title: X-ray absorption spectroscopic analysis of reductive [2Fe-2S] cluster degradation in hyperthermophilic archaeal succinate:caldariellaquinone oxidoreductase subunits.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA. zrli@ou.edu
authors.forename: Zhongrui
authors.initials: Z
authors.lastname: Li
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Shokes
authors.forename: Asako
authors.initials: A
authors.lastname: Kounosu
authors.forename: Takeo
authors.initials: T
authors.lastname: Imai
authors.forename: Toshio
authors.initials: T
authors.lastname: Iwasaki
authors.forename: Robert A
authors.initials: RA
authors.lastname: Scott
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D042963:Electron Transport Complex II / Q000737:chemistry* / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism; D011809:Quinones / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis / Q000379:methods; D016944:Sulfolobus / Q000201:enzymology
chemical_list: D019843:Archaeal Proteins; D007506:Iron-Sulfur Proteins; D021122:Protein Subunits; D011809:Quinones; D011994:Recombinant Proteins; C014380:caldariellaquinone; D042963:Electron Transport Complex II