The DnaJ proteins DJA6 and DJA5 are essential for chloroplast iron–sulfur cluster biogenesis

Abstract

Fe–S clusters are ancient, ubiquitous and highly essential prosthetic groups for numerous fundamental processes of life. The biogenesis of Fe–S clusters is a multistep process including iron acquisition, sulfur mobilization, and cluster formation. Extensive studies have provided deep insights into the mechanism of the latter two assembly steps. However, the mechanism of iron utilization during chloroplast Fe–S cluster biogenesis is still unknown. Here we identified two Arabidopsis DnaJ proteins, DJA6 and DJA5, that can bind iron through their conserved cysteine residues and facilitate iron incorporation into Fe–S clusters by interactions with the SUF (sulfur utilization factor) apparatus through their J domain. Loss of these two proteins causes severe defects in the accumulation of chloroplast Fe–S proteins, a dysfunction of photosynthesis, and a significant intracellular iron overload. Evolutionary analyses revealed that DJA6 and DJA5 are highly conserved in photosynthetic organisms ranging from cyanobacteria to higher plants and share a strong evolutionary relationship with SUFE1, SUFC, and SUFD throughout the green lineage. Thus, our work uncovers a conserved mechanism of iron utilization for chloroplast Fe–S cluster biogenesis.

Research Progress in J-Proteins in the Chloroplast

“…The other two are DJA4 and DJA7. When DJA5 or DJA6 was knocked out, the single mutant was compensated by the other protein since the functions of DJA5 and DJA6 overlapped [ 14 ]. Therefore, the phenotype and the chloroplast ultrastructure of single mutants did not show obvious differences compared with that of WT.…”

“…the protein content in the photosystem electron transport chain and the chloroplast SUF apparatus also decreased to a certain extent, which hindered the photosystem electron transport process. It can be seen that DJA5 and DJA6 are critical for maintaining a normal plastid shape, the normal phenotype of plant growth and Fe-S protein content [ 14 ].…”

“…If the cysteine in CR domain was replaced with other amino acids, the binding affinity of DJA5 and DJA6 to iron would be affected, and the Fe-S cluster assembly in the plastid would be affected, accordingly. After binding iron, DJA5 and DJA6 interact with SUF system components such as SUFE1 and SUFC in the chloroplast through their J-domains, and transfer the iron-bound by cysteine residues to the iron receptor SUFD to promote the assembly of Fe-S clusters [ 14 ]. Therefore, DJA5 and DJA6 were demonstrated to be the iron donor of the scaffold of Fe-S cluster biogenesis in the plastid.…”

“…CDJ3-5 are most similar to the Fd domain-containing DJC76 clade, including DJC76, DJC77 and DJC82 of Arabidopsis [ 8 ]. Therefore, it is interesting to explore the function of DJC76 clade proteins, since DJA5 and DJA6 are involved in plastid Fe-S cluster biogenesis [ 14 ]. Determining the relationship between DJC76 clade proteins and DJA5/6 requires further analysis.…”

“…It is reported that Arabidopsis contains two kinds of chloroplast heat shock protein 70 (cpHSP70), while this is true of at least 18 J-proteins and many J-like proteins in chloroplasts [ 8 , 11 , 12 ]. Except for the function as the co-chaperone of cpHSP70, some chloroplast J-proteins and J-like proteins have been demonstrated to play roles in many different biological processes [ 8 , 13 , 14 ].…”