Abstract
The correlation between the import of the Rieske iron-sulfur protein into the mitochondrial matrix and processing of the precursor protein by matrix processing peptidase was investigated using high concentrations of metal chelators and iron-sulfur protein in which the recognition site for the matrix processing peptidase was destroyed by site-directed mutagenesis. High concentrations of EDTA and o-phenanthroline inhibit import of iron-sulfur protein into the matrix. The non-chelating structural isomers m-phenanthroline and p-phenanthroline inhibit import similar to o-phenanthroline, indicating that inhibition of import is mainly independent of the metal chelating ability of the compounds. Iron-sulfur protein in which the recognition site for the matrix processing peptidase had been destroyed by a point mutation was efficiently imported into the matrix space. Import of this mutant iron-sulfur protein was inhibited by the same concentrations of EDTA and o-phenanthroline which inhibit import of the wild-type protein. These results indicate that import of the iron-sulfur protein into the mitochondrial matrix is independent of proteolytic processing of the presequence, and that o-phenanthroline together with EDTA inhibits import of iron-sulfur protein into the matrix space of mitochondria by inhibiting a step other than proteolysis of the presequence.
Highlights
The Rieske iron-sulfur protein is an essential subunit of mitochondrial cytochrome bc1 complexes and, like the majority of mitochondrial proteins, is encoded by a nuclear gene and synthesized on cytoplasmic ribosomes
Import and two-step processing of the iron-sulfur protein to mature size was demonstrated in S. cerevisiae mitochondria, and the effects of different concentrations of EDTA and o-phenanthroline on these processes were characterized [2,3,4]
It was found that increasing the concentration of ophenanthroline to 8 mM results in accumulation of precursor iron-sulfur protein (p-ISP), and it was proposed that this accumulation results from inhibition of the matrix processing peptidase (MPP) responsible for the first processing step [2]
Summary
The Rieske iron-sulfur protein is an essential subunit of mitochondrial cytochrome bc1 complexes and, like the majority of mitochondrial proteins, is encoded by a nuclear gene and synthesized on cytoplasmic ribosomes. These results indicate that import of the ironsulfur protein into the mitochondrial matrix is independent of proteolytic processing of the presequence, and that o-phenanthroline together with EDTA inhibits import of iron-sulfur protein into the matrix space of mitochondria by inhibiting a step other than proteolysis of the presequence.
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