1.15.1.2 evolution based on the number of metal centres, superoxide reductases can be divided into two major subclasses: neelaredoxins (Nlr) solely contain the active site (1Fe-SOR), while desulfoferrodoxins (Dfx) harbour an additional rubredoxin-like iron centre (2Fe-SOR) -, 746425 1.15.1.2 evolution Fe-SOR classification, detailed overview. One classification takes into consideration the primary and tertiary structures of SORs some enzymes contain only one Fe ion, but have a longer N-terminus with amino acid sequence and structural similarities with those of the respective domain of desulfoferrodoxins, but lacking the cysteine ligands to the desulforedoxin (Dfxs)-like center. According to the authors, SORs fall into three classes: classes I (Dfxs), II (neelaredoxins), and III (neelaredoxins structurally homologous to desulfoferrodoxins, with only one Fe center). In dendograms constructed from available amino acid sequences, class III enzymes cluster within the class I enzymes, it is plausible that class III SORs evolved from class I proteins by loss of the cysteine residues binding the desulforedoxin-like center, an event that may have occurred more than once because the Dfxs are not monophyletic. This classification misses the family of methanoferrodoxins. Another classification is based on the variability of N-terminal domains classifying SORs into seven classes. Class I or Dx-SOR includes the 2Fe-SORs, where the N-terminal is a desulforedoxin-like (Dx) domain. Class II includes the 1Fe-SORs that have no extra N-terminal domain. Class III SORs are analogous to Dx-SORs but lacking some or all of the Fe cysteine ligands (FeCys4) for the desulforedoxin-like Fe center and therefore lacking the FeCy4 site. Class IV includes SORs with an extra C-terminal domain containing an iron-sulfur center. The fifth class, termed HTH-Dx-SOR, includes Dx-SORs (2Fe-SOR) with an extended N-terminal helix-turn-helix domain present in transcription regulators. The sixth class, termed TAT-SOR, includes SORs from only a few organisms and the sequences are preceded by a putative twin-arginine signal peptide that suggests their periplasmic localization -, 744687 1.15.1.2 evolution Giardia trophozoite expresses an enzyme probably acquired from a prokaryote by lateral gene transfer. Rubredoxins, small proteins with a [FeCys4] center known to be involved in electron transfer processes, are generally assumed to be the direct electron donors to SOR, based on the fact that the genes encoding rubredoxin and SOR lie in the same operon in some bacteria. Consistently, reduced rubredoxins are shown to reduce both 1Fe- and 2Fe-SORs, but physiological electron donors other than rubredoxins must exist because rubredoxins are missing in a large number of organisms that encode SORs -, 727572 1.15.1.2 evolution the enzyme belongs to the class I superoxide reductase family -, 726902 1.15.1.2 evolution the enzyme belongs to the class II superoxide reductase family 727313 1.15.1.2 malfunction mutation of two residues in the second coordination sphere of the SOR iron active site, K48 and I118, leads to the formation of a high-valent iron-oxo species when the mutant proteins are reacted with H2O2 -, 744022 1.15.1.2 malfunction the enzyme-inactivated 1754M strain is significantly more air-sensitive than the wild-type strain on NOS agarose plates exposed to air -, 726989 1.15.1.2 metabolism the enzyme is involved in ROS detoxification -, 746936 1.15.1.2 additional information activity remains essentially unchanged with change in the growth condition (maltose + peptides, maltose, maltose + peptides + sulfur S(0), maltose + sulfur S(0), peptides + sulfur S(0)) 745202 1.15.1.2 additional information direct electron transfer measurements, in the presence of superoxide anion, overview -, 726902 1.15.1.2 additional information iron reduction does not lead to dissociation of glutamate from the catalytic metal or other structural changes, but the glutamate ligand undergoes X-ray-induced chemical changes, revealing high sensitivity of the GiSOR active site to X-ray radiation damage, enzyme structure modeling and structure comparisons 743942 1.15.1.2 additional information key catalytic residue is E23, catalytic Fe2+ binding residues are H25, H50, H56, C109, and H112 -, 744687 1.15.1.2 additional information key catalytic residue is K9, catalytic Fe2+ binding residues are H10, H35, H41, C97, and H100 744687 1.15.1.2 additional information key catalytic residues are E12 and K13, catalytic Fe2+ binding residues are H14, H40, H46, C110, and H113 744687 1.15.1.2 additional information key catalytic residues are E14 and K15, catalytic Fe2+ binding residues are H16, H41, H47, C111, and H114 -, 744687 1.15.1.2 additional information key catalytic residues are E15 and K16, catalytic Fe2+ binding residues are H17, H45, H51, C115, and H118 -, 744687 1.15.1.2 additional information key catalytic residues are E23, K24, H25, H50, H56, C111, and