Prediction model based on decision tree analysis for laccase mediators

Aflatoxin B1 Degradation by Ery4 Laccase: From In Vitro to Contaminated Corn

Aflatoxins (AFs) are toxic secondary metabolites produced by Aspergillus spp. and are found in food and feed as contaminants worldwide. Due to climate change, AFs occurrence is expected to increase also in western Europe. Therefore, to ensure food and feed safety, it is mandatory to develop green technologies for AFs reduction in contaminated matrices. With this regard, enzymatic degradation is an effective and environmentally friendly approach under mild operational conditions and with minor impact on the food and feed matrix. In this work, Ery4 laccase, acetosyringone, ascorbic acid, and dehydroascorbic acid were investigated in vitro, then applied in artificially contaminated corn for AFB₁ reduction. AFB₁ (0.1 µg/mL) was completely removed in vitro and reduced by 26% in corn. Several degradation products were detected in vitro by UHPLC-HRMS and likely corresponded to AFQ₁, epi-AFQ₁, AFB₁-diol, or AFB₁dialehyde, AFB_2a, and AFM₁. Protein content was not altered by the enzymatic treatment, while slightly higher levels of lipid peroxidation and H₂O₂ were detected. Although further studies are needed to improve AFB₁ reduction and reduce the impact of this treatment in corn, the results of this study are promising and suggest that Ery4 laccase can be effectively applied for the reduction in AFB₁ in corn.

A narrative review: The pharmaceutical evolution of phenolic syringaldehyde

To better understand the pharmacological characters of syringaldehyde (SA), which is a key-odorant compound of whisky and brandy, this review article is the first to compile the published literature for molecular docking that were subsequently validated by in vitro and in vivo assays to predict and develop insights into the medicinal properties of SA in terms of anti-oxidation, anti-inflammation, and anti-diabetes. The molecular docking displayed significantly binding affinity for SA towards tumor necrosis factor-α, interleukin-6, and antioxidant enzymes when inflammation from myocardial infarction and spinal cord ischemia. Moreover, SA nicely docked with dipeptidyl peptidase-IV, glucagon-like peptide 1 receptor, peroxisome proliferator-activated receptor, acetylcholine M2 receptor, and acetylcholinesterase in anti-diabetes investigations. These are associated with (1) an increase glucose utilization and insulin sensitivity to an anti-hyperglycemic effect; and (2) to potentiate intestinal contractility to abolish the α-amylase reaction when concurrently reducing retention time and glucose absorption of the intestinal tract to achieve a glucose-lowering effect. In silico screening of multi-targets concomitantly with preclinical tests could provide a potential exploration for new indications for drug discovery and development.

Laccase-Mediator System Using a Natural Mediator as a Whitening Agent for the Decolorization of Melanin

In this study, a laccase-mediator system (LMS) using a natural mediator was developed as a whitening agent for melanin decolorization. Seven natural mediators were used to replace synthetic mediators and successfully overcome the low redox potential of laccase and limited access of melanin to the active site of laccase. The melanin decolorization activity of laccases from Trametes versicolor (lacT) and Myceliophthora thermophila (lacM) was significantly enhanced using natural mediators including acetosyringone, syringaldehyde, and acetovanillone, which showed low cytotoxicity. The methoxy and ketone groups of natural mediators play an important role in melanin decolorization. The specificity constants of lacT and lacM for melanin decolorization were enhanced by 247 and 334, respectively, when acetosyringone was used as a mediator. LMS using lacM and acetosyringone could also decolorize the melanin present in the cellulose hydrogel film, which mimics the skin condition. Furthermore, LMS could decolorize not only synthetic eumelanin analogs prepared by the oxidation of tyrosine but also natural melanin produced by melanoma cells.

Comparative catalytic degradation of a metabolite 3,5-dichloroaniline derived from dicarboximide fungicide by laccase and MnO2 mediators

A ternary catalysis system was investigated to evaluate the comparative degradation of toxic fungicide metabolite 3,5-dichloroaniline (3,5-DCA) by laccase and MnO₂ with mediators. In this study, copper based fungal enzyme laccase (Trametes versicolor origin) and metal catalyst MnO₂ with various combinations of phenolic mediators (catechol, syringaldehyde, syringic acid, caffeic acid and gallic acid) were monitored to optimize and screen the better one for 3,5-DCA degradation assay. Catechol showed better potentiality in reduction of 3,5-DCA among the studied mediators. Catechol (2mM) showed the highest reduction rate (99-100%) followed by syringaldehyde (40.51%) with 2U/mL of laccase at 25 °C within 24 h reaction time. Similarly, complete degradation of 3,5-DCA was obtained by catechol (2mM) with 2 mg/mL of MnO₂ in MnO₂-mediator assay. The notable finding of current study indicated the triggering of catechol for better 3,5-DCA degradation at higher pH condition but inertness in laccase-mediator assay due to laccase destabilization. The reaction pathways of optimized mediator-based catalysis for laccase and MnO₂ were proposed. Finally, the optimized laccase-catechol based degradation was considered as a pioneer green catalysis approach to reduce the toxic metabolite 3,5-DCA concentrations in aqueous medium as compared to MnO₂-catechol catalysis.

