CONICET | Buscador de Institutos y Recursos Humanos

Friedreich Ataxia (FA) is a progressive hereditary disease of children and adolescents characterized by neurological impairment and cardiomyopathy. FA is caused by the deficiency in the expression of frataxin (FXN) and, in some cases, by mutations that alter the stability of this polypeptide. FXN is imported into the mitochondria where it binds Fe metal ion (working as an iron chaperone). The structure of human FXN (hFXN) is known by NMR and X-ray crystallography. Variations on the C-terminal region correlate with the conformation stability of different homologues (e.g. yeast, E. coli, human). However, we do not know which the molecular determinants of these stability variations are. In addition, nothing is known about the relationship between this region and the cooperativity of FXN fold. We hypothesize that stability of hFXN depends on the formation of a cooperative tertiary unit based on the modulation of the interaction between a-helix 1 and a-helix 2 (a-unit) by peptide 196-210. Therefore, we consider important to establish the consequences of truncation on structure, conformational flexibility/dynamics of hFXN. Here we explore experimentally the effect of the truncation of residues 196-210 on FXN stability and fold consolidation. Our approach involves light scattering, analytical ultracentrifugation, temperature unfolding experiments, CD and fluorescence characterization. In addition, we investigate by molecular dynamics simulation (full-atom MDS) whether native-like ensemble of the truncated form has particular flexibility properties that differ from full-length FXN. Interestingly, our results indicate that fragment 90-195 is compact, monomeric and highly soluble (35 mg/mL). Our results confirm the role of residues 196-210 on the stabilization of the fold. The analysis of MDS indicates that this fragment seems to conserve its native-like topology, although being highly flexible.