Tyrosinase: a comprehensive review of its mechanism

Catecholic Compounds in Ctenophore Colloblast and Nerve Net Proteins Suggest a Structural Role for DOPA-Like Molecules in an Early-Diverging Animal Lineage

Ctenophores, or comb jellies, are among the earliest-diverging extant animal lineages. Several recent phylogenomic studies suggest that they may even be the sister group to all other animals. This unexpected finding remains difficult to contextualize, particularly given ctenophores' unique and sometimes poorly understood physiology. Colloblasts, a ctenophore-specific cell type found on the surface of these animals' tentacles, are emblematic of this difficulty. The exterior of the colloblast is dotted with granules that burst and release an adhesive on contact with prey, ensnaring it for consumption. To date, little is known about the fast-acting underwater adhesive that these cells secrete or its biochemistry. We present evidence that proteins in the colloblasts of the ctenophore Pleurobrachia bachei incorporate catecholic compounds similar to the amino acid l-3,4-dihydroxyphenylalanine. These compounds are associated with adhesive-containing granules on the surface of colloblasts, suggesting that they may play a role in prey capture, akin to dihydroxyphenylalanine-based adhesives in mussel byssus. We also present unexpected evidence of similar catecholic compounds in association with the subepithelial nerve net. There, catecholic compounds are present in spatial patterns similar to those of l-3,4-dihydroxyphenylalanine and its derivatives in cnidarian nerves, where they are associated with membranes and possess unknown functionality. This "structural" use of catecholic molecules in ctenophores represents the earliest-diverging animal lineage in which this trait has been observed, though it remains unclear whether structural catechols are deeply rooted in animals or whether they have arisen multiple times.

Targeting Metalloenzymes for Therapeutic Intervention

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Transcriptional analysis of tyrosinase gene expression during Bufo bufo development

Tyrosinase (EC.1.14.18.1.) is a widespread enzyme, in the phylogenetic scale, that produces melanin, from bacteria to man, by using as substrates monophenols, o-diphenols and molecular oxygen. In this work we have confirmed and demonstrated that during Bufo bufo development tyrosinase activity and gene expression first occur at developmental stages 17–18 (tail bud-muscular response) as detected by a spectrophotometric assay and qRT-PCR. As expected, also during B. bufo development tyrosinase gene is expressed after the late gastrula (stage 12), differently from Rana pipiens development when tyrosinase mRNA appears at the neural plate stage and enzyme activity at stage 20 (gill circulation). We have cloned and sequenced the B. bufo tyrosinase cDNA in order to prepare B. bufo tyrosinase cDNA specific primers (forward and reverse). Tyrosinase mRNA cloning has been performed by using degenerate primers prepared according to the anuran tyrosinase gene sequence coding for the copper binding sites. The expressions of tyrosinase gene and enzymatic activity during B. bufo development support that until the developmental stage 17, embryo melanin is of maternal origin and at this stage can start embryo melanin synthesis. A correlation exists between tyrosinase expression and O₂ consumption during B. bufo development.

Synthesis and Antifungal Potential of Some Novel Benzimidazole-1,3,4-Oxadiazole Compounds

Discovery of novel anticandidal agents with clarified mechanisms of action, could be a rationalist approach against diverse pathogenic fungal strains due to the rise of resistance to existing drugs. In support to this hypothesis, in this paper, a series of benzimidazole-oxadiazole compounds were synthesized and subjected to antifungal activity evaluation. In vitro activity assays indicated that some of the compounds exhibited moderate to potent antifungal activities against tested Candida species when compared positive control amphotericin B and ketoconazole. The most active compounds 4h and 4p were evaluated in terms of inhibitory activity upon ergosterol biosynthesis by an LC-MS-MS method and it was determined that they inhibited ergosterol synthesis concentration dependently. Docking studies examining interactions between most active compounds and lanosterol 14-α-demethylase also supported the in vitro results.

Occurrence of tayras (Eira barbara Linnaeus, 1758) with anomalous coloration in Cerrado remnants in the state of São Paulo, Brazil

Abstract: Coloration anomalies are mainly genetically-based disorders in which body pigmentation is either reduced (hypopigmentation) or produced in excess (melanism), in parts or the totality of the body. Cases of hypopigmentation have been documented in many neotropical mammals, including the tayra (Eira barbara Linnaeus, 1758). We expand the account of anomalous coloration occurrence presenting new registers of hypopigmented tayras in Brazil. Data was collected during a mammal survey carried out in three agricultural landscapes within the Cerrado domain in the northeast of the state of São Paulo. We obtained two kinds of records of hypopigmented tayras, one from direct sighting and the other from a camera-trap. We discuss the likely implications of this conspicuous coloration to tayras and highlight some possibilities of study.

Pigmentation and vision: Is GPR143 in control?

Albinism, typically characterized by decreased melanin synthesis, is associated with significant visual deficits owing to developmental changes during neurosensory retina development. All albinism is caused by genetic mutations in a group of diverse genes including enzymes, transporters, G-protein coupled receptor. Interestingly, these genes are not expressed in the neurosensory retina. Further, regardless of cause of albinism, all forms of albinism have the same retinal pathology, the extent of which is variable. In this review, we explore the possibility that this similarity in retinal phenotype is because all forms of albinism funnel through the same final common pathway. There are currently seven known genes linked to the seven forms of ocular cutaneous albinism. These types of albinism are the most common, and result in changes to all pigmented tissues (hair, skin, eyes). We will discuss the incidence and mechanism, where known, to develop a picture as to how the mutations cause albinism. Next, we will examine the one form of albinism which causes tissue-specific pathology, ocular albinism, where the eye exhibits the retinal albinism phenotype despite near normal melanin synthesis. We will discuss a potential way to treat the disease and restore normal retinal development. Finally, we will briefly discuss the possibility that this same pathway may intersect with the most common cause of permanent vision loss in the elderly.

