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

• Published in: The Plant cell Vol. 16; no. 4; pp. 993 - 1007
• Main Authors: Yabe, Toshiki, Morimoto, Kozo, Kikuchi, Shingo, Nishio, Kazuaki, Terashima, Ichiro, Nakai, Masato
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01.04.2004
• Subjects: Amino Acid Sequence; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Bacterial Proteins - genetics; Biosynthesis; Chloroplasts; Chloroplasts - metabolism; Cyanobacteria - genetics; Dimerization; Dimers; DNA, Bacterial - genetics; E coli; Electron Transport; Ferredoxins; Ferredoxins - biosynthesis; Gels; Gene Expression; Genes, Plant; Iron; Iron-Sulfur Proteins - chemistry; Iron-Sulfur Proteins - genetics; Iron-Sulfur Proteins - metabolism; Models, Biological; Molecular Sequence Data; Mutation; Phenotype; Photosystem I Protein Complex - biosynthesis; Photosystem I Protein Complex - chemistry; Plant cells; Plants; Protein Subunits; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Scaffolds; Sequence Homology, Amino Acid; Species Specificity; Sulfur
• DOI: 10.1105/tpc.020511
• ISSN: 1040-4651; 1532-298X

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.