Differential regulation of genes encoding manganese peroxidase (MnP) in the basidiomycete Ceriporiopsis subvermispora

Metabolic Specialization and Codon Preference of Lignocellulolytic Genes in the White Rot Basidiomycete Ceriporiopsis subvermispora

Ceriporiopsis subvermispora is a white-rot fungus with a high specificity towards lignin mineralization when colonizing dead wood or lignocellulosic compounds. Its lignocellulose degrading system is formed by cellulose hydrolytic enzymes, manganese peroxidases, and laccases that catalyze the efficient depolymerization and mineralization of lignocellulose. To determine if this metabolic specialization has modified codon usage of the lignocellulolytic system, improving its adaptation to the fungal translational machine, we analyzed the adaptation to host codon usage (CAI), tRNA pool (tAI, and AAtAI), codon pair bias (CPB), and the number of effective codons (Nc). These indexes were correlated with gene expression of C. subvermispora, in the presence of glucose and Aspen wood. General gene expression was not correlated with the index values. However, in media containing Aspen wood, the induction of expression of lignocellulose-degrading genes, showed significantly (p < 0.001) higher values of CAI, AAtAI, CPB, tAI, and lower values of Nc than non-induced genes. Cellulose-binding proteins and manganese peroxidases presented the highest adaptation values. We also identified an expansion of genes encoding glycine and glutamic acid tRNAs. Our results suggest that the metabolic specialization to use wood as the sole carbon source has introduced a bias in the codon usage of genes involved in lignocellulose degradation. This bias reduces codon diversity and increases codon usage adaptation to the tRNA pool available in C. subvermispora. To our knowledge, this is the first study showing that codon usage is modified to improve the translation efficiency of a group of genes involved in a particular metabolic process.

Mixtures of aromatic compounds induce ligninolytic gene expression in the wood-rotting fungus Dichomitus squalens

Heterologous production of fungal ligninolytic cocktails is challenging due to the low yields of catalytically active lignin modifying peroxidases. Production using a natural system, such as a wood-rotting fungus, is a promising alternative if specific or preferential induction of the ligninolytic activities could be achieved. Using transcriptomics, gene expression of the white-rot Dichomitus squalens during growth on mixtures of aromatic compounds, with ring structures representing the two major lignin sub-units, was compared to a wood substrate. Most of the genes encoding lignin modifying enzymes (laccases and peroxidases) categorised as highly or moderately expressed on wood were expressed similarly on aromatic compounds. Higher expression levels of a subset of manganese and versatile peroxidases was observed on di- compared to mono-methoxylated aromatics. The expression of polysaccharide degrading enzymes was lower on aromatic compounds compared to wood, demonstrating that the induction of lignin modifying enzymes became more specific. This study suggests potential for aromatic waste streams, e.g. from lignocellulose pretreatment, to produce a lignin-specific enzyme cocktail from D. squalens or other white-rot fungi.

Stable and transient transformation, and a promoter assay in the selective lignin-degrading fungus, Ceriporiopsis subvermispora

A genetic transformation system was developed for the selective white rot basidiomycete Ceriporiopsis subvermispora using a modified protocol with polyethylene glycol and CaCl₂ treatment of the protoplasts and plasmids harboring recombinant hygromycin phosphotransferase (hph) driven by a homologous promoter. During repeated transfer on fresh potato dextrose agar plates containing 100 µg/ml hygromycin B, most transformants lost drug resistance, while the remaining isolates showed stable resistance over five transfers. No drug-resistant colonies appeared in control experiments without DNA or using a promoter-less derivative of the plasmid, indicating that a transient expression of the recombinant hph was driven by the promoter sequence in these unstable drug-resistant transformants. Southern blot analysis of the stable transformants revealed random integration of the plasmid DNA fragment in the chromosome at different copy numbers. This transformation system yielding mostly transient transformants was successfully used for promoter assay experiments, and only a 141-bp fragment was found to be essential for the basic promoter function of glyceraldehyde dehydrogenase gene (gpd) in this fungus. Subsequent mutational analyses suggested that a TATAA sequence is important for the basic promoter function of gpd gene. The promoter assay system will enable the functional analysis of gene expression control sequences quickly and easily, mostly in the absence of undesirable effects from differences in copy number and chromosomal position of an integrated reporter gene among stable transformants.

