The effect of mutations near the T1 copper site on the biochemical characteristics of the small laccase from Streptomyces coelicolor A3(2)

Harnessing the power of bacterial laccases for xenobiotic degradation in water: A 10-year overview

Industrialization and population growth are leading to the production of significant amounts of sewage containing hazardous xenobiotic compounds. These compounds pose a threat to human and animal health, as well as the overall ecosystem. To combat this issue, chemical, physical, and biological techniques have been used to remove these contaminants from water bodies affected by human activity. Biotechnological methods have proven effective in utilizing microorganisms and enzymes, particularly laccases, to address this problem. Laccases possess versatile enzymatic characteristics and have shown promise in degrading different xenobiotic compounds found in municipal, industrial, and medical wastewater. Both free enzymes and crude enzyme extracts have demonstrated success in the biotransformation of these compounds. Despite these advancements, the widespread use of laccases for bioremediation and wastewater treatment faces challenges due to the complex composition, high salt concentration, and extreme pH often present in contaminated media. These factors negatively impact protein stability, recovery, and recycling processes, hindering their large-scale application. These issues can be addressed by focusing on large-scale production, resolving operation problems, and utilizing cutting-edge genetic and protein engineering techniques. Additionally, finding novel sources of laccases, understanding their biochemical properties, enhancing their catalytic activity and thermostability, and improving their production processes are crucial steps towards overcoming these limitations. By doing so, enzyme-based biological degradation processes can be improved, resulting in more efficient removal of xenobiotics from water systems. This review summarizes the latest research on bacterial laccases over the past decade. It covers the advancements in identifying their structures, characterizing their biochemical properties, exploring their modes of action, and discovering their potential applications in the biotransformation and bioremediation of xenobiotic pollutants commonly present in water sources.

Engineering Site 228 of Streptomyces coelicolor Laccase for Optimizing Catalytic Activity

Malachite green (MG) poses a formidable threat to ecosystems and human health. Laccase emerges as a promising candidate for MG degradation, prompting an investigation into the catalytic activity modulation of a small laccase (SLAC) from Streptomyces coelicolor, with a focus on amino acid position 228. Through saturation mutagenesis, five mutants with a 50% increase in the specific activity were generated. Characterization revealed notable properties, Km of E228F was 8.8% of the wild type (WT), and E288T exhibited a 133% kcat compared to WT. Structural analyses indicated improved hydrophobicity and electrostatic potential on the mutants' surfaces, with the stable E228F-ABTS complex exhibiting reduced flexibility, possibly contributing to the observed decrease in turnover rate. Mutants demonstrated enhanced MG decolorization, particularly E228G. Site 228 acts as a crucial functional control switch, suggesting its potential role in SLAC engineering. This study provides insights into laccase modulation and offers promising avenues for enzymatic bioremediation applications.

A project-oriented biochemistry laboratory for protein engineering and structure-function using small laccase enzyme from Streptomyces coelicolor

An understanding of structure-function relationships in proteins is essential for modern biochemical studies. The integration of common freely accessible bioinformatics tools available online with the knowledge of protein-engineering tools provide a fundamental understanding of the application of protein structure-function for biochemical research. In order for students to apply their prior knowledge of recombinant protein technology into the understanding of protein structure-function relationships, we developed a semester-long project-oriented biochemistry laboratory experience that is the second laboratory course of a series. For easier integration of knowledge and application, we organized this course into four sequential modules: protein structure visualization/modification, mutagenesis target identification, site-directed mutagenesis, and mutant protein expression, purification, and characterization. These tasks were performed on the protein small laccase (SLAC) that was cloned and characterized by students in the previous semester during the first biochemistry laboratory course of the series. This goal-oriented project-based approach helped students apply their prior knowledge to newly introduced techniques to understand protein structure-function relationships in this research-like laboratory setting. A student assessment before and after the course demonstrated an overall increase in learning and enthusiasm for this topic.

