How to enjoy laccases

Secretory Production of the Hericium erinaceus Laccase from Saccharomyces cerevisiae

Mushroom laccases play a crucial role in lignin depolymerization, one of the most critical challenges in lignin utilization. Importantly, laccases can utilize a wide range of substrates, such as toxicants and antibiotics. This study isolated a novel laccase, named HeLac4c, from endophytic white-rot fungi Hericium erinaceus mushrooms. The cDNAs for this enzyme were 1569 bp in length and encoded a protein of 523 amino acids, including a 20 amino-acid signal peptide. Active extracellular production of glycosylated laccases from Saccharomyces cerevisiae was successfully achieved by selecting an optimal translational fusion partner. We observed that 5 and 10 mM Ca2+, Zn2+, and K+ increased laccase activity, whereas 5 mM Fe2+ and Al3+ inhibited laccase activity. The laccase activity was inhibited by the addition of low concentrations of sodium azide and L-cysteine. The optimal pH for the 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt was 4.4. Guaiacylglycerol-β-guaiacyl ether, a lignin model compound, was polymerized by the HeLac4c enzyme. These results indicated that HeLac4c is a novel oxidase biocatalyst for the bioconversion of lignin into value-added products for environmental biotechnological applications.

Biocatalytic characterization of Hericium erinaceus laccase isoenzymes for the oxidation of lignin derivative substrates

Mushroom laccases are biocatalysts that oxidize various substrates. To identify a novel enzyme involved in lignin valorization, we isolated and characterized laccase isoenzymes from the mushroom Hericium erinaceus. The laccase cDNAs (Lac1a and Lac1b) cloned from the mushroom mycelia consisted of 1536 bp and each encoded a protein with 511 amino acids, containing a 21-amino-acid signal peptide. Comparative phylogenetic analysis revealed high homology between the deduced amino acid sequences of Lac1a and Lac1b and those from basidiomycetous fungi. In the Pichia pastoris expression system, high extracellular production of Lac1a, a glycoprotein, was achieved, whereas Lac1b was not expressed as a secreted protein because of hyper-glycosylation. Biochemical characterization of the purified recombinant Lac1a (rLac1a) protein revealed its oxidizing efficacy toward 14 aromatic substrates. The highly substrate-specific rLac1a showed catalytic efficiencies of 877 s^-1 mM^-1, 829 s^-1 mM^-1, 520 s^-1 mM^-1, and 467 s^-1 mM^-1 toward 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), hydroquinone, guaiacol, and 2,6-dimethylphenol, respectively. Moreover, rLac1a showed approximately 10 % higher activity in non-ionic detergents and >50 % higher residual activity in various organic solvents. These results indicate that rLac1a is a novel oxidase biocatalyst for the bioconversion of lignin into value-added products.

The Biomodified Lignin Platform: A Review

A reliance on fossil fuel has led to the increased emission of greenhouse gases (GHGs). The excessive consumption of raw materials today makes the search for sustainable resources more pressing than ever. Technical lignins are mainly used in low-value applications such as heat and electricity generation. Green enzyme-based modifications of technical lignin have generated a number of functional lignin-based polymers, fillers, coatings, and many other applications and materials. These bio-modified technical lignins often display similar properties in terms of their durability and elasticity as fossil-based materials while also being biodegradable. Therefore, it is possible to replace a wide range of environmentally damaging materials with lignin-based ones. By researching publications from the last 20 years focusing on the latest findings utilizing databases, a comprehensive collection on this topic was crafted. This review summarizes the recent progress made in enzymatically modifying technical lignins utilizing laccases, peroxidases, and lipases. The underlying enzymatic reaction mechanisms and processes are being elucidated and the application possibilities discussed. In addition, the environmental assessment of novel technical lignin-based products as well as the developments, opportunities, and challenges are highlighted.

The Laccase of Myrothecium roridum VKM F-3565: A New Look at Fungal Laccase Tolerance to Neutral and Alkaline Conditions

Most of the currently known fungal laccases show their maximum activity under acidic environmental conditions. It is known that a decrease in the activity of a typical laccase at neutral or alkaline pH values is the result of an increase in the binding of the hydroxide anion to the T2/T3 copper center, which prevents the transfer of an electron from the T1 Cu to the trinuclear copper center. However, evolutionary pressure has resolved the existing limitations in the catalytic mechanism of laccase, allowing such enzymes to be functionally active under neutral/alkaline pH conditions, thereby giving fungi an advantage for their survival. Combined molecular and biochemical studies, homological modeling, calculation of the electrostatic potential on the Connolly surface at pH 5.0 and 7.0, and structural analysis of the novel alkaliphilic laccase of Myrothecium roridum VKM F-3565 and alkaliphilic and acidophilic fungal laccases with a known structure allowed a new intramolecular channel near the one of the catalytic aspartate residues at T2-copper atom to be found. The amino acid residues of alkaliphilic laccases forming this channel can presumably serve as proton donors for catalytic aspartates under neutral conditions, thus ensuring proper functioning. For the first time for ascomycetous laccases, the production of new trimeric products of phenylpropanoid condensation under neutral conditions has been shown, which could have a potential for use in pharmacology.

