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The "prismane" protein resolved: X-ray structure at 1.7 Å and multiple spectroscopy of two novel 4Fe clusters

Authors
  • Arendsen, Alexander F.1
  • Hadden, Jonathan1
  • Card, Graeme1
  • McAlpine, Alan S.1
  • Bailey, Susan1
  • Zaitsev, Vjacheslav1
  • Duke, Elizabeth H. M.1
  • Lindley, P. F.1
  • Kröckel, Monika2
  • Trautwein, Alfred X.2
  • Feiters, Martinus C.3
  • Charnock, John M.4
  • Garner, C. David4
  • Marritt, Sophie J.5
  • Thomson, Andrew J.5
  • Kooter, Ingeborg M.6
  • Johnson, Michael K.6
  • van den Berg, Willy A. M.7
  • van Dongen, Walter M. A. M.7
  • Hagen, W. R.7
  • 1 CCLRC Daresbury Laboratory, Warrington WA4 4AD, UK, GB
  • 2 Institut für Physik, Medizinische Universität, D-23538 Lübeck, Germany, DE
  • 3 Department of Organic Chemistry, NSR Centre, University of Nijmegen, Toernooiveld, NL-6525 ED Nijmegen, The Netherlands, NL
  • 4 Chemistry Department, The University of Manchester, Oxford Road, Manchester M13 9PL, GB
  • 5 School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, GB
  • 6 Department of Chemistry, University of Georgia, Athens GA 30602, USA, GE
  • 7 Department of Biochemistry, Agricultural University, Dreijenlaan 3, NL-6703 HA Wageningen, The Netherlands Tel.: +31-317-483860; Fax: +31-317-484801; e-mail: [email protected], NL
Type
Published Article
Journal
JBIC Journal of Biological Inorganic Chemistry
Publisher
Springer-Verlag
Publication Date
Feb 01, 1998
Volume
3
Issue
1
Pages
81–95
Identifiers
DOI: 10.1007/s007750050210
Source
Springer Nature
Keywords
License
Yellow

Abstract

The three-dimensional structure of the native "putative prismane" protein from Desulfovibrio vulgaris (Hildenborough) has been solved by X-ray crystallography to a resolution of 1.72 Å. The molecule does not contain a [6Fe-6S] prismane cluster, but rather two 4Fe clusters some 12 Å apart and situated close to the interfaces formed by the three domains of the protein. Cluster 1 is a conventional [4Fe-4S] cubane bound, however, near the N-terminus by an unusual, sequential arrangement of four cysteine residues (Cys 3, 6, 15, 21). Cluster 2 is a novel 4Fe structure with two μ2-sulfido bridges, two μ2-oxo bridges, and a partially occupied, unidentified μ2 bridge X. The protein ligands of cluster 2 are widely scattered through the second half of the sequence and include three cysteine residues (Cys 312, 434, 459), one persulfido-cysteine (Cys 406), two glutamates (Glu 268, 494), and one histidine (His 244). With this unusual mixture of bridging and external type of ligands, cluster 2 is named the "hybrid" cluster, and its asymmetric, open structure suggests that it could be the site of a catalytic activity. X-ray absorption spectroscopy at the Fe K-edge is readily interpretable in terms of the crystallographic model when allowance is made for volume contraction at 10 K; no Fe··Fe distances beyond 3.1 Å could be identified. EPR, Mössbauer and MCD spectroscopy have been used to define the oxidation states and the magnetism of the clusters in relation to the crystallographic structure. Reduced cluster 1 is a [4Fe-4S]1+ cubane with S = 3/2; it is the first biological example of a "spin-admixed" iron-sulfur cluster. The hybrid cluster 2 has four oxidation states from (formally) all FeIII to three FeII plus one FeIII. The four iron ions are exchange coupled resulting in the system spins S = 0, 9/2, 0 (and 4), 1/2, respectively, for the four redox states. Resonance Raman spectroscopy suggests that the bridging ligand X which could not be identified unambiguously in the crystal structure is a solvent-exchangeable oxygen.

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