Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P04179 (MnSOD)
 2,777 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The 2.9 A resolution structure of iron superoxide dismutase (FeSOD) (EC 1.15.1.1) from Pseudomonas ovalis complexed with the inhibitor azide was solved. Comparison of this structure with free enzyme shows that the inhibitor is bound at the open coordination position of the iron, with a bond length of 2.0 A. The metal moves by 0.4 A into the trigonal plane to produce an orthogonal geometry at the iron. Binding of the inhibitor also causes a movement of the axial ligand (histidine 26) away from the metal, a lengthening of the iron-histidine bond, and a rotation of the histidine 74 ring. The inhibitor possesses contacts in the binding pocket with a pair of conserved tryptophan residues and with the side chains of tyrosine 34 and glutamine 70. This glutamine is conserved between all FeSODs, but is absent in MnSOD. Comparisons with MnSOD show that a different glutamine which possesses the same interactions in the active site as Gln70 in FeSOD is conserved at position 154 in the overall SOD sequence, implying that while manganese and FeSODs are structural homologues in a global sense, their functional and evolutionary relationship is that of second-site mutation revertants.
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PMID:The structure of iron superoxide dismutase from Pseudomonas ovalis complexed with the inhibitor azide. 207 85

Structural and biochemical characterization of the nonliganding residue glutamine 143 near the manganese of human Mn superoxide dismutase (hMnSOD), a homotetramer of 22 kDa, reveals a functional role for this residue. In the wild-type protein, the side-chain amide group of Gln 143 is about 5 A from the metal and is hydrogen-bonded to Tyr 34, which is a second prominent side chain adjacent to the metal. We have prepared the site-specific mutant of hMnSOD with the conservative replacement of Gln 143 --> Asn (Q143N). The crystal structure of Q143N shows that the side-chain amide nitrogen of residue 143 is 1.7 A more distant from the manganese than in the wild-type enzyme. The Tyr 34 side-chain hydroxyl in Q143N is also moved to become 0.6 A more distant from the metal due to an additional water molecule. Differential scanning calorimetry showed that Q143N is slightly more stable than the wild-type enzyme with Tm for the main unfolding transition increased by 2 degrees C to 90.7 degrees C. Pulse radiolysis and stopped-flow spectrophotometry reveal that unlike wild-type hMnSOD, which is strongly inhibited by peroxide, Q143N MnSOD exhibits no product inhibition even at concentrations of O2. - in the millimolar range, and its catalysis follows Michaelis kinetics with no evidence of cooperativity. However, the overall catalytic activity of this mutant was decreased 2-3 orders of magnitude compared with the wild-type MnSOD, which can account for its lack of product inhibition. Q143N MnSOD lacked the visible absorption spectrum typical of wild-type Mn(III)SOD. Also, unlike the wild-type Mn(III)SOD, which is electron paramagnetic resonance (EPR) silent, Q143N MnSOD has a complex EPR spectrum with many resonances in the region below 2250 G. We conclude that the Gln 143 --> Asn mutation has increased the reduction potential of manganese to stabilize Mn(II), indicating that Gln 143 has a substantial role in maintaining a reduction potential favorable for the oxidation and reduction cycles in the catalytic disproportionation of superoxide. A solvent hydrogen isotope effect near 2 for kcat in catalysis by Q143N hMnSOD indicates rate-contributing proton transfers to form product hydroperoxide anion or hydrogen peroxide. The data demonstrate a prominent role for Gln 143 in maintaining the microenvironment of the manganese and in efficient catalysis of superoxide dismutation to oxygen and hydrogen peroxide.
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PMID:Probing the active site of human manganese superoxide dismutase: the role of glutamine 143. 953 88

A mangano-superoxide dismutase (EC 1.15.1.1) was purified to homogeneity from a strain of alkaliphilic Bacillus for the first time. The purified protein, with an isoelectric point of pH 4.5, had a molecular mass of approximately 50 kDa and consisted of two identical subunits (25 kDa). The N-terminal amino acid sequence was Ala-Tyr-Lys-Leu-Pro-Glu-Leu-Pro-Tyr-Ala-Ala-Asn-Ala-Leu-Glu-Pro-His-Ile- Asp-Glu-Ala. The optimum pH and temperature for the reaction were 7.5 and 35 degrees C, respectively. The properties of the superoxide dismutase were compared with those of the enzyme from thermophilic Bacillus stearothermophilus.
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PMID:Purification and properties of mangano-superoxide dismutase from a strain of alkaliphilic Bacillus. 968 Mar 5

