Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.59 (MIP)
 4,906 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown previously that cleavage of a number of precursors by the mitochondrial processing peptidase (MPP) requires an intermediate octapeptide (FXXSXXXX) between the MPP cleavage site and the mature protein amino terminus. We show now that these octapeptides, present at the amino termini of the intermediates, direct recognition of these substrates by the mitochondrial intermediate peptidase (MIP), leading to formation of mature proteins. Synthetic peptides, corresponding to the intermediate octapeptides of human ornithine transcarbamylase (OTC) and of Neurospora cytochrome c reductase Fe/S subunit (Fe/S), inhibit the processing activity of purified rat liver MIP in vitro, without affecting MPP activity; this indicates that the octapeptides can be recognized by MIP independent of the presence of the corresponding mature proteins and interact with a site that is crucial for MIP activity. MIP activity is not inhibited by a peptide lacking the amino-terminal hydrophobic residue, while substitution of such a residue by a polar amino acid causes a 10-fold reduction in the efficiency of MIP inhibition. To analyze the requirements for removal of the octapeptide from the intermediate proteins by MIP, artificial intermediates were synthesized and subjected to in vitro processing by purified MIP. The octapeptide can be cleaved by MIP only when the amino-terminal hydrophobic residue is also the amino terminus of the intermediate. Further, when the OTC octapeptide is joined to the mature amino terminus of another twice-cleaved precursor (pFe/S; rat malate dehydrogenase, pMDH), the chimeric intermediate is cleaved by MIP to the corresponding mature-sized protein. When the OTC octapeptide is joined to the mature amino terminus of a once-cleaved precursor (yeast F1-beta-ATPase, pF1-beta), however, this intermediate is not cleaved by MIP; rather, it is processed by MPP to mature-sized F1-beta. Therefore, amino-terminal octapeptides can be cleaved by MIP only within the structural context of twice-cleaved precursors.
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PMID:Amino-terminal octapeptides function as recognition signals for the mitochondrial intermediate peptidase. 156 19

Many precursors of mitochondrial proteins are processed in two successive steps by independent matrix peptidases (MPP and MIP), whereas others are cleaved in a single step by MPP alone. To explain this dichotomy, we have constructed deletions of all or part of the octapeptide characteristic of a twice cleaved precursor (human ornithine transcarbamylase [pOTC]), have exchanged leader peptide sequences between once-cleaved (human methylmalonyl-CoA mutase [pMUT]; yeast F1ATPase beta-subunit [pF1 beta]) and twice-cleaved (pOTC; rat malate dehydrogenase (pMDH); Neurospora ubiquinol-cytochrome c reductase iron-sulfur subunit [pFe/S]) precursors, and have incubated these proteins with purified MPP and MIP. When the octapeptide of pOTC was deleted, or when the entire leader peptide of a once-cleaved precursor (pMUT or pF1 beta) was joined to the mature amino terminus of a twice-cleaved precursor (pOTC or pFe/S), no cleavage was produced by either protease. Cleavage of these constructs by MPP was restored by re-inserting as few as two amino-terminal residues of the octapeptide or of the mature amino terminus of a once-cleaved precursor. We conclude that the mature amino terminus of a twice-cleaved precursor is structurally incompatible with cleavage by MPP; such proteins have evolved octapeptides cleaved by MIP to overcome this incompatibility.
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PMID:Cleavage of precursors by the mitochondrial processing peptidase requires a compatible mature protein or an intermediate octapeptide. 167 32

Mitochondrial preornithine transcarbamylase (p-OTC) and premalate dehydrogenase (p-MDH) are the only two matrix-located preproteins so far identified for which the proteolytic processing in vitro requires the formation of genuine processing intermediates, i-OTC and i-MDH, respectively. To establish the processing of other preproteins during import with respect to the two-step processing of p-OTC and p-MDH, the chelators EDTA and 1,10-phenanthroline were used to study the import and processing of rat prechaperonin 60 (p-cpn60) and p-OTC by mitochondria from four cpn60-containing organs. We found no evidence for a secondary processing step in the maturation of p-cpn60, but a clear requirement for two-step processing of p-OTC, even in three organs which do not contain ornithine transcarbamylase. The metal-ion requirement of the p-OTC processing activities in the organelle is consistent with the proposition that the mitochondrial processing protease (MPP) and mitochondrial intermediate peptidase (MIP) activities defined in vitro [Kalousek, F., Hendrick, J.P. & Rosenberg, L. E. (1988) Proc. Natl Acad. Sci. USA 85, 7536-7540] are responsible for precursor processing in vivo. The authenticity of two-step processing in vivo was, furthermore, established by demonstrating that i-OTC accumulates to high levels in Spodoptora frugiperda insect cells supplemented with MnCl2. The inability of the insect cells to process p-OTC fully is not a characteristic of cells grown in culture since cultured rat hepatoma cells process p-OTC to the fully processed m-OTC. Finally, we find that the import and processing of p-cpn60 and p-OTC is inhibited in an identical fashion by presequence-bovine-serum-albumin conjugates. The differences in proteolytic maturation between p-cpn60 and p-OTC are therefore not likely to result from different import pathways as the two precursors compete for common components of the import apparatus.
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PMID:Prechaperonin 60 and preornithine transcarbamylase share components of the import apparatus but have distinct maturation pathways in rat liver mitochondria. 809 70