Cloning, characterization and expression of two new polyphenol oxidase cDNAs from Agaricus bisporus

Isolation, Characterization, Genome Annotation, and Evaluation of Tyrosinase Inhibitory Activity in Secondary Metabolites of Paenibacillus sp. JNUCC32: A Comprehensive Analysis through Molecular Docking and Molecular Dynamics Simulation

A potential strain, Paenibacillus sp. JNUCC32, was isolated and subjected to whole-genome sequencing. Genome functional annotation revealed its active metabolic capabilities. This study aimed to investigate the pivotal secondary metabolites in the biological system. Fermentation and extraction were performed, resulting in the isolation of seven known compounds: tryptophol (1), 3-(4-hydroxyphenyl)propionic acid (2), ferulic acid (3), maculosin (4), brevianamide F (5), indole-3-acetic acid (6), and butyric acid (7). Tryptophol exhibited favorable pharmacokinetic properties and demonstrated certain tyrosinase inhibitory activity (IC50 = 999 μM). For further analysis of its inhibition mechanism through molecular docking and molecular dynamics (MD) simulation, tryptophol formed three hydrogen bonds and a pro-Michaelis complex with tyrosinase (binding energy = -5.3 kcal/mol). The MD simulation indicated favorable stability for the tryptophol-mushroom tyrosinase complex, primarily governed by hydrogen bond interactions. The crucial residues VAL-283 and HIS-263 in the docking were also validated. This study suggests tryptophol as a potential candidate for antibrowning agents and dermatological research.

Tyrosinase Inhibitory Peptides from Enzyme Hydrolyzed Royal Jelly: Production, Separation, Identification and Docking Analysis

Tyrosinase is inextricably related to the development of Alzheimer's disease. The effects of natural tyrosinase inhibitors on human health have attracted widespread attention. This study aimed to isolate and analyze the tyrosinase (TYR) inhibitory peptides in the enzymatic digestion products of royal jelly. We first analyzed optimal process conditions for the enzymatic digestion of royal jelly by single-factor and orthogonal experiments and then used gel filtration chromatography to obtain five fractions (D1~D5) with molecular weights ranging from 600 to 1100 Da. LC-MS/MS was applied to identify the fractions with the highest activity, and the obtained peptides were screened and molecularly docked using AutoDock Vina. The results showed that the optimal enzymatic conditions for tyrosinase inhibition rate were acid protease, enzyme addition 10,000 U/g, initial pH 4, feed-to-liquid ratio 1:4, enzymatic temperature 55 °C, and enzymatic time 4 h. The D4 fraction had the most significant TYR inhibitory activity. The IC₅₀ values of the three new peptides with the strongest TYR inhibitory activity, TIPPPT, IIPFIF, and ILFTLL, were obtained as 7.59 mg/mL, 6.16 mg/mL, and 9.25 mg/mL, respectively. The molecular docking results showed that aromatic and hydrophobic amino acids were more favorable to occupy the catalytic center of TYR. In conclusion, the new peptide extracted from royal jelly has the potential to be used as a natural TYR inhibitory peptide in food products with health-promoting properties.

Application progress of CRISPR/Cas9 genome-editing technology in edible fungi

Edible fungi are not only delicious but are also rich in nutritional and medicinal value, which is highly sought after by consumers. As the edible fungi industry continues to rapidly advance worldwide, particularly in China, the cultivation of superior and innovative edible fungi strains has become increasingly pivotal. Nevertheless, conventional breeding techniques for edible fungi can be arduous and time-consuming. CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated nuclease 9) is a powerful tool for molecular breeding due to its ability to mediate high-efficiency and high-precision genome modification, which has been successfully applied to many kinds of edible fungi. In this review, we briefly summarized the working mechanism of the CRISPR/Cas9 system and highlighted the application progress of CRISPR/Cas9-mediated genome-editing technology in edible fungi, including Agaricus bisporus, Ganoderma lucidum, Flammulina filiformis, Ustilago maydis, Pleurotus eryngii, Pleurotus ostreatus, Coprinopsis cinerea, Schizophyllum commune, Cordyceps militaris, and Shiraia bambusicola. Additionally, we discussed the limitations and challenges encountered using CRISPR/Cas9 technology in edible fungi and provided potential solutions. Finally, the applications of CRISPR/Cas9 system for molecular breeding of edible fungi in the future are explored.

