The laccase multi-gene family in Coprinopsis cinerea has seventeen different members that divide into two distinct subfamilies

Deciphering the distribution and types of Multicopper oxidases in Basidiomycota fungi

Multicopper oxidases (MCOs) comprise different types of enzymes widely distributed in nature with quite diverse functions. Laccases are the most interesting MCOs from a biotechnological point of view, particularly those secreted by ligninolytic Basidiomycota fungi due to their versatility to oxidize lignin and a variety of aromatic substrates. The term "laccase" has been broadly (but sometimes erroneously) applied due to their low sequence homology and some overlapping activities with other MCO groups. We examined the distribution and phylogenetic relationships of MCOs in Basidiomycota fungi aiming to provide a complete and precise picture of the different MCO types across the division, including fungal orders phylogenetically distant from those typically studied. The phylogenetic tree revealed eight clusters of MCOs, each sharing common sequence/structural features. With this information we classified the MCOs in eight groups and described their distinctive amino acid residues. These eight MCO types are: laccases (LAC), ferroxidases (FOX), laccase-ferroxidases (LAC-FOX), ascorbate oxidases (AO), fungal pigment MCOs, and three new groups of laccase-like enzymes or "atypical laccases" related to but different from laccases sensu stricto, namely novel laccases (NLAC), new MCO (NMCO) and new laccases with potential ferroxidase activity (NLF). Additionally, several MCOs already described in the literature were reclassified into the updated groups.

An apoptosis-inducing factor controls programmed cell death and laccase expression during fungal interactions

Apoptotic-like programmed cell death (PCD) is one of the main strategies for fungi to resist environmental stresses and maintain homeostasis. The apoptosis-inducing factor (AIF) has been shown in different fungi to trigger PCD through upregulating reactive oxygen species (ROS). This study identified a mitochondrial localized AIF homolog, CcAIF1, from Coprinopsis cinerea monokaryon Okayama 7. Heterologous overexpression of CcAIF1 in Saccharomyces cerevisiae caused apoptotic-like PCD of the yeast cells. Ccaif1 was increased in transcription when C. cinerea interacted with Gongronella sp. w5, accompanied by typical apoptotic-like PCD in C. cinerea, including phosphatidylserine externalization and DNA fragmentation. Decreased mycelial ROS levels were observed in Ccaif1 silenced C. cinerea transformants during cocultivation, as well as reduction of the apoptotic levels, mycelial growth, and asexual sporulation. By comparison, Ccaif1 overexpression led to the opposite phenotypes. Moreover, the transcription and expression levels of laccase Lcc9 decreased by Ccaif1 silencing but increased firmly in Ccaif1 overexpression C. cinerea transformants in coculture. Thus, in conjunction with our previous report that intracellular ROS act as signal molecules to stimulate defense responses, we conclude that CcAIF1 is a regulator of ROS to promote apoptotic-like PCD and laccase expression in fungal-fungal interactions. In an axenic culture of C. cinerea, CcAIF1 overexpression and H2O2 stimulation together increased laccase secretion with multiplied production yield. The expression of two other normally silent isozymes, Lcc8 and Lcc13, was unexpectedly triggered along with Lcc9. KEY POINTS: • Mitochondrial CcAIF1 induces PCD during fungal-fungal interactions • CcAIF1 is a regulator of ROS to trigger the expression of Lcc9 for defense • CcAIF1 overexpression and H2O2 stimulation dramatically increase laccase production.

Catalytic function of the laccase enzyme in response to chlorpyrifos and 2,4-dichlorophenoxyacetic acid: behavior in controlled and simulated environments

Enzymes secreted by white-rot fungi, such as laccase, offer a promising solution for treating xenobiotic compounds dangerous to the environment and human health. This study aimed to perform a comprehensive analysis of the tolerance of Pleurotus pulmonarius LBM 105 and its laccase activity toward the pesticides 2,4-D and chlorpyrifos both in vitro and in silico. The fungal strain was able to grow in different concentrations of the pesticides, showing evident morphological alterations. Laccase activity and a 53 kDa electromorph were present in all treatments, showing significant stability with peak activity achieved at a pH of 5.6 and within a temperature range of 50-60 °C. Three laccase genes were mapped, annotated, and characterized from the genome. PplacI obtained better structural validation and affinity energy of - 5.05 and - 7.65 kcal mol-1 with 2,4-D and chlorpyrifos, respectively. The Molecular Mechanics/Poisson-Boltzmann Surface Area analysis at 250 ns confirmed the docking results, revealing the existence of stronger hydrophobic interactions between laccase and chlorpyrifos and highlighting the importance of the Phe341 residue in stabilizing both complexes. Understanding the impact of pesticides on laccase's catalytic function is key to formulating and applying future biotechnological strategies with this enzyme.

Bifunctional Sesquiterpene/Diterpene Synthase Agr2 from Cyclocybe aegerita Gives Rise to the Novel Diterpene Cyclocybene

Cyclocybe aegerita is a model mushroom belonging to the fungal phylum Basidiomycota. Among others, C. aegerita is known for its diverse terpenome, containing various volatile and nonvolatile terpenes and terpenoids. Here, we deepen the knowledge on their biosynthetic pathways by studying the terpene synthase Agr2 in detail. In contrast to previous studies, the heterologous production of Agr2 in the agaric host Coprinopsis cinerea revealed the production of two terpenes, one of which was the already known sesquiterpene viridiflorene. The other one was a so far unknown diterpene that had to be isolated and purified by means of preparative RP-HPLC for structure elucidation. 1D- and 2D-NMR experiments revealed the compound as the novel diterpene cyclocybene, pointing to the bifunctionality of Agr2 to produce both a sesquiterpene and a diterpene.

Is Laccase derived from Pleurotus ostreatus effective in microplastic degradation? A critical review of current progress, challenges, and future prospects

Exploration of Pleurotus ostreatus as a biological agent in the degradation of persistent plastics like polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate, revealing a promising avenue toward mitigating the environmental impacts of plastic pollution. Leveraging the intrinsic enzymatic capabilities of this fungus, mainly its production of laccase, presents a sustainable and eco-friendly approach to breaking down complex polymer chains into less harmful constituents. This review focused on enhancements in the strain's efficiency through genetic engineering, optimized culture conditions, and enzyme immobilization to underscore the potential for scalability and practical application of this bioremediation process. The utilization of laccase from P. ostreatus in plastic waste management demonstrates a vital step forward in pursuing sustainable environmental solutions. By using the potential of fungal bioremediation, researchers can move closer to a future in which the adverse effects of plastic pollution are significantly mitigated, benefiting the health of our planet and future generations.

Biocatalytic Synthesis of Nitrile-Bearing All-Carbon Quaternary Stereocenters

The synthesis of all-carbon quaternary stereocenters containing nitriles is a very important and challenging subject in organic chemistry. We used a biocatalytic approach under mild conditions to obtain new derivatives of these scaffolds by oxidation of catechols by Myceliophthora thermophila laccase (Novozym 51003) to afford o-quinones and 1,4-addition of a series of carbon nucleophiles containing tertiary alkyle nitriles to these intermediates. Using this approach, α-cyano carbonyls bearing a quaternary stereocenter were also prepared. Finally, the yields for the prepared compounds were 72-94%.

Genome-wide analysis of the Pleurotus eryngii laccase gene (PeLac) family and functional identification of PeLac5

The laccase gene family encodes multiple isozymes that are crucial for the degradation of substrates and the regulation of developmental processes in fungi. Pleurotus eryngii is an important edible and medicinal fungus belonging to the Basidiomycota phylum and can grow on a variety of natural substrates. In the present study, genome-wide profiling of P. eryngii identified 10 genes encoding its laccase isoenzymes. Conservative sequence analysis demonstrated that all PeLacs possess classical laccase structural domains. Phylogenetic analysis yielded four major subgroups, the members of which are similar with respect to conserved gene organization, protein domain architecture, and consensus motifs. The 10 PeLacs formed three groups together with 12 PoLacs in Pleurotus ostreatus, indicating that they share a high level of evolutionary homology. Cis-responsive element analysis implied that PeLacs genes play a role in growth and development and lignocellulose degradation. Targeted overexpression of PeLac5 reduced the time to primordia formation and their development to fruiting bodies. Gene expression patterns in the presence of different lignocellulosic substrates indicate that three PeLacs genes (2, 4, and 9) are key to lignocellulose degradation. This work presents the first inventory of laccase genes in P. eryngii and preliminarily explores their functions, which may help to uncover the manner by which these proteins utilize substrates.

