X-ray absorption spectroscopic analysis of reductive [2Fe-2S] cluster degradation in hyperthermophilic archaeal succinate:caldariellaquinone oxidoreductase subunits

Biochemistry. 2003 Dec 23;42(50):15003-8. doi: 10.1021/bi035078h.


The biological [2Fe-2S] clusters play important roles in electron transfer and cellular signaling for a variety of organisms from archaea, bacteria to eukarya. The two recombinant hyperthermophilic archaeal [2Fe-2S] cluster-binding proteins, SdhC and the N-terminal domain fragment of SdhB, of Sulfolobus tokodaii respiratory complex II overproduced in Escherichia coli are thermostable as isolated, but moderately sensitive to reduction with excess dithionite. We used iron K-edge X-ray absorption spectroscopy to monitor the structural changes of their Fe sites in the irreversible [2Fe-2S] cluster degradation process. Regardless of the differences in the cluster-ligating cysteine motifs and the XAS-detectable [2Fe-2S](2+) cluster environments, a complete reductive breakdown of the [2Fe-2S] clusters resulted in the appearance of a new Fourier transform (FT) peak at approximately 3.3 A with a concomitant loss of the Fe-Fe interaction at ca. 2.7 A for both proteins. On the basis of the unambiguous assignment of the 3.3 A FT peak, our results suggest that a biological [2Fe-2S] cluster breakdown under reducing conditions generally releases Fe(2+) from the polypeptide chain into the aqueous solution, and the Fe(2+) might then be recruited as a secondary ferrous iron source for de novo biosynthesis and/or regulation of iron-binding enzymes in the cellular system.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Archaeal Proteins / chemistry*
  • Archaeal Proteins / metabolism
  • Electron Transport Complex II / chemistry*
  • Electron Transport Complex II / metabolism
  • Iron-Sulfur Proteins / chemistry*
  • Iron-Sulfur Proteins / metabolism
  • Oxidation-Reduction
  • Protein Subunits / chemistry*
  • Protein Subunits / metabolism
  • Quinones / metabolism*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Spectrum Analysis / methods
  • Sulfolobus / enzymology


  • Archaeal Proteins
  • Iron-Sulfur Proteins
  • Protein Subunits
  • Quinones
  • Recombinant Proteins
  • caldariellaquinone
  • Electron Transport Complex II