A plasmid DNA encoding chicken interleukin-6 and Escherichia coli K88 fimbrial protein FaeG stimulates the production of anti-K88 fimbrial antibodies in chickens

Immunization using a plasmid to deliver an encoded protein for expression in situ as the antigen is a promising technology. A plasmid encoding the enterotoxigenic Escherichia coli K88 fimbrial protein FaeG when injected into chickens stimulates the production of antibodies against the fimbrial protein, similar to what has been observed in mice. The efficacy of a genetic adjuvant on fimbrial antibody production was tested by introducing the gene for chicken interleukin-6 in tandem with the faeG gene. Expression of both the fimbrial FaeG protein and chicken interleukin-6 protein was confirmed in COS-M6 cells. Slightly higher antiFaeG antibody titer in chickens was obtained compared with immunization with the plasmid encoding FaeG alone, especially at 10 (19%, P < 0.05) and 12 (27%, P < 0.05) wk, respectively, after the secondary immunization. Elevated antiFaeG antibody titer induced by chicken interleukin-6 and FaeG proteins expressed jointly persisted longer than when induced by FaeG protein alone. This is the first report of an avian cytokine enhancing an immune response, and confirms that coexpression of the antigen and adjuvant from a plasmid delivered by DNA immunization is an effective protocol.

Diversity of structures and properties among catalases

More than 300 catalase sequences are now available, divided among monofunctional catalases (> 225), bifunctional catalase-peroxidases (> 50) and manganese-containing catalases (> 25). When combined with the recent appearance of crystal structures from at least two representatives from each of these groups (nine from the monofunctional catalases), valuable insights into the catalatic reaction mechanism in its various forms and into catalase evolution have been gained. The structures have revealed an unusually large number of modifications unique to catalases, a result of interacting with reactive oxygen species. Biochemical and physiological characterization of catalases from many different organisms has revealed a surprisingly wide range of catalatic efficiencies, despite similar sequences. Catalase gene expression in micro-organisms generally is controlled either by sensors of reactive oxygen species or by growth phase regulons, although the detailed mechanisms vary considerably.

The role of distal tryptophan in the bifunctional activity of catalase-peroxidases

Catalase-peroxidases are bifunctional peroxidases exhibiting an overwhelming catalase activity and a substantial peroxidase activity. Here we present a kinetic study of the formation and reduction of the key intermediate compound I by probing the role of the conserved tryptophan at the distal haem cavity site. Two wild-type proteins and three mutants of Synechocystis catalase-peroxidase (W122A and W122F) and Escherichia coli catalase-peroxidase (W105F) have been investigated by steady-state and stopped-flow spectroscopy. W122F and W122A completely lost their catalase activity whereas in W105F the catalase activity was reduced by a factor of about 5000. However, the mutations did not influence both formation of compound I and its reduction by peroxidase substrates. It was demonstrated unequivocally that the rate of compound I reduction by pyrogallol or o-dianisidine sometimes even exceeded that of the wild-type enzyme. This study demonstrates that the indole ring of distal Trp in catalase-peroxidases is essential for the two-electron reduction of compound I by hydrogen peroxide but not for compound I formation or for peroxidase reactivity (i.e. the one-electron reduction of compound I).

Substrate flow in catalases deduced from the crystal structures of active site variants of HPII from Escherichia coli

The active site of heme catalases is buried deep inside a structurally highly conserved homotetramer. Channels leading to the active site have been identified as potential routes for substrate flow and product release, although evidence in support of this model is limited. To investigate further the role of protein structure and molecular channels in catalysis, the crystal structures of four active site variants of catalase HPII from Escherichia coli (His128Ala, His128Asn, Asn201Ala, and Asn201His) have been determined at approximately 2.0-A resolution. The solvent organization shows major rearrangements with respect to native HPII, not only in the vicinity of the replaced residues but also in the main molecular channel leading to the heme distal pocket. In the two inactive His128 variants, continuous chains of hydrogen bonded water molecules extend from the molecular surface to the heme distal pocket filling the main channel. The differences in continuity of solvent molecules between the native and variant structures illustrate how sensitive the solvent matrix is to subtle changes in structure. It is hypothesized that the slightly larger H(2)O(2) passing through the channel of the native enzyme will promote the formation of a continuous chain of solvent and peroxide. The structure of the His128Asn variant complexed with hydrogen peroxide has also been determined at 2.3-A resolution, revealing the existence of hydrogen peroxide binding sites both in the heme distal pocket and in the main channel. Unexpectedly, the largest changes in protein structure resulting from peroxide binding are clustered on the heme proximal side and mainly involve residues in only two subunits, leading to a departure from the 222-point group symmetry of the native enzyme. An active role for channels in the selective flow of substrates through the catalase molecule is proposed as an integral feature of the catalytic mechanism. The Asn201His variant of HPII was found to contain unoxidized heme b in combination with the proximal side His-Tyr bond suggesting that the mechanistic pathways of the two reactions can be uncoupled.

Crystallization and preliminary X-ray analysis of clade I catalases from Pseudomonas syringae and Listeria seeligeri

Haem-containing catalases are homotetrameric molecules that degrade hydrogen peroxide. Phylogenetically, the haem-containing catalases can be grouped into three main lines or clades. The crystal structures of seven catalases have been determined, all from clades II and III. In order to obtain a structure of an enzyme from clade I, which includes all plant, algae and some bacterial enzymes, two bacterial catalases, CatF from Pseudomonas syringae and Kat from Listeria seeligeri, have been crystallized by the hanging-drop vapour-diffusion technique, using PEG and ammonium sulfate as precipitants, respectively. Crystals of P. syringae CatF, with a plate-like morphology, belong to the monoclinic space group P2(1), with unit-cell parameters a = 60.6, b = 153.9, c = 109.2 A, beta = 102.8 degrees. From these crystals a diffraction data set to 1.8 A resolution with 98% completeness was collected using synchrotron radiation. Crystals of L. seeligeri Kat, with a well developed bipyramidal morphology, belong to space group I222 (or I2(1)2(1)2(1)), with unit-cell parameters a = 74.4, b = 121.3, c = 368.5 A. These crystals diffracted beyond 2.2 A resolution when using synchrotron radiation, but presented anisotropic diffraction, with the weakest direction perpendicular to the long c axis.

