View the Current Issue

Article

  • The EMBO Journal (2002) 21, 5599 - 5610
  • doi:10.1093/emboj/cdf566

Structural basis for the oxidation of thiosulfate by a sulfur cycle enzyme

Vicki A. Bamford1,2, Stefano Bruno1,2,3, Tim Rasmussen1,2, Corinne Appia-Ayme3, Myles R. Cheesman2, Ben C. Berks3 and Andrew M. Hemmings1,2

  1. Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
  2. Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
  3. Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK

Correspondence to:

Ben C. Berks, E-mail: ben.berks@bioch.ox.ac.uk

Andrew M. Hemmings, E-mail: a.hemmings@uea.ac.uk

Received 11 December 2001; Accepted 4 September 2002; Revised 26 August 2002

Reduced inorganic sulfur compounds are utilized by many bacteria as electron donors to photosynthetic or respiratory electron transport chains. This metabolism is a key component of the biogeochemical sulfur cycle. The SoxAX protein is a heterodimeric c-type cytochrome involved in thiosulfate oxidation. The crystal structures of SoxAX from the photosynthetic bacterium Rhodovulum sulfidophilum have been solved at 1.75 Å resolution in the oxidized state and at 1.5 Å resolution in the dithionite-reduced state, providing the first structural insights into the enzymatic oxidation of thiosulfate. The SoxAX active site contains a haem with unprecedented cysteine persulfide (cysteine sulfane) coordination. This unusual post-translational modification is also seen in sulfurtransferases such as rhodanese. Intriguingly, this enzyme shares further active site characteristics with SoxAX such as an adjacent conserved arginine residue and a strongly positive electrostatic potential. These similarities have allowed us to suggest a catalytic mechanism for enzymatic thiosulfate oxidation. The atomic coordinates and experimental structure factors have been deposited in the PDB with the accession codes 1H31, 1H32 and 1H33.

  • Keywords:

    • cysteine persulfide haem ligand,
    • SoxAX complex,
    • sulfur cycle,
    • thiosulfate oxidation,
    • X-ray crystal structure