Studies on the Oxidation of Aromatic Amines Catalyzed by Trametes versicolor Laccase

The bio-oxidation of a series of aromatic amines catalyzed by T. versicolor laccase has been investigated exploiting either commercially available nitrogenous substrates [(E)-4-vinyl aniline and diphenyl amine] or ad hoc synthetized ones [(E)-4-styrylaniline, (E)-4-(prop-1-en-1-yl)aniline and (E)-4-(((4-methoxyphenyl)imino)methyl)phenol]. At variance to their phenolic equivalents, the investigated aromatic amines were not converted into the expected cyclic dimeric structures under T. versicolor catalysis. The formation of complex oligomeric/polymeric or decomposition by-products was mainly observed, with the exception of the isolation of two interesting but unexpected chemical skeletons. Specifically, the biooxidation of diphenylamine resulted in an oxygenated quinone-like product, while, to our surprise, in the presence of T. versicolor laccase (E)-4-vinyl aniline was converted into a 1,2-substited cyclobutane ring. To the best of our knowledge, this is the first example of an enzymatically triggered [2 + 2] olefin cycloaddition. Possible reaction mechanisms to explain the formation of these products are also reported.

Feasibility and potential of laccase-based enzyme in wastewater treatment through sustainable approach: A review

The worldwide increase in metropolitan cities and rise in industrialization have resulted in the assimilation of hazardous pollutants into the ecosystems. Different physical, chemical and biological techniques have been employed to remove these toxins from water bodies. Several bioprocess applications using microbes and their enzymes are utilized to achieve the goal. Biocatalysts, such as laccases, are employed explicitly to deplete a variety of organic pollutants. However, the degradation of contaminants using biocatalysts has many disadvantages concerning the stability and activity of the enzyme. Hence, they are immobilized on different supports to improve the enzyme kinetics and recyclability. Furthermore, standard wastewater treatment methods are not effective in eliminating all the contaminants. As a result, membrane separation technologies have emerged to overcome the limitations of traditional wastewater treatment methods. Moreover, enzymes immobilized onto these membranes have generated new avenues in wastewater purification technology. This review provides the latest information on laccases from diverse sources, their molecular framework and their mode of action. This report also gives information about various immobilization techniques and the application of membrane bioreactors to eliminate and biotransform hazardous contaminants. In a nutshell, laccases appear to be the most promising biocatalysts for green and cost-efficient wastewater treatment technologies.

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.

Nanomaterials as Redox Mediators in Laccase-Based Amperometric Biosensors for Catechol Assay

Laccase is a copper-containing enzyme that does not require hydrogen peroxide as a co-substrate or additional cofactors for an enzymatic reaction. Nanomaterials of various chemical structures are usually applied to the construction of enzyme-based biosensors. Metals, metal oxides, semiconductors, and composite NPs perform various functions in electrochemical transformation schemes as a platform for the enzyme immobilization, a mediator of an electron transfer, and a signal amplifier. We describe here the development of amperometric biosensors (ABSs) based on laccase and redox-active micro/nanoparticles (hereafter—NPs), which were immobilized on a graphite electrode (GE). For this purpose, we isolated a highly purified enzyme from the fungus Trametes zonatus, and then synthesized bi- and trimetallic NPs of noble and transition metals, as well as hexacyanoferrates (HCF) of noble metals; these were layered onto the surfaces of GEs. The electroactivity of many of the NPs immobilized on the GEs was characterized by cyclic voltammetry (CV) experiments. The most effective mediators of electron transfer were selected as the platform for the development of laccase-based ABSs. As a result, a number of catechol-sensitive ABSs were constructed and characterized. The laccase/CuCo/GE was demonstrated to possess the highest sensitivity to catechol (4523 A·M⁻¹·m⁻²) among the tested ABSs. The proposed ABSs may be promising for the analysis of phenolic derivatives in real samples of drinking water, wastewater, and food products.

Modification of Deoxynivalenol by a Fungal Laccase Paired with Redox Mediator TEMPO

Mycotoxins such as deoxynivalenol introduce a health risk to the food supply and are costly to manage or avoid. Technologies for reducing or eliminating the toxicity of deoxynivalenol could be useful in a variety of processes, such as in preserving the value as animal feed of byproducts of ethanol production. We characterized transformation products of deoxynivalenol that were formed by the combination of a fungal laccase paired with the chemical mediator 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), using chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy. Alcohol groups at the C3 and C15 positions of deoxynivalenol were oxidized to ketones, and the chemical mediator became covalently linked to the C4 position. Conditions experienced during gas chromatography led to the dissociation of TEMPO, forming 3,15-diketodeoxynivalenol. Understanding the range of possible modifications to deoxynivalenol and other trichothecenes is a necessary step toward effective remediation of contaminated grain.

An Overview on the Recent Advances in Alternative Solvents as Stabilizers of Proteins and Enzymes

Currently, the use of alternative solvents is increasing, namely ionic liquids (ILs) and deep eutectic solvents (DESs) in diverse fields of knowledge, such as biochemistry, chemistry, chemical engineering, biotechnology and biomedicine. Particularly, when compared to traditional solvents, these alternative solvents have great importance for biomolecules due to the enhanced solubility, structure stability and the biological activity of biomolecules, such as protein and enzymes. Thus, in this review article, the recent developments and efforts on the technological developments carried out with ILs and DESs for the stabilization and activation of proteins and enzymes are provided. The most studied IL- and DES-based formulations for proteins and enzymes are discussed and the molecular mechanisms and interactions related to the increased stability promoted by these alternative solvents are disclosed, while emphasizing their main advantages.