Genome-wide study of Cerrena unicolor 87613 laccase gene family and their mode prediction in association with substrate oxidation

BACKGROUND

Laccases are green biocatalysts with wide industrial applications. The study of efficient and specific laccase producers remains a priority. Cerrena species have been shown to be promising basidiomycete candidates for laccase production. Although two sets of Cerrena genome data have been publicly published, no comprehensive bioinformatics study of laccase gene family in C. unicolor has been reported, particularly concerning the analysis of their three-dimensional (3D) structures and molecular docking to substrates, like ABTS and aflatoxin B1 (AFB1).

RESULTS

In this study, we conducted a comprehensive genome-wide analysis of laccase gene family in C. unicolor 87613. We identified eighteen laccase genes (CuLacs) and classified them into three clades using phylogenetic analysis. We characterized these laccases, including their location in contig 5,6,9,12,15,19,26,27, gene structures of different exon-intron arrangements, molecular weight ranging from 47.89 to 141.41 kDa, acidic pI value, 5-15 conserved protein motifs, signaling peptide of extracellular secretion (harbored by 13 CuLacs) and others. In addition, the analysis of cis-acting element in laccase promoters indicated that the transcription response of CuLac gene family was regulatable and complex under different environmental cues. Furthermore, analysis of transcription pattern revealed that CuLac8, 12 and CuLac2, 13 were the predominant laccases in response to copper ions or oxidative stress, respectively. Finally, we focused on the 3D structure analysis of CuLac proteins. Seven laccases with extra transmembrane domains or special sequences were particularly interesting. Predicted structures of each CuLac protein with or without these extra sequences showed altered interacting amino acid residues and binding sites, leading to varied affinities to both ABTS and AFB1. As far as we know, it is the first time to discuss the influence of the extra sequence on laccase's affinity to substrates.

CONCLUSIONS

Our findings provide robust genetic data for a better understanding of the laccase gene family in C. unicolor 87613, and create a foundation for the molecular redesign of CuLac proteins to enhance their industrial applications.

Comparative genomic analysis of five coprinoid mushrooms species

Although coprinoid mushrooms are widely known for the phenomenon of deliquescence and production of fungal laccases and extracellular peroxygenases, the genome structure and genetic diversity of coprinoid mushroom species have not been extensively studied. To reveal the genomic structure and diversity in coprinoid mushroom species, the genomes of five coprinoid mushroom species were compared and analyzed. A total of 24,303 orthologous gene families, including 89,462 genes, were identified in the five species. The numbers of core, softcore, dispensable, and private genes were 5617 (25.6%), 1628 (7.4%), 2083 (9.5%), and 12,574 (57.4%), respectively. Differentiation time analysis revealed that Coprinellus micaceus and Coprinellus angulatus differentiated approximately 181.0 million years ago. Coprinopsis cinerea and Coprinopsis marcescibilis differentiated approximately 131.0 million years ago, and they were differentiated from Candolleomyces aberdarensis approximately 176.0 million years ago. Gene family contraction and expansion analyses showed that 1465 genes and 532 gene families were expanded, and 95 genes and 134 gene families were contracted. Ninety-five laccase-coding genes were detected in the five species, and the distribution of the laccase-coding genes in the five species was not uniform. These data provide a reference for a deeper understanding of the genetic structure of the genomes of coprinoid mushroom species. Furthermore, this study provides a reference for follow-up studies on the genome structure of coprinoid mushroom species and the diversity of specific functional genes.

Increased levels of cell wall degrading enzymes and peptidases are associated with aggressiveness in a virulent isolate of Pyrenophora teres f. maculata

Pyrenophora teres f. maculata (Ptm) is a fungal pathogen that causes the spot form of net blotch on barley and leads to economic losses in many of the world's barley-growing regions. Isolates of Ptm exhibit varying levels of aggressiveness that result in quantifiable changes in the severity of the disease. Previous research on plant-pathogen interactions has shown that such divergence is reflected in the proteome and secretome of the pathogen, with certain classes of proteins more prominent in aggressive isolates. Here we have made a detailed comparative analysis of the secretomes of two Ptm isolates, GPS79 and E35 (highly and mildly aggressive, respectively) using a proteomics-based approach. The secretomes were obtained in vitro using media amended with barley leaf sections. Secreted proteins therein were harvested, digested with trypsin, and fractionated offline by HPLC prior to LC-MS in a high-resolution instrument to obtain deep coverage of the proteome. The subsequent analysis used a label-free quantitative proteomics approach with relative quantification of proteins based on precursor ion intensities. A total of 1175 proteins were identified, 931 from Ptm and 244 from barley. Further analysis revealed 160 differentially abundant proteins with at least a two-fold abundance difference between the isolates, with the most enriched in the aggressive GPS79 secretome. These proteins were mainly cell-wall (carbohydrate) degrading enzymes and peptidases, with some oxidoreductases and other pathogenesis-related proteins also identified, suggesting that aggressiveness is associated with an improved ability of GPS79 to overcome cell wall barriers and neutralize host defense responses.

Laccase: Various types and applications

Laccase belongs to the polyphenol oxidase family and is very important in removing environmental pollutants due to its structural and functional properties. Recently, the ability of laccase to oxidize phenolic and nonphenolic substances has been considered by many researchers. This enzyme's application scope includes a broad range of chemical processes and industrial usages, such as bioremediation, nanobiotechnology, woodworking industries, bleaching of paper pulp, dyeing in the textile industry, biotechnological uses in food industries, biorefining, detoxification from wastewater, production of organic matter from phenolic and amine substrates, and biofuels. Although filamentous fungi produce large amounts of laccase, high-yield industrial-scale production of laccase is still faced with many problems. At present, researchers are trying to increase the efficiency and productivity and reduce the final price of laccase by finding suitable microorganisms and improving the process of production and purification of laccase. This article reviews the introduction of laccase, its properties, production processes, and the effect of various factors on the enzyme's stability and activity, and some of its applications in various industries.

pH Distribution along Growing Fungal Hyphae at Microscale

Creating unique microenvironments, hyphal surfaces and their surroundings allow for spatially distinct microbial interactions and functions at the microscale. Using a microfluidic system and pH-sensitive whole-cell bioreporters (Synechocystis sp. PCC6803) attached to hyphae, we spatially resolved the pH along surfaces of growing hyphae of the basidiomycete Coprinopsis cinerea. Time-lapse microscopy analysis of ratiometric fluorescence signals of >2400 individual bioreporters revealed an overall pH drop from 6.3 ± 0.4 (n = 2441) to 5.0 ± 0.3 (n = 2497) within 7 h after pH bioreporter loading to hyphal surfaces. The pH along hyphal surfaces varied significantly (p < 0.05), with pH at hyphal tips being on average ~0.8 pH units lower than at more mature hyphal parts near the entrance of the microfluidic observation chamber. Our data represent the first dynamic in vitro analysis of surface pH along growing hyphae at the micrometre scale. Such knowledge may improve our understanding of spatial, pH-dependent hyphal processes, such as the degradation of organic matter or mineral weathering.

