Iron Cofactor Assembly in Plants

Abstract

Iron is an essential element for all photosynthetic organisms. The biological use of this transition metal is as an enzyme cofactor, predominantly in electron transfer and catalysis. The main forms of iron cofactor are, in order of decreasing abundance, iron-sulfur clusters, heme, and di-iron or mononuclear iron, with a wide functional range. In plants and algae, iron-sulfur cluster assembly pathways of bacterial origin are localized in the mitochondria and plastids, where there is a high demand for these cofactors. A third iron-sulfur cluster assembly pathway is present in the cytosol that depends on the mitochondria but not on plastid assembly proteins. The biosynthesis of heme takes place mainly in the plastids. The importance of iron-sulfur cofactors beyond photosynthesis and respiration has become evident with recent discoveries of novel iron-sulfur proteins involved in epigenetics and DNA metabolism. In addition, increased understanding of intracellular iron trafficking is opening up research into how iron is distributed between iron cofactor assembly pathways and how this distribution is regulated.

Du fer et du soufre dans les protéines

“…Comme nous le verrons, les machineries ISC et SUF ne sont pas de simples duplications l'une de l'autre. Il apparaît donc que, durant l'évolution, plusieurs solutions différentes ont été sélectionnées pour satisfaire les besoins en centres Fe-S des différents organismes [5][6][7][8][9][10]. Enfin, les eucaryotes possèdent une troisième machinerie, la CIA (cytosolic iron-sulfur clusters assembly), que l'on pourrait désigner comme une « extension de la ligne de distribution » de la machinerie ISC, localisée dans le cytoplasme, et requise pour la maturation des protéines cytoplasmiques, voire nucléaires [11,12].…”

“…Étant donné le rôle central des protéines Fe-S dans le fonctionnement cellulaire, il n'est pas étonnant que des mutations invalidant ou alté-rant le fonctionnement des machineries ISC ou SUF provoquent des phénotypes marqués [5][6][7][8][9][10].…”

Chloroplastic iron-sulfur scaffold protein NFU3 is essential to overall plant fitness

“…[1][2][3] Iron-sulfur clusters may contain different numbers of iron and sulfur ions. The 4 most common iron-sulfur clusters in plants are: classic 2Fe-2S, Rieske-type 2Fe-2S, 3Fe-4S, and 4Fe-4S clusters.…”

“…[1][2][3] Three iron-sulfur assembly and transfer pathways have been identified in plants: the SUF (sulfur mobilization) pathway in plastids, the ISC (ironsulfur cluster) pathway in mitochondria, and the CIA (cytosolic iron-sulfur) assembly pathway. [1][2][3] The SUF pathway is responsible for the assembly and transfer of classic 2Fe-2S, Rieske-type 2Fe-2S, 3Fe-4S, and 4Fe-4S clusters in plastids; the ISC pathway is in charge of assembly and transfer of classic 2Fe-2S, 3Fe-4S, and 4Fe-4S clusters in mitochondria; and the CIA pathway assembles and transfers classic 2Fe-2S and 4Fe-4S clusters in the cytosol. 1 In all 3 pathways, the process can be divided into 2 steps: (1) assembly of iron-sulfur clusters on an iron-sulfur scaffold protein by cysteine desulfurase, and (2) subsequent transfer of iron-sulfur clusters from the ironsulfur scaffold protein to recipient apoproteins.…”

“…1 In all 3 pathways, the process can be divided into 2 steps: (1) assembly of iron-sulfur clusters on an iron-sulfur scaffold protein by cysteine desulfurase, and (2) subsequent transfer of iron-sulfur clusters from the ironsulfur scaffold protein to recipient apoproteins. [1][2][3] Recently, it was found that Nitrogen-Fixing-subunit-U-type protein NFU3 acts as a scaffold protein in the assembly and transfer of 4Fe-4S and 3Fe-4S clusters in the chloroplast. 4 The recombinant NFU3 protein showed characteristics of 4Fe-4S and 3Fe-4S clusters and an in vitro activity of iron-sulfur cluster reconstitution.…”