Lignin-degrading peroxidases in white-rot fungus Trametes hirsuta 072. Absolute expression quantification of full multigene family

Ligninolytic heme peroxidases comprise an extensive family of enzymes, which production is characteristic for white-rot Basidiomycota. The majority of fungal heme peroxidases are encoded by multigene families that differentially express closely related proteins. Currently, there were very few attempts to characterize the complete multigene family of heme peroxidases in a single fungus. Here we are focusing on identification and characterization of peroxidase genes, which are transcribed and secreted by basidiomycete Trametes hirsuta 072, an efficient lignin degrader. The T. hirsuta genome contains 18 ligninolytic peroxidase genes encoding 9 putative lignin peroxidases (LiP), 7 putative short manganese peroxidases (MnP) and 2 putative versatile peroxidases (VP). Using ddPCR method we have quantified the absolute expression of the 18 peroxidase genes under different culture conditions and on different growth stages of basidiomycete. It was shown that only two genes (one MnP and one VP) were prevalently expressed as well as secreted into cultural broth under all conditions investigated. However their transcriptome and protein profiles differed in time depending on the effector used. The expression of other peroxidase genes revealed a significant variability, so one can propose the specific roles of these enzymes in fungal development and lifestyle.

Increased delignification by white rot fungi after pressure refining Miscanthus

Pressure refining, a pulp making process to separate fibres of lignocellulosic materials, deposits lignin granules on the surface of the fibres that could enable increased access to lignin degrading enzymes. Three different white rot fungi were grown on pressure refined (at 6 bar and 8 bar) and milled Miscanthus. Growth after 28 days showed highest biomass losses on milled Miscanthus compared to pressure refined Miscanthus. Ceriporiopsis subvermispora caused a significantly higher proportion of lignin removal when grown on 6 bar pressure refined Miscanthus compared to growth on 8 bar pressure refined Miscanthus and milled Miscanthus. RM22b followed a similar trend but Phlebiopsis gigantea SPLog6 did not. Conversely, C. subvermispora growing on pressure refined Miscanthus revealed that the proportion of cellulose increased. These results show that two of the three white rot fungi used in this study showed higher delignification on pressure refined Miscanthus than milled Miscanthus.

Solid state fermentation of olive mill residues by wood- and dung-dwelling Agaricomycetes: effects on peroxidase production, biomass development and phenol phytotoxicity

The in vivo conversion of dry olive mill residue (DOR) by wood- and dung-dwelling fungi - Auricularia auricula-judae, Bjerkandera adusta and Coprinellus radians - increases peroxidase secretion up to 3.2-3.5-fold (∼1.3, 3.5 and 7.0 Ug(-1) DOR for dye-decolorizing peroxidase, manganese peroxidase and aromatic peroxygenases, respectively). The incubation of DOR with these fungi produced a sharp decrease in total phenolic content (100% within 4 wk), a reduction in phytotoxicity as well as a certain degree of plant growth caused by the stimulating effect of fungal-treated DOR. These findings correlate with a characteristic shift in the fragmentation pattern of water-soluble aromatics (detected at 280 nm) from low (0.2, 1.5 and 2.2 kDa, respectively) to high molecular mass (35 to >200 kDa), which demonstrates the presence of a polymerization process. Phenol-rich agricultural residues are a useful tool for enzyme expression and production studies of peroxidase-producing Agaricomycetes which could make DOR a valuable organic fertilizer.

