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Three-phase partitioning (TPP) is a simple, fast, cost-effective, and highly efficient process that can be used in the purification of laccases. In this study, microorganisms with laccase activity were isolated from water samples collected from the Agri-Diyadin hot spring. The isolate with the highest laccase activity was found to be the A2 strain. As a result of molecular (16S rRNA sequence) and conventional (morphological, biochemical, and physiological) analyses, it was determined that the A2 isolate was 99% similar to Enterococcus faecium (Genbank number: MH424896). The laccase was purified to 4.9-fold with 110% recovery using the TPP. The molecular mass of the enzyme was found by SDS-PAGE to be 50.11 kDa. Optimum pH 6.0 and optimum temperature for laccase were determined as 80 °C. The laccase exhibited pH stability over a wide range (pH 3.0-9.0) and a high thermostability, retaining over 90% of its activity after 1 h of incubation at 20-90 °C. The laccase exhibited high thermostability, with a heat inactivation half-life of approximately 24 h at 80 °C. The enzyme remained highly stable in the presence of surfactants and increased its activity in the presence of organic solvents, Cr

This study presents the exploration of laccase-like enzyme produced by thermophilic bacterial strains present in the Tattapani hotspring located in Chhattisgarh, India. Two bacterial isolates namely TPNR1 and TPNR6 were found to be positive for laccase-like enzyme production on screening with guaiacol as a substrate. The biochemical and 16S rRNA gene sequence analysis indicated that the isolates have similarity with Bacillus licheniformis strains and, thus, named as B. licheniformis TPNR1 and B. licheniformis TPNR6. The activity of crude enzymes was estimated using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) as a substrate and measured as 3.1 U/mL and 7.1 U/mL for TPNR1 and TPNR6, respectively. The SDS-PAGE of purified enzymes showed that the enzymes are monomers with molecular weight of 44 (TPNR1) and 38 (TPNR6) kDa. The native-PAGE technique followed by activity staining using ABTS confirms the presence of purified active enzyme with laccase-like activity in both cases. Kinetic studies displayed that catalytic efficiency of the enzymes was higher for the substrate ABTS than 2,6-dimethoxyphenol for both enzymes. The maximum enzyme activity was observed at 50°C for both enzymes while the optimal pH for TPNR1 and TPNR6 was 5.0 and 6.0, respectively. The TPNR1 exhibited half-life of 4 h at 70°C and was stable at 60°C for 180 min with a residual activity of 79%. Similarly, the TPNR6 possessed half-life of 3.1 h at 70°C and retained 88% of its activity at 60°C for 180 min. In addition, the catalytic efficiency of the enzymes was tested by decolourization of toxic dyes which showed that the both enzymes are highly potential to degrade them.

Laccase, an important oxidoreductase, is widely distributed in various organisms. Termites are known to decompose lignocellulose efficiently with the aid of gut microorganisms. However, few laccases have been characterized from termite or its gut microbes. We aimed to screen the strain capable of degrading lignocellulose from fungus-growing termites. In this study, Bacillus stratosphericus BCMC2 with lignocellulolytic activity was firstly isolated from the hindgut of fungus-growing termite Macrotermes barneyi. The laccase gene (BaCotA) was cloned both from the BCMC2 strain and termite intestinal metagenomic DNA. BaCotA was overexpressed in E. coli, and the recombinant BaCotA showed high specific activity (554.1 U/mg). BaCotA was thermostable with an optimum temperature of 70 °C, pH 5.0. Furthermore, BaCotA was resistant to alkali and organic solvents. The enzyme remained more than 70% residual activity at pH 8.0 for 120 min; and the organic solvents such as methanol, ethanol and acetone (10%) had no inhibitory effect on laccase activity. Additionally, BaCotA exhibited efficient decolorization ability towards indigo and crystal violet. The multiple enzymatic properties suggested the presented laccase as a potential candidate for industrial applications. Moreover, this study highlighted that termite intestine is a good resource for either new strains or enzymes.

