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

SANTIAGO FARAJ; LEANDRO VENTURUTTI; ERNESTO A ROMÁN; CRISTINA MARINO BUSLJE; ASTOR MIGNONE; SILVIO TOSATTO; JOSÉ MARÍA DELFINO; JAVIER SANTOS

FEBS OPEN BIO

ELSEVIER

Año: 2013

2211-5463

<!-- /* Font Definitions */ @font-face {font-family:"New York"; panose-1:2 4 5 3 6 5 6 2 3 4; mso-font-alt:"Times New Roman"; mso-font-charset:0; mso-generic-font-family:roman; mso-font-format:other; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} @font-face {font-family:Times; panose-1:0 0 0 0 0 0 0 0 0 0; mso-font-charset:0; mso-generic-font-family:auto; mso-font-format:other; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:10.0pt; margin-left:0cm; text-align:justify; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:Times; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt; mso-ascii-font-family:"New York"; mso-hansi-font-family:"New York";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The N-terminal stretch of human frataxin (hFXN) intermediate (residues 42-80) is not conserved throughout evolution and, under defined experimental conditions it behaves as a random-coil. However, overexpression of hFXN56-210 in E. coli yields a multimer, whereas hFXN81-210, the mature form of hFXN, 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. In this context, we explore 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. On the other hand, controlled proteolysis indicates that the N-terminal stretch is labile in the context of the multimer, whereas the FXN domain remains strongly resistant (residues 81-210). In addition, GdmCl at low concentration disrupts intermolecular interactions, shifting the ensemble toward the monomeric form. Furthermore, peptide 56-81, putatively responsible for promoting protein-protein interactions, was studied in its propensity to acquire ordered secondary structure by virtue of TFE or SDS addition. Depending on the environment, this peptide adopts α-helical or β-strand structure. Complementary, the analysis of mutual information along hFXN1-210 reveals three independent information networks. Interestingly, one of them involves residues in the 50-70 region, suggesting a common co-evolutionary relationship. The conformational plasticity of the N-terminal tail might impart hFXN the ability to act as a recognition signal as well as an oligomerization trigger. Understanding the fine tuning of these activities and the resulting balance will bear direct relevance for ultimately comprehending hFXN function.