Optimization of the Decolorization of the Reactive Black 5 by a Laccase-like Active Cell-Free Supernatant from Coriolopsis gallica

The textile industry generates huge volumes of colored wastewater that require multiple treatments to remove persistent toxic and carcinogenic dyes. Here we studied the decolorization of a recalcitrant azo dye, Reactive Black 5, using laccase-like active cell-free supernatant from Coriolopsis gallica. Decolorization was optimized in a 1 mL reaction mixture using the response surface methodology (RSM) to test the influence of five variables, i.e., laccase-like activity, dye concentration, redox mediator (HBT) concentration, pH, and temperature, on dye decolorization. Statistical tests were used to determine regression coefficients and the quality of the models used, as well as significant factors and/or factor interactions. Maximum decolorization was achieved at 120 min (82 ± 0.6%) with the optimized protocol, i.e., laccase-like activity at 0.5 U mL−1, dye at 25 mg L−1, HBT at 4.5 mM, pH at 4.2 and temperature at 55 °C. The model proved significant (ANOVA test with p < 0.001): coefficient of determination (R²) was 89.78%, adjusted coefficient of determination (R²A) was 87.85%, and root mean square error (RMSE) was 10.48%. The reaction conditions yielding maximum decolorization were tested in a larger volume of 500 mL reaction mixture. Under these conditions, the decolorization rate reached 77.6 ± 0.4%, which was in good agreement with the value found on the 1 mL scale. RB5 decolorization was further evaluated using the UV-visible spectra of the treated and untreated dyes.

Laccases and Tyrosinases in Organic Synthesis

Laccases (Lac) and tyrosinases (TYR) are mild oxidants with a great potential in research and industry. In this work, we review recent advances in their use in organic synthesis. We summarize recent examples of Lac-catalyzed oxidation, homocoupling and heterocoupling, and TYR-catalyzed ortho-hydroxylation of phenols. We highlight the combination of Lac and TYR with other enzymes or chemical catalysts. We also point out the biological and pharmaceutical potential of the products, such as dimers of piceid, lignols, isorhamnetin, rutin, caffeic acid, 4-hydroxychalcones, thiols, hybrid antibiotics, benzimidazoles, benzothiazoles, pyrimidine derivatives, hydroxytyrosols, alkylcatechols, halocatechols, or dihydrocaffeoyl esters, etc. These products include radical scavengers; antibacterial, antiviral, and antitumor compounds; and building blocks for bioactive compounds and drugs. We summarize the available enzyme sources and discuss the scalability of their use in organic synthesis. In conclusion, we assume that the intensive use of laccases and tyrosinases in organic synthesis will yield new bioactive compounds and, in the long-term, reduce the environmental impact of industrial organic chemistry.

The laccase mediator system at carbon nanotubes for anthracene oxidation and femtomolar electrochemical biosensing

We investigated the use of POXA1b laccase from Pleurotus ostreatus for the oxidation of anthracene into anthraquinone. We show that different pathways can occur depending on the nature of the redox mediator combined to laccase, leading to different structural isomers. The laccase combined with 2,2'-azine-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) leads to the formation of 1,4-anthraquinone and/or 1,2-anthraquinone. The unprecedented role of carbon nanotubes (CNTs) as redox mediators for oxidation of anthracene into 9,10-anthraquinone is shown and corroborated by density-functional theory (DFT) calculations. Owing to the efficient adsorption of anthraquinones at CNT electrodes, anthracene can be detected with low limit-of-detection using either laccase in solution, CNT-supported laccase or laccase immobilized at magnetic beads exploiting the adhesive property of a chimeric hydrophobin-laccase.

Bioactive Properties of a Novel Antibacterial Dye Obtained from Laccase-Mediated Oxidation of 8-Anilino-1-naphthalenesulfonic Acid

Fungal laccase obtained from a Cerrena unicolor strain was used as an effective biocatalyst for the transformation of 8-anilino-1-naphthalenesulfonic acid into a green-coloured antibacterial compound, which can be considered as both an antimicrobial agent and a textile dye, simultaneously. The process of biosynthesis was performed in buffered solutions containing methanol as a co-solvent, allowing better solubilisation of substrate. The transformation process was optimised in terms of the buffer pH value, laccase activity, and concentrations of the substrate and co-solvent. The crude product obtained exhibited low cytotoxicity, antibacterial properties against Staphylococcus aureus and Staphylococcus epidermidis, and antioxidant properties. Moreover, the synthesised green-coloured compound proved non-allergenic and demonstrated a high efficiency of dyeing wool fibres.

Enhancing the Thermostability of Engineered Laccases in Aqueous Betaine-Based Natural Deep Eutectic Solvents

In recent years, natural deep eutectic solvents (NADESs) have gained increasing attention as promising nontoxic solvents for biotechnological applications, due to their compatibility with enzymes and ability to enhance their activity. Betaine-based NADESs at a concentration of 25 wt % in a buffered aqueous solution were used as media to inhibit thermal inactivation of POXA1b laccase and its five variants when incubated at 70 and 90 °C. All the tested laccases showed higher residual activity when incubated in NADES solutions, with a further enhancement achieved also for the most thermostable variant. Furthermore, the residual activity of laccases in the presence of NADESs showed a clear advantage over the use of NADESs' individual components. Molecular docking simulations were performed to understand the role of NADESs in the stabilization of laccases toward thermal inactivation, evaluating the interaction between each enzyme and NADESs' individual components. A correlation within the binding energies between laccases and NADES components and the stabilization of the enzymes was demonstrated. These findings establish the possibility of preincubating enzymes in NADESs as a facile and cost-effective solution to inhibit thermal inactivation of enzymes when exposed to high temperatures. This computer-aided approach can assist the tailoring of NADES composition for every enzyme of interest.