Enzymatic Oxidation of Ca-Lignosulfonate and Kraft Lignin in Different Lignin-Laccase-Mediator-Systems and MDF Production

Laccase-mediator-oxidized lignin offers replacement for conventional chemical binders to produce fiberboards. Compared to the previously reported laccase–mediator system (LMS), a lignin-laccase-mediator-system (LLMS) has an advantage in that it requires much shorter fiber-enzyme incubation time due to significantly increased redox reactions. However, the cost of regularly applying laccase on an industrial scale is currently too high. We have employed CcLcc5 from cultures of the basidiomycete Coprinopsis cinerea as a novel basi-laccase (a CAZy subfamily AA1_1 laccase) in medium-density fiberboard (MDF) production, in comparison to the commercial formulation Novozym 51003 with recombinantly produced asco-laccase MtL (a CAZy subfamily AA1_3 laccase-like multicopper oxidase from the ascomycete Myceliophthora thermophila). With the best-performing natural mediator 2,6-dimethoxyphenol (DMP), unpurified CcLcc5 was almost as good as formulated Novozym 51003 in increasing the molecular weight (MW) of the technical lignins tested, the hydrophilic high-MW Ca-lignosulfonate and the hydrophobic low-MW kraft lignin (Indulin AT). Oxygen consumption rates of the two distantly related, poorly conserved enzymes (31% sequence identity) with different mediators and lignosulfonate were also comparable, but Indulin AT significantly reduced the oxidative activity of Novozym 51003 unlike CcLcc5, regardless of the mediator used, either DMP or guaiacol. Oxygen uptake by both laccases was much faster with both technical lignins with DMP than with guaiacol. In case of lignosulfonate and DMP, 20–30 min of incubation was sufficient for full oxygen consumption, which fits in well in time with the usual binder application steps in industrial MDF production processes. LLMS-bonded MDF was thus produced on a pilot-plant scale with either crude CcLcc5 or Novozym 51003 at reduced enzyme levels of 5 kU/kg absolutely dry wood fiber with lignosulfonate and mediator DMP. Boards produced with CcLcc5 were comparably good as those made with Novozym 51003. Boards reached nearly standard specifications in internal bond strength (IB) and modulus of rupture (MOR), while thickness swelling (TS) was less good based on the hydrophilic character of lignosulfonate. LLMS-bonded MDF with Indulin AT and DMP performed better in TS but showed reduced IB and MOR values.

Improvement of laccase activity by silencing PacC in Ganoderma lucidum

Ganoderma lucidum is a representative white-rot fungus that has great potential to degrade lignocellulose biomass. Laccase is recognized as a class of the most important lignin-degrading enzymes in G. lucidum. However, the comprehensive regulatory mechanisms of laccase are still lacking. Based on the genome sequence of G. lucidum, 15 laccase genes were identified and their encoding proteins were analyzed in this study. All of the laccase proteins are predicted to be multicopper oxidases with conserved copper-binding domains. Most laccase proteins were secreted enzymes in addition to Lac14 in which the signal peptide could not be predicted. The activity of all laccases showed the highest level at pH 3.0 or pH 7.0, with total laccase activity of approximately 200 U/mg protein. Silencing PacC resulted in a 5.2 fold increase in laccase activity compared with WT. Five laccase genes (lac1, lac6, lac9, lac10 and lac14) showed an increased transcription levels (approximately 1.5-5.6 fold) in the PacC-silenced strains versus that in WT, while other laccase genes were downregulated or unchanged. The extracellular pH value was about 3.1, which was more acidic in the PacC-silenced strains than in the WT (pH 3.5). Moreover, maintaining the fermentation pH resulted in a downregulation of laccase activity which is induced by silencing PacC. Our findings indicate that in addition to its function in acidification of environmental pH, PacC plays an important role in regulating laccase activity in fungi.

Illuminate the hidden: in vivo mapping of microscale pH in the mycosphere using a novel whole-cell biosensor

The pH of an environment is both a driver and the result of diversity and functioning of microbial habitats such as the area affected by fungal hyphae (mycosphere). Here we used a novel pH-sensitive bioreporter, Synechocystis sp. PCC6803_peripHlu, and ratiometric fluorescence microscopy, to spatially and temporally resolve the mycosphere pH at the micrometre scale. Hyphae of the basidiomycete Coprionopsis cinerea were allowed to overgrow immobilised and homogeneously embedded pH bioreporters in an agarose microcosm. Signals of >700 individual cells in an area of 0.4 × 0.8 mm were observed over time and used to create highly resolved (3 × 3 µm) pH maps using geostatistical approaches. C. cinerea changed the pH of the agarose from 6.9 to ca. 5.0 after 48 h with hyphal tips modifying pH in their vicinity up to 1.8 mm. pH mapping revealed distinct microscale spatial variability and temporally stable gradients between pH 4.4 and 5.8 over distances of ≈20 µm. This is the first in vivo mapping of a mycosphere pH landscape at the microscale. It underpins the previously hypothesised establishment of pH gradients serving to create spatially distinct mycosphere reaction zones.

Coprinopsis cinerea uses laccase Lcc9 as a defense strategy to eliminate oxidative stress during fungal-fungal interactions

Frequently, laccases are triggered during fungal cocultivation for overexpression. The function of these activated laccases during coculture has not been clarified. Previously, we reported that Gongronella sp. w5 (w5) (Mucoromycota, Mucoromycetes) specifically triggered the laccase Lcc9 overexpression in Coprinopsis cinerea (Basidiomycota, Agaricomycetes). To systematically analyze the function of the overexpressed laccase during fungal interaction, C. cinerea mycelia before and after the initial Lcc9 overexpression were chosen for transcriptome analysis. Results showed that accompanied by specific utilization of fructose as carbohydrate substrate, oxidative stress derived from antagonistic compounds secreted by w5 appears to be a signal critical for laccase production in C. cinerea. Reactive oxygen species (ROS) decrease in the C. cinerea wild-type strain followed the increase in laccase production and then, lcc9 transcription and laccase activity stopped. By comparison, increased H₂O₂ content and mycelial ROS levels were observed during the entire cocultivation in lcc9 silenced C. cinerea strains. Moreover, lcc9 silencing slowed down the C. cinerea mycelial growth, affected hyphal morphology, and decreased the asexual sporulation in coculture. Our results showed that intracellular ROS acted as signal molecules to stimulate defense responses by C. cinerea with the expression of oxidative stress response regulator Skn7 and various detoxification proteins. Lcc9 takes part as a defense strategy to eliminate oxidative stress during the interspecific interaction with w5. Importance: The overproduction of laccase during interspecific fungal interactions is notoriously known. However, the exact role of the up-regulated laccases remains underexplored. Based on comparative transcriptomic analysis of C. cinerea and gene silencing of laccase Lcc9, here we show that oxidative stress derived from antagonistic compounds secreted by Gongronella sp. w5 was a signal critical for laccase Lcc9 production in Coprinopsis cinerea. Intracellular ROS acted as signal molecules to stimulate defense responses by C. cinerea with the expression of oxidative stress response regulator Skn7 and various detoxification proteins. Ultimately, Lcc9 takes part as a defense strategy to eliminate oxidative stress and help cell growth and development during the interspecific interaction with Gongronella sp. w5. These findings deepened our understanding of fungal interactions in their natural population and communities.

Mushroom Ligninolytic Enzymes―Features and Application of Potential Enzymes for Conversion of Lignin into Bio-Based Chemicals and Materials

Mushroom ligninolytic enzymes are attractive biocatalysts that can degrade lignin through oxido-reduction. Laccase, lignin peroxidase, manganese peroxidase, and versatile peroxidase are the main enzymes that depolymerize highly complex lignin structures containing aromatic or aliphatic moieties and oxidize the subunits of monolignol associated with oxidizing agents. Among these enzymes, mushroom laccases are secreted glycoproteins, belonging to a polyphenol oxidase family, which have a powerful oxidizing capability that catalyzes the modification of lignin using synthetic or natural mediators by radical mechanisms via lignin bond cleavage. The high redox potential laccase within mediators can catalyze the oxidation of a wide range of substrates and the polymerization of lignin derivatives for value-added chemicals and materials. The chemoenzymatic process using mushroom laccases has been applied effectively for lignin utilization and the degradation of recalcitrant chemicals as an eco-friendly technology. Laccase-mediated grafting has also been employed to modify lignin and other polymers to obtain novel functional groups able to conjugate small and macro-biomolecules. In this review, the biochemical features of mushroom ligninolytic enzymes and their potential applications in catalytic reactions involving lignin and its derivatives to obtain value-added chemicals and novel materials in lignin valorization are discussed.

