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Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators

Ahlgren, Eva Christina LU ; Fekry, Mostafa; Wiemann, Mathias; Söderberg, Christopher A. LU ; Bernfur, Katja LU ; Gakh, Olex; Rasmussen, Morten; Højrup, Peter; Emanuelsson, Cecilia LU and Isaya, Grazia, et al. (2017) In PLoS ONE 12(12).
Abstract

Patients suffering from the progressive neurodegenerative disease Friedreich’s ataxia have reduced expression levels of the protein frataxin. Three major isoforms of human frataxin have been identified, FXN42-210, FXN56-210 and FXN81-210, of which FXN81-210 is considered to be the mature form. Both long forms, FXN42-210 and FXN56-210, have been shown to spontaneously form oligomeric particles stabilized by the extended N-terminal sequence. The short variant FXN81-210, on other hand, has only been observed in the monomeric state. However, a highly homologous E. coli frataxin CyaY, which also lacks an N-terminal extension, has been shown to oligomerize in the... (More)

Patients suffering from the progressive neurodegenerative disease Friedreich’s ataxia have reduced expression levels of the protein frataxin. Three major isoforms of human frataxin have been identified, FXN42-210, FXN56-210 and FXN81-210, of which FXN81-210 is considered to be the mature form. Both long forms, FXN42-210 and FXN56-210, have been shown to spontaneously form oligomeric particles stabilized by the extended N-terminal sequence. The short variant FXN81-210, on other hand, has only been observed in the monomeric state. However, a highly homologous E. coli frataxin CyaY, which also lacks an N-terminal extension, has been shown to oligomerize in the presence of iron. To explore the mechanisms of stabilization of short variant frataxin oligomers we compare here the effect of iron on the oligomerization of CyaY and FXN81-210. Using dynamic light scattering, small-angle X-ray scattering, electron microscopy (EM) and cross linking mass spectrometry (MS), we show that at aerobic conditions in the presence of iron both FXN81-210 and CyaY form oligomers. However, while CyaY oligomers are stable over time, FXN81-210 oligomers are unstable and dissociate into monomers after about 24 h. EM and MS studies suggest that within the oligomers FXN81-210 and CyaY monomers are packed in a head-to-tail fashion in ring-shaped structures with potential iron-binding sites located at the interface between monomers. The higher stability of CyaY oligomers can be explained by a higher number of acidic residues at the interface between monomers, which may result in a more stable iron binding. We also show that CyaY oligomers may be dissociated by ferric iron chelators deferiprone and DFO, as well as by the ferrous iron chelator BIPY. Surprisingly, deferiprone and DFO stimulate FXN81-210 oligomerization, while BIPY does not show any effect on oligomerization in this case. The results suggest that FXN81-210 oligomerization is primarily driven by ferric iron, while both ferric and ferrous iron participate in CyaY oligomer stabilization. Analysis of the amino acid sequences of bacterial and eukaryotic frataxins suggests that variations in the position of the acidic residues in helix 1, β-strand 1 and the loop between them may control the mode of frataxin oligomerization.

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PLoS ONE
volume
12
issue
12
publisher
Public Library of Science
external identifiers
  • scopus:85037039159
  • wos:000417033200023
ISSN
1932-6203
DOI
10.1371/journal.pone.0188937
language
English
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yes
id
9716f4b3-736c-4a89-b5a4-a2bf5dd8060b
date added to LUP
2017-12-18 10:40:28
date last changed
2018-01-16 13:28:06
@article{9716f4b3-736c-4a89-b5a4-a2bf5dd8060b,
  abstract     = {<p>Patients suffering from the progressive neurodegenerative disease Friedreich’s ataxia have reduced expression levels of the protein frataxin. Three major isoforms of human frataxin have been identified, FXN<sup>42-210</sup>, FXN<sup>56-210</sup> and FXN<sup>81-210</sup>, of which FXN<sup>81-210</sup> is considered to be the mature form. Both long forms, FXN<sup>42-210</sup> and FXN<sup>56-210</sup>, have been shown to spontaneously form oligomeric particles stabilized by the extended N-terminal sequence. The short variant FXN<sup>81-210</sup>, on other hand, has only been observed in the monomeric state. However, a highly homologous E. coli frataxin CyaY, which also lacks an N-terminal extension, has been shown to oligomerize in the presence of iron. To explore the mechanisms of stabilization of short variant frataxin oligomers we compare here the effect of iron on the oligomerization of CyaY and FXN<sup>81-210</sup>. Using dynamic light scattering, small-angle X-ray scattering, electron microscopy (EM) and cross linking mass spectrometry (MS), we show that at aerobic conditions in the presence of iron both FXN<sup>81-210</sup> and CyaY form oligomers. However, while CyaY oligomers are stable over time, FXN<sup>81-210</sup> oligomers are unstable and dissociate into monomers after about 24 h. EM and MS studies suggest that within the oligomers FXN<sup>81-210</sup> and CyaY monomers are packed in a head-to-tail fashion in ring-shaped structures with potential iron-binding sites located at the interface between monomers. The higher stability of CyaY oligomers can be explained by a higher number of acidic residues at the interface between monomers, which may result in a more stable iron binding. We also show that CyaY oligomers may be dissociated by ferric iron chelators deferiprone and DFO, as well as by the ferrous iron chelator BIPY. Surprisingly, deferiprone and DFO stimulate FXN<sup>81-210</sup> oligomerization, while BIPY does not show any effect on oligomerization in this case. The results suggest that FXN<sup>81-210</sup> oligomerization is primarily driven by ferric iron, while both ferric and ferrous iron participate in CyaY oligomer stabilization. Analysis of the amino acid sequences of bacterial and eukaryotic frataxins suggests that variations in the position of the acidic residues in helix 1, β-strand 1 and the loop between them may control the mode of frataxin oligomerization.</p>},
  articleno    = {e0188937},
  author       = {Ahlgren, Eva Christina and Fekry, Mostafa and Wiemann, Mathias and Söderberg, Christopher A. and Bernfur, Katja and Gakh, Olex and Rasmussen, Morten and Højrup, Peter and Emanuelsson, Cecilia and Isaya, Grazia and Al-Karadaghi, Salam},
  issn         = {1932-6203},
  language     = {eng},
  month        = {12},
  number       = {12},
  publisher    = {Public Library of Science},
  series       = {PLoS ONE},
  title        = {Iron-induced oligomerization of human FXN<sup>81-210</sup> and bacterial CyaY frataxin and the effect of iron chelators},
  url          = {http://dx.doi.org/10.1371/journal.pone.0188937},
  volume       = {12},
  year         = {2017},
}