title: The crystal structure of zinc-containing ferredoxin from the thermoacidophilic archaeon Sulfolobus sp. strain 7.
abstract: The crystal structure of ferredoxin from the thermoacidophilic archaeon Sulfolobus sp. strain 7 was determined by multiple isomorphous replacement supplemented with anomalous scattering effects of iron atoms in the Fe-S clusters, and refined at 2.0 A resolution to a crystallographic R value of 0.173. The structural model contains a polypeptide chain of 103 amino acid residues, 2 [3Fe-4S] clusters, and 31 water molecules; in this model, the cluster corresponding to cluster II in bacterial dicluster ferredoxins loses the fourth iron atom although it may originally be a [4Fe-4S] cluster. The structure of the archaeal ferredoxin consists of two parts: the core fold part (residues 37-103) and the N-terminal extension part (residues 1-36). The "core fold" part has an overall main-chain folding common to bacterial dicluster ferredoxins, containing two clusters as the active center, two alpha-helices near the clusters, and two sheets of two-stranded antiparallel beta-sheet (the terminal and central beta-sheets). The "N-terminal extension" part is mainly formed by a one-turn alpha-helix and a three-stranded antiparallel beta-sheet. The beta-sheet in the N-terminal extension is hydrogen-bonded with the terminal beta-sheet in the core fold to form a larger beta-sheet. The distinct structural feature of this archaeal ferredoxin lies in the zinc-binding center where the zinc ion is tetrahedrally ligated by four amino acid residues (His 16, His 19, and His 34 from the N-terminal extension, and Asp 76 from the core fold). The zinc ion in the zinc-binding center is located at the interface between the core fold and the N-terminal extension, and connects the beta-sheet in the N-terminal extension and the central beta-sheet in the core fold through the zinc ligation. Thus, the zinc ion plays an important role in stabilizing the structure of the present archaeal ferredoxin by connecting the N-terminal extension and the core fold, which may be common to thermoacidophilic archaeal ferredoxins.
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Fujii
authors.forename: Y
authors.initials: Y
authors.lastname: Hata
authors.forename: M
authors.initials: M
authors.lastname: Oozeki
authors.forename: H
authors.initials: H
authors.lastname: Moriyama
authors.forename: T
authors.initials: T
authors.lastname: Wakagi
authors.forename: N
authors.initials: N
authors.lastname: Tanaka
authors.forename: T
authors.initials: T
authors.lastname: Oshima
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D005288:Ferredoxins / Q000737:chemistry*; D005583:Fourier Analysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D016944:Sulfolobus
chemical_list: D005288:Ferredoxins