Active site structure of the catalase-peroxidases from Mycobacterium tuberculosis and Escherichia coli by extended X-ray absorption fine structure analysis

The catalase-peroxidase encoded by katG of Mycobacterium tuberculosis is a more effective activator of the antibiotic isoniazid than is the equivalent enzyme from Escherichia coli. The environment of the heme iron was investigated using X-ray absorption spectroscopy to determine if differences in this region were associated with the differences in reactivity. The variation in the distal side Fe-ligand distances between the two enzymes was the same within experimental error indicating that it was not the heme iron environment that produced the differences in reactivity. Analysis of variants of the E. coli catalase-peroxidase containing changes in active site residues Arg102 and His106 revealed small differences in Fe-water ligand distance including a shorter distance for the His106Tyr variant. The Arg102Leu variant was 5-coordinate, but His106Cys and Arg102Cys variants showed no changes within experimental error. These results are compared with those reported for other peroxidases.

Modulation of the activities of catalase-peroxidase HPI of Escherichia coli by site-directed mutagenesis

Catalase-peroxidases have a predominant catalatic activity but differ from monofunctional catalases in exhibiting a substantial peroxidatic reaction which has been implicated in the activation of the antitubercular drug isoniazid in Mycobacterium tuberculosis. Hydroperoxidase I of Escherichia coli encoded by katG is a catalase-peroxidase, and residues in its putative active site have been the target of a site directed-mutagenesis study. Variants of residues R102 and H106, on the distal side of the heme, and H267, the proximal side ligand, were constructed, all of which substantially reduced the catalatic activity and, to a lesser extent, the peroxidatic activity. In addition, the heme content of the variants was reduced relative to the wild-type enzyme. The relative ease of heme loss from HPI and a mixture of tetrameric enzymes with 2, 3, and 4 hemes was revealed by mass spectrometry analysis. Conversion of W105 to either an aromatic (F) or aliphatic (I) residue caused a 4-5-fold increase in peroxidatic activity, coupled with a >99% inhibition of catalatic activity. The peroxidatic-to-catalatic ratio of the W105F variant was increased 2800-fold such that compound I could be identified by both electronic and EPR spectroscopy as being similar to the porphyrin cation radical formed in other catalases and peroxidases. Compound I, when generated by a single addition of H(2)O(2), decayed back to the native or resting state within 1 min. When H(2)O(2) was generated enzymatically in situ at low levels, active compound I was evident for up to 2 h. However, such prolonged treatment resulted in conversion of compound I to a reversibly inactivated and, eventually, to an irreversibly inactivated species, both of which were spectrally similar to compound I.

Mutants that alter the covalent structure of catalase hydroperoxidase II from Escherichia coli

The three-dimensional structures of two HPII variants, V169C and H392Q, have been determined at resolutions of 1.8 and 2.1 A, respectively. The V169C variant contains a new type of covalent bond between the sulfur atom of Cys(169) and a carbon atom on the imidazole ring of the essential His(128). This variant enzyme has only residual catalytic activity and contains heme b. The chain of water molecules visible in the main channel may reflect the organization of the hydrogen peroxide substrates in the active enzyme. Two alternative mechanisms, involving either compound I or free radical intermediates, are presented to explain the formation of the Cys-His covalent bond. The H392Q and H392E variants exhibit 75 and 25% of native catalytic activity, respectively. The Gln(392) variant contains only heme b, whereas the Glu(392) variant contains a mixture of heme b and cis and trans isomers of heme d, suggesting of a role for this residue in heme conversion. Replacement of either Gln(419) and Ser(414), both of which interact with the heme, affected the cis:trans ratio of spirolactone heme d. Implications for the heme oxidation mechanism and the His-Tyr bond formation in HPII are considered.

Catalase HPII from Escherichia coli exhibits enhanced resistance to denaturation

Catalase HPII from Escherichia coli is a homotetramer of 753 residue subunits. The multimer displays a number of unusual structural features, including interwoven subunits and a covalent bond between Tyr415 and His392, that would contribute to its rigidity and stability. As the temperature of a solution of HPII in 50 mM potassium phosphate buffer (pH 7) is raised from 50 to 92 degrees C, the enzyme begins to lose activity at 78 degrees C and 50% inactivation has occurred at 83 degrees C. The inactivation is accompanied by absorbance changes at 280 and 407 nm and by changes in the CD spectrum consistent with small changes in secondary structure. The subunits in the dimer structure remain associated at 95 degrees C and show a significant level of dissociation only at 100 degrees C. The exceptional stability of the dimer association is consistent with the interwoven nature of the subunits and provides an explanation for the resistance to inactivation of the enzyme. For comparison, catalase-peroxidase HPI of E. coli and bovine liver catalase are 50% inactivated at 53 and 56 degrees C, respectively. In 5.6 M urea, HPII exhibits a coincidence of inactivation, CD spectral change, and dissociation of the dimer structure with a midpoint of 65 degrees C. The inactive mutant variants of HPII which fold poorly during synthesis and which lack the Tyr-His covalent bond undergo spectral changes in the 78 to 84 degrees C range, revealing that the extra covalent linkage is not important in the enhanced resistance to denaturation and that problems in the folding pathway do not affect the ultimate stability of the folded structure.

Role of the lateral channel in catalase HPII of Escherichia coli

The heme-containing catalase HPII of Escherichia coli consists of a homotetramer in which each subunit contains a core region with the highly conserved catalase tertiary structure, to which are appended N- and C-terminal extensions making it the largest known catalase. HPII does not bind NADPH, a cofactor often found in catalases. In HPII, residues 585-590 of the C-terminal extension protrude into the pocket corresponding to the NADPH binding site in the bovine liver catalase. Despite this difference, residues that define the NADPH pocket in the bovine enzyme appear to be well preserved in HPII. Only two residues that interact ionically with NADPH in the bovine enzyme (Asp212 and His304) differ in HPII (Glu270 and Glu362), but their mutation to the bovine sequence did not promote nucleotide binding. The active-site heme groups are deeply buried inside the molecular structure requiring the movement of substrate and products through long channels. One potential channel is about 30 A in length, approaches the heme active site laterally, and is structurally related to the branched channel associated with the NADPH binding pocket in catalases that bind the dinucleotide. In HPII, the upper branch of this channel is interrupted by the presence of Arg260 ionically bound to Glu270. When Arg260 is replaced by alanine, there is a threefold increase in the catalytic activity of the enzyme. Inhibitors of HPII, including azide, cyanide, various sulfhydryl reagents, and alkylhydroxylamine derivatives, are effective at lower concentration on the Ala260 mutant enzyme compared to the wild-type enzyme. The crystal structure of the Ala260 mutant variant of HPII, determined at 2.3 A resolution, revealed a number of local structural changes resulting in the opening of a second branch in the lateral channel, which appears to be used by inhibitors for access to the active site, either as an inlet channel for substrate or an exhaust channel for reaction products.

