Two-step Processing of Human Frataxin by Mitochondrial Processing Peptidase

Authors

• Patrizia Cavadini, Mayo Clinic and Foundation
• Jiri Adamec, University of Nebraska-LincolnFollow
• Franco Taroni, Istituto Nazionale Neurologico “Carlo Besta,” Milano, Italy
• Oleksandr Gakh, Academy of Sciences of the Czech Republic
• Grazia Isaya, Mayo Clinic and Foundation

Document Type

Article

Date of this Version

2000

Citation

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

Comments

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

Abstract

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.