Unlike the early phase of preconditioning (PC), which lasts 2 to 3 hours and protects against infarction but not against stunning, the late phase of PC lasts 3 to 4 days and protects against both infarction and stunning, suggesting that it may have greater clinical relevance. It is now clear that late PC is a polygenic phenomenon that requires the simultaneous activation of multiple stress-responsive genes. Chemical signals released by a sublethal ischemic stress (such as NO, reactive oxygen species, and adenosine) trigger a complex cascade of signaling events that includes the activation of protein kinase C, Src protein tyrosine kinases, and nuclear factor kappaB and culminates in increased synthesis of inducible NO synthase, cyclooxygenase-2, aldose reductase, Mn superoxide dismutase, and probably other cardioprotective proteins. An analogous sequence of events can be triggered by a variety of stimuli, such as heat stress, exercise, and cytokines. Thus, late PC appears to be a universal response of the heart to stress in general. Importantly, the cardioprotective effects of late PC can be reproduced pharmacologically with clinically relevant agents (eg, NO donors, adenosine receptor agonists, endotoxin derivatives, or opioid receptor agonists), suggesting that this phenomenon might be exploited for therapeutic purposes. The purpose of this review is to summarize current information regarding the pathophysiology and mechanism of late PC.
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PMID:The late phase of preconditioning. 1109 May 41

We have characterized the temporal changes in iNOS, MnSOD and nitrotyrosine immune reactivity in a rat model of permanent middle cerebral artery occlusion under acute hyperglycemic or normoglycemic conditions followed by either 3- or 24-h recovery. We found that the macroscopic labeling pattern for all three antibodies colocalized with the ischemic core and penumbra which was determined by cresyl violet histological evaluation in adjacent sections. Hyperglycemia induced prior to ischemia resulted in earlier infarction which correlated with increased immunoreactivity for iNOS, MnSOD and nitrotyrosine. In the penumbral region of the frontal cortex, labeling of specific cell structures was largely limited to cortical neurons near the corpus callosum and was apparent earlier in the hyperglycemic rats. Increased polymorphonuclear leukocyte adhesion in blood vessels was observed at 24 h in the hyperglycemic group. At both of the recovery times studied, we observed only minor vascular staining for nitrotyrosine and none for iNOS. Our results are consistent with hyperglycemia resulting in an early and concomitant increase in both superoxide and nitric oxide production which can lead to peroxynitrite formation that then nitrates tyrosine residues. It would appear that hyperglycemic ischemia contributes to the early induction of key enzymes involved in nitric oxide bioavailability.
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PMID:Immunohistochemical detection of inducible nitric oxide synthase, nitrotyrosine and manganese superoxide dismutase following hyperglycemic focal cerebral ischemia. 1168 37

The peroxynitrite anion is a potent oxidizing agent, formed by the diffusion-limited combination of nitric oxide and superoxide, and its production under physiological conditions is associated with the pathologies of a number of inflammatory and neurodegenerative diseases. Nitration of Escherichia coli iron superoxide dismutase (Fe-SOD) by peroxynitrite was investigated, and demonstrated by spectral changes and electrospray mass spectroscopic analysis. HPLC and mass studies of the tryptic digests of the mono-nitrated Fe-SOD indicated that tyrosine-34 was the residue most susceptible to nitration by peroxynitrite. Exclusive nitration of this residue occurred when Fe-SOD was exposed to a cumulative dose of 0.4 mM peroxynitrite. Unlike with human Mn-SOD, this single modification did not inactivate E. coli Fe-SOD at pH 7.4. When Fe-SOD was exposed to higher concentrations of peroxynitrite (7 mM), eight tyrosine residues per subunit of the protein, of the nine available, were nitrated without loss of catalytic activity of the enzyme. The pK(a) of nitrated tyrosine-34 was determined to be 7.95+/-0.15, indicating that the peroxynitrite-modified enzyme appreciably maintains its protonation state under physiological conditions.
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PMID:Peroxynitrite-induced nitration of tyrosine-34 does not inhibit Escherichia coli iron superoxide dismutase. 1173 45

Measurement of catalysis by MnSOD using direct observation of the UV absorbance of superoxide allows determination of steady-state catalytic constants. Stabilizing superoxide in aprotic solvents such as dimethyl sulfoxide permits the use of stopped-flow spectrophotometry, although significant information is lost in the 2- to 4-msec mixing time; generating superoxide by pulse radiolysis requires no mixing time. Studies show that kcat/Km for the decay of superoxide catalyzed by MnSOD proceeds at diffusion control. Investigations using solvent hydrogen isotope effects and enhancement of catalysis by exogenous proton donors show that kcat near 10(4) sec-1 contains a significant contribution from proton transfer steps. The active site of MnSOD is dominated by a hydrogen bond network comprising the manganese-bound aqueous ligand, the side chains of four residues (Gln-143, Tyr-34, His-30, and Tyr-166 from an adjacent subunit), as well as other water molecules. Interrupting this hydrogen bond network by conservative replacement of residues 30, 34, and 166 causes a 10- to 40-fold decrease in maximal velocity, interpreted as an effect on proton transport to the active site, with smaller effects on kcat/Km. Replacement of Gln-143 causes a much greater decrease in catalytic activity, by two to three orders of magnitude, and causes significant changes to the redox potential as well. During catalysis, MnSOD is inhibited by a peroxide complex of the metal in the active site, different from the inhibition of FeSOD and Cu,ZnSOD by Fenton chemistry. Site-specific mutagenesis of active-site residues alters the extent of product inhibition of MnSOD as well, indicating that this is not only a property of the metal. The replacement of Trp-161 with phenylalanine results in a variant that is completely blocked in catalysis by product inhibition.
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PMID:Catalytic pathway of manganese superoxide dismutase by direct observation of superoxide. 1191 30