Structure of catalase HPII from Escherichia coli at 1.9 A resolution

Catalase HPII from Escherichia coli, a homotetramer of subunits with 753 residues, is the largest known catalase. The structure of native HPII has been refined at 1.9 A resolution using X-ray synchrotron data collected from crystals flash-cooled with liquid nitrogen. The crystallographic agreement factors R and R(free) are respectively 16.6% and 21.0%. The asymmetric unit of the crystal contains a whole molecule that shows accurate 222-point group symmetry. The structure of the central part of the HPII subunit gives a root mean square deviation of 1.5 A for 477 equivalencies with beef liver catalase. Most of the additional 276 residues of HPII are located in either an extended N-terminal arm or in a C-terminal domain organized with a flavodoxin-like topology. A small number of mostly hydrophilic interactions stabilize the relative orientation between the C-terminal domain and the core of the enzyme. The heme component of HPII is a cis-hydroxychlorin gamma-spirolactone in an orientation that is flipped 180 degrees with respect to the orientation of the heme found in beef liver catalase. The proximal ligand of the heme is Tyr415 which is joined by a covalent bond between its Cbeta atom and the Ndelta atom of His392. Over 2,700 well-defined solvent molecules have been identified filling a complex network of cavities and channels formed inside the molecule. Two channels lead close to the distal side heme pocket of each subunit suggesting separate inlet and exhaust functions. The longest channel, that begins in an adjacent subunit, is over 50 A in length, and the second channel is about 30 A in length. A third channel reaching the heme proximal side may provide access for the substrate needed to catalyze the heme modification and His-Tyr bond formation. HPII does not bind NADPH and the equivalent region to the NADPH binding pocket of bovine catalase, partially occluded in HPII by residues 585-590, corresponds to the entrance to the second channel. The heme distal pocket contains two solvent molecules, and the one closer to the iron atom appears to exhibit high mobility or low occupancy compatible with weak coordination.

Intracellular location of catalase-peroxidase hydroperoxidase I of Escherichia coli

The catalase-peroxidase hydroperoxidase I of Escherichia coli has been confirmed to be located in the cytoplasm using two independent methods. Catalase activity was found predominantly (> 95%) in the cytoplasmic fraction following spheroplast formation. The cytoplasmic enzyme glucose-6-phosphate dehydrogenase and the periplasmic enzyme alkaline phosphatase were used as controls. The second method of immunogold staining for the enzyme in situ revealed an even distribution of the enzyme across the cell.

Regulation in the rpoS regulon of Escherichia coli

In Escherichia coli, the transcription factor sigma s, encoded by rpoS, controls the expression of a large number of genes involved in cellular responses to a diverse number of stresses, including starvation, osmotic stress, acid shock, cold shock, heat shock, oxidative DNA damage, and transition to stationary phase. A list of over 50 genes under the control of rpoS has been compiled. The transcription factor sigma s acts predominantly as a positive effector, but it does have a negative effect on some genes. The synthesis and accumulation of sigma s are controlled by mechanisms affecting transcription, translation, proteolysis, and the formation of the holoenzyme complex. Transcriptional control of rpoS involves guanosine 3',5'-bispyrophosphate (ppGpp) and polyphosphate as positive regulators and the cAMP receptor protein-cAMP complex (CRP-cAMP) as a negative regulator. Translation of rpoS mRNA is controlled by a cascade of interacting factors, including Hfq, H-NS, dsrA RNA, LeuO, and oxyS RNA that seem to modulate the stability of a region of secondary structure in the ribosome-binding region of the gene's mRNA. The transcription factor sigma s is sensitive to proteolysis by ClpPX in a reaction that is promoted by RssB and inhibited by the chaperone DnaK. Despite the demonstrated involvement of so many factors, arguments have been presented suggesting that sensitivity to proteolysis may be the single most important modulator of sigma s levels. The activity of sigma s may also be modulated by trehalose and glutamate, which activate holoenzyme formation and promote holoenzyme binding to certain promoters.

Truncation and heme pocket mutations reduce production of functional catalase HPII in Escherichia coli

The subunit of catalase HPII from Escherichia coli is 753 residues in length and contains a core of approximately 500 residues, with high structural similarity to all other heme catalases. To this core are added extensions of approximately 80 and 180 residues at the N- and C-termini, respectively. The tetrameric structure is made up of a pair of interwoven dimers in which 90 N-terminal residues of each subunit are inserted through a loop formed by the hinge region linking the beta-barrel and alpha-helical domains of the adjacent subunit. A high concentration of proline residues is found in the vicinity of the overlap regions. To study the influence of the extended regions on folding and subunit association of HPII, a diversity of modifications have been introduced. Removal of the complete C-terminal domain or the N-terminal extension, either separately or together, effectively creating a small subunit catalase, resulted in no enzyme accumulation. Systematic truncations showed that only nine C-terminal residues (Ile745 to Ala753) could be removed without significantly affecting the accumulation of active enzyme. Removal or even conservative replacements of the side chain of Arg744 significantly reduced the accumulation of active enzyme despite this residue interacting only with the C-terminal domain. Removal of as few as 18 residues from the N-terminus also reduced accumulation of active enzyme. Changes to other residues in the protein, including residues in the heme binding pocket, also reduced the accumulation of active protein without substantially affecting the enzyme specific activity. Implications of these data for the interdependence of subunit folding and subunit-subunit interactions are discussed.

Phylogenetic relationships among prokaryotic and eukaryotic catalases

Seventy-four catalase protein sequences, including 29 bacterial, 8 fungal, 7 animal, and 30 plant sequences, were compiled, and 70 were used for phylogenetic reconstruction. The core of the resulting tree revealed unique, separate groups of plant and animal catalases, two groups of fungal catalases, and three groups of bacterial catalases. The only overlap of kingdoms occurred within one branch and involved fungal and bacterial large-subunit enzymes. The other fungal branch was closely linked to the group of animal enzymes. Group I bacterial catalases were more closely related to the plant enzymes and contained such diverse taxa as the Gram-positive Listeria seeligeri, Deinocococcus radiodurans, and gamma-proteobacteria. Group III bacterial sequences were more closely related to fungal and animal sequences and included enzymes from a broad range of bacteria including high- and low-GC Gram positives, proteobacteria, and a bacteroides species. Group II was composed of large-subunit catalases from diverse sources including Gram positives (low-GC Bacilli and high-GC Mycobacteria), proteobacteria, and species of the filamentous fungus Aspergillus. These data can be interpreted in terms of two gene duplication events that produced a minimum of three catalase gene family members that subsequently evolved in response to environmental demands. Horizontal gene transfer may have been responsible for the group II mixture of bacterial and fungal large-subunit catalases.

