Cloning, sequence analysis, and expression of ligninolytic phenoloxidase genes of the white-rot basidiomycete Coriolus hirsutus

Aflatoxin B1 (AFB1) biodegradation by a lignolytic phenoloxidase of Trametes hirsuta

Aflatoxin B1 (AFB1) is a highly potent mycotoxin that poses a serious threat to human and animal health. This study investigated the biodegradation of AFB1 by the supernatant of submerged cultured Trametes hirsuta, with a focus on identifying and characterizing the responsible enzyme(s). The extracellular enzymes of the white-rot mushroom were extracted from the supernatant and pre-separated using anion exchange fast protein liquid chromatography (FPLC). To pinpoint the specific enzyme, the eluted protein fractions exhibiting the highest degradation activity were subjected to detailed biochemical and proteomic analyses. A second purification step, ultrafiltration, yielded an electrophoretically pure enzyme. Sequencing of tryptic peptides using a nano-LC system coupled to a qQTOF mass spectrometer identified the enzyme as a lignolytic phenoloxidase. The enzyme exhibited a molecular mass of 55.6 kDa and achieved an impressive AFB1 degradation rate of 77.9% under optimized experimental conditions. This is the first fungal lignolytic phenoloxidase capable of aflatoxin degradation without requiring hydrogen peroxide as a cofactor, highlighting its unique catalytic mechanism. It may be used in mycotoxin remediation strategies, such as treating the surfaces of contaminated fruits, vegetables, and nuts.

Laccase mediated delignification of wasted and non-food agricultural biomass: Recent developments and challenges

Utilization of microbial laccases is considered as the cleaner and target specific biocatalytic mechanism for the recovery of cellulose and hemicelluloses from nonfood and wasted agricultural, lignocellulosic biomass (LCB). The extent of lignin removal by laccase depends on the biochemical composition of biomass and the redox potential (E⁰) of the biocatalyst. Intensive research efforts are going on all over the world for the recognition of appropriate and easily available agricultural lignocellulosic feedstocks to exploit maximally for the production of value-added bioproducts and biofuels. In such circumstances, laccase can play a major role as a leading biocatalyst and potent substitute for chemical based deconstruction of the lignocellulosic materials. The limited commercialization of laccase at an industrial scale has been feasible due to its full working efficiency mostly expressed in the presence of cost intensive redox mediators only. Although, recently there are some reports that came on the mediator free biocatalysis of enzyme but still not considerably explored and neither understood in depth. The present review will address the various research gaps and shortcomings that acted as the big hurdles before the complete exploitation of laccases at an industrial scale. Further, this article also reveals insights on different microbial laccases and their diverse functional environmental conditions that affect the deconstruction process of LCB.

Feasible Cluster Model Method for Simulating the Redox Potentials of Laccase CueO and Its Variant

Laccases are regarded as versatile green biocatalysts, and recent scientific research has focused on improving their redox potential for broader industrial and environmental applications. The density functional theory (DFT) quantum mechanics approach, sufficiently rigorous and efficient for the calculation of electronic structures, is conducted to better comprehend the connection between the redox potential and the atomic structural feature of laccases. According to the crystal structure of wild type laccase CueO and its variant, a truncated miniature cluster model method was established in this research. On the basic of thermodynamic cycle, the overall Gibbs free energy variations before and after the one-electron reduction were calculated. It turned out that the trends of redox potentials to increase after variant predicted by the theoretical calculations correlated well with those obtained by experiments, thereby validating the feasibility of this cluster model method for simulating the redox potentials of laccases.

Protein Engineering Approaches to Enhance Fungal Laccase Production in S. cerevisiae

Laccases secreted by saprotrophic basidiomycete fungi are versatile biocatalysts able to oxidize a wide range of aromatic compounds using oxygen as the sole requirement. Saccharomyces cerevisiae is a preferred host for engineering fungal laccases. To assist the difficult secretion of active enzymes by yeast, the native signal peptide is usually replaced by the preproleader of S. cerevisiae alfa mating factor (MFα1). However, in most cases, only basal enzyme levels are obtained. During directed evolution in S. cerevisiae of laccases fused to the α-factor preproleader, we demonstrated that mutations accumulated in the signal peptide notably raised enzyme secretion. Here we describe different protein engineering approaches carried out to enhance the laccase activity detected in the liquid extracts of S. cerevisiae cultures. We demonstrate the improved secretion of native and engineered laccases by using the fittest mutated α-factor preproleader obtained through successive laccase evolution campaigns in our lab. Special attention is also paid to the role of protein N-glycosylation in laccase production and properties, and to the introduction of conserved amino acids through consensus design enabling the expression of certain laccases otherwise not produced by the yeast. Finally, we revise the contribution of mutations accumulated in laccase coding sequence (CDS) during previous directed evolution campaigns that facilitate enzyme production.

