Structure and Bioactive Properties of Novel Textile Dyes Synthesised by Fungal Laccase

Two Zn2Cys6-type transcription factors respond to aromatic compounds and regulate the expression of laccases in the white-rot fungus Trametes hirsuta

White-rot fungi differentially express laccases when they encounter aromatic compounds. However, the underlying mechanisms are still being explored. Here, proteomics analysis revealed that in addition to increased laccase activity, proteins involved in sphingolipid metabolism and toluene degradation as well as some cytochrome P450s (CYP450s) were differentially expressed and significantly enriched during 48 h of o-toluidine exposure, in Trametes hirsuta AH28-2. Two Zn2Cys6-type transcription factors (TFs), TH8421 and TH4300, were upregulated. Bioinformatics docking and isothermal titration calorimetry assays showed that each of them could bind directly to o-toluidine and another aromatic monomer, guaiacol. Binding to aromatic compounds promoted the formation of TH8421/TH4300 heterodimers. TH8421 and TH4300 silencing in T. hirsuta AH28-2 led to decreased transcriptional levels and activities of LacA and LacB upon o-toluidine and guaiacol exposure. EMSA and ChIP-qPCR analysis further showed that TH8421 and TH4300 bound directly with the promoter regions of lacA and lacB containing CGG or CCG motifs. Furthermore, the two TFs were involved in direct and positive regulation of the transcription of some CYP450s. Together, TH8421 and TH4300, two key regulators found in T. hirsuta AH28-2, function as heterodimers to simultaneously trigger the expression of downstream laccases and intracellular enzymes. Monomeric aromatic compounds act as ligands to promote heterodimer formation and enhance the transcriptional activities of the two TFs.IMPORTANCEWhite-rot fungi differentially express laccase isoenzymes when exposed to aromatic compounds. Clarification of the molecular mechanisms underlying differential laccase expression is essential to elucidate how white-rot fungi respond to the environment. Our study shows that two Zn2Cys6-type transcription factors form heterodimers, interact with the promoters of laccase genes, and positively regulate laccase transcription in Trametes hirsuta AH28-2. Aromatic monomer addition induces faster heterodimer formation and rate of activity. These findings not only identify two new transcription factors involved in fungal laccase transcription but also deepen our understanding of the mechanisms underlying the response to aromatics exposure in white-rot fungi.

Special Issue on Biotechnological Applications of Oxidoreductases

This Special Issue was launched in conjunction with the 10th edition of the OxiZymes meeting in Siena (Italy) in 2022 [...].

Potential of the enzyme laccase for the synthesis and derivatization of antimicrobial compounds

Laccases [E.C. 1.10.3.2, benzenediol:dioxygen oxidoreductase] can oxidize phenolic substances, e.g. di- and polyphenols, hydroxylated biaryls, aminophenols or aryldiamines. This large substrate spectrum is the basis for various reaction possibilities, which include depolymerization and polymerization reactions, but also the coupling of different substance classes. To catalyze these reactions, laccases demand only atmospheric oxygen and no depletive cofactors. The utilization of mild and environmentally friendly reaction conditions such as room temperature, atmospheric pressure, and the avoidance of organic solvents makes the laccase-mediated reaction a valuable tool in green chemistry for the synthesis of biologically active compounds such as antimicrobial substances. In particular, the production of novel antibiotics becomes vital due to the evolution of antibiotic resistances amongst bacteria and fungi. Therefore, laccase-mediated homo- and heteromolecular coupling reactions result in derivatized or newly synthesized antibiotics. The coupling or derivatization of biologically active compounds or its basic structures may allow the development of novel pharmaceuticals, as well as the improvement of efficacy or tolerability of an already applied drug. Furthermore, by the laccase-mediated coupling of two different active substances a synergistic effect may be possible. However, the coupling of compounds that have no described efficacy can lead to biologically active substances by means of laccase. The review summarizes laccase-mediated reactions for the synthesis of antimicrobial compounds valuable for medical purposes. In particular, reactions with two different reaction partners were shown in detail. In addition, studies with in vitro and in vivo experimental data for the confirmation of the antibacterial and/or antifungal efficacy of the products, synthesized with laccase, were of special interest. Analyses of the structure-activity relationship confirm the great potential of the novel compounds. These substances may represent not only a value for pharmaceutical and chemical industry, but also for other industries due to a possible functionalization of surfaces such as wood or textiles.

Bioactive Properties of a Novel Antibacterial Dye Obtained from Laccase-Mediated Oxidation of 8-Anilino-1-naphthalenesulfonic Acid

Fungal laccase obtained from a Cerrena unicolor strain was used as an effective biocatalyst for the transformation of 8-anilino-1-naphthalenesulfonic acid into a green-coloured antibacterial compound, which can be considered as both an antimicrobial agent and a textile dye, simultaneously. The process of biosynthesis was performed in buffered solutions containing methanol as a co-solvent, allowing better solubilisation of substrate. The transformation process was optimised in terms of the buffer pH value, laccase activity, and concentrations of the substrate and co-solvent. The crude product obtained exhibited low cytotoxicity, antibacterial properties against Staphylococcus aureus and Staphylococcus epidermidis, and antioxidant properties. Moreover, the synthesised green-coloured compound proved non-allergenic and demonstrated a high efficiency of dyeing wool fibres.

