Inhibitory effects of Na7PMo11CuO40 on mushroom tyrosinase and melanin formation and its antimicrobial activities

Synthesis, Antimicrobial Activity, and Tyrosinase Inhibition by Multifunctional 3,4-Dihydroxy-Phenyl Peptidomimetics

The purpose of the present study was to evaluate the synergistic effect of two important pharmacophores, 3,4-dihydroxyphenyl and peptidomimetic moieties, as mushroom tyrosinase inhibitors and antimicrobial agents targeting specific strains of pathogenic bacteria. The 3,4-dihydroxybenzaldehyde (protocatechuic aldehyde) was found to be an effective inhibitor of tyrosinase activity, and due to the fact that it is a safe natural substance with such a scaffolded structure, it is likely that dihydroxyl-substituted phenolic derivatives can exhibit potent tyrosinase inhibitory activity. Series of peptidomimetics with an incorporated 3,4-dihydroxyphenyl scaffold was synthesized and characterized. The inhibitory effects of peptidomimetics on a mushroom tyrosinase were studied. The results showed that among the compounds, five of them showed higher inhibitory activity than the parent 3,4-dihydroxybenzyl aldehyde. In silico docking studies with mushroom tyrosinase (PDB ID 2Y9X) predicted possible binding modes in the enzymatic pocket for these compounds. Furthermore, the antimicrobial activities of peptidomimetics against selected Gram-positive and Gram-negative bacterial strains (E. coli, A. baumannii, P. aeruginosa, E. cloacae, and S. aureus) were investigated. The results showed that all tested peptidomimetics have antimicrobial activities (MIC values from 0.25 to 4.0 μM) comparable with those observed for the commonly used antibiotics (ciprofloxacin, bleomycin, and cloxacillin). Notably, all evaluated compounds demonstrated significant activity against E. coli and S. aureus strains, which are primary sources of infections resulting in numerous fatalities. Additionally, the cytotoxicity of sixteen derivatives was assessed using the MTT assay on BALB/c3T3 mouse fibroblast cell lines. Cytotoxicity analyses indicated that the tested substances have a similar or reduced impact on cell proliferation compared to commonly utilized antibiotics within the range of therapeutic doses. This study presents the potential of peptidomimetics with 3,4-dihydroxyphenyl scaffolds could be beneficial for developing novel tyrosinase inhibitors and new potent food preservatives or cosmetic additives.

Mechanism of melanogenesis inhibition by Keggin-type polyoxometalates

Abnormal melanin overproduction can result in hyperpigmentation syndrome in human skin diseases and enzymatic browning of fruits and vegetables. Recently, our group found that Keggin-type polyoxometalates (POMs) can efficiently inhibit tyrosinase activity. However, it remains unclear whether Keggin-type POMs exhibit optimal effects in vivo. Additionally, the inhibitory effect and mechanism of action of POMs on cellular tyrosinase activity and melanogenesis have been rarely reported. Here we demonstrate that our screened and synthesised PMo11Zn and GaMo12 show superior inhibitory effects on melanin formation as well as inhibition of cellular tyrosinase activity compared to other Keggin-type POMs. Intriguingly, we reveal that Keggin-type POMs competitively bind to tyrosinase mainly through more interactions with Cu2+ ions and the amino acid residue is capable of forming van der Waals, cation-π and hydrogen bonds, resulting in a reversible non-covalent complex formation. Our findings provide valuable insights into the design, synthesis and screening of polyoxometalates as multifunctional metallodrugs and food preservatives against hyperpigmentation.