Microfluidic device for the point of need detection of a pathogen infection biomarker in grapes

Due to the rise of pathogenic infections amongst crops, there is an increased need for point-of-need monitoring of plant health. In this work we present a portable system capable of detecting signs of infection in grapes using a microfluidic device.

Synthesis, screening and biological activity of potent thiosemicarbazone compounds as a tyrosinase inhibitor

Inhibitors are designed based on coordination chemistry and catalytic circle of the tyrosinase, coordination atoms binds to copper and blocks enzyme activity, indicated that thiosemicarbazone species possess good potential as tyrosinase inhibitors.

Catalytic mechanism of the tyrosinase reaction toward the Tyr98 residue in the caddie protein

Tyrosinase (EC 1.14.18.1), a copper-containing monooxygenase, catalyzes the conversion of phenol to the corresponding ortho-quinone. The Streptomyces tyrosinase is generated as a complex with a “caddie” protein that facilitates the transport of two copper ions into the active center. In our previous study, the Tyr⁹⁸ residue in the caddie protein, which is accommodated in the pocket of active center of tyrosinase, has been found to be converted to a reactive quinone through the formations of the μ-η²:η²-peroxo-dicopper(II) and Cu(II)-dopasemiquinone intermediates. Until now—despite extensive studies for the tyrosinase reaction based on the crystallographic analysis, low-molecular-weight models, and computer simulations—the catalytic mechanism has been unable to be made clear at an atomic level. To make the catalytic mechanism of tyrosinase clear, in the present study, the cryo-trapped crystal structures were determined at very high resolutions (1.16–1.70 Å). The structures suggest the existence of an important step for the tyrosinase reaction that has not yet been found: that is, the hydroxylation reaction is triggered by the movement of Cu^A, which induces the syn-to-anti rearrangement of the copper ligands after the formation of μ-η²:η²-peroxo-dicopper(II) core. By the rearrangement, the hydroxyl group of the substrate is placed in an equatorial position, allowing the electrophilic attack to the aromatic ring by the Cu₂O₂ oxidant.

The cryo-trapped crystal structures of tyrosinase in a complex with its “caddie” protein reveal structural insight into the catalytic mechanism of tyrosinase, the rate-limiting enzyme in the production of melanin.

Tyrosinase is an enzyme that controls a rate-limiting reaction of melanogenesis: it catalyzes the conversion of a phenol to the corresponding ortho-quinone. Streptomyces tyrosinase is formed as a complex, with a “caddie” protein that assists with the transport of the two copper ions into the enzyme’s active center. In our previous study, we showed that the Tyr⁹⁸ residue in the caddie protein, which is accommodated in the pocket of active center of tyrosinase, is converted to a reactive quinone through the formations of the μ-η²:η²-peroxo-dicopper(II) and Cu(II)-dopasemiquinone intermediates. Until now—despite extensive studies of the tyrosinase reaction based on the crystallographic analysis, low-molecular-weight model systems, and computer simulations—the catalytic mechanism was unclear at an atomic level. To understand the catalytic mechanism of tyrosinase in detail, we determined the cryo-trapped crystal structures at very high resolutions, which suggest an important new step for the tyrosinase reaction: the hydroxylation reaction triggered by the movement of Cu^A, which induces the syn-to-anti rearrangement of the copper ligands after the formation of μ-η²:η²-peroxo-dicopper(II) core.

Improvement of Biological Activity of Morchella esculenta Protein Hydrolysate by Microwave-Assisted Selenization

Morchella esculenta protein hydrolysate (MPH) from a valued medicinal and edible fungus M. esculenta (L.) is an excellent material for functional food development. To promote MPH utilization, selenization of MPH was performed by applying a simple and environmentally friendly microwave irradiation procedure. The physicochemical characteristics of selenized MPH (Se-MPH) were investigated by SEM-EDX, FTIR, CD, and amino acid analyzer, and its biological activity were assessed by ABTS, DPPH, H₂ O₂ scavenging, and reducing power assays, as well as α-glucosidase, α-amylase, and tyrosinase inhibition tests. The results showed that MPH was successfully selenized, Se content in Se-MPH reached 59.0 ± 0.64 mg/g, and amino groups, hydroxyl groups, and sulfur atoms of methionine residues in the MPH molecule may participate in selenization. Furthermore, Se-MPH exhibited significantly enhanced antioxidant, antidiabetic, and tyrosinase inhibitory activities, compared with the native MPH and microwave-irradiated MPH. Thus, the microwave-assisted selenization is a feasible strategy for preparing organic Se and improving the biological activity of MPH. PRACTICAL APPLICATION: In this study, selenized Morchella esculenta protein hydrolysate (Se-MPH) was successfully prepared via conjugation with sodium selenite using the microwave-assisted method. The results showed that Se-MPH, synthesized with the aid of microwave, exhibited favorable selenium content and improved antioxidant, antidiabetic, and tyrosinase inhibitory activities. Therefore, microwave can be employed as an innovative and effective avenue for the production of organic selenium in nutraceutical and functional food industry.

