Spectroscopic characterization of the [Fe(His)4(Cys)] site in 2Fe-superoxide reductase from Desulfovibrio vulgaris

Abstract

The electronic and vibrational properties of the [Fe(His)(4)(Cys)] site (Center II) responsible for catalysis of superoxide reduction in the two-iron superoxide reductase (2Fe-SOR) from Desulfovibrio vulgaris have been investigated using the combination of EPR, resonance Raman, UV/visible/near-IR absorption, CD, and VTMCD spectroscopies. Deconvolution of the spectral contributions of Center II from those of the [Fe(Cys)(4)] site (Center I) has been achieved by parallel investigations of the C13S variant, which does not contain Center I. The resonance Raman spectrum of ferric Center II has been assigned based on isotope shifts for (34)S and (15)N globally labeled proteins. As for the [Fe(His)(4)(Cys)] active site in 1Fe-SOR from Pyrococcus furiosus, the spectroscopic properties of ferric and ferrous Center II in D. vulgaris 2Fe-SOR are indicative of distorted octahedral and square-pyramidal coordination geometries, respectively. Differences in the properties of the ferric [Fe(His)(4)(Cys)] sites in 1Fe- and 2Fe-SORs are apparent in the rhombicity of the S=5/2 ground state ( E/ D=0.06 and 0.28 in 1Fe- and 2Fe-SORs, respectively), the energy of the CysS(-)(p(pi))-->Fe(3+)(d(pi)) CT transition (15150+/-150 cm(-1) and 15600+/-150 cm(-1) in 1Fe- and 2Fe-SORs, respectively) and in changes in the Fe-S stretching region of the resonance Raman spectrum indicative of a weaker Fe-S(Cys) bond in 2Fe-SORs. These differences are interpreted in terms of small structural perturbations in the Fe coordination sphere with changes in the Fe-S(Cys) bond strength resulting from differences in the peptide N-H.S(Cys) hydrogen bonding within a tetrapeptide bidentate "chelate". Observation of the characteristic intervalence charge transfer transition of a cyano-bridged [Fe(III)-NC-Fe(II)(CN)(5)] unit in the near-IR VTMCD spectra of ferricyanide-oxidized samples of both P. furiosus 1Fe-SOR and D. vulgaris 2Fe-SOR has confirmed the existence of novel ferrocyanide adducts of the ferric [Fe(His)(4)(Cys)] sites in both 1Fe- and 2Fe-SORs.

Methanoferrodoxin represents a new class of superoxide reductase containing an iron–sulfur cluster

“…3A) showed the typical EPR signal of a high‐spin ( S = 5/2) ferric site. This signal at g = 4.3 is attributed to the [Fe(NHis) 4 (SCys)] center, and has also been detected in the SORs from P. furiosus and Desulfovibrio vulgaris , as well as in the D. desulfuricans desulfoferrodoxin [22–24].…”

Avoiding high-valent iron intermediates: Superoxide reductase and rubrerythrin

“…2). The mobility of the loop makes for an expansive pocket, as demonstrated by the remarkable observation of an apparently inner-sphere oxidation of the ferrous SOR site by ferricyanide, which occurs at $30 s À1 (with excess ferricyanide) [74] and forms a ferrocyanide adduct with a cyano bridge between the SOR and ferrocyano irons [64,75,76].…”

High unique diversity of sulfate‐reducing prokaryotes characterized in a depth gradient in an acidic fen

“…However, pure cultures of SRPs can tolerate certain amounts of O 2 (Dilling and Cypionka, 1990; Dannenberg et al ., 1992; Marschall et al ., 1993; Fuseler and Cypionka, 1995; LeGall and Xavier, 1996; Johnson et al ., 1997; Krekeler et al ., 1997; 1998; Sass et al ., 1998; Ito et al ., 2002a,b). Superoxide reductase protects cells against toxic superoxides derived from O 2 and is present in SRPs such as Desulfovibrio vulgaris (Lumppio et al ., 2001; Kurtz and Coulter, 2002; Clay et al ., 2003). Some Desulfovibrio species reduce O 2 in the periplasm, apparently as a protective mechanism (Baumgarten et al ., 2001).…”