H114 744687 1.15.1.2 additional information key catalytic residues are E47 and K48, catalytic Fe2+ binding residues are H49, H69, H74, C115, and H118 -, 744687 1.15.1.2 additional information key catalytic residues are E48, K40, H50, H70, H76, C119, and H122 -, 744687 1.15.1.2 additional information model structure of SOR-rubredoxin complex, docking simulations, overview 727313 1.15.1.2 additional information pH dependent ligand exchange in the final intermediate, overview -, 727572 1.15.1.2 additional information SORs can be classified as 1Fe-SORs, or neelaredoxins, or as 2Fe-SORs, or desulfoferrodoxins, according to the number of metal centres. Both share a common active site in which the reduction of superoxide anion occurs. This site is composed of a pentacoordinated iron with four equatorial histidine imidazoles and one axial cysteine sulfur in a square-pyramidal geometry [Fe(Cys)(His)4] 713642 1.15.1.2 additional information Superoxide reductases form a group of non-heme iron enzymes that supply one electron during substrate reduction. In the ferrous state, the active site iron is coordinated by four equatorial histidines and an axial cysteinate, forming a square pyramidal geometry with a vacant site for substrate binding. In the octahedral ferric state, coordination of the active site is not uniform: during turnover, the sixth coordination site is supposedly occupied by dioxygen species in different protonation and oxidation states. In contrast, the ferric resting state comprises an additional glutamate as a ligand in most, but not all, cases. Metal binding site and active site structure analysis, overview -, 746425 1.15.1.2 additional information the enzyme contains non-heme [Fe(His)4Cys] active sites, homology structural modeling using the Tp SOR structure, PDB ID 1Y07, as template, overview -, 726989 1.15.1.2 additional information the enzyme is used as an unprecedented model to study the mechanisms of O2 activation and of the formation of high-valent iron-oxo species in metalloenzymes. Formation of high-valent iron-oxo species in superoxide reductase, analysis by resonance Raman spectroscopy, overview -, 744022 1.15.1.2 additional information the SOR active site is located at the surface of the protein and consists of a mononuclear iron center, named center II, pentacoordinated in its ferrous state by four nitrogen atoms from histidine residues in an equatorial plane and one sulfur atom from a cysteine residue in an axial position. It displays a high redox potential. The lack of iron center I in the C13S SOR mutant does not significantly affect the folding of iron center II and its reactivity with superoxide 715670 1.15.1.2 physiological function enzyme SOR efficiently detoxifies reactive oxygen species. Overexpression of SOD can improve the tolerance of transgenic organisms to various oxidative stresses 745078 1.15.1.2 physiological function Giardia trophozoite expresses a SOR possibly involved in superoxide detoxification -, 727572 1.15.1.2 physiological function SOR is responsible for reductive elimination of toxic superoxide as part of the detoxifying system -, 714326 1.15.1.2 physiological function SOR is responsible for reductive eliminatioon of toxic superoxide as part of the detoxifying system 714326 1.15.1.2 physiological function superoxide reductase (SOR )is a small non-heme iron protein that is not involved in oxidation reactions, but in superoxide radical detoxification in microorganisms -, 744022 1.15.1.2 physiological function superoxide reductase (SOR) affords protection from oxidative stress by reducing the superoxide anion to hydrogen peroxide 743942 1.15.1.2 physiological function superoxide reductase from the air-sensitive oral spirochete Treponema denticola is a principal enzymatic scavenger of superoxide in this organism, role for the enzyme in oxidative stress protection of O2-exposed Treponema denticola 35405 -, 726989 1.15.1.2 physiological function superoxide reductase is involved in superoxide detoxification 714327 1.15.1.2 physiological function superoxide reductase, SOR, is a superoxide detoxification system, with a role of the rubredoxin-like iron center in the superoxide detoxifying activity of SOR, overview 715670 1.15.1.2 physiological function superoxide reductases play a key role in defence mechanisms against toxic oxygen species. SOR is responsible for scavenging toxic superoxide anion radicals, catalysing the one-electron reduction of superoxide to hydrogen peroxide 713639 1.15.1.2 physiological function the enzyme may contributes to the protection of cells from oxygen radicals formed by flavoproteins during periodic exposure to oxygen in natural environments -, 727470 1.15.1.2 physiological function the neelaredoxin-type SOR keeps toxic oxygen species levels under control. SORs are involved in scavenging superoxide radicals from the cell by catalyzing the reduction of superoxide to hydrogen peroxide 713642