Biochemistry, Department of


Document Type


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The Journal of Biological Chemistry, Vol. 275, No. 52, Issue of December 29, pp. 41469–41475, 2000


© 2000 by The American Society for Biochemistry and Molecular Biology, Inc.


We showed previously that maturation of the human

frataxin precursor (p-fxn) involves two cleavages by the

mitochondrial processing peptidase (MPP). This observation

was not confirmed by another group, however,

who reported only one cleavage. Here, we demonstrate

conclusively that MPP cleaves p-fxn in two sequential

steps, yielding a 18,826-Da intermediate (i-fxn) and a

17,255-Da mature (m-fxn) form, the latter corresponding

to endogenous frataxin in human tissues. The two cleavages

occur between residues 41–42 and 55–56, and both

match the MPP consensus sequence RX ↓ (X/S). Recombinant

rat and yeast MPP catalyze the pài step 4 and 40

times faster, respectively, than the i à m step. In isolated

rat mitochondria, p-fxn undergoes a sequence of

cleavages, p à i à m à d1 à d2, with d1 and d2 representing

two C-terminal fragments of m-fxn produced by

an unknown protease. The iàm step is limiting, and the

overall rate of p à i à m does not exceed the rate of mà

d1 à d2, such that the levels of m-fxn do not change

during incubations as long as 3 h. Inhibition of the iàm

step by a disease-causing frataxin mutation (W173G)

leads to nonspecific degradation of i-fxn. Thus, the second

of the two processing steps catalyzed by MPP limits

the levels of mature frataxin within mitochondria.