Characterization of two lignin peroxidase clones from Phanerochaete chrysosporium

Molecular approach for analysis of model fungal genes encoding ligninolytic peroxidases in wood-decaying soil systems

AIMS

Test the use of nondegenerated consensus polymerase chain reaction (PCR) primers targeting lip and mnp sequences to detect ligninolytic fungi in wood-decaying soil systems, avoiding the need for enrichment or isolation on traditional fungal media culture.

METHODS AND RESULTS

The PCR primers were tested with total DNA isolated from incubations of wood-soil systems inoculated or not with the white-rot fungi Phanerochaete chrysosporium, or a white-rot sample obtained from a Nothofagus forest. The PCR products for lip and mnp sequences were only obtained in soil with P. chrysosporium-colonized wood chips. In these soil samples, reverse transcription-PCR analysis of lip and mnp PCR products indicated expression of LipA, LipB, LipJ and MnP isoenzymes.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first assessment of the use of consensus PCR primers for direct detection of ligninolytic peroxidase genes in wood-decaying soil systems.

Organization and differential regulation of a cluster of lignin peroxidase genes of Phanerochaete chrysosporium

The lignin peroxidases of Phanerochaete chrysosporium are encoded by a minimum of 10 closely related genes. Physical and genetic mapping of a cluster of eight lip genes revealed six genes occurring in pairs and transcriptionally convergent, suggesting that portions of the lip family arose by gene duplication events. The completed sequence of lipG and lipJ, together with previously published sequences, allowed phylogenetic and intron/exon classifications, indicating two main branches within the lip family. Competitive reverse transcription-PCR was used to assess lip transcript levels in both carbon- and nitrogen-limited media. Transcript patterns showed differential regulation of lip genes in response to medium composition. No apparent correlation was observed between genomic organization and transcript levels. Both constitutive and upregulated transcripts, structurally unrelated to peroxidases, were identified within the lip cluster.

Isolation of mRNAs induced by a hazardous chemical in white-rot fungus, Coriolus versicolor, by differential display

White-rot fungus Coriolus versicolor, a ligninolytic basidiomycete, has been studied because of its ability to degrade hazardous chemicals. In this study, we searched for genes that are induced by a hazardous chemical using the mRNA differential-display technique and C. versicolor IFO30340 that has been exposed to pentachlorophenol (PCP). Five cDNA fragments were cloned and the DNA sequences of two fragments were analyzed in further detail. The clones corresponded to novel genes that have not previously been identified in C. versicolor. One of the cDNAs exhibited strong sequence homology to the gene for an enolase and the other exhibited homology to a heat shock protein. The expression of the two genes was up-regulated in PCP-treated C. versicolor.

Reductive activation markedly increases the stability of cathepsins B and L to extracellular ionic conditions

Cathepsins B and L are thought to function extracellularly in pathological conditions. pH-Activity profiles of cathepsin B, measured in phosphate and acetate-Mes-Tris buffers of constant ionic strength, indicated that cathepsin B is sensitive to specific buffer ions, as previously reported for cathepsin L. In assessing the activity of these enzymes in vitro the influence of the buffer must therefore be taken into account. In Hank's balanced salt solution, a buffer modeling the extracellular fluid, the half-life of activated human liver cathepsin B at 37 degrees C is 245 +/- 11.3 s, at pH 7.2, and 857 +/- 50.1 s, at pH 6.8 (the peritumor pH), indicating that cathepsin B is markedly stable under these conditions. The stability was increased by the additional presence of proteins. Without immediate activation, however, the stabilities of both cathepsins B and L were markedly decreased, a large proportion of their activity being lost before it could be measured. Enzymes injected into the extracellular space in the unactivated state would therefore survive for only a very short time in their native conformation. It is proposed that the active site thiolate-imidazolium ion pair contributes substantially to the stability of cathepsins B and L to extracellular ionic conditions.

