Iron-Sulfur Cluster Complex Assembly in the Mitochondria of Arabidopsis thaliana

Abstract

In plants, the cysteine desulfurase (AtNFS1) and frataxin (AtFH) are involved in the formation of Fe-S groups in mitochondria, specifically, in Fe and sulfur loading onto scaffold proteins, and the subsequent formation of the mature Fe-S cluster. We found that the small mitochondrial chaperone, AtISD11, and AtFH are positive regulators for AtNFS1 activity in Arabidopsis. Moreover, when the three proteins were incubated together, a stronger attenuation of the Fenton reaction was observed compared to that observed with AtFH alone. Using pull-down assays, we found that these three proteins physically interact, and sequence alignment and docking studies showed that several amino acid residues reported as critical for the interaction of their human homologous are conserved. Our results suggest that AtFH, AtNFS1 and AtISD11 form a multiprotein complex that could be involved in different stages of the iron–sulfur cluster (ISC) pathway in plant mitochondria.

Fe-S Protein Synthesis in Green Algae Mitochondria

“…It was shown that in plants, specifically in Arabidopsis, there are two isoforms, AtNFS1, located in mitochondria and AtNFS2, with chloroplastic localization [ 3 , 31 , 32 , 33 ]. ISD11 is a member of the LYR protein family, which lacks orthologs in prokaryotes but is highly conserved in yeast, humans, and plants [ 34 , 35 , 36 ], while IscU is a scaffold protein homologous to ISU from plants [ 37 ]. Three genes encoding ISU1-3 were found in Arabidopsis (At4g22220, At3g01020, At4g04080) [ 31 , 38 , 39 ], while ACP is an acyl group carrier protein, homologous to Arabidopsis AtACP1-3 [ 40 ].…”

“…In addition, we suggested that AtFH, AtNFS1 and AtISD11 form a multiprotein complex in Arabidopsis mitochondria. We found that AtFH and AtISD11 modulate the desulfurase activity of AtNFS1, indicating that the complex would have an important role in the early stages of Fe-S cluster synthesis [ 36 ]. Moreover, this complex would act in mitigating plant mitochondrial oxidative damage.…”

“…When we performed an alignment by Clustal Omega [ 94 ] of all sequences of Chlorophytes plus the homologs from Arabidopsis and corn, we detected that three of the critical residues for the interaction with AtNFS1 are absolutely conserved (Phe38, Leu61 and Arg66) [ 36 ]. The Arg66 residue is homologous to Arg68 in humans and it has been shown that the mutation of this amino acid, although it does not prevent the formation of the NFS1-ISD11 complex, causes a severe decrease in NFS1 activity [ 95 ].…”

“…Furthermore, AtFH has ferrochelatase activity and is involved in the metabolism of the heme group and the synthesis of hemeproteins in mitochondria [ 91 , 112 ]. Moreover, we recently demonstrated that AtFH interacts with AtISD11 and AtNFS1, forming a complex that would modulate ferrochelatase activity and cysteine desulfurization by AtNFS1 [ 36 , 91 ].…”

SSR1 is a vital regulator in plant mitochondrial iron-sulfur biosynthesis

“…Many Arabidopsis genes encoding the core components of ISC pathway have been identified based on sequence homology with their counterparts in bacteria or yeast, and some core proteins are encoded by a multiple-gene family (Tone et al, 2004; Leon et al, 2005; Frazzon et al, 2007; Xu et al, 2009; Balk and Schaedler, 2014). For instance, there are three genes for cysteine desulfurase in Arabidopsis, namely NFS1, NFS2 and ABA3 (Balk and Schaedler, 2014; Armas et al, 2020). Only NFS1 showed mitochondria localization and high homology with IscS, a bacterial cysteine desulfurase (Frazzon et al, 2007).…”