Molecular characterization of manganese peroxidases from white-rot fungus Polyporus brumalis

The cDNAs of six manganese-dependent peroxidases (MnPs) were isolated from white-rot fungus Polyporus brumalis. The MnP proteins shared similar properties with each other in terms of size (approximately 360-365 amino acids) and primary structure, showing 62-96 % amino acid sequence identity. RT-PCR analysis indicated that these six genes were predominantly expressed in shallow stationary culture (SSC) in a liquid medium. Gene expression was induced by treatment with dibutyl phthalate (DBP) and wood chips. Expression of pbmnp4 was strongly induced by both treatments, whereas that of pbmnp5 was induced only by DBP, while pbmnp6 was induced by wood chips only. Then, we overexpressed pbmnp4 in P. brumalis under the control of the GPD promoter. Overexpression of pbmnp4 effectively increased MnP activity; the transformant that had the highest MnP activity also demonstrated the most effective decolorization of Remazol Brilliant Blue R dye. Identification of MnP cDNAs can contribute to the efficient production of lignin-degradation enzymes and may lead to utilization of basidiomycetous fungi for degradation of lignin and numerous recalcitrant xenobiotics.

Effect of copper, nutrient nitrogen, and wood-supplement on the production of lignin-modifying enzymes by the white-rot fungus Phlebia radiata

Production of the oxidoreductive lignin-modifying enzymes - lignin and manganese peroxidases (MnPs), and laccase - of the white-rot basidiomycete Phlebia radiata was investigated in semi-solid cultures supplemented with milled grey alder or Norway spruce and charcoal. Concentrations of nutrient nitrogen and Cu-supplement varied also in the cultures. According to extracellular activities, production of both lignin peroxidase (LiP) and MnP was significantly promoted with wood as carbon source, with milled alder (MA) and low nitrogen (LN) resulting with the maximal LiP activities (550 nkat l(-1)) and noticeable levels of MnP (3 μkat l(-1)). Activities of LiP and MnP were also elevated on high nitrogen (HN) complex medium when supplemented with spruce and charcoal. Maximal laccase activities (22 and 29 μkat l(-1)) were obtained in extra high nitrogen (eHN) containing defined and complex media supplemented with 1.5 mM Cu(2+). However, the nitrogen source, either peptone or ammonium nitrate and asparagine, caused no stimulation on laccase production without Cu-supplement. This is also the first report to demonstrate a new, on high Cu(2+) amended medium produced extracellular laccase of P. radiata with pI value of 4.9, thereby complementing our previous findings on gene expression, and cloning of a second laccase of this fungus.

Fungal laccase, manganese peroxidase and lignin peroxidase: gene expression and regulation

Extensive research efforts have been dedicated to characterizing expression of laccases and peroxidases and their regulation in numerous fungal species. Much attention has been brought to these enzymes broad substrate specificity resulting in oxidation of a variety of organic compounds which brings about possibilities of their utilization in biotechnological and environmental applications. Research attempts have resulted in increased production of both laccases and peroxidases by the aid of heterologous and homologous expression. Through analysis of promoter regions, protein expression patterns and culture conditions manipulations it was possible to compare and identify common pathways of these enzymes' production and secretion. Although laccase and peroxidase proteins have been crystallized and thoroughly analyzed, there are still a lot of questions remaining about their evolutionary origin and the physiological functions. This review describes the present understanding of promoter sequences and correlation between the observed regulatory effects on laccase, manganese peroxidase and lignin peroxidase genes transcript levels and the presence of specific response elements.

Effect of manganese on the secretion of manganese-peroxidase by the basidiomycete Ceriporiopsis subvermispora

The ligninolytic machinery of the widely used model fungus Ceriporiopsis subvermispora includes the enzymes manganese-peroxidase (MnP) and laccase (Lcs). In this work the effect of Mn(II) on the secretion of MnP was studied. Cultures grown in the absence of Mn(II) showed high levels of mnp transcripts. However, almost no MnP enzyme was detected in the extracellular medium, either by enzymatic activity assays or Western blot hybridizations. In the corresponding mycelia, immuno-electron microscopy experiments showed high levels of MnP enzyme within intracellular compartments. These results suggest that in addition to its well-known effect on transcription regulation of mnp genes, manganese influences secretion of MnP to the extracellular medium. Experiments carried out in the presence of cycloheximide confirmed that the metal is required to secrete MnP already synthesized and retained within the cell.