A Novel Tyrosinase from Armillaria ostoyae with Comparable Monophenolase and Diphenolase Activities Suffers Substrate Inhibition

Tyrosinase is a bifunctional enzyme mediating the o-hydroxylation and two-electron oxidation of monophenols to o-quinones. The monophenolase activity of tyrosinase is much desired for the industrial synthesis of catechols. However, the generally low ratio of monophenolase/diphenolase activity of tyrosinase limited its utilization in the industry. In this study, a novel tyrosinase from Armillaria ostoyae strain C18/9 (AoTyr) was characterized, and the results showed that the enzyme has an optimal temperature of 25°C and an optimal pH of 6. The enzyme has comparable monophenolase and diphenolase activities and exhibits substrate inhibition in both of the activities. In silico analysis and mutagenesis experiments showed that residues 262 and 266 play important roles in modulating the substrate inhibition and enzymatic activities of AoTyr, and the replacement of D262 with asparagine significantly increased the monophenolase/diphenolase catalytic efficiencies (k_cat/K_m ratios) (1.63-fold) of the enzyme. The results from this study indicated that this novel tyrosinase could be a potential candidate for the industrial biosynthesis of catechols. IMPORTANCE Tyrosinase is able to oxidize various phenolic compounds, and its ability to convert monophenols into diphenols has caught great attention in the research field and industrial applications. However, the utilization of tyrosinase for the industrial synthesis of catechols has been limited due to the fact that the monophenolase activity of most of the known tyrosinases is much lower than the diphenolase activity. In the present study, a novel tyrosinase with comparable monophenolase and diphenolase activities was characterized. The enzyme exhibits substrate inhibition in both monophenolase and diphenolase activities. In silico analysis followed by mutagenesis experiments confirmed the important roles of residues 262 and 266 in the substrate inhibition and activity modulation of the enzyme, and the D262N variant showed an enhanced monophenolase/diphenolase catalytic efficiency ratio compared to the wild-type enzyme.

Agaricus bisporus Crude Extract: Characterization and Analytical Application

In the present work crude Agaricus bisporus extract (ABE) has been prepared and characterized by its tyrosinase activity, protein composition and substrate specificity. The presence of mushroom tyrosinase (PPO3) in ABE has been confirmed using two-dimensional electrophoresis, followed by MALDI TOF/TOF MS-based analysis. GH27 alpha-glucosidases, GH47 alpha-mannosidases, GH20 hexosaminidases, and alkaline phosphatases have been also detected in ABE. ABE substrate specificity has been studied using 19 phenolic compounds: polyphenols (catechol, gallic, caffeic, chlorogenic, and ferulic acids, quercetin, rutin, dihydroquercetin, l-dihydroxyphenylalanine, resorcinol, propyl gallate) and monophenols (l-tyrosine, phenol, p-nitrophenol, o-nitrophenol, guaiacol, o-cresol, m-cresol, p-cresol). The comparison of ABE substrate specificity and affinity to the corresponding parameters of purified A. bisporus tyrosinase has revealed no major differences. The conditions for spectrophotometric determination have been chosen and the analytical procedures for determination of 1.4 × 10^-4-1.0 × 10^-3 M l-tyrosine, 3.1 × 10^-6-1.0 × 10^-4 M phenol, 5.4 × 10^-5-1.0 × 10^-3 M catechol, 8.5 × 10^-5-1.0 × 10^-3 M caffeic acid, 1.5 × 10^-4-7.5 × 10^-4 M chlorogenic acid, 6.8 × 10^-5-1.0 × 10^-3 M l-DOPA have been proposed. The procedures have been applied for the determination of l-tyrosine in food supplements, l-DOPA in synthetic serum, and phenol in waste water from the food manufacturing plant. Thus, we have demonstrated the possibility of using ABE as a substitute for tyrosinase in such analytical applications, as food supplements, medical and environmental analysis.

