Purification and characterization of a novel type of catalase from the bacterium Klebsiella pneumoniae

The Peroxiredoxin Asp f3 Acts as Redox Sensor in Aspergillus fumigatus

The human pathogenic fungus Aspergillus fumigatus is readily eradicated by the innate immunity of immunocompetent human hosts, but can cause severe infections, such as invasive aspergillosis (IA), in immunocompromised individuals. During infection, the fungal redox homeostasis can be challenged by reactive oxygen species (ROS), either derived from the oxidative burst of innate immune cells or the action of antifungal drugs. The peroxiredoxin Asp f3 was found to be essential to cause IA in mice, but how Asp f3 integrates with fungal redox homeostasis remains unknown. Here, we show that in vivo, Asp f3 acts as a sensor for ROS. While global transcription in fungal hyphae under minimal growth conditions was fully independent of Asp f3, a robust induction of the oxidative stress response required the presence of the peroxiredoxin. Hyphae devoid of Asp f3 failed to activate several redox active genes, like members of the gliotoxin biosynthesis gene cluster and integral members of the Afyap1 regulon, the central activator of the ROS defense machinery in fungi. Upon deletion of the asp f3 gene Afyap1 displayed significantly reduced nuclear localization during ROS exposure, indicating that Asp f3 can act as an intracellular redox sensor for several target proteins.

Resistance and induction of viable but non culturable states (VBNC) during inactivation of E. coli and Klebsiella pneumoniae by addition of H2O2 to natural well water under simulated solar irradiation

Inactivation of E. coli and Klebsiella pneumoniae by addition of H₂O₂ 10 mg L^-1 into natural well water samples containing natural total iron concentrations (around 0.3 mg L^-1) under simulated solar light was followed by bacterial culturability (plate count) and viability (DVC-FISH). Results showed that culturability of both bacteria was totally reduced while viability was only completely depleted for E. coli in well water samples depending of total iron concentration. Post-irradiation effects in presence of residual H₂O₂ showed that viability of both bacteria kept dropping being totally reduced for E. coli cells while K. pneumoniae decreased only 1-log. SEM micrographs showed that E. coli and K. pneumoniae cells underwent morphological changes and size reduction according to VBNC states. Different dark and photo-induced processes where physical-chemical features of groundwater samples play an important role could be responsible of bacteria abatement.

Subcellular Localization of a Plant Catalase-Phenol Oxidase, AcCATPO, from Amaranthus and Identification of a Non-canonical Peroxisome Targeting Signal

AcCATPO is a plant catalase-phenol oxidase recently identified from red amaranth. Its physiological function remains unexplored. As the starting step of functional analysis, here we report its subcellular localization and a non-canonical targeting signal. Commonly used bioinformatics programs predicted a peroxisomal localization for AcCATPO, but failed in identification of canonical peroxisomal targeting signals (PTS). The C-terminal GFP tagging led the fusion protein AcCATPO-GFP to the cytosol and the nucleus, but N-terminal tagging directed the GFP-AcCATPO to peroxisomes and nuclei, in transgenic tobacco. Deleting the tripeptide (PTM) at the extreme C-terminus almost ruled out the peroxisomal localization of GFP-AcCATPOΔ3, and removing the C-terminal decapeptide completely excluded peroxisomes as the residence of GFP-AcCATPOΔ10. Furthermore, this decapeptide as a targeting signal could import GFP-10aa to the peroxisome exclusively. Taken together, these results demonstrate that AcCATPO is localized to the peroxisome and the nucleus, and its peroxisomal localization is attributed to a non-canonical PTS1, the C-terminal decapeptide which contains an internal SRL motif and a conserved tripeptide P-S/T-I/M at the extreme of C-terminus. This work may further the study as to the physiological function of AcCATPO, especially clarify its involvement in betalain biosynthesis, and provide a clue to elucidate more non-canonic PTS.

In Healthy Young Men, a Short Exhaustive Exercise Alters the Oxidative Stress Only Slightly, Independent of the Actual Fitness

The aim of the present study was to evaluate the apparent disagreement regarding the effect of a typical cycling progressive exercise, commonly used to assess VO_2max, on the kinetics of ex vivo copper induced peroxidation of serum lipids. Thirty-two (32) healthy young men, aged 24–30 years, who do not smoke and do not take any food supplements, participated in the study. Blood was withdrawn from each participant at three time points (before the exercise and 5 minutes and one hour after exercise). Copper induced peroxidation of sera made of the blood samples was monitored by spectrophotometry. For comparison, we also assayed TBARS concentration and the activity of oxidation-related enzymes. The physical exercise resulted in a slight and reversible increase of TBARS and slight changes in the activities of the studied antioxidant enzymes and the lag preceding peroxidation did not change substantially. Most altered parameters returned to baseline level one hour after exercise. Notably, the exercise-induced changes in OS did not correlate with the physical fitness of the subjects, as evaluated in this study (VO_2max = 30–60 mL/min/kg). We conclude that in healthy young fit men a short exhaustive exercise alters only slightly the OS, independent of the actual physical fitness.