Hydroquinone and HO differentially affect the ultrastructure and expression of ligninolytic genes in the basidiomycete Ceriporiopsis subvermispora

The biodegradation of lignin is a highly oxidative process in which various oxidases and peroxidases play a major role. During lignin decay, the generation of aromatic compounds and reactive oxygen species leads to oxidative stress. In this work, the effect of the oxidative compounds H(2)O(2) and hydroquinone in the ligninolytic fungus Ceriporiopsis subvermispora was studied, both at the ultrastructural and at the transcriptional level. Transmission electron microscopy revealed the presence of microvesicles and extensive cytoplasm degeneration after incubation with hydroquinone, but not with H(2)O(2). Studies of the intracellular redox state of the fungus showed that hydroquinone causes a transient decrease in the reduced glutathione/oxidized glutathione (GSH/GSSG) ratio and an increase in the glutathione-S-transferase mRNA levels. These results suggest that hydroquinone produces oxidative stress in this microorganism. On the other hand, it was observed that hydroquinone, but not H(2)O(2), affects Mn-dependent peroxide and laccase transcripts levels. We propose that the mechanism by which the fungus reacts against oxidative stress contributes to its selectivity toward lignin during wood decay.

Analysis of manganese-regulated gene expression in the ligninolytic basidiomycete Ceriporiopsis subvermispora

In this work, we explore the use of the unbiased cDNA-AFLP strategy to identify genes involved in Mn(2+) homeostasis in Ceriporiopsis subvermispora. In this ligninolytic white-rot fungus, whose genome has not yet been sequenced, three Mn peroxidase genes responding to Mn(2+) have been characterized. Using cDNA-AFLP to identify transcript-derived fragments (TDFs), a total of 37 differentially expressed cDNA fragments were identified by comparing band intensities among cDNA-AFLP patterns obtained from mycelia from cultures supplemented with different concentrations of Mn(2+). Of 21 differentially expressed TDFs, nine were classified as upregulated, five as downregulated and seven as unregulated. Of these, six upregulated and two downregulated TDFs were selected for further characterization. The expected TDFs for the known Mn peroxidases were not isolated, but several genes encoding proteins related to protein sorting, storage and excretion of excess Mn(2+) were identified. Transcripts induced under Mn(2+) supplementation exhibited homologies to the elongation factor eEF3, a HDEL sequence binding protein and the ARD1 subunit of the N-acetyltransferase complex, among others. Overall, the results obtained in this study suggest a complex picture of Mn(2+) homeostasis and provide the possibility to search for common regulatory elements in the promoters of the novel putatively identified genes.

Saline-dependent regulation of manganese peroxidase genes in the hypersaline-tolerant white rot fungus Phlebia sp. strain MG-60

The expression pattern of manganese peroxidases (MnPs) in nitrogen-limited cultures of the saline-tolerant fungus Phlebia sp. strain MG-60 is differentially regulated under hypersaline conditions at the mRNA level. When MG-60 was cultured in nitrogen-limited medium (LNM) containing 3% (wt/vol) sea salts (LN-SSM), higher activity of MnPs was observed than that observed in normal medium (LNM). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis demonstrated that two MnP isoenzymes were de novo synthesized in the culture of LN-SSM. Three MnP-encoding genes (MGmnp1, MGmnp2, and MGmnp3) were isolated by reverse transcription (RT)-PCR and rapid amplification of cDNA ends PCR techniques. The corresponding isozymes were identified by peptide mass fingerprinting analysis. MnP isozymes encoded by MGmnp2 and MGmnp3 were observed mainly in LN-SSM. Real-time RT-PCR analysis revealed high levels of MGmnp2 and MGmnp3 transcripts in LN-SSM 48 h after the addition of 2% NaCl. The induction of MnP production and the accumulation of gene transcripts by saline were well correlated in the presence of Mn(2+). However, in the absence of Mn(2+), there was no clear correlation between mnp transcripts levels and MnP activity, suggesting posttranscriptional regulation by Mn(2+).