Axial bonds at the T1 Cu site of Thermus thermophilus SG0.5JP17-16 laccase influence enzymatic properties

Laccase is a multi‐copper oxidase which oxidizes substrate at the type 1 copper site, simultaneously coupling the reduction of dioxygen to water at the trinuclear copper center. In this study, we used site‐directed mutagenesis to study the effect of axial bonds between the metal and amino acid residue side chains in lacTT. Our kinetic and spectral data showed that the replacement of the axial residue with non‐coordinating residues resulted in higher efficiency (k_cat/K_m) and a lower Cu²⁺ population at the type 1 copper site, while substitution with strongly coordinating residues resulted in lower efficiency and a higher Cu²⁺ population, as compared with the wild‐type. The redox potentials of mutants with hydrophobic axial residues (Ala and Phe) were higher than that of the wild‐type. In conclusion, these insights into the catalytic mechanism of laccase may be of use in protein engineering to fine‐tune its enzymatic properties for industrial application.

Yeast Hosts for the Production of Recombinant Laccases: A Review

Laccases are multi-copper oxidoreductases which catalyze the oxidation of a wide range of substrates during the simultaneous reduction of oxygen to water. These enzymes, originally found in fungi, plants, and other natural sources, have many industrial and biotechnological applications. They are used in the food, textile, pulp, and paper industries, as well as for bioremediation purposes. Although natural hosts can provide relatively high levels of active laccases after production optimization, heterologous expression can bring, moreover, engineered enzymes with desired properties, such as different substrate specificity or improved stability. Hence, diverse hosts suitable for laccase production are reviewed here, while the greatest emphasis is placed on yeasts which are commonly used for industrial production of various proteins. Different approaches to optimize the laccase expression and activity are also discussed in detail here.

The Trametes hirsuta 072 laccase multigene family: Genes identification and transcriptional analysis under copper ions induction

Laccases, blue copper-containing oxidases, ≿ an play an important role in a variety of natural processes. The majority of fungal laccases are encoded by multigene families that express closely related proteins with distinct functions. Currently, only the properties of major gene products of the fungal laccase families have been described. Our study is focused on identification and characterization of laccase genes, which are transcribed in basidiomycete Trametes hirsuta 072, an efficient lignin degrader, in a liquid medium, both without and with induction of laccase transcription by copper ions. We carried out production of cDNA libraries from total fungal RNA, followed by suppression subtractive hybridization and mirror orientation selection procedures, and then used Next Generation Sequencing to identify low abundance and differentially expressed laccase transcripts. This approach resulted in description of five laccase genes of the fungal family, which, according to the phylogenetic analysis, belong to distinct clusters within the Trametes genus. Further analysis established similarity of physical, chemical, and catalytic properties between laccases inside each cluster. Structural modeling suggested importance of the sequence differences in the clusters for laccase substrate specificity and catalytic efficiency. The implications of the laccase variations for the fungal physiology are discussed.

Identification of Single Nucleotide Polymorphism Markers in the Laccase Gene of Shiitake Mushrooms (Lentinula edodes)

We identified single nucleotide polymorphism (SNP) markers in the laccase gene to establish a line-diagnostic system for shiitake mushrooms. A total of 89 fungal isolates representing four lines, including Korean registered, Korean wild type, Chinese, and Japanese lines, were analyzed. The results suggest that SNP markers in the laccase gene can be useful for line typing in shiitake mushrooms.

Critical factors affecting laccase-mediated biobleaching of pulp in paper industry

Next to xylanases, laccases from fungi and alkali-tolerant bacteria are the most important biocatalysts that can be employed for eco-friendly biobleaching of hard and soft wood pulps in the paper industry. Laccases offer a potential alternative to conventional, environmental-polluting chlorine and chlorine-based bleaching and has no reductive effect on the final yield of pulp as compared to hemicellulases (xylanases and mannanases). In the last decade, reports on biobleaching with laccases are based on laboratory observations only. There are several critical challenges before this enzyme can be implemented for pulp bleaching at the industrial scale. This review discusses significant factors like redox potential, laccase mediator system (LMS)-synthetic or natural, pH, temperature, stability of enzyme, unwanted grafting reactions of laccase, and cost-intensive production at large scale which constitute a great hitch for the successful implementation of laccases at industrial level.