Recombinant polyphenol oxidases for production of theaflavins from tea polyphenols

Theaflavins (TFs) have attracted much attention due to their various bioactivities in black tea. This paper describes the first trial for enzymatic production of TFs by recombinant polyphenol oxidases (PPOs). PPO genes were cloned from nine species and expressed in E. coli. Crude enzyme assays by LC-MS revealed that eight recombinant PPOs were active for TFs production from tea polyphenols as substrates. Much higher activities were observed for crude enzymes of Md2 from Malus domestica (apple), Pp4 from Pyrus pashia (pear), and Ej2 from Eriobotrya japonica (loquat). When immobilized on mesoporous silica, crude Md2 was most active. The purified Md2 was immobilized and showed almost twice activity as high as its free enzyme. While the maximum activity of free enzyme was found at pH 5 and 10-30 °C, the immobilized enzyme had broader range of pH 4-6 and 10-40 °C. The activity of immobilized enzyme was relatively constant during the pH and thermal stability test. When used at 0.2 mg/ml in the beginning, the immobilized enzyme retained approximately 40% of its initial activity after 8 cycles of operation.

Versatile Fungal Polyphenol Oxidase with Chlorophenol Bioremediation Potential: Characterization and Protein Engineering

Polyphenol oxidases (PPOs) have been mostly associated with the undesirable postharvest browning in fruits and vegetables and have implications in human melanogenesis. Nonetheless, they are considered useful biocatalysts in the food, pharmaceutical, and cosmetic industries. The aim of the present work was to characterize a novel PPO and explore its potential as a bioremediation agent. A gene encoding an extracellular tyrosinase-like enzyme was amplified from the genome of Thermothelomyces thermophila and expressed in Pichia pastoris The recombinant enzyme (TtPPO) was purified and biochemically characterized. Its production reached 40 mg/liter, and it appeared to be a glycosylated and N-terminally processed protein. TtPPO showed broad substrate specificity, as it could oxidize 28/30 compounds tested, including polyphenols, substituted phenols, catechols, and methoxyphenols. Its optimum temperature was 65°C, with a half-life of 18.3 h at 50°C, while its optimum pH was 7.5. The homology model of TtPPO was constructed, and site-directed mutagenesis was performed in order to increase its activity on mono- and dichlorophenols (di-CPs). The G292N/Y296V variant of TtPPO 5.3-fold increased activity on 3,5-dichlorophenol (3,5-diCP) compared to the wild type.IMPORTANCE A novel fungal PPO was heterologously expressed and biochemically characterized. Construction of single and double mutants led to the generation of variants with altered specificity against CPs. Through this work, knowledge is gained regarding the effect of mutations on the substrate specificity of PPOs. This work also demonstrates that more potent biocatalysts for the bioremediation of harmful CPs can be developed by applying site-directed mutagenesis.

Heterologous expression and characterization of functional mushroom tyrosinase (AbPPO4)

Tyrosinases are an ubiquitous group of copper containing metalloenzymes that hydroxylate and oxidize phenolic molecules. In an application context the term 'tyrosinase' usually refers to 'mushroom tyrosinase' consisting of a mixture of isoenzymes and containing a number of enzymatic side-activities. We describe a protocol for the efficient heterologous production of tyrosinase 4 from Agaricus bisporus in Escherichia coli. Applying this procedure a pure preparation of a single isoform of latent tyrosinase can be achieved at a yield of 140 mg per liter of autoinducing culture medium. This recombinant protein possesses the same fold as the enzyme purified from the natural source as evidenced by single crystal X-ray diffraction. The latent enzyme can be activated by limited proteolysis with proteinase K which cleaves the polypeptide chain after K382, only one The latent enzyme can amino acid before the main in-vivo activation site. Latent tyrosinase can be used as obtained and enzymatic activity may be induced in the reaction mixture by the addition of an ionic detergent (e.g. 2 mM SDS). The proteolytically activated mushroom tyrosinase shows >50% of its maximal activity in the range of pH 5 to 10 and accepts a wide range of substrates including mono- and diphenols, flavonols and chalcones.