Discovery of two novel laccase-like multicopper oxidases from Pleurotus citrinopileatus and their application in phenolic oligomer synthesis

BACKGROUND

Laccases and laccase-like multicopper oxidases (LMCOs) oxidize a vast array of phenolic compounds and amines, releasing water as a byproduct. Their low substrate specificity is responsible for their tremendous biotechnological interest, since they have been used for numerous applications. However, the laccases characterized so far correspond to only a small fraction of the laccase genes identified in fungal genomes. Therefore, the knowledge regarding the biochemistry and physiological role of minor laccase-like isoforms is still limited.

RESULTS

In the present work, we describe the isolation, purification and characterization of two novel LMCOs, PcLac1 and PcLac2, from Pleurotus citrinopileatus. Both LMCOs were purified with ion-exchange chromatographic methods. PcLac2 was found to oxidize a broader substrate range than PcLac1, but both LMCOs showed similar formal potentials, lower than those reported previously for laccases from white-rot fungi. Proteomic analysis of both proteins revealed their similarity with other well-characterized laccases from Pleurotus strains. Both LMCOs were applied to the oxidation of ferulic and sinapic acid, yielding oligomers with possible antioxidant activity.

CONCLUSIONS

Overall, the findings of the present work can offer new insights regarding the biochemistry and variability of low-redox potential laccases of fungal origin. Low-redox potential biocatalysts could offer higher substrate selectivity than their high-redox counterparts, and thus, they could be of applied value in the field of biocatalysis.

Alternative Splicing of Heat Shock Transcription Factor 2 Regulates the Expression of Laccase Gene Family in Response to Copper in Trametes trogii

White-rot fungi, especially Trametes strains, are the primary source of industrial laccases in bioenergy and bioremediation. Trametes strains express members of the laccase gene family with different physicochemical properties and expression patterns. However, the literature on the expression pattern of the laccase gene family in T. trogii S0301 and the response mechanism to Cu²⁺, a key laccase inducer, in white-rot fungal strains is scarce. In the present study, we found that Cu²⁺ could induce the mRNAs and proteins of the two alternative splicing variants of heat shock transcription factor 2 (TtHSF2). Furthermore, the overexpression of alternative splicing variants TtHSF2α and TtHSF2β-I in the homokaryotic T. trogii S0301 strain showed opposite effects on the extracellular total laccase activity, with the maximum laccase activity of approximately 0.6 U mL^-1 and 3.0 U mL^-1, respectively, on the eighth day, which is 0.4 and 2.3 times that of the wild type strain. Similarly, TtHSF2α and TtHSF2β-I play opposite roles in the oxidation tolerance to H₂O₂ In addition, the direct binding of TtHSF2α to the promoter regions of the representative laccase isoenzymes (TtLac1 and TtLac13) and protein-protein interactions between TtHSF2α and TtHSF2β-I were detected. Our results demonstrate the crucial roles of TtHSF2 and its alternative splicing variants in response to Cu²⁺ We believe that these findings will deepen our understanding of alternative splicing of HSFs and their regulatory mechanism of the laccase gene family in white-rot fungi.Importance The members of laccase gene family in Trametes strains are the primary source of industrial laccase and have gained widespread attention. Increasing the yield and enzymatic properties of laccase through various methods has always been a topic worthy of attention, and there is no report on the regulation of laccase expression through HSF transcription factor engineering. Here, we found that two alternative splicing variants of TtHSF2 functioned oppositely in regulating the expression of laccase genes, and copper can induce the expression of almost all members of the laccase gene family. Most importantly, our study suggested that TtHSF2 and its alternative splicing variants are vital for copper-induced production of laccases in T. trogii S0301.

Molecular Mechanism by Which the GATA Transcription Factor CcNsdD2 Regulates the Developmental Fate of Coprinopsis cinerea under Dark or Light Conditions

Coprinopsis cinerea has seven homologs of the Aspergillus nidulans transcription factor NsdD. Of these, CcNsdD1 and CcNsdD2 from C. cinerea show the best identities of 62 and 50% to A. nidulans NsdD, respectively. After 4 days of constant darkness cultivation, CcnsdD2, but not CcnsdD1, was upregulated on the first day of light/dark cultivation to induce fruiting bodies, and overexpression of CcnsdD2, but not CcnsdD1, produced more fruiting bodies under a light/dark rhythm. Although single knockdown of CcnsdD2 did not affect fruiting body production due to upregulation of its homolog CcnsdD1, the double-knockdown CcNsdD1/NsdD2-RNAi transformant showed defects in fruiting body formation under a light/dark rhythm. Knockdown of CcnsdD1/nsdD2 led to the differentiation of primary hyphal knots into sclerotia rather than secondary hyphal knots under a light/dark rhythm, similar to the differentiation of primary hyphal knots into sclerotia of the wild-type strain under darkness. The CcNsdD2-overexpressing transformant produced more primary hyphal knots, secondary hyphal knots, and fruiting bodies under a light/dark rhythm but only more primary hyphal knots and sclerotia under darkness. RNA-seq revealed that some genes reported previously to be involved in formation of hyphal knots and primordia, cyclopropane-fatty-acyl-phospholipid synthases cfs1-3, galectins cgl1-3, and hydrophobins hyd1-3 were downregulated in the CcNsdD1/NsdD2-RNAi transformant compared to the mock transformant. ChIP-seq and electrophoretic mobility shift assay demonstrated that CcNsdD2 bound to promoter regulatory sequences containing a GATC motif in cfs1, cfs2, cgl1, and hyd1. A molecular mechanism by which CcNsdD2 regulates the developmental fate of C. cinerea under dark or light conditions is proposed. IMPORTANCE The model mushroom Coprinopsis cinerea exhibits remarkable photomorphogenesis during fruiting body development. This study reports that the C. cinerea transcription factor CcNsdD2 promotes primary hyphal knot formation by upregulating cfs1, cfs2, cgl1, and hyd1. Although the induction of CcnsdD2 is not under direct control of light and photoreceptors, the CcNsdD2-mediated developmental fates of the primary hyphal knots depend on the following light/dark rhythm cultivation or dark cultivation after full growth of mycelia in the constant dark cultivation. This study provides new insight into the molecular mechanism by which CcNsdD2 regulates the developmental fate of C. cinerea under dark or light conditions. In addition, the result that overexpression of CcnsdD2 induced more secondary hyphal knots, primordia, and fruiting bodies under light/dark rhythm cultivation conditions has potential applied value in the edible mushroom industry.

Characterization of a Yellow Laccase from Botrytis cinerea 241

Typical laccases have four copper atoms, which form three different copper centers, of which the T1 copper is responsible for the blue color of the enzyme and gives it a characteristic absorbance around 610 nm. Several laccases have unusual spectral properties and are referred to as yellow or white laccases. Only two yellow laccases from the Ascomycota phylum have been described previously, and only one amino acid sequence of those enzymes is available. A yellow laccase Bcl1 from Botrytis cinerea strain 241 has been identified, purified and characterized in this work. The enzyme appears to be a dimer with a molecular mass of 186 kDa. The gene encoding the Bcl1 protein has been cloned, and the sequence analysis shows that the yellow laccase Bcl1 is phylogenetically distinct from other known yellow laccases. In addition, a comparison of amino acid sequences, and 3D modeling shows that the Bcl1 laccase lacks a conservative tyrosine, which is responsible for absorption quenching at 610 nm in another yellow asco-laccase from Sclerotinia sclerotiorum. High thermostability, high salt tolerance, broad substrate specificity, and the ability to decolorize dyes without the mediators suggest that the Bcl1 laccase is a potential enzyme for various industrial applications.