Structural Insight into the Amino Acid Environment of the Two-Domain Laccase's Trinuclear Copper Cluster

Laccases are industrially relevant enzymes. However, their range of applications is limited by their functioning and stability. Most of the currently known laccases function in acidic conditions at temperatures below 60 °C, but two-domain laccases (2D) oxidize some substrates in alkaline conditions and above 70 °C. In this study, we aim to establish the structural factors affecting the alkaline activity of the 2D laccase from Streptomyces griseoflavus (SgfSL). The range of methods used allowed us to show that the alkaline activity of SgfSL is influenced by the polar residues located close to the trinuclear center (TNC). Structural and functional studies of the SgfSL mutants Met199Ala/Asp268Asn and Met199Gly/Asp268Asn revealed that the substitution Asp268Asn (11 Å from the TNC) affects the orientation of the Asn261 (the second coordination sphere of the TNC), resulting in hydrogen-bond-network reorganization, which leads to a change in the SgfSL-activity pH profile. The combination of the Met199Gly/Arg240His and Asp268Asn substitutions increased the efficiency (kcat/KM) of the 2,6-DMP oxidation by 34-fold compared with the SgfSL. Our results extend the knowledge about the structure and functioning of 2D laccases' TNC active sites and open up new possibilities for the directed engineering of laccases.

Isolation and Characterization of a Novel Laccase-Producing Bacteria Bhargavaea beijingensis from Paper and Pulp Effluent-Treated Soil Using In Silico Approaches

Laccases (EC 1.10.3.2) are considered one of the most prominent multicopper enzymes that exhibit the inherent properties of oxidizing a range of phenolic substrates. Mostly, reported laccases have been isolated from the plants and fungi species, whereas bacterial laccases are yet to be explored. Bacterial laccases have numerous distinctive properties over fungal laccases, including stability at high temperatures and high pH. This study includes the isolation of bacteria through the soil sample collected from the paper and pulp industry; the highest laccase-producing bacteria was identified as Bhargavaea bejingensis, using 16S rRNA gene sequencing. The extracellular and intracellular activities after 24 h incubation were 1.41 U/mL and 4.95 U/mL, respectively. The laccase-encoding gene of the bacteria was sequenced; moreover, the in vitro translated protein was bioinformatically characterized and asserted that the laccase produced by the bacteria Bhargavaea bejingensis was structurally and sequentially homologous to the CotA protein of Bacillus subtilis. The enzyme laccase produced from B. bejingensis was classified as three-domain laccase with several copper-binding residues, where a few crucial copper-binding residues of the laccase enzyme were also predicted.

Molecular Docking of Lac_CB10: Highlighting the Great Potential for Bioremediation of Recalcitrant Chemical Compounds by One Predicted Bacteroidetes CopA-Laccase

Laccases are multicopper oxidases (MCOs) with a broad application spectrum, particularly in second-generation ethanol biotechnology and the bioremediation of xenobiotics and other highly recalcitrant compounds. Synthetic pesticides are xenobiotics with long environmental persistence, and the search for their effective bioremediation has mobilized the scientific community. Antibiotics, in turn, can pose severe risks for the emergence of multidrug-resistant microorganisms, as their frequent use for medical and veterinary purposes can generate constant selective pressure on the microbiota of urban and agricultural effluents. In the search for more efficient industrial processes, some bacterial laccases stand out for their tolerance to extreme physicochemical conditions and their fast generation cycles. Accordingly, to expand the range of effective approaches for the bioremediation of environmentally important compounds, the prospection of bacterial laccases was carried out from a custom genomic database. The best hit found in the genome of Chitinophaga sp. CB10, a Bacteroidetes isolate obtained from a biomass-degrading bacterial consortium, was subjected to in silico prediction, molecular docking, and molecular dynamics simulation analyses. The putative laccase CB10_180.4889 (Lac_CB10), composed of 728 amino acids, with theoretical molecular mass values of approximately 84 kDa and a pI of 6.51, was predicted to be a new CopA with three cupredoxin domains and four conserved motifs linking MCOs to copper sites that assist in catalytic reactions. Molecular docking studies revealed that Lac_CB10 had a high affinity for the molecules evaluated, and the affinity profiles with multiple catalytic pockets predicted the following order of decreasing thermodynamically favorable values: tetracycline (-8 kcal/mol) > ABTS (-6.9 kcal/mol) > sulfisoxazole (-6.7 kcal/mol) > benzidine (-6.4 kcal/mol) > trimethoprim (-6.1 kcal/mol) > 2,4-dichlorophenol (-5.9 kcal/mol) mol. Finally, the molecular dynamics analysis suggests that Lac_CB10 is more likely to be effective against sulfisoxazole-like compounds, as the sulfisoxazole-Lac_CB10 complex exhibited RMSD values lower than 0.2 nm, and sulfisoxazole remained bound to the binding site for the entire 100 ns evaluation period. These findings corroborate that LacCB10 has a high potential for the bioremediation of this molecule.