A combined spectroscopic/computational approach has been utilized to explore the chemical origins of the active-site pKs of the structurally homologous Fe- and Mn-dependent superoxide dismutases (SODs). Absorption, circular dichroism, magnetic circular dichroism, and variable-temperature, variable-field magnetic circular dichroism spectroscopic experiments have permitted us to determine electronic transition energies and polarizations, as well as ground-state spin Hamiltonian parameters. These experimental data have been used in conjunction with semiempirical intermediate neglect of differential overlap/spectroscopic parametrization configuration interaction (INDO/S-CI) computations for evaluating hypothetical active-site models for the high-pH species generated by density functional theory (DFT) geometry optimizations. Our experimental and computational data indicate that both reduced FeSOD and oxidized MnSOD do not bind hydroxide at high pH; rather, the active-site pK for these two species is attributed to deprotonation of a second-sphere tyrosine. Conversely, our data obtained on oxidized FeSOD indicate that hydroxide binding is responsible for the observed active-site pK for this species. Intriguingly, in the Fe-substituted form of MnSOD this identical chemical event occurs at a significantly lower pH. Overall, our results suggest an important role for second-sphere amino acids in tuning the active sites' interaction with small anions and bring into question the assumption that these homologous enzymes operate by the same molecular mechanism.
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PMID:Spectroscopic and computational studies on iron and manganese superoxide dismutases: nature of the chemical events associated with active-site pKs. 1220 39

NF kappa B is a critical transcription factor involved in modulating cellular responses to environmental injuries. Tyrosine 42 phosphorylation of I kappa B alpha has been shown to mediate NF kappa B activation following hypoxia/reoxygenation (H/R) or pervanadate treatment. This pathway differs from the canonical proinflammatory pathways, which mediate NF kappa B activation through serine phosphorylation of I kappa B alpha by the IKK complex. In the present study, we investigated the involvement of c-Src in the redox activation of NFkappaB following H/R or pervanadate treatment. Our results demonstrate that pervanadate or H/R treatment leads to tyrosine phosphorylation of I kappa B alpha and NF kappa B transcriptional activation independent of the IKK pathway. In contrast, inhibition of c-Src by pp2 treatment or in c-Src (-/-) knockout cell lines, demonstrated a significant reduction in I kappa B alpha tyrosine phosphorylation and NF kappa B activation following pervanadate or H/R treatment. Overexpression of glutathione peroxidase-1 or catalase, but not Mn-SOD or Cu,Zn-SOD, significantly reduced both NF kappa B activation and tyrosine phosphorylation of I kappa B alpha. In vitro kinase assays further demonstrated that immunoprecipitated c-Src has the capacity to directly phosphorylate GST-I kappa B alpha and that this I kappa B alpha kinase activity is significantly reduced by Gpx-1 overexpression. These results suggest that c-Src-dependent tyrosine phosphorylation of I kappa B alpha and subsequent activation of NF kappa B is controlled by intracellular H(2)O(2) and defines an important redox-regulated pathway for NF kappa B activation following H/R injury that is independent of the IKK complex.
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PMID:Tyrosine phosphorylation of I kappa B alpha activates NF kappa B through a redox-regulated and c-Src-dependent mechanism following hypoxia/reoxygenation. 1242 43

Fe-containing superoxide dismutase (FeSOD) and MnSOD are widely assumed to employ the same catalytic mechanism. However this has not been completely tested. In 1985, Bull and Fee showed that FeSOD took up a proton upon reduction [J. Am. Chem. Soc. 107 (1985) 3295]. We now demonstrate that MnSOD incorporates the same crucial coupling between electron transfer and proton transfer. The redox-coupled H(+) acceptor has been presumed to be the coordinated solvent molecule, in both FeSOD and MnSOD, however this is very difficult to test experimentally. We have now examined the most plausible alternative: that Tyr34 accepts a proton upon SOD reduction. We report specific incorporation of 13C in the C(zeta) positions of Tyr residues, assignment of the C(zeta) signal of Tyr34 in each of oxidized FeSOD and MnSOD, and direct NMR observations showing that in both cases, Tyr34 is in the neutral protonated state. Thus Tyr34 cannot accept a proton upon SOD reduction, and coordinated solvent is concluded to be the redox-coupled H(+) acceptor instead, in both FeSOD and MnSOD. We have also confirmed by direct 13C observation that the pK of 8.5 of reduced FeSOD corresponds to deprotonation of Tyr34. This work thus provides experimental proof of important commonalities between the detailed mechanisms of FeSOD and MnSOD.
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PMID:Proton-coupled electron transfer in Fe-superoxide dismutase and Mn-superoxide dismutase. 1253 55


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