On the Search of a Comprehensive Representation of Human Frataxin

ARAN M, FARAJ SE, GALLO M, NOGUERA ME, GONZÁLEZ LEBRERO R, ROMAN EA AND JAVIER SANTOS

Sierra de la Ventana, Buenos Aires

Congreso; XLIII Reunión Anual de SAB; 2014

SAB

Friedreich´s ataxia (FRDA) is a neurodegenerative disease linked to a deficiency of frataxin (FXN), a protein involved in iron-sulfur cluster biosynthesis. Human FXN contains a folded C―terminal domain starting at residue 90 with a/b topology followed by a C-terminal region (CTR) that packs against the protein´s core. We have investigated the impact of the alteration of the CTR on the stability, internal dynamics and folding dynamics of FXN. The pathological mutation L198R yields a global destabilization and a significant and highly localized alteration of dynamics, mainly involving residues that are in contact with L198 in wild type FXN. Variant FXN90―195, which is closely related to the FRDA―associated mutant FXN81―193, preserves its native-like structure. However, the truncation of the CTR results in an extreme decrease of global stability and alteration of protein dynamics over a vast range of timescales, including regions far from the CTR. Moreover, both mutants exhibit an important deficiency in iron-binding, suggesting coupling dynamics between the CTR and the acidic ridge (helix 1, loop1, strand 1) involved in iron binding. The increased sensitivity to proteolysis observed in vitro, the reduced ability to bind iron, and the enhanced tendency to aggregate exhibited by the truncated variant may explain why the alteration of the CTR causes FRDA. The alteration of the dynamics and stability of FXNL198R is in line with the rapid disease progression observed in patients carrying this mutation. Folding kinetic experiments firmly suggest that the change in global stability observed in CTR mutations is most probably caused by a native-state destabilization than by a change in the stability of the transition state ensembles. These results contribute to understanding how stability and activity are linked to protein motions, and might be valuable for the design of target-specific binders to control local protein motions for stability and activity enhancement.