title: ISC-like [2Fe-2S] ferredoxin (FdxB) dimer from Pseudomonas putida JCM 20004: structural and electron-nuclear double resonance characterization.
abstract: The crystal structure of the ISC-like [2Fe-2S] ferredoxin (FdxB), probably involved in the de novo iron-sulfur cluster biosynthesis (ISC) system of Pseudomonas putida JCM 20004, was determined at 1.90-Å resolution and displayed a novel tail-to-tail dimeric form. P. putida FdxB lacks the consensus free cysteine usually present near the cluster of ISC-like ferredoxins, indicating its primarily electron transfer role in the iron-sulfur cluster. Orientation-selective electron-nuclear double resonance spectroscopic analysis of reduced FdxB in conjunction with the crystal structure has identified the innermost Fe2 site with a high positive spin population as the nonreducible iron retaining the Fe(3+) valence and the outermost Fe1 site as the reduced iron with a low negative spin density. The average g (max) direction is skewed, forming an angle of about 27.3° (±4°) with the normal of the [2Fe-2S] plane, whereas the g (int) and g (min) directions are distributed in the cluster plane, presumably tilted by the same angle with respect to this plane. These results are related to those for other [2Fe-2S] proteins in different electron transport chains (e.g. adrenodoxin) and suggest a significant distortion of the electronic structure of the reduced [2Fe-2S] cluster under the influence of the protein environment around each iron site in general.
authors.affiliation: Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan. tiwasaki@nms.ac.jp
authors.forename: Toshio
authors.initials: T
authors.lastname: Iwasaki
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kappl
authors.forename: Gerhard
authors.initials: G
authors.lastname: Bracic
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Shimizu
authors.forename: Daijiro
authors.initials: D
authors.lastname: Ohmori
authors.forename: Takashi
authors.initials: T
authors.lastname: Kumasaka
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005288:Ferredoxins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D055503:Protein Multimerization; D016958:Pseudomonas putida / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: C081714:2Fe-2S ferredoxin; D001426:Bacterial Proteins; D005288:Ferredoxins