Background: Laccase has been considered important for the degradation of lignocellulose by wood rot fungi. The properties and functions of laccase in white rot fungi have been investigated extensively, but those from brown rot fungi remain largely unknown. In this paper, a laccase isoforms Pplcc2 from the brown rot fungus Postia placenta MAD-698-R was expressed heterologously in Pichia pastoris GS115 , purified and the properties of the enzyme were determined. Results: The molecular weight of the protein was determined to be 67 kDa using SDS-PAGE. It cannot oxidize syringaldazine (SGZ), but it can oxidize 2,2'-azino-di-(3-ethylbenzothialozin-6-Sulfonic acid) (ABTS) and 2,6-dimethoxyphenol (DMP). Specific activity for ABTS was 1960 ± 19 Unit/mg. The catalytic constant ( k cat ) was 1213 ± 18.3 s - 1 for ABTS and 293.2 ± 21.9 s - 1 for DMP. K m was 22.08 μM for ABTS and 11.62 μM for DMP. The optimal pH for the oxidation of ABTS and DMP was 3.5 and 5.0 respectively. The optimal temperature for the oxidation of ABTS and DMP was 60°C. Conclusions: This is the first identified thermo activated and thermostable laccase in brown rot fungi. This investigation will contribute to the understanding the roles played by laccases in brown rot fungi.

Laccases are multicopper polyphenol oxidases that are able to catalyze the oxidation of a wide range of phenolic compounds with the simultaneous reduction of O2 to H2O. Despite their promising industrial uses, feasible incorporation of laccases in harsh processes requires the bioprospecting and/or engineering of enzymes to be stable and active in acidic or alkaline pHs, high temperatures, oxidative conditions and tolerant to high salinity and/or organic solvents. Here we used a PCR-based screening to clone two novel laccase coding sequences from the white-rot basidiomycete Trametes trogii. Recombinant expression of lcc3 gene in Komagataella (=Pichia) pastoris showed that it encodes a thermo active and thermostable laccase with an optimum temperature of 50°C and with a half-life of 45 minutes at 70°C and a stability higher than 3 h at 60°C. Furthermore, recombinant LCC3 was capable of decolorizing between 50% and 100% of indigoid, triarylmethane, azoic and anthraquinonic synthetic dyes in the presence of the natural redox mediator acetosyringone within 2 h of incubation at pH 6 and 70°C. Fil: Campos, Paula Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina Fil: Levin, Laura Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Micología y Botánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Micología y Botánica; Argentina Fil: Wirth, Sonia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina

Laccase from a tree legume, Leucaena leucocephala, was purified to homogeneity using a quick two-step procedure: alginate bead entrapment and celite adsorption chromatography. Laccase was purified 110.6-fold with an overall recovery of 51.0% and a specific activity of 58.5 units/mg. The purified laccase was found to be a heterodimer (∼220 kDa), containing two subunits of 100 and 120 kDa. The affinity of laccase was found to be highest for catechol and lowest for hydroquinone, however, highest Kcat and Kcat/Km were obtained for hydroquinone. Purified laccase exhibited pH and temperature optima of 7.0 and 80 °C, respectively. Mn2+, Cd2+, Fe2+, Cu2+ and Na+ activated laccase while Ca2+ treatment increased laccase activity up to 3 mM, beyond which it inhibited laccase. Co2+, Hg2+, DTT, SDS and EDTA showed an inhibition of laccase activity. The Leucaena laccase was found to be fairly tolerant to organic solvents; upon exposure for 1 h individually to 50% (v/v) each of ethanol, DMF, DMSO and benzene, more than 50% of the activity was retained, while in the presence of 50% (v/v) each of methanol, isopropanol and chloroform, a 40% residual activity was observed. The purified laccase efficiently decolorized synthetic dyes such as indigocarmine and congo red in the absence of any redox mediator.

For the first time, the investigation of Indigo carmine decolorization was done using an atypical Scytalidium thermophilum laccase. Crude and purified laccases required high temperatures and slight acidic pH to achieve maximum Indigo decolorization. Kinetic parameters (Km and kcat) of the homotrimeric laccase toward Indigo carmine were determined and laccase efficacy toward repeated dye decolorization process was studied. For the first time, 5 g l−1 as initial Indigo carmine concentration were efficiently transformed up to 50% within 6 h of incubation using 0.1 U ml−1 of laccase and without presence of any mediators. In this study, we showed that the atypical laccase transformed the indigoid dye structure, confirmed by the color changing from blue to red. This intermediate (red) was a subject to an efficient microbial consortium treatment monitored by measuring the decrease in optical density and the total organic carbon removal efficiencies. Toxicological studies via micro-toxicity test showed that the released enzymatic and adapted consortium degradation products were both non-toxic while the initial product was toxic.