Identification and analysis of the rpoS-dependent promoter of katE, encoding catalase HPII in Escherichia coli

The rpoS gene of Escherichia coli encodes an alternative sigma factor of RNA polymerase sigma38 (or sigma(s)) that is required for transcription of katE encoding catalase HPII. The transcription start site of the single katE transcript identified by ribonuclease protection has been determined by primer extension analysis to be either 53 or 54 bp (depending on the strain used) upstream of the open reading frame. A series of promoter fragments were constructed and fused to lacZ to confirm the start site location. A - 10 sequence similar to that found in other sigma70- and sigma38-dependent E. coli promoters was identified 8 or 7 bp upstream of the start site but a sigma70-dependent -35 sequence was not evident.

Identification of a novel bond between a histidine and the essential tyrosine in catalase HPII of Escherichia coli

A bond between the N delta of the imidazole ring of His 392 and the C beta of the essential Tyr 415 has been found in the refined crystal structure at 1.9 A resolution of catalase HPII of Escherichia coli. This novel type of covalent linkage is clearly defined in the electron density map of HPII and is confirmed by matrix-assisted laser desorption/ionization mass spectrometry analysis of tryptic digest mixtures. The geometry of the bond is compatible with both the sp3 hybridization of the C beta atom and the planarity of the imidazole ring. Two mutated variants of HPII active site residues, H128N and N201H, do not contain the His 392-Tyr 415 bond, and their crystal structures show that the imidazole ring of His 392 was rotated, in both cases, by 80 degrees relative to its position in HPII. These mutant forms of HPII are catalytically inactive and do not convert heme b to heme d, suggesting a relationship between the self-catalyzed heme conversion reaction and the formation of the His-Tyr linkage. A model coupling the two processes and involving the reaction of one molecule of H2O2 on the proximal side of the heme with compound 1 is proposed.

Reaction of E. coli catalase HPII with cyanide as ligand and as inhibitor

Cyanide forms an inhibitory complex with the haem d-containing E. coli catalase HPII, spectrally similar to the cyanide complex of beef liver enzyme but with absorption bands shifted 90 nm towards the red end of the spectrum. Both the Kd and Ki values are approximately 7 microM in the wild-type enzyme. The cyanide reaction is slow, with a bimolecular 'on' constant approx. 2000 x smaller than that of eukaryotic enzyme, and an 'off' constant diminished by a similar amount. Catalases with a mutated distal histidine (H128) fail to bind cyanide at cyanide concentrations below 50 mM. Catalases with a mutated distal asparagine (N201) show only small changes in cyanide affinity from the wild type. The major fraction of HPII N201A has a Kd approximately 40 microM, and a minor fraction has a lower cyanide affinity; the major fraction of HPII N201Q has a Kd approximately 15 microM. The Kd and Ki for HPII N201D is approximately 8 microM, essentially identical with that of the wild type but N201D appears to bind cyanide somewhat more rapidly than does wild-type enzyme. The HPII mutant N201H can be obtained in both haem d and protohaem forms; it exhibits two types of cyanide binding behaviour. In its protohaem form it binds cyanide poorly (Kd > or = 0.25 mM). After peroxide treatment converts t into haem d or a closely related species it binds cyanide with a much higher affinity (Kd approximately 15 microM). Cyanide binding to HPII requires a distal histidine to provide hydrogen-bonding stability, but not a distal asparagine. Rates of cyanide binding and release are controlled by haem group accessibility through the channel leading to the outside. In HPII N201H channel opening may depend upon oxidation of the haem from the starting protohaem to the final haem d form.

Structure of the heme d of Penicillium vitale and Escherichia coli catalases

A heme d prosthetic group with the configuration of a cis-hydroxychlorin gamma-spirolactone has been found in the crystal structures of Penicillium vitale catalase and Escherichia coli catalase hydroperoxidase II (HPII). The absolute stereochemistry of the two heme d chiral carbon atoms has been shown to be identical. For both catalases the heme d is rotated 180 degrees about the axis defined by the alpha-gamma-meso carbon atoms, with respect to the orientation found for heme b in beef liver catalase. Only six residues in the heme pocket, preserved in P. vitale and HPII, differ from those found in the bovine catalase. In the crystal structure of the inactive N201H variant of HPII catalase the prosthetic group remains as heme b, although its orientation is the same as in the wild type enzyme. These structural results confirm the observation that heme d is formed from protoheme in the interior of the catalase molecule through a self-catalyzed reaction.

Comparison of isoniazid oxidation catalyzed by bacterial catalase-peroxidases and horseradish peroxidase

The physical properties and activities of the purified catalase-peroxidase hydroperoxidase I (HPI) of Escherichia coli (EcHPI) and HPI with a carboxyl-terminal extension of Mycobacterium tuberculosis (MtHPI-e) are compared to those of commercial preparations of horseradish peroxidase (HRP). The catalase-peroxidase proteins had similar absorption spectra and differed primarily in that MtHPI-e has a higher peroxidatic to catalatic activity ratio than EcHPI. Trypsin cleavage of MtHPI-e resulted in the formation of an active catalase-peroxidase lacking the carboxyl-terminal extension. The three enzymes, HRP, MtHPI-e, and EcHPI, mediated the isoniazid- and H2O2-dependent production of radical species, as detected by nitroblue tetrazolium reduction. A constant flux of H2O2, generated in situ from glucose oxidase and glucose was used. MtHPI-e was more effective at isoniazid-dependent radical production than EcHPI and HRP. Similar qualitative results were obtained by staining nondenaturing polyacrylamide gels for activity with nitroblue tetrazolium in the presence of isoniazid and H2O2. The absorbance spectrum of HRP exhibited changes during incubation with isoniazid and H2O2 consistent with the formation of several typical reaction intermediates, whereas the catalase-peroxidases exhibited no distinct spectral changes. The results suggest that the sensitivity of M. tuberculosis to isoniazid may be the result of isoniazid-dependent radical formation by the catalase-peroxidase in the absence of other catalase activities to remove substrate H2O2.

Template secondary structure can increase the error frequency of the DNA polymerase from Thermus aquaticus

Amplification of portions of the intergenic spacer between the katE gene and cryptic cel operon of Escherichia coli was accomplished by the polymerase chain reaction using the DNA polymerase from Thermus aquaticus. Nine different segments were amplified and cloned without error, but one 83-bp fragment was amplified with a high error rate such that 32 of 34 selected clones had three or more nucleotide changes from the expected sequence. The changes were all located in two 9-bp segments immediately adjacent to the 3'-ends of the two primers. Moving the end points of the primers to increase the spacing between them resulted in the isolation of significantly fewer error-containing products. It is proposed that stem-loop structures in the template immediately downstream from the primers interfere with an early stage of elongation and cause misincorporation. This is supported by the observation that destabilisation of one of the stem-loop structures reduced the frequency of errors.