New bacteria Bacillus nitroreducens PLC9 with hydrogen peroxide-degrading activity with high survival rate in hydrogen peroxide

Bacteria were isolated from wastewater containing highly concentrated hydrogen peroxide that had been used to clean the pure water delivery system in a semiconductor plant. One bacterium was selected for its high hydrogen peroxide degradation activity. In the presence of 1% hydrogen peroxide, it degraded 72.5% in 5 min. It showed 100% viability after 6 h at 1% hydrogen peroxide. Even at 3% hydrogen peroxide, it survived for more than 6 h. This bacterium was named as Bacillus nitroreducens PLC9 since its 16S rRNA showed 100% similarity with the recently reported new species B. nitroreducens. Purified catalase from B. nitroreducens PLC9 was characterized as a thermo-alkali-stable hydroperoxidase type II catalase, and it is suggested as a new type of catalase based on following: (1) it is stable over a broad pH range (pH 4-11); (2) it is consisted of homodimers with a molecular weight of 66 kDa (total molecular weight, 134 kDa); (3) its activity was not inhibited by 3-amino-1,2,4-triazole; and (4) its N-terminal sequence has never been reported before. Both B. nitroreducens PLC9 and the isolated catalase can be used for efficient degradation of hydrogen peroxide at high concentrations.

Cloning, expression and characterization of the catalase-peroxidase (KatG) gene from a fast-growing Mycobacterium sp. strain JC1 DSM 3803

The gene encoding a catalase-peroxidase (KatG) was cloned from chromosomal DNA of a fast-growing Mycobacterium sp. strain JC1 DSM 3803. The nucleotide sequence of a 5.7 kb EcoRI fragment containing the katG and its flanking regions was determined. The fragment (5,706 bps) contained two complete open reading frames (ORFs) encoding putative ferric uptake regulator A (FurA) and KatG proteins. The cloned gene, katG, had an ORF of 2241 nt, encoding a protein with calculated molecular mass of 81,748 Da. The furA was located in the upstream of the katG with the same transcriptional direction and there was a 38 bp gap space between them. The deduced KatG and FurA protein sequences showed significant homologies to KatG2 and Fur2 of Mycobacterium smegmatis and clustered with other mycobacterial KatG and Fur-like proteins in phylogenetic trees, respectively. The recombinant KatG overproduced in Escherichia coli was nearly indistinguishable from the native JC1 catalase-peroxidase in enzymatic properties and also possessed the resistance to organic solvents, indicating that the cloned katG truly encodes the Mycobacterium sp. JC1 catalase-peroxidase. Difference spectroscopy revealed Mn(II) binding near the haem of the KatG. Transcript analysis of the furA-katG using RT-PCR suggests that the katG is independently transcribed from the furA.

Crystallization and preliminary X-ray analysis of a bifunctional catalase-phenol oxidase from Scytalidium thermophilum

Catalase-phenol oxidase from Scytalidium thermophilum is a bifunctional enzyme: its major activity is the catalase-mediated decomposition of hydrogen peroxide, but it also catalyzes phenol oxidation. To understand the structural basis of this dual functionality, the enzyme, which has been shown to be a tetramer in solution, has been purified by anion-exchange and gel-filtration chromatography and has been crystallized using the hanging-drop vapour-diffusion technique. Streak-seeding was used to obtain larger crystals suitable for X-ray analysis. Diffraction data were collected to 2.8 A resolution at the Daresbury Synchrotron Radiation Source. The crystals belonged to space group P2(1) and contained one tetramer per asymmetric unit.

Purification, characterization, and identification of a novel bifunctional catalase-phenol oxidase from Scytalidium thermophilum

A novel bifunctional catalase with an additional phenol oxidase activity was isolated from a thermophilic fungus, Scytalidium thermophilum. This extracellular enzyme was purified ca. 10-fold with 46% yield and was biochemically characterized. The enzyme contains heme and has a molecular weight of 320 kDa with four 80 kDa subunits and an isoelectric point of 5.0. Catalase and phenol oxidase activities were most stable at pH 7.0. The activation energies of catalase and phenol oxidase activities of the enzyme were found to be 2.7 +/- 0.2 and 10.1 +/- 0.4 kcal/mol, respectively. The pure enzyme can oxidize o-diphenols such as catechol, caffeic acid, and L-DOPA in the absence of hydrogen peroxide and the highest oxidase activity is observed against catechol. No activity is detected against tyrosine and common laccase substrates such as ABTS and syringaldazine with the exception of weak activity with p-hydroquinone. Common catechol oxidase inhibitors, salicylhydroxamic acid and p-coumaric acid, inhibit the oxidase activity. Catechol oxidation activity was also detected in three other catalases tested, from Aspergillus niger, human erythrocyte, and bovine liver, suggesting that this dual catalase-phenol oxidase activity may be a common feature of catalases.

The Aspergillus fumigatus transcriptional regulator AfYap1 represents the major regulator for defense against reactive oxygen intermediates but is dispensable for pathogenicity in an intranasal mouse infection model

Macrophages and neutrophils kill the airborne fungal pathogen Aspergillus fumigatus. The dependency of this killing process on reactive oxygen intermediates (ROI) has been strongly suggested. Therefore, we investigated the enzymatic ROI detoxifying system by proteome analysis of A. fumigatus challenged by H(2)O(2). Since many of the identified proteins and genes are apparently regulated by a putative Saccharomyces cerevisiae Yap1 homolog, the corresponding gene of A. fumigatus was identified and designated Afyap1. Nuclear localization of a functional AfYap1-eGFP fusion was stress dependent. Deletion of the Afyap1 gene led to drastically increased sensitivity of the deletion mutant against H(2)O(2) and menadione, but not against diamide and NO radicals. Proteome analysis of the DeltaAfyap1 mutant strain challenged with 2 mM H(2)O(2) indicated that 29 proteins are controlled directly or indirectly by AfYap1, including catalase 2. Despite its importance for defense against reactive agents, the Afyap1 deletion mutant did not show attenuated virulence in a murine model of Aspergillus infection. These data challenge the hypothesis that ROI such as superoxide anions and peroxides play a direct role in killing of A. fumigatus in an immunocompromised host. This conclusion was further supported by the finding that killing of A. fumigatus wild-type and DeltaAfyap1 mutant germlings by human neutrophilic granulocytes worked equally well irrespective of whether the ROI scavenger glutathione or an NADPH-oxidase inhibitor was added to the cells.