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.

Removal of dye pollution by an oxidase derived from mutagenesis of the Deuteromycete Myrothecium with high potential in industrial applications

It is estimated that over 700,000 tons of synthetic dyes are produced annually, 15% of which are emitted as effluents. These highly stable dyes enter the world water ecosystems and stay in the environment, and eventually cause adverse impacts to the environment. Current wastewater treatment methods, such as filtration, coagulation, and chemical oxidation, have sideeffects, including toxic residue formation, membrane fouling, bioaccumulation, and secondary pollutant formation. Given the issues mentioned, it is necessary to study how to improve the degradation of synthetic dye with a cost-effective and ecofriendly approach. Natural oxidation provides a greener option. Recently, Deuteromycetes fungus Myrothecium verrucaria G-1 (M. verrucaria G-1) has shown great potential in producing high level of dye oxidase. This study aims to generate a dye oxidase hyperproducer, 3H6 from M. verrucaria G-1 by using atmospheric and room temperature plasma (ARTP) coupled with ultraviolet (UV) irradiation. This method increases oxidase production by nearly 106.15%. After a simple precipitation and dialysis, this mutant oxidase increases by 1.97-fold in a specific activity with dye degradation rates at 70% for Mmethylene blue (MB) and 85% for Congo red (CR). It is found that the genetic stability of 3H6 remains active for ten generations. The size of oxidase is 65 kDa, and optimum temperature for reaction is 30 °C with 4.5 pH. This study presents that the first combined mutagenesis approach by ARPT-UV on fungus species generates an impressive increment of acid dye oxidases production. As such, this method presents a cost-effective alternative to mitigate hazardous dye pollution.

Broad thermal spectrum metagenomic laccase with action for dye decolorization and fentin hydroxide treatment

Laccases are multicopper oxidases that act on various phenolic and non-phenolic compounds, enabling numerous applications including xenobiotic bioremediation, biofuel production, drug development, and cosmetic production, and they can be used as additives in the textile and food industries. This wide range of uses makes these enzymes extremely attractive for novel biotechnology applications. Here, we undertook the kinetic characterization of LacMeta, a predicted as homotrimeric (~ 107,93 kDa) small laccase, and demonstrated that this enzyme performs best at an acidic pH (pH 3–5) towards ABTS as substrate and has a broad thermal spectrum (10–60 °C), which can promote high plastic action potential through dynamic environmental temperature fluctuations. This enzyme showed following kinetic parameters: k_cat = 6.377 s⁻¹ ± 0.303, K_m = 4.219 mM, and V_max = 24.43 µM/min (against ABTS as substrate). LacMeta almost completely degraded malachite green (50 mg/mL) in only 2 h. Moreover, the enzyme was able to degrade seven dyes from four distinct classes and it respectively achieved 85% and 83% decolorization of methylene blue and trypan blue with ABTS as the mediator. In addition, LacMeta showed potential for the degradation of two thirds of an agricultural fungicide: fentin hydroxide, thus demonstrating its biotechnological aptitude for bioremediation. The results of this study suggest that LacMeta has potential in textile wastewater treatment and that it could help in the bioremediation of other human/environmental toxins such as pesticides and antibiotic compounds belonging to the same chemical classes as the degraded dyes.