Crystal structure of catalase HPII from Escherichia coli

BACKGROUND

Catalase is a ubiquitous enzyme present in both the prokaryotic and eukaryotic cells of aerobic organisms. It serves, in part, to protect the cell from the toxic effects of small peroxides. Escherichia coli produces two catalases, HPI and HPII, that are quite distinct from other catalases in physical structure and catalytic properties. HPII, studied in this work, is encoded by the katE gene, and has been characterized as an oligomeric, monofunctional catalase containing one cis-heme d prosthetic group per subunit of 753 residues.

RESULTS

The crystal structure of catalase HPII from E. coli has been determined to 2.8 A resolution. The asymmetric unit of the crystal contains a whole molecule, which is a tetramer with accurate 222 point group symmetry. In the model built, that includes residues 27-753 and one heme group per monomer, strict non-crystallographic symmetry has been maintained. The crystallographic agreement R-factor is 20.1% for 58,477 reflections in the resolution shell 8.0-2.8 A.

CONCLUSIONS

Despite differences in size and chemical properties, which were suggestive of a unique catalase, the deduced structure of HPII is related to the structure of catalase from Penicillium vitale, whose sequence is not yet known. In particular, both molecules have an additional C-terminal domain that is absent in the bovine catalase. This extra domain contains a Rossmann fold but no bound nucleotides have been detected, and its physiological role is unknown. In HPII, the heme group is modified to a heme d and inverted with respect to the orientation determined in all previously reported heme catalases. HPII is the largest catalase for which the structure has been determined to almost atomic resolution.

The cysteines of catalase HPII of Escherichia coli, including Cys438 which is blocked, do not have a catalytic role

Site-directed mutagenesis of the katE gene of Escherichia coli was used to change, individually and in combination, Cys438 and Cys669 to serine in catalase HPII. The Cys438-->Ser mutation caused a 30% reduction in the specific activity of the enzyme, whereas the Cys669-->Ser mutation did not affect enzyme activity. The titration of free sulfhydryl groups in HPII revealed that Cys669 was reactive whereas Cys438 was unreactive. Properties of the modification on Cys438 included alkali lability, insensitivity to methylamine, hydroxylamine or reducing agents, and a mass determined by mass spectrometry to be approximately 43 +/- 2 Da. A hemithioacetal structure is consistent with these properties. Although free sulfhydryl groups do not play a significant role in the stability or catalytic mechanism of HPII, the sulfhydryl agent 2-mercaptoethanol caused a 50% inactivation of HPII along with an irreversible change in the absorption spectrum of the protein. Other sulfhydryl agents, including dithiothreitol, cysteine and glutathione, and the organic peroxide, t-butylhydroperoxide, which cannot directly access the active site, do not affect HPII activity, but they do cause a small reversible change in the absorption spectrum, possibly by a mechanism involving superoxide.

DNA repair is more important than catalase for Salmonella virulence in mice

Pathogenic microorganisms possess antioxidant defense mechanisms for protection from reactive oxygen metabolites such as hydrogen peroxide (H2O2), which are generated during the respiratory burst of phagocytic cells. These defense mechanisms include enzymes such as catalase, which detoxify reactive oxygen species, and DNA repair systems which repair damage resulting from oxidative stress. To determine the relative importance of these two potentially protective defense mechanisms against oxidative stress encountered by Salmonella during infection of the host, a Salmonella typhimurium double mutant unable to produce either the HPI or HPII catalase was constructed, and compared with an isogenic recA mutant deficient in DNA repair. The recA mutant was hypersusceptible to H2O2 at low cell densities in vitro, while the catalase mutant was more susceptible to high H2O2 concentrations at high cell densities. The catalase mutant was found to be resistant to macrophages and retained full murine virulence, in contrast to the recA mutant which previously was shown to be macrophage-sensitive and attenuated in mice. These observations suggest that Salmonella is subjected to low concentrations of H2O2 while at relatively low cell density during infection, conditions requiring an intact DNA repair system but not functional catalase activity.

The role of the sigma factor sigma S (KatF) in bacterial global regulation

The protein encoded by katF (also known as nur, appR, csi-2, abrD, and rpoS in various alleles) has been biochemically confirmed to be an alternate sigma transcription factor and renamed sigma S. Its synthesis is controlled transcriptionally and posttranscriptionally by as yet undefined mechanisms that are active well into stationary phase. sigma S controls a regulon of 30 or more genes expressed in response to starvation and during the transition to stationary phase. Proteins in the regulon, many of which have not been characterized, enhance long-term survival in nutrient-deficient medium and have a diverse group of functions including protection against DNA damage, the determination of morphological changes, the mediation of virulence, osmoprotection, and thermotolerance. Differential expression of subfamilies of genes within the regulon is effected by supplementary regulatory factors, working both individually and in combination to modulate activity of different sigma S-dependent promoters.

NADPH binding and control of catalase compound II formation: comparison of bovine, yeast, and Escherichia coli enzymes

1. NADPH binds to bovine catalase and to yeast catalases A and T, but not to Escherichia coli catalase HPII. The association was demonstrated using chromatography and fluorimetry. Bound NADPH fluoresces in a similar way to NADPH in solution. 2. Bound NADPH protects bovine and yeast catalases against forming inactive peroxide compound II either via endogenous reductant action or by ferrocyanide reduction during catalytic activity in the presence of slowly generated peroxide. 3. Bound NADPH reduces neither compound I nor compound II of catalase. It apparently reacts with an intermediate formed during the decay of compound I to compound II; this postulated intermediate is an immediate precursor of stable compound II either when the latter is formed by endogenous reductants or when ferrocyanide is used. It represents therefore a new type of hydrogen donor that is not included in the original classification of Keilin and Nicholls [Keilin, D. and Nicholls, P. (1958) Biochim. Biophys. Acta 29, 302-307] 4. A model for NADPH action is presented in which concerted reduction of the ferryl iron and of a neighbouring protein free radical is responsible for the observed NADPH effects. The roles of migrant radical species in mammalian and yeast catalases are compared with similar events in metmyoglobin and cytochrome c peroxidase reactions with peroxides.