The gene encoding Thermus thermophilus HJ6 laccase (Tt-laccase) was cloned, sequenced, and comprised of 1,389 nucleotides encoding a protein (462 amino acids) with a predicted molecular mass of 51,049 Da. The deduced amino acid sequence of Tt-laccase showed 99.7% and 44.3% identities to the Thermus thermophilus HB27 laccase and Synechococcus sp. RS9917 laccase, respectively. Tt-laccase gene was expressed as a fusion protein with six histidine residues in E. coli Rosetta-gami (DE3) cells, and the recombinant protein was purified to homogeneity. UV-Vis spectrum analysis revealed that the enzyme has copper atoms, a type I Cu(II) and a type III binuclear Cu(II). The optimum pH for the oxidation of guaiacol was 5.0 and the optimum temperature was 90℃ The half-life of heat inactivation was about 120 min at 90℃ The enzyme reaction was inhibited by sodium azide, L-cystein, EDTA, dithiothreitol, tropolone, and kojic acid. The enzyme oxidized various known laccase substrates, its lowest K m value being for 4-hydroxyindole, highest kcat value for syringaldazine, and highest k cat /K m for guaiacol.

A thermostable laccase was isolated from an unidentified fungal isolate [Enz. Microb. Technol. 33 (2003) 212], and tentatively named UD4. This work indicates that the enzyme has unique properties other than its thermostability. Investigation into the kinetic parameters of the thermostable laccase yielded an unusually high affinity for ABTS as a substrate (low Km) when compared with available published data for other laccase isozymes. The specificity constant (kcat/Km) was found to be considerably higher than laccase from other sources and is comparable to “white” laccase from Pleurotus ostreatus (POXA1). However, POXA1 isozyme exhibits a large turnover number (kcat) that contributes to its high specificity constant whereas the high specificity constant for UD4 laccase is achieved by having a high substrate affinity. The UD4 thermostable laccase, like most other laccases, is able to utilize guaiacol as a substrate, whereas POXA1 is unable to oxidize guaiacol, indicating a broader substrate range for the thermostable laccase from UD4. The thermostable laccase is inhibited by sodium azide through non-competitive inhibition, and by thioglycolic acid and hydroxylamine through competitive inhibition. The high specificity constant, substrate affinity and broader substrate range of the thermostable laccase from UD4 indicates that it is a highly favourable candidate enzyme for industrial application.

The fungus Cladosporium cladosporioides was isolated from a coal sample as a dye decolorizing microorganism. The maximum production of laccase from this fungus was found to be 4160 U/l with 0.05 mM CuSO4, 4% (w/v) glucose and lignin 0.04% (w/v). The laccase was purified from C. cladosporioides to homogeneity in a very active state using ammonium salt precipitation and gel permeation chromatography. Analysis with SDS–PAGE showed that the purified laccase was a monomeric protein of 71.2 kDa, and the apparent molecular mass of this enzyme was 75.17 kDa (m/z = 75,174), which was accurately determined by MALDI/TOF-MS. The UV–vis absorbance and electron paramagnetic resonance spectra of the purified laccase showed the presence of type 1 and type 3 copper ions. The optimum pH and temperature of the purified laccase were 3.5 and 40–70 °C, respectively, and the N-terminal amino acid sequence was determined to be IGPTGDMYIVNEDVS. The purified laccase was effective in the biotransformation of aromatic compounds as well as in the decolorization of various dyes.

Dye decolorizing potential of the white rot fungus Ganoderma lucidum KMK2 was demonstrated for recalcitrant textile dyes. G. lucidum produced laccase as the dominant lignolytic enzyme during solid state fermentation (SSF) of wheat bran (WB), a natural lignocellulosic substrate. Crude enzyme shows excellent decolorization activity to anthraquinone dye Remazol Brilliant Blue R (RBBR) without redox mediator whereas diazo dye Remazol Black-5 (RB-5) requires a redox mediator. Polyacrylamide gel electrophoresis (PAGE) of crude enzyme confirms that the laccase enzyme was the major enzyme involved in decolorization of either dyes. Native and SDS-PAGE indicates that the presence of single laccase with molecular weight of 43 kDa. N-Hydroxybenzotriazole (HBT) at a concentration of 1 mM was found as the best redox mediator. RB-5 (50 mg l−l) was decolorized by 62% and 77.4% within 1 and 2 h, respectively by the crude laccase (25 U ml−1). RBBR (50 mg l−l) was decolorized by 90% within 20 h, however, it was more efficient in presence of HBT showing 92% decolorization within 2 h. Crude laccase showed high thermostability and maximum decolorization activity at 60 °C and pH 4.0. The decolorization was completely inhibited by the laccase inhibitor sodium azide (0.5 mM). Enzyme inactivation method is a good method which averts the undesirable color formation in the reaction mixture after decolorization. High thermostability and efficient decolorization suggest that this crude enzyme could be effectively used to decolorize the synthetic dyes from effluents.

