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

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.

Heterologous expression and characterization of a novel laccase isoenzyme with dyes decolorization potential from Coprinus comatus

Two new laccase genes, named lac1 and lac2, were cloned from the edible basidiomycete Coprinus comatus. Comparison of the deduced amino acid sequences revealed two laccases showed 66.12 % identity and clustered with lac2 and lac3 from Coprinopsis cinerea in same phylogenetic group. Lac1 and lac2 encode proteins of 517 and 523 amino acids preceded by 18 and 21-residue signal peptides, respectively. Lac1 was functionally expressed in Pichia pastoris. The optimum pHs of recombinant Lac1 were 3.0, 6.0, 5.5 and 6.0 and the optimum temperatures were 65, 55, 70 and 50 °C for ABTS, guaiacol, 2,6-dimethylphenol and syringaldazine, respectively. The Km values of Lac1 were 34, 4,317, 7,611 and 14 μM, and the corresponding kcat values were 465.79, 7.67, 1.15 and 0.60 (s(-1) mM), for ABTS, guaiacol, 2,6-dimethylphenol and syringaldazine, respectively. The enzyme activity was completely inhibited by sodium azide (NaN(3)) and 1,4-dithiothreitol (DTT) at the concentration of 5 mM. Laccase activity was also inhibited by several metal ions, especially Fe(2+), while K(+) and NH(4) (+) slightly enhanced laccase activity. Twelve synthetic dyes belonging to anthraquinone, azo and triphenylmethane dyes were decolorized by the recombinant Lac1 at different extents. The recombinant Lac1 decolorized azo dye Reactive Dark Blue KR up to 90 % without any mediator and increasing to 96 % with mediator, indicating its potential in the treatment of industrial effluent containing some recalcitrant synthetic dyes.

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.

Decolorization of different dyes by a newly isolated white-rot fungi strain Ganoderma sp.En3 and cloning and functional analysis of its laccase gene

A laccase-producing white-rot fungi strain Ganoderma sp.En3 was newly isolated from the forest of Tzu-chin Mountain in China. Ganoderma sp.En3 had a strong ability of decolorizing four synthetic dyes, two simulated dye bath effluents and the real textile dye effluent. Induction in the activity of laccase during the decolorization process indicated that laccase played an important role in the efficient decolorization of different dyes by this fungus. Phytotoxicity study with respect to Triticum aestivum and Oryza sativa demonstrated that Ganoderma sp.En3 was able to detoxify four synthetic dyes, two simulated dye effluents and the real textile dye effluent. The laccase gene lac-En3-1 and its corresponding full-length cDNA were then cloned and characterized from Ganoderma sp.En3. The deduced protein sequence of LAC-En3-1 contained four copper-binding conserved domains of typical laccase protein. The functionality of lac-En3-1 gene encoding active laccase was verified by expressing this gene in the yeast Pichia pastoris successfully. The recombinant laccase produced by the yeast transformant could decolorize the synthetic dyes, simulated dye effluents and the real textile dye effluent. The ability of decolorizing different dyes was positively related to the laccase activity. In addition, the 5'-flanking sequence upstream of the start codon ATG in lac-En3-1 gene was obtained. Many putative cis-acting responsive elements were predicted in the promoter region of lac-En3-1.

Molecular cloning and heterologous expression of a laccase gene from Pleurotus eryngii in free and immobilized Saccharomyces cerevisiae cells

A full length cDNA encoding an extracellular laccase was isolated by reverse transcription polymerase chain reaction from the mycelia of the mushroom Pleurotus eryngii. The isolated sequence, denoted Ery3, encodes for a mature laccase isoenzyme of 531 amino acid residues with a predicted molecular weight of 56.6 kDa. All sequence motifs, being the signature sequences used to identify the laccases, were found in the Ery3 protein sequence. The Ery3 cDNA was expressed in Saccharomyces cerevisiae and the effects of copper concentration and cultivation temperature were investigated. S. cerevisiae cells were immobilized in calcium alginate gel and the optimal immobilization parameters for the enhanced production of laccase were determined. The immobilization was most effective with 3% sodium alginate, 0.1 M calcium chloride and an initial biomass of 4.5 x 10(8) cells. The enzyme yield obtained with immobilized cells (139 mU ml(-1)) showed a 1.6-fold increase compared to the highest yield obtained with free cells. The alginate beads showed good stability and retained 84% capacity of enzyme production after seven repeated cycles of batch fermentation. The immobilization system proved to increase the proteolytic stability of the recombinant Ery3 protein. To our knowledge, this is the first report on S. cerevisiae whole-cell immobilization for recombinant laccase production.

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.

Cloning of a laccase gene from a novel basidiomycete Trametes sp. 420 and its heterologous expression in Pichia pastoris

The laccase gene lacD, cloned from a novel laccase-producing basidiomycete Trametes sp. 420, contained 2,052 base pairs (bp) interrupted by 8 introns. lacD displayed a relatively high homology with laccase genes from other white rot fungi, whereas the homology between lacD and laccase genes from plants, insects, or bacteria was less than 25%. A 498-amino acid peptide encoded by the lacD cDNA was heterologously expressed in the Pichia pastoris strain GS115, resulting in the highest yield of laccase (8.3 x 10(4) U/l) as determined with ABTS (2,2'-azinobis [3-ethylbenzothia-zoline-6-sulfonic acid]) as the substrate. Additionally, the enzyme activity of recombinant laccase on decolorization of some industrial dyes was assessed.