LacMeta is a new two-domain laccase with activity over a wide temperature range

LacMeta maintained 50% activity after 5 months of storage at 4 °C.

Laccase was able to degrade in 2 h the Malachite Green dye, and had the potential to degrade fentin hydroxide

Substitution of the Methionine Axial Ligand of the T1 Copper for the Fungal-like Phenylalanine Ligand (M298F) Causes Local Structural Perturbations that Lead to Thermal Instability and Reduced Catalytic Efficiency of the Small Laccase from Streptomyces coelicolor A3(2)

Many industrial processes operate at elevated temperatures or within broad pH and salinity ranges. However, the utilization of enzymes to carry out biocatalysis in such processes is often impractical or even impossible. Laccases (EC 1.10.3.2), which constitute a large family of multicopper oxidases, have long been used in the industrial setting. Although fungal laccases are in many respects considered superior to their bacterial counterparts, the bacterial laccases have been receiving greater attention recently. Albeit lower in redox potential than fungal laccases, bacterial laccases are commonly thermally more stable, act within broader pH ranges, do not contain posttranslational modifications, and could therefore serve as a high potential scaffold for directed evolution for the production of enzymes with enhanced properties. Several examples focusing on the axial ligand mutations of the T1 copper site have been published in the past. However, structural evidence on the local and global changes induced by those mutations have thus far been of computational nature only. In this study, we set out to structurally and kinetically characterize a few of the most commonly reported axial ligand mutations of a bacterial small laccase (SLAC) from Streptomyces coelicolor. While one of the mutations (Met to Leu) equips the enzyme with better thermal stability, the other (Met to Phe) induces an opposite effect. These mutations cause local structural rearrangement of the T1 site as demonstrated by X-ray crystallography. Our analysis confirms past findings that for SLACs, single point mutations that change the identity of the axial ligand of the T1 copper are not enough to provide a substantial increase in the catalytic efficiency but can in some cases have a detrimental effect on the enzyme's thermal stability parameters instead.

A Novel Polyphenol Oxidoreductase OhLac from Ochrobactrum sp. J10 for Lignin Degradation

Identifying the enzymes involved in lignin degradation by bacteria is important in studying lignin valorization to produce renewable chemical products. In this paper, the catalytic oxidation of lignin by a novel multi-copper polyphenol oxidoreductase (OhLac) from the lignin degrader Ochrobactrum sp. J10 was explored. Following its expression, reconstitution, and purification, a recombinant enzyme OhLac was obtained. The OhLac enzyme was characterized kinetically against a range of substrates, including ABTS, guaiacol, and 2,6-DMP. Moreover, the effects of pH, temperature, and Cu²⁺ on OhLac activity and stability were determined. Gas chromatography-mass spectrometer (GC-MS) results indicated that the β-aryl ether lignin model compound guaiacylglycerol-β-guaiacyl ether (GGE) was oxidized by OhLac to generate guaiacol and vanillic acid. Molecular docking analysis of GGE and OhLac was then used to examine the significant amino residues and hydrogen bonding sites in the substrate–enzyme interaction. Altogether, we were able to investigate the mechanisms involved in lignin degradation. The breakdown of the lignocellulose materials wheat straw, corn stalk, and switchgrass by the recombinant OhLac was observed over 3 days, and the degradation results revealed that OhLac plays a key role in lignin degradation.