Decavanadate and metformin-decavanadate effects in human melanoma cells

Decavanadate is a polyoxometalate (POMs) that has shown extensive biological activities, including antidiabetic and anticancer activity. Importantly, vanadium-based compounds as well as antidiabetic biguanide drugs, such as metformin, have shown to exert therapeutic effects in melanoma. A combination of these agents, the metformin-decavanadate complex, was also recognized for its antidiabetic effects and recently described as a better treatment than the monotherapy with metformin enabling lower dosage in rodent models of diabetes. Herein, we compare the effects of decavanadate and metformin-decavanadate on Ca2+-ATPase activity in sarcoplasmic reticulum vesicles from rabbit skeletal muscles and on cell signaling events and viability in human melanoma cells. We show that unlike the decavanadate-mediated non-competitive mechanism, metformin-decavanadate inhibits Ca2+-ATPase by a mixed-type competitive-non-competitive inhibition with an IC50 value about 6 times higher (87 μM) than the previously described for decavanadate (15 μM). We also found that both decavanadate and metformin-decavanadate exert antiproliferative effects on melanoma cells at 10 times lower concentrations than monomeric vanadate. Western blot analysis revealed that both, decavanadate and metformin-decavanadate increased phosphorylation of extracellular signal-regulated kinase (ERK) and serine/threonine protein kinase AKT signaling proteins upon 24 h drug exposure, suggesting that the anti-proliferative activities of these compounds act independent of growth-factor signaling pathways.

Preparation and Characterization of Biodegradable κ-Carrageenan Based Anti-Bacterial Film Functionalized with Wells-Dawson Polyoxometalate

In the present study, an anti-bacterial film (Carr/POM film) was prepared through the incorporation of Wells-Dawson polyoxometalate K₆[Mo₁₈O₆₂P₂] into κ-carrageenan-based polymers using the tape-casting method. The mechanical properties, thermal stability, and morphology of the prepared film were characterized. The obtained results showed that incorporation of K₆[Mo₁₈O₆₂P₂] significantly affected the morphology and structure of the films. Moreover, the polyoxometalate-based film demonstrated desirable bactericidal activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Carr/POM (@8 mg/mL) film resulted in an obvious inhibition zone around the film in Kirby-Bauer disk diffusion test, which could also remove 99% of S. aureus and E. coli on plastic, glass, and stainless steel. In addition, this anti-bacterial film also demonstrated good biodegradability, which could be decomposed in soil in around 1 week. In conclusion, the polyoxometalate-based film showed good anti-bacterial property against food-borne pathogenic microbes, suggesting the prepared film has great potential to be developed as promising food packaging.

Inhibition of Mitochondrial ATP Synthesis and Regulation of Oxidative Stress Based on {SbW8 O30 } Determined by Single-Cell Proteomics Analysis

The 10-nuclear heteroatom cluster modified {SbW₈ O₃₀ } was successfully synthesized and exhibited inhibitory activity (IC₅₀ =0.29 μM). Based on proteomics analysis, Na₄ Ni₂ Sb₂ W₂ -SbW₈ inhibited ATP production by affecting the expression of 16 related proteins, hindering metabolic functions in vivo and cell proliferation due to reactive oxygen species (ROS) stress. In particular, the low expression of FAD/FMN-binding redox enzymes (relative expression ratio of the experimental group to the control=0.43843) could be attributed to the redox mechanism of Na₄ Ni₂ Sb₂ W₂ -SbW₈ , which was consistent with the effect of polyoxometalates (POMs) and FMN-binding proteins on ATP formation. An electrochemical study showed that Na₄ Ni₂ Sb₂ W₂ -SbW₈ combined with FMN to form Na₄ Ni₂ Sb₂ W₂ -SbW₈ -2FMN complex through a one-electron process of the W atoms. Na₄ Ni₂ Sb₂ W₂ -SbW₈ acted as catalase and glutathione peroxidase to protect the cell from ROS stress, and the inhibition rates were 63.3 % at 1.77 μM of NADPH and 86.06 % at 10.62 μM of 2-hydroxyterephthalic acid. Overall, our results showed that POMs can be specific oxidative/antioxidant regulatory agents.

