title: Structural analysis of Arabidopsis CnfU protein: an iron-sulfur cluster biosynthetic scaffold in chloroplasts.
abstract: CnfU, a key iron-sulfur (Fe-S) cluster biosynthetic scaffold that is required for biogenesis of ferredoxin and photosystem I in chloroplasts, consists of two tandemly repeated domains in which only the N-terminal domain contains a conserved CXXC motif. We have determined the crystal structure of the metal-free dimer of AtCnfU-V from Arabidopsis thaliana at 1.35 A resolution. The N-terminal domains of the two monomers are linked together through two intermolecular disulfide bonds between the CXXC motifs. At the dimer interface, a total of four cysteine sulfur atoms provide a Fe-S cluster assembly site surrounded by uncharged but hydrophilic structurally mobile segments. The C-terminal domain of one monomer interacts with the N-terminal domain of the opposing monomer and thereby stabilizes dimer formation. Furthermore, Fe K-edge X-ray absorption spectroscopic analysis of the holo-CnfU dimer in solution suggests the presence of a typical [2Fe-2S]-type cluster coordinated by four thiolate ligands. Based on these data, a plausible model of the holo-AtCnfU-V dimer containing a surface-exposed [2Fe-2S] cluster assembled in the dimer interface was deduced. We propose that such a structural framework is important for CnfU to function as a Fe-S cluster biosynthetic scaffold.
authors.affiliation: Laboratory of Regulation of Biological Reactions, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita 565-0871, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Yabe
authors.forename: Eiki
authors.initials: E
authors.lastname: Yamashita
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kikuchi
authors.forename: Kozo
authors.initials: K
authors.lastname: Morimoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nakagawa
authors.forename: Tomitake
authors.initials: T
authors.lastname: Tsukihara
authors.forename: Masato
authors.initials: M
authors.lastname: Nakai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D002736:Chloroplasts / Q000378:metabolism*; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D004220:Disulfides / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013057:Spectrum Analysis; D040681:Structural Homology, Protein
chemical_list: D029681:Arabidopsis Proteins; C508776:CnfU-V protein, Arabidopsis; D004220:Disulfides; D007506:Iron-Sulfur Proteins