Fungal Laccases: Fundamentals, Engineering and Classification Update

Biodegradation and mineralization of bisphenol A by a novel soil-derived fungus Paraconiothyrium brasiliense mediated by extracellular laccase

Bisphenol A (BPA), involved in plastic manufacturing, has indeed raised major threats due to its pervasive and potentially hazardous effects on human life and the environment. Therefore, a global concern with the elimination and biodegradation of diverse plastic material pollution is necessary. The purpose of this study was to investigate and thoroughly screen promising fungi for efficacy BPA biodegradation. Totally, 15 soil fungi were isolated. Among them, 6 isolates exhibited greater levels of BPA degradation with varied rates from 60 ± 0.8-100 ± 0.1 % and were then identified in accordance with (ITS) regions. The highly promising BPA degradation isolate (100 %) was confirmed as Paraconiothyrium brasiliense strain HMA1, with a removal concentration of (0.5-500 mg/L) after 10 days with an optimal temperature at 30 °C, pH at 7.5, and ammonium sulphate as nitrogen source. Moreover, multiple intermediate metabolites were detected and confirmed during the BPA biodegradation process using high-performance liquid chromatography-mass spectrometry (HPLC-MS) with the help of quadrupole time-of-flight (Q-TOF). The HMA1 exhibited a considerable mineralization rate of 150 mg/L BPA reached up to 78 % of total organic carbon in the culture media after 5 days. Depending on the properties of intermediate components, the potential BPA degradation pathway of HMA1 was proposed. Furthermore, the activity of extracellular laccase and its potential for BPA degradation was studied to elucidate the mechanism of BPA biodegradation by HMA1. Conclusively, our findings provide the first report combined with distinct characteristics of P. brasiliense with a maximum BPA elimination to be a promising candidate for plastic-based material degradation.

Two stage enzymatic pretreatment of rice straw for its valorisation using Silicase and Laccase

The present study investigated the cumulative effect of pretreatment of rice straw with two enzymes-Silicase (first report) and Laccase as initial stages. The optimal conditions for silicase pretreatment were determined to be a dosage of 100 U/10 g of rice straw, pH 7.0, temperature 40 ºC, and a treatment duration of 30 h. For laccase pretreatment, the ideal parameters were enzyme dose of 40 U/10 g of rice straw, pH 5.0, temperature 50 ºC, and a treatment time of 30 h. At optimized conditions, the silica reduction of ~ 20% was achieved by Silicase pretreatment, whereas the reduction in lignin was upgraded by ~ 29.8% after two stage pretreatment. A reduction of 28.6% in ash content of rice straw and 29.4% in silica was obtained during two stage enzymatic pretreatment. The FTIR studies of the pretreated and untreated straw also depicted the delignification, ash and silica removal of agro-waste. A peak observed at 1542 cm-1 and 1643 cm-1 suggests cyclic stretching in phenolic lignin, while the absorption band at 1419 cm-1 corresponds to the bending (scissoring) of - OCH3 in the syringyl and guaiacyl units of the phenolic composition. A notable decrease in these vibrations was observed in the silicase + laccase-treated sample, likely resulting from the removal of syringols and guaiacols during the enzymatic pretreatment. Using present outcomes, the study presented that the cumulative impact of Silicase and Laccase was proficient in preparing rice straw for industrial applications and reducing environmental barriers during its conversion.

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.

Positive effects of composite material immobilized enzymes in 2,4,6-trichlorophenol degradation on soil properties and plant growth

2,4,6-Trichlorophenol (2,4,6-TCP) is recognized as a bio-toxic compound which is widely present in water and soil, and immobilized enzymes technology is widely used to degrade 2,4,6-TCP efficiently. However, previous studies have primarily focused on the degradation capability of immobilized enzymes towards 2,4,6-TCP, while the impacts on soil after degradation remain largely unexplored. In this study, sodium alginate/hydroxyapatite/chitosan microspheres immobilized with enzymes were used for 2,4,6-TCP degradation, and the impacts of degradation on soil properties and plant growth were explored. The results indicated that sodium alginate/hydroxyapatite/chitosan microsphere-immobilized enzymes achieved a removal rate of 94.72% for 160 mg L-1 2,4,6-TCP over 24 h and 73.17% for 160 mg kg-1 2,4,6-TCP contaminated soil over 72 h. Soil dehydrogenase and catalase activities were enhanced during degradation. The inhibitory effects of 2,4,6-TCP on wheat root and leaf elongation were mitigated by immobilized enzymes that degrade 2,4,6-TCP. Nutrients, such as fast-acting phosphorus and fast-acting potassium, were increased by immobilized enzymes that release nutrient elements. The changes of wheat growth observed in the soil after 2,4,6-TCP degradation by immobilized enzymes were driven by nutrients and degradation. These insights may facilitate the advancement of future applications of immobilized enzyme degradation technologies, contributing to sustainable soil management and ecological restoration.