Bioevaluation and molecular docking analysis of novel phenylpropanoid derivatives as potent food preservative and anti-microbials

Novel derivatives were synthesized using natural scaffold, like phenylpropanoids C₆-C₃ backbone to reduce unfavorable browning of food due to tyrosinase and oxidative spoilage. Most of the compounds displayed mushroom tyrosinase inhibition better than kojic acid. Compound CE48 exhibited better anti-tyrosinase (IC₅₀-29.64 μM) and antioxidant (EC₅₀-12.67 μM) activity than the reference compounds, kojic acid (IC₅₀-50.30 μM) and ascorbic acid (EC₅₀-14.55 μM), respectively. Compounds SAM30, SE78, 11F, and CE48 showed better anti-B. subtilis, anti-S. aureus, and anti-A. niger activity, respectively, compared to their parents. Molecular docking studies between inhibitors and mushroom tyrosinase corroborated the experimental reports, except SAM30 (glide score - 8.117) and SE78 (glide score - 6.151). In silico absorption, distribution, metabolism, excretion/toxicity (ADME/T) and toxicological studies of these newly synthesized compounds exhibited acceptable pharmacokinetic and safety profiles, like good aqueous solubility (- 3.34 to - 7.57), low human oral absorption (e.g., SAM30, SE78, FAM34), low gut-blood barrier permeability [36.67-209.88 nm/s in Cancer coli-2 (Caco-2) cells] and [19.45-91.51 nm/s in Madin-Darby Canine Kidney (MDCK) cells], low blood-brain barrier penetration, non-mutagenicity, and non-carcinogenicity. Interestingly, the synthesized compounds also possessed multifunctional properties, like microbial growth inhibitor, free radicals scavenger, and it also prevented browning of raw fruits and vegetables by inhibiting tyrosinase enzyme.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02636-0.

Isolation, identification, and inhibitory enzyme activity of phenolic substances present in Spirulina

Spirulina species are edible with high nutritional as well as potential therapeutic values. In this work, we show that phenolic extracts from Spirulina (p-Coumaric acid) possessed inhibitory potential on α-glucosidase (IC₅₀  = 1.67 ± 0.02 mM) and tyrosinase (IC₅₀  = 52.71 ± 3.01 mM). Moreover, p-Coumaric acid inhibited α-glucosidase and tyrosinase in a reversible mixed-type manner. Interestingly, molecular docking demonstrated that p-Coumaric acid penetrated in depth of the active-site of tyrosinase and α-glucosidase by the noncovalent force or interaction. Among them, making polar interactions with Cu²⁺ ions and the amino acid residue capable of forming cation-π significantly contribute to the strong binding of p-Coumaric acid on tyrosinase. p-Coumaric acid was isolated and identified from Spirulina for the first time, which can be used as a lead compound for the design of functional food additives and skin-lightening active ingredient in cosmetics, and pharmaceuticals against type 2 diabetes. PRACTICAL APPLICATIONS: A natural, food-derived compound possessing the potential for the development of an anti-hyperglycaemic and skin-lightening supplement is very promising in cosmetics, functional food, and pharmaceuticals against type 2 diabetes. Herein, the present study is the first to present high levels of p-Coumaric acid from Spirulina, which simultaneously possessed inhibition potential on α-glucosidase and tyrosinase. Importantly, we gained initial information about the polypeptide-inhibitor interactions and underlying mechanisms for Spirulina's therapeutic effects, which will provide the bases for developing new drugs for preventing or treating type 2 diabetes and enzyme inhibitors. Moreover, this work also demonstrates the potential of the extraction of high-value chemicals from Spirulina waste.

