Fungal laccases as tools for the synthesis of new hybrid molecules and biomaterials

Laccase-Mediated Grafting on Biopolymers and Synthetic Polymers: A Critical Review

Laccase-mediated grafting on lignocelluloses has gained considerable attention as an environmentally benign method to covalently modify wood, paper and cork. In recent decades this technique has also been employed to modify fibres with a polysaccharide backbone, such as cellulose or chitosan, to infer colouration, antimicrobial activity or antioxidant activity to the material. The scope of this approach has been further widened by researchers, who apply mediators or high redox potential laccases and those that modify synthetic polymers and proteins. In all cases, the methodology relies on one- or two-electron oxidation of the surface functional groups or of the graftable molecule in solution. However, similar results can very often be achieved through simple deposition, even after extensive washing. This unintended adsorption of the active substance could have an adverse effect on the durability of the applied coating. Differentiating between actual covalent binding and adsorption is therefore essential, but proves to be challenging. This review not only covers excellent research on the topic of laccase-mediated grafting over the last five to ten years, but also provides a critical comparison to highlight either the lack or presence of compelling evidence for covalent grafting.

Bio-coloration of bacterial cellulose assisted by immobilized laccase

In this work a process for the bio-coloration of bacterial cellulose (BC) membranes was developed. Laccase from Myceliophthora thermophila was immobilized onto BC membranes and retained up to 88% of residual activity after immobilization. Four compounds belonging to the flavonoids family were chosen to test the in situ polymerase activity of immobilized laccase. All the flavonoids were successfully polymerized by laccase giving rise to yellow, orange and dark brown oligomers which conferred color to the BC support. The optimal bio-coloration conditions were studied for two of the tested flavonoids, catechol and catechin, by varying the concentration and time of incubation. High color depth and resistance to washing were obtained for both compounds. The highly porous bacterial cellulose material demonstrated great performance as a bio-coloration support, in contrast to other materials cited in literature, like cotton or wool. The process developed is presented as an environmentally friendly alternative for bacterial cellulose bio-coloration and will contribute deeply for the development of new fashionable products within this material.

Laccase production in bioreactor scale under saline condition by the marine-derived basidiomycete Peniophora sp. CBMAI 1063

Laccase production in saline conditions is still poorly studied. The aim of the present study was to investigate the production of laccase in two different types of bioreactors by the marine-derived basidiomycete Peniophora sp. CBMAI 1063. The highest laccase activity and productivity were obtained in the Stirred Tank (ST) bioreactor, while the highest biomass concentration in Air-lift (AL) bioreactor. The main laccase produced was purified by ion exchange and size exclusion chromatography and appeared to be monomeric with molecular weight of approximately 55 kDa. The optimum oxidation activity was obtained at pH 5.0. The thermal stability of the enzyme ranged from 30 to 50 °C (120 min). The Far-UV Circular Dichroism revealed the presence of high β-sheet and low α-helical conformation in the protein structure. Additional experiments carried out in flask scale showed that the marine-derived fungus was able to produce laccase only in the presence of artificial seawater and copper sulfate. Results from the present study confirmed the fungal adaptation to marine conditions and its potential for being used in saline environments and/or processes.

Expression of a new laccase from Moniliophthora roreri at high levels in Pichia pastoris and its potential application in micropollutant degradation

Laccases have gained significant attention due to their emerging applications including bioremediation, biomass degradation and biofuel cells. One of the prerequisites for the industrial application of laccases is their sufficient availability. However, expression levels of recombinantly expressed laccases are often low. In this study Mrl2, a new laccase from the basidiomycete Moniliophthora roreri, was cloned in Pichia pastoris and produced in an optimized fed-batch process at an exceptionally high yield of 1.05 g l⁻¹. With a redox potential of 0.58 V, Mrl2 belongs to mid-redox potential laccases. However, Mrl2 demonstrated high k_cat values of 316, 20, 74, and 36 s⁻¹ towards 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), syringaldazine (SGZ), 2,6-dimethoxyphenol (2,6-DMP) and guaiacol, respectively. Mrl2 remained stable above pH 6 and in the presence of many metal ions, which is important for application in bioremediation. Mrl2 was investigated for the ability to degrade endocrine disrupting chemicals (EDCs) and non-steroidal anti-inflammatory drugs (NSDAIs) at neutral pH value. The enzyme accepted and converted estrone, 17β-estradiol, estriol, the synthetic contraceptive 17α-ethinyl estradiol and bisphenol A at pH 7 faster than high-potential laccases from Trametes versicolor. For example, within 30 min Mrl2 removed more than 90% bisphenol A, 17ß-estradiol, 17α-ethinyl estradiol and estriol, respectively. The concentration of the recalcitrant drug diclofenac dropped by 56% after 20 h incubation with Mrl2.