Laccases as green and versatile biocatalysts: from lab to enzyme market-an overview

Laccases are multi-copper oxidase enzymes that catalyze the oxidation of different compounds (phenolics and non-phenolics). The scientific literature on laccases is quite extensive, including many basic and applied research about the structure, functions, mechanism of action and a variety of biotechnological applications of these versatile enzymes. Laccases can be used in various industries/sectors, from the environmental field to the cosmetics industry, including food processing and the textile industry (dyes biodegradation and synthesis). Known as eco-friendly or green enzymes, the application of laccases in biocatalytic processes represents a promising sustainable alternative to conventional methods. Due to the advantages granted by enzyme immobilization, publications on immobilized laccases increased substantially in recent years. Many patents related to the use of laccases are available, however, the real industrial or environmental use of laccases is still challenged by cost-benefit, especially concerning the feasibility of producing this enzyme on a large scale. Although this is a compelling point and the enzyme market is heated, articles on the production and application of laccases usually neglect the economic assessment of the processes. In this review, we present a description of laccases structure and mechanisms of action including the different sources (fungi, bacteria, and plants) for laccases production and tools for laccases evolution and prediction of potential substrates. In addition, we both compare approaches for scaling-up processes with an emphasis on cost reduction and productivity and critically review several immobilization methods for laccases. Following the critical view on production and immobilization, we provide a set of applications for free and immobilized laccases based on articles published within the last five years and patents which may guide future strategies for laccase use and commercialization.

Selection of a pH- and temperature-stable laccase from Ganoderma australe and its application for bioremediation of textile dyes

By virtue of screening, purification, and properties characterization, this study captures a new pH- and temperature-stable laccase, designated Galacc-F, from Ganoderma australe for dye bioremediating applications. The enzyme was purified to homogeneity by salt precipitation, ionic exchange, and size exclusion chromatography with a final specific activity of 22.214 U mg^-1, yielding a purification fold of 23.989 and recovery of 38.44%. Its molecular weight was estimated to be 48.0 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, zymography, Sephadex G-100 column, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, which confirmed its monomeric nature. Galacc-F exhibited high levels of activity and stability over wide ranges of pH (5.0-8.0) and temperature (10-60 °C), which are highly valuable properties in industrial processes. Broad substrate specificity was observed, wherein a better affinity was found for 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) with a low value of K_m (164.137 μM) and higher k_cat/K_m ratio (1.663 s^-1 μM^-1). Activity was stimulated by Cu²⁺ and β-mercaptoethanol but inhibited by ethylenediaminetetraacetic acid, diethylpyrocarbonate, iodoacetic acid, phenylmethylsulfonyl fluoride, and Hg²⁺, indicating that Galacc-F is a metalloprotease containing a typical histidine-cysteine-serine catalytic triad. It had high tolerance to surfactants, oxidants, and salts. Additionally, a fabricated protocol for native Galacc-F immobilization onto Fe₃O₄@Chitosan composite nanoparticles using glutaraldehyde as a crosslinker was developed. Most importantly, the enzyme was determined to be ideal for use in efficient treatment of dye effluents as compared with the laccases requiring redox mediators.

Degradation of zearalenone and aflatoxin B1 by Lac2 from Pleurotus pulmonarius in the presence of mediators

The contamination of foods and feeds with mycotoxins has been an issue of global significance. For mycotoxin detoxification, enzymatic biodegradation using laccase has received much attention. In this study, a laccase gene lac2 from the fungus Pleurotus pulmonarius was expressed in the Pichia pastoris X33 yeast strain to produce recombinant proteins. Enzymatic properties of recombinant Lac2 and its ability to degrade zearalenone (ZEN) and Aflatoxin B1 (AFB1) in the presence of four mediators (ABTS, TEMPO, AS and SA) were investigated. Result showed that the optimum pH and temperature of recombinant Lac2 were 3.5 and 55 °C, respectively. Lac2 was not sensitive to heat and stable under both acidic and alkaline conditions. Lac2-ABTS and Lac2-AS were efficient systems for ZEN degradation over a wide range of pH (4-8) and temperature (40-60 °C). Lac2-AS was the most efficient system for AFB1 degradation, reaching 99.82% of degradation at pH 7 and 37 °C after 1 h of incubation. Finally, the Lac2-mediator oxidation products were structurally characterized. This study lays a solid foundation for the application of Lac2 laccase combined with AS for degrading mycotoxin in food and feed.

Effect of ultrasound on protein functionality

The review focus on the effect of ultrasound on protein functionality. The presence of transient ultrasonic mechanical waves induce various sonochemical and sonomechanical effects on a protein. Sonochemical effects include the breakage of chains and/or the modification of side groups of aminoacids. Sonomechanical modifications by enhanced molecular agitation, might lead to the transient or permanent modification of the 3D structure of the folded protein. Since the biological function of proteins depends on the maintenance of its 3D folded structure, both sonochemical and sonomechanical effects might affect its properties. A protein might maintain its 3D structure and functionality after minor sonochemical effects, however, the enhanced mass transfer by sonomechanical effects might expose internal hydrophobic residues of the protein, making protein unfolding to an irreversible denatured state. Ultrasound enhanced mass transport effects are unique pathways to change the 3D folded structure of proteins which lead to a new functionality of proteins as support shield materials during the formation microspheres. Enzymes are proteins and their reactions should be conducted in a reactor set-up where enzymes are protected from sonic waves to maximize their catalytic efficiency. In this review, focused examples on protein dispersions/emulsions and enzyme catalysis are given.