Biological evaluation of Keggin-type polyoxometalates on tyrosinase: Kinetics and molecular modeling

Abnormal overexpression of tyrosinase activity can lead to the production of hyperpigmentation in human skin and enzymatic browning in fruits and vegetables. Herein, the inhibition and mechanism of the H₃ PMo₁₂ O₄₀ and two transition metal-substituted Keggin-type polyoxometalates (Na₇ PMo₁₁ CoO₄₀ and Na₇ PMo₁₁ ZnO₄₀ ) on tyrosinase were studied by kinetics and molecular modeling. Kinetic studies indicated that all compounds had more potent inhibitory activities than standard arbutin, and H₃ PMo₁₂ O₄₀ (IC₅₀  = 0.443 ± 0.006 mm) is ~15-fold stronger inhibition than arbutin. Additionally, all compounds inhibited tyrosinase in a reversible competitive manner. Intriguingly, molecular modeling elucidated that three compounds competitively bind to tyrosinase mainly through more interactions with Cu²⁺ ions and the amino acid residue capable of forming cation-π and hydrogen bonding, forming a reversible non-covalent complex. Molecular simulation study correlated well with the biological activity of three compounds in vitro. This work provided new insights into design and synthesis of polyoxometalates as tyrosinase inhibitors in the field of medicine, cosmetic, and food.

The Aquaporin-3-Inhibiting Potential of Polyoxotungstates

Polyoxometalates (POMs) are of increasing interest due to their proven anticancer activities. Aquaporins (AQPs) were found to be overexpressed in tumors bringing particular attention to their inhibitors as anticancer drugs. Herein, we report for the first time the ability of polyoxotungstates (POTs), such as of Wells-Dawson P2W18, P2W12, and P2W15, and Preyssler P5W30 structures, to affect aquaporin-3 (AQP3) activity and impair melanoma cell migration. The tested POTs were revealed to inhibit AQP3 function with different effects, with P2W18, P2W12, and P5W30 being the most potent (50% inhibitory concentration (IC50) = 0.8, 2.8, and 3.2 µM), and P2W15 being the weakest (IC50 > 100 µM). The selectivity of P2W18 toward AQP3 was confirmed in yeast cells transformed with human aquaglyceroporins. The effect of P2W12 and P2W18 on melanoma cells that highly express AQP3 revealed an impairment of cell migration between 55% and 65% after 24 h, indicating that the anticancer properties of these compounds may in part be due to the blockage of AQP3-mediated permeability. Altogether, our data revealed that P2W18 strongly affects AQP3 activity and cancer cell growth, unveiling its potential as an anticancer drug against tumors where AQP3 is highly expressed.

Extraction and antioxidant activity of sericin, a protein from silk

Abstract Sericin is a globular protein that represents 20% to 30% of the silk fiber from Bombyx mori silkworm cocoon. This protein is usually removed from the raw fiber and discarded by silk producers, a process known as degumming. However, sericin possesses significant biological properties that allows its application in various fields. The antioxidant activity is one of its most relevant benefits. Several authors have reported its anti-tyrosinase activity, lipid peroxidation inhibition and free radical neutralization. The antioxidant potential of sericin protein varies according to the extraction method used. Even though a wide variety of extraction techniques have been studied, simple technics including water at high temperature have exhibited efficient results. Furthermore, this method does not interfere with the safety of sericin for subsequent applications in food.

Research progress on the inhibition of enzymes by polyoxometalates

Polyoxometalates (POMs) are a kind of inorganic cluster metal complex with various biological activities, such as anti-Alzheimer's disease, antibacterial, anti-cancer, anti-diabetes, anti-virus and so on.

Molecular docking of polyoxometalates as potential α-glucosidase inhibitors

α-Glucosidase is an important target enzyme for the treatment of type 2 diabetes in humans. In our previous studies, it was found that polyoxometalates exhibited an effective inhibitory effect on the activity of α-glucosidase, while polyoxometalates have the characteristics of structural diversity and unique properties. Herein, we investigated the inhibition of two different series of polyoxometalates on α-glucosidases by enzyme kinetics and molecular docking. The results demonstrated that all of the studied compounds had a significant inhibitory ability on α-glucosidase as compared with the positive control acarbose. H₈[P₂Mo₁₇Cr(OH₂)O₆₁] reversibly inhibited α-glucosidase in a competitive manner with IC₅₀ of 115.50 ± 1.64 μM and K_I value of 44.31 μM. All other compounds reversibly inhibited enzymatic activity in a mixed manner. H₆PMo₉V₃O₄₀ and H₈[P₂Mo₁₇Cu(OH₂)O₆₁] were the best inhibitors in the Keggin and Dawson series, respectively, with IC₅₀ of 9.63 ± 0.43 and 40.13 ± 0.61 μM, respectively. We conducted molecular docking study and found that the compound and α-glucosidase were mainly non-covalently interacting with hydrogen bonds and van der Waals forces. This result further confirmed the inhibition mechanism of enzyme kinetic experiments.