Pycnoporous sanguineus was identified as a laccase producer when grown on diluted molasses. The single laccase was purified with a purification factor of 967 by ammonium sulphate precipitation, ion exchange and dye affinity chromatography, to a specific activity of 32.9 U/mg. The molecular mass of 58,000 Da, the optimum pH range between 3 and 5 with ABTS, DMP and guaiacol as substrates and the isoelectric point of 6.7, was similar to some other laccases of filamentous fungi. The optimum temperature was 55 °C and the enzyme displayed enhanced thermal stability with a half-life of 170 min at 75 °C. In terms of k cat / K m values for ABTS, syringaldazine and DMP, DMP was the best substrate. Kinetic analysis of fifteen more compounds revealed that, the enzyme was a true laccase with a requirement for a free –OH group with an adjacent free or derivatised –OH. The o -diphenols were preferred above their p- counterparts. Compounds with three adjacent –OH groups displayed higher binding affinities but phloroglucinol, an m -substituted phenol was unreactive. The apparent higher stability of this laccase makes it a good candidate for further investigation into it possible application in biotechnology.

Carpophores of mesophilic basidiomycetes were isolated from the Eastern Cape region of South Africa. These isolates were screened for manganese peroxidase and laccase with high temperature optima. This bio-prospecting has led to the discovery of a thermostable laccase, which exhibits an optimum temperature of 70 °C. The enzyme remains fully active after 9 h incubation at 60 °C. The laccase is also capable of catalyzing the oxidative coupling of 3-dimethylaminobenzoic acid and 3-methyl-2-benzothiazolinone hydrazone, which are characterized as manganese peroxidase specific substrates. The wide temperature range, thermostability, and potentially wider than usual substrate range, make this an excellent candidate enzyme for industrial application.

We found a polyphenoloxidase (PPO) in the cell extract of Streptomyces lavendulae REN-7. About 0.8 mg of purified PPO was obtained from 200 g of the mycelia with a yield of 9.0%. REN-7-PPO showed broad substrate specificity toward various aromatic compounds. Moreover, this enzyme was capable of oxidation of syringaldazine, which is a specific substrate for laccase. Interestingly, REN-7-PPO retained its original activity after 20 min of incubation at even 70 degrees C. The gene encoding the PPO was cloned. Four copper-binding sites characteristics of laccases were contained in the deduced amino acid sequence. We constructed a high-level expression system of this gene in Escherichia coli. The properties of the recombinant enzyme were identical that of wild-type. In conclusion, this PPO is a thermostable laccase.

The goal of this study was to determine the optimum conditions for the enzymatic decolorization of eleven dyes by laccase. The dyes Cibacron Orange P-4 R, Direct Black VSF 600, Cibacron Red P-4B, Remazol Red, Burdirect Brown M, Burdirect Black Metakonz, Burdirect Dark Blue BH, Burdirect Blue 6B, Cibacron Black PSG, Burdirect Green B, and Remazol Turquoise Blau G133 were characterized spectrophotometrically. The dye that had the highest degree of decolorization (97%), Cibacron Orange P-4 R, was selected for further study. Optimum conditions for decolorization were a 1 mM initial dye concentration at pH 7.0 and an initial enzyme activity of 0.084 U at 25°C for 135 min. Sodium sulfate was selected as the activator at 50 mM. The decolorized products were characterized by infrared spectroscopy and gas chromatography–mass spectrometry. No degradation products were identified following removal of 97% of the dye. © 2016, Copyright © Taylor & Francis Group, LLC.

A highly thermostable laccase from Geobacillus sp. strain WSUCF1 was cloned into Escherichia coli (E. coli) using pRham N-His SUMO expression system. The thermostable laccase with a molecular weight ~30 kDa had a t1/2 (pH 6.0) of 120 h at 50 °C. The homology modelling for laccase structure showed the presence of Cu active centers with His and Cys residues involved in the active site and ligand binding activity of the enzyme, respectively. The Km, Vmax, Kcat and Kcat/Km values of the purified enzyme with ABTS were found to be 0.146 mM, 1.52 U/mg, 1037 s−1 and 7102.7 s−1 mM−1, respectively. The doping of recombinant WSUCF1 laccase to commercial enzyme cocktails Accellerase® 1500 and Cellic CTec2 improved the hydrolysis of untreated, alkali and acid treated corn stover by 1.31–2.28 times and bagasse by 1.32–2.02 times. Further, in-house enzyme cocktails with laccase hydrolyzed untreated, alkali and acid treated bagasse and gave 1.44, 1.1, and 0.92 folds higher sugar, respectively, when compared with Accellerase 1500. The results suggested that thermostable laccase can aid in the improved hydrolysis of lignocellulosic biomass.

