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.

Computationally Guided Enzymatic Studies on Schizochytrium-Sourced Malonyl-CoA:ACP Transacylase.

The malonyl-CoA:ACP transacylase (MAT) domain is responsible for the selection and incorporation of malonyl building blocks in the biosynthesis of polyunsaturated fatty acids (PUFAs) in eukaryotic microalgae (Schizochytrium) and marine bacteria (Moritella marina, Photobacterium profundum, and Shewanella). Elucidation of the structural basis underlying the substrate specificity and catalytic mechanism of the MAT will help to improve the yield and quality of PUFAs. Here, a methodology guided by molecular dynamics simulations was carried out to identify and mutate specificity-conferring residues within the MAT domain of Schizochytrium. Combining mutagenesis, cell-free protein synthesis, and in vitro biochemical assay, we dissected nearby interactions and molecular mechanisms relevant for binding and catalysis and found that the reorientation of the Ser154 Cß-Oγ bond establishes distinctive proton-transfer chains (His153-Ser154 and Asn235-His153-Ser154) for catalysis. Gln66 can be replaced by tyrosine to shorten the distance between His153 (Nε2) and Ser154 (Oγ), which facilitates a faster proton-transfer rate, allowing better use of acyl substrates than the wild type. Furthermore, we screened a mutant that displayed an 18.4% increase in PUFA accumulation. These findings provide important insights into the study of MAT through protein engineering and will benefit dissecting the molecular mechanisms of other PUFA-related catalytic domains.

Production of polyunsaturated fatty acids by Schizochytrium (Aurantiochytrium) spp.

Diverse health benefits are associated with dietary consumption of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFA), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Traditionally, these fatty acids have been obtained from fish oil, but limited supply, variably quality, and an inability to sustainably increase production for a rapidly growing market, are driving the quest for alternative sources. DHA derived from certain marine protists (heterotrophic thraustochytrids) already has an established history of commercial production for high-value dietary use, but is too expensive for use in aquaculture feeds, a much larger potential market for ω-3 LC-PUFA. Sustainable expansion of aquaculture is prevented by its current dependence on wild-caught fish oil as the source of ω-3 LC-PUFA nutrients required in the diet of aquacultured animals. Although several thraustochytrids have been shown to produce DHA and EPA, there is a particular interest in Schizochytrium spp. (now Aurantiochytrium spp.), as some of the better producers. The need for larger scale production has resulted in development of many strategies for improving productivity and production economics of ω-3 PUFA in Schizochytrium spp. Developments in fermentation technology and metabolic engineering for enhancing LC-PUFA production in Schizochytrium spp. are reviewed.

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.

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 ±â€¯1.64 µM and KI 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 ±â€¯0.43 and 40.13 ±â€¯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.

Polyoxometalates: Study of inhibitory kinetics and mechanism against α-glucosidase.

Alpha-glucosidase is considered to be an important target for the treatment of noninsulin-dependent diabetes. In this work, the inhibitory effects of polyoxometalates (POMs) affected by three different factors (heteroatom, transition metal substitution element and vanadium substitution number) on α-glucosidase were studied. We found that POMs with Keggin-type and vanadium-substituted Dawson-type structures act as effective and mostly competitive inhibitors for α-glucosidase (IC50 values around 40-160 µM), and most compounds can compete with the substrate for the active site of α-glucosidase. By analyzing and comparing the inhibitory effects of each series of POMs on α-glucosidase, the results demonstrated that the structure and composition of the POMs themselves may indirect influence on their inhibitory capabilities. Moreover, we gained initial information about the structure-inhibition relationship of different POMs. More intriguingly, molecular docking simulation suggested that all compounds bind into the active site of α-glucosidase by multiple van-der-Waals and hydrogen bond interactions. Our kinetic data demonstrate the considerable potential of POMs for the development of clinically valuable α-glucosidase inhibitors.

Uranium-rich diagenetic fluids provide the key to unconformity-related uranium mineralization in the Athabasca Basin.

The Proterozoic Athabasca Basin is well known for its unusually large-tonnage and high-grade 'unconformity-related' uranium (U) deposits, however, explanations for the basin-wide U endowment have not been clearly identified. Previous studies indicate that U-rich brines with up to ~600 ppm U and variable Na/Ca ratios (from Na-dominated to Ca-dominated) were present at the sites of U mineralization, but it is unknown whether such fluids were developed solely in the vicinity of the U deposits or at a basinal scale. Our microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz overgrowths from the barren part of the basin indicate that U-rich brines (0.6 to 26.8 ppm U), including Na-dominated and Ca-dominated varieties, were widely developed in the basin. These U concentrations, although not as high as the highest found in the U deposits, are more than two orders of magnitude higher than most naturally occurring geologic fluids. The basin-scale development of U-rich diagenetic fluids is interpreted to be related to several geologic factors, including availability of basinal brines and U-rich lithologies, and a hydrogeologic framework that facilitated fluid circulation and U leaching. The combination of these favorable conditions is responsible for the U fertility of the Athabasca Basin.

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 ±â€¯0.38 µM, 52.33 ±â€¯1.41 µM, 161.90 ±â€¯7.68 µM and 103.10 ±â€¯2.88 µM, respectively. Moreover, H3PMo12O40, Na4PMo11VO40, and Na7PMo11CoO40 are reversible, competitive inhibitors with KI values of 0.018 mM, 0.146 mM and 0.121 mM, respectively. Na6PMo11FeO40 inhibited α-glucosidase in a reversible noncompetitive manner with KI and KIS 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.