Keggin-type polyoxotungstates as mushroom tyrosinase inhibitors - A speciation study

Mushroom tyrosinase abPPO4 is a commercially relevant polyphenol oxidase and has been being targeted for numerous inhibition studies including polyoxometalates (POMs). In the present work, its diphenolase activity was inhibited at pH 6.8 by a series of structurally related polyoxotungstates (POTs) of the α-Keggin archetype, exhibiting the general formula [Xn+W12O40](8-n)- in order to elucidate charge-dependent activity correlations. Kinetic data were obtained from the dopachrome assay and 183W NMR was applied to obtain crucial insights into the actual Keggin POT speciation in solution, facilitating a straightforward assignment of inhibition effects to the identified POT species. While [PW12O40]3- was completely hydrolyzed to its moderately active lacunary form Hx[PW11O39](7-x)- (Ki = 25.6 mM), [SiW12O40]4- showed the most pronounced inhibition effects with a Ki of 4.7 mM despite of partial hydrolysis to its ineffective lacunary form Hx[SiW11O39](8-x)-. More negative Keggin cluster charges of 5- and 6- generally resulted in preclusion of inhibitory efficacy as well as hydrolysis, but with the Ni-substituted cluster [PW11O39{Ni(H2O)}]5- enzymatic inhibition was clearly restored (Ki = 9.7 mM). The inhibitory capacity of the structurally intact Keggin POTs was found to be inversely correlated to their net charge. The here applied speciation strategy is of utmost importance for any biological POM application to identify the actually active POM species.

Polyoxometalates as Potential Next-Generation Metallodrugs in the Combat Against Cancer

Polyoxometalates (POMs) are an emerging class of inorganic metal oxides, which over the last decades demonstrated promising biological activities by the virtue of their great diversity in structures and properties. They possess high potential for the inhibition of various tumor types; however, their unspecific interactions with biomolecules and toxicity impede their clinical usage. The current focus of the field of biologically active POMs lies on organically functionalized and POM-based nanocomposite structures as these hybrids show enhanced anticancer activity and significantly reduced toxicity towards normal cells in comparison to unmodified POMs. Although the antitumor activity of POMs is well documented, their mechanisms of action are still not well understood. In this Review, an overview is given of the cytotoxic effects of POMs with a special focus on POM-based hybrid and nanocomposite structures. Furthermore, we aim to provide proposed mode of actions and to identify molecular targets. POMs are expected to develop into the next generation of anticancer drugs that selectively target cancer cells while sparing healthy cells.

Polyoxomolybdates as α-glucosidase inhibitors: Kinetic and molecular modeling studies

Noninsulin dependent diabetes mellitus is a serious global disease that is treated by inhibiting α-glucosidase to reduce the glucose content in the blood. Several incompletely satisfactory therapeutic drugs are already on the market. In this report, we showed that polyoxomolybdates based on Keggin-type architecture are promising candidates. Kinetic studies indicate that H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, Na₆PMo₁₁FeO₄₀ and Na₇PMo₁₁CoO₄₀ strongly inhibit α-glucosidase with IC₅₀ values of 6.14 ± 0.38 μM, 52.33 ± 1.41 μM, 161.90 ± 7.68 μM and 103.10 ± 2.88 μM, respectively. Moreover, H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, and Na₇PMo₁₁CoO₄₀ are reversible, competitive inhibitors with K_I values of 0.018 mM, 0.146 mM and 0.121 mM, respectively. Na₆PMo₁₁FeO₄₀ inhibited α-glucosidase in a reversible noncompetitive manner with K_I and K_IS of 0.312 mM and 0.412 mM, respectively. Molecular docking simulation suggested that H₃PMo₁₂O₄₀ binds into the substrate binding site in accordance with competitive inhibition behavior and offered, in addition, an initial insight into the polypeptide-inhibitor interactions. This work presents a promising new perspective for designing effective α-glucosidase inhibitors and further demonstrates the enormous potential of polyoxomolybdates as enzyme inhibitors.

