The sulphur oxygenase reductase from Acidianus ambivalens is a multimeric protein containing a low-potential mononuclear non-haem iron centre

Tim Urich, Tiago M. Bandeiras, Sónia S. Leal, Reinhard Rachel, Till Albrecht, Peter Zimmermann, Corinna Scholz, Miguel Teixeira, Cláudio M. Gomes, Arnulf Kletzin

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)

Abstract

The SOR (sulphur oxygenase reductase) is the initial enzyme in the sulphur-oxidation pathway of Acidianus ambivalens. Expression of the sor gene in Escherichia coli resulted in active, soluble SOR and in inclusion bodies from which active SOR could be refolded as long as ferric ions were present in the refolding solution. Wild-type, recombinant and refolded SOR possessed indistinguishable properties. Conformational stability studies showed that the apparent unfolding free energy in water is approx. 5 kcal· mol -1 (1 kcal = 4.184 kJ), at pH 7. The analysis of the quaternary structures showed a ball-shaped assembly with a central hollow core probably consisting of 24 subunits in a 432 symmetry. The subunits form homodimers as the building blocks of the holoenzyme. Iron was found in the wild-type enzyme at a stoichiometry of one iron atom/subunit. EPR spectroscopy of the colourless SOR resulted in a single isotropic signal at g = 4.3, characteristic of high-spin ferric iron. The signal disappeared upon reduction with dithionite or incubation with sulphur at elevated temperature. Thus both EPR and chemical analysis indicate the presence of a mononuclear iron centre, which has a reduction potential of - 268 mV at pH 6.5. Protein database inspection identified four SOR protein homologues, but no other significant similarities. The spectroscopic data and the sequence comparison led to the proposal that the Acidianus ambivalens SOR typifies a new type of non-haem iron enzyme containing a mononuclear iron centre co-ordinated by carboxylate and/or histidine ligands.

Original languageEnglish
Pages (from-to)137-146
Number of pages10
JournalBiochemical Journal
Volume381
Issue number1
DOIs
Publication statusPublished - 1 Jul 2004

Keywords

  • Electron paramagnetic resonance (EPR)
  • Hyperthermophilic archaea
  • Quaternary structure
  • Reversible denaturation
  • Sulphur oxidation

Fingerprint

Dive into the research topics of 'The sulphur oxygenase reductase from Acidianus ambivalens is a multimeric protein containing a low-potential mononuclear non-haem iron centre'. Together they form a unique fingerprint.

Cite this