Phanerochaete chrysosporium glyoxal oxidase is encoded by two allelic variants: structure, genomic organization, and heterologous expression of glx1 and glx2

A cDNA clone (glx-2c) encoding glyoxal oxidase (GLOX) was isolated from a Phanerochaete chrysosporium lambda gt11 library, and its nucleotide sequence was shown to be distinct from that of the previously described clone glx-1c (P. J. Kersten and D. Cullen, Proc. Natl. Acad. Sci. USA 90:7411-7413, 1993). Genomic clones corresponding to both cDNAs were also isolated and sequenced. overall nucleotide sequence identity was 98%, and the predicted proteins differed by a single residue: Lys-308<==>Thr-308. Analyses of parental dikaryotic strain BKM-F-1767 and homokaryotic progeny firmly established allelism for these structural variants. Southern blots of pulsed-field gels localized the GLOX gene (glx) to a dimorphic chromosome separate from the peroxidase and cellobiohydrolase genes of P. chrysosporium. Controlled expression of active GLOX was obtained from Aspergillus nidulans transformants when glx-1c was fused to the promoter and secretion signal of the A. niger glucoamylase gene. The GLOX isozyme corresponding to glx-2c was also efficiently secreted by A. nidulans following site-specific mutagenesis of the expression vector at codon 308 of glx-1c.

Establishment of genetic linkage by allele-specific polymerase chain reaction: application to the lignin peroxidase gene family of Phanerochaete chrysosporium

Determining linkage is problematic for genes lacking easily identifiable phenotypes and for organisms without well-defined genetic recombination systems. Phanerochaete chrysosporium with its lignin peroxidase (LiP) gene family typifies these difficulties. We describe an experimental approach whereby the segregation of specific alleles is directly monitored during sexual fruiting. The method establishes linkage relationships among genes for which there are no mutations, and it is applicable to a wide range of genes, gene families and organisms. Using this approach, five P. chrysosporium linkage groups were identified. Ten LiP genes were distributed among three of these groups. One co-segregating group contained eight closely linked LiP genes. Another LiP gene was linked to a cellobiohydrolase gene cluster. These genetic linkages were consistent with physical mapping by pulsed field gel electrophoresis. Based on the identification of allelic relationships, a uniform nomenclature for LiP genes is also described.

Characterization of a cDNA encoding a manganese peroxidase from Phanerochaete chrysosporium: genomic organization of lignin and manganese peroxidase-encoding genes

Two heme proteins, manganese peroxidase (MnP) and lignin peroxidase (LiP), play key roles in the fungal depolymerization of lignin. Many cDNA and genomic clones encoding these peroxidases have been published. We report here on the cDNA lambda MP-2 encoding the MnP isozyme H3 from Phanerochaete chrysosporium strain BKM-F-1767. We also demonstrate that the MnP-encoding gene, lambda MP-1, encoding isozyme H4, and lambda MP-2 reside on separate chromosomes from each other and from the LiP-encoding genes. From these results, it is apparent that lambda MP-2 is not linked to lambda MP-1 or other genes believed to be involved in lignin depolymerization, such as the LiP and glyoxal oxidase.

Physiology and molecular biology of the lignin peroxidases of Phanerochaete chrysosporium

The white-rot basidiomycete Phanerochaete chrysosporium produces lignin peroxidases (LiPs), a family of extracellular glycosylated heme proteins, as major components of its lignin-degrading system. Up to 15 LiP isozymes, ranging in M(r) values from 38,000 to 43,000, are produced depending on culture conditions and strains employed. Manganese-dependent peroxidases (MnPs) are a second family of extracellular heme proteins produced by P. chrysosporium that are also believed to be important in lignin degradation by this organism. LiP and MnP production is seen during secondary metabolism and is completely suppressed under conditions of excess nitrogen and carbon. Excess Mn(II) in the medium, on the other hand, suppresses LiP production but enhances MnP production. Nitrogen regulation of LiP and MnP production is independent of carbon and Mn(II) regulation. LiP activity is also affected by idiophasic extracellular proteases. Intracellular cAMP levels appear to be important in regulating the production of LiPs and MnPs, although LiP production is affected more than MnP production. Studies on the sequencing and characterization of lip cDNAs and genes of P. chrysosporium have shown that the major LiP isozymes are each encoded by a separate gene. Each lip gene encodes a mature protein that is 343-344 amino acids long, contains 1 putative N-glycosylation site, a number of putative O-glycosylation sites, and is preceded by a 27-28-amino acid leader peptide ending in a Lys-Arg cleavage site. The coding region of each lip gene is interrupted by 8-9 introns (50-63 bp), and the positions of the last two introns appear to be highly conserved. There are substantial differences in the temporal transcription patterns of the major lip genes. The sequence data suggest the presence of three lip gene subfamilies. The genomic DNA of P. chrysosporium strain BKMF-1767 was resolved into 10 chromosomes (genome size of 29 Mb), and that of strain ME-446 into 11 chromosomes (genome size of 32 Mb). The lip genes have been localized to five chromosomes in BKMF-1767 and to four chromosomes in ME-446. DNA transformation studies have reported both integrative and non-integrative transformation in P. chrysosporium.

