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Nitric Oxide Dioxygenase (NOD): A • NO Detoxification Enzyme

The Virtual Free Radical School. Nitric Oxide Dioxygenase (NOD): A • NO Detoxification Enzyme. Paul R. Gardner, Ph.D. Children’s Hospital Research Foundation 3333 Burnet Ave., MLC7006, Cincinnati, OH 45229 USA Tel.: 513-636-4885 e-mail: paul.gardner@chmcc.org.

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Nitric Oxide Dioxygenase (NOD): A • NO Detoxification Enzyme

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  1. The Virtual Free Radical School Nitric Oxide Dioxygenase (NOD):A •NO Detoxification Enzyme Paul R. Gardner, Ph.D. Children’s Hospital Research Foundation 3333 Burnet Ave., MLC7006, Cincinnati, OH 45229 USA Tel.: 513-636-4885 e-mail: paul.gardner@chmcc.org NODSFRBM EducationProgram Gardner 1

  2. •NO is ubiquitous. It can be a lethal poison. Various life forms have evolved strategies for NO detoxification NODSFRBM EducationProgram Gardner 2

  3. •NO is ubiquitous Common Biological Sources: 1. Oxidation-oxygenation of amines •NO synthases (L-arginine) / immune defense (animals + plants) organic combustions/ cigarette smoke (lung) 2. Reduction of nitrogen oxides (nitrate and nitrite) microbial denitrification pathways (soil) nitrite reduction by oxidoreductases (gut) NODSFRBM EducationProgram Gardner 3

  4. •NO Can Be a Lethal Poison •NO Can Poison Cell Energy Production Sensitive Targets are: Aconitase and Cytochrome Oxidase that affect Respiration. NODSFRBM EducationProgram Gardner 4

  5. Aconitase, a citric acid cycle enzyme, is a sensitive and critical target of •NO •NO Solvent accessible iron attacked by NO + S [•NO] >100 nM Fe S Fe cluster dissolution + aconitase inactivation Cys S S S Cys Fe S Fe Iron liberation S Cys NODSFRBM EducationProgram Gardner 5

  6. 100 50 0 1.0 0 0.5 [•NO] (µM) •NO rapidly inhibits cytochrome oxidase and thereby inhibits mitochondrial respiration Human A549 lung cells respiring with a physiological level of O2 (5 µM) are poisoned by submicromolar •NO levels. Gardner et al. 2001 FRBM 31, 191. NODSFRBM EducationProgram Gardner 6

  7. Multiple Secondary Mechanisms for •NO Toxicity Fe-S center Iron liberation H2O2 toxicity & Dinitrosyl-iron complexes Catalase inhibition •NO -e– O2•— +NO +e– O2 ONOO– RSNO NO– ONO• •OH ONO• NODSFRBM EducationProgram Gardner 7

  8. •NO + O2 + e– ONO– (nitrate) O Cellular Strategies for •NO Detoxification-Metabolism 1. Non-enzymatic and enzymatic ‘Oxidations’ (•NO oxidases) 2. Reduction (•NO reductases) 3. Dioxygenation (•NO dioxygenases) •NO + O2•-/O2/H2O2 {ONOO–, ONO•, or ONO–} Toxic products? NOR 2 •NO + 2 e– N2O (nitrous oxide) NOD NODSFRBM EducationProgram Gardner 8

  9. •NO dioxygenase (NOD) NO3- •NO FAD active O2 NAD(P)H binding site (flavohemoglobin, structure by U. Ermler et al. 1995) NODSFRBM EducationProgram Gardner 9

  10. 2 •NO + 2 O2 + NAD(P)H 2 NO3– + NAD(P)+ + H+ Proposed •NO Dioxygenase Rxn Mechanism NAD(P)H + FAD + H+ NAD(P)+ + FADH2 FADH2 + Fe3+ Fe2+ + FADH• + H+ Fe2+ + O2 Fe3+(O2•-) Fe3+(O2•-) + •NO Fe3+ + NO3– FADH• + Fe3+ FAD + Fe2+ + H+ FAD reduction (-) CN— iron reduction (-) •NO, CO O2 binding •NO dioxygenation (-) CN— iron reduction NODSFRBM EducationProgram Gardner 10

  11. 100 control 80 Rate of + 960 ppm •NO (<2 µM), 60 min •NO Consumption 60 (nanomol/ min/ 108 cells) 40 0.08 ± 0.07 0.06 ± 0.03 20 0 + hmp plasmid Dhmp parent JM109 Flavohemoglobin (hmp) catalyzes constitutive and inducible aerobic •NO consumption in Escherichia coli E. coli lacking flavohemoglobin (Dhmp) lack constitutive and inducible aerobic •NO consumption activity. A multi-copy plasmid bearing hmp increases the •NO consumption activity in host JM109. Gardner et al. 1998 PNAS 95, 10378. NODSFRBM EducationProgram Gardner 11

  12. FlavoHb (hmp) protects aconitase inaerobic Escherichia coli Aconitase israpidly inactivated in E. coli lacking NOD (hmp) when exposed to an aerobic atmosphere containing 960 ppm •NO (≤ 2 µM in solution). NOD (hmp) protects aconitase. Gardner et al. 2002 JBC 277, 8166. NODSFRBM EducationProgram Gardner 12