The thioredoxin system of the filamentous fungus Aspergillus nidulans: impact on development and oxidative stress response

Redox regulation has been shown to be of increasing importance for many cellular processes. Here, redox homeostasis was addressed in Aspergillus nidulans, an important model organism for fundamental biological questions such as development, gene regulation or the regulation of the production of secondary metabolites. We describe the characterization of a thioredoxin system from the filamentous fungus A. nidulans. The A. nidulans thioredoxin A (AnTrxA) is an 11.6-kDa protein with a characteristic thioredoxin active site motif (WCGPC) encoded by the trxA gene. The corresponding thioredoxin reductase (AnTrxR), encoded by the trxR gene, represents a homodimeric flavoprotein with a native molecular mass of 72.2 kDa. When combined in vitro, the in Escherichia coli overproduced recombinant proteins AnTrxA and AnTrxR were able to reduce insulin and oxidized glutathione in an NADPH-dependent manner indicating that this in vitro redox system is functional. Moreover, we have created a thioredoxin A deletion strain that shows decreased growth, an increased catalase activity, and the inability to form reproductive structures like conidiophores or cleistothecia when cultivated under standard conditions. However, addition of GSH at low concentrations led to the development of sexual cleistothecia, whereas high GSH levels resulted in the formation of asexual conidiophores. Furthermore, by applying the principle of thioredoxin-affinity chromatography we identified several novel putative targets of thioredoxin A, including a hypothetical protein with peroxidase activity and an aldehyde dehydrogenase.

Catalases of Aspergillus fumigatus and inflammation in aspergillosis

The article describes various features of aspergillosis and a discussed the role of calatases produced by Aspergillus fumigatus during infection. Since a large body of invasive Aspergillus infection occurs as an opportunistic infection in variously impaired defense mechanisms, there is a wide spectrum of histopathological features of lesions demonstrated at the site of infection. Accordingly, histopathology of the lesions can be understood as a phenotypical representation of interaction between differently impaired functions of neutrophils and macrophages and virulence factors of invading Aspergilli. Consideration of previous pathological knowledge regarding infection and inflammation provides much important information to predict the pathophysiology of a patient. Meanwhile, detoxification of hydrogen peroxide by catalases has been proposed as a way to overcome this host response. A. fumigatus produces three active catalases, one from conidia and two from mycelia. CatAp, a spore specific monofunctional catalase, is resistant to heat and metal ions. In spite of their increased sensitivity to H(2)O(2), killing of catA conidia by alveolar macrophages, virulence in animals was similar to wild type conidia. In contrast to mycelial Cat1p, and CatAp catalases, the mycelial Cat2p is a bifunctional catalase-peroxidase enzyme and is also sensitive to heat, metal ions and detergent. Surprisingly, the mycelium of the double cat1 cat2 mutant with no catalase activity has only a slightly increased sensitivity to H(2)O(2) and was as sensitive to the killing of polymorphonuclear neutrophils as the wild type strain. However, it showed a delayed infection in the rat model of aspergillosis compared to the wild type strain. Consequently, it should be emphasized that conidial catalase is not a virulence factor but that mycelial catalases transiently protect the fungus from the host defence reactions.

Characterization of enzymatic antioxidants in the lichen Ramalina lacera and their response to rehydration

Lichens are slow-growing associations of fungi and green algae or cyanobacteria. This symbiotic association forms a common thallus that does not possess roots or a waxy cuticle and depends mainly on atmospheric input of mineral nutrients. The lifestyle of most lichens is composed of alternating periods of desiccation with low metabolic activity and hydration that induces increase in their metabolism. We have previously shown that rehydration of the naturally desiccated lichen Ramalina lacera resulted in a rapid increase in photosynthesis and was accompanied by a burst of intracellular production of reactive oxygen species and nitric oxide, as well as a transient decrease in water-soluble antioxidant capacity. We report here on enzymatic antioxidants of R. lacera and their response to rehydration. Native gel electrophoresis of crude extracts of R. lacera stained for superoxide dismutase (SOD) activity revealed four Fe-SOD and four Mn-SOD electromorphs that are synthesized by the alga, a Cu/Zn-SOD and a Mn-SOD that are the product of the fungus, and two catalases synthesized one by the fungus and the other by the algae. In addition, we detected glutathione reductase and glucose-6-phosphate dehydrogenase activities in crude extracts of R. lacera. Rehydration of the thalli resulted in a decrease in SOD activity of all forms, and a transient decrease in total catalase activity, as well as a decrease in the antioxidant auxiliary enzymes glutathione reductase and glucose-6-phosphate dehydrogenase.