Decolorization of Azo, Triphenyl Methane, Heterocyclic, and Polymeric Dyes by Lignin Peroxidase Isoenzymes from Phanerochaete chrysosporium

The ligninolytic enzyme system of Phanerochaete chrysosporium decolorizes several recalcitrant dyes. Three isolated lignin peroxidase isoenzymes (LiP 4.65, LiP 4.15, and LiP 3.85) were compared as decolorizers with the crude enzyme system from the culture medium. LiP 4.65 (H2), LiP 4.15 (H7), and LiP 3.85 (H8) were purified by chromatofocusing, and their kinetic parameters were found to be similar. Ten different types of dyes, including azo, triphenyl methane, heterocyclic, and polymeric dyes, were treated by the crude enzyme preparation. Most of the dyes lost over 75% of their color; only Congo red, Poly R-478, and Poly T-128 were decolorized less than the others, 54, 46, and 48%, respectively. Five different dyes were tested for decolorization by the three purified isoenzymes. The ability of the isoenzymes to decolorize the dyes in the presence of veratryl alcohol was generally comparable to that of the crude enzyme preparation, suggesting that lignin peroxidase plays a major role in the decolorization and that manganese peroxidase is not required to start the degradation of these dyes. In the absence of veratryl alcohol, the decolorization activity of the isoenzymes was in most cases dramatically reduced. However, LiP 3.85 was still able to decolorize 20% of methylene blue and methyl orange and as much as 60% of toluidine blue O, suggesting that at least some dyes can function as substrates for isoenzyme LiP 3.85 but not to the same extent for LiP 4.15 or LiP 4.65. Thus, the isoenzymes have different specificities towards dyes as substrates.

Molecular biology of the lignin-degrading basidiomycete Phanerochaete chrysosporium

The white rot basidiomycete Phanerochaete chrysosporium completely degrades lignin and a variety of aromatic pollutants during the secondary metabolic phase of growth. Two families of secreted heme enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP), are major components of the extracellular lignin degradative system of this organism. MnP and LiP both are encoded by families of genes, and the lip genes appear to be clustered. The lip genes contain eight or nine short introns; the mnp genes contain six or seven short introns. The sequences surrounding active-site residues are conserved among LiP, MnP, cytochrome c peroxidase, and plant peroxidases. The eight LiP cysteine residues align with 8 of the 10 cysteines in MnP. LiPs are synthesized as preproenzymes with a 21-amino-acid signal sequence followed by a 6- or 7-amino-acid propeptide. MnPs have a 21- or 24-amino-acid signal sequence but apparently lack a propeptide. Both LiP and MnP are regulated at the mRNA level by nitrogen, and the various isozymes may be differentially regulated by carbon and nitrogen. MnP also is regulated at the level of gene transcription by Mn(II), the substrate for the enzyme, and by heat shock. The promoter regions of mnp genes contain multiple heat shock elements as well as sequences that are identical to the consensus metal regulatory elements found in mammalian metallothionein genes. DNA transformation systems have been developed for P. chrysosporium and are being used for studies on gene regulation and for gene replacement experiments.

Lignin-degrading peroxidases of Phanerochaete chrysosporium

Lignin and manganese peroxidases are secreted by the basidiomycete Phanerochaete chrysosporium during secondary metabolism. These enzymes play major roles in lignin degradation. The active site amino acid sequence of these lignin-degrading peroxidases is similar to that of horseradish peroxidase (HRP) and cytochrome c peroxidase (CcP). The mechanism by which they oxidize substrates also appears to be the similar. pH has a similar effect on lignin peroxidase compound I formation as on HRP or CcP; however, the pKa controlling compound I formation for lignin peroxidase appears to be much lower. Lignin-degrading peroxidases are able to catalyze the oxidation of substrates with high redox potential. This unique ability is consistent with a heme active site of low electron density, which is indicated by high redox potential.

