The yeast frataxin homolog Yfh1p plays a specific role in the maturation of cellular Fe/S proteins

Abstract

The mitochondrial matrix protein frataxin is depleted in patients with Friedreich's ataxia, the most common autosomal recessive ataxia. While frataxin is important for intracellular iron homeostasis, its exact cellular role is unknown. Deletion of the yeast frataxin homolog YFH1 yields mutants ((Delta)yfh1) that, depending on the genetic background, display various degrees of phenotypic defects. This renders it difficult to distinguish primary (early) from secondary (late) consequences of Yfh1p deficiency. We have constructed a yeast strain (Gal-YFH1) that carries the YFH1 gene under the control of a galactose-regulated promoter. Yfh1p-deficient Gal-YFH1 cells are far less sensitive to oxidative stress than (Delta)yfh1 mutants, maintain mitochondrial DNA, and synthesize heme at wild-type rates. Yfh1p depletion causes a strong reduction in the assembly of mitochondrial Fe/S proteins both in vivo and in detergent extracts of mitochondria. Impaired Fe/S protein biogenesis explains the respiratory deficiency of Gal-YFH1 cells. Furthermore, Yfh1p-depleted Gal-YFH1 cells show decreased maturation of cytosolic Fe/S proteins and accumulation of mitochondrial iron. This latter phenotype is common for defects in cytosolic Fe/S protein assembly. Together, our data demonstrate a specific role of frataxin in the biosynthesis of cellular Fe/S proteins and exclude most of the previously suggested functions. Friedreich's ataxia may therefore represent a disorder caused by defects in Fe/S protein maturation.

Metal Ion availability in mitochondria

“…Thus, metallochaperones for Fe(II) and Mn(II) may be important in controlling the reactivity of these ions together with ensuring their bioavailability and specific delivery. Iron donation to ferrochelatase and Isu1 for formation of heme and Fe-S cluster biogenesis, respectively, may involve the matrix protein frataxin (Lesuisse et al 2003;Muhlenhoff et al 2002). Consistent with these roles, Yfh1 interacts with both the Hem15 ferrochelatase and Isu1.…”

“…Consistent with these roles, Yfh1 interacts with both the Hem15 ferrochelatase and Isu1. Cells lacking the yeast frataxin (Yfh1) are heme deficient (Lesuisse et al 2003) and compromised in Fe-S cluster biogenesis (Muhlenhoff et al 2002). However, frataxin is not essential for donating iron to ferrochelatase, as limited heme formation occurs in yfh1Δ cells.…”

“…Likewise, depletion of yeast frataxin compromises but does not preclude Fe-S cluster biogenesis (Muhlenhoff et al 2002). Frataxin adopts a well defined αβ-sandwich structural motif and is capable of binding Fe(II) ions in a N-terminal conserved acidic patch (He et al 2004).…”

Analysis of iron–sulfur protein maturation in eukaryotes

“…Likewise, Table 3 provides representative specific enzyme activities in galactose-grown wild-type cells. Appropriate non-Fe/S enzymes should be measured in parallel as controls 10,19,68 . Figure 3 shows typical results for an in vivo 55 Fe incorporation experiment in yeast.…”

Iron Sulfur Cluster Biosynthesis

“…53 Interestingly, our in vitro data is consistent with Saccharomyces cerevisiae in organello and in vivo studies by Lill and colleagues in which they too proposed a role for frataxin in Fe-S biosynthesis, although the precise function was not established. 56,57 With known iron and sulfide donors in hand and by successful reconstitution of the biosynthesis system in vitro, we proposed a working model for Fe-S cluster assembly on ISU 53 ( Figure 3). Initial studies led to speculation that the first step in Fe-S cluster biogenesis is IscS-mediated sulfur delivery to IscU.…”