A Combined Spectroscopic and In Silico Approach to Evaluate the Interaction of Human Frataxin with Mitochondrial Superoxide Dismutase

Abstract

Frataxin (FXN) is a highly conserved mitochondrial protein whose deficiency causes Friedreich’s ataxia, a neurodegenerative disease. The precise physiological function of FXN is still unclear; however, there is experimental evidence that the protein is involved in biosynthetic iron–sulfur cluster machinery, redox imbalance, and iron homeostasis. FXN is synthesized in the cytosol and imported into the mitochondria, where it is proteolytically cleaved to the mature form. Its involvement in the redox imbalance suggests that FXN could interact with mitochondrial superoxide dismutase (SOD2), a key enzyme in antioxidant cellular defense. In this work, we use site-directed spin labelling coupled to electron paramagnetic resonance spectroscopy (SDSL-EPR) and fluorescence quenching experiments to investigate the interaction between human FXN and SOD2 in vitro. Spectroscopic data are combined with rigid body protein–protein docking to assess the potential structure of the FXN-SOD2 complex, which leaves the metal binding region of FXN accessible to the solvent. We provide evidence that human FXN interacts with human SOD2 in vitro and that the complex is in fast exchange. This interaction could be relevant during the assembly of iron-sulfur (FeS) clusters and/or their incorporation in proteins when FeS clusters are potentially susceptible to attacks by reactive oxygen species.

Antigen-specific downregulation of miR-150 in CD4 T cells promotes cell survival

“…Among them, 66 genes were upregulated in miR-150-KO antigen-specific CD4 + T cells and 4 genes were known to participate in reducing superoxide byproducts that are pro-apoptotic. Both superoxidedismutase-2 (SOD2) and netrin-1 (Ntn1) directly reduce superoxide products (35), while Nfe2l2 and Frataxin (Fxn) enhance and promote SOD2 function (36,37). Therefore, either directly or indirectly, miR-150 may control superoxide levels in antigen-specific CD4 + T cells.…”

Searching for Frataxin Function: Exploring the Analogy with Nqo15, the Frataxin-like Protein of Respiratory Complex I from Thermus thermophilus

“…As expected, inherently flexible regions, such as unstructured loops, show increased flexibility in solution compared to the crystal structure, but the overall fold of the protein is not grossly distorted. The structure of isolated Nqo15 is more dynamic than that of human FXN, as determined by the comparison of the MD simulations [38]: aside from the C-terminus, the RMSF of FXN peaks at 2 Å and is, on average, lower than 1.5 Å, whereas several regions of Nqo15 have an RMSF of 2 Å or higher.…”

“…The involvement of the protein in redox homeostasis is still unclear as well, but it has been demonstrated that human FXN interacts, at least in vitro, with mitochondrial superoxide dismutase (SOD2), a key enzyme involved in the defense against oxidative stress [38].…”