Is an activator protein-2-like transcription factor involved in regulating gene expression during nitrogen limitation in fungi?

The upstream sequences of all published lignin peroxidase and manganese peroxidase genomic clones from Phanerochaete chrysosporium were analyzed. This analysis revealed the presence of putative activator protein-2 (AP-2) recognition sequences in 11 of 15 lignin peroxidase genes. The lignin peroxidase clone GLG6 and the manganese peroxidase gene (mnp-1) have two copies of putative AP-2 sequence in the upstream region. Interestingly, the lignin peroxidase gene VLG4 of another white rot fungus, Trametes versicolor, and the nit-2 gene of Neurospora crassa also contain putative AP-2-binding sequences. Since all of these genes are regulated by nutrient nitrogen, I hypothesize that an AP-2-like transcription factor may be involved in inducing gene expression during nitrogen limitation in fungi.

Amino acid sequence of Coprinus macrorhizus peroxidase and cDNA sequence encoding Coprinus cinereus peroxidase. A new family of fungal peroxidases

Sequence analysis and cDNA cloning of Coprinus peroxidase (CIP) were undertaken to expand the understanding of the relationships of structure, function and molecular genetics of the secretory heme peroxidases from fungi and plants. Amino acid sequencing of Coprinus macrorhizus peroxidase, and cDNA sequencing of Coprinus cinereus peroxidase showed that the mature proteins are identical in amino acid sequence, 343 residues in size and preceded by a 20-residue signal peptide. Their likely identity to peroxidase from Arthromyces ramosus is discussed. CIP has an 8-residue, glycine-rich N-terminal extension blocked with a pyroglutamate residue which is absent in other fungal peroxidases. The presence of pyroglutamate, formed by cyclization of glutamine, and the finding of a minor fraction of a variant form lacking the N-terminal residue, indicate that signal peptidase cleavage is followed by further enzymic processing. CIP is 40-45% identical in amino-acid sequence to 11 lignin peroxidases from four fungal species, and 42-43% identical to the two known Mn-peroxidases. Like these white-rot fungal peroxidases, CIP has an additional segment of approximately 40 residues at the C-terminus which is absent in plant peroxidases. Although CIP is much more similar to horseradish peroxidase (HRP C) in substrate specificity, specific activity and pH optimum than to white-rot fungal peroxidases, the sequences of CIP and HRP C showed only 18% identity. Hence, CIP qualifies as the first member of a new family of fungal peroxidases. The nine invariant residues present in all plant, fungal and bacterial heme peroxidases are also found in CIP. The present data support the hypothesis that only one chromosomal CIP gene exists. In contrast, a large number of secretory plant and fungal peroxidases are expressed from several peroxidase gene clusters. Analyses of three batches of CIP protein and of 49 CIP clones revealed the existence of only two highly similar alleles indicating less peroxidase polymorphism in C. cinereus strains than observed in plants and white-rot fungi.

Characterization of a highly expressed lignin peroxidase-encoding gene from the basidiomycete Phanerochaete chrysosporium

The genomic clone, LG2, encoding LiP2, the major lignin peroxidase (LiP) isozyme from Phanerochaete chrysosporium strain OGC101, was isolated and characterized. The 5'-untranslated region of LG2 contains sequences similar to CRE and XRE promoter elements. Comparison with its transcript indicates that eight introns, each less than 59 bp, interrupt the coding sequence. Comparison with genes encoding other LiP isozymes shows five related patterns of intron location, whose incidence coincides with described LiP structural subfamilies. Codon bias indices calculated for all known P. chrysosporium genes, including trpC and genes encoding LiP, MnP, and exo-cellobiohydrolase I, demonstrate that LG2 has the most biased codon usage. We conclude that subdivisions of the LiP family may be based on intron location in the encoding genes, and that ranking of isozyme production levels can be estimated by the extent of bias in codon usage in the cognate gene.

