Metals in Redox Biology C O R Y B O O N E, C E C I L I A H A G E R T, Q I A N G MA R E D O X - C O U R S E

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1 Metals in Redox Biology C O R Y B O O N E, C E C I L I A H A G E R T, Q I A N G MA R E D O X - C O U R S E

2 Metals Producing ROS M A Q I A N G

3 ROS as a class includes superoxide radical anion (O 2 ), hydrogen peroxide (H 2 O 2 ), and hydroxyl radical (. OH). Hydroxyl radical (OH) is one of the most strongly oxidizing ROS species.

4 Fer present is responsible for most of the generation of ROS. Similar reactions can occur with Cu, Cr, Ni and some other heavy metals.

5 Damage of these interactions: lipid peroxidation, protein oxidation, DNA/RNA oxidation and DNA lesions overwhelm the cellular antioxidant defense mechanisms and lead to cell damage and death

6 Systemic iron transport DMT1: Divalent metal transporter 1. Fpn: Ferroportin. Hp: Hephaestin. Ce: Ceruloplasmin. Tf: Transferrin. TfR: Transferrin receptor.

7 Iron signaling in the mitochondria CI CIV: complexes I through IV. ISC: iron/sulfur cluster.

8 Fumarate-Nitrate Reduction (FNR) O X Y G E N S E N S I N G M E T A L L O P R O T E I N - C O R Y B O O N E

9 FNR Overview Named after the Fumarate and Nitrate Reductionnegative phenotype of an fnr gene-defective E. coli strain Transcriptional activator under anaerobic conditions Crp/Fnr family 294 genes within 184 operons regulated by FNR and/or O 2 levels Recognizes palindromic sequences in DNA Functions as a homodimer [4Fe-4S] containing enzyme ligated most often by 4 Cys residues (3 Cys, 1 Asp in B. subtillis) O 2 or ROS oxidize the [4Fe-4S] cluster to a [2Fe-2S] cluster deactivating the enzyme

10 Altered Gene Expression Under Anaerobic Conditions Δ Δ Gene product (+) regulated by FNR Gene product (-) regulated by FNR

11 FNR/CRP Family Structure [Fe-S] cluster locatio n DNA recognitio n domain Monomer - Inactive PDB: 2GAU Dimer - Active

12 FNR O 2 Sensing Mechanism Release of cys side chain from cluster Conformational rearrangement Reattachment of cys residues to cluster H 2 O 2 Reaction with Amplex Red Arrows correspond to abs changes with increasing concentrations of O 2 H 2 O 2 Formation

13 FNR Unanswered Questions FNR crystal structure Exact location of bound Fe-S cluster(s) Conformational change Fe-S cluster location/changes upon conformational change Is reaction of FNR bound to DNA same as unbound reaction? Is the oxidation of a single [4Fe-4S] cluster sufficient to cause FNR to release DNA?

14 References J. Crack, J. Green, A. J. Thomson, Journal of Biological Chemistry 279, 9278 (2004). P. A. Jordan, A. J. Thomson, E. T. Ralph, J. R. Guest, J. Green, FEBS Letters 416, 349 (1997). P. J. Kiley, H. Beinert, FEMS Microbiology Reviews 22, 341 (1998). I. Gruner et al., Journal of Biological Chemistry 286, 2017 (2011). Yisheng Kang, et al, J Bacteriol. 187, 1135 (2005).

15 Antioxidant Enzymes with Metal Cofactors - C E C I L I A H A G E R T

16 Metals works as cofactors in SOD Copper and zinc Cu-Zn-SOD Most common in the cytosols of virtually all eukaryotic cells The Cu-Zn enzyme is a homodimer of molecular weight 32,500 Iron Fe-SOD E. coli and many other bacteria also contain a form of the enzyme with iron plastids of plants Manganese Mn-SOD exists in many bacteria (such as E. coli) human mitochondria Nickel NiSOD prokaryotic Proc Natl Acad Sci U S A Jun 8;101(23): Acta Crystallogr B Dec 1;47 ( Pt 6):918-27

17 Human SODs 3 forms of SOD are present in mammals; SOD1 is located in the cytoplasm Contain copper and zinc SOD2 in the mitochondria Contain manganese SOD3 is extracellular Contain copper and zinc Free Radic Biol Med Aug 1;33(3):

18 SOD1 SOD2 SOD 3

19 The reaction The SOD-catalysed dismutation of superoxide may be written with the following half-reactions : M (n+1)+ -SOD + O 2 M n+ -SOD + O 2 M n+ -SOD + O 2 + 2H + M (n+1)+ -SOD + H 2 O 2 * Where M = Cu (n=1) ; Mn (n=2) ; Fe (n=2) ; Ni (n=2). * In this reaction the oxidation state of the metal cation oscillates between n and n+1.

20 Mechanisms of thioredoxin reduction Thioredoxins are reduced by either a) reduced ferredoxin (via the iron-sulfur enzyme) a) NADPH (via the flavin enzyme) The ferredoxin-linked system Chloroplasts xygenic photosynthetic prokaryotes NADPH is used as in a broad spectrum of cells: grow on organic compounds (heterotrophs) photosynthetic anaerobe bacteria heterotrophic eukaryotes explastidic compartments of oxygenic photosynthetic eukaryotes FTR = ferredoxin- thioredoxin reductase NTR = NADP-dependent thioredoxin reductase Metal: Iron Trends Plant Sci May;7(5):191-3.