Cloning and characterization of the genes encoding the high-affinity iron-uptake protein complex Fet3/Ftr1 in the basidiomycete Phanerochaete chrysosporium

MCO1, a multicopper oxidase from Phanerochaete chrysosporium exhibiting strong ferroxidase activity, has recently been described. This enzyme shows biochemical and structural similarities with the yeast Fet3p, a type I membrane glycoprotein that efficiently oxidizes Fe(II) to Fe(III) for its subsequent transport to the intracellular compartment by the iron permease Ftr1p. The genome database of P. chrysosporium was searched to verify whether it includes a canonical fet3 in addition to mco1, and single copies of fet3 and ftr1 orthologues were found, separated by a divergent promoter. Pc-fet3 encodes a 628 aa protein that exhibits overall identities of about 40 % with other reported Fet3 proteins. In addition to a secretion signal, it has a C-terminal transmembrane domain, characteristic of these cell-surface-attached ferroxidases. Structural modelling of Pc-Fet3 revealed that the active site has all the residues known to be essential for ferroxidase activity. Pc-ftr1 encodes a 393 aa protein that shows about 38 % identity with several Ftr1 proteins from ascomycetes. Northern hybridization studies showed that the mRNA levels of both genes are reduced upon supplementation of the growth medium with iron, supporting the functional coupling of Fet3 and Ftr1 proteins in vivo.

Manganese affects the production of laccase in the basidiomycete Ceriporiopsis subvermispora

The authors have previously identified and characterized lcs, a gene encoding laccase in the white-rot basidiomycete Ceriporiopsis subvermispora. In this work, the effect of Mn2+ in the production of extracellular laccase in liquid cultures of this fungus has been assessed. It was observed that at low (0-10 microM) concentrations of Mn2+, high titers of lcs-mRNA were obtained, whereas at high (160-194 microM) concentrations of this metal ion, transcripts levels decreased markedly. This phenomenon was observed at different days of growth. On the other hand, Cu2+ or Ag+, but not Zn2+ or Cd2+, led to an accumulation of lcs transcripts only in cultures grown in the absence of Mn2+. A dramatic increase in lcs transcript levels was also obtained with syringic acid, a lignin-related aromatic compound. This effect was more pronounced in cultures lacking Mn2+. In the course of these studies it was observed that Mn2+ stimulates mycelium growth. Thus, although extracellular laccase activity appeared higher in cultures containing 160 or 194 microM Mn2+, i.e. when lcs transcripts were lower, a correlation between lcs-mRNA levels and enzymatic activity was observed when values of the latter were corrected by the amount of mycelium present in the cultures.

Extracellular oxidative systems of the lignin-degrading Basidiomycete Phanerochaete chrysosporium

The US Department of Energy has assembled a high quality draft genome of Phanerochaete chrysosporium, a white rot Basidiomycete capable of completely degrading all major components of plant cell walls including cellulose, hemicellulose and lignin. Hundreds of sequences are predicted to encode extracellular enzymes including an impressive number of oxidative enzymes potentially involved in lignocellulose degradation. Herein, we summarize the number, organization, and expression of genes encoding peroxidases, copper radical oxidases, FAD-dependent oxidases, and multicopper oxidases. Possibly relevant to extracellular oxidative systems are genes involved in posttranslational processes and a large number of hypothetical proteins.