Laccase: a multi-purpose biocatalyst at the forefront of biotechnology

Laccases are multicopper containing enzymes capable of performing one electron oxidation of a broad range of substrates. Using molecular oxygen as the final electron acceptor, they release only water as a by-product, and as such, laccases are eco-friendly, versatile biocatalysts that have generated an enormous biotechnological interest. Indeed, this group of enzymes has been used in different industrial fields for very diverse purposes, from food additive and beverage processing to biomedical diagnosis, and as cross-linking agents for furniture construction or in the production of biofuels. Laccases have also been studied intensely in nanobiotechnology for the development of implantable biosensors and biofuel cells. Moreover, their capacity to transform complex xenobiotics makes them useful biocatalysts in enzymatic bioremediation. This review summarizes the most significant recent advances in the use of laccases and their future perspectives in biotechnology.

Simple screening protocol for identification of potential mycoremediation tools for the elimination of polycyclic aromatic hydrocarbons and phenols from hyperalkalophile industrial effluents

A number of fungal strains belonging to the ascomycota, basidiomycota and zygomycota genera were subjected to an in vitro screening regime to assess their ligninolytic activity potential, with a view to their potential use in mycoremediation-based strategies to remove phenolic compounds and polycyclic aromatic hydrocarbons (PAHs) from industrial wastewaters. All six basidiomycetes completely decolorized remazol brilliant blue R (RBBR), while also testing positive in both the guaiacol and gallic acid tests indicating good levels of lignolytic activity. All the fungi were capable of tolerating phenanthrene, benzo-α- pyrene, phenol and p-chlorophenol in agar medium at levels of 10 ppm. Six of the fungal strains, Pseudogymnoascus sp., Aspergillus caesiellus, Trametes hirsuta IBB 450, Phanerochate chrysosporium ATCC 787, Pleurotus ostreatus MTCC 1804 and Cadophora sp. produced both laccase and Mn peroxidase activity in the ranges of 200-560 U/L and 6-152 U/L, respectively, in liquid media under nitrogen limiting conditions. The levels of adsorption of the phenolic and PAHs were negligible with 99% biodegradation being observed in the case of benzo-α-pyrene, phenol and p-chlorophenol. The aforementioned six fungal strains were also found to be able to effectively treat highly alkaline industrial wastewater (pH 12.4). When this wastewater was supplemented with 0.1 mM glucose, all of the tested fungi, apart from A. caesiellus, displayed the capacity to remove both the phenolic and PAH compounds. Based on their biodegradative capacity we found T. hirsuta IBB 450 and Pseudogymnoascus sp., to have the greatest potential for further use in mycoremediation based strategies to treat wastestreams containing phenolics and PAHs.

Laccase: a green catalyst for the biosynthesis of poly-phenols

Laccases (benzene diol: oxidoreductases, EC 1.10.3.2) are able to catalyze the oxidation of various compounds containing phenolic and aniline structures using dissolved oxygen in water. Laccase structural features and catalytic mechanisms focused on the polymerization of aromatic compounds are reported. A description about the most recent research on the biosynthesis of chemicals and polymers is made. Selected applications of this technology are considered as well as the advantages, shortcomings and future needs related with the use of laccases.

Laccase-catalyzed green synthesis and cytotoxic activity of novel pyrimidobenzothiazoles and catechol thioethers

Laccase-catalyzed green reaction between catechols and 2-thioxopyrimidin-4-ones delivers novel pyrimidobenzothiazoles and catechol thioethers with antiproliferative activities against HepG2 cell line.

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.

Enzymatic synthesis of bioactive compounds with high potential for cosmeceutical application

Cosmeceuticals are cosmetic products containing biologically active ingredients purporting to offer a pharmaceutical therapeutic benefit. The active ingredients can be extracted and purified from natural sources (botanicals, herbal extracts, or animals) but can also be obtained biotechnologically by fermentation and cell cultures or by enzymatic synthesis and modification of natural compounds. A cosmeceutical ingredient should possess an attractive property such as anti-oxidant, anti-inflammatory, skin whitening, anti-aging, anti-wrinkling, or photoprotective activity, among others. During the past years, there has been an increased interest on the enzymatic synthesis of bioactive esters and glycosides based on (trans)esterification, (trans)glycosylation, or oxidation reactions. Natural bioactive compounds with exceptional theurapeutic properties and low toxicity may offer a new insight into the design and development of potent and beneficial cosmetics. This review gives an overview of the enzymatic modifications which are performed currently for the synthesis of products with attractive properties for the cosmeceutical industry.

