Characterization of a Manganese Superoxide Dismutase from the Higher Plant Pisum sativum

A manganese-containing superoxide dismutase (EC 1.15.1.1) was fully characterized from leaves of the higher plant Pisum sativum L., var. Lincoln. The amino acid composition determined for the enzyme was compared with that of a wide spectrum of superoxide dismutases and found to have a highest degree of homology with the mitochondrial manganese superoxide dismutases from rat liver and yeast. The enzyme showed an apparent pH optimum of 8.6 and at 25°C had a maximum stability at alkaline pH values. By kinetic competition experiments, the rate constant for the disproportionation of superoxide radicals by pea leaf manganese superoxide dismutase was found to be 1.61 × 10⁹ molar⁻¹·second⁻¹ at pH 7.8 and 25°C. The enzyme was not sensitive to NaCN or to H₂O₂, but was inhibited by N₃⁻. The sulfhydryl reagent p-hydroxymercuribenzoate at 1 mm concentration produced a nearly complete inhibition of the manganese superoxide dismutase activity. The metal chelators o-phenanthroline, EDTA, and diethyldithiocarbamate all inhibited activity slightly in decreasing order of intensity. A comparative study between this higher plant manganese superoxide dismutase and other dismutases from different origins is presented.     

Cloning and characterization of a new manganese superoxide dismutase from deep-sea thermophile Geobacillus sp. EPT3

A new gene encoding a superoxide dismutase (SOD) was identified from a thermophile Geobacillus sp. EPT3 isolated from a deep-sea hydrothermal field in east Pacific. The open reading frame of this gene encoded 437 amino acid residues. It was cloned, overexpressed in Escherichia coli (DE3), and the recombinant protein was purified to homogeneity. Geobacillus sp. EPT3 SOD was of the manganese-containing SOD type, as judged by the insensitivity of the recombinant enzyme to both KCN and H₂O₂, and the activity analysis of Fe or Mn reconstituted SODs by polyacrylamide gel electrophoresis. The recombinant SOD was determined to be a homodimer with monomeric molecular mass of 59.0 kDa. In comparison with other Mn–SODs, the manganese-binding sites are conserved in the sequence (His260, His308, Asp392, His396). The recombinant enzyme had high thermostability at 50 °C. It retained 57 % residual activity after incubation at 90 °C for 1 h, which indicated that this SOD was thermostable. The enzyme also showed striking stability over a wide range of pH 5.0–11.0. At tested conditions, the recombinant SOD from Geobacillus sp. EPT3 showed a relatively good tolerance to some inhibitors, detergents, and denaturants, such as β-mercaptoethanol, dithiothreitol, phenylmethylsulfonyl fluoride, Chaps, Triton X-100, urea, and guanidine hydrochloride.     

Manganese superoxide dismutase from a higher plant

A manganese-containing superoxide dismutase (EC 1.15.1.1) was purified to homogeneity from a higher plant for the first time. The enzyme was isolated fromPisum sativum leaf extracts by thermal fractionation, ammonium sulfate salting out, ion-exchange and gel-filtration column chromatography, and preparative polyacrylamide gel electrophoresis. Pure manganese superoxide dismutase had a specific activity of about 3,000 U mg^-1 and was purified 215-fold, with a yield of 1.2 mg enzyme per kg whole leaf. The manganese superoxide dismutase had a molecular weight of 94,000 and contained one g-atom of Mn per mol of enzyme. No iron and copper were detected. Activity reconstitution experiments with the pure enzyme ruled out the possibility of a manganese loss during the purification procedure. The stability of manganese superoxide dismutase at-20°C, 4°C, 25°C, 50°C, and 60°C was studied, and the enzyme was found more labile at high temperatures than bacterial manganese superoxide dismutases and iron superoxide dismutases from an algal and bacterial origin.Abbreviations NBT nitro blue tetrazolium - SOD superoxide dismutase (EC 1.15.1.1)     

The hyper-thermostable Fe-superoxide dismutase from the Archaeon Acidianus ambivalens: characterization, recombinant expression, crystallization and effects of metal exchange