Differential regulation of manganese peroxidases and characterization of two variable MnP encoding genes in the white-rot fungus Physisporinus rivulosus

Manganese peroxidase (MnP) production in the white-rot basidiomycete Physisporinus rivulosus T241i was studied. Separate MnP isoforms were produced in carbon-limited liquid media supplemented with Mn(2+), veratryl alcohol, or sawdust. The isoforms had different pH ranges for the oxidation of Mn(2+) and 2,6-dimethoxyphenol. Although lignin degradation by white-rot fungi is often triggered by nitrogen depletion, MnPs of P. rivulosus were efficiently produced also in the presence of high-nutrient nitrogen, especially in cultures supplemented with veratryl alcohol. Two MnP encoding genes, mnpA and mnpB, were identified, and their corresponding cDNAs were characterized. Structurally, the genes showed marked dissimilarity, and the expression of the two genes implicated quantitative variation and differential regulation in response to manganese, veratryl alcohol, or sawdust. The variability in regulation and properties of the isoforms may widen the operating range for efficient lignin degradation by P. rivulosus.

Lignin modifying enzymes of Coriolopsis polyzona and their role in olive oil mill wastewaters decolourisation

In order to decolourise olive oil mill wastewaters (OOMW) efficiently, production and differential induction of ligninolytic enzymes by the white rot Coriolopsis polyzona, were studied by varying growth media composition and/or inducer addition. Among various possible inducers, veratryl alcohol appeared to be the most efficient to enhance specific productions of lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase by a factor of 18.5, 20.8 and 55, respectively. Ligninolytic enzymes were better produced in glucose based medium with a low nitrogen level (2.2 mM) under O2 atmosphere. The addition of 5 mM veratryl alcohol resulted in a maximal production of LiP, whereas maximal MnP and laccase were obtained at 10 mM. LiP production was totally repressed in presence of 100 microM Mn2+. The extrapolation of these conditions on OOMW based media was carried out at different effluent dilutions and the possible role of the different ligninolytic enzymes in OOMW decolourisation was studied. A better effluent decolourisation was obtained under LiP induction condition (5 mM veratryl alcohol) than when LiP was repressed (100 microM Mn2+). Furthermore, high levels of laccase had a detrimental effect on OOMW decolourisation concomitant to the formation of soluble polymeric aromatic compounds.

Expression on wood, molecular cloning and characterization of three lignin peroxidase (LiP) encoding genes of the white rot fungus Phlebia radiata

Lignin peroxidase (LiP) is the first enzyme connected to oxidative breakdown of the aromatic plant heteropolymer lignin and related xenobiotics. However, this extracellular enzyme has been described in only a few species of wood-decaying basidiomycetous fungi. The white rot basidiomycete Phlebia radiata 79 readily produces a versatile set of lignin-oxidizing enzymes including lignin and manganese peroxidases (LiPs and MnPs) and laccases. Here we describe genomic and primary structure of two new LiP-encoding genes, Pr-lip1 and Pr-lip4, and genomic characterization for isozyme LiP3/LIII of P. radiata, encoded by the gene depicted Pr-lip3. Pr-lip1 and Pr-lip4 code for 370- and 361-amino-acid long proteins beginning with 26- and 24-amino-acid secretion pre-propeptides, respectively. Translated LiP1 and LiP4 share the highest protein sequence identity (74 and 86%) with P. radiata LiP3, and 70% identity with the one deduced LiP from Bjerkandera adusta. The three P. radiata LiP sequences form a coherent phylogenetic cluster, which is further supported by similarities within gene organization interrupted by 11-introns. To find out the significance of LiP upon fungal growth on natural lignocellulose, such as wood, we studied ligninolytic gene expression on hardwood (milled alder) and softwood (spruce chips). All the LiP-encoding genes were expressed on wood with predominance of Pr-lip3 transcript abundance, in particular on spruce wood chips, where also time-dependent expression of the multiple lip genes was observed.

