Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.64 (MPP)
 1,876 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Most mitochondrial proteins are synthesized in the cytoplasm as larger precursors carrying N-terminal matrix-targeting presequences, and are subsequently transported to the mitochondria. The presequence mediates the interaction between the precursor polypeptide and components of the mitochondrial protein import machinery, a complex apparatus that is responsible for translocation of the precursor across the two mitochondrial membranes. Once the precursor has reached the mitochondrial matrix, the presequence is removed by the general mitochondrial processing peptidase (MPP). Some precursors undergo additional processing steps carried out by specialized processing peptidases. For most mitochondrial proteins, however, cleavage by MPP is the step that precedes folding and assembly into the native form. We describe methods to isolate import-competent mitochondria from rat liver and to perform import reactions with precursor proteins synthesized in vitro by coupled transcription-translation. We also describe methods to perform in vitro processing reactions of mitochondrial precursors by recombinant MPP and to identify the cleavage sites used by this enzyme.
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PMID:Protein import and processing reconstituted with isolated rat liver mitochondria and recombinant mitochondrial processing peptidase. 1205 20

Deficiency in the nuclear-encoded mitochondrial protein frataxin causes Friedreich ataxia (FRDA), a progressive neurodegenerative disorder associating spinocerebellar ataxia and cardiomyopathy. Although the exact function of frataxin is still a matter of debate, it is widely accepted that frataxin is a mitochondrial iron chaperone involved in iron-sulfur cluster and heme biosynthesis. Frataxin is synthesized as a precursor polypeptide, directed to the mitochondrial matrix where it is proteolytically cleaved by the mitochondrial processing peptidase to the mature form via a processing intermediate. The mature form was initially reported to be encoded by amino acids 56-210 (m(56)-FXN). However, two independent reports have challenged these studies describing two different forms encoded by amino acids 78-210 (m(78)-FXN) and 81-210 (m(81)-FXN). Here, we provide evidence that mature human frataxin corresponds to m(81)-FXN, and can rescue the lethal phenotype of fibroblasts completely deleted for frataxin. Furthermore, our data demonstrate that the migration profile of frataxin depends on the experimental conditions, a behavior which most likely contributed to the confusion concerning the endogenous mature frataxin. Interestingly, we show that m(56)-FXN and m(78)-FXN can be generated when the normal maturation process of frataxin is impaired, although the physiological relevance is not clear. Furthermore, we determine that the d-FXN form, previously reported to be a degradation product, corresponds to m(78)-FXN. Finally, we demonstrate that all frataxin isoforms are generated and localized within the mitochondria. The clear identification of the N-terminus of mature FXN is an important step for designing therapeutic approaches for FRDA based on frataxin replacement.
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PMID:The in vivo mitochondrial two-step maturation of human frataxin. 1872 97