Plant biomass degradation by fungi is a critical step for production of biofuels, and laccases are common ligninolytic enzymes envisioned for ligninolysis. Bilirubin oxidases (BODs)-like are related to laccases, but their roles during lignocellulose degradation have not yet been fully investigated. The two BODs of the ascomycete fungus Podospora anserina were characterized by targeted gene deletions. Enzymatic assay revealed that the bod1(Δ) and bod2(Δ) mutants lost partly a thermostable laccase activity. A triple mutant inactivated for bod1, bod2 and mco, a previously investigated multicopper oxidase gene distantly related to laccases, had no thermostable laccase activity. The pattern of fruiting body production in the bod1(Δ) bod2(Δ) double mutant was changed. The bod1(Δ) and bod2(Δ) mutants were reduced in their ability to grow on ligneous and cellulosic materials. Furthermore, bod1(Δ) and bod2(Δ) mutants were defective towards resistance to phenolic substrates and H2 O2 , which may also impact lignocellulose breakdown. Double and triple mutants were more affected than single mutants, evidencing redundancy of function among BODs and mco. Overall, the data show that bod1, bod2 and mco code for non-canonical thermostable laccases that participate in the degradation of lignocellulose. Thanks to their thermal stability, these enzymes may be more promising candidate for biotechnological application than canonical laccases.

This study aimed to produce a novel, highly thermostable laccase from Bacillus licheniformis O12 bacterial DNA using a recombinant method and investigate the effects of some dyes found in textile wastewaters on decolorization. A putative laccase gene (CotA) from B. licheniformis O12 was cloned and expressed as a fusion protein in Escherichia coli BL21 (DE3) cells. The recombinant laccase was purified using the Ni-NTA affinity chromatography method. Accordingly, 411.76-fold purification was achieved with 0.014 U/mg specific activity, and the molecular mass of the enzyme was calculated as 66 kDa. The optimum temperature and pH values of the laccase were determined as 92 degrees C and pH 5.0, respectively. It was also found to be quite stable for 75 min under acidic and alkaline conditions. The activity was measured for 12 h at 60 degrees C and 92 degrees C. At 92 degrees C, it was observed that the activity halved after 12 h. The highest value at 60 degrees C was obtained at 9 h. While an activity decrease of approximately 10 % was observed in the first three hours, a slow increase was detected afterward. These results proved that the obtained laccase was highly resistant to pH and temperature. The recombinant laccase was significantly activated by Al3+, Cd2+, Cr2+, Cu2+, Fe2+, Hg2+, Pb2+, and was inhibited in the presence of organic solvents, surfactants, and laccase inhibitors. Finally, the effects of some textile dyes on decolorization were investigated using the fused recombinant laccase and found to be generally effective. The highest decolorization of the laccase treated with dye for 2 h was 51.2 % in acid black 1, while the lowest decolorization was 1.9 % in the congo red.

The aim of this study is to determine the key laccase-encoding gene in the life cycle of Morchella importuna SCYDJ1-A1, and to characterize the biochemical properties of the laccase. Two laccase-like multicopper oxidase (LMCO) genes were identified in the genome of M. importuna SCYDJ1-A1 as putative laccase-encoding genes. The two genes, belonging to Auxiliary Activity family 1 subfamily 3, were named as MiLacA and MiLacB. Phylogenetic analysis of deduced amino acid sequences showed that MiLacA is closest to a LMCO of M. importuna 22J1, while MiLacB had low similarity with known Morchella LMCOs. Real-time quantitative PCR results showed that MiLacA was expressed at much higher levels than MiLacB throughout the entire course of artificial cultivation. MiLacA was overexpressed in Pichia pastoris as a recombinant protein. Biochemical characterization of the purified enzyme showed that MiLacA simultaneously possessed laccase and polyphenol-oxidase activities. MiLacA could be strongly inhibited by Fe2+, which is unusual. The optimum pH was four and optimum temperature was 60 °C. The enzyme retained over 74% of the laccase activity after 16-h incubation at 60 °C, which means that its thermostability is at the forefront among the currently known laccases. Our findings may help to elucidate how the laccase of M. importuna is involved in decaying lignin in plant litter, and could also provide a candidate thermostable laccase for potential industrial application.