The nop gene from Phanerochaete chrysosporium encodes a peroxidase with novel structural features

Inspection of the genome of the ligninolytic basidiomycete Phanerochaete chrysosporium revealed an unusual peroxidase_like sequence. The corresponding full length cDNA was sequenced and an archetypal secretion signal predicted. The deduced mature protein (NoP, novel peroxidase) contains 295 aa residues and is therefore considerably shorter than other Class II (fungal) peroxidases, such as lignin peroxidases and manganese peroxidases. Comparative modeling of NoP was conducted using the crystal structures of Coprinus cinereus and Arthromyces ramosus peroxidases as templates. The model was validated by molecular dynamics and showed several novel structural features. In particular, NoP has only three disulfide bridges and tryptophan replaces the distal phenylalanine within the heme pocket.

Incomplete processing of peroxidase transcripts in the lignin degrading fungus Phanerochaete chrysosporium

Phanerochaete chrysosporium has been thoroughly studied as a microbial model for lignin degradation. The enzymes lignin peroxidase (LiP) and manganese peroxidase (MnP), both encoded by several genes, play the main role in the cleavage of different lignin substructures. In this work, the expression of specific LiP and MnP transcripts in liquid medium and in a wood-containing soil system was studied by reverse transcription-PCR and subsequent cloning and sequencing of the products obtained. Splice variants of different LiP and MnP transcripts were observed in wood-containing soil incubations and in liquid cultures. The processed transcripts contained different numbers of complete introns. Since the presence of stop codons in several of these introns would prevent the synthesis of active enzyme, we propose that these transcripts arise as a result of incomplete processing rather than alternative splicing. Interestingly, analysis of splice variants from mnp genes led to the identification of a fourth actively transcribed gene coding for MnP in P. chrysosporium.

Mn2+ is dispensable for the production of active MnP2 by Pleurotus ostreatus

The regulation mechanism for expression of versatile peroxidase MnP2 by the basidiomycete fungus Pleurotus ostreatus was examined using chemically defined synthetic media. Expression of MnP2 was down-regulated at the transcription level by nutrient nitrogen, e.g., NH(4)(+), arginine or urea. As is often the case with other fungal manganese peroxidases, active MnP2 was not detected when Mn(2+) was omitted from the culture, while mnp2 transcription was barely affected by Mn(2+). However, Mn(2+) can be substituted by an MnP2 substrate, Poly R-478, since active MnP2 was detected extracellularly when the compound was added to the culture without Mn(2+). Enzyme stability assays with the purified MnP2 indicated an indispensable requirement for a substrate that can be used to complete the catalytic cycle, and avoid inactivation resulting from an excess H(2)O(2). This report is the first of the Mn(2+)-independent production of an active versatile peroxidase by P. ostreatus.

Characterization of a multicopper oxidase gene cluster in Phanerochaete chrysosporium and evidence of altered splicing of the mco transcripts

A cluster of multicopper oxidase genes (mco1, mco2, mco3, mco4) from the lignin-degrading basidiomycete Phanerochaete chrysosporium is described. The four genes share the same transcriptional orientation within a 25 kb region. mco1, mco2 and mco3 are tightly grouped, with intergenic regions of 2.3 and 0.8 kb, respectively, whereas mco4 is located 11 kb upstream of mco1. All are transcriptionally active, as shown by RT-PCR. Comparison of cDNAs and the corresponding genomic sequences identified 14-19 introns within each gene. Based on homology and intron composition, two subfamilies of mco sequences could be identified. The sequences have copper-binding motifs similar to ferroxidase proteins, but different from fungal laccases. Thus, these sequences constitute a novel branch of the multicopper oxidase family. Analysis of several cDNA clones obtained from poly(A) RNA revealed the presence of transcripts of various lengths. Splice variants from mco2, mco3 and mco4 were characterized. They generally exhibited the presence of one to five introns, whereas other transcripts lacked some exons. In all cases, the presence of introns leads to frame shifts that give rise to premature stop codons. In aggregate, these investigations show that P. chrysosporium possesses a novel family of multicopper oxidases which also feature clustering and incomplete processing of some of their transcripts, a phenomenon referred to in this paper as 'altered splicing'.