  13. 5.0 4.0 parent 3.0 Growth (A550 nm) 2.0 hmp D •NO parent + 960 ppm •NO 1.0 hmp + 960 ppm •NO D 0.0 0 120 240 360 480 Minutes FlavoHb protects aerobic E. coli against •NO-mediated growth inhibition E. coli lacking NOD (Dhmp) that are exposed to an aerobic atmosphere containing •NO do not grow well. Gardner et al. 1998 PNAS 95, 10378; 2002 JBC 277, 8166, 8172. NODSFRBM EducationProgram Gardner 13

  14. •NO dioxygenation is a primal (1.8 billion year old) functionof hemoglobin/myoglobinNOD O2 storage/transport The first hemoglobin/myoglobin most likely functioned as an enzyme utilizing bound ‘activated’ O2 to dioxygenate NO, or other substrates in microbes. Multicellular organisms that benefit from the O2 storage-transport functions of hemoglobin/myoglobin appeared much later. Gardner et al. 1998 PNAS 95, 10378. NODSFRBM EducationProgram Gardner 14

  15. His(E7) Muscle Myoglobins & RBC Hemoglobins Microbial flavohemoglobin (Hb domain) Tyr(B10) His(E7) NODs, SODs, etc. Elevated O2 = O2•-, H2O2 •NO, CO, etc. O2 transport/storage function NOD function ~ 3.6 Billion years of life on earth today beginning 3.0 By 1.8 By NODSFRBM EducationProgram Gardner 15

  16. flavoHbs*Sperm Whale Mb Vmax NOD 112-670 s-1 -- kon O2 1.7-5.0 x 107 M-1 s-1 1.7 x 107 M-1 s-1 koff O2 0.2-0.6 s-1 15 s-1 Kd O2 4-36 nM 800 nM kox•NO 0.9-2.9 x 109 M-1 s-1 3.4 x 107 M-1 s-1 kon•NO 1.0-2.6 x 107 M-1 s-1 2.2 x 107 M-1 s-1 koff•NO 0.0002 s-1 0.0001 s-1 KM (O2) 60-90 µM -- KM (•NO) 100-250 nM -- Structure and Kinetics Control Diverse Hemoglobin and Myoglobin Functions *E. coli, S.cerevisiae and A. eutrophus; Gardner et al. 2000 JBC 275, 12581, 31581 NODSFRBM EducationProgram Gardner 16

  17. 2 •NO + 2 O2 + NADPH 2 NO3– + NADP+ + H+ Mammalian Cells Produce a flavoHb-like NOD Activity for •NO Metabolism-Detoxification Human Intestinal Epithelial Cells (CaCo-2) 20-30 nmol •NO/min/107 cells Apparent Km (O2) = 17 µM Apparent Km (•NO) = 0.2 µM CO sensitive Ki (CO) = 3 µM (heme-dependent) Cyanide sensitive Ki (CN-)  20 µM (heme-dependent) Diphenylene iodonium sensitive (flavin-dependent) Gardner et al. 2001 FRBM 31, 191 NODSFRBM EducationProgram Gardner 17

  18. Key Points:1) •NO can be a potent toxin;2)•NO dioxygenase (NOD) is one enzyme that efficiently detoxifies •NO in bacteria, fungi, and mammals; and3)•NO dioxygenation is an ancient function for the hemoglobin/myoglobin family. NODSFRBM EducationProgram Gardner 18

  19. References Gardner, P. R. et al., Nitric oxide sensitivity of the aconitases (1997) JBC 272, 25071. Gardner, P. R. et al.,Constitutive and adaptive detoxification of nitric oxide inEscherichia coli Role of nitric oxide dioxygenase in the protection of aconitase (1998) JBC 273, 26528. Gardner, P. R. et al., Nitric oxide dioxygenase: an enzymic function for flavohemoglobin (1998) PNAS 95, 10378. Gardner, A. M. et al., Flavohemoglobin detoxifies nitric oxide in aerobic, but not anaerobic, Escherischia coli. Evidence for a novel inducible anaerobic nitric oxide scavenging activity (2002) JBC 277, 8166. Gardner, A. M. et al., Flavorubredoxin, an inducible catalyst for nitric oxide reduction and detoxification in Escherichia coli (2002) JBC 277, 8172. Gardner, P. R. et al., Nitric oxide dioxygenase activity and function of flavohemoglobins. Sensitivity to nitric oxide and carbon monoxide inhibition (2000) JBC 275, 31581. Gardner, A. M. et al., Steady-state and transient kinetics of the Escherichia coli nitric oxide dioxygenase (flavohemoglobin). The tyrosine B10 hydroxyl is essential for dioxygen binding and catalysis (2000) JBC 275, 12581. Frauenfelder, H. et al. The role of structure, energy landscape, dynamics, and allostery in the enzymatic function of myoglobin (2001) PNAS 98, 2370. Gardner, P. R. et al., Dioxygen-dependent metabolism of nitric oxide in mammalian cells (2001) FRBM 31, 191-204. NODSFRBM EducationProgram Gardner 19

  20. Acknowledgements Drs. John Olson and Yi Dou are gratefully acknowledged for their contribution of hemoglobin structure graphics. This work was supported by grants from the Children’s Hospital Research Foundation Trustees, the American Heart Association (9730193N), and the National Institutes of Health (R01 GM65090). NODSFRBM EducationProgram Gardner 20

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