An iron-containing superoxide dismutase (SOD; EC 1.15.1.1) of the hyperthermophilic archaeon Acidianus ambivalens (Aa-SOD) has been purified and characterized and the gene has been cloned and sequenced. The SOD from the facultatively aerobic member of the crenarchaeota could be expressed in E. coli. Both, the native as well as the heterologously overproduced protein turned out to have extraordinarily high melting temperatures of 128 degrees C and 124.5 degrees C, respectively. To the best of our knowledge, this is the highest directly measured melting temperature of a native protein. Surprisingly, neither the native nor the recombinant superoxide dismutase displays 100% occupation of the metal coordination sites. Obviously it is not the incorporation of a metal ion that confers the extreme thermostability. Expression of the superoxide dismutase in the presence of different metals such as Fe, Co, Ni, Mn and Cu offered the possibility of studying the hitherto unknown cofactor preference of iron-superoxide dismutase. The recombinant enzyme displayed the highest preference for incorporation of cobalt although iron is used as the natural cofactor. Spectroscopic analysis by EPR, atomic absorption and UVNis spectroscopy as well as activity measurements and differential scanning calorimetry of the metal substituted superoxide dismutases were performed. However, the superoxide dismutase of A. ambivalens is active only with iron but may incorporate other metals equally well in the catalytic center without loss of conformational stability or heat tolerance. The co-form of the enzyme could be crystallized.     

Crystal structure of the cambialistic superoxide dismutase from Aeropyrum pernix K1--insights into the enzyme mechanism and stability

Aeropyrum pernix K1, an aerobic hyperthermophilic archaeon, produces a cambialistic superoxide dismutase that is active in the presence of either of Mn or Fe. The crystal structures of the superoxide dismutase from A. pernix in the apo, Mn-bound and Fe-bound forms were determined at resolutions of 1.56, 1.35 and 1.48 ?, respectively. The overall structure consisted of a compact homotetramer. Analytical ultracentrifugation was used to confirm the tetrameric association in solution. In the Mn-bound form, the metal was in trigonal bipyramidal coordination with five ligands: four side chain atoms and a water oxygen. One aspartate and two histidine side chains ligated to the central metal on the equatorial plane. In the Fe-bound form, an additional water molecule was observed between the two histidines on the equatorial plane and the metal was in octahedral coordination with six ligands. The additional water occupied the postulated superoxide binding site. The thermal stability of the enzyme was compared with superoxide dismutase from Thermus thermophilus, a thermophilic bacterium, which contained fewer ion pairs. In aqueous solution, the stabilities of the two enzymes were almost identical but, when the solution contained ethylene glycol or ethanol, the A. pernix enzyme had significantly higher thermal stability than the enzyme from T. thermophilus. This suggests that dominant ion pairs make A. pernix superoxide dismutase tolerant to organic media.     

Manganese-containing superoxide dismutase from Escherichia coli: reversible resolution and metal replacements.

Exposure of the manganese-containing Superoxide dismutase of Escherichia coli to pH 3.2, in the presence of 0.7 m guanidinium chloride, causes a rapid loss of manganese and of activity. The apoenzyme so produced can be reconstituted by addition of MnCl₂ followed by neutralization. In contrast, manganese cannot be restored to the apoenzyme by adding MnCl₂after neutralization. The reconstituted enzyme is indistinguishable from the native enzyme in terms of its catalytic activity or electrophoretic behavior on polyacrylamide gels. Co(II), Ni(II), Zn(II), Fe(II), or Cu(II) could compete with Mn(II) during reconstitution of the apoenzyme. In the cases of Co(II), Ni(II), and Zn(II), it was shown that, in preventing reconstitution by Mn(II), they were themselves bound to the enzyme in stoichiometric amounts, in place of Mn(II). The binding of Fe(II) was also explored and was distinct in that the enzyme could bind more than stoichiometric amounts of this metal. None of the derivatives, in which Mn(II) had been replaced by another metal, were catalytically active. Nevertheless, these derivatives could be again resolved by exposure to acid guanidinium chloride and could then be converted back into the active holoenzyme by neutralization after addition of MnCl₂. It appears that the active site of this enzyme can accommodate and can tightly bind several metals other than manganese, but exhibits activity only with manganese. It also appears that movement of metal out of or into this site is only feasible at low pH and in the presence of a chaotropic agent. A substantial amount of the cobalt-substituted enzyme was prepared and its optical properties were recorded.     