Enzyme Catalyzed Copolymerization of Lignosulfonates for Hydrophobic Coatings

Enzymatic polymerization of lignin can generate a variety of value-added products concomitantly replacing fossil-based resources. In line with this approach, a laccase from the thermophilic fungus Myceliophthora thermophila (MtL) was used to couple a hydrophobicity enhancing fluorophenol (FP) molecule, namely 4-[4-(trifluoromethyl)phenoxy]phenol (4,4-F3MPP), as a model substrate onto lignosulfonate (LS). During the coupling reaction changes in fluorescence, phenol content, viscosity and molecular weight (size exclusion chromatography; SEC) were monitored. The effects of enzymatic coupling of FP onto LS on hydrophobicity were investigated by the means of water contact angle (WCA) measurement and determination of swelling capacity. Full polymerization of LS resulting in the production of water-insoluble polymers was achieved at a pH of 7 and 33°C. Incorporation of 2% (w/v) of FP led to an increase in WCA by 59.2% while the swelling capacity showed a decrease by 216.8%. Further, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis indicated successful covalent coupling of the FP molecule onto LS by an emerging peak at 1,320 cm^–1 in the FTIR spectrum and the evidence of Fluor in the XPS spectrum. This study shows the ability of laccase to mediate the tailoring of LS properties to produce functional polymers.

'Laccase-like' properties of coral-like silver citrate micro-structures for the degradation and determination of phenolic pollutants and adrenaline

Laccases are multicopper containing oxidase enzymes that are highly important in environmental remediation and biotechnology. To date, complex Copper containing materials have been reported as laccase mimic, and the possibility of a non-Cu laccase mimic remained unknown. In this work, we report an exceptionally simple functional laccase mimic based on coral-like silver citrate (AgCit) microstructures. The AgCit was synthesized by a simple precipitation method and was found to possess excellent laccase-like activity capable of oxidizing phenolic substrates and the endocrine hormone adrenaline. Compared to the natural laccase enzyme, our reported laccase-mimic has a higher υ_max and lower K_m value using adrenaline as a substrate. In addition, the AgCit laccase mimic was observed to be stable at extreme pH, higher temperature, and suitable for long-term storage at room temperature. The laccase-like properties of the AgCit nanozyme were successfully applied for the quantification and degradation of various phenolic pollutants and the adrenaline hormone.

Purification and Characterization of Mannanase from Aspergillus awamori for Fruit Juice Clarification

BACKGROUND

Fruit juice clarification is a challenging aspect of beverage industry which needs to be addressed for economical and hygienic production of fruit juices.

OBJECTIVE

Current study is focused on the complete purification, characterization and thermodynamic analysis of an efficient mannanase enzyme to analyze its applicability in biological clarification fruit juice.

METHODS

Mannanase production using Aspergillus awamori IIB037 in a 25 L stirred fermenter at pre optimized reaction conditions was carried out. Enzyme purification was carried out via series of steps. Characterization of enzyme along with kinetics and thermodynamic studies was conducted. Purified and characterized enzyme was assessed for its applicability in fruit juice clarification through clarification experiments on fresh apple juice.

RESULTS

Purification fold of 3.98 was obtained along with 86.80% purification yield of mannanase with specific activity of 158.16 U/mg. The molecular size of purified enzyme was determined as 66 kDa. The enzyme depicted 56% residual activity at 60°C after 8 hrs. Thermodynamic studies of an enzyme revealed enthalpy of activation (ΔH) and activation energy (Ea) as 30.53KJ/mol, 27.76KJ/mol, respectively. The enzyme activity increased in the presence of ß-mercaptoethanol surprisingly. On the other hand, methyl alcohol, ethanol, Hg2+ and Cu2+ inhibited enzyme activity. The enzyme showed Km and Vmax values of 11.07 mM and 19.08 μM min-1 for Locust Bean Gum (LBG) under optimal conditions. Juice treated with mannanase showed decrease in absorbance and increase in reducing sugar content.

CONCLUSION

The current study demonstrated that mannanase from Aspergillus awamori in its purified form has significant characteristics to be employed industrially for juice clarification.

Comparison of performances of different fungal laccases in delignification and detoxification of alkali-pretreated corncob for bioethanol production

The performance of the alkaline fungal laccase PIE5 (pH 8.5) in the delignification and detoxification of alkali-pretreated corncob to produce bioethanol was evaluated and compared with that of the neutral counterpart (rLcc9, 6.5), with the acidic laccase rLacA (4.0) was used as an independent control. Treatment with the three laccases facilitated bioethanol production compared with their respective controls. The lignin contents of alkali-pretreated corncob reduced from 4.06%, 5.06%, and 7.80% to 3.44%, 3.95%, and 5.03%, after PIE5, rLcc9, and rLacA treatment, respectively. However, the performances of the laccases were in the order rLacA > rLcc9 > PIE5 in terms of decreasing total phenol concentration (0.18, 0.36, and 0.67 g/l), boosting ethanol concentration (8.02, 7.51, and 7.31 g/l), and volumetric ethanol productivity (1.34, 0.94, and 0.91 g/l hr), and shortening overall fermentation time. Our results would inform future attempts to improve laccases for ethanol production. Furthermore, based on our data and the fact that additional procedures, such as pH adjustment, are needed during neutral/alkaline fungal laccase treatment, we suggest acidic fungal laccases may be a better choice than neutral/alkaline fungal laccases in bioethanol production.

