The Arabidopsis chloroplastic NifU-like protein CnfU, which can act as an iron-sulfur cluster scaffold protein, is required for biogenesis of ferredoxin and photosystem I.
The biosynthesis of iron-sulfur clusters is a highly regulated process involving several proteins. Among them, so-called scaffold proteins play pivotal roles in both the assembly and delivery of iron-sulfur clusters. Here, we report the identification of two chloroplast-localized NifU-like proteins, AtCnfU-V and AtCnfU-IVb, from Arabidopsis (Arabidopsis thaliana) with high sequence similarity to a cyanobacterial NifU-like protein that was proposed to serve as a molecular scaffold. AtCnfU-V is constitutively expressed in several tissues of Arabidopsis, whereas the expression of AtCnfU-IVb is prominent in the aerial parts. Mutant Arabidopsis lacking AtCnfU-V exhibited a dwarf phenotype with faint pale-green leaves and had drastically impaired photosystem I accumulation. Chloroplasts in the mutants also showed a decrease in both the amount of ferredoxin, a major electron carrier of the stroma that contains a [2Fe-2S] cluster, and in the in vitro activity of iron-sulfur cluster insertion into apo-ferredoxin. When expressed in Escherichia coli cells, AtCnfU-V formed a homodimer carrying a [2Fe-2S]-like cluster, and this cluster could be transferred to apo-ferredoxin in vitro to form holo-ferredoxin. We propose that AtCnfU has an important function as a molecular scaffold for iron-sulfur cluster biosynthesis in chloroplasts and thereby is required for biogenesis of ferredoxin and photosystem I.
Yabe
Toshiki
T
Institute for Protein Research, Osaka University, Suita, 565-0871, Japan.
Morimoto
Kozo
K
Kikuchi
Shingo
S
Nishio
Kazuaki
K
Terashima
Ichiro
I
Nakai
Masato
M
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics; D002736:Chloroplasts / Q000378:metabolism; D000458:Cyanobacteria / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D019281:Dimerization; D004579:Electron Transport; D005288:Ferredoxins / Q000096:biosynthesis*; D015870:Gene Expression; D017343:Genes, Plant; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D045331:Photosystem I Protein Complex / Q000096:biosynthesis* / Q000737:chemistry; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D045331:Photosystem I Protein Complex; D021122:Protein Subunits; D011994:Recombinant Proteins; C036483:T-DNA