POXA1b is the most thermostable laccase isoenzyme from Pleurotus ostreatus. POXA1b is remarkably stable at alkaline pH (the t1/2 at pH 10 was 30 days), and its C-terminal affects its catalytic and stability properties. We cloned POXA1c from P. florida, which showed 99 % identity with POXA1b. POXA1c was functionally expressed in Pichia pastoris. The functions of the N and C termini of POXA1c were investigated using site-directed mutagenesis. Compared with POXA1c, the N-terminal R5V site effectively increased the specific activities for 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and guaiacol by 2- and 3.5-fold, respectively. A C-terminal truncated mutant, POXA1c△13, also increased the specific activities for ABTS and guaiacol by 2.3- and 3.4-fold, respectively. A double mutant, POXA1cΔ13-R5V, combined the R5V and △13 effects. The specific activity of this double mutant for ABTS was 1,321 U/mg, which indicated a 4-fold increase compared with the wild type. The role of residue V5 on laccase catalytic properties was also observed for laccases from Trametes versicolor and Rigidoporus lignosus. The specific activities of the V5R of the laccases from T. versicolor and R. lignosus were half of that of the wild type. The pH and thermal stability analysis of POXA1c and its mutants showed that the enzymes were remarkably stable because they showed 63 % residual activity after incubation for 108 h at 30 °C over a pH range of 4.5 to 9.0. Similar results were observed for POXA1cΔ13-R5V. POXA1cΔ13-R5V can be widely used in industrial biotechnology because of its excellent catalytic properties.

Structure-function relationships underlying laccases properties are very limited that makes these enzymes interesting for protein engineering approaches. Therefore in the current study, a thermostable laccase that was isolated from Bacillus sp. HR03 with the ability of bilirubin oxidation besides its laccase and tyrosinase activity is used. The extensive application of this enzyme is limited by its low expression level in Escherichia coli. Based on sequence alignments and structural studies, three single amino acid substitutions, D500G, D500E, D500S and a glycine insertion, are introduced using site-directed mutagenesis to evaluate the role of Asp(500) located in the C-terminal segment close to the T1 copper center. Substitution of aspartic acid with less sterically hindered, conserved residue such as glycine increase kcat (2.3 fold) and total activity (7.3 fold) which is accompanied by a significant increase in the expression level up to 3 fold. Biochemical characterization and structural studies using far-UV CD and fluorescence spectroscopy reveal the importance of C-terminal copper-binding loop in the laccase functional expression and catalytic efficiency. Kinetic characterization of the purified mutants toward 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), syringaldazine (SGZ) and bilirubin, shows that substrate specificity is left unchanged.

Laccase belongs to the family of multicopper oxidase and have wide range of biotechnological applications starting from the food industry to bioremediation. However, the use of laccase at commercial scale is hindered by factors like high enzyme cost, low activity and /or stability under given conditions. This study was carried out with aim of screening for extracellular thermostable laccase producing bacteria. Twenty-two (22) laccase positive strains were isolated from the selected environmental samples while extracellular laccase activity was detected only in six strains namely TM1, TMT1, PK4, PS1, TMS1 and ASP3. The laccase enzyme produced from PK4 was found to be more thermostable with a half-life of 60 min at 80°C. The strain PK4 was identified and designated as Bacillus sp. PK4. The laccase production was optimized using one- factor-at-a-time method and maximum enzyme production were observed at the temperature of 37°C, pH 7.5, 10% inoculum size with yeast extract and glucose as the nitrogen and carbon sources, respectively at an agitation rate of 150 rpm. Copper sulphate at 0.1 mM concentration was found to maximize the laccase production among the tested inducers. Among the trace elements, FeSO4 and ZnSO4 gave the maximum laccase production for the isolated strain in comparison with the control. The effect of copper-induced time showed that the addition of copper before inoculation effectively increased the laccase production compared to the addition of copper after 2, 4, 6 and 8 h of inoculation. The optimization of the media resulted in 11.8 fold increase in laccase production. Key words: Laccase, thermostability, Bacillus sp., optimization.

At present, few organisms are known to and capable of naturally producing laccases and white rot fungi are one such group. In the present study, three fungal species, namely,Ganoderma lucidum-CDBT1, Ganoderma japonicum,andLentinula edodes, isolated from their native habitat in Nepal were screened for laccase production, andG. lucidum-CDBT1 was found to express highest levels of enzyme (day 10 culture media showed 0.92 IU/mg total protein or 92 IU/mL laccase activity with ABTS as substrate). Lignin extracted from rice straw was used in Olga medium for laccase production and isolation fromG. lucidum-CDBT1. Presence of lignin (5 g/L) and copper sulfate (30 μM) in the media increased the extracellular laccase content by 111% and 114%, respectively. The laccase enzyme produced byG. lucidum-CDBT1 was fractionated by ammonium sulfate and purified by DEAE Sepharose anion exchange chromatography. The purified enzyme was found to have a molecular mass of 43 kDa and exhibits optimal activity at pH 5.0 and 30°C. The isolated laccase was thermally stable for up to 70°C for 1 h and exhibited broad pH stability. The kinetic constants,Km,Vmax, andKcat, determined using 2,2′-azinobis-(-3-ethylbenzothiazoline-6-sulfonic acid) as substrate were found to be 110 μM, 36 μmol/min/mg, and 246 min−1, respectively. The isolated thermostable laccase will be used in future experiments for delignification process.