Interactions between polyoxometalates and biological systems: from drug design to artificial enzymes

Polyoxometalates have long been studied in a variety of biological applications. Interactions between the highly charged POM molecules and biological molecules frequently occur through hydrogen-bonding and electrostatic interactions. Tellurium-centred Anderson-Evans POMs show exceptional promise as crystallization agents, while acidic and metal-substituted POMs may provide interesting alternatives to enzymes in proteomics applications. While POMs also show interesting results in a number of medicinal applications, for example as anti-amyloid agents for the treatment of Alzheimer's disease and as anti-tumoral agents, their use is often impeded by their toxicity. Many recent studies have therefore focussed on POM-functionalization to reduce toxicity and increase activity by addition of biological targeting molecules.

Effect of Carnauba Wax-Based Coating Containing Glycerol Monolaurate on Decay and Quality of Sweet Potato Roots during Storage

Because of high water loss and rot observed in postharvest sweet potato ( Ipomoea batatas (L.) Lam.) roots, a carnauba wax (CW)-based nanoemulsion without or with glycerol monolaurate (CW-GML) was developed by a high-energy emulsification approach. The effects of the two coatings on decay, respiration rate, weight loss, surface color, total soluble sugar, and starch content as well as the sensory quality of sweet potato roots were investigated during storage at 20°C for 50 days. Compared with the control treatment (water) and CW coating alone, CW-GML coating exhibited higher emulsion stability and antifungal activity, and treatment resulted in a uniform and continuous coating on roots. The CW-GML and CW coatings both effectively reduced root weight loss and respiration rate and inhibited decay incidence compared with control roots during storage. The CW-GML coating showed markedly stronger inhibition of root rot than the CW coating. Both the CW-GML and CW coatings promoted an increase in root sweetness but did not negatively impact perceived flavor. The overall results demonstrate that the CW-GML coating holds great promise as an effective postharvest technology to preserve food quality and extend shelf life of sweet potato roots.

Combating pathogens with Cs2.5H0.5PW12O40 nanoparticles: a new proton-regulated antimicrobial agent

The transfer of pathogens from contaminated surfaces to patients is one of the main causes of health care-associated infections (HCAIs). Cases of HCAIs due to multidrug-resistant organisms have been growing worldwide, whereas inorganic nano-antimicrobials are valuable today for the prevention and control of HCAIs. Here, we present a cesium salt of phosphotungstic heteropolyacid (Cs_2.5H_0.5PW₁₂O₄₀) as a promising nanomaterial for use in antimicrobial product technologies. This water-insoluble Keggin salt exhibits a broad biocide spectrum against Gram-positive and Gram-negative bacteria, yeasts, and filamentous fungi even under dark conditions. The Cs_2.5H_0.5PW₁₂O₄₀ nanoparticles (NPs) act as a proton-regulated antimicrobial whose activity is mediated on the release of hydronium ions (H₃O⁺), yielding an in situ acidic pH several units below those tolerable by most of the fungal and bacterial nosocomial pathogens.

Acidic electrolysed water delays browning by destroying conformation of polyphenoloxidase

BACKGROUND

Browning frequently occurs at fruits, vegetables and aquatic products during storage, and it drastically reduces the consumer's acceptability, with considerable financial loss. The objective of this paper was to investigate the effects of acidic electrolysed water (AEW) technology on polyphenoloxidase (PPO), which is an essential enzyme for browning.