Introducing a Thermo-Alkali-Stable, Metallic Ion-Tolerant Laccase Purified From White Rot Fungus Trametes hirsuta

This study introduces a valuable laccase, designated ThLacc-S, purified from white rot fungus Trametes hirsuta. ThLacc-S is a monomeric protein in nature with a molecular weight of 57.0 kDa and can efficiently metabolize endocrine disrupting chemicals. The enzyme was successfully purified to homogeneity via three consecutive steps consisting of salt precipitation and column chromatography, resulting in a 20.76-fold increase in purity and 46.79% yield, with specific activity of 22.111 U/mg protein. ThLacc-S was deciphered as a novel member of the laccase family and is a rare metalloenzyme that contains cysteine, serine, histidine, and tyrosine residues in its catalytic site, and follows Michaelis-Menten kinetic behavior with a K _m and a k _cat /K _m of 87.466 μM and 1.479 s^-1μM^-1, respectively. ThLacc-S exerted excellent thermo-alkali stability, since it was markedly active after a 2-h incubation at temperatures ranging from 20 to 70°C and retained more than 50% of its activity after incubation for 72 h in a broad pH range of 5.0-10.0. Enzymatic activities of ThLacc-S were enhanced and preserved when exposed to metallic ions, surfactants, and organic solvents, rendering this novel enzyme of interest as a green catalyst for versatile biotechnological and industrial applications that require these singularities of laccases, particularly biodegradation and bioremediation of environmental pollutants.

Evaluation of a novel nano-size collagenous matrix film cross-linked with gallotannins catalyzed by laccase

The effect of hydrolysis degree of gallotannins (GT, 1 mg/g) on cross-linking of nano-size collagen catalyzed by laccase (12 U/g) was studied, and the antibacterial properties of GT hydrolysates (HGT)-laccase (Lac) collagen films on minced cod were also investigated. The results showed that the tensile strength of HGT-Lac films (87.23-100.77 MPa) was higher than those added HGT alone (85.59-95.58 MPa) under the same hydrolysis degree of GT. Compared to the denaturation temperature (78.05 °C) of pure nano-size collagen film without addition of HGT and laccase, the denaturation temperature of HGT (80.75-86.30 °C) and HGT-Lac (91.97-101.64 °C) films increased greatly, especially for HGT-Lac films. Moreover, both HGT and HGT-Lac films showed some mild antibacterial properties for minced cod during storage at 4 °C for 8 days. Therefore, the combination of HGT and laccase could improve the performance of nano-size collagen film and extend the application of collagen in biodegradable/edible packaging.

Application of laccases for mycotoxin decontamination

Several food commodities can be infected by filamentous fungi, both in the field and during storage. Some of these fungi, under appropriate conditions, are capable of producing a wide range of secondary metabolites, including mycotoxins, which may resist food processing and arise in the final feed and food products. Contamination of these products with mycotoxins still occurs very often and that is why research in this area is valuable and still evolving. The best way to avoid contamination is prevention; however, when it is not possible, remediation is the solution. Enzymatic biodegradation of mycotoxins is a green solution for removal of these compounds that has attracted growing interest over recent years. Due to their ability to detoxify a wide variety of recalcitrant pollutants, laccases have received a lot of attention. Laccases are multi-copper proteins that use molecular oxygen to oxidise various aromatic and non-aromatic compounds, by a radical-catalysed reaction mechanism. Being non-specific, they are capable of degrading a wide range of compounds and the radical species formed can evolve towards both synthetic and degradative processes. The present review provides an overview of structural features, biological functions and catalytic mechanisms of laccases. The utilisation of laccases for mycotoxin degradation is reviewed, as well as shortcomings and future needs related with the use of laccases for mycotoxin decontamination from food and feed.

Biocatalysis with Laccases: An Updated Overview

Laccases are multicopper oxidases, which have been widely investigated in recent decades thanks to their ability to oxidize organic substrates to the corresponding radicals while producing water at the expense of molecular oxygen. Besides their successful (bio)technological applications, for example, in textile, petrochemical, and detoxifications/bioremediations industrial processes, their synthetic potentialities for the mild and green preparation or selective modification of fine chemicals are of outstanding value in biocatalyzed organic synthesis. Accordingly, this review is focused on reporting and rationalizing some of the most recent and interesting synthetic exploitations of laccases. Applications of the so-called laccase-mediator system (LMS) for alcohol oxidation are discussed with a focus on carbohydrate chemistry and natural products modification as well as on bio- and chemo-integrated processes. The laccase-catalyzed Csp2-H bonds activation via monoelectronic oxidation is also discussed by reporting examples of enzymatic C-C and C-O radical homo- and hetero-couplings, as well as of aromatic nucleophilic substitutions of hydroquinones or quinoids. Finally, the laccase-initiated domino/cascade synthesis of valuable aromatic (hetero)cycles, elegant strategies widely documented in the literature across more than three decades, is also presented.

Purification and Characterization of Two Novel Laccases from Peniophora lycii

Although, currently, more than 100 laccases have been purified from basidiomycete fungi, the majority of these laccases were obtained from fungi of the Polyporales order, and only scarce data are available about the laccases from other fungi. In this article, laccase production by the white-rot basidiomycete fungus Peniophora lycii, belonging to the Russulales order, was investigated. It was shown that, under copper induction, this fungus secreted three different laccase isozymes. Two laccase isozymes—Lac5 and LacA—were purified and their corresponding nucleotide sequences were determined. Both purified laccases were relatively thermostable with periods of half-life at 70 °C of 10 and 8 min for Lac5 and LacA, respectively. The laccases demonstrated the highest activity toward ABTS (97 U·mg⁻¹ for Lac5 and 121 U·mg⁻¹ for LacA at pH 4.5); Lac5 demonstrated the lowest activity toward 2,6-DMP (2.5 U·mg⁻¹ at pH 4.5), while LacA demonstrated this towards gallic acid (1.4 U·mg⁻¹ at pH 4.5). Both Lac5 and LacA were able to efficiently decolorize such dyes as RBBR and Bromcresol Green. Additionally, phylogenetic relationships among laccases of Peniophora spp. were reconstructed, and groups of orthologous genes were determined. Based on these groups, all currently available data about laccases of Peniophora spp. were systematized.