A 2,5-Dihydroxybenzoic Acid-Gelatin Conjugate: The Synthesis, Antiviral Activity and Mechanism of Antiviral Action Against Two Alphaherpesviruses

Various natural and synthetic polyanionic polymers with different chemical structures are known to exhibit potent antiviral activity in vitro toward a variety of enveloped viruses and may be considered as promising therapeutic agents. A water-soluble conjugate of 2,5-dihydroxybezoic acid (2,5-DHBA) with gelatin was synthesized by laccase-catalyzed oxidation of 2,5-DHBA in the presence of gelatin, and its antiviral activity against pseudorabies virus (PRV) and bovine herpesvirus type 1 (BoHV-1), two members of the Alphaherpesvirinae subfamily, was studied. The conjugate produced no direct cytotoxic effect on cells, and did not inhibit cell growth at concentrations up to 1000 µg/mL. It exhibited potent antiviral activity against PRV (IC50, 1.5-15 µg/mL for different virus strains) and BoHV-1 (IC50, 0.5-0.7 µg/mL). When present during virus adsorption, the conjugate strongly inhibited the attachment of PRV and BoHV-1 to cells. The 2,5-DHBA-gelatin conjugate had no direct virucidal effect on the viruses and did not influence their penetration into cells, cell-to-cell spread, production of infectious virus particles in cells, and expression of PRV glycoproteins E and B. The results indicated that the 2,5-DHBA-gelatin conjugate strongly inhibits the adsorption of alphaherpesviruses to cells and can be a promising synthetic polymer for the development of antiviral formulations against alphaherpesvirus infections.

Structural and functional roles of glycosylation in fungal laccase from Lentinus sp

Laccases are multi-copper oxidases that catalyze the oxidation of various organic and inorganic compounds by reducing O2 to water. Here we report the crystal structure at 1.8 Å resolution of a native laccase (designated nLcc4) isolated from a white-rot fungus Lentinus sp. nLcc4 is composed of three cupredoxin-like domains D1-D3 each folded into a Greek key β-barrel topology. T1 and T2/T3 copper binding sites and three N-glycosylated sites at Asn75, Asn238, and Asn458 were elucidated. Initial rate kinetic analysis revealed that the kcat, Km, and kcat/Km of nLcc4 with substrate ABTS were 3,382 s-1, 65.0 ± 6.5 μM, and 52 s-1μM-1, respectively; and the values with lignosulfonic acid determined using isothermal titration calorimetry were 0.234 s-1, 56.7 ± 3.2 μM, and 0.004 s-1μM-1, respectively. Endo H-deglycosylated nLcc4 (dLcc4), with only one GlcNAc residue remaining at each of the three N-glycosylation sites in the enzyme, exhibited similar kinetic efficiency and thermal stability to that of nLcc4. The isolated Lcc4 gene contains an open reading frame of 1563 bp with a deduced polypeptide of 521 amino acid residues including a predicted signaling peptide of 21 residues at the N-terminus. Recombinant wild-type Lcc4 and mutant enzymes N75D, N238D and N458D were expressed in Pichia pastoris cells to evaluate the effect on enzyme activity by single glycosylation site deficiency. The mutant enzymes secreted in the cultural media of P. pastoris cells were observed to maintain only 4-50% of the activity of the wild-type laccase. Molecular dynamics simulations analyses of various states of (de-)glycosylation in nLcc support the kinetic results and suggest that the local H-bond networks between the domain connecting loop D2-D3 and the glycan moieties play a crucial role in the laccase activity. This study provides new insights into the role of glycosylation in the structure and function of a Basidiomycete fungal laccase.

Effect of Direct-Current Electric Field on Enzymatic Activity and the Concentration of Laccase

This work investigates the effect of direct-current electric field on the extracellular enzymatic activity, concentration and other experimental parameters of laccase from Trametes versicolor. The results showed that laccase could significantly contribute to the change of pH at the end of graphite electrode. In addition, it increased the electrical conductivity of the water. In the experiment, the optimum pH and catalytic pH range for laccase activity were 3.0 and pH 2.5-4.0. The application of 6 V direct current showed significant effects on the laccase enzyme activity. The activity of laccase was enhanced in the anodic region, but at the same time was strongly inhibited at the cathode. The electric charge characteristics of laccase were changed when exposed to electric field, and some laccases molecules moved to the anode, which produced a slight migration phenomenon. This study is the basis of combination of laccase and electrical technology, at the same time, providing a new direction of enhancing laccase activity. Compared to immobilization, using electric field is simple, no chemical additives, and great potential.