Lignin peroxidase gene family of Phanerochaete chrysosporium: complex regulation by carbon and nitrogen limitation and identification of a second dimorphic chromosome

Lignin peroxidases (LiP) of Phanerochaete chrysosporium are encoded by a family of six closely related genes. Five LiP genes have been localized to the same dimorphic chromosome. In this investigation, relative transcript levels of the LiP genes were determined. Transcripts of the LiPA, LiPB, and O282 genes were at similar levels in both carbon- and nitrogen-limited cultures. In contrast, transcription of the GLG5, V4, and GLG4 genes was dramatically altered by culture conditions. Under carbon-limited conditions, GLG4 transcripts were, by far, the most abundant. Southern blot analyses of clamped homogeneous field gels were used to map the GLG4 gene to a dimorphic chromosome separate from the other LiP genes.

Production and characterization of recombinant lignin peroxidase isozyme H2 from Phanerochaete chrysosporium using recombinant baculovirus

Recombinant Phanerochaete chrysosporium lignin peroxidase isozyme H2 (pI 4.4) was produced in insect cells infected with a genetically engineered baculovirus containing a copy of the cDNA clone lambda ML-6. The recombinant enzyme was purified to near homogeneity and is capable of oxidizing veratryl alcohol, iodide, and, to a lesser extent, guaiacol. The Km of the recombinant enzyme for veratryl alcohol and H2O2 is similar to that of the fungal enzyme. The guaiacol oxidation activity or any other activity is not dependent upon Mn2+. The purified recombinant peroxidase is glycosylated with N-linked carbohydrate(s). The recombinant lignin peroxidase eluted from an anion exchange resin similar to that of native isozyme H1 rather than H2. However, the pI of the recombinant enzymes is different from both H1 and H2 isozymes. Further characterization of native isozymes H1 and H2 from the fungal cultures revealed identical N-terminus residues. This indicates that isozymes H1 and H2 differ in post-translational modification.

Expression of a single lignin peroxidase-encoding gene in Phanerochaete chrysosporium strain ME446

A previously described linked set of lignin peroxidase-encoding genes (Lpo) from Phanerochaete chrysosporium (P.c.) ME446 is not expressed under standard growth conditions for ligninolytic activity. However, a single unlinked Lpo gene, not previously described in P.c. strain ME446, is expressed. The transcription start points of this gene are mapped and the gene is assigned to a genetic linkage group by the use of restriction-site polymorphism segregation analysis. No transcripts from Lpo-related genes, including that normally expressed in ME446, could be detected within RNA extracted from three nonligninolytic mutant strains, but a hyper-ligninolytic strain showed an increased level of Lpo expression. This increase is due to expression of additional Lpo genes, rather than to an increased level of transcription from the normally expressed sequence.

Method to identify specific alleles of a Phanerochaete chrysosporium gene encoding lignin peroxidase

A method to identify and differentiate allelic variants of the gene encoding lignin peroxidase isozyme H8 is presented. The strategy involves amplifying a variable region of the gene's carboxy terminus by use of the polymerase chain reaction and then probing with allele-specific oligonucleotides.

Lignin peroxidase from the basidiomycete Phanerochaete chrysosporium is synthesized as a preproenzyme

The cDNA clone L18 encoding lignin peroxidase LiP2, the most highly expressed LiP isozyme from Phanerochaete chrysosporium strain OGC101, was isolated and sequenced. Comparison of the cDNA sequence with the N-terminal sequence of the mature LiP2 protein isolated from culture medium suggests that the mature protein contains 343 amino acids (aa) and is preceded by a 28-aa leader sequence. In vitro transcription followed by in vitro translation and processing by signal peptidase resulted in cleavage at a site following the Ala21 (counted from the N-terminal Met1 of the initial translation product). The resultant protein contains a 7-aa propeptide, indicating that LiP is synthesized as a preproenzyme.