Effect of the L499M mutation of the ascomycetous Botrytis aclada laccase on redox potential and catalytic properties

Laccases are members of a large family of multicopper oxidases that catalyze the oxidation of a wide range of organic and inorganic substrates accompanied by the reduction of dioxygen to water. These enzymes contain four Cu atoms per molecule organized into three sites: T1, T2 and T3. In all laccases, the T1 copper ion is coordinated by two histidines and one cysteine in the equatorial plane and is covered by the side chains of hydrophobic residues in the axial positions. The redox potential of the T1 copper ion influences the enzymatic reaction and is determined by the nature of the axial ligands and the structure of the second coordination sphere. In this work, the laccase from the ascomycete Botrytis aclada was studied, which contains conserved Ile491 and nonconserved Leu499 residues in the axial positions. The three-dimensional structures of the wild-type enzyme and the L499M mutant were determined by X-ray crystallography at 1.7 Å resolution. Crystals suitable for X-ray analysis could only be grown after deglycosylation. Both structures did not contain the T2 copper ion. The catalytic properties of the enzyme were characterized and the redox potentials of both enzyme forms were determined: E0 = 720 and 580 mV for the wild-type enzyme and the mutant, respectively. Since the structures of the wild-type and mutant forms are very similar, the change in the redox potential can be related to the L499M mutation in the T1 site of the enzyme.

A novel laccase with potent antiproliferative and HIV-1 reverse transcriptase inhibitory activities from mycelia of mushroom Coprinus comatus

A novel laccase was isolated and purified from fermentation mycelia of mushroom Coprinus comatus with an isolation procedure including three ion-exchange chromatography steps on DEAE-cellulose, CM-cellulose, and Q-Sepharose and one gel-filtration step by fast protein liquid chromatography on Superdex 75. The purified enzyme was a monomeric protein with a molecular weight of 64 kDa. It possessed a unique N-terminal amino acid sequence of AIGPVADLKV, which has considerably high sequence similarity with that of other fungal laccases, but is different from that of C. comatus laccases reported. The enzyme manifested an optimal pH value of 2.0 and an optimal temperature of 60^°C using 2,2′-azinobis(3-ethylbenzothiazolone-6-sulfonic acid) diammonium salt (ABTS) as the substrate. The laccase displayed, at pH 2.0 and 37^°C, K_m values of 1.59 mM towards ABTS. It potently suppressed proliferation of tumor cell lines HepG2 and MCF7, and inhibited human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) with an IC₅₀ value of 3.46 μM, 4.95 μM, and 5.85 μM, respectively, signifying that it is an antipathogenic protein.

Purification and Characterization of Cellobiose Dehydrogenase from White-Rot BasidiomyceteTrametes hirsuta

In order to save energy during the pulp making process, we tried to use white-rot basidiomycete, Trametes hirsuta, which degrades lignin efficiently. But a decrease in paper strength caused by cellulolytic activity ruled this out for practical application. Since the cellulolytic activity of the fungus must be decreased, we purified and characterized a cellobiose dehydrogenase (CDH) that was reported to damage pulp fiber. The CDH in the culture filtrate of C. hirsutus was purified by freeze-thawing and chromatographic methods. The pI of the enzyme was 4.2 and its molecular weight was 92 kDa. The optimal temperature and pH of the enzyme were 60-70 degrees C and 5.0 respectively. Since the purified CDH decreased the viscosity of pulp in the presence of Fe(III) and cellobiose, it was shown that the suppression of CDH should be an effective way to reduce cellulose damage.

Copper-Dependent Production of aPycnoporus coccineusExtracellular Laccase inAspergillus oryzaeandSaccharomyces cerevisiae

Laccase is a multicopper-containing enzyme that catalyzes the oxidation of phenolic compounds. lcc1 cDNA coding for a secretory laccase of Pycnoporus coccineus was expressed under the maltose inducible amyB promoter in Aspergillus oryzae and under the galactose inducible GAL10 promoter in Saccharomyces cerevisiae. Laccase activities, which were undetectable in the absence of copper, were observed by increasing copper concentrations in the media for both systems. The amounts of secreted laccase protein but not lcc1 mRNA increased in proportion to copper concentrations in A. oryzae. The extracellular activities of native A. oryzae amylase and recombinant RNase-T1 expressed from the same amyB promoter in A. oryzae were constant regardless of copper concentrations. Our results indicate that a high copper concentration is required for the production of active laccase in heterologous hosts and that the copper is required for a post-transcriptional process.

