Purification of a manganese-containing superoxide dismutase from Halobacterium halobium

Purification and Characterization of Superoxide Dismutases from Sea Buckthorn and Chestnut Rose

Superoxide dismutases (SODs) were purified from sea buckthorn and chestnut rose by ammonium sulfate precipitation and anion-exchange chromatography, and the detection methods of water-soluble tetrazolium-1 (WST-1), nitrobluetetrazolium (NBT) and pyrogallol autoxidation (PA) for SOD activity were compared. WST-1 method was selected due to its coefficient of variation (CV) <6% in this study. Two SODs exhibited similar characteristics. Their molecular mass and isoelectric point were about 30 kDa and 4.8 to 5.0 estimated by electrophoresis, and the K_m was 0.05 to 0.08 mmol/L, respectively. Dynamic light scattering analysis suggested their hydrodynamic radius distributes from 60 to 1500 nm. The activity of two SODs was unchanged at <80 °C or pH 2 to 9 or in simulated human gastric fluid. Their circular dichroism spectra suggested a main β-sheet structure, the fluorescence spectra reflected that the tryptophan residues of two SODs is partially exposed, these structures were rather stable at pH 2 to 9 or 50 to 90 °C. PRACTICAL APPLICATION: Superoxide dismutase (SOD) is an important antioxidant enzyme. SODs from sea buckthorn and chestnut rose were stable at high temperature or low pH or simulated gastric fluid. This result can provide a new approach for the potential application of SOD in the food and pharmaceutical fields.

A superoxide dismutase from the archaeon Sulfolobus solfataricus is an extracellular enzyme and prevents the deactivation by superoxide of cell-bound proteins

An oxygen-induced iron superoxide dismutase was found in the culture fluid of the thermoacidophilic crenarchaeon Sulfolobus solfataricus during growth on glucose-rich media. This protein was also identified as being associated with the cell-surface, with the amount of the released and cell-bound protein fractions depending on the growth phase of the cells. The steady decrease in cell-associated superoxide dismutase during continued growth correlated with the increase of free superoxide dismutase in the medium. Both enzyme fractions were purified to homogeneity and found to be active with different catalytic efficiency, with the released superoxide dismutase showing a fourfold lower specific activity. Characterization in comparison with the cytosolic superoxide dismutase revealed identical N-terminal sequences, electrophoretic mobility, isoelectric point, and molecular mass for all three differently located enzymes. In order to clarify the physiological role of the cell-associated superoxide dismutase, the prevention of cell-bound protein deactivation by oxyradicals was also investigated. Glucose dehydrogenase, which was chosen as a model enzyme, was demonstrated to be located on the cell surface and to be inactivated by potassium superoxide by in vivo assays. The direct protective effect of superoxide dismutase on glucose dehydrogenase was demonstrated by in vitro assays on the free released enzyme. Similarly, the prevention of deactivation by potassium superoxide was also demonstrated for the integral membrane protein succinate dehydrogenase by intact cell assay. Superoxide dismutase added to cells was shown to moderately reduce the critical damaging peroxidation and hence play a major role in maintaining the integrity of the outer cell envelope components.

Mn-superoxide dismutase from the halophilic halotolerant bacterium Ba1--isolation and active site spectroscopic studies

The superoxide-dismutase (SOD) enzyme, isolated from the halophilic halotolerant bacterium Ba1, was found to be a dimer with a molecular weight of 40 kD and a subunit weight of 23.5 kD. The partial N-terminal sequence showed significant homology to SODs isolated from various sources. Metal analysis showed that SOD from Ba1 contains manganese and iron with the following stoichiometries: 0.9 +/- 0.4 Mn/dimer and 0.6 +/- 0.2 Fe/dimer. Two bands were obtained by isoelectric-focusing, at pI of 4.45 and at 4.40. Native SOD from Ba1 at room temperature was ESR silent. An ESR spectrum of hydrated Mn(II) was obtained from denaturated enzyme. Native enzyme cooled to 97 K showed an ESR spectrum identified as being due to Fe(III). The spectrum was pH-independent. SOD from Ba1 was not inactivated by H2O2. On the basis of these observations, SOD from Ba1 was characterized as MnSOD. The excitation fluorescence spectrum of SOD from Ba1 showed four main peaks in the visible region. The effects on the spectra of KSCN, NaN3, NaF, and ascorbate were examined. Measurements of H2(17)O-nmr relaxation times T1 and T2, for solutions containing E. coli MnSOD and FeSOD, showed no paramagnetic contribution. These results support the assumption that the water molecule at the active site is strongly bound.

Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium

When subjected to the stress of growth in a relatively low-salt environment (1.25 M NaCl), the halophilic bacterium Halobacterium halobium induces a catalase. The protein has been purified to electrophoretic homogeneity and has an M(r) of 240,000 and a subunit size of approximately 62,000. The enzyme is active over a broad pH range of 6.5 to 10.0, with a peak in activity at pH 7.0. It has an isoelectric point of 4.0. This catalse, which is not readily reduced by dithionite, shows a Soret peak at 406 nm. Cyanide and azide inhibit the enzyme at micromolar concentrations, whereas maleimide is without effect. The addition of 20 mM 3-amino-1,2,4-triazole results in a 33% inhibition in enzymatic activity. The tetrameric protein binds NADP in a 1:1 ratio but does not peroxidize NADPH, NADH, or ascorbate. Although the enzymatic activity is maximal when assayed in a 50 mM potassium phosphate buffer with no NaCl, prolonged incubation in a buffer lacking NaCl results in inactive enzyme. Moreover, purification must be performed in the presence of 2 M NaCl. Equally as effective in retaining enzymatic function are NaCl, LiCl, KCl, CsCl, and NH4Cl, whereas divalent salts such as MgCl2 and CaCl2 result in the immediate loss of activity. The catalase is stained by pararosaniline, which is indicative of a glycosidic linkage. The Km for H2O2 is 60 mM, with inhibition observed at concentrations in excess of 90 mM. Thus, the mesohalic catalase purified from H. halobium seems to be similar to other catalases, except for the salt requirements, but differs markedly from the constitutive halobacterial hydroperoxidase.

Purification of a catalase-peroxidase from Halobacterium halobium: characterization of some unique properties of the halophilic enzyme

A hydroperoxidase purified from the halophilic archaeon Halobacterium halobium exhibited both catalase and peroxidase activities, which were greatly diminished in a low-salt environment. Therefore, the purification was carried out in 2 M NaCl. Purified protein exhibited catalase activity over the narrow pH range of 6.0 to 7.5 and exhibited peroxidase activity between pH 6.5 and 8.0. Peroxidase activity was maximal at NaCl concentrations above 1 M, although catalase activity required 2 M NaCl for optimal function. Catalase activity was greatest at 50 degrees C; at 90 degrees C, the enzymatic activity was 20% greater than at 25 degrees C. Peroxidase activity decreased rapidly above its maximum at 40 degrees C. An activation energy of 2.5 kcal (ca. 10 kJ)/mol was calculated for catalase, and an activation energy of 4.0 kcal (ca. 17 kJ)/mol was calculated for peroxidase. Catalase activity was not inhibited by 3-amino-1,2,4-triazole but was inhibited by KCN and NaN3 (apparent Ki [KiApp] of 50 and 67.5 microM, respectively). Peroxidative activity was inhibited equally by KCN and NaN3 (KiApp for both, approximately 30 microM). The absorption spectrum showed a Soret peak at 404 nm, and there was no apparent reduction by dithionite. A heme content of 1.43 per tetramer was determined. The protein has a pI of 3.8 and an M(r) of 240,000 and consists of four subunits of 60,300 each.

Structure, function, and evolution of the family of superoxide dismutase proteins from halophilic archaebacteria

The protein sequences of seven members of the superoxide dismutase (SOD) family from halophilic archaebacteria have been aligned and compared with each other and with the homologous Mn and Fe SOD sequences from eubacteria and the methanogenic archaebacterium Methanobacterium thermoautotrophicum. Of 199 common residues in the SOD proteins from halophilic archaebacteria, 125 are conserved in all seven sequences, and 64 of these are encoded by single unique triplets. The 74 remaining positions exhibit a high degree of variability, and for almost half of these, the encoding triplets are connected by at least two nonsynonymous nucleotide substitutions. The majority of nucleotide substitutions within the seven genes are nonsynonymous and result in amino acid replacement in the respective protein; silent third-codon-position (synonymous) substitutions are unexpectedly rare. Halophilic SODs contain 30 specific residues that are not found at the corresponding positions of the methanogenic or eubacterial SOD proteins. Seven of these are replacements of highly conserved amino acids in eubacterial SODs that are believed to play an important role in the three-dimensional structure of the protein. Residues implicated in formation of the active site, catalysis, and metal ion binding are conserved in all Mn and Fe SODs. Molecular phylogenies based on parsimony and neighbor-joining methods coherently group the halophile sequences but surprisingly fail to distinguish between the Mn SOD of Escherichia coli and the Fe SOD of M. thermoautotrophicum as the outgroup. These comparisons indicate that as a group, the SODs of halophilic archaebacteria have many unique and characteristic features. At the same time, the patterns of nucleotide substitution and amino acid replacement indicate that these genes and the proteins that they encode continue to be subject to strong and changing selection. This selection may be related to the presence of oxygen radicals and the inter- and intracellular composition and concentration of metal cations.