Molecular analysis of a Bjerkandera adusta lignin peroxidase gene

A cDNA clone, lambda LPO-1, encoding a major lignin peroxidase from the basidiomycete Bjerkandera adusta was isolated and characterized. The nucleotide sequence of lambda LPO-1 predicts a mature protein consisting of 349 amino acids with a molecular weight of 37,225 preceded by a signal peptide of 23 amino acid residues. We have also cloned and sequenced the gene encoding lignin peroxidase from B. adusta. Comparison of these sequences reveals a lignin peroxidase gene structure consisting of 1,116 bp of protein-encoding DNA that is interrupted by four intervening sequences. The putative eukaryotic regulatory sequence, a TATA box, is present at position -75 relative to the translational initiation codon. Amino acid sequence homology between the coding regions of lambda LPO-1 and of the lignin peroxidase cDNA clone lambda ML-1 from Phanerochaete chrysosporium is 61%.

Heterologous expression of active manganese peroxidase from Phanerochaete chrysosporium using the baculovirus expression system

The cDNA encoding Mn peroxidase isozyme H4 from Phanerochaete chrysosporium was recombined into a baculovirus and heterologously expressed in Sf9 cells. The recombinant Mn peroxidase has the same molecular weight as the native enzyme as determined by SDS-PAGE and cross-reacts with a Mn peroxidase-specific antibody. The recombinant enzyme has a slightly lower pI than the native fungal isozyme H4 indicating some differences in post-translational modification. Phenol red, guaiacol, and vanillylacetone, substrates of the native Mn peroxidase, are oxidized by the recombinant enzyme. All of the activities are dependent on both Mn (II) and H2O2.

Genomic organization of lignin peroxidase genes of Phanerochaete chrysosporium

Three lignin peroxidase (LiP) genes from the basidiomycete Phanerochaete chrysosporium were cloned on a single 30 kb cosmid insert. One gene, GLG5, is the genomic equivalent of a previously reported cDNA clone, CLG5. The other two LiP genes are transcriptionally convergent and map to a position approximately 15 kb downstream of GLG5. The translational stop codons of these genes are separated by 1.3 kb. Analysis of homokaryons established allelic relationships to previously described LiP clones. Using clamped homogeneous electrical field electrophoresis (CHEF), seven chromosomal bands were resolved from P. chrysosporium genomic DNA. On CHEF gel Southern blots, the LiP gene family was localized to a single, dimorphic chromosome.

Cloning of several lignin peroxidase (LIP)-encoding genes: sequence analysis of the LIP6 gene from the white-rot basidiomycete, Phanerochaete chrysosporium

A Phanerochaete chrysosporium BKMF1767 genomic library, constructed in the BamHI site of vector YRp12, was screened with the lignin peroxidase(LIP)-encoding cDNAs, CLG4 and CLG5, that have been shown to encode LIP2 (previously H2) and LIP6 (previously H10), respectively. Six distinct LIP genomic clones, designated pGLG1, pGLG2, pGLG3, pGLG4, pGLG5, and pGLG6, were isolated in this study. Probe CLG4 hybridized only to pGLG1. Probe CLG5 gave intense hybridization to pGLG2 and weaker hybridization to clones pGLG3 through pGLG6, but showed little or no hybridization to pGLG1. These results, in agreement with previous biochemical results, indicate the existence of LIP gene subfamilies. The limits and transcriptional orientation of the LIP gene in each clone were determined. The sequence data showed that pGLG2 contains the LIP6 gene, which encodes a protein identical in amino acid (aa) composition to that encoded by CLG5. It contains a leader sequence of 27 aa and a mature protein of 344 aa (Mr 36,607). Archetypal TATA-box-like and CAAT-box-like sequences in the 5'-noncoding region are located 51 and 97 nt upstream from the cDNA start point, respectively. S1 nuclease analysis of the 5' region of LIP6 revealed two transcription start points 8 nt apart downstream from the TATA box. Comparison of the sequence of LIP6 with its corresponding cDNA CLG5 showed that the gene contains nine small introns which range in size from 50 to 62 bp. These introns contained consensus splice junction sequences similar to those reported in other fungal and yeast introns.