Effect of pretreatment of hydrothermally processed rice straw with laccase-displaying yeast on ethanol fermentation

A gene encoding laccase I was identified and cloned from the white-rot fungus Trametes sp. Ha1. Laccase I contained 10 introns and an original secretion signal sequence. After laccase I without introns was prepared by overlapping polymerase chain reaction, it was inserted into expression vector pULD1 for yeast cell surface display. The oxidation activity of a laccase-I-displaying yeast as a whole-cell biocatalyst was examined with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), and the constructed yeast showed a high oxidation activity. After the pretreatment of hydrothermally processed rice straw (HPRS) with laccase-I-displaying yeast with ABTS, fermentation was conducted with yeast codisplaying endoglucanase, cellobiohydrolase, and β-glucosidase with HPRS. Fermentation of HPRS treated with laccase-I-displaying yeast was performed with 1.21-fold higher activities than those of HPRS treated with control yeast. The results indicated that pretreatment with laccase-I-displaying yeast with ABTS was effective for direct fermentation of cellulosic materials by yeast codisplaying endoglucanase, cellobiohydrolase, and β-glucosidase.

Requirement of a Tsp2-type tetraspanin for laccase repression and stress resistance in the basidiomycete Cryptococcus neoformans

Fungal laccases have been widely used in industry. The expression of laccase often is repressible by the primary carbon source glucose in many fungi. The underlying basis is largely unclear. We demonstrate here that a gene, TSP2-1, was required for laccase repression by glucose in the basidiomycete Cryptococcus neoformans. TSP2-1 encodes a Tsp2-type tetraspanin. The disruption of TSP2-1 resulted in constant melanin formation and the expression of the laccase gene LAC1. This derepression phenotype was restorable by 10 mM exogenous cyclic AMP (cAMP). A capsule defect in the mutant tsp2-1Δ also was restored by cAMP. The results indicate an interaction of Tsp2-1 with the cAMP-dependent protein kinase A (PKA) pathway that has been shown to modulate laccase repression and capsule biosynthesis in this fungus. Other roles of TSP2-1, e.g., in maintaining cell membrane integrity and stress resistance, also were defined. This work reveals a Tsp2-1-dependent glucose repression in C. neoformans. The function of Tsp2-type tetraspanin Tsp2-1 is described for the first time.

Heterologous laccase production and its role in industrial applications

Laccases are blue multicopper oxidases, catalyzing the oxidation of an array of aromatic substrates concomitantly with the reduction of molecular oxygen to water. These enzymes are implicated in a variety of biological activities. Most of the laccases studied thus far are of fungal origin. The large range of substrates oxidized by laccases has raised interest in using them within different industrial fields, such as pulp delignification, textile dye bleaching, and bioremediation. Laccases secreted from native sources are usually not suitable for large-scale purposes, mainly due to low production yields and high cost of preparation/purification procedures. Heterologous expression may provide higher enzyme yields and may permit to produce laccases with desired properties (such as different substrate specificities, or improved stabilities) for industrial applications. This review surveys researches on heterologous laccase expression focusing on the pivotal role played by recombinant systems towards the development of robust tools for greening modern industry.

Cryptococcus neoformans serotype A and Cryptococcus gattii serotype B isolates differ in their susceptibilities to fluconazole and voriconazole

This study presents antifungal susceptibility data for environmental isolates of Cryptococcus neoformans serotype A (n=32) and Cryptococcus gattii serotype B (n=18) to fluconazole and voriconazole employing disc diffusion and Etest methods. The disc diffusion test was performed on Mueller-Hinton agar as recommended by the Clinical and Laboratory Standards Institute (CLSI). For comparison, the disc diffusion test and Etest were also performed on RPMI-1640 agar supplemented with 2% glucose. The plates were incubated at 35 degrees C and read after 48h. Comparison of geometric mean inhibition zone diameters revealed that C. gattii isolates were significantly less susceptible than C. neoformans isolates to fluconazole (P=0.001) and voriconazole (P<0.0001). Similar results were obtained on RPMI agar by disc diffusion test and Etest, showing significantly reduced susceptibility for C. gattii isolates. Notwithstanding differences in the susceptibilities of the two species to fluconazole and voriconazole, they appeared susceptible according to the CLSI breakpoints recommended for some Candida spp. To what extent these differences in the susceptibilities of C. neoformans and C. gattii impact on the therapeutic management of cryptococcosis is unclear, although some studies have reported less favourable response in cases caused by the latter species.

Engineering and Applications of fungal laccases for organic synthesis

Laccases are multi-copper containing oxidases (EC 1.10.3.2), widely distributed in fungi, higher plants and bacteria. Laccase catalyses the oxidation of phenols, polyphenols and anilines by one-electron abstraction, with the concomitant reduction of oxygen to water in a four-electron transfer process. In the presence of small redox mediators, laccase offers a broader repertory of oxidations including non-phenolic substrates. Hence, fungal laccases are considered as ideal green catalysts of great biotechnological impact due to their few requirements (they only require air, and they produce water as the only by-product) and their broad substrate specificity, including direct bioelectrocatalysis.