Extracellular ligninolytic oxidoreductases produced by Cerrena sp. strain Ra, a soil-isolated basidiomycete with high artificial dye-decolorizing activity, were purified and characterized. One thermostable laccase, one typical manganese peroxidase, and two versatile peroxidases (VPI and VPII) were found in the culture of this fungus. The different characteristics of each enzyme enable the strain express wide-range of oxidizing activity under various conditions. VPI decolorizing activity was observed toward various kinds of dye compounds, and the activity and specificity varied depending on the oxidizing mediators added to the reaction mixture. Optimized VPI/mediator-coupling decolorizing will be widely used for industrial wastewater treatment.

SummaryFungal laccases are remarkable green catalysts that have a broad substrate specificity and many potential applications in bioremediation, lignocellulose processing, organic synthesis, and more. However, most of these transformations must be carried out at high concentrations of organic cosolvents in which laccases undergo unfolding, thereby losing their activity. We have tailored a thermostable laccase that tolerates high concentrations of cosolvents, the genetic product of five rounds of directed evolution expressed in Saccharomyces cerevisiae. This evolved laccase—R2 variant—was capable of resisting a wide array of cosolvents at concentrations as high as 50% (v/v). Intrinsic laccase features such as the redox potential and the geometry of catalytic coppers varied slightly during the course of the molecular evolution. Some mutations at the protein surface stabilized the laccase by allowing additional electrostatic and hydrogen bonding to occur.

In this work, a thermostable laccase from the fungus Melanocarpus albomyces was produced in the efficient protein producer Trichoderma reesei in batch, fed-batch and continuous cultivations on lactose medium in a laboratory fermenter. The rate of consumption of base for pH control (DELTABAS) was measured in all the cultivations and was used as a control parameter in one fed-batch run and in a 1000 h continuous cultivation. The dynamic DELTABAS control parameter can be used to maintain optimal production of secreted protein by fitting the rate of substrate feeding to the amount of substrate available to the growing fungus in the fermenter, thus maintaining growth limitation due to availability of carbon source while avoiding total carbon source depletion. The use of this parameter, capable of maintaining the biomass in a physiological state of imminent but not actual exhaustion of carbon source, was successful in both the fed-batch and continuous production of heterologous laccase. Laccase production in fed-batch and continuous runs was considerably improved in comparison to the batch cultivation, both in terms of volumetric productivity and yield on lactose. The DELTABAS-control algorithm was shown to be a useful research tool for process optimization.

Laccases have been used for the decolorization and detoxification of synthetic dyes due to their ability to oxidize a wide variety of dyes with water as the sole byproduct. A putative laccase gene (LacTT) from Thermus thermophilus SG0.5JP17-16 was screened using the genome mining approach, and it was highly expressed in Pichia pastoris, yielding a high laccase activity of 6130 U/L in a 10-L fermentor. The LacTT open reading frame encoded a protein of 466 amino acid residues with four putative Cu-binding regions. The optimal pH of the recombinant LacTT was 4.5, 6.0, 7.5 and 8.0 with 2,2'-azino-bis(3-ethylbenzothazoline-6-sulfonic acid) (ABTS), syringaldazine (SGZ), guaiacol, and 2,6-dimethoxyphenol (2,6-DMP) as the substrate, respectively. The optimal temperature of LacTT was 90°C with guaiacol as the substrate. LacTT was highly stable at pH 4.0–11.0 and thermostable at 40°C–90°C, confirming that it is a pH-stable and thermostable laccase. Furthermore, LacTT also exhibited high tolerance to halides such as NaCl, NaBr and NaF, and decolorized 100%, 94%, 94% and 73% of Congo Red, Reactive Black B and Reactive Black WNN, and Remazol Brilliant Blue R, respectively. Interestingly, addition of high concentration of NaCl increased the RBBR decolorization efficiency of LacTT. These results suggest that LacTT is a good candidate for industrial applications such as dyestuff processing and degradation of dyes in textile wastewaters.