Genes Identification, Molecular Docking and Dynamics Simulation Analysis of Laccases from Amylostereum areolatum Provides Molecular Basis of Laccase Bound to Lignin

An obligate mutualistic relationship exists between the fungus Amylostereum areolatum and woodwasp Sirex noctilio. The fungus digests lignin in the host pine, providing essential nutrients for the growing woodwasp larvae. However, the functional properties of this symbiosis are poorly described. In this study, we identified, cloned, and characterized 14 laccase genes from A. areolatum. These genes encoded proteins of 508 to 529 amino acids and contained three typical copper-oxidase domains, necessary to confer laccase activity. Besides, we performed molecular docking and dynamics simulation of the laccase proteins in complex with lignin compounds (monomers, dimers, trimers, and tetramers). AaLac2, AaLac3, AaLac6, AaLac8, and AaLac10 were found that had low binding energies with all lignin model compounds tested and three of them could maintain stability when binding to these compounds. Among these complexes, amino acid residues ALA, GLN, LEU, PHE, PRO, and SER were commonly present. Our study reveals the molecular basis of A. areolatum laccases interacting with lignin, which is essential for understanding how the fungus provides nutrients to S. noctilio. These findings might also provide guidance for the control of S. noctilio by informing the design of enzyme mutants that could reduce the efficiency of lignin degradation.

Selection markers for transformation of the sequenced reference monokaryon Okayama 7/#130 and homokaryon AmutBmut of Coprinopsis cinerea

BACKGROUND

Two reference strains have been sequenced from the mushroom Coprinopsis cinerea, monokaryon Okayama 7/#130 (OK130) and the self-compatible homokaryon AmutBmut. An adenine-auxotrophy in OK130 (ade8-1) and a para-aminobenzoic acid (PABA)-auxotrophy in AmutBmut (pab1-1) offer selection markers for transformations. Of these two strains, homokaryon AmutBmut had been transformed before to PABA-prototrophy and with the bacterial hygromycin resistance marker hph, respectively.

RESULTS

Gene ade8 encodes a bifunctional enzyme with an N-terminal glycinamide ribonucleotide synthase (GARS) and a C-terminal aminoimidazole ribonucleotide synthase (AIRS) domain required for steps 2 and 5 in the de novo biosynthesis of purines, respectively. In OK130, a missense mutation in ade8-1 rendered residue N231 for ribose recognition by the A loop of the GARS domain into D231. The new ade8 + vector pCcAde8 complements the auxotrophy of OK130 in transformations. Transformation rates with pCcAde8 in single-vector and co-transformations with ade8 +-selection were similarly high, unlike for trp1 + plasmids which exhibit suicidal feedback-effects in single-vector transformations with complementation of tryptophan synthase defects. As various other plasmids, unselected pCcAde8 helped in co-transformations of trp1 strains with a trp1 +-selection vector to overcome suicidal effects by transferred trp1 +. Co-transformation rates of pCcAde8 in OK130 under adenine selection with nuclear integration of unselected DNA were as high as 80% of clones. Co-transformation rates of expressed genes reached 26-42% for various laccase genes and up to 67% with lcc9 silencing vectors. The bacterial gene hph can also be used as another, albeit less efficient, selection marker for OK130 transformants, but with similarly high co-transformation rates. We further show that the pab1-1 defect in AmutBmut is due to a missense mutation which changed the conserved PIKGT motif for chorismate binding in the C-terminal PabB domain to PIEGT in the mutated 4-amino-4-deoxychorismate synthase.

CONCLUSIONS

ade8-1 and pab1-1 auxotrophic defects in C. cinerea reference strains OK130 and AmutBmut for complementation in transformation are described. pCcAde8 is a new transformation vector useful for selection in single and co-transformations of the sequenced monokaryon OK130 which was transformed for the first time. The bacterial gene hph can also be used as an additional selection marker in OK130, making in combination with ade8 + successive rounds of transformation possible.

Enzyme Activity Profiles Produced on Wood and Straw by Four Fungi of Different Decay Strategies

Four well-studied saprotrophic Basidiomycota Agaricomycetes species with different decay strategies were cultivated on solid lignocellulose substrates to compare their extracellular decomposing carbohydrate-active and lignin-attacking enzyme production profiles. Two Polyporales species, the white rot fungus Phlebia radiata and brown rot fungus Fomitopsis pinicola, as well as one Agaricales species, the intermediate "grey" rot fungus Schizophyllum commune, were cultivated on birch wood pieces for 12 weeks, whereas the second Agaricales species, the litter-decomposing fungus Coprinopsis cinerea was cultivated on barley straw for 6 weeks under laboratory conditions. During 3 months of growth on birch wood, only the white rot fungus P. radiata produced high laccase and MnP activities. The brown rot fungus F. pinicola demonstrated notable production of xylanase activity up to 43 nkat/mL on birch wood, together with moderate β-glucosidase and endoglucanase cellulolytic activities. The intermediate rot fungus S. commune was the strongest producer of β-glucosidase with activities up to 54 nkat/mL, and a notable producer of xylanase activity, even up to 620 nkat/mL, on birch wood. Low lignin-attacking but moderate activities against cellulose and hemicellulose were observed with the litter-decomposer C. cinerea on barley straw. Overall, our results imply that plant cell wall decomposition ability of taxonomically and ecologically divergent fungi is in line with their enzymatic decay strategy, which is fundamental in understanding their physiology and potential for biotechnological applications.

Expression Profile of Laccase Gene Family in White-Rot Basidiomycete Lentinula edodes under Different Environmental Stresses

Laccases belong to ligninolytic enzymes and play important roles in various biological processes of filamentous fungi, including fruiting-body formation and lignin degradation. The process of fruiting-body development in Lentinula edodes is complex and is greatly affected by environmental conditions. In this paper, 14 multicopper oxidase-encoding (laccase) genes were analyzed in the draft genome sequence of L. edodes strain W1-26, followed by a search of multiple stress-related Cis-elements in the promoter region of these laccase genes, and then a transcription profile analysis of 14 laccase genes (Lelcc) under the conditions of different carbon sources, temperatures, and photoperiods. All laccase genes were significantly regulated by varying carbon source materials. The expression of only two laccase genes (Lelcc5 and Lelcc6) was induced by sodium-lignosulphonate and the expression of most laccase genes was specifically upregulated in glucose medium. Under different temperature conditions, the expression levels of most laccase genes decreased at 39 °C and transcription was significantly increased for Lelcc1, Lelcc4, Lelcc5, Lelcc9, Lelcc12, Lelcc13, and Lelcc14 after induction for 24 h at 10 °C, indicating their involvement in primordium differentiation. Tyrosinase, which is involved in melanin synthesis, was clustered with the same group as Lelcc4 and Lelcc7 in all the different photoperiod treatments. Meanwhile, five laccase genes (Lelcc8, Lelcc9, Lelcc12, Lelcc13, and Lelcc14) showed similar expression profiles to that of two blue light receptor genes (LephrA and LephrB) in the 12 h light/12 h dark treatment, suggesting the involvement of laccase genes in the adaptation process of L. edodes to the changing environment and fruiting-body formation. This study contributes to our understanding of the function of the different Lelcc genes and facilitates the screening of key genes from the laccase gene family for further functional research.

Heterologous expression of Stlac2, a laccase isozyme of Setosphearia turcica, and the ability of decolorization of malachite green

The active laccases of ascomycetous fungus Setosphaeria turcica were identified by Native-PAGE and ESI-MS/MS, and one of these isozymes Stlac2 was heterologous expressed to investigate the decolorization of malachite green. Setosphaeria turcica produced three active laccase isozymes: Stlac1, Stlac2, and Stlac6. Stlac2 was heterologously expressed in both eukaryotic and prokaryotic expression systems. The eukaryotic recombinant Stlac2 expressed in Pichia pastoris was inactive, and also showed a higher molecular weight than predicted because of glycosylation. The depression of laccase activity was attributable to the incorrect glycosylation at Asn97. Stlac2 expressed in Escherichia coli and the recombinant Stlac2 exhibited activity of 28.23 U/mg with 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as the substrate. The highest activity was observed at pH of 4.5 and the temperature of 60 °C. The activity of recombinant Stlac2 was inhibited by 10 mM Na⁺, Mg²⁺, Ca²⁺, Mn²⁺, and increased by 10 mM of Fe³⁺ with a relatively activity of 315% compared with no addition. Cu²⁺ did not affect enzyme activity. Recombinant Stlac2 was capable of decolorizing 67.08% of 20 mg/L malachite green in 15 min without any mediators. CONCLUSIONS: Generally, recombinant protein of fungal laccase Stlac2 was active without glycosylation and decolorize malachite green efficiently, which has potential industrial applications.

