5,6 as model substrate, we demonstrate that MPP has an additional role in preprotein maturation, beyond the removal of presequences. Arg5,6 is synthesized as a polyprotein precursor that is imported into mitochondria and subsequently separated into two distinct enzymes. This internal processing is performed by MPP, which cleaves the Arg5,6 precursor at its N-terminus and at an internal site. The peculiar organization of Arg5,6 is conserved across fungi and reflects the polycistronic arginine operon in prokaryotes. MPP cleavage sites are also present in other mitochondrial fusion proteins from fungi, plants and animals. Hence, besides its role as “ticket canceller” for removal of presequences, MPP exhibits a second, conserved activity as internal processing peptidase for complex mitochondrial precursor proteins.

In-Depth Characterization of Apoptosis N-terminome Reveals a Link Between Caspase-3 Cleavage and Post-Translational N-terminal Acetylation

“…The neo-acetylated-Nt-peptides identified were mainly from the mitochondria and relate to the removal of the mitochondria targeting sequence (mitochondria transit peptide). This type of proteolytic processing is done after the protein is imported into the mitochondria and reaches the mitochondrial matrix (Friedl et al, 2020). Next, we looked for additional hints for post-translational neo-Nt-acetylation that occur following other proteolytic cleavages.…”

Protein Processing in Plant Mitochondria Compared to Yeast and Mammals

“…Using the precursor of mitochondrial tandem protein Arg5,6 as a model substrate from S. cerevisiae mitochondria, Friedl et al (2020) have demonstrated that MPP not only removes the N-terminal targeting sequence from this precursor tandem protein but is also required for specific internal processing generating two functional enzymes, Arg5 and Arg6. Further, in silico searching for internal matrix targeting signal-like sequences (iMTS-L) and canonical MPP cleavage sites in mitochondrial precursor proteins with composite structure in different species (Atp25 from S. cerevisiae and Emericella nidulans, Etp1, Rsm22-Cox11, and the uncharacterized SPAC22A12.08c from Schizosaccharomyces pombe, as well as RPS14 from Oryza sativa japonica) led to the identification of both types of motifs in these organisms (Friedl et al, 2020). This study indicates that internal precursor processing by MPP is conserved among fungi and plants, and possibly other eukaryotes.…”

Mitochondrial Processing Peptidases—Structure, Function and the Role in Human Diseases

“…Besides, MPP has been shown responsible for the processing of precursor proteins that are post-translationally cleaved into polypeptides functioning as separate enzymes. For example, Arg5,6 from S. cerevisiae synthesized in the cytosol is after the import into mitochondria first cleaved by MPP to be disposed of its MTS and then internally processed to form two distinct enzymes, Arg5 (N-acetyl-gamma-glutamyl-phosphate reductase) and Arg6 (acetylglutamate kinase) [29].…”