Aminoluciferin 4-hydroxyphenyl amide enables bioluminescence detection of endogenous tyrosinase

Tyrosinase, a copper-containing enzyme existing widely in plants, animals and microorganisms, usually serves as an important biomarker in melanoma, and is also related to hyperpigmentation of the skin, melasma, age spots and albinism. At present, only one bioluminescent probe has been applied to image tyrosinase in cells. Thus, it's of great significance to develop a new bioluminescent probe that can detect tyrosinase in living cells and in live animals. In the current work, we report a new BL probe, TyrBP-3, which not detect tyrosinase in vitro and in living cells, but can also visualize the level of tyrosinase activity in tumors of living animals. In summary, TyrBP-3 is the first bioluminescent probe that can image tyrosinase on a cellular level. Hence, we anticipate that TyrBP-3 can be a good tool to monitor tyrosinase in complex biosystems in the future.

Determination of the volatile and polyphenol constituents and the antimicrobial, antioxidant, and tyrosinase inhibitory activities of the bioactive compounds from the by-product of Rosa rugosa Thunb. var. plena Regal tea

Background

The phytochemical constituents and biological activities of Rosa rugosa Thunb. var. plena Regal flower cell sap (RFCS) were investigated.

Methods

Volatile constituent, such as linalool, phenylethyl alcohol, citronellol, α-bisabolol, were identified by GC-MS. The contents of hyperoside, kaempferol-3-O-rutinosid, rutin, and luteolin as well as the total flavonoid content in RFCS were determined by HPLC and HPLC-MS. The total polyphenol content was evaluated by the Folin-Ciocalteu colorimetric method. The antioxidant activities of RFCS and the standards were evaluated by DPPH and ABTS radical scavenging assays. The tyrosinase inhibitory activities of the rose samples and standard substance were determined by a spectrophotometric method. The antimicrobial effects of RFCS were evaluated in terms of minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) or minimum Fungicidal concentrations (MFCs).

Results

The rose fraction exhibited a high content of biologically active ingredients. The total content of volatile compounds in RFCS was approximately 48.21 ± 2.76 ng/mL. The total phenolic acid content and total flavonoid content were 0.31 ± 0.01 mg/mL and 0.43 ± 0.01 mg/mL, respectively. Its IC₅₀ value in the DPPH assay was 1120 ± 42 μg/mL, and its IC₅₀ value for ABTS radical scavenging activity was 1430 ± 42 μg/mL.RFCS strongly inhibited L-tyrosine oxidation with an IC₅₀ value of 570 ± 21 μg/mL. Every compound identified in RFCS exhibited broad-spectrum antimicrobial activity. F. nucleatum was most susceptible to RFCS with an MIC of 64 μg/mL and MBC of 250 μg/mL.

Conclusions

Due to its rose-like aroma, phenylethyl alcohol may be combined with linalool for use as a natural skin-whitening agent and skin care additive in the and pharmaceutical industries.

Tyrosinase Is a Novel Endogenous Regulator of Developmental and Inflammatory Lymphangiogenesis

Lymphangiogenesis is critically involved in tissue fluid balance, graft rejection, and tumor metastasis. Endogenous regulation of lymphangiogenesis is poorly understood. Herein, we use the lymphatic vessel architecture at the limbal border of the normally avascular cornea, a quantitative trait under strong genetic influence, as a model system to identify new candidate genes regulating lymphangiogenesis. Comparing low-lymphangiogenic BALB/cN with high-lymphangiogenic C57BL/6N mice, we performed quantitative trait loci analysis of five phenotypes in a large BALB/cN × C57BL/6N intercross (n = 795) and identified three to eight genome-wide significant loci, the strongest on chromosome 7 containing tyrosinase (Tyr). Tyrosinase-negative mice showed significantly increased limbal lymph vascularized areas, a higher number of lymphatic vessel end points, and branching points and increased inflammation-induced lymphangiogenesis. These findings confirm that tyrosinase is a novel lymphangiogenesis regulator in developmental and inflammatory lymphangiogenesis. Our findings link melanin synthesis with lymphangiogenesis and open new treatment options in lymphangiogenesis-related diseases.

An albino mutant of the Japanese rat snake (Elaphe climacophora) carries a nonsense mutation in the tyrosinase gene

The Japanese rat snake (Elaphe climacophora) is a common species in Japan and is widely distributed across the Japanese islands. An albino mutant of the Japanese rat snake ("pet trade" albino) has been bred and traded by hobbyists for around two decades because of its remarkable light-yellowish coloration with red eyes, attributable to a lack of melanin. Another albino Japanese rat snake mutant found in a natural population of the Japanese rat snake at high frequency in Iwakuni City, Yamaguchi Prefecture is known as "Iwakuni no Shirohebi". It has been conserved by the government as a natural monument. The Iwakuni albino also lacks melanin, having light-yellowish body coloration and red eyes. Albino mutants of several organisms have been studied, and mutation of the tyrosinase gene (TYR) is responsible for this phenotype. By determining the sequence of the TYR coding region of the pet trade albino, we identified a nonsense mutation in the second exon. Furthermore, RT-PCR revealed that TYR transcripts were not detected in this snake. These findings suggest that mutation of TYR is responsible for the albino phenotype of the pet trade line of the Japanese rat snake. However, the Iwakuni albino did not share this TYR mutation; thus, these two albino lines differ in their origins.

1,2,3-Triazole-based kojic acid analogs as potent tyrosinase inhibitors: Design, synthesis and biological evaluation

A series of kojic acid-derived compounds 6a-p bearing aryloxymethyl-1H-1,2,3-triazol-1-yl moiety were designed by modifying primary alcoholic group of kojic acid as tyrosinase inhibitors. The target compounds 6a-p were synthesized via click reaction. All compounds showed very potent anti-tyrosinase activity (IC₅₀s = 0.06-6.80 µM), being superior to reference drug, kojic acid. In particular, the naphthyloxy analogs 6o and 6p were found to be 31-155 times more potent than kojic acid. The metal-binding study of selected compound 6o revealed that the prototype compound possesses metal-chelating ability, particularly with Cu²⁺ ions. The promising compounds 6o and 6p had acceptable safety profile as demonstrated by cytotoxicity assay against melanoma (B16) cell line and Human Foreskin Fibroblast (HFF) cells.