Thus, laccases and/or laccase-mediator systems find potential applications in bioremediation, paper pulp bleaching, finishing of textiles, bio-fuel cells and more. Significantly, laccases can be used in organic synthesis, as they can perform exquisite transformations ranging from the oxidation of functional groups to the heteromolecular coupling for production of new antibiotics derivatives, or the catalysis of key steps in the synthesis of complex natural products. In this review, the application of fungal laccases and their engineering by rational design and directed evolution for organic synthesis purposes are discussed.

"Blue" laccases

This review concerns copper-containing oxidases--laccases. Principal biochemical and electrochemical properties of laccases isolated from different sources are described, as well as their structure and mechanism of catalysis. Possible applications of laccases in different fields of biotechnology are discussed.

Laccase production at reactor scale by filamentous fungi

Laccases have received much attention from researchers during the past decades due to their broad substrate specificity and to the fact that they use molecular oxygen as the final electron acceptor instead of hydrogen peroxide as used by peroxidases. This makes laccases highly interesting for a wide variety of processes, such as textile dye decolouration, pulp bleaching, effluent detoxification, biosensors and bioremediation. The successful application of laccases to the above-mentioned processes requires the production of large quantities of enzyme at low cost. Filamentous fungi are able to produce laccases in high amounts, however, an efficient production system at bioreactor scale is still lacking. This is mainly due to the fact that laccase production by wild-type strains of filamentous fungi is linked to secondary metabolism, which implies that the following drawbacks must be overcome: uncontrolled fungal growth, the formation of polysaccharides around mycelia and the secretion of certain compounds (i.e. proteases) that inactivate laccases. This review summarizes the current status of laccase production by wild-type strains of filamentous fungi at the bioreactor scale.

Characterization of two new multiforms of Trametes pubescens laccase

Electrochemical properties of two multiforms of laccase from Trametes pubescens basidiomycete (LAC1 and LAC2) have been studied. The standard redox potentials of the T1 sites of the enzymes were found to be 746 and 738 mV vs. NHE for LAC1 and LAC2, respectively. Bioelectroreduction of oxygen based on direct electron transfer between each of the two forms of Trametes pubescens laccase and spectrographic graphite electrodes has been demonstrated and studied. It is concluded that the T1 site of laccase is the first electron acceptor, both in solution (homogeneous case) and when the enzymes are adsorbed on the surface of the graphite electrode (heterogeneous case). Thus, the previously proposed mechanism of oxygen bioelectroreduction by adsorbed fungal laccase was additionally confirmed using two forms of the enzyme. Moreover, the assumed need for extracellular laccase to communicate directly and electronically with a solid matrix (lignin) in the course of lignin degradation is discussed. In summary, the possible roles of multiforms of the enzyme based on their electrochemical, biochemical, spectral, and kinetic properties have been suggested to consist in broadening of the substrate specificity of the enzyme, in turn yielding the possibility to dynamically regulate the process of lignin degradation according to the real-time survival needs of the organism.

Cloning of novel laccase isozyme genes from Trametes sp. AH28-2 and analyses of their differential expression

Three novel laccase isozyme genes, lacA, lacB, and lacC, have been identified from basidiomycete Trametes sp. AH28-2. These genes display a high similarity with other basidiomycete laccases at the amino acid level. An inferred TATA box and several putative CAAT, MRE, XRE, and CreA consensus sequences were identified in the lacA, lacB, and lacC promoter regions. Different from the TATA boxes of lacA and lacB at about -100, the TATA box of lacC is located at -172. For all the isozymes, copper ion is essential for laccase synthesis in Trametes sp. AH28-2. More interestingly, different aromatic compounds can selectively induce the production of distinct laccase isozymes, with o-toluidine inducing the expression of laccase A (LacA) while 3,5-dihydroxytoluene mainly stimulating the production of laccase B (LacB). Quantitative reverse transcriptase-polymerase chain reaction showed that the accumulation of laccase messenger RNA transcripts is accompanied by the increase of corresponding enzyme activity in cultures. The glucose-repression effect on laccase expression in Trametes sp. AH28-2 was also observed. Furthermore, lower Cu2+ concentration (lower than 0.5 mM) can induce LacA and a novel laccase (LacC), and the latter will disappear when Cu2+ concentration is increased up to 1-2 mM. Upon induction by 3,5-dihydroxytoluene, the ratio of LacA to LacB decreased in the later phase of induction.