Pharmacoinformatics exploration of polyphenol oxidases leading to novel inhibitors by virtual screening and molecular dynamic simulation study

Polyphenol oxidases (PPOs)/tyrosinases are metal-dependent enzymes and known as important targets for melanogenesis. Although considerable attempts have been conducted to control the melanin-associated diseases by using various inhibitors. However, the exploration of the best anti-melanin inhibitor without side effect still remains a challenge in drug discovery. In present study, protein structure prediction, ligand-based pharmacophore modeling, virtual screening, molecular docking and dynamic simulation study were used to screen the strong novel inhibitor to cure melanogenesis. The 3D structures of PPO1 and PPO2 were built through homology modeling, while the 3D crystal structures of PPO3 and PPO4 were retrieved from PDB. Pharmacophore modeling was performed using LigandScout 3.1 software and top five models were selected to screen the libraries (2601 of Aurora and 727, 842 of ZINC). Top 10 hit compounds (C1-10) were short-listed having strong binding affinities for PPO1-4. Drug and synthetic accessibility (SA) scores along with absorption, distribution, metabolism, excretion and toxicity (ADMET) assessment were employed to scrutinize the best lead hit. C4 (name) hit showed the best predicted SA score (5.75), ADMET properties and drug-likeness behavior among the short-listed compounds. Furthermore, docking simulations were performed to check the binding affinity of C1-C10 compounds against target proteins (PPOs). The binding affinity values of complex between C4 and PPOs were higher than those of other complexes (-11.70, -12.1, -9.90 and -11.20kcal/mol with PPO1, PPO2, PPO3, or PPO4, respectively). From comparative docking energy and binding analyses, PPO2 may be considered as better target for melanogenesis than others. The potential binding modes of C4, C8 and C10 against PPO2 were explored using molecular dynamics simulations. The root mean square deviation and fluctuation (RMSD/RMSF) graphs results depict the significance of C4 over the other compounds. Overall, bioactivity and ligand efficiency profiles suggested that the proposed hit may be more effective inhibitors for melanogenesis.

Boosting LPMO-driven lignocellulose degradation by polyphenol oxidase-activated lignin building blocks

BACKGROUND

Many fungi boost the deconstruction of lignocellulosic plant biomass via oxidation using lytic polysaccharide monooxygenases (LPMOs). The application of LPMOs is expected to contribute to ecologically friendly conversion of biomass into fuels and chemicals. Moreover, applications of LPMO-modified cellulose-based products may be envisaged within the food or material industry.

RESULTS

Here, we show an up to 75-fold improvement in LPMO-driven cellulose degradation using polyphenol oxidase-activated lignin building blocks. This concerted enzymatic process involves the initial conversion of monophenols into diphenols by the polyphenol oxidase MtPPO7 from Myceliophthora thermophila C1 and the subsequent oxidation of cellulose by MtLPMO9B. Interestingly, MtPPO7 shows preference towards lignin-derived methoxylated monophenols. Sequence analysis of genomes of 336 Ascomycota and 208 Basidiomycota reveals a high correlation between MtPPO7 and AA9 LPMO genes.

CONCLUSIONS

The activity towards methoxylated phenolic compounds distinguishes MtPPO7 from well-known PPOs, such as tyrosinases, and ensures that MtPPO7 is an excellent redox partner of LPMOs. The correlation between MtPPO7 and AA9 LPMO genes is indicative for the importance of the coupled action of different monooxygenases in the concerted degradation of lignocellulosic biomass. These results will contribute to a better understanding in both lignin deconstruction and enzymatic lignocellulose oxidation and potentially improve the exploration of eco-friendly routes for biomass utilization in a circular economy.