Modified recipe to inhibit fruiting body formation for living fungal biomaterial manufacture

Living fungal mycelium with abolished ability to form fruiting bodies is a self-healing substance, which is particularly valuable for further engineering and development as materials sensing environmental changes and secreting signals. Suppression of fruiting body formation is also a useful tool for maintaining the stability of a mycelium-based material with ease and lower cost. The objective of this study was to provide a biochemical solution to regulate the fruiting body formation, which may replace heat killing of mycelium in practice. The concentrations of glycogen synthase kinase-3 (GSK-3) inhibitors, such as lithium chloride or CHIR99021 trihydrochloride, were found to directly correlate with the development of fruiting bodies in the mushroom forming fungi such as Coprinopsis cinerea and Pleurotus djamor. Sensitive windows to these inhibitors throughout the fungal life cycle were also identified. We suggest the inclusion of GSK-3 inhibitors in the cultivation recipes for inhibiting fruiting body formation and regulating mycelium growth. This is the first report of using a GSK-3 inhibitor to suppress fruiting body formation in living fungal mycelium-based materials. It provides an innovative strategy for easy, reliable, and low cost maintenance of materials containing living fungal mycelium.

Laccases with Variable Properties from Different Strains of Steccherinum ochraceum: Does Glycosylation Matter?

Laccases are blue multi-copper oxidases with an extensive number of actual and potential industrial applications. It is known that laccases from different fungal strains may vary in properties; however, the reason of this remains unclear. In the current study we have isolated and characterized seven laccases from different strains of Steccherinum ochraceum obtained from regions of central Russia. Although all seven laccases had the same primary sequences, there was a little variation in their molecular weights and thermostabilities. Moreover, statistically significant differences in laccases' catalytic parameters of oxidation of phenolic substrates and ABTS were observed. After the deglycosylation of four selected laccases by Endo H and PNGase F, their affinities to pyrocatechol and ABTS became the same, suggesting a substantial role of N-linked glycosylation in moderation of enzymatic properties of laccases.

Production of polyextremotolerant laccase by Achromobacter xylosoxidans HWN16 and Citrobacter freundii LLJ16

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The biochemical properties of two proteobacteria laccases were assessed.

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Polyextremotolerant qualities of the laccases were identified.

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Multiple laccase-encoding genes were observed in laccase-producing strains.

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Their implication in biotechnological applications was deliberated.

Given the upwelling of a variety of potential applications laccases could participate in, it would be fitting to equally make available laccases that are well suited for the aforementioned. Therefore historian understanding of the catalytic and physicochemical properties is desirable. Owing to this, the biochemical properties of the crude laccases from Achromobacter xylosoxidans HWN16 (Hb9c) and Citrobacter freundii LLJ 16 (Ie1c) were assessed. Furthermore, a hint of the molecular basis for their production from respective organisms was presented. Results showed that both laccases were tolerant, and sometimes had their activities improved by the set of parameters tested. They were active at broad range of temperature (0–90 °C), pH (3–11), and were equally thermo- and pH-stable. Their activities were either improved, or left unabated by cations, detergents, and chloride (5–40%), however, the highlight of the study was their augmented activity, when they were incubated with certain concentrations of fluoride (2–20%), a potent inhibitor. They were depicted to have multiple homologous laccase encoding genes, on molecular evaluation, which may be responsible the conferral of these remarkable qualities they possess. Therefore, the laccases might be beneficial, if employed in formulations for a wide range of environmental and biotechnological applications. Moreover, the molecular machinery of their production be exploited for economical benefits in the immediate future.

Signal peptide replacement resulted in recombinant homologous expression of laccase Lcc8 in Coprinopsis cinerea

Although the model agaricomycete Coprinopsis cinerea possess 17 different laccase genes, up to now only four C. cinerea laccases have been purified and characterized to some degree. By exchanging the nucleotide sequence of the deduced signal peptide of Lcc8 it was possible to homologously express lcc8 in C. cinerea under control of the Agaricus bisporus gdpII promoter and the C. cinerea lcc1 terminator. The purified Lcc8 showed two bands in the SDS-PAGE with a molecular weight of 64 kDa and 77 kDa, respectively. The IEF determined pI values of 3.3 and 3.4 for both bands. The optimal pH for oxidation of the substrates ABTS, 2,6-dimethoxyphenol, guaiacol and syringaldazine was pH 4.0, pH 5.0, pH 4.5 and pH 5.0, respectively. Best pH for enzyme storage was pH 8.0. The optimal temperature for oxidation of ABTS was 63 °C, while Lcc8 showed activity of at least 50% over 300 min at 50 °C. The comparable high stability of Lcc8 at alkaline pH and higher temperatures can be of interest for biotechnical applications.

Genome and secretome of Chondrostereum purpureum correspond to saprotrophic and phytopathogenic life styles

The basidiomycete Chondrostereum purpureum (Silverleaf fungus) is a saprotroph and plant pathogen commercially used for combatting forest "weed" trees in vegetation management. However, little is known about its lignocellulose-degrading capabilities and the enzymatic machinery that is responsible for the degradative potential, and it is not yet clear to which group of wood-rot fungi it actually belongs. Here, we sequenced and analyzed the draft genome of C. purpureum (41.2 Mbp) and performed a quantitative proteomic approach during growth in submerged and solid-state cultures based on soybean meal suspension or containing beech wood supplemented with phenol-rich olive mill residues, respectively. The fungus harbors characteristic lignocellulolytic hydrolases (GH6 and GH7) and oxidoreductases (e.g. laccase, heme peroxidases). High abundance of some of these genes (e.g. 45 laccases, nine GH7) can be explained by gene expansion, e.g. identified for the laccase orthogroup ORTHOMCL11 that exhibits a total of 18 lineage-specific duplications. Other expanded genes families encode for proteins more related to a pathogenic lifestyle (e.g. protease and cytochrome P450s). The fungus responds to the presence of complex growth substrates (lignocellulose, phenolic residues) by the secretion of most of these lignocellulolytic and lignin-modifying enzymes (e.g. alcohol and aryl alcohol oxidases, laccases, GH6, GH7). Based on the genetic and enzymatic constitution, we consider the 'marasmioid' fungus C. purpureum as a 'phytopathogenic' white-rot fungus (WRF) that possesses a complex extracellular enzyme machinery to accomplish efficient lignocellulose degradation during both saprotrophic and phytopathogenic life phases.

Gongronella sp. w5 elevates Coprinopsis cinerea laccase production by carbon source syntrophism and secondary metabolite induction

When sucrose was used as the carbon source, the Basidiomycete Coprinopsis cinerea showed poor growth and low laccase activity in pure culture, but greatly enhanced the level of laccase activity (>1800 U/L) during coculture with the Mucoromycete Gongronella sp. w5. As a result, the mechanism of laccase overproduction in coculture was investigated by starting from clarifying the function of sucrose. Results demonstrated that Gongronella sp. w5 in the coculture system hydrolyzed sucrose to glucose and fructose by an intracellular invertase. Fructose rather than glucose was supplied by Gongronella sp. w5  as the readily available carbon source for C. cinerea, and contributed to an alteration of its growth behavior and a basal laccase secretion of 110.6 ± 3.3 U/L. On the other hand, separating Gongronella sp. w5 of C. cinerea by transfer into dialysis tubes yielded the same level of laccase activity as without separation, indicating that enhanced laccase production probably resulted from the metabolites in the fermentation broth. Further investigation showed that the ethyl acetate-extracted metabolites generated by Gongronella sp. w5 induced C. cinerea laccase production. One of the laccase-inducing compounds namely p-hydroxybenzoic acid (HBA) was purified and identified from the extract. When using HBA as the inducer and fructose as the carbon source in monoculture, C. cinerea observed similar high laccase activity to that in coculture, and zymograms revealed the same expression of laccase Lcc9 as the main and Lcc1 and Lcc5 as the minor enzymes. Overall, our experiments verified that Gongronella sp. w5 elevates Coprinopsis cinerea laccase production by carbon source syntrophism and secondary metabolite induction.