Bilirubin oxidase activity of Bacillus subtilis CotA

The spore coat protein CotA from Bacillus subtilis was previously identified as a laccase. We have now found that CotA also shows strong bilirubin oxidase activity and markedly higher affinity for bilirubin than conventional bilirubin oxidase. This is the first characterization of bilirubin oxidase activity in a bacterial protein.

A laccase study by electrospray ionization Fourier transform ion cyclotron resonance MS: copper depletion, glycoforms and stability

The molecular properties and stability of a laccase from the white-rot fungus Trametes hirsuta (ThL) were studied to exploit the unique capability of electrospray ionization mass spectrometry (ESI-MS) to monitor conformational and molecular-based heterogeneities and metal ion binding simultaneously. Acid and organic solvents were applied as denaturing agents. In aqueous acidic solution, ThL existed in two major forms, distinguished by their mass difference; in addition to these, two other forms were detected. This molecular heterogeneity was due to the variable glycan content of ThL. Additionally, copper-depleted forms of laccase were observed in mass spectra measured from aqueous acidic solution. A small amount of organic solvent (acetonitrile, CH(3)CN) increased the loss of one Cu atom from folded states and led to unfolding. In the unfolded state, ThL was depleted of all four copper atoms, and the charge state distribution was shifted to lower mass-to-charge region. Thus, denaturation took place in two stages: first, the loss of one Cu resulting in an inactive form; second, complete denaturation with the loss of the three remaining Cu atoms. After all coppers were lost, ThL was unfolded, as was clearly seen in the increased number of charge states in the mass spectra. Different stabilities of the glycoforms were observed in the denaturation triggered in acid and organic solvents.

Optimization of the expression of a laccase gene from Trametes versicolor in Pichia methanolica

A cDNA encoding for laccase (Lcc1) was isolated from the ligninolytic fungus Trametes versicolor by reverse transcriptase polymerase chain reaction. The Lcc1 gene was subcloned into the Pichia methanolica expression vector pMETalphaA and transformed into the P. methanolica strains PMAD11 and PMAD16. The extracellular laccase activity of the PMAD11 recombinants was found to be 1.3-fold higher than that of the PMAD16 recombinants. The identity of the recombinant protein was further confirmed by immunodetection using the Western blot analysis. As expected, the molecular mass of the mature laccase was 64.0 kDa, similar to that of the native form. The effects of copper concentration, cultivation temperature, pH and methanol concentration in the BMMY on laccase expression were investigated. The laccase activity in the PMAD11 recombinant was up to 12.6 U ml(-1) by optimization.

Molecular cloning of the cDNA encoding laccase from Trametes versicolor and heterologous expression in Pichia methanolica

A cDNA encoding for laccase was isolated from the ligninolytic fungus Trametes versicolor by RNA-PCR. The cDNA corresponds to the gene Lcc1, which encodes a laccase isoenzyme of 498 amino acid residues preceded by a 22-residue signal peptide. The Lcc1 cDNA was cloned into the vectors pMETA and pMETalphaA and expressed in Pichia methanolica. The laccase activity obtained with the Saccharomyces cerevisiae alpha-factor signal peptide was found to be twofold higher than that obtained with the native secretion signal peptide. The extracellular laccase activity in recombinants with the alpha-factor signal peptide was 9.79 U ml(-1). The presence of 0.2 mM copper was necessary for optimal activity of laccase. The expression level was favoured by lower cultivation temperature. The identity of the recombinant protein was further confirmed by immunodetection using Western blot analysis. As expected, the molecular mass of the mature laccase was 64.0 kDa, similar to that of the native form.

Role of laccase in the biology and virulence of Cryptococcus neoformans

Laccase is an important virulence factor for the human pathogen, Cryptococcus neoformans. In this review, we examine the structural, biological and genetic features of the enzyme and its role in the pathogenesis of cryptococcosis. Laccase is expressed in C. neoformans as a cell wall enzyme that possesses a broad spectrum of activity oxidizing both polyphenolic compounds and iron. Two paralogs, CNLAC1 and CNLAC2, are present in the fungus, of which the first one expresses the dominant enzyme activity under glucose starvation conditions. Regulation of the enzyme is in response to various environmental signals including nutrient starvation, the presence of multivalent cations and temperature stress, and is mediated through multiple signal transduction pathways. Study of the function and regulation of this important virulence factor has led to further understanding of mechanisms of fungal pathogenesis and the regulation of stress response in the host cell environment.