Gap-free genome assembly and comparative analysis reveal the evolution and lignin degradation mechanisms of Cylindrobasidium torrendii

The Physalacriaceae family comprises numerous saprophytic edible and medicinal fungi with significant ecological and economic importance. However, the lack of high-quality genomic data has hindered systematic studies of this family. Here, we report the chromosome-level genome assembly of Cylindrobasidium torrendii, a species identified in China, using a combination of Illumina, PacBio HiFi, and Hi-C sequencing technologies. The 33.67 Mb genome, featuring a GC content of 52.00 %, demonstrates enhanced continuity and completeness. Phylogenetic analysis based on 1685 single-copy orthologous gene families places C. torrendii in close evolutionary proximity to Armillaria mellea and Gymnopus necrorhizus, with a divergence time of 112.39 Mya. Comparative genomics reveals conserved syntenic blocks between chromosomes of C. torrendii and those of Pleurotus ostreatus and Lentinula edodes. Gene family analysis identified 980 expanded and 487 contracted gene families, with expanded genes significantly enriched in secondary metabolite biosynthesis pathways. CAZyme, P450, and laccase gene family comparisons highlighted the evolutionary dynamics of these gene families in C. torrendii. Transcriptomic analysis under fungal dark stress revealed significant upregulation of genes such as CtoLAC7 and CAZymes (GH and CE families). This study provides a high-quality genomic resource and novel insights into the genetic and functional characteristics of C. torrendii and the Physalacriaceae family.

Laccase-based biocatalytic systems application in sustainable degradation of pharmaceutically active contaminants

The outflow of pharmaceutically active chemicals (PhACs) exerts a negative impact on biological systems even at extremely low concentrations. For instance, enormous threats to human and aquatic species have resulted from the widespread use of antibiotics in ecosystems, which stimulate the emergence and formation of antibiotic-resistant bacterial species and associated genes. Additionally, it is challenging to eliminate these PhACs by employing conventional physicochemical water treatment techniques. Enzymatic approaches, including laccase, have been identified as a promising alternative to eliminate a broad array of PhACs from water matrices. However, their application in environmental bioremediation is hindered by several factors, including the enzyme's stability and its location in the aqueous environment. Such obstacles may be surmounted by employing laccase immobilization, which enables enhanced stability (including inactivation caused by the substrate), and thus improved catalysis. This review emphasizes the potential hazards of PhACs to aquatic organisms within the detection concentration range of ngL-1 to µgL-1, as well as the deployment of laccase-based multifunctional biocatalytic systems for the environmentally friendly mitigation of anticancer drugs, analgesics/NSAIDs, antibiotics, antiepileptic agents, and beta blockers as micropollutants. This approach could reduce the underlying toxicological consequences. In addition, current developments, potential applications, and viewpoints have focused on computer-assisted investigations of laccase-PhACs binding at enzyme cavities and degradability prediction.

Increased Antioxidant Performance of Lignin by Biodegradation Obtained from an Extract of the Mushroom Pleurotus eryngii

The aim of this study was to evaluate the antioxidant properties of the products derived from the biodegradation of lignin by the ligninolytic enzymes present in an aqueous extract of the mushroom P. eryngii. A mixture obtained after the incubation of lignin for 18 h with P. eryngii extract was tested in vitro for its total polyphenol content, reducing power, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl (OH) radical-scavenging activities. The results showed that the enzymatic treatment of lignin enhanced its antioxidant performance. The biocompatibility of the products of lignin biodegradation and their ability to scavenge reactive oxygen species (ROS) were also tested on the astrocytic cell line DI-TNC1. The results obtained indicated that a lignin mixture incubated for 18 h does not affect cell viability or inhibit the H2O2-induced ROS production. These results suggest that the enzymatic degradation of lignin represents an efficient and ecofriendly approach to obtain lignin derivatives potentially useful for antioxidant applications.