Lipid peroxidation of lung surfactant due to reactive oxygen species released from phagocytes stimulated by bacteria from children with cystic fibrosis

We used Pseudomonas aeruginosa, Burkholderia cepacia and Stenotrophomonas maltophilia, live or heat-killed, isolated from the airways of children with Cystic Fibrosis, to stimulate human neutrophils (PMN) and rat alveolar macrophages (AM) to produce reactive oxygen metabolites in the presence or absence of Curosurf, a natural porcine lung surfactant. We determined: (1) the amount of lipid peroxidation (LPO) as assessed by the amounts of malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE) using the LPO 586 test kit; (2) the production by AM of superoxide with the nitroblue tetrazolium test and (3) of nitric oxide (NO) with the Griess reaction. Stimulation of PMN or AM increases LPO of Curosurf and cell wall lipids. In both types of phagocytes, B. cepacia induced the highest LPO levels followed by P. aeruginosa and S. maltophilia. PMN, stimulated by live bacteria, induced higher LPO than those stimulated by heat-killed bacteria. B. cepacia stimulated AM to produce more superoxide and NO than did P. aeruginosa and S. maltophilia. The high phagocyte-stimulating ability of B. cepacia and its higher surfactant LPO than those of the other bacteria used in this in vitro study may play a role in vivo in the serious clinical condition known as the "Cepacia syndrome".

Catalase is the bacteria-derived detoxifying substance against paramecia-killing toxin in wheat grass powder infusion

Paramecium cells are usually cultured in a wheat grass powder infusion inoculated with Klebsiella pneumoniae. However, non-bacterized wheat grass powder infusion is toxic to paramecia, and bacteria-derived substance detoxifies the toxic substance. Here, the detoxifying substance from K. pneumoniae, which was found to be proteinaceous, was purified to homogeneity. The protein had an apparent molecular mass of about 200 kDa by gel filtration and 92 kDa by SDS-polyacrylamide gel electrophoresis. Although the amino acid sequence of the amino terminal region did not show a high sequence homology with any reported proteins, amino acid sequences of internal regions of the protein were nearly identical to catalase HPII from Escherichia coli. When the wheat grass powder infusion was treated at 25 degrees C for 1 h with commercially available catalase from bovine liver, the toxicity of the infusion against paramecia was completely abolished. The initial concentration of hydrogen peroxide in the wheat grass powder infusion was about 30 microM and was completely decomposed by the catalase treatment. Therefore, the toxic substance in the wheat grass powder infusion and the detoxifying substance from K. pneumoniae are considered as hydrogen peroxide and catalase, respectively.

Catalases of Aspergillus fumigatus

Upon infection of a host, the pathogenic fungus Aspergillus fumigatus is attacked by the reactive oxygen species produced by phagocytic cells. Detoxification of hydrogen peroxide by catalases was proposed as a way to overcome this host response. A. fumigatus produces three active catalases; one is produced by conidia, and two are produced by mycelia. The mycelial catalase Cat1p was studied previously. Here we characterized the two other catalases, their genes, and the phenotypes of gene-disrupted mutants. CatAp, a spore-specific monofunctional catalase, is resistant to heat, metal ions, and detergent. This enzyme is a dimeric protein with 84.5-kDa subunits. The 749-amino-acid polypeptide exhibits high levels of similarity to the Aspergillus nidulans CatA catalase and to bacterial catalase HPII of Escherichia coli. In spite of increased sensitivity to H(2)O(2), killing of DeltacatA conidia by alveolar macrophages and virulence in animals were similar to the killing of conidia by alveolar macrophages and virulence in animals observed for the wild type. In contrast to the Cat1p and CatAp catalases, the mycelial Cat2p enzyme is a bifunctional catalase-peroxidase and is sensitive to heat, metal ions, and detergent. This enzyme, an 82-kDa monomer, is homologous to catalase-peroxidases of several fungi and bacteria. Surprisingly, mycelium of the double Deltacat1Deltacat2 mutant with no catalase activity exhibited only slightly increased sensitivity to H(2)O(2) and was as sensitive to killing by polymorphonuclear neutrophils as mycelium of the wild-type strain. However, this mutant exhibited delayed infection in the rat model of aspergillosis compared to infection by the wild-type strain. These results indicate that conidial catalase is not a virulence factor and that mycelial catalases transiently protect the fungus from the host.

Characterization of Escherichia coli null mutants for glutaredoxin 2

Three Escherichia coli glutaredoxins catalyze GSH-disulfide oxidoreductions, but the atypical 24-kDa glutaredoxin 2 (Grx2, grxB gene), in contrast to the 9-kDa glutaredoxin 1 (Grx1, grxA gene) and glutaredoxin 3 (Grx3, grxC gene), is not a hydrogen donor for ribonucleotide reductase. To improve the understanding of glutaredoxin function, a null mutant for grxB (grxB(-)) was constructed and combined with other mutations. Null mutants for grxB or all three glutaredoxin genes were viable in rich and minimal media with little changes in their growth properties. Expression of leaderless alkaline phosphatase showed that Grx1 and Grx2 (but not Grx3) contributed in the reduction of cytosolic protein disulfides. Moreover, Grx1 could catalyze disulfide formation in the oxidizing cytosol of combined null mutants for glutathione reductase and thioredoxin 1. grxB(-) cells were more sensitive to hydrogen peroxide and other oxidants and showed increased carbonylation of intracellular proteins, particularly in the stationary phase. Significant up-regulation of catalase activity was observed in null mutants for thioredoxin 1 and the three glutaredoxins, whereas up-regulation of glutaredoxin activity was observed in catalase-deficient strains with additional defects in the thioredoxin pathway. The expression of catalases is thus interconnected with the thioredoxin/glutaredoxin pathways in the antioxidant response.

