The Mitochondrial Processing Peptidase

The mitochondrial processing peptidase is an essential zinc-dependent met-allopeptidase (Yaffe et al. 1985 Luciano and Geli 1996 Gakh et al. 2002 Nomura et al. 2006). It cleaves the N-terminal presequence from precursors to matrix-targeted proteins, and from precursors destined for the inner mem- 

Surveys of mitochondrial presequences showed that, though quite common, these above motifs are not found in all of them, and that the primary sequence for the cleavage site is quite degenerate. 

The role of the Arg at the - 2 or - 3 position is unclear and may be presequence-dependent as studies on a variety of precursors revealed that mutating the Arg results in cleavage inhibition or modification in some cases, but not in others. It may be that the structure, rather than the primary sequence composition of the presequence and perhaps of the mature protein, determines the MPP cleavage site (Gakh et al. 2002). 

but given the occurrence of presequence-independent protein import in microsporidia (Burri et al. 2006), they may have dispensed with processing peptidases during their reductive evolution. The only hydrogenosomal or mitosomal species reported to have a homologue to a-MPP is N. ovalis (Boxma et al. 2005). There have been no reports of MIP-like proteins, nor of any R-10 motif on protein precursors in any of the hydrogenosomal or mitosomal species. 

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Luciano, P., and Geli, V. (1996). The mitochondrial processing peptidase function and specificity. Experientia 52, 1077-1082. 

This zinc-dependent enzyme [EC 3.4.24.59] of the peptidase M3 family catalyzes the hydrolysis of a peptide bond such that there is a release of an N-terminal octa-peptide at the second stage of processing of some proteins imported into the mitochondrion. The natural substrates are precursor proteins that already have been processed by the mitochondrial processing peptidase. 

This a-helix is amphipathic, containing patches of positively charged and hydrophobic amino acids, respectively, on opposite surfaces of the theoretical cylinder. The presequence is usually processed by the mitochondrial processing peptidase (MPP) and the mature protein is sorted to either the matrix, or to the inner membrane if it bears a hydrophobic stop-transfer sequence. Some mitochondrial proteins, mostly destined to the membranes, do not have cleavable N-terminal presequences but have internal targeting signals that are not well characterized (Pfanner and Geissler 2001). 

After translocation into the mitosome, the N-terminal presequences of mitosomal proteins are cleaved off, most likely by a peptidase that is homologous to the mitochondrial processing peptidase (MPP). The MPP is a matrix-localized metallopeptidase with a zinc binding motif His-X-X-Glu-His that is conserved in the putative mitosomal processing peptidase reported in G. intestinalis (Dolezal et al. 2005). 

Mitochondria arise by division and growth of preexisting mitochondria. Because they synthesize only a few proteins and RNA molecules, they must import many proteins and other materials from the cytoplasm. A mitochondrion contains at least 100 proteins that are encoded by nuclear genes.50,50a The mechanisms by which proteins are taken up by mitochondria are complex and varied. Many of the newly synthesized proteins carry, at the N terminus, presequences that contain mitochondrial targeting signals51-53 (Chapter 10). These amino acid sequences often lead the protein to associate with receptor proteins on the outer mitochondrial membrane and subsequently to be taken up by the mitochondria. While the targeting sequences are usually at the N terminus of a polypeptide, they are quite often internal. The N-terminal sequences are usually removed by action of the mitochondrial processing peptidase (MPP) in... 

Song, M.-C., Shimokata, K, Kitada, S., Ogishima, T., and Ito, A. (1996). Role of basic amino acids in the cleavage of synthetic peptide substrate by mitochondrial processing peptidase./. Biochem.. (Tokyo) 120, 1163-1166. 

Fig-i Mitochondrial protein import machinery as defined in S. cerevisiae. TOM translo-case of the outer mitochondrial membrane SAM sorting and assembly machinery TIM translocase of the inner mitochondrial membrane MIA mitochondrial IMS import and assembly machine PAM presequence translocase associated motor IMP inner membrane protease MPP mitochondrial processing peptidase. The numbers on the individual Tom, Sam, Tim or Pam components represent their approximate molecular masses in kDa. See text for mechanistic details. Adopted from Dolezal et al. 2006... 

Gabriel et al. (2007) Novel mitochondrial intermembrane space proteins as substrates of the MIA import pathway. J Mol Biol 365 612-620 Gakh O, Cavadini P, Isaya G (2002) Mitochondrial processing peptidases. Biochim Biophys Acta 1592 63-77... 

Nomura H, Athauda SB, Wada H, Maruyama Y, Takahashi K, Inoue H (2006) Identification and reverse genetic analysis of mitochondrial processing peptidase and the core protein of the cytochrome bcl complex of Caenorhabditis elegans, a model parasitic nematode. J Biochem (Tokyo) 139 967-979... 

Braun, H. P., Emmermann, M., Kruft, V., and Schmitz, U. K., 1992, The general mitochondrial processing peptidase from potato is an integral part of cytochrome c reductase of the respiratory chain, EMBO J. Il 3219n3227. 

Specific peptidase and protease systems which involve Mn(II) include thrombin limited-proteolysis of prothrombin [122], insulin protease [123], enkephalin-degrading amino-peptidase [124], camosinase [125,129], ki-ninase [127], and trypsin activation [128]. A metalIo(Mn)-protease is involved in the processing of mitochondrial precursor proteins [130]. Several aminopeptidases are also specifically manganese-dependent, namely Leu-aminopeptidase [131] and prolidase or C-terminal proline dipeptidase [132-135]. Other systems that hydrolyze linear and cyclic G-N bonds include various amino-acylases, deacetylases, amidases and methylene-... 

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