Muta-mycosynthesis of naphthalene analogs

A mutasynthetic strategy is introduced for the mycosynthesis of naphthalene-based molecules (mutadalesols A-F) with directed substitution patterns and new frameworks by generating and using the ΔpksTL mutant strain of Daldinia eschscholzii. (±)-Mutadalesol A and its (+)-enantiomer are cytotoxic, and its (-)-enantiomer inhibits Toll-like receptor 5 (TLR5). The in-culture reactability of fungal oligoketide intermediates with 5-aminonaphthalen-1-ol (ANL) is demonstrated, shedding light on bioorthogonal accesses to unnatural molecule libraries valuable in drug discovery pipelines.

Spectroscopic and computational characterization of laccases and their substrate radical intermediates

Laccases are multicopper oxidases which oxidize a wide variety of aromatic compounds with the concomitant reduction of oxygen to water as by-product. Due to their high stability and biochemical versatility, laccases are key enzymes to be used as eco-friendly biocatalyst in biotechnological applications. The presence of copper paramagnetic species in the catalytic site paired with the substrate radical species produced in the catalytic cycle makes laccases particularly attractive to be studied by spectroscopic approaches. In this review, the potentiality of a combined multifrequency electron paramagnetic spectroscopy /computational approach to gain information on the nature of the catalytic site and radical species is presented. The knowledge at molecular level of the enzyme oxidative process can be of great help to model new enzymes with increased efficiency and robustness.

How to enjoy laccases

An analysis of the scientific literature published in the last 10 years reveals a constant growth of laccase applicative research in several industrial fields followed by the publication of a great number of patents. The Green Chemistry journal devoted the cover of its September 2014 issue to a laccase as greener alternative for chemical oxidation. This indicates that laccase "never-ending story" has found a new promising trend within the constant search for efficient (bio)catalysts able to meet the 12 green chemistry principles. A survey of ancient and cutting-edge uses of laccase in different industrial sectors is offered in this review with the aim both to underline their potential and to provide inspiration for new ones. Applications in textile and food fields have been deeply described, as well as examples concerning polymer synthesis and laccase-catalysed grafting. Recent applications in pharmaceutical and cosmetic industry have also been reviewed.

Xanthone dimers: a compound family which is both common and privileged

This Review seeks to systematically describe, for the first time, the widely-occurring and highly biologically-active family of dimeric xanthones from nature, encompassing several aspects of their biosynthesis, occurrence, contrasting structural features and wide variety of bioactivities.

Modeling laccase-induced lignin removal in prehydrolysis liquor from kraft-based dissolving pulp production

Laccase treatment is a promising approach to remove lignin from prehydrolysis liquor (PHL) for value added utilization of hemicellulose rich waste streams. Modeling the lignin removal process is of practical interest for prediction and control of laccase treatment of PHL. The present study focused on the lignin removal through variation of laccase charge and treatment time. Results showed that the lignin removal may be divided into two phases, i.e. a fast initial phase followed by a second slow phase. A kinetic model based on the experimental results was developed, which can be used to predict the lignin removal of PHL during the laccase treatment.

Biotransformation of huperzine A by a fungal endophyte of Huperzia serrata furnished sesquiterpenoid-alkaloid hybrids

Biotransformation of huperzine A (hupA) by a fungal endophyte, Ceriporia lacerate HS-ZJUT-C13A, afforded compounds 1-5 and three tremulane sesquiterpenoids, 6-8. Huptremules A-D (1-4) feature unusual sesquiterpenoid-alkaloid hybrid structures that integrate the characteristics of fungal metabolites (tremulane sesquiterpenoids) and the exogenous substrate (hupA). These results support the use of fungal endophytes as biocatalysts for the biotransformation of natural products, particularly those originating from the host plant.

Expanding the laccase-toolbox: a laccase from Corynebacterium glutamicum with phenol coupling and cuprous oxidase activity

Laccases are oxidases with potential for application in biotechnology. Up to now only fungal laccases have been applied in technical processes, although bacterial laccases are generally easier to handle and more stable at alkaline pH values and elevated temperatures. To increase the toolbox of bacterial laccases and to broaden our knowledge about them, new enzymes have to be characterized. Within this study, we describe the new bacterial laccase CgL1 from Corynebacterium glutamicum. CgL1 was found to oxidize typical laccase substrates like 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), syringaldazine and 2,6-dimethoxyphenol. The enzyme also demonstrates cuprous oxidase activity. Furthermore, CgL1 is active for several hours at temperatures up to 60°C and at alkaline pH, as well as stable in different organic solvents. This makes CgL1 a potential candidate for technical applications. In addition, CgL1 was found to catalyze the CC/CO coupling of several phenolic compounds which can serve as precursors for the synthesis of natural products like antibiotics and phytohormones. This activity and product distribution were influenced by pH value and mediators used.