Recombinant Tyrosinase from Polyporus arcularius: Overproduction in Escherichia coli, Characterization, and Use in a Study of Aurones as Tyrosinase Effectors

Tyrosinases act in the development of organoleptic properties of tea, raisins, etc., but also cause unwanted browning of fruits, vegetables, and mushrooms. The tyrosinase from Agaricus bisporus has been used as a model to study tyrosinase inhibitors, which are also indispensable in the treatment of skin pigmentation disorders. However, this model has disadvantages such as side enzyme activities and the presence of multiple isoenzymes. Therefore, we aimed to introduce a new tyrosinase model. The pro-tyrosinase from Polyporus arcularius was overproduced in Escherichia coli. Trypsin digestion led to a cleavage after R388 and hence enzyme activation. The tyrosinase was a homodimer and transformed L-DOPA and tert-butylcatechol preferentially. Various aurons were examined as effectors of this enzyme. 2'- and 3'-hydroxyaurones acted as its activators and 2',4'-dihydroxyaurone as an inhibitor, whereas 4'-hydroxyaurones were its substrates. The enzyme is a promising model for tyrosinase effector studies, being a single isoenzyme and void of side enzyme activities.

Inhibitory effects of α-Na8SiW11CoO40 on tyrosinase and its application in controlling browning of fresh-cut apples

α-Na8SiW11CoO40 was synthesized and characterized. The inhibitory effects of α-Na8SiW11CoO40 on the activity of mushroom tyrosinase and the effects of α-Na8SiW11CoO40 on the browning of fresh-cut apples were studied. The Native-PAGE result showed that α-Na8SiW11CoO40 had a significant inhibitory effect on tyrosinase. Kinetic analyses showed that α-Na8SiW11CoO40 was an irreversible and competitive inhibitor. The inhibitor concentration leading to a 50% reduction in activity (IC50) was estimated to be 0.239 mM. Additionally, the results also showed that α-Na8SiW11CoO40 treatment could significantly decrease the browning process of apple slices and inhibit the polyphenol oxidase (PPO) activity. Moreover, application of α-Na8SiW11CoO40 resulted in higher peroxidase activity and promoted high amounts of phenolic compounds and ascorbic acid. This study may provide a promising method for the use of polyoxometalates to inhibit tyrosinase activity and control the browning of fresh-cut apples.

Site-directed mutagenesis around the CuA site of a polyphenol oxidase from Coreopsis grandiflora (cgAUS1)

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Site-directed mutations of AUS1 around the CuA site were generated and verified.

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All mutations led to loss of diphenolase activity with butein as substrate.

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Exchange of histidines in the CuA resulted in enzymes containing only one Cu.

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F273 mutation to alanine did not increase the monophenolase activity.

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C97 mutation eliminated the diphenolase activity, but 2 Cu atoms were incorporated.

Aurone synthase from Coreopsis grandiflora (cgAUS1), catalyzing conversion of butein to sulfuretin in a type-3 copper center, is a rare example of a polyphenol oxidase involved in anabolism. Site-directed mutagenesis around the CuA site of AUS1 was performed, and recombinant enzymes were analyzed by mass spectrometry. Replacement of the coordinating CuA histidines with alanine resulted in the presence of a single copper and loss of diphenolase activity. The thioether bridge-building cysteine and a phenylalanine over the CuA site, exchanged to alanine, have no influence on copper content but appear to play an important role in substrate binding.

Latent and active abPPO4 mushroom tyrosinase cocrystallized with hexatungstotellurate(VI) in a single crystal

Tyrosinases, bifunctional metalloenzymes, catalyze the oxidation of monophenols and o-diphenols to o-quinones, the precursor compounds of the brown-coloured pigment melanin. In eukaryotic organisms, tyrosinases are expressed as latent zymogens that have to be proteolytically cleaved in order to form highly active enzymes. This activation mechanism, known as the tyrosinase maturation process, has scientific and industrial significance with respect to biochemical and technical applications of the enzyme. Here, not only the first crystal structure of the mushroom tyrosinase abPPO4 is presented in its active form (Ser2-Ser383) and in its 21 kDa heavier latent form (Ser2-Thr545), but furthermore the simultaneous presence of both forms within one single-crystal structure is shown. This allows for a simple approach to investigate the transition between these two forms. Isoform abPPO4 was isolated and extensively purified from the natural source (Agaricus bisporus), which contains a total of six polyphenol oxidases (PPOs). The enzyme formed crystals (diffracting to a resolution of 2.76 Å) owing to the employment of the 6-tungstotellurate(VI) salt (Na6[TeW6O24]·22H2O) as a cocrystallization agent. Two of these disc-shaped Anderson-type polyoxoanions [TeW6O24](6-) separate two asymmetric units comprising one crystallographic heterodimer of abPPO4, thus resulting in very interesting crystal packing.