Systematic Analysis of the Pleurotus ostreatus Laccase Gene (PoLac) Family and Functional Characterization of PoLac2 Involved in the Degradation of Cotton-Straw Lignin

Fungal laccases play important roles in the degradation of lignocellulose. Although some PoLacs have been reported in several studies, still no comprehensive bioinformatics study of the LAC family in Pleurotus ostreatus has been reported. In this study, we identified 12 laccase genes in the whole genome sequence of P. ostreatus and their physical characteristics, gene distribution, phylogenic relationships, gene structure, conserved motifs, and cis-elements were also analyzed. The expression patterns of 12 PoLac genes at different developmental stages and under different culture substrates were also analyzed. The results revealed that PoLac2 and PoLac12 may be involved in the degradation of lignin and the formation of the fruiting body, respectively. Subsequently, we overexpressed PoLac2 in P. ostreatus by the Agrobacterium tumefaciens-mediated transformation (ATMT) method. The transformants' laccase activity increased in varying degrees, and the gene expression level of PoLac2 in transformants was 2-8 times higher than that of the wild-type strain. Furthermore, the lignin degradation rate by transgenic fungus over 30 days was 2.36-6.3% higher than that of wild-type. Our data show that overexpression of PoLac2 significantly enhanced the lignin degradation of cotton-straw. To our knowledge, this study is the first report to demonstrate the functions of PoLac2 in P. ostreatus.

Multiplicity of enzymatic functions in the CAZy AA3 family

The CAZy auxiliary activity family 3 (AA3) comprises enzymes from the glucose-methanol-choline (GMC) family of oxidoreductases, which assist the activity of other AA family enzymes via their reaction products or support the action of glycoside hydrolases in lignocellulose degradation. The AA3 family is further divided into four subfamilies, which include cellobiose dehydrogenase, glucose oxidoreductases, aryl-alcohol oxidase, alcohol (methanol) oxidase, and pyranose oxidoreductases. These different enzymes catalyze a wide variety of redox reactions with respect to substrates and co-substrates. The common feature of AA3 family members is the formation of key metabolites such as H2O2 or hydroquinones, which are required by other AA enzymes. The multiplicity of enzymatic functions in the AA3 family is reflected by the multigenicity of AA3 genes in fungi, which also depends on their lifestyle. We provide an overview of the phylogenetic, molecular, and catalytic properties of AA3 enzymes and discuss their interactions with other carbohydrate-active enzymes.

De novo transcriptome assembly: a new laccase multigene family from the marine-derived basidiomycete Peniophora sp. CBMAI 1063

Laccases are multicopper oxidases that are able to catalyze reactions involving a range of substrates, including phenols and amines, and this ability is related to the existence of different laccases. Basidiomycetes usually have more than one gene for laccase, but until now, this feature has not been demonstrated in a marine-derived fungus. Peniophora sp. CBMAI 1063 is a basidiomycete fungus isolated from a marine sponge that exhibits the ability to secrete significant amounts of laccase in saline conditions. In the present study, we identified laccase sequences from the transcriptome of Peniophora sp. CBMAI 1063 and used them to perform different molecular in silico analyses. The results revealed the presence of at least eight putative genes, which may encode ten different laccases with peptide lengths ranging from 482 to 588 aa and molecular weights ranging from 53.5 to 64.4 kDa. These laccases seem to perform extracellular activities, with the exception of one that may represent an intracellular laccase. The 10 predicted laccases expressed by Peniophora sp. CBMAI 1063 in laccase-induced media showed different patterns of N-glycosylation and isoelectric points and are divided into two classes based on the residue associated with the regulation of the redox potential of the enzyme. None of the predicted laccases showed more than 61% similarity to other fungal laccases. Based on the differences among the laccases expressed by Peniophora sp. CBMAI 1063, this marine-derived basidiomycete represents a valuable resource with strong potential for biotechnological exploitation.

Laccases: Production, Expression Regulation, and Applications in Pharmaceutical Biodegradation

Laccases are a family of copper-containing oxidases with important applications in bioremediation and other various industrial and biotechnological areas. There have been over two dozen reviews on laccases since 2010 covering various aspects of this group of versatile enzymes, from their occurrence, biochemical properties, and expression to immobilization and applications. This review is not intended to be all-encompassing; instead, we highlighted some of the latest developments in basic and applied laccase research with an emphasis on laccase-mediated bioremediation of pharmaceuticals, especially antibiotics. Pharmaceuticals are a broad class of emerging organic contaminants that are recalcitrant and prevalent. The recent surge in the relevant literature justifies a short review on the topic. Since low laccase yields in natural and genetically modified hosts constitute a bottleneck to industrial-scale applications, we also accentuated a genus of laccase-producing white-rot fungi, Cerrena, and included a discussion with regards to regulation of laccase expression.

Upgrading Laccase Production and Biochemical Properties: Strategies and Challenges

Improving laccases continues to be crucial in novel biotechnological developments and industrial applications, where they are concerned. This review breaks down and explores the potential of the strategies (conventional and modern) that can be used for laccase enhancement (increased production and upgraded biochemical properties such as stability and catalytic efficiency). The challenges faced with these approaches are briefly discussed. We also shed light on how these strategies merge and give rise to new options and advances in this field of work. Additionally, this article seeks to serve as a guide for students and academic researchers interested in laccases. This document not only gives basic information on laccases, but also provides updated information on the state of the art of various technologies that are used in this line of investigation. It also gives the readers an idea of the areas extensively studied and the areas where there is still much left to be done. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1015-1034, 2017.

Characterization of three pyranose dehydrogenase isoforms from the litter-decomposing basidiomycete Leucoagaricus meleagris (syn. Agaricus meleagris)

Multigenicity is commonly found in fungal enzyme systems, with the purpose of functional compensation upon deficiency of one of its members or leading to enzyme isoforms with new functionalities through gene diversification. Three genes of the flavin-dependent glucose-methanol-choline (GMC) oxidoreductase pyranose dehydrogenase (AmPDH) were previously identified in the litter-degrading fungus Agaricus (Leucoagaricus) meleagris, of which only AmPDH1 was successfully expressed and characterized. The aim of this work was to study the biophysical and biochemical properties of AmPDH2 and AmPDH3 and compare them with those of AmPDH1. AmPDH1, AmPDH2 and AmPDH3 showed negligible oxygen reactivity and possess a covalently tethered FAD cofactor. All three isoforms can oxidise a range of different monosaccarides and oligosaccharides including glucose, mannose, galactose and xylose, which are the main constituent sugars of cellulose and hemicelluloses, and judging from the apparent steady-state kinetics determined for these sugars, the three isoforms do not show significant differences pertaining to their reaction with sugar substrates. They oxidize glucose both at C2 and C3 and upon prolonged reaction C2 and C3 double-oxidized glucose is obtained, confirming that the A. meleagris genes pdh2 (AY753308.1) and pdh3 (DQ117577.1) indeed encode CAZy class AA3_2 pyranose dehydrogenases. While reactivity with electron donor substrates was comparable for the three AmPDH isoforms, their kinetic properties differed significantly for the model electron acceptor substrates tested, a radical (the 2,2'-azino-bis[3-ethylbenzothiazoline-6-sulphonic acid] cation radical), a quinone (benzoquinone) and a complexed iron ion (the ferricenium ion). Thus, a possible explanation for this PDH multiplicity in A. meleagris could be that different isoforms react preferentially with structurally different electron acceptors in vivo.