Biochemical characterization and molecular evidence of a laccase from the bird’s nest fungus Cyathus bulleri

Cyathus bulleri, a bird's nest fungus, known to decolorize polymeric dye Poly R-478, was found to produce 8 U ml(-1) of laccase in malt extract broth. Laccase activity appeared as a single band on non-denaturing gel. Laccase was purified to homogeneity by anion exchange chromatography and gel filtration. The enzyme was a monomer with an apparent molecular mass of 60 kD, pI of 3.7 and was stable in the pH range of 2-6 with an optimum pH of 5.2. The optimal reaction temperature was 45 degrees C and the enzyme lost its activity above 70 degrees C. Enzyme could oxidize a broad range of various phenolic substrates. K(m) values for ABTS, 2,6-dimethoxyphenol, guaiacol, and ferulic acid were found to be 48.6, 56, 22, and 14 mM while K(cat) values were 204, 180, 95.6, and 5.2, respectively. It was completely inhibited by KCN, NaN(3), beta-mercaptoethanol, HgCl(2), and SDS, while EDTA had no effect on enzyme activity. The N-terminal amino acid sequence of C. bulleri laccase showed close homology to N-terminal sequences of laccase from other white-rot fungi. A 150 bp gene sequence encoding copper-binding domains I and II was most similar to the sequence encoding a laccase from Pycnoporus cinnabarinus with 74.8% level of similarity.

Electrochemical redox transformations of T1 and T2 copper sites in native Trametes hirsuta laccase at gold electrode

Mediatorless, electrochemically driven, redox transformations of T1 (type 1) and T2 copper sites in Trametes hirsuta laccase were studied by cyclic voltammetry and spectroelectrochemical redox titrations using bare gold electrode. DET (direct electron transfer) between the electrode and the enzyme was observed under anaerobic conditions. From analysis of experimental data it is concluded that the T2 copper site is in DET contact with gold. It was found that electron transfer between the gold surface and the T1 copper site progresses through the T2 copper site. From EPR measurements and electrochemical data it is proposed that the redox potential of the T2 site for high-potential 'blue' laccase is equal to about 400 mV versus NHE (normal hydrogen electrode) at pH 6.5. The hypothesis that the redox potentials of the T2 copper sites in low- and high-potential laccases/oxidases from totally different sources might be very similar, i.e. approx. 400 mV, is discussed.

Recombinant expression of Pleurotus ostreatus laccases in Kluyveromyces lactis and Saccharomyces cerevisiae

Heterologous expression of Pleurotus ostreatus POXC and POXA1b laccases in two yeasts, Kluyveromyces lactis and Saccharomyces cerevisiae, was performed. Both transformed hosts secreted recombinant active laccases, although K. lactis was much more effective than S. cerevisiae. rPOXA1b transformants always had higher secreted activity than rPOXC transformants did. The lower tendency of K. lactis with respect to S. cerevisiae to hyperglycosylate recombinant proteins was confirmed. Recombinant laccases from K. lactis were purified and characterised. Specific activities of native and recombinant POXA1b are similar. On the other hand, rPOXC specific activity is much lower than that of the native protein, perhaps due to incomplete or incorrect folding. Both recombinant laccase signal peptides were correctly cleaved, with rPOXA1b protein having two C-terminal amino acids removed. The availability of the established recombinant expression system provides better understanding of laccase structure-function relationships and allows the development of new oxidative catalysts through molecular evolution techniques.

Heterologous production of a laccase from the basidiomycete Pycnoporus cinnabarinus in the dimorphic yeast Yarrowia lipolytica

Pycnoporus cinnabarinus lac1 gene was expressed in Yarrowia lipolytica. Different secretion signals and culture media were tested. Production was correlated to both culture growth rate and cell morphology (highest at low growth rate, without mycelium). Recombinant laccase was characterized (immunodetection, N-terminal sequencing) and purified. Production was estimated to 20 mgl(-1) in a bioreactor. Thus, complex metalloenzymes can be produced in Yarrowia, assuming some control of host physiology. Lac1p production was compared in Yarrowia, Pichia and Aspergillus: recombinant proteins were active, but host systems differed in transformation efficiency, production, and glycosylation. If not the best producer, Yarrowia offers very high transformation efficiencies, allowing the genetic engineering of laccases for industrial applications.

Direct electron transfer between copper-containing proteins and electrodes

The electrochemistry of some copper-containing proteins and enzymes, viz. azurin, galactose oxidase, tyrosinase (catechol oxidase), and the "blue" multicopper oxidases (ascorbate oxidase, bilirubin oxidase, ceruloplasmin, laccase) is reviewed and discussed in conjunction with their basic biochemical and structural characteristics. It is shown that long-range electron transfer between these enzymes and electrodes can be established, and the mechanistic schemes of the DET processes are proposed.

