The role of the N-terminal tail for the oligomerization, folding and stability of human frataxin

FARAJ, S; VENTURUTTI L; ROMAN E; C MARINO-BUSLJE; MIGNONE A; TOSATTO S; DELFINO JM; SANTOS J

FEBS Open Bio

Elsevier

Año: 2013 vol. 3 p. 310 - 320

2211-5463

The N-terminal stretch of human frataxin (hFXN) intermediate (residues 42-80) is not conserved throughout evolution and, under defined experimental conditions, behaves as a random-coil. Over- expression of hFXN56?210 in Escherichia coli yields a multimer, whereas the mature form of hFXN (hFXN81-210) is monomeric. Thus, cumulative experimental evidence points to the N-terminal moiety as an essential element for the assembly of a high molecular weight oligomer. The secondary structure propensity of peptide 56-81, the moiety putatively responsible for promoting protein?protein inter- actions, was also studied. Depending on the environment (TFE or SDS), this peptide adopts α-helical or β-strand structure. In this context, we explored the conformation and stability of hFXN56-210. The biophysical characterization by fluorescence, CD and SEC-FPLC shows that subunits are well folded, sharing similar stability to hFXN90?210. However, controlled proteolysis indicates that the N-terminal stretch is labile in the context of the multimer, whereas the FXN domain (residues 81-210) remains strongly resistant. In addition, guanidine hydrochloride at low concentration disrupts intermolecular interactions, shifting the ensemble toward the monomeric form. The conformational plasticity of the N-terminal tail might impart on hFXN the ability to act as a recognition signal as well as an oligomerization trigger. Understanding the fine-tuning of these activities and their resulting balance will bear direct relevance for ultimately comprehending hFXN function.