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

Eva Christina Ahlgren, Mostafa Fekry, Mathias Wiemann, Christopher A. Söderberg, Katja Bernfur, Olex Gakh, Morten Rasmussen, Peter Højrup, Cecilia Emanuelsson, Grazia Isaya, Salam Al-Karadaghi*

*Corresponding author for this work

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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 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.

Original languageEnglish
Article numbere0188937
JournalPLOS ONE
Volume12
Issue number12
Number of pages25
ISSN1932-6203
DOIs
Publication statusPublished - 2017

Fingerprint

Oligomerization
Chelating Agents
chelating agents
Oligomers
Iron
iron
Monomers
Electron microscopy
Mass spectrometry
Electron Microscopy
Stabilization
electron microscopy
Neurodegenerative diseases
Friedreich Ataxia
frataxin
oligomerization
mass spectrometry
Protein Sequence Analysis
Dynamic light scattering
X ray scattering

Cite this

Ahlgren, E. C., Fekry, M., Wiemann, M., Söderberg, C. A., Bernfur, K., Gakh, O., ... Al-Karadaghi, S. (2017). Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators. PLOS ONE, 12(12), [e0188937]. https://doi.org/10.1371/journal.pone.0188937
Ahlgren, Eva Christina ; Fekry, Mostafa ; Wiemann, Mathias ; Söderberg, Christopher A. ; Bernfur, Katja ; Gakh, Olex ; Rasmussen, Morten ; Højrup, Peter ; Emanuelsson, Cecilia ; Isaya, Grazia ; Al-Karadaghi, Salam. / Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators. In: PLOS ONE. 2017 ; Vol. 12, No. 12.
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title = "Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators",
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 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.",
author = "Ahlgren, {Eva Christina} and Mostafa Fekry and Mathias Wiemann and S{\"o}derberg, {Christopher A.} and Katja Bernfur and Olex Gakh and Morten Rasmussen and Peter H{\o}jrup and Cecilia Emanuelsson and Grazia Isaya and Salam Al-Karadaghi",
year = "2017",
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language = "English",
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Ahlgren, EC, Fekry, M, Wiemann, M, Söderberg, CA, Bernfur, K, Gakh, O, Rasmussen, M, Højrup, P, Emanuelsson, C, Isaya, G & Al-Karadaghi, S 2017, 'Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators', PLOS ONE, vol. 12, no. 12, e0188937. https://doi.org/10.1371/journal.pone.0188937

Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators. / Ahlgren, Eva Christina; Fekry, Mostafa; Wiemann, Mathias; Söderberg, Christopher A.; Bernfur, Katja; Gakh, Olex; Rasmussen, Morten; Højrup, Peter; Emanuelsson, Cecilia; Isaya, Grazia; Al-Karadaghi, Salam.

In: PLOS ONE, Vol. 12, No. 12, e0188937, 2017.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators

AU - Ahlgren, Eva Christina

AU - Fekry, Mostafa

AU - Wiemann, Mathias

AU - Söderberg, Christopher A.

AU - Bernfur, Katja

AU - Gakh, Olex

AU - Rasmussen, Morten

AU - Højrup, Peter

AU - Emanuelsson, Cecilia

AU - Isaya, Grazia

AU - Al-Karadaghi, Salam

PY - 2017

Y1 - 2017

N2 - 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.

AB - 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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DO - 10.1371/journal.pone.0188937

M3 - Journal article

C2 - 29200434

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JO - P L o S One

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