Structure and function in rhodopsin: replacement by alanine of cysteine residues 110 and 187, components of a conserved disulfide bond in rhodopsin, affects the light-activated metarhodopsin II state

A disulfide bond that is evidently conserved in the guanine nucleotide-binding protein-coupled receptors is present in rhodopsin between Cys-110 and Cys-187. We have replaced these two cysteine residues by alanine residues and now report on the properties of the resulting rhodopsin mutants. The mutant protein C110A/C187A expressed in COS cells resembles wild-type rhodopsin in the ground state. It folds correctly to bind 11-cis-retinal and form the characteristic rhodopsin chromophore. It is inert to hydroxylamine in the dark, and its stability to dark thermal decay is reduced, relative to that of the wild type, by a delta delta G not equal to of only -2.9 kcal/mol. Further, the affinities of the mutant and wild-type rhodopsins to the antirhodopsin antibody rho4D2 are similar, both in the dark and in light. However, the metarhodopsin II (MII) and MIII photointermediates of the mutant are less stable than those formed by the wild-type rhodopsin. Although the initial rates of transducin activation are the same for both mutant and wild-type MII intermediates at 4 degrees C, at 15 degrees C the MII photointermediate in the mutant decays more than 20 times faster than in wild type. We conclude that the disulfide bond between Cys-110 and Cys-187 is a key component in determining the stability of the MII structure and its coupling to transducin activation.

The delta (argF-lacZ)205(U169) deletion greatly enhances resistance to hydrogen peroxide in stationary-phase Escherichia coli

In this study, we demonstrate that a strain bearing the delta (argF-lacZ)205(U169) deletion exhibits a high level of resistance to hydrogen peroxide compared with its undeleted parent. Our initial investigation of the mechanism behind the observed differences in peroxide resistance when parent and mutant strains are compared indicates that the parent strain carries a region near argF that is responsible for the H2O2-sensitive phenotype, which we have named katC. The H2O2 resistance phenotype of the delta katC [delta (argF-lacZ)205(U169)] mutant strain can be duplicated by Tn9 insertion in a specific locus (katC5::Tn9) which maps near argF. The increased H2O2 resistance of the delta katC and katC5::Tn9 mutant strains can be seen only when cells are grown to stationary phase; exponential-phase cells are unaffected by the presence or absence of katC. This H2O2 resistance mechanism requires functional katE and katF genes, which suggests that the mechanism of H2O2 resistance may involve the activity of the stationary-phase-specific catalase HPII. Cloning, DNA sequencing, and analysis of the katC5::Tn9 insertion allele in comparison with its parent allele implicate two insertion elements, IS1B and IS30B, and suggest that their presence sensitizes parent cells to H2O2.

Catalase HPII of Escherichia coli catalyzes the conversion of protoheme to cis-heme d

Catalase HPII from aerobically grown Escherichia coli normally contains heme d but cultures grown with poor or no aeration produce HPII containing a mixture of heme d and protoheme IX. The protoheme component of HPII from anaerobically grown cells is converted into heme d during treatment of the purified enzyme with hydrogen peroxide. It is concluded that heme d found in catalase HPII is formed by the cis-hydroxylation of protoheme in a reaction catalyzed by catalase HPII using hydrogen peroxide as a substrate. The distal His128 residue of HPII is absolutely required for the protoheme to heme d conversion. Two mutant enzymes, Ala128 and Asn128, are catalytically inactive and contain only protoheme, which is unaffected by hydrogen peroxide treatment. The Asn201 residue is not an absolute requirement for heme conversion. The mutant enzyme Ala201 contains predominantly heme d and is partially active. However, insertion of a histidyl residue to give the His201 enzyme interferes with the heme conversion reaction. This mutant form is isolated as a protoheme enzyme with limited activity, and a reversible conversion to a heme d-like species occurs in vitro in the presence of continuously generated hydrogen peroxide.

Molecular evolutionary analysis based on the amino acid sequence of catalase

Heme-containing catalase sequences from 20 different organisms representing prokaryotes, fungi, animals, and plants have been compiled for phylogenetic reconstruction. Phylogenies based on distance and parsimony analysis show that fungal and animal catalases can be derived from one ancestor, whereas bacterial catalases fail to form a monophyletic group. Plant catalases appear to form a second class of catalases that arose independently from a possible prokaryotic ancestor.

KatF (sigma S) synthesis in Escherichia coli is subject to posttranscriptional regulation

A transcriptional fusion of katF to the lacZ gene was expressed at increasingly higher levels throughout the exponential phase, but a translational fusion was expressed at low levels during exponential-phase growth and was induced 160-fold during the transition to stationary phase, implicating a posttranscriptional mechanism in the regulation of KatF synthesis. Mutational analyses suggested that the initiation codon of katF is the second ATG in the previously identified open reading frame.

The alternative sigma factor katF (rpoS) regulates Salmonella virulence

Nutrient limitation is a critical signal in Salmonella virulence gene regulation. The katF (rpoS) gene mediates the expression of the Salmonella spv plasmid virulence genes during bacterial starvation. A katF Salmonella mutant has increased susceptibility to nutrient deprivation, oxidative stress, acid stress, and DNA damage, conditions which are relevant to the intraphagosomal environment of host macrophages. Moreover, the katF mutant has significantly reduced virulence in mice. katF encodes an alternative sigma factor of RNA polymerase which coordinately regulates Salmonella virulence.

Identification of heme macrocycle type by near-infrared magnetic circular dichroism spectroscopy at cryogenic temperatures

The electron paramagnetic resonance (EPR) and near-infrared magnetic circular dichroism (MCD) spectra of the azide and cyanide adducts of nitrimyoglobin and hydroperoxidase II from Escherichia coli have been measured at cryogenic temperatures. For the first time, ligand-to-metal charge-transfer transitions in the near-infrared have been observed for an Fe(III)-chlorine system. It is shown that near-ultraviolet-to-visible region electronic spectra of 'green' hemes such as these are an unreliable indicator of macrocycle type. However, the combined application of EPR and near-infrared MCD spectroscopies clearly distinguishes between the porphyrin-containing nitrimyoglobin and the chlorine-containing hydroperoxidase II.

The active site structure of E. coli HPII catalase. Evidence favoring coordination of a tyrosinate proximal ligand to the chlorin iron

E. coli produces 2 catalases known as HPI and HPII. While the heme prosthetic group of the HPII catalase has been established to be a dihydroporphyrin or chlorin, the identity of the proximal ligand to the iron has not been addressed. The magnetic circular dichroism (MCD) spectrum of native ferric HPII catalase is very similar to those of a 5-coordinate phenolate-ligated ferric chlorin complex, a model for tyrosinate proximal ligation, as well as of chlorin-reconstituted ferric horseradish peroxidase, a model for 5-coordinate histidine ligation. However, further MCD comparisons of chlorin-reconstituted myoglobin with parallel ligand-bound adducts of the catalase clearly rule out histidine ligation in the latter, leaving tyrosinate as the best candidate for the proximal ligand.

