Figure 8
The role of frataxin isoforms in cells. Canonical full-length frataxin isoform A (1–210) is targeted to mitochondria, where the first 80 amino acids (including the mitochondrial targeting sequence) are removed by MPP to give the mature form (81–210). Frataxin isoform E (76–210) does not contain a mitochondrial targeting sequence, and so it is retained in the cytosol where it is cleaved by an MPP-like protease to give extra-mitochondrial mature frataxin identical with that found in the mitochondria. It has been suggested by Lill et al. that extra-mitochondrial frataxin could facilitate the assembly of iron sulfur cluster proteins involved in DNA repair and telomere length control4. Erythrocytes, which lack mitochondria, contain only isoform E. They also lack the MPP-like protease present in the cytosol of non-hematopoietic cells.