Search for cytotoxic compounds against ovarian cancer cells: Synthesis, characterization and assessment of the activity of new camphor carboxylate and camphor carboxamide silver complexes

Five silver camphor complexes of formulae [Ag₂(L)(L')₂] (1,3,5) or [Ag(L)₂(L')] (2,4) were synthesized from silver nitrate and the suitable camphor carboxylate (L¹) or camphor carboxamides (L³, L⁴). The complexes were characterized by elemental analysis and spectroscopic techniques (NMR, FTIR, XPS). Computational calculations support coordination of the carboxylate group to silver, in the case of complex 2 and combined mixed keto/carboxylate in the case of complex 1. The stability of the complexes highly relies on the tetrahedral geometry of the lithium ion that binds to four oxygen atoms of the camphor carboxylate ligands. The redox properties of complexes 1 and 4 studied by cyclic voltammetry confirm the facile reduction of the metal sites that depending on the experimental conditions may lead to formation of silver nanoparticles as confirmed by XPS and TEM. Complexes 1, 2 and 4 were tested for cytotoxic activities against A2780 (IC₅₀, 11-14 μM) and A2780 cisplatin resistant (A2780cisR) (IC₅₀, 4-7 μM) cells using the MTT assay. The result showed that the complexes have anticancer activity higher than cisplatin. Complex 1 was also probed for cytotoxicity against the non-tumoral human embryonic kidney (HEK 293, IC₅₀, 62.2 ± 16 μM) cells showing low toxicity in agreement with the silver camphor carboxylate complexes having a considerable selectivity for the ovarian cancer cells A2780 and cisplatin resistant A2780cisR which is a key point under pharmacological uses.

Developments in support materials for immobilization of oxidoreductases: A comprehensive review

Bioremediation, a biologically mediated transformation or degradation of persistent chemicals into nonhazardous or less-hazardous substances, has been recognized as a key strategy to control levels of pollutants in water and soils. The use of enzymes, notably oxidoreductases such as laccases, tyrosinases, various oxygenases, aromatic dioxygenases, and different peroxidases (all of EC class 1) is receiving significant research attention in this regard. It should be stated that immobilization is emphasized as a powerful tool for enhancement of enzyme activity and stability as well as for protection of the enzyme proteins against negative effects of harsh reaction conditions. As proper selection of support materials for immobilization and their performance is overlooked when it comes to comparing performance of immobilized enzyme in academic studies, this review summarizes the current state of knowledge regarding the materials used for enzyme immobilization of these oxidoreductase enzymes for environmental applications. In the presented study, thorough physicochemical characteristics of the support materials was presented. Moreover, various types of reactions and notably operational modes of enzymatic processes for biodegradation of harmful pollutants are summarized, and future trends in use of immobilized oxidoreductases for environmental applications are discussed. Our goal is to provide an improved foundation on which new technological advancements can be made to achieve efficient enzyme-assisted bioremediation.

De Novo Molecular Design of a Novel Octapeptide That Inhibits In Vivo Melanogenesis and Has Great Transdermal Ability

Cutaneous hyperpigmentation from excess melanogenesis causes serious pigmentary disorders and even melasma. Short peptides (SPs) are garnering attention lately owing to their therapeutic potential in dermatological diseases and low systemic side effects. Here, we show an octapeptide, ansin2, designed de novo from antioxidant SPs we previously reported, significantly inhibiting melanogenesis in B16 cells by decreasing tyrosinase production via regulating the MITF pathway. Ansin2 could also inhibit tyrosinase function by covering its catalytic pocket, which was simulated in docking and LIGPLOT studies. Topical application of ansin2 exhibited evident protection in UVB-induced pigmentation in guinea pig models both in terms of prophylaxis and treatment. Interestingly, unlike other hydrophilic and peptidic drugs that need delivery systems, ansin2 can be efficiently delivered topically to the epidermis and dermis per se without an affiliated moiety. Given that ansin2 lacks unwanted toxicities and immunogenicity, it holds great potential in treating hyperpigmentation in the cosmetics and pharmaceutical industries.

Identification of a gene encoding microphthalmia-associated transcription factor and its association with shell color in the clam Meretrix petechialis

The microphthalmia-associated transcription factor (MITF) is a master regulator of melanocyte development through the direct transcriptional control of related genes, e.g., the phenoloxidase gene. In this study, an MITF gene, MpMITF2, was identified in the clam Meretrix petechialis. The full-length cDNA of MpMITF2 was 2026 bp, and the molecular mass of the predicted protein was 42.6 kDa. A basic helix-loop-helix leucine zipper domain was detected in the deduced protein sequence, which can bind the E-box motif within the promoter of the downstream genes. The mRNA of MpMITF2 was more highly expressed in the mantle compared to the other four tissues. Furthermore, there was a significant difference in the mRNA expression of MpMITF2 among three clam strains with different shell colors. The protein level of MpMITF2 was also different among these strains. These results implied that MpMITF2 was associated with shell color formation in the clam M. petechialis. When the mRNA expression of MpMITF2 was knocked down, the new shell showed discontinuous pigment distribution, suggesting that the reduced expression of MpMITF2 influenced pigment synthesis. A gene encoding phenoloxidase (MpPO) was identified as related to the shell color of the clam and was also a putative downstream gene of MITF. Both the mRNA and protein levels of MpPO decreased significantly at 12 h post-MpMITF-suppression, suggesting that MpMITF2 is required for the expression of MpPO. Our results indicate the close relationships among MpMITF2, MpPO and shell color. This study implicates the role of MITF in shell color formation in the clam M. petechialis.