Laccase: addressing the ambivalence associated with the calculation of enzyme activity

Laccase (benzenediol: oxygen oxidoreductase) a unique multi-copper oxidase enzyme has been studied rigorously since its identification. However, there is ambivalence associated with various aspects of laccase, e.g., assay conditions and calculations. Our aim was to minimize its ambivalence, thus, total of five formulas (F1-F5) were used to determine laccase activity of white and blue laccase. In case of enzymatic profiling of blue laccase, its activity ranged from 0.04 to 464.3 U L^-1 whereas in case of white laccase it ranged from 0.05 to 1404.7 U L^-1. The affinity of laccase at various enzyme concentration (0.3-0.9 mg mL^-1), time (5 and 10 min) along with various substrates, i.e., 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), guaiacol (GCL), 2,6-dimethoxyphenol (DMP) and syringaldazine (SYZ), and its concentration (ABTS 0.5-1.5 mM, GCL 20-30 mM, DMP 1-5 mM, SYZ 10-30 mM) were inferred. The optimal substrate concentrations were 1.5 and 0.5 mM ABTS for blue and white laccase, respectively, with 30 mM GCL and 2 mM DMP being the common parameter. The optimal substrate concentrations were 0.5 mM ABTS, 20 mM GCL, 1 mM DMP and 30 mM SYZ for commercial laccase. It was observed that the optimal protein load and reaction time was 0.3 mg mL^-1 and 5 min in all the cases, however, in case of white laccase it was 0.6 mg mL^-1 at 10 min for DMP and in case of commercial laccase it was 0.9 mg mL^-1 and 5 min for SYZ. In the present study, F1 was most appropriate among the five formula used as it incorporates all the significant factors and use of single formula will help reduce future ambiguity.

Correlation between the T1 copper reduction potential and catalytic activity of a small laccase

Laccases are multicopper enzymes that catalyze oxidation of electron-rich substrates coupled to reduction of molecular oxygen to water. Since the Type 1 copper (T1 Cu) is the site where electrons are withdrawn from the substrate, it is assumed that the reduction potential of this copper correlates with enzyme activity. Herein, we studied the correlation of the T1 Cu reduction potential and the enzymatic activity of the small two-domain laccase Ssl1 from Streptomyces sviceus. For a systematic approach, we aimed to minimize any effects other than the reduction potential difference. To this end, we constructed a series of Ssl1 mutants with reduction potentials varying from <290 to 560 mV. Along with the hydrophobicity of the axial ligand of the T1 Cu also structural changes in the substrate binding site and additional hydrogen bonding increased the reduction potential. Enzyme activity experiments demonstrated that the T1 Cu reduction potential has a different effect on oxidation of different substrates. Whereas there was no obvious correlation between the T1 Cu reduction potential and kinetic parameters for the oxidation of syringaldazine (with a reduction potential of 390 mV), a good correlation was observed between the T1 Cu reduction potential and the conversion of substituted phenols with reduction potentials between 660 and 820 mV. This correlation was pronounced for the Ssl1 variants with reduction potentials above 470 mV, which demonstrated increased activities also during the oxidation of two dyes, alizarin red S and indigo carmine.

Aptitude of Oxidative Enzymes for Treatment of Wastewater Pollutants: A Laccase Perspective

Natural water sources are very often contaminated by municipal wastewater discharges which contain either of xenobiotic pollutants and their sometimes more toxic degradation products, or both, which frustrates the universal millenium development goal of provision of the relatively scarce pristine freshwater to water-scarce and -stressed communities, in order to augment their socioeconomic well-being. Seeing that both regulatory measures, as regards the discharge limits of wastewater, and the query for efficient treatment methods remain unanswered, partially, the prospects of enzymatic treatment of wastewater is advisable. Therefore, a reconsideration was assigned to the possible capacity of oxidative enzymes and the respective challenges encountered during their applications in wastewater treatment, and ultimately, the prospects of laccase, a polyphenol oxidase that oxidizes aromatic and inorganic substrates with electron-donating groups in treatment aromatic contaminants of wastewater, in real wastewater situations, since it is assumed to be a vehicle for a greener community. Furthermore, the importance of laccase-driven catalysis toward maintaining mass-energy balance, hence minimizing environmental waste, was comprehensibly elucidated, as well the strategic positioning of laccase in a model wastewater treatment facility for effective treatment of wastewater contaminants.