Endospores produced by the Gram-positive soil bacterium Bacillus subtilis are shielded by a proteinaceous coat formed by over 30 structural components, which self-assemble into a lamellar inner coat and a thicker striated electrodense outer coat. The 65-kDa CotA protein is an abundant component of the outer coat layer. CotA is a highly thermostable laccase, assembly of which into the coat is required for spore resistance against hydrogen peroxide and UV light. Here, we report the structure of CotA at 1.7-A resolution, as determined by x-ray crystallography. This is the first structure of an endospore coat component, and also the first structure of a bacterial laccase. The overall fold of CotA comprises three cupredoxin-like domains and includes one mononuclear and one trinuclear copper center. This arrangement is similar to that of other multicopper oxidases and most similar to that of the copper tolerance protein CueO of Escherichia coli. However, the three cupredoxin domains in CotA are further linked by external interdomain loops, which increase the packing level of the structure. We propose that these interdomain loops contribute to the remarkable thermostability of the enzyme, but our results suggest that additional factors are likely to play a role. Comparisons with the structure of other monomeric multicopper oxidases containing four copper atoms suggest that CotA may accept the largest substrates of any known laccase. Moreover, and unlike other laccases, CotA appears to have a flexible lidlike region close to the substrate-binding site that may mediate substrate accessibility. The implications of these findings for the properties of CotA, its assembly and the properties of the bacterial spore coat structure are discussed.

A genomic DNA segment encoding an extracellular laccase was isolated from the thermophilic fungus Myceliophthora thermophila, and the nucleotide sequence of this gene was determined. The deduced amino acid sequence of M. thermophila laccase (MtL) shows homology to laccases from diverse fungal genera. A vector containing the M. thermophila laccase coding region, under transcriptional control of an Aspergillus oryzae alpha-amylase gene promoter and terminator, was constructed for heterologous expression in A. oryzae. The recombinant laccase expressed in A. oryzae was purified to electrophoretic homogeneity by anion-exchange chromatography. Amino-terminal sequence data suggests that MtL is synthesized as a preproenzyme. The molecular mass was estimated to be approximately 100 to 140 kDa by gel filtration on Sephacryl S-300 and to be 85 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Carbohydrate analysis revealed that MtL contains 40 to 60% glycosylation. The laccase shows an absorbance spectrum that is typical of blue copper oxidases, with maxima at 276 and 589 nm, and contains 3.9 copper atoms per subunit. With syringaldazine as a substrate, MtL has optimal activity at pH 6.5 and retains nearly 100% of its activity when incubated at 60 degrees C for 20 min. This is the first report of the cloning and heterologous expression of a thermostable laccase.

High-redox potential laccases are powerful biocatalysts with a wide range of applications in biotechnology. We have converted a thermostable laccase from a white-rot fungus into a blood tolerant laccase. Adapting the fitness of this laccase to the specific composition of human blood (above neutral pH, high chloride concentration) required several generations of directed evolution in a surrogate complex blood medium. Our evolved laccase was tested in both human plasma and blood, displaying catalytic activity while retaining a high redox potential at the T1 copper site. Mutations introduced in the second coordination sphere of the T1 site shifted the pH activity profile and drastically reduced the inhibitory effect of chloride. This proof of concept that laccases can be adapted to function in extreme conditions opens an array of opportunities for implantable nanobiodevices, chemical syntheses, and detoxification., This study was based upon work funded by EU Projects (NMP4-SL-2009-229255-3D-Nanobiodevice, FP7-KBBE-2010-4-26537-Peroxicats and COST Action CM0701) and a project from the Spanish Government (BIO2010-19697). D.M.M. was supported by a JAE grant and D.G.P. was supported by a Peroxicats contract. M.P. received support from the 2009 Ramón y Cajal programme of the Spanish MINECO.

Organophosphorus (OP) insecticides and nerve agents that contain P-S bond are relatively more resistant to enzymatic hydrolysis. Purified phenol oxidase (laccase) from the white rot fungus Pleurotus ostreatus (Po) together with the mediator 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) displayed complete and rapid oxidative degradation of the nerve agents VX and Russian VX (RVX) and the insecticide analog diisopropyl-Amiton with specific activity: k(sp) = 2200, 667 and 1833 nmol min(-1) mg(-1), respectively (pH 7.4, 37 degrees C). A molar ratio of 1:20 for OP/ABTS and 0.05 M phosphate at pH 7.4 provided the highest degradation rate of VX and RVX. The thermostable laccase purified from the fungus Chaetomium thermophilium (Ct) in the presence of ABTS caused a 52-fold slower degradation of VX with k(sp) = 42 nmol min(-1) mg(-1). The enzymatic biodegradation products were identified by 31P-NMR and GC/MS analysis.