Phylogenomic analyses reveal the diversity of laccase-coding genes in Fonsecaea genomes

The genus Fonsecaea comprises black yeast-like fungi of clinical relevance, including etiologic agents of chromoblastomycosis and cerebral phaeohyphomycosis. Presence of melanin and assimilation of monoaromatic hydrocarbons and alkylbenzenes have been proposed as virulence factors. Multicopper oxidase (MCO) is a family of enzymes including laccases, ferroxidases and ascorbate oxidases which are able to catalyze the oxidation of various aromatic organic compounds with the reduction of molecular oxygen to water. Additionally, laccases are required for the production of fungal melanins, a cell-wall black pigment recognized as a key polymer for pathogenicity and extremotolerance in black yeast-like fungi. Although the activity of laccase enzymes has previously been reported in many wood-rotting fungi, the diversity of laccase genes in Fonsecaea has not yet been assessed. In this study, we identified and characterized laccase-coding genes and determined their genomic location in five clinical and environmental Fonsecaea species. The identification of laccases sensu stricto will provide insights into carbon acquisition strategies as well as melanin production in Fonsecaea.

The good, the bad and the tasty: The many roles of mushrooms

Fungi are often inconspicuous in nature and this means it is all too easy to overlook their importance. Often referred to as the "Forgotten Kingdom", fungi are key components of life on this planet. The phylum Basidiomycota, considered to contain the most complex and evolutionarily advanced members of this Kingdom, includes some of the most iconic fungal species such as the gilled mushrooms, puffballs and bracket fungi. Basidiomycetes inhabit a wide range of ecological niches, carrying out vital ecosystem roles, particularly in carbon cycling and as symbiotic partners with a range of other organisms. Specifically in the context of human use, the basidiomycetes are a highly valuable food source and are increasingly medicinally important. In this review, seven main categories, or 'roles', for basidiomycetes have been suggested by the authors: as model species, edible species, toxic species, medicinal basidiomycetes, symbionts, decomposers and pathogens, and two species have been chosen as representatives of each category. Although this is in no way an exhaustive discussion of the importance of basidiomycetes, this review aims to give a broad overview of the importance of these organisms, exploring the various ways they can be exploited to the benefit of human society.

Laccase Gene Family in Cerrena sp. HYB07: Sequences, Heterologous Expression and Transcriptional Analysis

Laccases are a class of multi-copper oxidases with industrial potential. In this study, eight laccases (Lac1-8) from Cerrena sp. strain HYB07, a white-rot fungus with high laccase yields, were analyzed. The laccases showed moderate identities to each other as well as with other fungal laccases and were predicted to have high redox potentials except for Lac6. Selected laccase isozymes were heterologously expressed in the yeast Pichia pastoris, and different enzymatic properties were observed. Transcription of the eight laccase genes was differentially regulated during submerged and solid state fermentation, as shown by quantitative real-time polymerase chain reaction and validated reference genes. During 6-day submerged fermentation, Lac7 and 2 were successively the predominantly expressed laccase gene, accounting for over 95% of all laccase transcripts. Interestingly, accompanying Lac7 downregulation, Lac2 transcription was drastically upregulated on days 3 and 5 to 9958-fold of the level on day 1. Consistent with high mRNA abundance, Lac2 and 7, but not other laccases, were identified in the fermentation broth by LC-MS/MS. In solid state fermentation, less dramatic differences in transcript abundance were observed, and Lac3, 7 and 8 were more highly expressed than other laccase genes. Elucidating the properties and expression profiles of the laccase gene family will facilitate understanding, production and commercialization of the fungal strain and its laccases.

Grouping of multicopper oxidases in Lentinula edodes by sequence similarities and expression patterns

The edible white rot fungus Lentinula edodes possesses a variety of lignin degrading enzymes such as manganese peroxidases and laccases. Laccases belong to the multicopper oxidases, which have a wide range of catalytic activities including polyphenol degradation and synthesis, lignin degradation, and melanin formation. The exact number of laccases in L. edodes is unknown, as are their complete properties and biological functions. We analyzed the draft genome sequence of L. edodes D703PP-9 and identified 13 multicopper oxidase-encoding genes; 11 laccases in sensu stricto, of which three are new, and two ferroxidases. lcc8, a laccase previously reported in L. edodes, was not identified in D703PP-9 genome. Phylogenetic analysis showed that the 13 multicopper oxidases can be classified into laccase sensu stricto subfamily 1, laccase sensu stricto subfamily 2 and ferroxidases. From sequence similarities and expression patterns, laccase sensu stricto subfamily 1 can be divided into two subgroups. Laccase sensu stricto subfamily 1 group A members are mainly secreted from mycelia, while laccase sensu stricto subfamily 1 group B members are expressed mainly in fruiting bodies during growth or after harvesting but are lowly expressed in mycelia. Laccase sensu stricto subfamily 2 members are mainly expressed in mycelia, and two ferroxidases are mainly expressed in the fruiting body during growth or after harvesting, and are expressed at very low levels in mycelium. Our data suggests that L. edodes laccases in same group share expression patterns and would have common biological functions.

Cloning and Expression Analysis of Vvlcc3, a Novel and Functional Laccase Gene Possibly Involved in Stipe Elongation

Volvariella volvacea, usually harvested in its egg stage, is one of the most popular mushrooms in Asia. The rapid transition from the egg stage to elongation stage, during which the stipe stretches to almost full length leads to the opening of the cap and rupture of the universal veil, and is considered to be one of the main factors that negatively impacts the yield and value of V. volvacea. Stipe elongation is a common phenomenon in mushrooms; however, the mechanisms, genes and regulation involved in stipe elongation are still poorly understood. In order to study the genes related to the stipe elongation, we analyzed the transcription of laccase genes in stipe tissue of V. volvacea, as some laccases have been suggested to be involved in stipe elongation in Flammulina velutipes. Based on transcription patterns, the expression of Vvlcc3 was found to be the highest among the 11 laccase genes. Moreover, phylogenetic analysis showed that VvLCC3 has a high degree of identity with other basidiomycete laccases. Therefore, we selected and cloned a laccase gene, named Vvlcc3, a cDNA from V. volvacea, and expressed the cDNA in Pichia pastoris. The presence of the laccase signature L1-L4 on the deduced protein sequence indicates that the gene encodes a laccase. Phylogenetic analysis showed that VvLCC3 clusters with Coprinopsis cinerea laccases. The ability to catalyze ABTS (2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) oxidation proved that the product of the Vvlcc3 gene was a functional laccase. We also found that the expression of the Vvlcc3 gene in V. volvacea increased during button stage to the elongation stage; it reached its peak in the elongation stage, and then decreased in the maturation stage, which was similar to the trend in the expression of Fv-lac3 and Fv-lac5 in F. velutipes stipe tissue. The similar trend in expression level of these laccase genes of F. velutipes suggested that this gene could be involved in stipe elongation in V. volvacea.

Diversity of laccase-coding genes in Fusarium oxysporum genomes

Multiple studies confirm laccase role in fungal pathogenicity and lignocellulose degradation. In spite of broad genomic research, laccases from plant wilt pathogen Fusarium oxysporum are still not characterized. The study aimed to identify F. oxysporum genes that may encode laccases sensu stricto and to characterize the proteins in silico in order to facilitate further research on their impact on the mentioned processes. Twelve sequenced F. oxysporum genomes available on Broad Institute of Harvard and MIT (2015) website were analyzed and three genes that may encode laccases sensu stricto were found. Their amino acid sequences possess all features essential for their catalytic activity, moreover, the homology models proved the characteristic 3D laccase structures. The study shades light on F. oxysporum as a new source of multicopper oxidases, enzymes with possible high redox potential and broad perspective in biotechnological applications.