Maturation of frataxin within mammalian and yeast mitochondria: one-step processing by matrix processing peptidase.
Friedreich's ataxia is a neurodegenerative disease caused by mutations in the nuclear gene encoding frataxin (FRDA). FRDA is synthesized with an N-terminal signal sequence, which is removed after import into mitochondria. We have shown that FRDA was imported efficiently into isolated mammalian or yeast mitochondria. In both cases, the processing cleavage that removed the N-terminal signal sequence occurred in a single step on import, generating mature products of identical mobility. The processing cleavage could be reconstituted by incubating the FRDA preprotein with rat or yeast matrix processing peptidase (MPP) expressed in Escherichia coli. We used these assays to evaluate the import and processing of an altered form of FRDA containing the disease-causing I154F mutation. No effects on import or maturation of this mutated FRDA were observed. Likewise, no effects were observed on import and maturation of the yeast frataxin homolog (Yfh1p) carrying a homologous I130F mutation. These results argue against the possibility that the I154F mutation interferes with FRDA function via effects on maturation. Other mutations can be screened for effects on FRDA biogenesis as described here, by evaluating import into isolated mitochondria and by testing maturation with purified MPP.
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Department of Physiology, University of Pennsylvania School of Medicine, D403 Richards Building, 3700 Hamilton Walk, Philadelphia, PA 19104-6085, USA.
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D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D017931:DNA Primers; D005621:Friedreich Ataxia / Q000378:metabolism*; D033862:Iron-Binding Proteins; D008666:Metalloendopeptidases / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D000096122:Mitochondrial Processing Peptidase; D000096923:Frataxin
D017931:DNA Primers; D033862:Iron-Binding Proteins; D008666:Metalloendopeptidases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011994:Recombinant Proteins; D000096122:Mitochondrial Processing Peptidase; D000096923:Frataxin