Microbial tyrosinases: promising enzymes for pharmaceutical, food bioprocessing, and environmental industry

Tyrosinase is a natural enzyme and is often purified to only a low degree and it is involved in a variety of functions which mainly catalyse the o-hydroxylation of monophenols into their corresponding o-diphenols and the oxidation of o-diphenols to o-quinones using molecular oxygen, which then polymerizes to form brown or black pigments. The synthesis of o-diphenols is a potentially valuable catalytic ability and thus tyrosinase has attracted a lot of attention with respect to industrial applications. In environmental technology it is used for the detoxification of phenol-containing wastewaters and contaminated soils, as biosensors for phenol monitoring, and for the production of L-DOPA in pharmaceutical industries, and is also used in cosmetic and food industries as important catalytic enzyme. Melanin pigment synthesized by tyrosinase has found applications for protection against radiation cation exchangers, drug carriers, antioxidants, antiviral agents, or immunogen. The recombinant V. spinosum tryosinase protein can be used to produce tailor-made melanin and other polyphenolic materials using various phenols and catechols as starting materials. This review compiles the recent data on biochemical and molecular properties of microbial tyrosinases, underlining their importance in the industrial use of these enzymes. After that, their most promising applications in pharmaceutical, food processing, and environmental fields are presented.

Purification and characterization of tyrosinase from walnut leaves (Juglans regia)

Polyphenol oxidase (PPO) is a type-3 copper enzyme catalyzing the oxidation of phenolic compounds to their quinone derivates, which are further converted to melanin, a ubiquitous pigment in living organisms. In this study a plant originated tyrosinase was isolated from walnut leaves (Juglans regia) and biochemically characterized. It was possible to isolate and purify the enzyme by means of an aqueous two-phase extraction method followed by chromatographic purification and identification. Interestingly, the enzyme showed a rather high monophenolase activity considering that the main part of plant PPOs with some exceptions solely possess diphenolase activity. The average molecular mass of 39,047 Da (Asp(101)→Arg(445)) was determined very accurately by high resolution mass spectrometry. This proteolytically activated tyrosinase species was identified as a polyphenol oxidase corresponding to the known jrPPO1 sequence by peptide sequencing applying nanoUHPLC-ESI-MS/MS. The polypeptide backbone with sequence coverage of 96% was determined to start from Asp(101) and not to exceed Arg(445).

High level protein-purification allows the unambiguous polypeptide determination of latent isoform PPO4 of mushroom tyrosinase

Tyrosinases catalyze two initial reaction steps in the formation of melanin. Purification of tyrosinases had always been a process accompanied with various problems caused by enzymatic browning processes. Here, an approach is presented for the purification of the latent enzyme from mushrooms which averts and removes interfering compounds (e.g. polyphenols) in advance to the extraction process. The described method is supposed being well suitable as a general protein purification protocol from natural sources like fungi and plants. The purified enzyme was investigated in detail by means of mass spectrometry: its intact protein mass was determined as 64,247.3 Da and it was identified as number four of in total six isoforms (PPO1-6) by means of sequence analysis. Some PTMs, strain specific sequence disparities and several cleavage sites including the one causing enzyme-activation (Ser³⁸³) were determined, thus, providing insights on the maturation process of this latent tyrosinase zymogen. Based on these sequence data it can be concluded that the polypeptide backbone of the latent form of the tyrosinase PPO4 ranges from Ser² to Thr⁵⁶⁵, missing when compared to the gene-derived sequence a small part (46 amino acids) of the C-terminal tail. The high content on hydrophobic amino acids within this missing tail gives rise to speculations whether this part might have a function as a membrane anchor.