Molecular cloning, sequencing analysis and expression of the catalase-peroxidase gene from Halobacterium salinarum

The gene encoding catalase-peroxidase was cloned from chromosomal DNA from the Archaea, Halobacterium salinarum. The nucleotide sequence of a 3.5 kb fragment, containing the catalase-peroxidase gene and its flanking regions was determined. A 2.16 kb open reading frame was obtained, encoding the enzyme which was comprised of 720 amino acid residues with a calculated molecular weight of 80 kDa. The deduced amino acid sequence of the H. salinarum catalase-peroxidase showed a high degree of identity to other bifunctional catalase-peroxidases. A transcriptional start site was identified 183 bp upstream of the translational start codon. Southern blot analysis indicated that catalase-peroxidase was a single copy gene. The Archaeal catalase-peroxidase gene was expressed in Escherichia coli, and the expressed fusion protein exhibited both catalase and peroxidase activities.

Purification and characterization of a novel bromoperoxidase-catalase isolated from bacteria found in recycled pulp white water

A bacterial strain, Pseudomonad EF group 70B, containing a high catalase-like activity was found in process water (white water) from pulp using recycled fibers. The enzyme was purified and characterized, and found to be a hydroperoxidase. The active enzyme has an apparent molecular mass of about 153 kDa with two identical subunits and a pI value of 4.7. It has a rather sharp pH optimum for catalase activity at 6.0 but exhibits catalase, peroxidase and brominating activities over a broad pH range from 4 to 8. It was not inhibited by 3-amino-1,2,4-triazole. Peroxidase-like activity was found when adding o-dianisidine, pyrogallol, guaiacol and 4-aminoantipyrine. Brominating activity was noticed using monochlorodimedone as a substrate. The absorption spectrum exhibited a Soret band at 404 nm. Upon reduction with dithionite the Soret peak decreased and shifted to 436 nm. Pyridine hemochrome spectra indicated the presence of a protophorfyrin IX heme group and the enzyme was inhibited by the known heme ligands cyanide and azide. N-terminal amino acid analysis gave the sequence STEVKLPYAVAGGGTTILDAFPGE, which showed no homology with those of known catalases or peroxidases. It is concluded that the enzyme is a novel type of catalase-peroxidase or, more specifically, a bromoperoxidase-catalase, and that future developments of inhibitors of hydrogen peroxide-degrading activities in white water may be based on this enzyme and other catalase-peroxidases.

Purification and characterization of an iron superoxide dismutase and a catalase from the sulfate-reducing bacterium Desulfovibrio gigas

The iron-containing superoxide dismutase (FeSOD; EC 1.15.1.1) and catalase (EC 1.11.1.6) enzymes constitutively expressed by the strictly anaerobic bacterium Desulfovibrio gigas were purified and characterized. The FeSOD, isolated as a homodimer of 22-kDa subunits, has a specific activity of 1,900 U/mg and exhibits an electron paramagnetic resonance (EPR) spectrum characteristic of high-spin ferric iron in a rhombically distorted ligand field. Like other FeSODs from different organisms, D. gigas FeSOD is sensitive to H(2)O(2) and azide but not to cyanide. The N-terminal amino acid sequence shows a high degree of homology with other SODs from different sources. On the other hand, D. gigas catalase has an estimated molecular mass of 186 +/- 8 kDa, consisting of three subunits of 61 kDa, and shows no peroxidase activity. This enzyme is very sensitive to H(2)O(2) and cyanide and only slightly sensitive to sulfide. The native enzyme contains one heme per molecule and exhibits a characteristic high-spin ferric-heme EPR spectrum (g(y,x) = 6.4, 5.4); it has a specific activity of 4,200 U/mg, which is unusually low for this class of enzyme. The importance of these two enzymes in the context of oxygen utilization by this anaerobic organism is discussed.

Understanding the structure and function of catalases: clues from molecular evolution and in vitro mutagenesis

This review gives an overview about the structural organisation of different evolutionary lines of all enzymes capable of efficient dismutation of hydrogen peroxide. Major potential applications in biotechnology and clinical medicine justify further investigations. According to structural and functional similarities catalases can be divided in three subgroups. Typical catalases are homotetrameric haem proteins. The three-dimensional structure of six representatives has been resolved to atomic resolution. The central core of each subunit reveals a characteristic "catalase fold", extremely well conserved among this group. In the native tetramer structure pairs of subunits tightly interact via exchange of their N-terminal arms. This pseudo-knot structures implies a highly ordered assembly pathway. A minor subgroup ("large catalases") possesses an extra flavodoxin-like C-terminal domain. A > or = 25 A long channel leads from the enzyme surface to the deeply buried active site. It enables rapid and selective diffusion of the substrates to the active center. In several catalases NADPH is tightly bound close to the surface. This cofactor may prevent and reverse the formation of compound II, an inactive reaction intermediate. Bifunctional catalase-peroxidase are haem proteins which probably arose via gene duplication of an ancestral peroxidase gene. No detailed structural information is currently available. Even less is know about manganese catalases. Their di-manganese reaction centers may be evolutionary.

Role of oxidants in microbial pathophysiology

Reactive oxidant species (superoxide, hydrogen peroxide, hydroxyl radical, hypohalous acid, and nitric oxide) are involved in many of the complex interactions between the invading microorganism and its host. Regardless of the source of these compounds or whether they are produced under normal conditions or those of oxidative stress, these oxidants exhibit a broad range of toxic effects to biomolecules that are essential for cell survival. Production of these oxidants by microorganisms enables them to have a survival advantage in their environment. Host oxidant production, especially by phagocytes, is a counteractive mechanism aimed at microbial killing. However, this mechanism may be contribute to a deleterious consequence of oxidant exposure, i.e., inflammatory tissue injury. Both the host and the microorganism have evolved complex adaptive mechanisms to deflect oxidant-mediated damage, including enzymatic and nonenzymatic oxidant-scavenging systems. This review discusses the formation of reactive oxidant species in vivo and how they mediate many of the processes involved in the complex interplay between microbial invasion and host defense.