The DEAD-box RNA helicase Vad1 regulates multiple virulence-associated genes in Cryptococcus neoformans

The study of fungal regulatory networks is essential to the understanding of how these pathogens respond to host environmental signals with effective virulence-associated traits. In this study, a virulence-associated DEAD-box RNA helicase-encoding gene (VAD1) was isolated from a mutant defective in the virulence factor laccase. A Deltavad1 mutant exhibited a profound reduction in virulence in a mouse model that was restored after reconstitution with WT VAD1. Loss of VAD1 resulted in upregulation of NOT1, a gene encoding a global repressor of transcription. NOT1 was found to act as an intermediary transcriptional repressor of laccase. Vad1 was located within macromolecular complexes that formed cytoplasmic granular bodies in mature cells and during infection of mouse brain. In addition, VAD1 was shown by in situ hybridization to be expressed in the brain of an AIDS patient coinfected with C. neoformans. To understand the role of VAD1 in virulence, a functional genomics approach was used to identify 3 additional virulence determinants dependent on VAD1: PCK1, TUF1, and MPF3, involved in gluconeogenesis, mitochondrial protein synthesis, and cell wall integrity, respectively. These data show that fungal virulence-associated genes are coordinately regulated and that an analysis of such transcriptomes allows for the identification of important new genes involved in the normal growth and virulence of fungal pathogens.

Comparison of physico-chemical characteristics of four laccases from different basidiomycetes

New strains of basidiomycetes producing extracellular laccases (Trametes ochracea 92-78, and Trametes hirsuta 56) have been found by screening of isolates of Trametes fungi. The laccases from T. hirsuta 56 and T. ochracea 92-78 as well as two laccases from previously found and described strains of basidiomycetes, namely Cerrena maxima and Coriolopsis fulvocinerea, were purified to homogeneity. The standard redox potentials of type 1 copper in the enzymes were determined and found to be 780, 790, 750, and 780 mV, respectively. The spectral and biochemical studies showed that the enzymes had no significant differences between the structures of their active sites (T1, T2, and T3). In spite of this fact, the basic biochemical properties as well as the redox potentials of the T1 sites of the enzymes were found to be different. The molecular weights of the laccases range from 64 to 70 kDa, and their pI values range from 3.5 to 4.7. The pH-optima are in the range 3.5-5.2. The temperature optimum for activity is about 50 degrees C. The thermal stabilities of the enzymes were studied. The catalytic and Michaelis constants for catechol, guaiacol, hydroquinone, sinapinic acid, and K(4)Fe(CN)(6) were determined. Based on these results as well as results obtained by comparing with published properties of several laccases, it could be concluded that T. hirsuta and Cerrena maxima laccases have some superior characteristics such as high stability, high activity, and low carbohydrate content, making them attractive objects for further investigations as well as for application in different areas of biotechnology.

Purification and characterization of two laccase isoenzymes from a ligninolytic fungus Trametes gallica

Constant laccase activities were detected in culture supernatant of newly isolated basidiomycete Trametes gallica. Tryptone and glucose have great effects on the production of laccase. Two laccase isoenzymes (Lac I and Lac II) produced by T. gallica were purified to homogeneity (51- and 50-fold, respectively) by gel filtration chromatography, anion exchange chromatography, and improved native PAGE, with an overall yield of 24.8%. Lac I and Lac II from this fungus are glycoproteins with 3.6% and 4% carbohydrate content, the same molecular masses (by SDS-PAGE) of 60 kDa, and the pI of 3.1 and 3.0, respectively. Native gel electrophoresis indicates that the two laccases have different migration ratios. Lac I and Lac II have the same optimal pH of 3.0 on 2,6-dimethoxyphenol (DMP), pH 2.2 on 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and of pH 4.0 on guaiacol. The highest rate of ABTS oxidation for both laccases was reached at 70 degrees C. Both laccases are stable from pH 6 to 9, retaining 88-90% activity after 24 hr incubation, and show good stability when incubated at temperatures lower than 40 degrees C. The Km values of Lac I for ABTS, DMP, and guaiacol are 0.118 x 10(-2), 0.420, and 0.405 mM, respectively; the Km values of Lac II for ABTS, DMP, and guaiacol are 0.086 x 10(-2), 0.41, and 0.40 mM, respectively. Their N-terminal sequences are determined and show strong similarity with those from other basidiomycetes. Graphite-furnace atomic absorption analysis revealed that both laccases have four copper atoms per protein molecule, but they have no type I copper signal at around 600 nm and a type III copper signal near 330 nm. Cyanide, azide, and halides completely inhibit the enzyme activity, whereas EDTA has less inhibition.