Heterologous expression and biochemical characterization of a highly active and stable chloroplastic CuZn-superoxide dismutase from Pisum sativum

Background

CuZn-Superoxide dismutase (SOD) is a unique enzyme, which can catalyzes the dismutation of inevitable metabolic product i.e.; superoxide anion into molecular oxygen and hydrogen peroxide. The enzyme has gained wide interest in pharmaceutical industries due to its highly acclaimed antioxidative properties. The recombinant expression of this protein in its enzymatically active and stable form is highly desired and hence optimization of culture conditions and characterization of the related biochemical properties are essential to explore the significance of the enzyme in physiological, therapeutic, structural and transgenic research.

Results

High-level expression of the chloroplastic isoform of Pisum sativum CuZn-SOD was achieved at 18°C, upon isopropyl β-D-1-thiogalactopyranoside induction and the process was optimized for maximum recovery of the protein in its soluble (enzymatically active) form. Both crude and purified protein fractions display significant increase in activity following supplementation of defined concentration Cu (CuSO₄) and Zn (ZnSO₄). Yield of the purified recombinant protein was ~ 4 mg L⁻¹ of culture volume and the bacterial biomass was ~ 4.5 g L⁻¹. The recombinant pea chloroplastic SOD was found to possess nearly 6 fold higher superoxide dismutase activity and the peroxidase activity was also 5 fold higher as compared to commercially available CuZn-superoxide dismutase. The computational, spectroscopic and biochemical characterization reveals that the protein harbors all the characteristics features of this class of enzyme. The enzyme was found to be exceptionally stable as evident from pH and temperature incubation studies and maintenance of SOD activity upon prolonged storage.

Conclusions

Overexpression and purification strategy presented here describes an efficient protocol for the production of a highly active and stable CuZn-superoxide dismutase in its recombinant form in E. coli system. The strategy can be utilized for the large-scale preparation of active CuZn-superoxide dismutase and thus it has wide application in pharmaceutical industries and also for elucidating the potential of this protein endowed with exceptional stability and activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0117-0) contains supplementary material, which is available to authorized users.     

In Vitro Reconstitution of an NADPH-Dependent Superoxide Reduction Pathway from Pyrococcus furiosus

A scheme for the detoxification of superoxide in Pyrococcus furiosus has been previously proposed in which superoxide reductase (SOR) reduces (rather than dismutates) superoxide to hydrogen peroxide by using electrons from reduced rubredoxin (Rd). Rd is reduced with electrons from NAD(P)H by the enzyme NAD(P)H:rubredoxin oxidoreductase (NROR). The goal of the present work was to reconstitute this pathway in vitro using recombinant enzymes. While recombinant forms of SOR and Rd are available, the gene encoding P. furiosus NROR (PF1197) was found to be exceedingly toxic to Escherichia coli, and an active recombinant form (rNROR) was obtained via a fusion protein expression system, which produced an inactive form of NROR until cleavage. This allowed the complete pathway from NAD(P)H to the reduction of SOR via NROR and Rd to be reconstituted in vitro using recombinant proteins. rNROR is a 39.9-kDa protein whose sequence contains both flavin adenine dinucleotide (FAD)- and NAD(P)H-binding motifs, and it shares significant similarity with known and putative Rd-dependent oxidoreductases from several anaerobic bacteria, both mesophilic and hyperthermophilic. FAD was shown to be essential for activity in reconstitution assays and could not be replaced by flavin mononucleotide (FMN). The bound FAD has a midpoint potential of −173 mV at 23°C (−193 mV at 80°C). Like native NROR, the recombinant enzyme catalyzed the NADPH-dependent reduction of rubredoxin both at high (80°C) and low (23°C) temperatures, consistent with its proposed role in the superoxide reduction pathway. This is the first demonstration of in vitro superoxide reduction to hydrogen peroxide using NAD(P)H as the electron donor in an SOR-mediated pathway.     

