title: Turning Escherichia coli into a Frataxin-Dependent Organism.
abstract: Fe-S bound proteins are ubiquitous and contribute to most basic cellular processes. A defect in the ISC components catalyzing Fe-S cluster biogenesis leads to drastic phenotypes in both eukaryotes and prokaryotes. In this context, the Frataxin protein (FXN) stands out as an exception. In eukaryotes, a defect in FXN results in severe defects in Fe-S cluster biogenesis, and in humans, this is associated with Friedreich's ataxia, a neurodegenerative disease. In contrast, prokaryotes deficient in the FXN homolog CyaY are fully viable, despite the clear involvement of CyaY in ISC-catalyzed Fe-S cluster formation. The molecular basis of the differing importance in the contribution of FXN remains enigmatic. Here, we have demonstrated that a single mutation in the scaffold protein IscU rendered E. coli viability strictly dependent upon a functional CyaY. Remarkably, this mutation changed an Ile residue, conserved in prokaryotes at position 108, into a Met residue, conserved in eukaryotes. We found that in the double mutant IscUIM ΔcyaY, the ISC pathway was completely abolished, becoming equivalent to the ΔiscU deletion strain and recapitulating the drastic phenotype caused by FXN deletion in eukaryotes. Biochemical analyses of the "eukaryotic-like" IscUIM scaffold revealed that it exhibited a reduced capacity to form Fe-S clusters. Finally, bioinformatic studies of prokaryotic IscU proteins allowed us to trace back the source of FXN-dependency as it occurs in present-day eukaryotes. We propose an evolutionary scenario in which the current mitochondrial Isu proteins originated from the IscUIM version present in the ancestor of the Rickettsiae. Subsequent acquisition of SUF, the second Fe-S cluster biogenesis system, in bacteria, was accompanied by diminished contribution of CyaY in prokaryotic Fe-S cluster biogenesis, and increased tolerance to change in the amino acid present at the 108th position of the scaffold.
authors.affiliation: Laboratoire de Chimie Bactérienne, UMR 7283, Aix-Marseille Université-CNRS, Institut de Microbiologie de la Méditerranée, Marseille, France.
authors.forename: Béatrice
authors.initials: B
authors.lastname: Roche
authors.affiliation: De Duve Institute, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: Rym
authors.initials: R
authors.lastname: Agrebi
authors.affiliation: Laboratoire de Chimie Bactérienne, UMR 7283, Aix-Marseille Université-CNRS, Institut de Microbiologie de la Méditerranée, Marseille, France.
authors.forename: Allison
authors.initials: A
authors.lastname: Huguenot
authors.affiliation: DSV/iRTSV/CBM, UMR 5249 CEA-Université de Grenoble I-CNRS/Equipe Biocatalyse, CEA-Grenoble, Grenoble, France.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Ollagnier de Choudens
authors.affiliation: Laboratoire de Chimie Bactérienne, UMR 7283, Aix-Marseille Université-CNRS, Institut de Microbiologie de la Méditerranée, Marseille, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Barras
authors.affiliation: Laboratoire de Chimie Bactérienne, UMR 7283, Aix-Marseille Université-CNRS, Institut de Microbiologie de la Méditerranée, Marseille, France.
authors.forename: Béatrice
authors.initials: B
authors.lastname: Py
mesh_terms: D019295:Computational Biology; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D033862:Iron-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000235:genetics* / Q000378:metabolism; D050296:Microbial Viability; D009154:Mutation; D010802:Phylogeny; D013385:Succinate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000096923:Frataxin
chemical_list: D029968:Escherichia coli Proteins; D033862:Iron-Binding Proteins; D007506:Iron-Sulfur Proteins; D013385:Succinate Dehydrogenase; D000096923:Frataxin; C120906:CyaY protein, E coli; C411665:IscU protein, E coli