Directed evolution of the multicopper oxidase laccase for cell surface proximity labeling and electron microscopy

Enzymes that oxidize aromatic substrates have shown utility in a range of cell-based technologies including live cell proximity labeling (PL) and electron microscopy (EM), but are associated with drawbacks such as the need for toxic H 2 O 2 . Here, we explore laccases as a novel enzyme class for PL and EM in mammalian cells. LaccID, generated via 11 rounds of directed evolution from an ancestral fungal laccase, catalyzes the one-electron oxidation of diverse aromatic substrates using O 2 instead of toxic H 2 O 2 , and exhibits activity selective to the surface plasma membrane of both living and fixed cells. We show that LaccID can be used with mass spectrometry-based proteomics to map the changing surface composition of T cells that engage with tumor cells via antigen-specific T cell receptors. In addition, we use LaccID as a genetically-encodable tag for EM visualization of cell surface features in mammalian cell culture and in the fly brain. Our study paves the way for future cell-based applications of LaccID.

Fungal Laccases and Fumonisin Decontamination in Co-Products of Bioethanol from Maize

Maize (Zea mays L.) may be infected by Fusarium verticillioides and F. proliferatum, and consequently contaminated with fumonisins (FBs), as well as the co-products of bioethanol intended for animal feed. Laccase enzymes have a wide industrial application such as mycotoxin degradation. The aims were to isolate and identify fungal laccase-producing strains, to evaluate laccase production, to determine the enzymatic stability under fermentation conditions, and to analyse the effectiveness in vitro of enzymatic extracts (EEs) containing laccases in degrading FB1. Strains belonging to Funalia trogii, Phellinus tuberculosus, Pleurotus ostreatus, Pycnoporus sanguineus and Trametes gallica species showed laccase activity. Different isoforms of laccases were detected depending on the evaluated species. For the FB1 decontamination assays, four enzymatic activities (5, 10, 15 and 20 U/mL) were tested, in the absence and presence of vanillic acid (VA) and 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as redox mediators (1 and 10 mM). Trametes gallica B4-IMICO-RC EE was the most effective strain in buffer, achieving a 60% of FB1 reduction. Laccases included in EEs remained stable at different alcoholic degrees in maize steep liquor (MSL), but no significant FB1 reduction was observed under the conditions evaluated using MSL. This study demonstrate that although laccases could be good candidates for the development of a strategy to reduce FB1, further studies are necessary to optimise this process in MSL.

Two Zn2Cys6-type transcription factors respond to aromatic compounds and regulate the expression of laccases in the white-rot fungus Trametes hirsuta

White-rot fungi differentially express laccases when they encounter aromatic compounds. However, the underlying mechanisms are still being explored. Here, proteomics analysis revealed that in addition to increased laccase activity, proteins involved in sphingolipid metabolism and toluene degradation as well as some cytochrome P450s (CYP450s) were differentially expressed and significantly enriched during 48 h of o-toluidine exposure, in Trametes hirsuta AH28-2. Two Zn2Cys6-type transcription factors (TFs), TH8421 and TH4300, were upregulated. Bioinformatics docking and isothermal titration calorimetry assays showed that each of them could bind directly to o-toluidine and another aromatic monomer, guaiacol. Binding to aromatic compounds promoted the formation of TH8421/TH4300 heterodimers. TH8421 and TH4300 silencing in T. hirsuta AH28-2 led to decreased transcriptional levels and activities of LacA and LacB upon o-toluidine and guaiacol exposure. EMSA and ChIP-qPCR analysis further showed that TH8421 and TH4300 bound directly with the promoter regions of lacA and lacB containing CGG or CCG motifs. Furthermore, the two TFs were involved in direct and positive regulation of the transcription of some CYP450s. Together, TH8421 and TH4300, two key regulators found in T. hirsuta AH28-2, function as heterodimers to simultaneously trigger the expression of downstream laccases and intracellular enzymes. Monomeric aromatic compounds act as ligands to promote heterodimer formation and enhance the transcriptional activities of the two TFs.IMPORTANCEWhite-rot fungi differentially express laccase isoenzymes when exposed to aromatic compounds. Clarification of the molecular mechanisms underlying differential laccase expression is essential to elucidate how white-rot fungi respond to the environment. Our study shows that two Zn2Cys6-type transcription factors form heterodimers, interact with the promoters of laccase genes, and positively regulate laccase transcription in Trametes hirsuta AH28-2. Aromatic monomer addition induces faster heterodimer formation and rate of activity. These findings not only identify two new transcription factors involved in fungal laccase transcription but also deepen our understanding of the mechanisms underlying the response to aromatics exposure in white-rot fungi.

