title: Mononuclear iron enzymes are primary targets of hydrogen peroxide stress.
abstract: This study tested whether nonredox metalloenzymes are commonly charged with iron in vivo and are primary targets of oxidative stress because of it. Indeed, three sample mononuclear enzymes, peptide deformylase, threonine dehydrogenase, and cytosine deaminase, were rapidly damaged by micromolar hydrogen peroxide in vitro and in live Escherichia coli. The first two enzymes use a cysteine residue to coordinate the catalytic metal atom; it was quantitatively oxidized by the radical generated by the Fenton reaction. Because oxidized cysteine can be repaired by cellular reductants, the effect was to avoid irreversible damage to other active-site residues. Nevertheless, protracted H(2)O(2) exposure gradually inactivated these enzymes, consistent with the overoxidation of the cysteine residue to sulfinic or sulfonic forms. During H(2)O(2) stress, E. coli defended all three proteins by inducing MntH, a manganese importer, and Dps, an iron-sequestration protein. These proteins appeared to collaborate in replacing the iron atom with nonoxidizable manganese. The implication is that mononuclear metalloproteins are common targets of H(2)O(2) and that both structural and metabolic arrangements exist to protect them.
authors.affiliation: Department of Microbiology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Adil
authors.initials: A
authors.lastname: Anjem
authors.forename: James A
authors.initials: JA
authors.lastname: Imlay
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000581:Amidohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055162:Biocatalysis / Q000187:drug effects; D015153:Blotting, Western; D020134:Catalytic Domain; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D043525:Cytosine Deaminase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D009154:Mutation; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects
chemical_list: D001059:Apoproteins; D001425:Bacterial Outer Membrane Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; C492412:MntH protein, E coli; D016877:Oxidants; C088010:dps protein, E coli; D008345:Manganese; D006861:Hydrogen Peroxide; D007501:Iron; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase; D000581:Amidohydrolases; C084507:peptide deformylase; D043525:Cytosine Deaminase; D003545:Cysteine