RESULTS

AEW ice exhibited a good ability in delaying browning in shrimp. Kinetic study revealed that AEW exhibited the mixed type inhibition of PPO with a K_i value of 1.96 mmol L^-1 . Moreover, both the circular dichroism spectrum and Fourier transform infrared spectroscopy analyses revealed that the α-helix in PPO decreased whereas random coil increased which indicates that PPO conformation was destroyed.

CONCLUSION

Thus, this paper may provide a deeper understanding of the application of AEW technology for preventing browning in the food industry. © 2017 Society of Chemical Industry.

Applications of Panax ginseng leaves-mediated gold nanoparticles in cosmetics relation to antioxidant, moisture retention, and whitening effect on B16BL6 cells

Background

Bioactive compounds in plant extracts are able to reduce metal ions to nanoparticles through the process of green synthesis. Panax ginseng is an oriental medicinal herb and an adaptogen which has been historically used to cure various diseases. In addition, the P. ginseng leaves-mediated gold nanoparticles are the value-added novel materials. Its potential as a cosmetic ingredient is still unexplored. The aim of this study was to evaluate the antioxidant, moisture retention and whitening properties of gold nanoparticles (PgAuNPs) in cosmetic applications.

Methods

Cell-free experiments were performed to evaluate PgAuNP's antioxidant and moisture retention properties and inhibition activity on mushroom tyrosinase. Furthermore, in vitro cell cytotoxicity was evaluated using normal human dermal fibroblast and murine B16BL6 melanoma cells (B16) after treatment with increasing concentrations of PgAuNPs for 24 h, 48 h, and 72 h. Finally, in vitro cell assays on B16 cells were performed to evaluate the whitening effect of PgAuNPs through reduction of cellular melanin content and tyrosinase activity.

Results

In vitro DPPH radical scavenging assay results revealed that PgAuNPs exhibited antioxidant activity in a dose-dependent manner. PgAuNPs exhibited moisture retention capacity and effectively inhibited mushroom tyrosinase. In addition, 3-(4,5-dimethyl-thiazol-2yl)-2,5-diphenyl tetrazolium bromide results revealed that PgAuNPs were not toxic to human dermal fibroblast and B16 cells; in addition, they significantly reduced melanin content, tyrosinase activity, and mRNA expression of melanogenesis-associated transcription factor and tyrosinase in B16 cells.

Conclusion

Our study is the first report to provide evidence supporting that P. ginseng leaves-capped gold nanoparticles could be used as multifunctional ingredients in cosmetics.

Large-Scale Recombinant Expression and Purification of Human Tyrosinase Suitable for Structural Studies

Human tyrosinase (TYR) is a glycoprotein that initiates the first two reactions in the melanin biosynthesis pathway. Mutations in its encoding gene cause Oculocutaneous Albinism type I (OCA1), the most severe form of albinism, which is a group of autosomal recessive disorders characterized by reduced or absent production of melanin in skin, hair and eyes. Despite extensive structural and characterization studies of its homologues in lower eukaryotic organisms, the catalytic mechanism of human TYR and the molecular basis of OCA1 are largely unknown. In this work, we have carried out a large-scale recombinant expression of TYR that has enabled us to obtain high yields of pure and active protein, required for crystallization trials and screening of skin whitening agents, which is highly demanded in the cosmetic industry. Addition of an N-terminal honeybee melittin signal peptide for secretion of the produced protein into the (protein-free) medium, as well as a cleavable His-tag at the C-terminus, was crucial for increasing the yield of pure protein. We have successfully crystallized two TYR variants, in both glycosylated and deglycosylated forms, showing preliminary X-ray diffraction patterns at 3.5 Å resolution. Hence, we have established an expression and purification protocol suitable for the crystal structure determination of human TYR, which will give unique atomic insight into the nature and conformation of the residues that shape the substrate binding pocket that will ultimately lead to efficient compound design.