Regulation of transcription of katE and katF in Escherichia coli

Fusion plasmids with lacZ under the control of the katE (encoding catalase or hydroperoxidase HPII) and katF (encoding a sigma factor-like protein required for katE expression) promoters were constructed. Expression from both katE and katF promoters was low in rich medium but elevated in poor medium during log-phase growth. Furthermore, the slowdown in growth as cells entered the stationary phase in rich medium, a result of carbon source depletion, was associated with an increase in katE and katF expression. A simple reduction in the carbon source level as the cells entered the stationary phase was not responsible for the increase in expression, because transferring the culture to a medium with no glucose did not induce expression from either promoter. Spent rich medium from stationary-phase cells was capable of inducing expression, as were simple aromatic acids such as benzoate, o-hydroxybenzoate, and p-aminobenzoate added to new medium. Anaerobiosis did not cause an increase in expression, nor did it significantly change the pattern of expression. Regardless of the medium, katF expression was always turned on before or coincidently with katE expression; in the presence of benzoate katF was fully induced, whereas katE was only partially induced, suggesting that a factor in addition to KatF protein was involved in katE expression. During prolonged aerobic incubation, cells lacking katF died off more rapidly than did cells lacking either katE or katG.

Nucleotide sequence of katG of Salmonella typhimurium LT2 and characterization of its product, hydroperoxidase I

The nucleotide sequence of katG from Salmonella typhimurium was determined revealing an open reading frame of 2181 bp that could encode a 727 amino acid protein. The predicted sequence of the encoded hydroperoxidase I (HPI) was found to be 90% similar to HPI from Escherichia coli and was one amino acid longer. The physical and enzymatic properties of HPI from both Salmonella typhimurium and Escherichia coli were found to be virtually identical despite the 10% divergence in sequence.

Homology among bacterial catalase genes

Catalase activities in crude extracts of exponential and stationary phase cultures of various bacteria were visualized following gel electrophoresis for comparison with the enzymes from Escherichia coli. Citrobacter freundii, Edwardsiella tarda, Enterobacter aerogenes, Klebsiella pneumoniae, and Salmonella typhimurium exhibited patterns of catalase activity similar to E. coli, including bifunctional HPI-like bands and a monofunctional HPII-like band. Proteus mirabilis, Erwinia carotovora, and Serratia marcescens contained a single band of monofunctional catalase with a mobility intermediate between the HPI-like and HPII-like bands. The cloned genes for catalases HPI (katG) and HPII (katE) from E. coli were used as probes in Southern hybridization analyses for homologous sequences in genomic DNA of the same bacteria. katG was found to hybridize with fragments from C. freudii, Ent. aerogenes, Sal. typhimurium, and K. pneumoniae but not at all with Ed. tarda, P. mirabilis, S. marcesens, or Er. carotovora. katE hybridized with C. freundii and K. pneumoniae DNAs and not with the other bacterial DNAs.

Molecular characterization of three mutations in katG affecting the activity of hydroperoxidase I of Escherichia coli

Hydroperoxidase I (HPI) of Escherichia coli is a bifunctional enzyme exhibiting both catalase and peroxidase activities. Mutants lacking appreciable HPI have been generated using nitrosoguanidine and the gene encoding HPI, katG, has been cloned from three of these mutants using either classical probing methods or polymerase chain reaction amplification. The mutant genes were sequenced and the changes from wild-type sequence identified. Two mutants contained G to A changes in the coding strand, resulting in glycine to aspartate changes at residues 119 (katG15) and 314 (katG16) in the deduced amino acid sequence of the protein. A third mutant contained a C to T change resulting in a leucine to phenylalanine change at residue 139 (katG14). The Phe139-, Asp119-, and Asp314-containing mutants exhibited 13, less than 1, and 18%, respectively, of the wild-type catalase specific activity and 43, 4, and 45% of the wild-type peroxidase specific activity. All mutant enzymes bound less protoheme IX than the wild-type enzyme. The sensitivities of the mutant enzymes to the inhibitors hydroxylamine, azide, and cyanide and the activators imidazole and Tris were similar to those of the wild-type enzyme. The mutant enzymes were more sensitive to high temperature and to beta-mercaptoethanol than the wild-type enzyme. The pH profiles of the mutant catalases were unchanged from the wild-type enzyme.

Crystallization and preliminary X-ray diffraction analysis of catalase HPII from Escherichia coli

Green crystals of the hexameric catalase HPII from Escherichia coli have been obtained by the hanging-drop method. The crystals belong to the monoclinic space group P2 with a = 123 A, b = 132 A, c = 93 A, beta = 112.5 degrees. There are three subunits in the asymmetric unit. The crystals diffract at least to 3.2 A resolution and are suitable for further X-ray diffraction studies.

Nucleotide sequence of katF of Escherichia coli suggests KatF protein is a novel sigma transcription factor

The katF gene of Escherichia coli has been sequenced revealing a 1086 base pair open reading frame from which the sequence of a 362 amino acid protein has been deduced. The direction of transcription of katF was confirmed by expression of the gene cloned in both directions behind a T7 promoter. The KatF protein expressed in vitro migrates with an apparent size of 42 kDa. Comparison of the katF sequence to the sequence of rpoD, which encodes the sigma subunit of RNA polymerase, revealed a 181 bp region with 65% homology and a 38 bp segment that was 87% homologous. A 62 amino acid region of the predicted KatF protein sequence was found to be 85% homologous to the corresponding sequence of sigma 70, including a segment implicated in core polymerase binding. Homology was also observed with the heat shock regulatory protein encoded by htpR.

Genetic mapping of katB, a locus that affects catalase 2 levels in Bacillus subtilis

A locus affecting the synthesis of spore-specific catalase 2 in Bacillus subtilis was mapped using two- and three-factor transductional crosses at 342 degrees between hsrE and iol. It was named katB. Strains lacking catalase 2 remained sporulation proficient, but blockage of sporulation at stage IV or earlier affected the electrophoretic mobility of the native enzyme.

Cloning and physical characterization of katE and katF required for catalase HPII expression in Escherichia coli

Two genes, katE and katF, affecting the synthesis of catalase HPII in Escherichia coli, have been cloned. The multistep cloning protocol involved: screening for the tet gene in a transposon interrupting the genes, selecting DNA adjacent to the transposon, and using it to probe a library of wild-type DNA to select clones from which katE and katF were subcloned into pAT153. The clones were physically characterized and the presence of the genes confirmed by complementation of their respective mutations. The location of the transposon insertions in the two genes was determined by Southern blotting of genomic digests to further confirm the identity of the cloned genes. A 93-kDa protein, the same size as the subunit of HPII, was encoded by the katE plasmid, indicating that katE was the structural gene for HPII. A 44-kDa protein was encoded by the katF plasmid.