Inhibitors of Melanogenesis: An Updated Review

Melanins are pigment molecules that determine the skin, eye, and hair color of the human subject to its amount, quality, and distribution. Melanocytes synthesize melanin and provide epidermal protection from various stimuli, such as harmful ultraviolet radiation, through the complex process called melanogenesis. However, serious dermatological problems occur when there is excessive production of melanin in different parts of the human body. These include freckles, melasma, senile lentigo, pigmented acne scars, and cancer. Therefore, controlling the production of melanin is an important approach for the treatment of pigmentation related disorderes. In this Perspective, we focus on the inhibitors of melanogenesis that directly/indirectly target a key enzyme tyrosinase as well as its associated signaling pathways.

Electrochemical enzymatic fenitrothion sensor based on a tyrosinase/poly(2-hydroxybenzamide)-modified graphite electrode

This paper reports the electrosynthesis and characterisation of a polymeric film derived from 2-hydroxybenzamide over a graphite electrode and its application as an enzymatic biosensor for the determination and quantification of the pesticide fenitrothion. The material was analysed by scanning electron microscopy and its electrochemical properties characterised by cyclic voltammetry and electrochemical impedance spectroscopy. The enzyme tyrosinase was immobilised over the modified electrode by the drop and dry technique. Catechol was determined by direct reduction of biocatalytically formed o-quinone by employing the flow injection analysis technique. The analytical characteristics of the proposed sensor were optimised as follows: phosphate buffer 0.050 M at pH 6.5, flow rate 5.0 mL min^-1, sample injection volume 150 μL, catechol concentration 1.0 mM and maximum inhibition time by fenitrothion of 6 min. The biosensors showed a linear response to pesticide concentration from 0.018 to 3.60 μM. The limit of detection and limit of quantification were calculated as 4.70 nM and 15.9 nM (RSD < 2.7%), respectively. The intra- and inter-electrode RSDs were 3.35% (n = 15) and 8.70% (n = 7), respectively. In addition, water samples spiked with the pesticide showed an average recovery of 97.6% (±1.53).

The Colorful Sex Chromosomes of Teleost Fish

Teleost fish provide some of the most intriguing examples of sexually dimorphic coloration, which is often advantageous for only one of the sexes. Mapping studies demonstrated that the genetic loci underlying such color patterns are frequently in tight linkage to the sex-determining locus of a species, ensuring sex-specific expression of the corresponding trait. Several genes affecting color synthesis and pigment cell development have been previously described, but the color loci on the sex chromosomes have mostly remained elusive as yet. Here, we summarize the current knowledge about the genetics of such color loci in teleosts, mainly from studies on poeciliids and cichlids. Further studies on these color loci will certainly provide important insights into the evolution of sex chromosomes.

Laccase 1 gene from Plutella xylostella (PxLac1) and its functions in humoral immune response

Laccase (EC 1.10.3.2) is a phenoloxidase found in many insect species. The Laccase 1 gene from Plutella xylostella (PxLac1) was cloned, and its expression patterns and functions were determined using qPCR and RNAi methods. The results showed that the expression levels of PxLac1 were consistently high in all larval stages, and the most abundant was in the midgut during the 4th instar stage. Moreover, the expression of PxLac1 was up-regulated in response to bacterial infection, and decreased 24 h after being parasitized by Cotesia vestalis. Further analyses indicated that the effect of parasitization on PxLac1 was induced by active C. vestalis Bracovirus (CvBV). Haemocyte-free hemolymph phenoloxidase (PO) activity was suppressed when PxLac1 was treated with RNAi. Our results provide evidence for a connection between the Laccase 1 gene and insect immunity, and revealed that parasitoid polydnavirus suppresses host PO activity via PxLac1 regulation.

Adhesive gland transcriptomics uncovers a diversity of genes involved in glue formation in marine tube-building polychaetes

Tube-building sabellariid polychaetes are hermatypic organisms capable of forming vast reefs in highly turbulent marine habitats. Sabellariid worms assemble their tube by gluing together siliceous and calcareous clastic particles using a polyelectrolytic biocement. Here, we performed transcriptomic analyses to investigate the genes that are differentially expressed in the parathorax region, which contains the adhesive gland and tissues, from the rest of the body. We found a large number of candidate genes to be involved in the composition and formation of biocement in two species: Sabellaria alveolata and Phragmatopoma caudata. Our results indicate that the glue is likely to be composed by a large diversity of cement-related proteins, including Poly(S), GY-rich, H-repeat and miscellaneous categories. However, sequences divergence and differences in expression profiles between S. alveolata and P. caudata of cement-related proteins may reflect adaptation to the type of substratum used to build their tube, and/or to their habitat (temperate vs tropical, amplitude of pH, salinity …). Related to the L-DOPA metabolic pathways and linked with the genes that were differentially expressed in the parathorax region, we found that tyrosinase and peroxidase gene families may have undergone independent expansion in the two Sabellariidae species investigated. Our data also reinforce the importance of protein modifications in cement formation. Altogether these new genomic resources help to identify novel transcripts encoding for cement-related proteins, but also important enzymes putatively involved in the chemistry of the adhesion process, such as kinases, and may correspond to new targets to develop biomimetic approaches.