Crystallization and preliminary X-ray crystallographic analysis of latent isoform PPO4 mushroom (Agaricus bisporus) tyrosinase

Tyrosinase exhibits catalytic activity for the ortho-hydroxylation of monophenols to diphenols as well as their subsequent oxidation to quinones. Owing to polymerization of these quinones, brown-coloured high-molecular-weight compounds called melanins are generated. The latent precursor form of polyphenol oxidase 4, one of the six tyrosinase isoforms from Agaricus bisporus, was purified to homogeneity and crystallized. The obtained crystals belonged to space group C121 (two molecules per asymmetric unit) and diffracted to 2.78 Å resolution. The protein only formed crystals under low-salt conditions using the 6-tungstotellurate(VI) salt Na6[TeW6O24] · 22H2O as a co-crystallization agent.

Experimental and bioinformatic investigation of the proteolytic degradation of the C-terminal domain of a fungal tyrosinase

Proteolytic processing is a key step in the production of polyphenol oxidases such as tyrosinases, converting the inactive proenzyme to an active form. In general, the fungal tyrosinase gene codes for a ~60 kDa protein that is, however, isolated as an active enzyme of ~40 kDa, lacking the C-terminal domain. Using the secreted tyrosinase 2 from Trichoderma reesei as a model protein, we performed a mutagenesis study of the residues in proximity of the experimentally determined cleavage site which are possibly involved in the proteolytic process. However, the mutant forms of tyrosinase 2 were not secreted in a full-length form retaining the C-terminal domain, but they were processed to give a ~45 kDa active form. Aiming at explaining this phenomenon, we analysed in silico the properties of the C-terminal domain of tyrosinase 2, of 23 previously retrieved homologous tyrosinase sequences from fungi (C. Gasparetti, G. Faccio, M. Arvas, J. Buchert, M. Saloheimo, K. Kruus, Appl. Microbiol. Biotechnol. 86 (2010) 213-226) and of nine well-characterised polyphenol oxidases. Based on the results of our study, we exclude the key role of specific amino acids at the cleavage site in the proteolytic process and report an overall higher sensitivity to proteolysis of the linker region and of the whole C-terminal domain of fungal tyrosinases.

Production of recombinant Agaricus bisporus tyrosinase in Saccharomyces cerevisiae cells

It has been demonstrated that Agaricus bisporus tyrosinase is able to oxidize various phenolic compounds, thus being an enzyme of great importance for a number of biotechnological applications. The tyrosinase-coding PPO2 gene was isolated by reverse-transcription polymerase chain reaction (RT-PCR) using total RNA extracted from the mushroom fruit bodies as template. The gene was sequenced and cloned into pYES2 plasmid, and the resulting pY-PPO2 recombinant vector was then used to transform Saccharomyces cerevisiae cells. Native polyacrylamide gel electrophoresis followed by enzymatic activity staining with l-3,4-dihydroxyphenylalanine (l-DOPA) indicated that the recombinant tyrosinase is biologically active. The recombinant enzyme was overexpressed and biochemically characterized, showing that the catalytic constants of the recombinant tyrosinase were higher than those obtained when a commercial tyrosinase was used, for all the tested substrates. The present study describes the recombinant production of A. bisporus tyrosinase in active form. The produced enzyme has similar properties to the one produced in the native A. bisporus host, and its expression in S. cerevisiae provides good potential for protein engineering and functional studies of this important enzyme.

Melanin biosynthesis pathway in Agaricus bisporus mushrooms

With the full genome sequence of Agaricus bisporus available, it was possible to investigate the genes involved in the melanin biosynthesis pathway of button mushrooms. Based on different BLAST and alignments, genes were identified in the genome which are postulated to be involved in this pathway. Seven housekeeping genes were tested of which 18S rRNA was the only housekeeping gene that was stably expressed in various tissues of different developmental stages. Gene expression was determined for most gene homologs (26 genes) involved in the melanin pathway. Of the analysed genes, those encoding polyphenol oxidase (PPO), the PPO co-factor L-chain (unique for A. bisporus), and a putative transcription factor (photoregulator B) were among the highest expressed in skin tissue. An in depth look was taken at the clustering of several PPO genes and the PPO co-factor gene on chromosome 5, which showed that almost 25% of the protein encoding genes in this cluster have a conserved NACHT and WD40 domain or a P-loop nucleoside triphosphate hydrolase. This article will be the start for an in depth study of the melanin pathway and its role in quality losses of this economically important product.

