Partial conservation of functions between eukaryotic frataxin and theEscherichia colifrataxin homolog CyaY

Abstract

Frataxin is a mitochondrial protein structurally conserved from bacteria to humans. Eukaryotic frataxins are known to be involved in the maintenance of mitochondrial iron balance via roles in iron delivery and iron detoxification. The prokaryotic frataxin homolog, CyaY, has been shown to bind and donate iron for the assembly of [2Fe-2S] clusters in vitro. However, in contrast to the severe phenotypes associated with the partial or complete loss of frataxin in humans and other eukaryotes, deletion of the cyaY gene does not cause any obvious alteration of iron balance in bacterial cells, an effect that probably reflects functional redundancy between CyaY and other bacterial proteins. To study CyaY function in a nonredundant setting, we have expressed a mitochondria-targeted form of CyaY in a Saccharomyces cerevisiae strain depleted of the endogenous yeast frataxin protein (yfh1Delta). We show that in this strain CyaY complements to a large extent the loss of iron-sulfur cluster enzyme activities and heme synthesis, and thereby maintains a nearly normal respiratory growth. In addition, CyaY effectively protects yfh1Delta from oxidative damage during treatment with hydrogen peroxide but is less efficient in detoxifying excess labile iron during aerobic growth.

Architecture of the Human Mitochondrial Iron-Sulfur Cluster Assembly Machinery

“…In addition, in yeast cells expressing human frataxin precursor instead of yeast frataxin precursor, we detected complexes containing heterologous FXN bound to endogenous Nfs1 and Isu1, which underscored the structural and functional conservation between the yeast and the human Fe-S cluster assem-bly systems (7). These previous data together with the high degree of conservation between prokaryotic and mitochondrial Fe-S cluster assembly systems (2,3,34) led us to hypothesize that simultaneous co-expression of FXN , NFS1, ISD11 , and ISCU in E. coli might mimic the mitochondrial environment and yield similar complexes in sufficient quantities to enable structural studies. We therefore co-expressed the four proteins in E. coli as described under "Experimental Procedures."…”

Fe-S Cluster Assembly Pathways in Bacteria

“…Thus, the lack of a strong phenotype for the cyaY deletion in bacteria may reflect multiple redundant systems (such as YggX) that are not present in eukaryotes rather than the lack of a role in Fe-S cluster assembly. In support of this interpretation, the bacterial CyaY protein is capable of partially rescuing a frataxin (Yfh1) deletion in yeast if it is expressed with a mitochondrial targeting sequence (10).…”

The Molecular Basis of Iron-induced Oligomerization of Frataxin and the Role of the Ferroxidation Reaction in Oligomerization

“…CyaY was purified according to (37) with the difference that the second-step anion exchange using Macro-Prep High Q was not performed.…”