In silico Design of Laccase Thermostable Mutants From Lacc 6 of Pleurotus Ostreatus

Fungal laccase enzymes have a great biotechnological potential for bioremediation processes due to their ability to degrade compounds such as ρ-diphenol, aminophenols, polyphenols, polyamines, and aryldiamines. These enzymes have activity at different pH and temperature values, however, high temperatures can cause partial or total loss of enzymatic activity, so it is appropriate to do research to modify their secondary and/or tertiary structure to make them more resistant to extreme temperature conditions. In silico, a structure of the Lacc 6 enzyme of Pleurotus ostreatus was constructed using a laccase of Trametes versicolor as a template. From this structure, 16 mutants with possible resistance at high temperature due to ionic interactions, salt bridges and disulfide bonds were also obtained in silico. It was determined that 12 mutants called 4-DB, 3-DB, D233C-T310C, F468P, 3-SB, L132T, N79D, N372D, P203C, P203V, T147E, and W85F, presented the lowest thermodynamic energy. Based on the previous criterion and determining the least flexibility in the protein structures, three mutants (4-DB, 3-DB, and P203C) were selected, which may present high stability at high temperatures without affecting their active site. The obtained results allow the understanding of the molecular base that increase the structural stability of the enzyme Lacc 6 of Pleurotus ostreatus, achieving the in silico generation of mutants, which could have activity at high temperatures.

Biocatalytic potential of Streptomyces spp. isolates from rhizosphere of plants and mycorrhizosphere of fungi

Biocatalytic potential of Streptomyces strains isolated from the rhizosphere of plants and from mycorrhizosphere of fungi has been investigated. A total of 118 Streptomyces isolates were selected and functionally screened for 10 different biotechnologically important enzymatic activities: hydrolase (cellulase, cutinase, gelatinase, lipase, protease, polyhydroxyalkanoate (PHA) depolymerase), phenol oxidase and peroxidase (laccase, tyrosinase, and lignin peroxidase), and aminotransferase. Out of 118 tested Streptomyces spp., 90% showed at least one enzymatic activity. The most abundant were enzymes involved in the biomass degradation, as the production of cutinase, cellulase, and lignin peroxidase were detected in 31%, 40%, and 48% of the isolates, respectively. The improved specific activities of lipase (isolates BV315 and BV100) and tyrosinase (isolates BV87 and BV88) were shown in comparison with the industrially relevant activities of Pseudomonas strains. Plant rhizosphere soils were more prolific source of Streptomyces strains with biocatalytic potential in comparison with mycorrhizosphere soils. Overall, 284 enzyme activities among 118 Streptomyces isolates have been detected. This is the first comprehensive screening of Streptomyces isolates from rhizosphere and mycorrhizosphere soils for novel biocatalysts, showing that specific environmental habitats, such as rhizosphere soils, are "treasure troves" of Streptomyces with biocatalytic potential.

Characterization of a laccase from a wood-feeding termite, Coptotermes formosanus

Coptotermes formosanus Shiraki is a wood-feeding termite which secretes a series of lignolytic and cellulolytic enzymes for woody biomass degradation. However, the lignin modification mechanism in the termite is largely elusive, and the characteristics of most lignolytic enzymes in termites remain unknown. In this study, a laccase gene lac1 from C. formosanus was heterogeneously expressed in insect Sf9 cells. The purified Lac1 showed strong activities toward hydroquinone (305 mU/mg) and 2,6-dimethoxyphenol (2.9 mU/mg) with low K_m values, but not veratryl alcohol or 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid). Lac1 could function well from pH 4.5 to 7.5, and its activity was significantly inhibited by H₂ O₂ at above 4.85 mmol/L (P < 0.01). In addition, the lac1 gene was found to be mainly expressed in the salivary glands and foregut of C. formosanus, and seldom in the midgut or hindgut. These findings suggested that Lac1 is a phenol-oxidizing laccase like RflacA and RflacB from termite Reticulitermes flavipes, except that Lac1 was found to be more efficient in phenol oxidation, and it did not require H₂ O₂ for its function. It is suspected that this kind of termite laccase might only be able to directly oxidize low redox-potential substrates, and the high redox-potential groups in lignin might be oxidized by other enzymes in the termite or by using the Fenton reaction.

