The role of frataxin in fission yeast iron metabolism: Implications for Friedreich's ataxia |
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Authors: | Yu Wang Yiwei Wang S. Marcus L.S. Busenlehner |
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Affiliation: | 1. Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487, USA;2. Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL 35487, USA |
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Abstract: | BackgroundThe neurodegenerative disease Friedreich's ataxia is the result of frataxin deficiency. Frataxin is a mitochondrial protein involved in iron–sulfur cluster (Fe–S) cofactor biogenesis, but its functional role in this pathway is debated. This is due to the interconnectivity of iron metabolic and oxidative stress response pathways that make distinguishing primary effects of frataxin deficiency challenging. Since Fe–S cluster assembly is conserved, frataxin overexpression phenotypes in a simple eukaryotic organism will provide additional insight into frataxin function.MethodsThe Schizosaccharomyces pombe frataxin homologue (fxn1) was overexpressed from a plasmid under a thiamine repressible promoter. The S. pombe transformants were characterized at several expression strengths for cellular growth, mitochondrial organization, iron levels, oxidative stress, and activities of Fe–S cluster containing enzymes.ResultsObserved phenotypes were dependent on the amount of Fxn1 overexpression. High Fxn1 overexpression severely inhibited S. pombe growth, impaired mitochondrial membrane integrity and cellular respiration, and led to Fxn1 aggregation. Cellular iron accumulation was observed at moderate Fxn1 overexpression but was most pronounced at high levels of Fxn1. All levels of Fxn1 overexpression up-regulated oxidative stress defense and mitochondrial Fe–S cluster containing enzyme activities.ConclusionsDespite the presence of oxidative stress and accumulated iron, activation of Fe–S cluster enzymes was common to all levels of Fxn1 overexpression; therefore, Fxn1 may regulate the efficiency of Fe–S cluster biogenesis in S. pombe.General SignificanceWe provide evidence that suggests that dysregulated Fe–S cluster biogenesis is a primary effect of both frataxin overexpression and deficiency as in Friedreich's ataxia. |
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Keywords: | FA, Friedreich's ataxia Fe&ndash S, iron&ndash sulfur hFxn, human frataxin Yfh1, S. cerevisiae frataxin homologue CyaY, E. coli frataxin homologue Nfs1, cysteine desulfurase Isu1, iron sulfur scaffold protein Isd11, Fe&ndash S accessory protein nmt1, no message in thiamine promoter EMM, Edinburgh minimal media SDH2, succinate dehydrogenase sdh2-GFP, green fluorescent protein fused-SDH2 qRT-PCR, quantitative real-time PCR BCA, bicinchoninic acid BPS, bathophenanthrolinedisulfonic acid NADP+/NADPH, nicotinamide adenine dinucleotide phosphate PMS, phenazine methosulfate DCIP, 2,6-dichlorophenolindophenol SOD, S. pombe superoxide dismutase Fxn1Δ2&ndash 11, S. pombe Fxn1 with deletion of residues 2&ndash 11 MALDI-TOF, matrix assisted laser desorption ionization time of flight Frp1, S. pombe ferric reductase DTPA, diethylene triamine pentaacetic acid DFO, deferoxamine TCA, citric acid cycle ROS, reactive oxygen species |
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