ORIGINAL ARTICLE

JBIC Journal of Biological Inorganic Chemistry

, Volume 4, Issue 2, pp 162-165

First online:

Ab initio structure solution of a dimeric cytochrome c3 from Desulfovibrio gigas containing disulfide bridges

  • Carlos FrazãoAffiliated withInstituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apart. 127, P-2780 Oeiras, Portugal e-mail: corrondo@itqb.un1.pt Tel.: +351-1-4469657 Fax: +351-1-4433644
  • , Larry SiekerAffiliated withDepartment of Biological Structure, University of Washington Seattle, WA 98195, USA
  • , George SheldrickAffiliated withInstitut für Anorganische Chemie der Universität Göttingen Tammannstrasse 4, D-37077 Göttingen, Germany
  • , Victor LamzinAffiliated withEuropean Molecular Biology Laboratory, c/o DESY Notkestrasse 85, D-22603 Hamburg, Germany
  • , Jean LeGallAffiliated withDepartment of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA
  • , M. A. CarrondoAffiliated withInstituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apart. 127, P-2780 Oeiras, Portugal e-mail: corrondo@itqb.un1.pt Tel.: +351-1-4469657 Fax: +351-1-4433644

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Abstract

 The 1.2 Å resolution crystal structure of the 29 kDa di-tetrahaem cytochrome c 3 from the sulfate reducing bacterium Desulfovibrio gigas was solved by ab initio methods, making this the largest molecule to be solved by this procedure. The actual refined model of the cysteine-linked dimeric molecule reveals that this molecule is very similar to the non-covalently linked symmetrical dimer of the di-tetrahaem cytochrome c 3 from Desulfomicrobium norvegicum. Each monomer has the typical polypeptide fold, haem arrangement and iron coordination found for the tetrahaem cytochrome c 3 molecules. The interface between the covalently linked monomers in the asymmetric unit of the crystal shows a pseudo two-fold arrangement, disturbed from symmetry by crystal packing forces. The fact that D. gigas contains a dimeric tetrahaem cytochrome with solvent accessible disulfide bridges and that this cytochrome specifically couples hydrogen oxidation to thiosulfate reduction in bacterial extracts provides an interesting aspect related to disulfide exchange reactions in this microorganism.

Key words Dimeric cytochrome c3 Ab initio structure Disulfide bridges Thiosulfate reduction