Effect of divalent metal ions on soluble and membrane-bound alkaline phosphatase activity in suckling rat intestine.

EDTA treatment of intestinal brush border membranes (BBM) and epithelial cell supernatant completely inhibited alkaline phosphatase (AP) activity in suckling rat intestine. AP activity was fully regained upon dialysis of the preparations against Zn2+ and to a lesser extent against Co2+, Ca2+ and Mn2+ ions. Other metal ions (Cd2+ and Mg2+) tested were essentially ineffective in restoring the enzyme activity. Considerable differences were observed in kinetic characteristics of the membrane-bound and soluble AP activities in response to various metal ions. There were apparent differences in Km, Vmax, energy of activation (Ea) and thermal stability of the soluble and membrane-bound AP activities, after metal ion substitutions. Nearly 35% AP activity was solubilized on sodium dodecyl sulphate treatment of brush borders (membrane protein: detergent ratio 1:3; w/w). Dialysis of detergent solubilized BBM against different metal ions reconstituted AP activity in the particulate fraction: the order of effectiveness was Zn greater than Ca greater than Mn greater than Co. The kinetic properties of the reconstituted AP were essentially similar to the non-integrated enzyme activity in response to various divalent metal ions examined. But there were apparent differences in Km, Vmax, Ea and thermal stability of the reconstituted AP activity compared to native brush border enzyme. The results suggest the unique requirement of Zn ions for stability and catalytic activity of the soluble and membrane-bound AP activity in suckling rat intestine.     

Expression, purification and characterization of flavin reductase from Citrobacter freundii A1

Flavin reductase plays an important biological role in catalyzing the reduction of flavin by NAD(P)H oxidation. The gene that codes for flavin reductase from Citrobacter freundii A1 was cloned and expressed in Escherichia coli BL21(DE3)pLysS. In this study, we aimed to characterize the purified recombinant flavin reductase of C. freundii A1. The recombinant enzyme was purified to homogeneity and the biochemical profiles, including the effect of pH, temperature, metal ions and anions on flavin reductase activity and stability, were determined. This enzyme exhibited optimum activity at 45 °C in a 10-min reaction at pH 7.5 and was stable at temperatures up to 30 °C. At 0.1 mM concentration of metal ions, flavin reductase activity was stimulated by divalent cations including Mn²⁺, Sr²⁺, Ni²⁺, Sn²⁺, Ba²⁺, Co²⁺, Mg²⁺, Ca²⁺ and Pb²⁺. Ag⁺ was noticeably the strongest inhibitor of recombinant flavin reductase of C. freundii A1. This enzyme should not be defined as a standard flavoprotein. This is the first attempt to characterize flavin reductase of C. freundii origin.     

X-ray structure of the cambialistic superoxide dismutase from Propionibacterium shermanii active with Fe or Mn

The first structure of a cambialistic superoxide dismutase (SOD) from Propionibacterium shermanii exhibiting similar activity with iron and with manganese was solved at a resolution of 1.6?Å and 1.9?Å respectively. Surprisingly, no obvious differences between the two SODs were observable. The protein crystallises as a homo dimer in the asymmetric unit. Because of the crystallographic symmetry, it forms a tetramer. Structures of both the manganese and the ferric form were solved using molecular replacement techniques and multiple isomorphous replacement. The tertiary structure is similar to that of the other superoxide dismutases, the metal being fivefold coordinated by three histidines, one aspartate and one water molecule. The second shell of residues consists of hydrophobic amino acids, histidines and two water molecules, which are assumed to be involved in both the catalytic activity and structural stability of this superoxide dismutase. This shell may also be responsible for the cambialistic behaviour. This work shows that the reason for the metal specificity is not trivial, although minor alterations in the metal environment might be responsible for this behaviour.     