Elevation of superoxide dismutase in Halobacterium halobium by heat shock

Exposure of Halobacterium halobium to 50 degrees C for 2.5 h in an aerobic environment resulted in a greater than twofold increase in the activity of the manganese-containing superoxide dismutase. Nondenaturing polyacrylamide gels stained for enzymatic activity did not reveal any additional isozymes of superoxide dismutase induced by the heat shock. The maximal effect was observed at 50 degrees C, and the elevated levels of activity remained constant during 5 h of recovery at 40 degrees C. The induction of enzymatic activity was sensitive to protein synthesis inhibitors. The results are discussed relative to heat shock and stress-related proteins as well as alterations in metabolism brought about by elevated temperatures.

Halobacterium halobium Mn-SOD gene: archaebacterial and eubacterial features

A 1.8 kb PstI fragment from Halobacterium halobium DNA was found to hybridize to synthetic oligonucleotide probes constructed by using the sequence of the N-terminus of a Mn-containing superoxide dismutase purified from H. halobium. The entire insert containing a 600-bp coding sequence for Mn-SOD and its 5' and 3' flanking regions was sequenced. The derived amino acid sequence of the structural gene showed a similarity to other manganic and iron-containing superoxide dismutases in normally conserved regions. Primer extension analysis of the H. halobium Mn-SOD mRNA showed that gene transcription begins 14 bases upstream of the translational start. A Shine-Dalgarno sequence and archaebacterial consensus promoter sequences were observed. Several other promoter and terminator nucleotide sequences homologous to prokaryotic and eukaryotic organisms were found.

Unusual evolution of a superoxide dismutase-like gene from the extremely halophilic archaebacterium Halobacterium cutirubrum

The archaebacterium Halobacterium cutirubrum contains a single detectable, Mn-containing superoxide dismutase, which is encoded by the sod gene (B. P. May and P. P. Dennis, J. Biol. Chem. 264:12253-12258, 1989). The genome of H. cutirubrum also contains a closely related sod-like gene (slg) of unknown function that has a pattern of expression different from that of sod. The four amino acid residues that bind the Mn atom are conserved, but the flanking regions of the two genes are unrelated. Although the genes have 87% nucleotide sequence identity, the proteins they encode have only 83% amino acid sequence identity. Mutations occur randomly at the first, second, and third codon positions, and transversions outnumber transitions. Most of the mutational differences between the two genes are confined to two limited regions; other regions totally lack differences. These two gene sequences are apparently in the initial stage of divergent evolution. Presumably, this divergence is being driven by strong selection at the molecular level for either acquisition of new functions or partition and refinement of ancestral functions in one or both of the respective gene products.

Cloning and determination of the nucleotide sequence of the Mn-containing superoxide dismutase gene from Halobacterium halobium

A group of synthetic 17-mer oligodeoxynucleotides (oligos) was constructed to correspond to a sequence of amino acids situated near the N terminus of the manganese-containing superoxide dismutase (Mn-SOD) purified from the halophilic bacterium, Halobacterium halobium. A cosmid library of a Sau3AI partial digest of halobium DNA, cloned into the BamHI site of pHC79, was probed with the radiolabeled oligos. Cosmid DNA was purified from the clone that showed hybridization at the highest stringency. A 1.8-kb PstI fragment of this DNA which hybridized the probes was subcloned into bacteriophage M13 and transfected into Escherichia coli JM101. The entire insert containing a 600-bp sequence coding for Mn-SOD and its 5'- and 3'-flanking regions was sequenced. The derived amino acid sequence of the structural gene showed a similarity to other manganese and iron-containing SODs in normally conserved regions.