Cloning, sequencing and disruption of a bromoperoxidase-catalase gene in Streptomyces venezuelae: evidence that it is not required for chlorination in chloramphenicol biosynthesis

Genomic DNA libraries of Streptomyces venezuelae ISP5230 and of a mutant blocked at the chlorination step of chloramphenicol biosynthesis were probed by hybridization with a synthetic oligonucleotide corresponding to the N-terminal amino acid sequence of a bromoperoxidase-catalase purified from the wild-type strain. Hybridizing fragments obtained from the two strains were cloned and sequenced. Analysis of the nucleotide sequences demonstrated that the fragments contained the same 1449 bp open reading frame with no differences in nucleotide sequence. The deduced polypeptide encoded 483 amino acids with a calculated M(r) of 54,200; the N-terminal sequence was identical to that of the bromoperoxidase-catalase purified from wild-type S. venezuelae. Comparison of the amino acid sequence predicted for the cloned bromoperoxidase-catalase gene (bca) with database protein sequences showed a significant similarity to a group of prokaryotic and eukaryotic catalases, but none to other peroxidases or haloperoxidases. Replacement of the bca gene in the wild-type strain of S. venezuelae with a copy disrupted by insertion of a DNA fragment encoding apramycin resistance did not prevent chloramphenicol production. The results suggest that the role of the enzyme in S. venezuelae is related to its activity as a catalase rather than as a halogenating agent.

Purification and characterization of an intracellular catalase-peroxidase from Penicillium simplicissimum

The first dimeric catalase-peroxidase of eucaryotic origin, an intracellular hydroperoxidase from Penicillium simplicissimum which exhibited both catalase and peroxidase activities, has been isolated. The enzyme has an apparent molecular mass of about 170 kDa and is composed of two identical subunits. The purified protein has a pH optimum for catalase activity at 6.4 and for peroxidase at 5.4. Both activities are inhibited by cyanide and azide whereas 3-amino-1,2,4-triazole has no effect. 3,3'-Diaminobenzidine, 3,3'-dimethoxybenzidine, guaiacol, 2,6-dimethoxyphenol and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) all serve as substrates. The optical spectrum of the purified enzyme shows a Soret band at 407 nm. Reduction by dithionite results in the disappearance of the Soret band and formation of three absorption maxima at 440, 562 and 595 nm. The prosthetic group was identified as a protoheme IX and EPR spectroscopy revealed the presence of a histidine residue as proximal ligand. In addition to the catalase-peroxidase, an atypical catalase which is active over a broad pH range was also partially purified from P. simplicissimum. This catalase is located in the periplasm and contains a chlorin-type heme as prosthetic group.

An immunodominant 90-kilodalton Aspergillus fumigatus antigen is the subunit of a catalase

We have identified, purified, and characterized structurally and functionally a 90-kDa immunodominant antigen associated with the water-soluble fraction of Aspergillus fumigatus. This antigen is recognized by 90.3% of serum samples from patients with aspergilloma and should be considered either by itself or better in combination with other purified antigens as a candidate for developing a standardized immunoassay for the detection of aspergilloma. p90 is a glycoprotein containing at least two two N-linked sugar chains of 2 and 5 kDa, respectively, which are not necessary for its reactivity with aspergilloma serum samples. Using specific anti-p90 rabbit serum, we have demonstrated that under native conditions, p90 exists in oligomeric form and has associated catalase activity. This activity is resistant to extreme temperatures (> 60 degrees C), reducing agents (40 mM dithiothreitol), high concentrations of denaturing agents such as 8 M urea and 8% sodium dodecyl sulfate, and treatments with ethanol-chloroform-water (5:3:10 [vol/vol]) mixtures.

Cloning, characterization and phenotypic expression in Escherichia coli of catF, which encodes the catalytic subunit of catalase isozyme CatF of Pseudomonas syringae

The phytophathogenic, gram-negative bacterium Pseudomonas syringae pv. syringae 61 contains three isozymes of catalase (EC 1.11.1.6), which have been proposed to play a role in the bacterium's responses to various environmental stresses. To study the role of individual isozymes, the gene coding for the catalytic subunit of one catalase isozyme was cloned from a cosmid library hosted in Escherichia coli DH5 alpha by using a designed catalase-specific DNA probe for the screening. One out of four clones with a catalase-positive genotype was subcloned and a pUC19-based 2.7 x 10(3)-base (2.7-kb) insert subclone, pMK3E5, was used to transform catalase-deficient E. coli strain UM255 (HPI-, HPII-). The transformants contained a single isozyme of catalase that had electrophoretic and enzymic properties similar to catalase isozyme CatF from P. syringae pv. syringae 61. Analysis of the sequenced 2.7-kb insert DNA revealed six putative open-reading frames (ORF). The 1542-base-pair DNA sequence of ORF2, called catF, encodes a peptide of 513 amino acid residues with a calculated molecular mass of 66.6 kDa. The amino acid sequence deduced from catF had homology to the primary structure of true catalases from mammals, plants, yeasts and bacteria. The activity of the recombinant catalase was inhibited by 3-amino-1,2,4-triazole and azide and stimulated by chloramphenicol. The N terminus contained a signal sequence of 26 amino acids necessary for secretion into the periplasm, a so-far unique property of Pseudomonas catalases.