STATEMENTS OF SIGNIFICANCE

The diversity of bioadhesives elaborated by marine invertebrates is a tremendous source of inspiration to develop biomimetic approaches for biomedical and technical applications. Recent studies on the adhesion system of mussel, barnacle and sea star had highlighted the usefulness of high-throughput RNA sequencing in accelerating the development of biomimetic adhesives. Adhesion in sandcastle worms, which involves catechol and phosphate chemistries, polyelectrolyte complexes, supramolecular architectures, and a coacervation process, is a useful model to develop multipurpose wet adhesives. Using transcriptomic tools, we have explored the diversity of genes encoding for structural and catalytic proteins involved in cement formation of two sandcastle worm species, Sabellaria alveolata and Phragmatopoma caudata. The important genomic resource generated should help to design novel "blue" adhesives.

Design, synthesis and evaluation of cinnamic acid ester derivatives as mushroom tyrosinase inhibitors

Tyrosinase is a key enzyme in melanin biosynthesis, and is also involved in the enzymatic browning of plant-derived foods. Tyrosinase inhibitors are very important in medicine, cosmetics and agriculture. In order to develop more active and safer tyrosinase inhibitors, an efficient approach is to modify natural product scaffolds. In this work, two series of novel tyrosinase inhibitors were designed and synthesized by the esterification of cinnamic acid derivatives with paeonol or thymol. Their inhibitory effects on mushroom tyrosinase were evaluated. Most of these compounds (IC50: 2.0 to 163.8 μM) are found to be better inhibitors than their parent compounds (IC50: 121.4 to 5925.0 μM). Among them, (E)-2-acetyl-5-methoxyphenyl-3-(4-hydroxyphenyl)acrylate (5a), (E)-2-acetyl-5-methoxyphenyl-3-(4-methoxyphenyl)acrylate (5g) and (E)-2-isopropyl-5-methylphenyl-3-(4-hydroxyphenyl)acrylate (6a) showed strong inhibitory activities; the IC50 values were 2.0 μM, 8.3 μM and 10.6 μM, respectively, compared to the positive control, kojic acid (IC50: 32.2 μM). Analysis of the inhibition mechanism of 5a, 5g and 6a demonstrated that their inhibitory effects on tyrosinase are reversible. The inhibition kinetics, analyzed by Lineweaver-Burk plots, revealed that 5a acts as a non-competitive inhibitor while 5g and 6a are mixed-type inhibitors. Furthermore, docking experiments were carried out to study the interactions between 6a and mushroom tyrosinase.

Biocatalytic versatility of engineered and wild-type tyrosinase from R. solanacearum for the synthesis of 4-halocatechols

We evaluated the kinetic characteristics of wild type (WT) and three engineered variants (RVC10, RV145, and C10_N322S) of tyrosinase from Ralstonia solanacearum and their potential as biocatalysts to produce halogenated catechols. RV145 exhibited a 3.6- to 14.5-fold improvement in catalytic efficiency (k_cat/K_m) with both reductions in K_m and increases in k_cat compared to WT, making it the best R. solanacearum tyrosinase variant towards halogenated phenols. RVC10 also exhibited increases in catalytic efficiency with all the tested phenols. A single-mutation variant (C10_N322S) exhibited the greatest improvement in k_cat but lowest improvement in catalytic efficiency due to an increase in K_m compared to WT. Consistent with kinetic characteristics, biotransformation experiments showed that RV145 was a superior biocatalyst in comparison to WT. To prevent through conversion of the catechol to quinone, ascorbic acid (AA) was added to the biotransformation medium in 1:2 (substrate:AA) ratio resulting in a catechol yield of > 90%. Flask experiments with 10 mM 4-iodophenol and 10 μg/mL of the RV145 enzyme yielded 9.5 mM 4-iodocatechol in the presence of 20 mM AA in 30 min. Similarly, 10 mM 4-fluorophenol was completely consumed by 20 μg/mL of RV145 enzyme and yielded 9.2 mM 4-fluorocatechol in the presence of 20 mM AA in 80 min. The biotransformation of 20 mM 4-fluorphenol was incomplete (93%) and the yield of 4-flurocatechol was 87.5%. The 4-halophenol conversion rates and product yields obtained in this study are the highest reported using tyrosinase or any other enzyme.

Identification of TYR mutations in patients with oculocutaneous albinism

Oculocutaneous albinism (OCA) is a set of autosomal recessive disorders characterized by hypopigmented hair, skin and eyes. Homozygous or compound heterozygous mutations in the tyrosinase (TYR) gene can cause OCA1, which is the most common and severe subtype of albinism. In the present study, 17 patients with non‑syndromic OCA were enrolled from eight provinces of China and were non‑consanguineous, with the exception of Patient 4000301. Total genomic DNA was isolated from peripheral blood. Screening was performed for the whole exons and their flanking regions of the TYR gene using Sanger sequencing and the pathogenicity of variants was predicted using in silico analysis. In total, 12 TYR mutations were identified in 10 patients, respectively. Of these, two patients carried homozygous mutations and eight patients carried compound heterozygous mutations. Among the 12 TYR mutations, two missense mutations c.1198T>G (p.W400G) and c.819G>T (p.Q273H) were novel. The results of the present study expand the mutation spectrum of the TYR gene, which may further assist in the prenatal examination and genetic diagnosis of OCA.

