A Global Proteomic Approach Sheds New Light on Potential Iron-Sulfur Client Proteins of the Chloroplastic Maturation Factor NFU3.

Nathalie Berger,Valérie Rofidal,Florence Vignols,Maël Taupin-Broggini,Frédéric Gaymard,Brigitte Touraine,Nicolas Rouhier,Vincent Demolombe,Christian Dubos,Véronique Santoni

doi:10.3390/ijms21218121

Abstract

Iron-sulfur (Fe-S) proteins play critical functions in plants. Most Fe-S proteins are synthetized in the cytosol as apo-proteins and the subsequent Fe-S cluster incorporation relies on specific protein assembly machineries. They are notably formed by a scaffold complex, which serves for the de novo Fe-S cluster synthesis, and by transfer proteins that insure cluster delivery to apo-targets. However, scarce information is available about the maturation pathways of most plastidial Fe-S proteins and their specificities towards transfer proteins of the associated SUF machinery. To gain more insights into these steps, the expression and protein localization of the NFU1, NFU2, and NFU3 transfer proteins were analyzed in various Arabidopsis thaliana organs and tissues showing quite similar expression patterns. In addition, quantitative proteomic analysis of an nfu3 loss-of-function mutant allowed to propose novel potential client proteins for NFU3 and to show that the protein accumulation profiles and thus metabolic adjustments differ substantially from those established in the nfu2 mutant. By clarifying the respective roles of the three plastidial NFU paralogs, these data allow better delineating the maturation process of plastidial Fe-S proteins.

Highlights

Iron is a transition metal essential for both prokaryotic and eukaryotic organisms
In Arabidopsis thaliana, there are three machineries for Fe-S protein maturation: the CIA, the ISC and the SUF machineries that are respectively localized in the cytosol, the mitochondria and the plastids
Hypotheses on the role of NFU2 in the maturation of specific Fe-S proteins, notably explaining the root phenotype described for Arabidopsis nfu2 mutants, were based on Western blot experiments showing that NFU2, but not NFU3, was present in roots [15,22]

Summary

Introduction

Iron is a transition metal essential for both prokaryotic and eukaryotic organisms. Iron is part of cofactors associated to proteins involved in numerous physiological processes such as respiration or photosynthesis [1]. Iron is found under diverse forms (i.e., as single atom or in complex with other elements) among which are hemes and iron-sulfur (Fe-S) clusters [2]. Apo-proteins are targeted to their final destination/cell compartments (i.e., nucleus, mitochondria, and plastids) for their maturation, including in particular the acquisition of their Fe-S cluster. In Arabidopsis thaliana, there are three machineries for Fe-S protein maturation: the CIA (cytosolic iron-sulfur protein assembly), the ISC (iron-sulfur cluster) and the SUF (sulfur mobilization) machineries that are respectively localized in the cytosol, the mitochondria and the plastids. The de novo Fe-S cluster synthesis primarily necessitates the activity of cysteine desulfurases that provide sulfur atoms (together with its associated regulatory proteins), of electron donors to reduce the sulfane sulfur species into sulfide, and of iron donors that remain, for the three machineries, to be identified [2]. The preformed Fe-S cluster is transferred to the apo-targets via late-acting maturation factors including so-called Fe-S cluster carrier/transfer proteins [2]

Methods

Results

Conclusion