Some sulphate-reducing and microaerophilic bacteria rely on the enzyme superoxide reductase (SOR) to eliminate the toxic superoxide anion radical (O2.-). SOR catalyses the one-electron reduction of O2.- to hydrogen peroxide at a non-haeme ferrous iron centre. The three-dimensional structures of Desulfovibrio desulfuricans and Pyrococcus furiosus SORs have revealed a catalytic domain formed by a seven-stranded beta-sandwich displaying an immunoglobulin-like fold. Catalysis occurs at a ferrous iron centre (named Centre II). Three classes of SORs have been described so far, all of which display a highly similar active site. D. desulfuricans, Desulfovibrio vulgaris, and Desulfoarculus baarsii SORs are representatives of class I, in which the catalytic domain is linked to a small N-terminal domain structurally similar to desulphoredoxin and containing an additional iron centre, named Centre I. SORs of class II, as P. furiosus SOR, are characterised by the absence of the additional N-terminal domain (Yeh et al., 2000). In class III, this domain is present, but centre I is absent, such as in T. pallidum SOR.

DOI:10.1016/j.str.2004.07.013,PFAM:PF01880,INTERPRO:IPR002742