Characterization of Fish Cu/Zn–Superoxide Dismutase and Its Protection from Oxidative Stress

Copper/zinc superoxide dismutase was cloned from the zebrafish (Danio rerio). The full coding region of the zebrafish superoxide dismutase (ZSOD) complementary DNA was ligated with pET-20b(+) and successfully expressed in Escherichia coli strain AD494(DE3)pLysS. The active enzyme was purified by His tagging. The ZSOD yield was 6 mg from 0.2 L of E. coli culture, and the specific activity was 2000 U/mg as assayed using a RANSOD kit. The enzyme stability was characterized by reaction to temperature, pH, and detergent treatment. The results showed enzyme activity was still active after heat treatment at 70°C for 10 minutes, resistant to pH treatment from 2.3 to 12, and resistant to treatment with sodium dodecyl sulfate (SDS) under 4%. In addition, the recombinant ZSOD was used to protect fish from 100 ppm of paraquat-induced oxidative injury by soaking fish larva in 55 µg/ml SOD enzyme. The results were significant.     

Immunocytochemical evidence for a peroxisomal localization of manganese superoxide dismutase in leaf protoplasts from a higher plant

The controversial question of the intracellular location of manganese-containing superoxide dismutase in higher plants was examined under a new experimental approach by applying the more rigorous and specific methods of immunocytochemistry to protoplasts isolated fromPisum sativum L. leaves. Manganese superoxide dismutase (EC 1.15.1.1) was purified to homogeneity from 15 kg of leaves ofPisum sativum L. Rabbits were immunized with the mangano enzyme and the antibody specific for pea manganese superoxide dismutase was purified and found not to contain antigenic sites in common with (i) human manganese superoxide dismutase, (ii) iron superoxide dismutase from eitherEscherichia coli or higher plants, or (iii) plant or animal cuprozinc-superoxide dismutase.Pisum sativum L. manganese superoxide dismutase only appears to have antigenic determinants similar to other manganese superoxide dismutases from higher land plants. The antibody to pea Mn-superoxide dismutase was used to locate the enzyme in protoplasts isolated from young pea leaves by indirect immunofluorescence, and by electron microscopy using the unlabelled antibody peroxidase-antiperoxidase method. Results from immunofluorescence showed that chloroplasts were devoid of specific fluorescence which appeared scattered over the cytosolic spaces among chloroplasts, and demonstrate the absence of manganese superoxide dismutase inside chloroplasts. The metalloenzyme was found to be localized only in peroxisomes, whereas mitochondria, the traditionally accepted site for this enzyme in many eukaryotic organisms, did not show any specific staining. The possible subcellular roles of manganese superoxide dismutase inPisum sativum L. leaves are discussed in the light of its peroxisomal location.     

Structural and denaturation studies of two mutants of a cold adapted superoxide dismutase point to the importance of electrostatic interactions in protein stability

A peculiar feature of the psychrophilic iron superoxide dismutase from Pseudoalteromonas haloplanktis (PhSOD) is the presence in its amino acid sequence of a reactive cysteine (Cys57). To define the role of this residue, a structural characterization of the effect of two PhSOD mutations, C57S and C57R, was performed. Thermal and denaturant-induced unfolding of wild type and mutant PhSOD followed by circular dichroism and fluorescence studies revealed that C→R substitution alters the thermal stability and the resistance against denaturants of the enzyme, whereas C57S only alters the stability of the protein against urea. The crystallographic data on the C57R mutation suggest an involvement of the Arg side chain in the formation of salt bridges on protein surface. These findings support the hypothesis that the thermal resistance of PhSOD relies on optimization of charge–charge interactions on its surface. Our study contributes to a deeper understanding of the denaturation mechanism of superoxide dismutases, suggesting the presence of a structural dimeric intermediate between the native state and the unfolded state. This hypothesis is supported by the crystalline and solution data on the reduced form of the enzyme.     