Recovery of laccase-producing gammaproteobacteria from wastewater

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Selective enrichment was used to isolate active biodegradative bacteria.

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The role of chemotaxis in xenobiotic metabolism was elucidated.

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Wastewater mesocosms were identified as a repository for biodegradative bacteria.

Wastewater environment is a rich source of microorganisms with the capability for the degradation of malicious aromatic pollutants. Although wastewater could be regarded as both a resource and a problem, we intended to elucidate its beneficial aspect in this study sourcing for laccase-producing proteobacteria. Different wastewater samples, from selected wastewater treatment plants (WWTPs), were selectively enriched with some model compounds (vanillin, lignin and potassium hydrogen phthalate) to screen out bacterial isolates that possess excellent degradation potentials. Thereafter, positive isolates were screened for the production of laccase and degradation on phenolic (guaiacol, α-naphthol and syringaldazine) and non-phenolic (ABTS; 2,2 azino-bis -(3-ethylbenzothiazoline 6 sulphonic acid) and PFC; potassium ferrocyanoferrate) substrates characteristic of laccase oxidation. Remarkable laccase producers were identified based on their 16 S rRNA sequences and their secreted enzymes were subjected to substrate specificity test, employing laccase substrates; ABTS, PFC, guaiacol, α-naphthol, 2,6-dimethoxyphenol and pyrogallol. Results showed that wastewater and selective enrichment, in tandem, produced the gammaproteobacteria Pseudomonas aeruginosa DEJ16, Pseudomonas mendocina AEN16 and Stenotrophomonas maltophila BIJ16, which preferably oxidized the non-phenolic substrates. Units of extracellular laccase activity ranging between cca. 490 and cca. 600 U/mL were recorded for ABTS whereas outputs recorded from PFC catalysis ranged from cca. 320 to cca. 430 U/mL. Stenotrophomonas maltophila BIJ16 presented an unparalleled high laccase activity and had a responsive substrate specificity to aromatic and inorganic substrates, thereby suggesting its employment for in situ biodegradation studies. In conclusion, wastewater serves as an ideal milieu for the isolation of laccase producing bacteria.

Stable ABTS Immobilized in the MIL-100(Fe) Metal-Organic Framework as an Efficient Mediator for Laccase-Catalyzed Decolorization

The successful encapsulation of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), a well-known laccase mediator, within a mesoporous metal-organic framework sample (i.e., MIL-100(Fe)) was achieved using a one-pot hydrothermal synthetic method. The as-prepared ABTS@MIL-100(Fe) was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, nitrogen sorption, and cyclic voltammetry (CV). Our ABTS@MIL-100(Fe)-based electrode exhibited an excellent electrochemical response, indicating that MIL-100(Fe) provides an appropriate microenvironment for the immobilization and electroactivity of ABTS molecules. ABTS@MIL-100(Fe) was then evaluated as an immobilized laccase mediator for dye removal using indigo carmine (IC) as a model dye. Through the application of laccase in combination with a free (ABTS) or immobilized (ABTS@MIL-100(Fe)) mediator, decolorization yields of 95% and 94%, respectively, were obtained for IC after 50 min. In addition, following seven reuse cycles of ABTS@MIL-100(Fe) for dye treatment, a decolorization yield of 74% was obtained. Dye decolorization occurred through the breakdown of the chromophoric group by the Laccase/ABTS@MIL-100(Fe) system, and a catalytic mechanism was proposed. We therefore expect that the stability, reusability, and validity of ABTS@MIL-100(Fe) as a laccase mediator potentially render it a promising tool for dye removal, in addition to reducing the high running costs and potential toxicity associated with synthetic mediators.