Antioxidant, Antibacterial and Dyeing Potential of Crude Pigment Extract of Gonatophragmium triuniae and Its Chemical Characterization

Filamentous fungi synthesize natural products as an ecological function. In this study, an interesting indigenous fungus producing orange pigment exogenously was investigated in detail as it possesses additional attributes along with colouring properties. An interesting fungus was isolated from a dicot plant, Maytenus rothiana. After a detailed study, the fungal isolate turned out to be a species of Gonatophragmium belonging to the family Acrospermaceae. Based on the morphological, cultural, and sequence-based phylogenetic analysis, the identity of this fungus was confirmed as Gonatophragmium triuniae. Although this fungus grows moderately, it produces good amounts of pigment on an agar medium. The fermented crude extract isolated from G. triuniae has shown antioxidant activity with an IC50 value of 0.99 mg/mL and antibacterial activity against Gram-positive bacteria (with MIC of 3.91 μg/mL against Bacillus subtilis, and 15.6 μg/mL and 31.25 μg/mL for Staphylococcus aureus and Micrococcus luteus, respectively). Dyeing of cotton fabric mordanted with FeSO4 using crude pigment was found to be satisfactory based on visual observation, suggesting its possible use in the textile industry. The orange pigment was purified from the crude extract by preparative HP-TLC. In addition, UV-Vis, FTIR, HRMS and NMR (1H NMR, 13C NMR), COSY, and DEPT analyses revealed the orange pigment to be "1,2-dimethoxy-3H-phenoxazin-3-one" (C14H11NO4, m/z 257). To our understanding, the present study is the first comprehensive report on Gonatophragmium triuniae as a potential pigment producer, reporting "1,2-dimethoxy-3H-phenoxazin-3-one" as the main pigment from the crude hexane extract. Moreover, this is the first study reporting antioxidant, antibacterial, and dyeing potential of crude extract of G. triuniae, suggesting possible potential applications of pigments and other bioactive secondary metabolites of the G. triuniae in textile and pharmaceutical industry.

Hyaluronic Acid Allows Enzyme Immobilization for Applications in Biomedicine

Enzymes are proteins that control the efficiency and effectiveness of biological reactions and systems, as well as of engineered biomimetic processes. This review highlights current applications of a diverse range of enzymes for biofuel production, plastics, and chemical waste management, as well as for detergent, textile, and food production and preservation industries respectively. Challenges regarding the transposition of enzymes from their natural purpose and environment into synthetic practice are discussed. For example, temperature and pH-induced enzyme fragilities, short shelf life, low-cost efficiency, poor user-controllability, and subsequently insufficient catalytic activity were shown to decrease pertinence and profitability in large-scale production considerations. Enzyme immobilization was shown to improve and expand upon enzyme usage within a profit and impact-oriented commercial world and through enzyme-material and interfaces integration. With particular focus on the growing biomedical market, examples of enzyme immobilization within or onto hyaluronic acid (HA)-based complexes are discussed as a definable way to improve upon and/or make possible the next generation of medical undertakings. As a polysaccharide formed in every living organism, HA has proven beneficial in biomedicine for its high biocompatibility and controllable biodegradability, viscoelasticity, and hydrophilicity. Complexes developed with this molecule have been utilized to selectively deliver drugs to a desired location and at a desired rate, improve the efficiency of tissue regeneration, and serve as a viable platform for biologically accepted sensors. In similar realms of enzyme immobilization, HA’s ease in crosslinking allows the molecule to user-controllably enhance the design of a given platform in terms of both chemical and physical characteristics to thus best support successful and sustained enzyme usage. Such examples do not only demonstrate the potential of enzyme-based applications but further, emphasize future market trends and accountability.

Laccases: Versatile Biocatalysts for the Synthesis of Heterocyclic Cores

Laccases are multicopper oxidases that have shown a great potential in various biotechnological and green chemistry processes mainly due to their high relative non-specific oxidation of phenols, arylamines and some inorganic metals, and their high redox potentials that can span from 500 to 800 mV vs. SHE. Other advantages of laccases include the use of readily available oxygen as a second substrate, the formation of water as a side-product and no requirement for cofactors. Importantly, addition of low-molecular-weight redox mediators that act as electron shuttles, promoting the oxidation of complex bulky substrates and/or of higher redox potential than the enzymes themselves, can further expand their substrate scope, in the so-called laccase-mediated systems (LMS). Laccase bioprocesses can be designed for efficiency at both acidic and basic conditions since it is known that fungal and bacterial laccases exhibit distinct optimal pH values for the similar phenolic and aromatic amines. This review covers studies on the synthesis of five- and six-membered ring heterocyclic cores, such as benzimidazoles, benzofurans, benzothiazoles, quinazoline and quinazolinone, phenazine, phenoxazine, phenoxazinone and phenothiazine derivatives. The enzymes used and the reaction protocols are briefly outlined, and the mechanistic pathways described.

Laccase-Catalyzed 1,4-Dioxane-Mediated Synthesis of Belladine N-Oxides with Anti-Influenza A Virus Activity

Belladine N-oxides active against influenza A virus have been synthetized by a novel laccase-catalyzed 1,4-dioxane-mediated oxidation of aromatic and side-chain modified belladine derivatives. Electron paramagnetic resonance (EPR) analysis confirmed the role of 1,4-dioxane as a co-oxidant. The reaction was chemo-selective, showing a high functional-group compatibility. The novel belladine N-oxides were active against influenza A virus, involving the early stage of the virus replication life cycle.