Structures of the superoxide reductase from Pyrococcus furiosus in the oxidized and reduced states

Superoxide reductase (SOR) is a blue non-heme iron protein that functions in anaerobic microbes as a defense mechanism against reactive oxygen species by catalyzing the reduction of superoxide to hydrogen peroxide [Jenney, F. E., Jr., Verhagen, M. F. J. M., Cui, X., and Adams, M. W. W. (1999) Science 286, 306−309]. Crystal structures of SOR from the hyperthermophilic archaeon Pyrococcus furiosus have been determined in the oxidized and reduced forms to resolutions of 1.7 and 2.0 A, respectively. SOR forms a homotetramer, with each subunit adopting an immunoglobulin-like β-barrel fold that coordinates a mononuclear, non-heme iron center. The protein fold and metal center are similar to those observed previously for the homologous protein desulfoferrodoxin from Desulfovibrio desulfuricans [Coelho, A. V., Matias, P., Fulop, V., Thompson, A., Gonzalez, A., and Carrondo, M. A. (1997) J. Bioinorg. Chem. 2, 680−689]. Each iron is coordinated to imidazole nitrogens of four histidines in a planar arrangement, with...