Investigating the discrimination potential of linear and nonlinear spectral multivariate calibrations for analysis of phenolic compounds in their binary and ternary mixtures and calculation pKa values

Vanillin (VA), vanillic acid (VAI) and syringaldehyde (SIA) are important food additives as flavor enhancers. The current study for the first time is devote to the application of partial least square (PLS-1), partial robust M-regression (PRM) and feed forward neural networks (FFNNs) as linear and nonlinear chemometric methods for the simultaneous detection of binary and ternary mixtures of VA, VAI and SIA using data extracted directly from UV-spectra with overlapped peaks of individual analytes. Under the optimum experimental conditions, for each compound a linear calibration was obtained in the concentration range of 0.61-20.99 [LOD=0.12], 0.67-23.19 [LOD=0.13] and 0.73-25.12 [LOD=0.15] μgmL(-1) for VA, VAI and SIA, respectively. Four calibration sets of standard samples were designed by combination of a full and fractional factorial designs with the use of the seven and three levels for each factor for binary and ternary mixtures, respectively. The results of this study reveal that both the methods of PLS-1 and PRM are similar in terms of predict ability each binary mixtures. The resolution of ternary mixture has been accomplished by FFNNs. Multivariate curve resolution-alternating least squares (MCR-ALS) was applied for the description of spectra from the acid-base titration systems each individual compound, i.e. the resolution of the complex overlapping spectra as well as to interpret the extracted spectral and concentration profiles of any pure chemical species identified. Evolving factor analysis (EFA) and singular value decomposition (SVD) were used to distinguish the number of chemical species. Subsequently, their corresponding dissociation constants were derived. Finally, FFNNs has been used to detection active compounds in real and spiked water samples.

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.

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

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

Electron beam-induced immobilization of laccase on porous supports for waste water treatment applications

The versatile oxidase enzyme laccase was immobilized on porous supports such as polymer membranes and cryogels with a view of using such biocatalysts in bioreactors aiming at the degradation of environmental pollutants in wastewater. Besides a large surface area for supporting the biocatalyst, the aforementioned porous systems also offer the possibility for simultaneous filtration applications in wastewater treatment. Herein a "green" water-based, initiator-free, and straightforward route to highly reactive membrane and cryogel-based bioreactors is presented, where laccase was immobilized onto the porous polymer supports using a water-based electron beam-initiated grafting reaction. In a second approach, the laccase redox mediators 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and syringaldehyde were cross-linked instead of the enzyme via electron irradiation in a frozen aqueous poly(acrylate) mixture in a one pot set-up, yielding a mechanical stable macroporous cryogel with interconnected pores ranging from 10 to 50 µm in size. The membranes as well as the cryogels were characterized regarding their morphology, chemical composition, and catalytic activity. The reactivity towards waste- water pollutants was demonstrated by the degradation of the model compound bisphenol A (BPA). Both membrane- and cryogel-immobilized laccase remained highly active after electron beam irradiation. Apparent specific BPA removal rates were higher for cryogel- than for membrane-immobilized and free laccase, whereas membrane-immobilized laccase was more stable with respect to maintenance of enzymatic activity and prevention of enzyme leakage from the carrier than cryogel-immobilized laccase. Cryogel-immobilized redox mediators remained functional in accelerating the laccase-catalyzed BPA degradation, and especially ABTS was found to act more efficiently in immobilized than in freely dissolved state.

Laccase versus laccase-like multi-copper oxidase: a comparative study of similar enzymes with diverse substrate spectra

Laccases (EC 1.10.3.2) are multi-copper oxidases that catalyse the one-electron oxidation of a broad range of compounds including substituted phenols, arylamines and aromatic thiols to the corresponding radicals. Owing to their broad substrate range, copper-containing laccases are versatile biocatalysts, capable of oxidizing numerous natural and non-natural industry-relevant compounds, with water as the sole by-product. In the present study, 10 of the 11 multi-copper oxidases, hitherto considered to be laccases, from fungi, plant and bacterial origin were compared. A substrate screen of 91 natural and non-natural compounds was recorded and revealed a fairly broad but distinctive substrate spectrum amongst the enzymes. Even though the enzymes share conserved active site residues we found that the substrate ranges of the individual enzymes varied considerably. The EC classification is based on the type of chemical reaction performed and the actual name of the enzyme often refers to the physiological substrate. However, for the enzymes studied in this work such classification is not feasible, even more so as their prime substrates or natural functions are mainly unknown. The classification of multi-copper oxidases assigned as laccases remains a challenge. For the sake of simplicity we propose to introduce the term "laccase-like multi-copper oxidase" (LMCO) in addition to the term laccase that we use exclusively for the enzyme originally identified from the sap of the lacquer tree Rhus vernicifera.