His86 from the N-Terminus of Frataxin Coordinates Iron and Is Required for Fe–S Cluster Synthesis

Gentry, Leslie E.; Thacker, Matthew A.; Doughty, Reece; Timkovich, Russell; Busenlehner, Laura S.

doi:10.1021/bi400443n

Cited by 23 publications

(36 citation statements)

References 44 publications

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“…A number of studies have addressed the issue of iron binding by frataxin [ 5 , 10 , 13 , 28 , 31 – 33 ]. Using isothermal titration calorimetry (ITC), it was shown that yeast and bacterial frataxin CyaY under anaerobic conditions bind two ferrous ions/monomer [ 25 , 28 , 32 ].…”

Section: Introductionmentioning

confidence: 99%

“…However, it should be noted that the authors of this study used a His-tagged protein, which may have affected the measured metal binding capacity. A more recent study showed that the number of bound metal atoms (ferrous, ferric and cobalt were tested) was 3/monomer, with His86 being involved in the highest affinity metal binding site [ 33 ]. The longer FXN 56-210 isomer, which is spontaneously assembled into oligomeric particles upon expression in E .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…This residue is located in the disordered N-terminal tail and had not been previously reported to be involved in metal coordination. They calculated that this site would have an affinity for Fe 2+ higher than the iron chelator ferrozine, while the remaining two sites would have lower affinities [ 21 ]. His86 is not included in most of the frataxin structures that are found in the protein data bank nor is conserved in yeast and bacterial homologues.…”

Section: Frataxin Functionmentioning

confidence: 99%

Iron in Friedreich Ataxia: A Central Role in the Pathophysiology or an Epiphenomenon?

et al. 2018

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Friedreich ataxia is a neurodegenerative disease with an autosomal recessive inheritance. In most patients, the disease is caused by the presence of trinucleotide GAA expansions in the first intron of the frataxin gene. These expansions cause the decreased expression of this mitochondrial protein. Many evidences indicate that frataxin deficiency causes the deregulation of cellular iron homeostasis. In this review, we will discuss several hypotheses proposed for frataxin function, their caveats, and how they could provide an explanation for the deregulation of iron homeostasis found in frataxin-deficient cells. We will also focus on the potential mechanisms causing cellular dysfunction in Friedreich Ataxia and on the potential use of the iron chelator deferiprone as a therapeutic agent for this disease.

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“…The shortest isoform of human frataxin, FXN 81-210 , which due to the absence of a long N-terminal extension may have properties comparable to those of CyaY, is the most abundant form of human frataxin in mitochondria. It is believed to exist predominantly in a monomeric state and to have labile iron binding capacity [ 28 , 35 , 36 ]. However, in a recent study of the effect of iron chelators on frataxin oligomerization we showed that FXN 81-210 may form oligomers in vitro at aerobic conditions in the presence of iron and that the addition of ferric iron chelators deferiprone and DFO stabilizes these oligomers and even stimulates the formation of a larger number of oligomers [ 37 ].…”

Section: Introductionmentioning

confidence: 99%

SAXS and stability studies of iron-induced oligomers of bacterial frataxin CyaY

et al. 2017

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Frataxin is a highly conserved protein found in both prokaryotes and eukaryotes. It is involved in several central functions in cells, which include iron delivery to biochemical processes, such as heme synthesis, assembly of iron-sulfur clusters (ISC), storage of surplus iron in conditions of iron overload, and repair of ISC in aconitase. Frataxin from different organisms has been shown to undergo iron-dependent oligomerization. At least two different classes of oligomers, with different modes of oligomer packing and stabilization, have been identified. Here, we continue our efforts to explore the factors that control the oligomerization of frataxin from different organisms, and focus on E. coli frataxin CyaY. Using small-angle X-ray scattering (SAXS), we show that higher iron-to-protein ratios lead to larger oligomeric species, and that oligomerization proceeds in a linear fashion as a results of iron oxidation. Native mass spectrometry and online size-exclusion chromatography combined with SAXS show that a dimer is the most common form of CyaY in the presence of iron at atmospheric conditions. Modeling of the dimer using the SAXS data confirms the earlier proposed head-to-tail packing arrangement of monomers. This packing mode brings several conserved acidic residues into close proximity to each other, creating an environment for metal ion binding and possibly even mineralization. Together with negative-stain electron microscopy, the experiments also show that trimers, tetramers, pentamers, and presumably higher-order oligomers may exist in solution. Nano-differential scanning fluorimetry shows that the oligomers have limited stability and may easily dissociate at elevated temperatures. The factors affecting the possible oligomerization mode are discussed

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His86 from the N-Terminus of Frataxin Coordinates Iron and Is Required for Fe–S Cluster Synthesis

Cited by 23 publications

References 44 publications

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

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

Iron in Friedreich Ataxia: A Central Role in the Pathophysiology or an Epiphenomenon?

SAXS and stability studies of iron-induced oligomers of bacterial frataxin CyaY

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