Spectrosopic characterization of superoxide reductases

Abstract

A new pathway of reactive oxygen species detoxification in anaerobic and microaerophilic microorganisms has recently been discovered. The enzyme at the center of this pathway, superoxide reductase (SOR), catalyzes the reduction rather than the disproportionation of superoxide. Two distinct forms of SOR containing 1Fe and 2Fe have been structurally characterized by X-ray crystallography. Both contain a novel superoxide-reducing mononuclear non-heme iron active-site, while 2Fe-SORs contain an additional desulforedoxin-type non-heme iron site. The research in this dissertation focuses on understanding the structural and electronic determinants of enzymatic superoxide reduction through detailed spectroscopic characterization of the unique mononuclear non-heme iron active-site in wild-type and variant forms of the 1Fe-SOR in Pyrococcus furiosus and the 2Fe-SOR in Desulfovibrio vulgaris, using the combination of absorption, CD, magnetic circular dichroism, electron paramagnetic resonance, resonance Raman and FTIR. The results confirm a common SOR active-site in both 1Fe- and 2Fe-SORs and emphasize the importance of utilizing a high-spin iron center with axial cysteinyl ligation for mediating electron transfer, reductive superoxide binding, and effecting release of the product peroxide.