Nucleotide sequence of katG, encoding catalase HPI of Escherichia coli

The gene katG, encoding catalase HPI of Escherichia coli, was sequenced, predicting a 726-amino-acid protein. The sequence was confirmed by identification of potential regulatory elements and amino acid sequencing of peptides. HPI shows no homology to other catalases. The distances between katG, metF, and ppc were defined.

Purification and characterization of spore-specific catalase-2 from Bacillus subtilis

Catalase-2, the catalase found in spores of Bacillus subtilis, has been purified to homogeneity from a nonsporulating strain. The apparent native molecular weight is 504,000. The enzyme appears to be composed of six identical protomers with a molecular weight of 81,000 each. The amino acid composition is similar to the composition of other catalases. Like most catalases, catalase-2 exhibits a broad pH optimum from pH 4 to pH 12 and is sensitive to cyanide, azide, thiol reagents, and amino triazole. The apparent Km for H2O2 is 78 mM. The enzyme exhibits extreme stability, losing activity only slowly at 93 degrees C and remaining active in 1% SDS-7 M urea. The green-colored enzyme exhibits a spectrum like heme d with a Soret absorption at 403 nm and a molar absorptivity consistent with one heme per subunit. The heme cannot be extracted with acetone-HCl or ether, suggesting that it is covalently bound to the protein.

Effect of ascorbate on oxygen uptake and growth of Escherichia coli B

The addition of ascorbate to aerobically growing cultures of Escherichia coli B caused only a short pause in growth and no subsequent change in the rate or extent of growth. The effect of ascorbate on oxygen uptake varied from inhibition in minimal medium to stimulation in rich medium. Cyanide-resistant growth and oxygen uptake were stimulated by ascorbate. Both the rate and extent of anaerobic growth were stimulated in proportion to the amount of ascorbate added when fumarate was the terminal electron acceptor. Ascorbate had no effect on any aspect of anaerobic growth in the absence of a terminal electron acceptor or in the presence of nitrate.

Genetic mapping of katA, a locus that affects catalase 1 level in Bacillus subtilis

Several mutants of Bacillus subtilis deficient in catalase synthesis generated by nitrosoguanidine mutagenesis have been used to map a locus affecting catalase activity. Two- and three-factor bacteriophage PBS1 transductional crosses were used to locate the locus, named katA, between recH and thiA with 98% linkage to thiA at 70 degrees on the B. subtilis genome. The synthesis of catalase 1, found only in vegetative cells, was affected by katA.

Purification and characterization of catalase-1 from Bacillus subtilis

The catalase activity produced in vegetative Bacillus subtilis, catalase-1, has been purified to homogeneity. The apparent native molecular weight was determined to be 395,000. Only one subunit type with a molecular weight of 65,000 was present, suggesting a hexamer structure for the enzyme. In other respects, catalase-1 was a typical catalase. Protoheme IX was identified as the heme component on the basis of the spectra of the enzyme and of the isolated hemochromogen. The ratio of protoheme/subunit was 1. The enzyme remained active over a broad pH range of 5-11 and was only slowly inactivated at 65 degrees C. It was inhibited by cyanide, azide, and various sulfhydryl compounds. The apparent Km for hydrogen peroxide was 40.1 mM. The amino acid composition was typical of other catalases in having relatively low amounts of tryptophan and cysteine.

Multiple catalases in Bacillus subtilis

Vegetative cells of Bacillus subtilis in logarithmic growth phase produced one catalase, labeled catalase 1, with a nondenatured molecular weight of 205,000. As growth progressed, other activity bands with slower electrophoretic mobilities on polyacrylamide gels appeared, including a series of bands with a common nondenatured molecular weight of 261,000, collectively labeled catalase 2, and a minor band, with a molecular weight of 387,000, labeled catalase 3. Purified spores contained only catalase 2, and it was not produced in spo0A- or spo0F-containing mutants. Strains deficient in catalase 1 or catalase 2 or both were selected after mutagenesis. Sensitivities of the two main catalases to NaCN, NaN3, hydroxylamine, and temperature were similar, but the apparent Kms for H2O2 differed, being 36.6 and 64.4 mM, respectively, for catalase 1 and catalase 2. The levels of catalase 1 increased 15-fold during growth into stationary phase and could be increased 30-fold by the addition of H2O2 to the medium. Catalase 2, which was not affected by H2O2, appeared only after the cells had reached stationary phase, and the maximum levels were only half of the basal level of catalase 1.

Physical characterization of katG, encoding catalase HPI of Escherichia coli

The gene encoding the bifunctional catalase-peroxidase HPI from Escherichia coli was located on a 3.8-kb HindIII fragment of the Clarke and Carbon plasmid pLC36-19 using transposon Tn5 insertions. This fragment was subcloned into the HindIII site of pAT153 to create pBT22. The size of the insert was reduced by BAL 31 digestion of one end to an apparent minimum size for catalase expression of approx. 2.5 kb as determined by complementation and expression in maxicell strains. Further reduction in size or digestion from the opposite end inactivated the gene. The location and orientation of the promoter at the 0 kb end of the insert in pBT22 was confirmed by cloning a 320-bp BglII fragment into the promoter-cloning vector pKK232-8. Differences in the Southern blots of genomic DNA from a wild-type strain and a katG17::Tn10 mutant digested with HincII and probed with pBT22 confirmed that the transposon previously mapped in katG was located in the 2.5-kb coding region for HPI.

Purification and characterization of catalase HPII from Escherichia coli K12

Catalase (hydroperoxidase II or HPII) of Escherichia coli K12 has been purified using a protocol that also allows the purification of the second catalase HPI in large amounts. The purified HPII was found to have equal amounts of two subunits with molecular weights of 90,000 and 92,000. Only a single 92,000 subunit was present in the immunoprecipitate created when HPII antiserum was added directly to a crude extract, suggesting that proteolysis was responsible for the smaller subunit. The apparent native molecular weight was determined to be 532,000, suggesting a hexamer structure for the enzyme, an unusual structure for a catalase. HPII was very stable, remaining maximally active over the pH range 4-11 and retaining activity even in a solution of 0.1% sodium dodecyl sulfate and 7 M urea. The heme cofactor associated with HPII was also unusual for a catalase, in resembling heme d (a2) both spectrally and in terms of solubility. On the basis of heme-associated iron, six heme groups were associated with each molecule of enzyme or one per subunit.