Human frataxin: a model to understand sequence-structure-function relationships.

ASTOR MIGNONE; SANTIAGO FARAJ; LEANDRO VENTURUTTI; ERNESTO A ROMÁN; MARIANO CAMILO GONZÁLEZ LEBRERO; JOSÉ MARÍA DELFINO; JAVIER SANTOS

Salta, Argentina

Congreso; XXXIX Annual Meeting of the Argentinean Biophysical Society 2010. 3rd. Latin American Protein Society Meeting.; 2010

Latin American Protein Society

Friedreich ataxia (FA) is caused by the deficiency in the expression of frataxin (FXN), an α+β protein of 120 amino acid residues. FXN is able to sequester high quantities of Fe metal ion. The 3D structure of human FXN (hFXN) in its monomeric version is well known by NMR and X-ray crystallography. Variations in the C-terminal region correlate with the conformational stability of different homologues. It is necessary a detailed study of this part of the molecule to understand its role in the consolidation of the tertiary and quaternary structure. The quaternary structure of yeast FXN (yFXN) is induced by iron. On the contrary, in the case of hFXN, this phenomenon does not occur, and it is not clear whether multimerization of hFXN occurs in-vivo or not. The N-terminal region of the molecule that is not conserved along the evolution of FXNs has a role in the oligomerization process. However, we do not know the molecular mechanism that defines the in-vitro multimerization of hFXN. For this project we decided to explore the role of N- and C-terminal regions on FXN stability. We studied three FXN variants: (a) FXN56-210, that aggregates during in-vitro expression and can be unfolded and refolded into a monomeric form; (b) FXN90-210, a truncated and monomeric form that is very stable, folds cooperatively and retains biological function; and (c) FXN90-180, a partially folded fragment endowed with iron binding sites, exhibiting secondary structure but only residual tertiary structure and experiencing a non-cooperative temperature unfolding. In addition, we ran molecular dynamics simulations of fragments FXN90-195 and FXN90-210 and applied bioinformatics tools to study sequence 56-90. Our results confirm the role of C-terminal moiety on the stabilization of the cooperative a‑unit of human FXN. We hypothesize that the N-terminal may have a role in the multimerization through the stabilization of a partially folded state. Acknowledgements: This work was supported by ANPCyT, CONICET, UBACyT and UNQ.