Biochemical and genetic analyses of a catalase from the anaerobic bacterium Bacteroides fragilis

A single catalase enzyme was produced by the anaerobic bacterium Bacteroides fragilis when cultures at late log phase were shifted to aerobic conditions. In anaerobic conditions, catalase activity was detected in stationary-phase cultures, indicating that not only oxygen exposure but also starvation may affect the production of this antioxidant enzyme. The purified enzyme showed a peroxidatic activity when pyrogallol was used as an electron donor. It is a hemoprotein containing one heme molecule per holomer and has an estimated molecular weight of 124,000 to 130,000. The catalase gene was cloned by screening a B. fragilis library for complementation of catalase activity in an Escherichia coli catalase mutant (katE katG) strain. The cloned gene, designated katB, encoded a catalase enzyme with electrophoretic mobility identical to that of the purified protein from the B. fragilis parental strain. The nucleotide sequence of katB revealed a 1,461-bp open reading frame for a protein with 486 amino acids and a predicted molecular weight of 55,905. This result was very close to the 60,000 Da determined by denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified catalase and indicates that the native enzyme is composed of two identical subunits. The N-terminal amino acid sequence of the purified catalase obtained by Edman degradation confirmed that it is a product of katB. The amino acid sequence of KatB showed high similarity to Haemophilus influenzae HktE (71.6% identity, 66% nucleotide identity), as well as to gram-positive bacterial and mammalian catalases. No similarities to bacterial catalase-peroxidase-type enzymes were found. The active-site residues, proximal and distal hemebinding ligands, and NADPH-binding residues of the bovine liver catalase-type enzyme were highly conserved in B. fragilis KatB.

Oxidative stress and living cells

The review deals with the effects of reactive oxygen species, both radical and nonradical (e.g. hydrogen peroxide), on cells and organisms. The chemical and biochemical aspects include description of individual reactive oxygen species, chemical reactions giving rise to them, their interconversions and interactions with metals (Fe2+, Cu2+, Cu+) and other substances (scavengers, antioxidants). The biological aspects concern the specific features and locations of cellular enzyme systems involved in radical production and/or removal. Major harmful effects of the species on the molecular (protein oxidation, lipid peroxidation, damage to DNA) and cellular level (effect on signal transduction, on cell membrane functions and on gene expression) are surveyed. Methods whereby cells and organisms cope with the onslaught of these reactive species are reviewed as well as implications for plant, animal and human health.

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.

Characterization of the catalase of the genus Porphyromonas isolated from cats

Crude cell extracts from members of the genus Porphyromonas isolated from cats were examined in SDS-PAGE and nondenaturing PAGE. In each of the species catalase activity was detected as a single band with characteristics of typical bacterial catalases, i.e. each catalase functioned over a broad pH range (pH 5-10), was not inhibited by chloroform-ethanol, did not possess detectable peroxidase activity, and was irreversibly inhibited by 3-amino-1,2,4 triazole. The catalase enzyme of P. gingivalis VPB 3492, P. circumdentaria NCTC 12469, P. salivosa VPB 3313 and VPB 3444 was inactivated at 71, 66.5, 63.5 and 57 degrees C respectively. The molecular weights of the enzymes from P. gingivalis VPB 3492, P. circumdentaria NCTC 12469, P. salivosa NCTC 11632 and P. salivosa VPB 3444 were 200,000, 216,000, 209,000 and 200,000 Da respectively.

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.

Multiple periplasmic catalases in phytopathogenic strains of Pseudomonas syringae

Phytopathogenic strains of Pseudomonas syringae are exposed to plant-produced, detrimental levels of hydrogen peroxide during invasion and colonization of host plant tissue. When P. syringae strains were investigated for their capacity to resist H2O2, they were found to contain 10- to 100-fold-higher levels of total catalase activity than selected strains belonging to nonpathogenic related taxa (Pseudomonas fluorescens and Pseudomonas putida) or Escherichia coli. Multiple catalase activities were identified in both periplasmic and cytoplasmic fluids of exponential- and stationary-phase P. syringae cells. Two of these activities were unique to the periplasm of P. syringae pv. glycinea. During the stationary growth phase, the specific activity of cytoplasmic catalases increased four- to eightfold. The specific activities of catalases in both fluids from exponential-phase cells increased in response to treatment with 0.25 to 10 mM H2O2 but decreased when higher H2O2 concentrations were used. In stationary-growth phase cultures, the specific activities of cytoplasmic catalases increased remarkably after treatment with 0.25 to 50 mM H2O2. The growth of P. syringae into stationary phase and H2O2 treatment did not induce synthesis of additional catalase isozymes. Only the stationary-phase cultures of all of the P. syringae strains which we tested were capable of surviving high H2O2 stress at concentrations up to 50 mM. Our results are consistent with the involvement of multiple catalase isozymes in the reduction of oxidative stress during plant pathogenesis by these bacteria.