A novel extrachromosomally maintained transformation vector for the lignin-degrading basidiomycete Phanerochaete chrysosporium

A stable extrachromosomally maintained transformation vector (pG12-1) for the lignin-degrading filamentous fungus Phanerochaete chrysosporium is described. The vector is 6.3 kb and contains a Kanr marker, pBR322 ori, and a 2.2-kb fragment (ME-1) derived from an endogenous extrachromosomal DNA element of P. chrysosporium. Vector pG12-1 was able to transform P. chrysosporium to G418 resistance and was readily and consistently recoverable from the total DNA of transformants via Escherichia coli transformation. Southern blot analyses indicated that pG12-1 is maintained at a low copy number in the fungal transformants. The vector is demonstrable in the total DNA of individual G418-resistant basidiospore progeny of the transformants only after amplification by polymerase chain reaction. Exonuclease III and dam methylation analyses, respectively, indicated that pG12-I undergoes replication in P. chrysosporium and that it is maintained extrachromosomally in a circular form. The vector is stably maintained in the transformants even after long-term nonselective growth. There is no evidence for integration of the vector into the chromosome at any stage.

Characterization of a new lignin peroxidase gene (GLG6) from Phanerochaete chrysosporium

Sequence analysis of a new lignin peroxidase (LIP) gene, GLG6, from P. chrysosporium showed that it encodes a mature LIP protein with a predicted Mr of 36,454. A 28 aa signal peptide precedes the mature protein. The coding region of GLG6 is interrupted by nine introns ranging in size from 50-57 bp. GLG6 encoded-LIP has 72%, 88% and 82% homology, respectively, to the LIP isozymes H2, H3, and H10. Comparison of the N-terminal sequence of GLG6-encoded LIP to that of the LIP proteins H2, H8, H10 also showed that the former is relatively less related to the H2 protein than it is to the H8 and H10 proteins. Expression of GLG6, similar to the other LIP genes, occurs only during secondary metabolism.

Characterization of lignin peroxidase-encoding genes from lignin-degrading basidiomycetes

Two closely linked lignin peroxidase (LPO)-encoding genes (lpo) from Phanerochaete chrysosporium were isolated. Nucleotide sequence studies indicated that the two genes are separated by 1.3 kb of flanking DNA and transcribed in opposite directions. Cloned P. chrysosporium lpo gene probes have been shown to hybridize to multiple sequences present in the DNAs of the white-rot fungi, Bjerkandera adusta, Coriolus versicolor and Fomes lignosus, but no hybridization was detected with DNA from Pleurotus ostreatus. Thus, lpo gene families appear to be common in a number of lignin-degrading basidiomycetes, some of which have not yet been shown to produce LPO proteins.

Characterization of the oxycomplex of lignin peroxidases from Phanerochaete chrysosporium: equilibrium and kinetics studies

The oxycomplexes (compound III, oxyperoxidase) of two lignin peroxidase isozymes, H1 (pI = 4.7) and H8 (pI = 3.5), were characterized in the present study. After generation of the ferroperoxidase by photochemical reduction with deazoflavin in the presence of EDTA, the oxycomplex is formed by mixing ferroperoxidase with O2. The oxycomplex of isozyme H8 is very stable, with an autoxidation rate at 25 degrees C too slow to measure at pH 3.5 or 7.0. In contrast, the oxycomplex of isozyme H1 has a half-life of 52 min at pH 4.5 and 29 min at pH 7.5 at 25 degrees C. The decay of isozyme H1 oxycomplex follows a single exponential. The half-lives of lignin peroxidase oxycomplexes are much longer than those observed with other peroxidases. The binding of O2 to ferroperoxidase to form the oxycomplex was studied by stopped-flow methods. At 20 degrees C, the second-order rate constants for O2 binding are 2.3 X 10(5) and 8.9 X 10(5) M-1 s-1 for isozyme H1 and 6.2 X 10(4) and 3.5 X 10(5) M-1 s-1 for isozyme H8 at pH 3.6 and pH 6.8, respectively. The dissociation rate constants for the oxycomplex of isozyme H1 (3.8 Z 10(-3) s-1) and isozyme H8 (1.0 X 10(-3) s-1) were measured at pH 3.6 by CO trapping. Thus, the equilibrium constants (K, calculated from kon/koff) for both isozymes H1 (7.0 X 10(7) M-1) and H8 (6.2 X 10(7) M-1) are higher than that of myoglobin (1.9 Z 10(6) M-1).(ABSTRACT TRUNCATED AT 250 WORDS)