Frataxin is a mitochondrial protein that is defective in Friedreich's ataxia resulting in iron accumulation and an environment prone to Fenton reactions. We report that frataxin is Susceptible to carbonylation and nitration modifications in residues from the beta-sheet surface (Tyr143, Tyr174, Tyr205 and Trp155). Frataxin functions are not significantly affected: frataxin-mediated protection against ROS is still observed, as well as iron-binding (5 Fe3+ mol(-1), K-d from 13-36 mu M) necessary for the metallochaperone activity. However, the protein is up to 1.0 kcal mol(-1) destabilized, with conformational opening. Interestingly, the strictly conserved Trp155, which is mutated in patients, may be a functional hotspot in frataxin. (C) 2009 Elsevier Inc. All rights reserved.