Characterisation of coupling products formed by biotransformation of biphenyl and diphenyl ether by the white rot fungus Pycnoporus cinnabarinus

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.

Laccase-Catalyzed Derivatization of Antibiotics with Sulfonamide or Sulfone Structures

Trametes spec. laccase (EC 1.10.3.2.) mediates the oxidative coupling of antibiotics with sulfonamide or sulfone structures with 2,5-dihydroxybenzene derivatives to form new heterodimers and heterotrimers. These heteromolecular hybrid products are formed by nuclear amination of the p-hydroquinones with the primary amino group of the sulfonamide or sulfone antibiotics, and they inhibited in vitro the growth of Staphylococcus species, including multidrug-resistant strains.

Ring-Closure Mechanisms Mediated by Laccase to Synthesize Phenothiazines, Phenoxazines, and Phenazines

The green and environmentally friendly synthesis of highly valuable organic substances is one possibility for the utilization of laccases (EC 1.10.3.2). As reactants for the herein described syntheses, different o-substituted arylamines or arylthiols and 2,5-dihydroxybenzoic acid and its derivatives were used. In this way, the formation of phenothiazines, phenoxazines, and phenazines was achieved in aqueous solution mediated by the laccase of Pycnoporus cinnabarinus in the presence of oxygen. Two types of phenothiazines (3-hydroxy- and 3-oxo-phenothiazines) formed in one reaction assay were described for the first time. The cyclization reactions yielded C-N, C-S, or C-O bonds. The syntheses were investigated with regard to the substitution pattern of the reaction partners. Differences in C-S and C-N bond formations without cyclization are discussed.

Synthetic Gene Network with Positive Feedback Loop Amplifies Cellulase Gene Expression in Neurospora crassa

Second-generation or lignocellulosic biofuels are a tangible source of renewable energy, which is critical to combat climate change by reducing the carbon footprint. Filamentous fungi secrete cellulose-degrading enzymes called cellulases, which are used for production of lignocellulosic biofuels. However, inefficient production of cellulases is a major obstacle for industrial-scale production of second-generation biofuels. We used computational simulations to design and implement synthetic positive feedback loops to increase gene expression of a key transcription factor, CLR-2, that activates a large number of cellulases in a filamentous fungus, Neurospora crassa. Overexpression of CLR-2 reveals previously unappreciated roles of CLR-2 in lignocellulosic gene network, which enabled simultaneous induction of approximately 50% of 78 lignocellulosic degradation-related genes in our engineered Neurospora strains. This engineering results in dramatically increased cellulase activity due to cooperative orchestration of multiple enzymes involved in the cellulose degradation pathway. Our work provides a proof of principle in utilizing mathematical modeling and synthetic biology to improve the efficiency of cellulase synthesis for second-generation biofuel production.

Novel, biocatalytically produced hydroxytyrosol dimer protects against ultraviolet-induced cell death in human immortalized keratinocytes

Compounds derived from botanicals, such as olive trees, have been shown to possess various qualities that make them function as ideal antioxidants and, in doing so, protect them against the damaging effect of ultraviolet (UV)-derived oxidative stress. The aim of this study was to biocatalytically synthesize a dimeric product (compound II) from a known botanical, 3-hydroxytyrosol, and test it for its antioxidant ability using a human immortalized keratinocyte cell line (HaCaT). 2,2-Diphenyl-picryhydrazyl (DPPH) antioxidant assays showed 33 and 86.7% radical scavenging activity for 3-hydroxytyrosol and its dimer, respectively. The ferric-reducing antioxidant power (FRAP) assay corroborated this by showing a 3-fold higher antioxidant activity for the dimer than 3-hydroxytyrosol. Western blot analyses, showing cells exposed to 500 μM of the dimeric product when ultraviolet A (UVA)-irradiated, increased the anti-apoptotic protein Bcl-2 expression by 16% and reduced the pro-apoptotic protein Bax by 87.5%. Collectively, the data show that the dimeric product of 3-hydroxytyrosol is a more effective antioxidant and could be considered for use in skin-care products, health, and nutraceuticals.

Enhanced transformation of triclosan by laccase in the presence of redox mediators

Triclosan (TCS), an antimicrobial agent, is an emerging and persistent environmental pollutant that is often found as a contaminant in surface waters and sediments; hence, knowledge of its degradability is important. In this study we investigated laccase-mediated TCS transformation and detoxification, using laccase (from the fungus Ganoderma lucidum) in the presence and absence of redox mediators. Transformation products were identified using HPLC, ESI-MS and GC-MS, and transformation mechanisms were proposed. In the absence of redox mediator, 56.5% TCS removal was observed within 24h, concomitant with formation of new products with molecular weights greater than that of TCS. These products were dimers and trimers of TCS, as confirmed by ESI-MS analysis. Among the various mediators tested, 1-hydroxybenzotriazole (HBT) and syringaldehyde (SYD) significantly enhanced TCS transformation ( approximately 90%). The presence of these mediators resulted in products with lower molecular weights than TCS, including 2,4-dichlorophenol (2,4-DCP; confirmed by GC-MS) and dechlorinated forms of 2,4-DCP. When SYD was used as the mediator, dechlorination resulted in 2-chlorohydroquinone (2-CHQ). Bacterial growth inhibition studies revealed that laccase-mediated transformation of TCS effectively decreased its toxicity, with ultimate conversion to less toxic or nontoxic products. Our results confirmed the involvement of two mechanisms of laccase-catalyzed TCS removal: (i) oligomerization in the absence of redox mediators, and (ii) ether bond cleavage followed by dechlorination in the presence of redox mediators. These results suggest that laccase in combination with natural redox mediator systems may be a useful strategy for the detoxification and elimination of TCS from aqueous systems.

A carbon–carbon-coupled dimeric bergenin derivative biotransformed by Pleurotus ostreatus

A novel C-C-coupled dimer derivative of bergenin was produced by the biotransformation of cultured mycelia of white rot fungus Pleurotus ostreatus. Its structure was elucidated by detailed spectroscopic analysis.

Dehalogenation of chlorinated hydroxybiphenyls by fungal laccase

We have investigated the transformation of chlorinated hydroxybiphenyls by laccase produced by Pycnoporus cinnabarinus. The compounds used were transformed to sparingly water-soluble colored precipitates which were identified by gas chromatography-mass spectrometry as oligomerization products of the chlorinated hydroxybiphenyls. During oligomerization of 2-hydroxy-5-chlorobiphenyl and 3-chloro-4-hydroxybiphenyl, dechlorinated C---C-linked dimers were formed, demonstrating the dehalogenation ability of laccase. In addition to these nonhalogenated dimers, both monohalogenated and dihalogenated dimers were identified.