Enhancing the decolorization activity of Bacillus pumilus W3 CotA-laccase to Reactive Black 5 by site-saturation mutagenesis

Reactive Black 5 (RB5) is a typical refractory azo dye. Widespread utilization of RB5 has caused a variety of environmental and health problems. The enzymatic degradation of RB5 can be a promising solution due to its superiority as an eco-friendly and cost-competitive process. Bacterial CotA-laccase shows great application prospect to eliminate hazardous dyes from wastewater. However, efficient decolorization of RB5 CotA-laccase generally requires the participation of costly, toxic mediators. In the present study, we modified the amino acids Thr415 and Thr418 near the type 1 copper site and the amino acid Gln442 at the entrance of the substrate-binding pocket of Bacillus pumilus W3 CotA-laccase to boost its RB5 decolorization activity based on molecular docking analysis and site-saturation mutagenesis. Through the strategies, two double site mutants T415D/Q442A and T418K/Q442A obtained demonstrated 43.94 and 52.64% RB5 decolorization rates in the absence of a mediator at pH 10.0, respectively, which were about 3.70- and 4.43-fold higher compared with the wild-type CotA-laccase. Unexpectedly, the catalytic efficiency of the T418K/Q442A to ABTS was enhanced by 5.33-fold compared with the wild-type CotA-laccase. The mechanisms of conferring enhanced activity to the mutants were proposed by structural analysis. In summary, the mutants T415D/Q442A and T418K/Q442A have good application potentials for the biodegradation of RB5. KEY POINTS: • Three amino acids of CotA-laccase were manipulated by site-saturation mutagenesis. • Decolorization rate of two mutants to RB5 was enhanced 3.70- and 4.43-fold, respectively. • The mechanisms of awarding enhanced activity to the mutants were supposed.

Comparative Genomics Platform and Phylogenetic Analysis of Fungal Laccases and Multi-Copper Oxidases

Laccases (EC 1.10.3.2), a group of multi-copper oxidases (MCOs), play multiple biological functions and widely exist in many species. Fungal laccases have been extensively studied for their industrial applications, however, there was no database specially focused on fungal laccases. To provide a comparative genomics platform for fungal laccases, we have developed a comparative genomics platform for laccases and MCOs (http://laccase.riceblast.snu.ac.kr/). Based on protein domain profiles of characterized sequences, 3,571 laccases were predicted from 690 genomes including 253 fungi. The number of putative laccases and their properties exhibited dynamic distribution across the taxonomy. A total of 505 laccases from 68 genomes were selected and subjected to phylogenetic analysis. As a result, four clades comprised of nine subclades were phylogenetically grouped by their putative functions and analyzed at the sequence level. Our work would provide a workbench for putative laccases mainly focused on the fungal kingdom as well as a new perspective in the identification and classification of putative laccases and MCOs.

Innovative hydrolysis of corn stover biowaste by modified magnetite laccase immobilized nanoparticles

Intensive studies have been performed on the improvement of bioethanol production by transformation of lignocellulose biomass. In this study, the digestibility of corn stover was dramatically improved by using laccase immobilized on Cu²⁺ modified recyclable magnetite nanoparticles, Fe₃O₄-NH₂. After digestion, the laccase was efficiently separated from slurry. The degradation rate of lignin reached 40.76%, and the subsequent cellulose conversion rate 38.37% for 72 h at 35 °C with cellulase at 50 U g^-1 of corn stover. Compared to those of free and inactivated mode, the immobilized laccase pre-treatment increased subsequent cellulose conversion rates by 23.98% and 23.34%, respectively. Moreover, the reusability of immobilized laccase activity remained 50% after 6 cycles. The storage and thermal stability of the fixed laccase enhanced by 70% and 24.1% compared to those of free laccase at 65 °C, pH 4.5, respectively. At pH 10.5, it exhibited 16.3% more activities than its free mode at 35 °C. Our study provides a new avenue for improving the production of bioethanol with immobilized laccase for delignification using corn stover as the starting material.

Recent developments in enzyme immobilization technology for high-throughput processing in food industries

The demand for food and beverage markets has increased as a result of population increase and in view of health awareness. The quality of products from food processing industry has to be improved economically by incorporating greener methodologies that enhances the safety and shelf life via the enzymes application while maintaining the essential nutritional qualities. The utilization of enzymes is rendered more favorable in industrial practices via the modification of their characteristics as attested by studies on enzyme immobilization pertaining to different stages of food and beverage processing; these studies have enhanced the catalytic activity, stability of enzymes and lowered the overall cost. However, the harsh conditions of industrial processes continue to increase the propensity of enzyme destabilization thus shortening their industrial lifespan namely enzyme leaching, recoverability, uncontrollable orientation and the lack of a general procedure. Innovative studies have strived to provide new tools and materials for the development of systems offering new possibilities for industrial applications of enzymes. Herein, an effort has been made to present up-to-date developments on enzyme immobilization and current challenges in the food and beverage industries in terms of enhancing the enzyme stability.