Mechanism of non-phenolic substrate oxidation by the fungal laccase Type 1 copper site from Trametes versicolor: the case of benzo[a]pyrene and anthracene

Laccases (EC 1.10.3.2) are multicopper oxidases with the capability to oxidize diverse phenolic and non-phenolic substrates. While the molecular mechanism of their activity towards phenolic substrates is well-established, their reactivity towards non-phenolic substrates, such as polycyclic aromatic hydrocarbons (PAHs), remains unclear. To elucidate the oxidation mechanism of PAHs, particularly the activation mechanism of the sp2 aromatic C-H bond, we conducted a density functional theory investigation on the oxidation of two PAHs (anthracene and benzo[a]pyrene) using an extensive model of the T1 copper catalytic site of the fungal laccase from Trametes versicolor.

Laccase-Treated Polystyrene Surfaces with Caffeic Acid, Dopamine, and L-3,4-Dihydroxyphenylalanine Substrates Facilitate the Proliferation of Melanocytes and Embryonal Carcinoma Cells NTERA-2

This study presents the effects of treating polystyrene (PS) cell culture plastic with oxidoreductase enzyme laccase and the catechol substrates caffeic acid (CA), L-DOPA, and dopamine on the culturing of normal human epidermal melanocytes (NHEMs) and human embryonal carcinoma cells (NTERA-2). The laccase-substrate treatment improved PS hydrophilicity and roughness, increasing NHEM and NTERA-2 adherence, proliferation, and NHEM melanogenesis to a level comparable with conventional plasma treatment. Cell adherence dynamics and proliferation were evaluated. The NHEM endpoint function was quantified by measuring melanin content. PS surfaces treated with laccase and its substrates demonstrated the forming of polymer-like structures. The surface texture roughness gradient and the peak curvature were higher on PS treated with a combination of laccase and substrates than laccase alone. The number of adherent NHEM and NTERA-2 was significantly higher than on the untreated surface. The proliferation of NHEM and NTERA-2 correspondingly increased on treated surfaces. NHEM melanin content was enhanced 6-10-fold on treated surfaces. In summary, laccase- and laccase-substrate-modified PS possess improved PS surface chemistry/hydrophilicity and altered roughness compared to untreated and plasma-treated surfaces, facilitating cellular adherence, subsequent proliferation, and exertion of the melanotic phenotype. The presented technology is easy to apply and creates a promising custom-made, substrate-based, cell-type-specific platform for both 2D and 3D cell culture.

Effects of Orange Peel Extract on Laccase Activity and Gene Expression in Trametes versicolor

The genome of Trametes versicolor encodes multiple laccase isozymes, the expression of which is responsive to various conditions. Here, we set out to investigate the potential of orange peel extract as an inducer of laccase production in this white-rot fungus, in comparison to the previously identified inducing chemical compound, veratryl alcohol. For four geographically distinct T. versicolor strains, a positive correlation has been observed between their oxidative activity and incubation time in liquid cultures. The addition of 20% orange peel extract or 5 mM veratryl alcohol caused a rapid increase in the oxidative potential of T. versicolor M99 after 24 h, with a more pronounced effect observed for the orange peel extract. To elucidate the underlying molecular mechanisms of the induced laccase activity, a transcriptional gene expression analysis was performed for the seven individual laccase genes in T. versicolor, revealing the upregulation of several laccase genes in response to the addition of each inducer. Notably, the gene encoding TvLac5 demonstrated a substantial upregulation in response to the addition of 20% orange peel extract, likely contributing to the observed increase in its oxidative potential. In conclusion, our results demonstrate that orange peels are a promising agro-industrial side stream for implementation as inducing agents in large-scale laccase production with T. versicolor.

Special Issue on Biotechnological Applications of Oxidoreductases

This Special Issue was launched in conjunction with the 10th edition of the OxiZymes meeting in Siena (Italy) in 2022 [...].