Purification and characterization of a catalase-peroxidase from the fungus Septoria tritici

Three classes of heme proteins, commonly designated hydroperoxidases, are involved in the metabolism of hydrogen peroxide: catalases, peroxidases, and catalase-peroxidases. While catalases and peroxidases are widely spread in animals, plants, and microorganisms, catalase-peroxidases were characterized only in prokaryotes. We report here, for the first time, on a catalase-peroxidase in a eukaryotic organism. The enzyme was purified from the fungal wheat pathogen Septoria tritici, and is one of three different hydroperoxidases synthesized by this organism. The S. tritici catalase-peroxidase, designated StCP, is similar to the enzymes previously isolated from the bacteria Rhodobacter capsulatus, Escherichia coli, and Klebsiella pneumoniae, although it is significantly more sensitive to denaturing conditions. In addition to its catalatic activity StCP catalyzes peroxidatic activity with o-dianisidine, diaminobenzidine, pyrogallol, NADH, and NADPH as electron donors. The enzyme is a tetramer with identical subunits of 61,000 Da molecular weight. StCP shows a typical high-spin ferric heme spectrum with a Soret band at 405 nm and a peak at 632 nm, and binding of cyanide causes a shift of the Soret band to 421 nm, the appearance of a peak at 537 nm, and abolition of the peak at 632 nm. Reduction with dithionite results in a decrease in the intensity of the Soret band and its shift to 436 nm, and in the appearance of a peak at 552 nm. The pH optimum is 6-6.5 and 5.4 for the catalatic and peroxidatic activities, respectively. Fifty percent of the apparent maximal activity is reached at 3.4 mM and 0.26 mM for the catalatic and peroxidatic activities, respectively. The enzyme is inactivated by ethanol/chloroform, and is inhibited by KCN and NaN3, but not by the typical catalase inhibitor 3-amino-1,2,4-triazole.

Isolation and characterization of catalase from Penicillium chrysogenum

Catalase from a crude preparation of Penicillium chrysogenum was isolated in a single chromatographic step by immobilized metal ion affinity chromatography (IMAC) on Cu(II)-Chelating Sepharose Fast Flow. A chromatographically and electrophoretically homogeneous enzyme was obtained in 89% yield. IMAC was found to be superior to ion-exchange, hydrophobic interaction, size-exclusion and concanavalin A affinity chromatography. Analytical and preparative chromatography gave essentially the same chromatograms. Isoelectric point, molecular weight (by ultracentrifugation), amino acid composition, carbohydrate content and subunit organization were determined. The apparent Michaelis-Menten constant, KM, and the azide competitor constant, Ki, were calculated and found to be 59 microM and 6.1 microM, respectively.

Microbial strategies to prevent oxygen-dependent killing by phagocytes

Microorganisms which are taken up by professional phagocytic cells of a host organism (e.g., by macrophages and polymorphonuclear leukocytes) encounter a series of antimicrobial events including confrontation with toxic oxygen species, derived mainly from the superoxide radical produced by phagocytic NADPH oxidase after uptake of the microorganism. Many microbes are susceptible to the oxygen-dependent phagocytic stress and are efficiently killed. The strategies of some microorganisms to bypass an encounter with the phagocytes' reactive oxygen species, and biochemical systems contributing to the microbes' resistance to killing by reactive oxygen species are outlined.

Cloning, characterization, and expression in Escherichia coli of a gene encoding Listeria seeligeri catalase, a bacterial enzyme highly homologous to mammalian catalases

A gene coding for catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase; EC 1.11.1.6) of the gram-positive bacterium Listeria seeligeri was cloned from a plasmid library of EcoRI-digested chromosomal DNA, with Escherichia coli DH5 alpha as a host. The recombinant catalase was expressed in E. coli to an enzymatic activity approximately 50 times that of the combined E. coli catalases. The nucleotide sequence was determined, and the deduced amino acid sequence revealed 43.2% amino acid sequence identity between bovine liver catalase and L. seeligeri catalase. Most of the amino acid residues which are involved in catalytic activity, the formation of the active center accession channel, and heme binding in bovine liver catalase were also present in L. seeligeri catalase at the corresponding positions. The recombinant protein contained 488 amino acid residues and had a calculated molecular weight of 55,869. The predicted isoelectric point was 5.0. Enzymatic and genetic analyses showed that there is most probably a single catalase of this type in L. seeligeri. A perfect 21-bp inverted repeat, which was highly homologous to previously reported binding sequences of the Fur (ferric uptake regulon) protein of E. coli, was detected next to the putative promoter region of the L. seeligeri catalase gene.

Purification and characterization of a catalase-peroxidase and a typical catalase from the bacterium Klebsiella pneumoniae

The bacterium Klebsiella pneumoniae synthesizes three different types of catalase: a catalase-peroxidase, a typical catalase and an atypical catalase, designated KpCP, KpT and KpA, respectively (Goldberg, I. and Hochman, A. (1989) Arch. Biochem. Biophys. 268, 124-128). KpCP, but not the other two enzymes, in addition to the catalatic activity, catalyzes peroxidatic activities with artificial electron donors, as well as with NADH and NADPH. Both KpCP and KpT are tetramers, with heme IX as a prosthetic group, and they show a typical high-spin absorption spectrum which is converted to low-spin when a cyanide complex is formed. The addition of dithionite to KpCP causes a shift in the absorption maxima typical of ferrous heme IX. KpCP has a pH optimum of 6.3 for the catalatic activity and 5.2-5.7 for the peroxidatic activity, and relatively low 'Km' values: 6.5 mM and 0.65 H2O2 for the catalatic and peroxidatic activities, respectively. The activity of the catalase-peroxidase is inhibited by azide and cyanide, but not by 3-amino-1,2,4-triazole. KpT has wide pH optimum: 5-10.5 and a 'Km' of 50 mM H2O2, it is inhibited by incubation with 3-amino-1,2,4-triazole and by the acidic forms of cyanide and azide. A significant distinction between the typical catalase and the catalase-peroxidase is the stability of their proteins: KpT is more stable than KpCP to H2O2, temperature, pH and urea.