Superoxide reductase-like (SORL) domain; present in a family of mononuclear non-heme iron proteins that includes superoxide reductase and desulfoferrodoxin. Superoxide reductase-like proteins scavenge superoxide anion radicals as a defense mechanism against reactive oxygen species and are found in anaerobic bacteria and archeae, and microaerophilic Treponema pallidum. The SORL domain contains an active iron site, Fe[His4Cys(Glu)], which in the reduced state loses the glutamate ligand. Superoxide reductase (class II) forms a homotetramer with four Fe[His4Cys(Glu)] centers. Desulfoferrodoxin (class I) is a homodimeric protein, with each protomer comprised of two domains, the N-terminal desulforedoxin (DSRD) domain and C-terminal SORL domain. Each domain has a distinct iron center: the DSRD iron center I, Fe(S-Cys)4; and the SORL iron center II, Fe[His4Cys(Glu)].
Feature 1:non-heme iron binding site [ion binding site]
Evidence:
Comment:Each iron is coordinated to imidazole nitrogens of four histidines in a planar arrangement, with a cysteine ligand occupying an axial position.
Structure:1DQI; Superoxide reductase (SOR) in oxidized form.
Comment:In two of the subunits of oxidized SOR, a Glu carboxylate serves as the sixth ligand to form an overall six-coordinate, octahedral coordinate environment.
Structure:1DQK; Superoxide reductase (SOR) in reduced form.
Comment:The iron centers in all four subunits of reduced SOR exhibit pentacoordination.
Jiyao W et al.(2023). "The conserved domain database in 2023.",