New insight into the allosteric effect of L-tyrosine on mushroom tyrosinase during L-dopa production

Kinetics studies of L-tyrosine (LTy) ortho-hydroxylation by mushroom tyrosinase (MT) confirmed that MT was severely, but not completely, inhibited at higher concentrations of LTy. Despite the availability of the crystal structure reports, no allosteric site has been identified on MT. To examine the assumption that a non-specific binding site works as a regulatory site, docking simulations were run for the second molecule of L-tyrosine (LTy₂) on the complexes of the first L-tyrosine molecule (LTy₁) with the heavy chain (H) of MT (LTy₁/HMT) and its dimer with the light chain (Ty₁/LHMT). In both, LTy₂ occupied a non-specific binding site (MTPc). MD simulations revealed LTy₂/HMT/LTy₁ and LTy₂/LHMT/LTy₁ were stable. Binding free-energy analysis supported the formation of LTy₂/HMT/LTy₁ and LTy₂/LHMT/LTy₁ at higher concentrations of LTy and disclosed the importance of ΔE_elec and ΔG_polar during binding of LTy₂ to MTPc. Upon LTy₂ binding to MTPc, the Cu-Cu distance remained unchanged while the spatial position of LTy₁ in the active site (MTPa) changed so that it would not be able to participate in ortho-hydroxylation. This study suggests a tuning role for L chain during binding of the ligands to MTPa and MTPc. Given these results, a plausible mechanism was proposed for the MT substrate inhibition.

Methylquercetins stimulate melanin biosynthesis in a three-dimensional skin model

In a previous study, we found that both synthetic 3-O-methylquercetin (3MQ) and 3,4',7-O-trimethylquercetin (34'7TMQ) increased extracellular melanin content. 34'7TMQ increased the activity of melanogenic enzymes by stimulating the p38 pathway and the expression of microphthalmia-associated transcription factor (MITF). In contrast, 3MQ increased the activity of melanogenic enzymes without the involvement of MITF, which suggests that 3MQ inhibits the degradation of melanogenic enzymes. In the present study, we investigated the effects of 3MQ and 34'7TMQ on melanogenesis in normal human melanocytes and using a commercial three-dimensional (3D) skin model system. Both 3MQ and 34'7TMQ elongated the dendrites of normal human melanocytes from a Caucasian donor, but did not stimulate melanogenesis in the melanocytes. In the 3D skin model, which included melanocytes from an Asian donor, 3MQ and 34'7TMQ increased and elongated the melanocytes and showed a tendency to stimulate melanogenesis. These results suggest that 3MQ and 34'7TMQ could be put to practical use in skin care products and agents aimed at preventing hair graying.

Phenols as Diamagnetic T2 -Exchange Magnetic Resonance Imaging Contrast Agents

Although T2 -exchange (T2ex ) NMR phenomena have been known for decades, there has been a resurgence of interest to develop T2ex MRI contrast agents. One indispensable advantage of T2ex MR agents is the possibility of using non-toxic and/or bio-compatible diamagnetic compounds with intermediate exchangeable protons. Herein a library of phenol-based compounds is screened and their T2ex contrast (exchange relaxivity, r2ex ) at 9.4 T determined. The T2ex contrast of phenol protons allows direct detection by MRI at a millimolar concentration level. The effect of chemical modification of the phenol on the T2ex MRI contrast through modulation of exchange rate and chemical shift was also studied and provides a guideline for use of endogenous and exogenous phenols for T2ex MRI contrast. As a proof-of-principle application, phenol T2ex contrast can be used to detect enzyme activity in a tyrosinase-catalyzed catechol oxidation reaction.

Enzymatic browning in avocado (Persea americana) revisited: History, advances, and future perspectives

Considering nearly 80 years of research regarding one of the enzymes responsible for catalyzing the formation of pigments in higher animals, plants, fungi and bacteria, this review will focus on collecting and categorizing the existing information about polyphenol oxidase (PPO) in fruits, with particular emphasis on the information in relation to avocado, which is one of the hardiest species in terms of inactivation, has documented dual activity (EC 1.14.18.1/EC 1.10.3.1), and represents one of the oldest challenges for food science research and fruit processors. It is expected that this review will contribute to the further development of the field by highlighting the questions that have arisen during the characterization of PPO, the progress that has been made and the questions that remain today, in addition to new methodologies that are being applied to study this system. Holistic methodologies offer unexplored potential for advancing our understanding of the complex phenomena that govern PPO activity in fruits, because these methodologies will enable the characterization of this family of enzymes in all of its complexity. Subsequently, it will be possible to develop better techniques for controlling enzymatic browning in this valuable fruit.

Novel tyrosinase inhibitors from liquid culture of Neolentinus lepideus

Tyrosinase is the key enzyme that controls melanin formation in the human skin. We performed a screening of 96 extracts of mushroom cultures and fruiting bodies for examining their inhibitory activity against mushroom tyrosinase. The ethyl acetate extracts of culture filtrate of Neolentinus lepideus exhibited the strongest inhibitory activity. The active compounds 1 and 2 were purified by repeated chromatographic separations from the extract. On the basis of spectroscopic analyses, 1 and 2 were identified to be 1,3-dihydroisobenzofuran-4,5,7-triol and 5-methoxy-1,3-dihydroisobenzofuran-4,7-diol, respectively. Lineweaver-Burk plot of the enzyme reaction in the presence of 1 indicated that 1 was a potent competitive inhibitor. The respective IC₅₀ values of 1 and 2 were 173 and 263 μg/mL. Compound 1 at 15 μg/mL suppressed melanin accumulation stimulated by α-MSH in the murine melanoma B16 cells, as well as the induced accumulation of both tyrosinase transcript and protein without inhibiting cell proliferation.

Predicting tyrosinase inhibition by 3D QSAR pharmacophore models and designing potential tyrosinase inhibitors from Traditional Chinese medicine database

BACKGROUND

Tyrosinase plays a key role in the formation of skin melanin. The excessive accumulation of skin melanin will cause the serious aesthetic problems for human beings.

