Frataxin participates in the mitochondrial assembly of FeS clusters, redox cofactors of the respiratory complexes I, II and III. To date it is still unclear how frataxin deficiency culminates in the decrease of bioenergetics efficiency in FRDA patients' cells. The authors previously demonstrated that in healthy cells frataxin is closely attached to the mitochondrial cristae, which contain both the FeS cluster assembly machinery and the respiratory chain complexes, whereas in FRDA patients' cells with impaired respiration the residual frataxin is largely displaced in the matrix. To gain novel insights into the function of frataxin in the mitochondrial pathophysiology, and in the upstream metabolic defects leading to FRDA disease onset and progression, here the authors explored the potential interaction of frataxin with the FeS cluster-containing respiratory complexes I, II and III. Using healthy cells and different FRDA cellular models frataxin was found to interact with these three respiratory complexes. Furthermore, by EPR spectroscopy, the authors observed that in mitochondria from FRDA patients' cells the decreased level of frataxin specifically affects the FeS cluster content of complex I. Remarkably, the frataxin-like protein Nqo15 from T. thermophilus complex I ameliorates the mitochondrial respiratory phenotype when expressed in FRDA patient's cells. These data point to a structural and functional interaction of frataxin with complex I and open a perspective to explore therapeutic rationales for FRDA targeted to this respiratory complex.

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