变性过程中铜锌超氧化物歧化酶的活性通道

在酶的盐酸胍变性和热变性过程中,尝试采用电荷传递反应分析方法和电子自旋共振方法考察了酶活性部位的构象变化。酶活力与构象的变化行为表明,酶的活性部位通道先于酶分子的整体构象而发生变化,它是与酶的失活同时发生的。尽管酶活性部位中的金属离子保证了酶较高的稳定性,但酶的活性部位,特别是活性通道仍然是相对脆弱的。     

Self-immobilized recombinant Acetobacter xylinum for biotransformation

Biofilms have been successfully applied for biotransformation for decades, especially in the area of bioremediation due to the feature of harsh reaction condition resistance. Acetobacter xylinum is known for its cellulose pellicle forming capability. Like biofilm, A. xylinum cells are immobilized by simultaneously produced cellulose nanofibers in the pellicle. A recombinant A. xylinum was constructed with the expectation that the cells could be self-immobilized and achieve a desired and stable biotransformation. d-Amino acid oxidase (DAAO) of Rhodosporidium toruloides was used as the model enzyme to be expressed in the recombinant A. xylinum. The constructed recombinant A. xylinum not only successfully produced DAAO activity but also self-immobilized by cellulose nanofibers in both the static and shaken culture. Although self-immobilized cells demonstrated a DAAO activity approximately 10% of the cell crude extract activity, it provided the benefits of improved thermal stability, operational stability, and easy retrieval for repeated use.     

Expression and characterization of an iron-containing superoxide dismutase from Burkholderia pseudomallei

A superoxide dismutase (SOD) gene from Burkholderia pseudomallei, the causative agent of melioidosis, was cloned and expressed in Escherichia coli, and its product was functionally and physically characterized. The gene has an open-reading frame of 579 bp. The deduced amino acid sequence has 192 residues with a calculated molecular mass of ～22 kDa. Sequence comparison with other bacterial SODs showed that the protein contains typical metal-binding motifs and other Fe-SOD-conserved residues. The sequence has substantial similarity with other bacterial Fe-SOD sequences. The enzymatic activity of the expressed protein was inhibited by hydrogen peroxide but not by sodium azide or potassium cyanide, attributes that indeed are characteristic of typical bacterial Fe-SODs. Western blotting with antiserum against the recombinant Fe-SOD revealed that it is expressed in B. pseudomallei. Transformed E. coli that expressed the Fe-SOD had significantly increased SOD activity and was highly tolerant to paraquat-mediated replication inhibition, compared to transformed cells carrying an empty vector. Our results provide a basis for further biochemical characterization of the enzyme and elucidation of its role in the pathogenesis of B. pseudomallei.     

Thermal stability and redox properties of M. tuberculosis CuSOD

The superoxide dismutase from Mycobacterium tuberculosis is the only Cu-containing superoxide dismutase that lacks zinc in the active site. To explore the structural properties of this unusual enzyme, we have investigated its stability by differential scanning calorimetry. We have found that the holo-enzyme is significantly more stable than the apo-protein or the partially metallated enzyme, but that its melting temperature is markedly lower than that of all the other characterized eukaryotic and prokaryotic Cu,Zn superoxide dismutases. We have also observed that, unlike the zinc-free eukaryotic or bacterial enzymes, the active site copper of the mycobacterial enzyme is not reduced by ascorbate, confirming that its redox properties are comparable to those typical of the enzymes containing zinc in the active site. Our findings highlight the role of zinc in conferring stability to Cu,Zn superoxide dismutases and indicate that the structural rearrangements observed in M. tuberculosis Cu,SOD compensate for the absence of zinc in achieving a fully active enzyme.     

Isolation and characterization of an iron-containing superoxide dismutase from a eucaryote, Brassica campestris

A cyanide-insensitive superoxide dismutase was purified from mustard leaves, Brassica campestris. The protein had a molecular weight of 41,000 and was composed of two equally sized subunits. Metal analysis revealed that the enzyme contained 1.6 g atoms of iron per dimer. The isolation of an iron-containing superoxide dismutase from mustard leaves represents the first report of this enzyme in a multicellular eucaryotic organism.