Multifunctions of MelB, a fungal tyrosinase from Aspergillus oryzae

The pro form of melB tyrosinase from the melB gene of Aspergillus oryzae was over-produced from E. coli and formed a homodimer that exhibited the spectral features of met-tyrosinase. In the presence of NH(2)OH (reductant), the proenzyme bound dioxygen to give a stable (μ-η(2):η(2) -peroxo)dicopper(II) species (oxy form), thus indicating that the pro form tyrosinase can function as an oxygen carrier or storage protein like hemocyanin. The pro form tyrosinase itself showed no catalytic activity toward external substrates, but proteolytic digestion with trypsin activated it to induce tyrosinase activity. Mass spectroscopy analyses, mutagenesis experiments, and colorimetry assays have demonstrated that the tryptic digestion induced cleavage of the C-terminal domain (Glu458-Ala616), although the dimeric structure of the enzyme was retained. The structural changes induced by proteolytic digestion might open the entrance to the enzyme active site for substrate incorporation.

Crystal structure of Agaricus bisporus mushroom tyrosinase: identity of the tetramer subunits and interaction with tropolone

Tyrosinase catalyzes the conversion of phenolic compounds into their quinone derivatives, which are precursors for the formation of melanin, a ubiquitous pigment in living organisms. Because of its importance for browning reactions in the food industry, the tyrosinase from the mushroom Agaricus bisporus has been investigated in depth. In previous studies the tyrosinase enzyme complex was shown to be a H(2)L(2) tetramer, but no clues were obtained of the identities of the subunits, their mode of association, and the 3D structure of the complex. Here we unravel this tetramer at the molecular level. Its 2.3 Å resolution crystal structure is the first structure of the full fungal tyrosinase complex. The complex comprises two H subunits of ∼392 residues and two L subunits of ∼150 residues. The H subunit originates from the ppo3 gene and has a fold similar to other tyrosinases, but it is ∼100 residues larger. The L subunit appeared to be the product of orf239342 and has a lectin-like fold. The H subunit contains a binuclear copper-binding site in the deoxy-state, in which three histidine residues coordinate each copper ion. The side chains of these histidines have their orientation fixed by hydrogen bonds or, in the case of His85, by a thioether bridge with the side chain of Cys83. The specific tyrosinase inhibitor tropolone forms a pre-Michaelis complex with the enzyme. It binds near the binuclear copper site without directly coordinating the copper ions. The function of the ORF239342 subunits is not known. Carbohydrate binding sites identified in other lectins are not conserved in ORF239342, and the subunits are over 25 Å away from the active site, making a role in activity unlikely. The structures explain how calcium ions stabilize the tetrameric state of the enzyme.

Crystallization and preliminary X-ray crystallographic analysis of tyrosinase from the mushroom Agaricus bisporus

Tyrosinase catalyzes the conversion of tyrosine to dihydroxyphenylalanine quinone, which is the main precursor for the biosynthesis of melanin. The enzyme from Agaricus bisporus, the common button mushroom, was purified and crystallized in two different space groups. Crystals belonging to space group P2(1) (unit-cell parameters a = 104.2, b = 105.0, c = 119.1 Å, β = 110.6°, four molecules per asymmetric unit) diffracted to 3.0 Å resolution. Crystals belonging to space group P2(1)2(1)2 (unit-cell parameters a = 104.0, b = 104.5, c = 108.4 Å, two molecules per asymmetric unit) diffracted to 2.6 Å resolution. It was essential to include 5 mM HoCl(3) in all crystallization conditions in order to obtain well diffracting crystals.