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Two-step processing of human frataxin by mitochondrial processing peptidase. Precursor and intermediate forms are
P Cavadini1, J Adamec, F Taroni
1Department of Pediatric & Adolescent Medicine and Biochemistry & Molecular Biology, Mayo Clinic and Foundation, 200 First Street SW, Rochester, Minnesota 55905, USA.
The Journal of Biological Chemistry
|October 6, 2000
Summary
Mitochondrial processing peptidase (MPP) cleaves precursor frataxin (p-fxn) in two steps, generating intermediate (i-fxn) and mature (m-fxn) forms. The second cleavage step is rate-limiting for mature frataxin levels.
Area of Science:
- Mitochondrial biology
- Protein processing
- Biochemistry
Background:
- Frataxin is crucial for mitochondrial iron homeostasis.
- Previous studies conflicted on the number of cleavages in human frataxin maturation.
- Mitochondrial processing peptidase (MPP) is the key enzyme in this process.
Purpose of the Study:
- To conclusively determine the number of cleavages in human precursor frataxin (p-fxn) maturation.
- To characterize the kinetics of these processing steps.
- To investigate the rate-limiting step in frataxin maturation and its implications.
Main Methods:
- In vitro cleavage assays using recombinant MPP.
- Analysis of protein fragments by mass spectrometry.
- Incubation of isolated rat mitochondria with precursor frataxin.
Main Results:
- MPP mediates two sequential cleavages of p-fxn, producing an intermediate (i-fxn) and mature (m-fxn) form.
- The p-fxn to i-fxn cleavage is significantly faster than the i-fxn to m-fxn cleavage.
- The i-fxn to m-fxn step is rate-limiting for mature frataxin production in mitochondria.
Conclusions:
- The maturation of human frataxin involves two sequential cleavages by MPP.
- The second cleavage step is the bottleneck for generating mature frataxin.
- Disease-associated mutations affecting this step can lead to frataxin deficiency.