Jonathan Przybyla-Toscano, étudiant au sein de l’équipe Redox de l’unité, défendra publiquement sa thèse vendredi 3 février à 13h (amphi 7 FST).

Venez nombreux !

Vendredi 3 février, 13h, (Amphi 7, FST): Jonathan Przybyla-Toscano (IAM)

Functional analysis of NFU and ISCA: proteins involved in Fe-S cluster maturation in Arabidopsis thaliana mitochondria

Abstract: In plants, iron-sulfur (Fe-S) proteins are involved in crucial processes such as photosynthesis and respiration. The maturation of these proteins requires the de novo synthesis of their Fe-S clusters through dedicated assembly machineries. Plants have three Fe-S cluster assembly machineries, namely SUF, ISC and CIA, devoted to the maturation of plastidial, mitochondrial and nuclear or cytosolic proteins, respectively. During the mitochondrial Fe-S protein maturation, a [2Fe-2S] cluster is first assembled on the ISU scaffold protein then transferred to target proteins with the help of chaperones and various transfer proteins. If these steps are sufficient for the maturation of [2Fe-2S] proteins, a reductive coupling process of two [2Fe-2S] clusters is required for the maturation of [4Fe-4S] proteins. This conversion needs transfer proteins and an electrons donor, potentially the same ferredoxin which acts during the first step of the Fe-S cluster biogenesis for sulfur reduction. By combining molecular, biochemical and genetic approaches, the involvement of NFU and ISCA transfer protein and mitochondrial ferredoxin (mFDX) in the late transfer and conversion steps has been explored during this PhD project by using the Arabidopsis thaliana plant model. Yeast complementation experiments have demonstrated that plant NFU and ISCA proteins have functions similar to their respective orthologs, suggesting that these late steps are conserved. However, unlike yeast, the characterization of nfu mutant lines indicates that both proteins are essential for early embryonic development. At the molecular level, in vivo and in vitro approaches have shown an interaction between ISCA1a or ISCA1b and ISCA2, NFU4 and NFU5 but no interaction with the two mFDX whose participation in the late steps remains uncertain. The formation of ISCA1-ISCA2 holo-heterocomplexes has been confirmed by co-expression in E. coli and purification of recombinant proteins. Overall, the literature and results obtained here highlight a model where ISCA1/2 heterocomplexes would act immediately downstream of NFU proteins which would a minima allow [4Fe-4S] cluster maturation of the lipoate synthase. This sole partner could primarily explain the lethality of a nfu4 x nfu5 double mutant because the activity of several proteins central for the mitochondrial metabolism depends on lipoic acid.