Isolation, identification of a laccase-producing fungal strain and enzymatic properties of the laccase

A new type of thermostable laccase was isolated from Paraphoma sp. GZS18, and its partial enzymatic properties were determined. A strain GZS18 of laccase with high yield was screened from forest soil and identified as Paraphoma sp. GZS18 through morphological characteristics and ITS sequence analysis. The laccase of Paraphoma sp. GZS18 (Lac-P) was obtained through cation-anion exchange chromatography, gel filtration chromatography, and other purification processes. The testing result shows that Lac-P is a single protein of 75 kDa, and the 11 amino acid sequences in the N-terminal are AX^aVSVASREMT (X^a was the non-standard protein). The optimum temperature and optimum pH of lac-P activity are substrate-independent. The temperature is in the range of 50-70 °C, and pH has high catalytic efficiency in the acidic range. Lac-P has good stability in the temperature and pH. The half time at 70-60 °C is 1.5 and 4 h, respectively. At pH 6-9 and room temperature, there is more than 80% activity 24 h later. Lac-P is tolerant of most metal ions and low concentrations of inhibitors but is inhibited by Hg²⁺, Fe²⁺ and NaN₃. The laccase from Paraphoma sp. GZS18 at high temperature and pH 6-9, with strong stability, has better industrial application characteristics.

Secretory expression of recombinant small laccase from Streptomyces coelicolor A3(2) in Pichia pastoris

This work reports for the first time the secretory expression of the small laccase (SLAC) from Streptomyces coelicolor A3(2) in Pichia pastoris. Using an AOX1 promoter and α factor as a secretion signal, the recombinant P. pastoris harbouring the laccase gene (rSLAC) produced high titres of extracellular laccase (500 ± 10 U/l), which were further increased seven fold by pre-incubation at 80 °C for 30 min. The enzyme (∼38 kDa) had an optimum activity at 80 °C, but optimum pH varied with substrate used. K_m values for ABTS, SGZ and 2,6-DMP were 142.85 μM, 10 μM and 54.55 μM and the corresponding k_cat values were 60.6 s^-1, 25.36 s^-1 and 27.84 s^-1, respectively. The t_1/2 values of the rSLAC at 60 °C, 70 °C, 80 °C were 60 h, 32 h and 10 h, respectively. The enzyme deactivation energy (E_d) was 117.275 kJ/mol while ΔG, ΔH and ΔS for thermal inactivation of the rSLAC were all positive. The rSLAC decolourised more than 90% of Brilliant Blue G and Trypan Blue dye in 6 h without the addition of a mediator. High titres of SLAC expressed in P. pastoris enhance its potential for various industrial applications.

Evolving stability and pH-dependent activity of the high redox potential Botrytis aclada laccase for enzymatic fuel cells

Fungal high redox potential laccases are proposed as cathodic biocatalysts in implantable enzymatic fuel cells to generate high cell voltages. Their application is limited mainly through their acidic pH optimum and chloride inhibition. This work investigates evolutionary and engineering strategies to increase the pH optimum of a chloride-tolerant, high redox potential laccase from the ascomycete Botrytis aclada. The laccase was subjected to two rounds of directed evolution and the clones screened for increased stability and activity at pH 6.5. Beneficial mutation sites were investigated by semi-rational and combinatorial mutagenesis. Fourteen variants were characterised in detail to evaluate changes of the kinetic constants. Mutations increasing thermostability were distributed over the entire structure. Among them, T383I showed a 2.6-fold increased half-life by preventing the loss of the T2 copper through unfolding of a loop. Mutations affecting the pH-dependence cluster around the T1 copper and categorise in three types of altered pH profiles: pH-type I changes the monotonic decreasing pH profile into a bell-shaped profile, pH-type II describes increased specific activity below pH 6.5, and pH-type III increased specific activity above pH 6.5. Specific activities of the best variants were up to 5-fold higher (13 U mg⁻¹) than BaL WT at pH 7.5.

