Characterization of the mitochondrial processing peptidase of Neurospora crassa

The mitochondrial processing peptidase (MPP) of Neurospora crassa is constituted by an alpha- and a beta-subunit. We have purified alpha-MPP after expression in Escherichia coli while beta-MPP was purified from mitochondria. A fusion protein between precytochrome b2 and mouse dihydrofolate reductase was expressed in E. coli, and the purified protein was used as substrate for MPP. Both subunits of MPP are required for processing. MPP removes the matrix targeting signal of cytochrome b2 by a single cut, and the resulting presequence peptide is 31 amino acid residues in length. It acts as a competitive inhibitor of processing but has a approximately 30-fold lower affinity for MPP than the preprotein. Competition assays show that MPP recognizes the COOH- terminal portion of the presequence of cytochrome b2 rather than the NH2-terminal part which has the potential to form an amphiphilic helix. Substitution of arginine in position -2 of the matrix targeting sequence of cytochrome b2 prevents processing but not import of a chimeric precursor. Substitution of the tyrosyl residue in position +1 also prevents processing, indicating that MPP interacts with sequences COOH-terminal to the cleavage site. Non-cleavable preprotein is still recognized by MPP. Our data suggest that processing peptidase and import machinery recognize distinct structural elements in preproteins which, however, can be overlapping

Matrix processing peptidase of mitochondria

The mitochondrial processing peptidase (MPP) and the processing enhancing protein (PEP) cooperate in the proteolytic cleavage of matrix targeting sequences from nuclear-encoded mitochondrial precursor proteins. We have determined the cDNA sequence of Neurospora MPP after expression cloning. MPP appears to contain two domains of approximately equal size which are separated by a loop-like sequence. Considerable structural similarity exists to the recently sequenced yeast MPP as well as to Neurospora and yeast PEP. Four cysteine residues are conserved in Neurospora and yeast MPP. Inactivation of MPP can be achieved by using sulfhydryl reagents. MPP (but not PEP) depends on the presence of divalent metal ions for activity. Both MPP and PEP are synthesized as precursors containing matrix targeting signals which are processed during import into mitochondria by the mature forms of MPP and PEP

Corporate Social Responsibility as Subsidiary Co-Responsibility: A Macroeconomic Perspective

Corporate Social Responsibility, subsidiarity, social market economy, globalization, co-responsibility, ISO 26000, Catholic encyclicals,