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Mammalian mitochondrial intermediate peptidase: structure/function analysis of a new homologue from Schizophyllum
G Isaya1, W R Sakati, R A Rollins
1Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Abstract:
Mitochondrial intermediate peptidase (MIP) is a component of the mitochondrial protein import machinery required for maturation of nuclear-encoded precursor proteins targeted to the mitochondrial matrix or inner membrane. We previously characterized this enzyme in rat (RMIP) and Saccharomyces cerevisiae (YMIP) and showed that MIP activity is essential for mitochondrial function in yeast. We have now defined the structure of a new MIP homologue (SMIP) from the basidiomycete fungus Schizophyllum commune. SMIP includes 4 exons of 523, 486, 660, and 629 bp separated by 3 short introns. The predicted SMIP, YMIP, and RMIP sequences share 31-37% identity and 54-57% similarity over 700 amino acids. When SMIP and RMIP were expressed in a yeast mip1 delta mutant, they were both able to rescue the respiratory-deficient phenotype caused by genetic inactivation of YMIP, indicating that the function of this enzyme is conserved in eukaryotes. Moreover, the MIP sequences show 20-24% identity and 40-47% similarity to a family of oligopeptidases from bacteria, yeast, and mammals. MIP and these proteins are characterized by a highly conserved motif, F-H-E-X-G-H-(X)2-H-(X)12-G-(X)5-D-(X)2-E-X-P-S-(X)3-E-X, centered around a zinc-binding site and appear to represent a new family of genes associated with proteolytic processing in the mitochondrial and cytosolic compartments.
Insights
Mitochondrial intermediate peptidase (MIP) is crucial for protein maturation in mitochondria. A newly identified fungal homolog (SMIP) rescues yeast lacking MIP, confirming conserved function across eukaryotes.
Area of Science:
- Mitochondrial biology
- Enzymology
- Molecular genetics
Background:
- Mitochondrial intermediate peptidase (MIP) is vital for mitochondrial protein import and maturation.
- Previous studies characterized rat (RMIP) and yeast (YMIP) MIP, establishing its essential role in yeast mitochondrial function.
Purpose of the Study:
- To define the structure of a novel MIP homologue (SMIP) from the fungus Schizophyllum commune.
- To investigate the functional conservation of MIP across eukaryotes by testing SMIP and RMIP in a yeast mutant.
Main Methods:
- Sequence analysis of the SMIP gene, including exon-intron structure.
- Expression of SMIP and RMIP in a yeast mip1Δ mutant.
- Assessment of respiratory-deficient phenotype rescue.
Main Results:
- The SMIP gene consists of 4 exons and 3 introns.
- SMIP and RMIP sequences share significant identity with YMIP and RMIP.
- Both SMIP and RMIP successfully rescued the respiratory-deficient phenotype in the yeast mip1Δ mutant.
- MIP sequences exhibit homology to bacterial, yeast, and mammalian oligopeptidases, suggesting a new gene family.
Conclusions:
- The function of mitochondrial intermediate peptidase is conserved across eukaryotes.
- SMIP represents a functional homolog of MIP in fungi.
- MIP and related oligopeptidases form a conserved family involved in proteolytic processing in mitochondria and cytoplasm.