Bacterial laccase: recent update on production, properties and industrial applications

Laccases (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) are multi-copper enzymes which catalyze the oxidation of a wide range of phenolic and non-phenolic aromatic compounds in the presence or absence of a mediator. Till date, laccases have mostly been isolated from fungi and plants, whereas laccase from bacteria has not been well studied. Bacterial laccases have several unique properties that are not characteristics of fungal laccases such as stability at high temperature and high pH. Bacteria produce these enzymes either extracellularly or intracellularly and their activity is in a wide range of temperature and pH. It has application in pulp biobleaching, bioremediation, textile dye decolorization, pollutant degradation, biosensors, etc. Hence, comprehensive information including sources, production conditions, characterization, cloning and biotechnological applications is needed for the effective understanding and application of these enzymes at the industrial level. The present review provides exhaustive information of bacterial laccases reported till date.

Overexpression of a Laccase with Dye Decolorization Activity from sp. Induced in

Laccases from bacteria have been widely studied in the past 2 decades due to the higher growth rate of bacteria and their excellent thermal and alkaline pH stability. In this study, a novel laccase gene was cloned from<i> Bacillus</i> sp., analyzed, and functionally expressed in<i> Escherichia coli</i>. The laccase was highly induced in the <i>E. coli</i> expression system with a maximum intracellular activity of 16 U mg^-1 protein. The optimal temperature and pH of the purified laccase were 40°C and 4.6, respectively, when ABTS (2,2'-azino-bis[3-ethylbenzothiazoline-6-sulfonate]) was used as the substrate. The purified laccase showed high stability in the pH range of 3.0-9.0, and retained more than 70% of its activity after 24 h of incubation at 40°C with a pH value of 9.0. Furthermore, the enzyme exhibited extremely high temperature and ion metal tolerance. The half-life of the purified laccase at 70°C was 15.9 h. The purified laccase could efficiently decolorize 3 chemical dyes, especially in the presence of ABTS as a mediator. The high production of this laccase in<i> E. coli</i> and exceptional characteristics of the recombinant enzyme protein make it a promising candidate for industrial applications.

Laccase catalysis for the synthesis of bioactive compounds

The demand for compounds of therapeutic value is increasing mainly because of new applications of bioactive compounds in medicine, pharmaceutical, agricultural, and food industries. This has necessitated the search for cost-effective methods for producing bioactive compounds and therefore the intensification of the search for enzymatic approaches in organic synthesis. Laccase is one of the enzymes that have shown encouraging potential as biocatalysts in the synthesis of bioactive compounds. Laccases are multicopper oxidases with a diverse range of catalytic activities revolving around synthesis and degradative reactions. They have attracted much attention as potential industrial catalysts in organic synthesis mainly because they are essentially green catalysts with a diverse substrate range. Their reaction only requires molecular oxygen and releases water as the only by-product. Laccase catalysis involves the abstraction of a single electron from their substrates to produce reactive radicals. The free radicals subsequently undergo homo- and hetero-coupling to form dimeric, oligomeric, polymeric, or cross-coupling products which have practical implications in organic synthesis. Consequently, there is a growing body of research focused on the synthetic applications of laccases such as organic synthesis, hair and textile dyeing, polymer synthesis, and grafting processes. This paper reviews the major advances in laccase-mediated synthesis of bioactive compounds, the mechanisms of enzymatic coupling, structure-activity relationships of synthesized compounds, and the challenges that might guide future research directions.