HYPOTHESIS/PURPOSE

To find the potent tyrosinase inhibitors using computational simulation from TCM Database@Taiwan.

STUDY DESIGN

Inhibitors of tyrosinase have been thought as potential drugs for the decrease of melanin synthesis in the process of pigmentation. To develop new tyrosinase inhibitors, we performed a virtual screening from Traditional Chinese medicine (TCM) and Druglike Databases using the best 3D QSAR pharmacophore model as a 3D search query.

METHODS

A total of 109 compounds were obtained after filtering by Lipinski's rule of five. Finally, 148 compounds (22 from training set, 17 from test set, 109 from TCM and Druglike databases) were selected for further docking studies. De Novo Evolution designed the top 10 candidates from the docking results.

RESULTS

Hypo1 was selected as the best quantitative pharmacophore model, because Hypo1 has characters of the highest cost difference (353.773), the lowest RMS (1.985), the lowest Error (121.440), and the best correlation coefficient (0.933). By the analysis of interaction amino acids in the top 10 hits including two controls, HIS42, HIS60, HIS204, HIS208, ARG209 and VAL218 are identified as the key binding site residues, ARG209 and VAL218 are the critical residues for the inhibitory activity of tyrosinase. This finding is consistent with the results from literatures.

CONCLUSION

De Novo Evolution study suggested Tyrosinase_1*_Evo_4, Tyrosinase_23*_Evo_7, magnolone.cdx_15_Evo_4, compound_2.cdx_2_Evo_2, Compound_B_Evo_5, Compound_C_Evo_9, Compound_D_Evo_6 and malabaricone_C.cdx_3_Evo_10 as the potential tyrosinase inhibitor candidates. De Novo Evolution study also suggested compound_2.cdx_2_Evo_2 as the most potential tyrosinase inhibitor candidate. A total of ten novel leading compounds were identified to have the favorable interaction with tyrosinase by the docking analyses.

Cu(ii) complexes of a tridentate N,N,O-donor Schiff base of pyridoxal: synthesis, X-ray structures, DNA-binding properties and catecholase activity

DNA binding and catecholase activities of two Cu(ii) complexes [Cu(L₁)X] (X = N₃, NCS) of pyridoxal derived ligands are reported.

Skin whitening agents: medicinal chemistry perspective of tyrosinase inhibitors

Melanogenesis is a process to synthesize melanin, which is a primary responsible for the pigmentation of human skin, eye and hair. Although numerous enzymatic catalyzed and chemical reactions are involved in melanogenesis process, the enzymes such as tyrosinase and tyrosinase-related protein-1 (TRP-1) and TRP-2 played a major role in melanin synthesis. Specifically, tyrosinase is a key enzyme, which catalyzes a rate-limiting step of the melanin synthesis, and the downregulation of tyrosinase is the most prominent approach for the development of melanogenesis inhibitors. Therefore, numerous inhibitors that target tyrosinase have been developed in recent years. The review focuses on the recent discovery of tyrosinase inhibitors that are directly involved in the inhibition of tyrosinase catalytic activity and functionality from all sources, including laboratory synthetic methods, natural products, virtual screening and structure-based molecular docking studies.

Structural and kinetic considerations on the catalysis of deoxyarbutin by tyrosinase

Deoxyarbutin, a potent inhibitor of tyrosinase, could act as substrate of the enzyme. Oxytyrosinase is able to hydroxylate deoxyarbutin and finishes the catalytic cycle by oxidizing the formed o-diphenol to quinone, while the enzyme becomes deoxytyrosinase, which evolves to oxytyrosinase in the presence of oxygen. This compound is the only one described that does not release o-diphenol after the hydroxylation step. Oxytyrosinase hydroxylates the deoxyarbutin in ortho position of the phenolic hydroxyl group by means of an aromatic electrophilic substitution. As the oxygen orbitals and the copper atoms are not coplanar, but in axial/equatorial position, the concerted oxidation/reduction cannot occur and the release of a copper atom to bind again in coplanar position, enabling the oxidation/reduction or release of the o-diphenol from the active site to the medium. In the case of deoxyarbutin, the o-diphenol formed is repulsed by the water due to its hydrophobicity, and so can bind correctly and be oxidized to a quinone before being released. Deoxyarbutin has been characterized with: [Formula: see text] = 1.95 ± 0.06 s-1 and [Formula: see text] = 33 ± 4 μM. Computational simulations of the interaction of β-arbutin, deoxyarbutin and their o-diphenol products with tyrosinase show how these ligands bind at the copper centre of tyrosinase. The presence of an energy barrier in the release of the o-diphenol product of deoxyarbutin, which is not present in the case of β-arbutin, together with the differences in polarity and, consequently differences in their interaction with water help understand the differences in the kinetic behaviour of both compounds. Therefore, it is proposed that the release of the o-diphenol product of deoxyarbutin from the active site might be slower than in the case of β-arbutin, contributing to its oxidation to a quinone before being released from the protein into the water phase.

Action of tyrosinase on caffeic acid and its n-nonyl ester. Catalysis and suicide inactivation

Different mechanisms for inhibiting tyrosinase can be designed to avoid postharvest quality losses of fruits and vegetables. The action of tyrosinase on caffeic acid and its n-nonyl ester (n-nonyl caffeate) was characterized kinetically in this work. The results lead us to propose that both compounds are suicide substrates of tyrosinase, for which we establish the catalytic and inactivation efficiencies. The ester is more potent as inactivator than the caffeic acid and the number of turnovers made by one molecule of the enzyme before its inactivation (r) is lower for the ester. We proposed that the anti-browning and antibacterial properties may be due to suicide inactivation processes.