Antioxidant Compounds for the Inhibition of Enzymatic Browning by Polyphenol Oxidases in the Fruiting Body Extract of the Edible Mushroom Hericium erinaceus

Mushrooms are attractive resources for novel enzymes and bioactive compounds. Nevertheless, mushrooms spontaneously form brown pigments during food processing as well as extraction procedures for functional compounds. In this study, the dark browning pigment in the extract derived from the edible mushroom Hericium erinaceus was determined to be caused by the oxidation of endogenous polyphenol compounds by the polyphenol oxidase (PPO) enzyme family. These oxidized pigment compounds were measured quantitatively using a fluorospectrophotometer and, through chelation deactivation and heat inactivation, were confirmed to be enzymatic browning products of reactions by a metalloprotein tyrosinase in the PPO family. Furthermore, a transcript analysis of the identified putative PPO-coding genes in the different growth phases showed that tyrosinase and laccase isoenzymes were highly expressed in the mushroom fruiting body, and these could be potential PPOs involved in the enzymatic browning reaction. A metabolite profiling analysis of two different growth phases also revealed a number of potential enzymatic browning substances that were grouped into amino acids and their derivatives, phenolic compounds, and purine and pyrimidine nucleobases. In addition, these analyses also demonstrated that the mushroom contained a relatively high amount of natural antioxidant compounds that can effectively decrease the browning reaction via PPO-inhibitory mechanisms that inhibit tyrosinase and scavenge free radicals in the fruiting body. Altogether, these results contribute to an understanding of the metabolites and PPO enzymes responsible for the enzymatic browning reaction of H. erinaceus.

Immobilization of Laccase on Magnetic Chelator Nanoparticles for Apple Juice Clarification in Magnetically Stabilized Fluidized Bed

The juice clarification, one of the key steps in juice processing, suffers from haze formation that results from residual phenolic compounds. In this study, laccase was immobilized on metal-chelated magnetic silica nanoparticles and used for continuous juice clarification in a magnetically stabilized fluidized bed (MSFB) assisted by alternating magnetic field. Furthermore, a new combination of laccase catalysis and microfiltration was developed for the juice clarification. Immobilized laccase provided high relative activity within broader ranges of pH and temperature compared to the free enzyme. Magnetic immobilized laccase exhibited the best reaction rate of 12.1 μmol g^–1 min^–1 for catechol oxidation under the alternating magnetic field of 400 Hz, 60 Gs. No activity loss occurred in immobilized laccase after 20 h continuous operation of juice treatment in MSFB under an alternating magnetic field. Combined with microfiltration after treatment with immobilized laccase, the color of apple juice was decreased by 33.7%, and the light transmittance was enhanced by 20.2%. Furthermore, only 16.3% of phenolic compounds and 15.1% of antioxidant activity was reduced for apple juice after the clarification. By this combination strategy, the apple juice possessed good freeze–thaw and thermal stability.

From Graphite to Laccase Biofunctionalized Few-Layer Graphene: A "One Pot" Approach Using a Chimeric Enzyme

A chimeric enzyme based on the genetic fusion of a laccase with a hydrophobin domain was employed to functionalize few-layer graphene, previously exfoliated from graphite in the presence of the hydrophobin. The as-produced, biofunctionalized few-layer graphene was characterized by electrochemistry and Raman spectroscopy, and finally employed in the biosensing of phenols such as catechol and dopamine. This strategy paves the way for the functionalization of nanomaterials by hydrophobin domains of chimeric enzymes and their use in a variety of electrochemical applications.

Laccase Immobilized Fe3O4-Graphene Oxide Nanobiocatalyst Improves Stability and Immobilization Efficiency in the Green Preparation of Sulfa Drugs

This paper, reports on the novel and green synthesis procedure for sulfonamides that involved the immobilization of Trametes Versicolor laccase onto the Fe3O4–graphene nanocomposite via glutaraldehyde (GA) crosslinking (Lac/Fe3O4/GO). Various parameters, mainly, activation time, GA, and laccase concentration were investigated and optimized. The results showed that the optimal contact time was 4 h, GA concentration was 5% while laccase concentration was 5 mg·mL−1, at which a high enzyme activity recovery was achieved (86%). In terms of the stability of immobilized laccase to temperature and storage conditions, the performance of the nanobiocatalyst was found to significantly exceed that of free laccase. The results have indicated that nearly 70% of relative activity for immobilized laccase remained after the incubation period of 2 h at 55 °C, but only 48% of free laccase remained within the same time period. Moreover, the immobilized laccase retained 88% of its initial activity after storage for 20 days. In case of the free laccase, the activity retained within the same time period was 32%. In addition, the nanobiocatalyst possessed better recycling performance as evidenced from the observation that after eight cycles of repeated use, it retained 85% of its original activity.

The heterologous expression, characterization, and application of a novel laccase from Bacillus velezensis

Laccases have a huge potential in numerous environmental and industrial applications due to the ability to oxidized a wide range of substrates. Here, a novel laccase gene from the identified Bacillus velezensis TCCC 111904 was heterologously expressed in Escherichia coli. The optimal temperature and pH for oxidation by recombinant laccase (rLac) were 80 °C and 5.5, respectively, in the case of the substrate 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 80 °C and 7.0, respectively, in the case of 2,6-dimethoxyphenol (2,6-DMP). rLac exhibited high thermostability and pH stability over a wide range (pH 3.0, 7.0, and 9.0). Additionally, most of the metal ions did not inhibit the activity of rLac significantly. rLac showed great tolerance against high concentration of NaCl, and 50.8% of its initial activity remained in the reaction system containing 500 mM NaCl compared to the control. Moreover, rLac showed a high efficiency in decolorizing different types of dyes including azo, anthraquinonic, and triphenylmethane dyes at a high temperature (60 °C) and over an extensive pH range (pH 5.5, 7.0, and 9.0). These unique characteristics of rLac indicated that it could be a potential candidate for applications in treatment of dye effluents and other industrial processes.