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Japanese encephalitis virus (JEV) is a mosquito-borneFlavivirus, which may cause severe encephalitis in humans, horses, and other animals. TIM-1 has been identified to be a receptor that promotes various viruses to enter into target cells in recent years. In the present study, we found that TIM-1 protein was significantly increased in A549 cells at the late stage of JEV infection, while the transcription levels of TIM-1 remained unaltered. Interestingly, we found that NS1’ protein plays a key role in increasing the expression of TIM-1 in cells infected with JEV. Further, we found that the NS1’ protein also efficiently regulates TIM-1 protein to distribute in the cytoplasm in JEV-infected cells, and the amount of TIM-1 protein located on the cell membrane was reduced instead. As a consequence, NS1’ protein antagonize TIM-1 mediated viral restriction for further viral infection and propagation in the late stage of infection. In molecular mechanism, the molecular weight of TIM-1 increased a bit in the present of NS1’. Expression of NEU1 down-regulated TIM-1 expression and oseltamivir treatment increased the expression of TIM-1. Therefore, our data indicated that JEV NS1’ protein facilitated the sialylation modification of TIM-1 to up-regulate the level of TIM-1 expression and regulate its distribution. Collectively, our study revealed that JEV NS1’ protein regulates the expression and distribution of TIM-1 by facilitating its sialylation to antagonize TIM-1-mediated JEV restriction for further infection. Understanding the functional interplays between TIM-1 and NS1’ proteins will offer new insights into virushost interaction.IMPORTANCET-cell immunoglobulin and mucin domain protein 1 (TIM-1) is known to promote cellular entry of various enveloped viruses. We discovered a novel phenomenon of dynamic expression and functional regulation of TIM-1 during JEV infection. Firstly, TIM-1 protein increased in the cytoplasm at the late stage of JEV infection. Furthermore, JEV NS1’ protein up-regulated the intracellular expression of TIM-1 and antagonize TIM-1-mediated viral restriction for further viral infection. In molecular mechanism, JEV NS1’ protein facilitated the sialylation of TIM-1 to increase the level of TIM-1 expression and cytoplasm distribution. Taken together, at the late stage of infection, JEV employs a strategy in which NS1’ promotes JEV release by promoting the sialylation of TIM-1, causing it to be primarily localized in the cytoplasm. Therefore, we discovered new functions of TIM-1 and JEV NS1’ during the process of JEV infection, and provide a new insight into the interactions between JEV and cell hosts.

In this study, the antiglycation potential and mechanisms of vitexin were explored in vitro by multispectroscopy, microscope imaging, high-resolution mass spectrometry, and computational simulations. Vitexin was found to show much stronger antiglycation effects than aminoguanidine. The inhibition against the fluorescent advanced glycation end products was more than 80% at 500 μM vitexin in both bovine serum albumin (BSA)-fructose and BSA-methylglyoxal (MGO) models. Treated with 100 and 200 μM vitexin for 24 h, the contents of MGO were reduced to 4.97 and 0.2%, respectively, and only one vitexin-mono-MGO adduct was formed. LC-Orbitrap-MS/MS analysis showed that vitexin altered the glycated sites and reduced the glycation degree of some sites. The mechanisms of vitexin against protein glycation were mainly through BSA structural protection, MGO trapping, and alteration of glycation sites induced by interaction with BSA. These findings provided valuable information about the functional development of vitexin as a potential antiglycation agent.

Japanese encephalitis virus (JEV) is a major causative agent of neurological infection affecting humans and pigs. Human T Cell Immunoglobulin and Mucin Domain 1 (hTIM-1) enhances the infection of JEV through virion-associated phosphatidylserine (PS) binding. Here, five swine TIM-1 (sTIM-1) gene variants were cloned from pig lung tissues by reverse-transcriptase polymerase chain reaction (RT-PCR). Sequence alignment analysis revealed that the gene homology between the sTIM-1 and hTIM-1 was 42.3-43.8%. Furthermore, ectopic expression of all five sTIM-1 variants in 293 T cells can promote JEV entry and infection. However, sTIM-1 V3 exhibited significantly less potent at promoting virus entry compared to the other four variants. Further studies revealed that the 34th amino acid of sTIM-1is critical for the entry of JEV, which is Pro34 in sTIM-1V3 while Leu34 in other four sTIM-1 variants. Mechanically, leucine at locus 34 was associated with the membrane distribution of sTIM-1, thereby affecting viral entry and infection. In total, our findings provide evidence that the PS receptor sTIM-1 promotes the infection of JEV and that the 34th amino acid position is critical for sTIM-1 to mediate viral infection.

The inhibition mechanism of epicatechin gallate (ECG) on tyrosinase was investigated by multispectroscopic techniques combined with molecular docking and molecular dynamics simulation. The results demonstrated that ECG suppressed the activity of tyrosinase in a reversible mixed-inhibition with a half inhibitory concentration (IC50) of (1.13 ± 0.82) × 10-5 mol L-1. Binding of ECG to tyrosinase led to the formation of a complex with the binding constant (Ksv) of 4.03 × 104 L mol-1 at 298 K which was stabilized by hydrophobic forces. The complex formation induced the intrinsic fluorescence quenching and secondary structure change of tyrosinase. Molecular docking results showed that hydrophobic and hydrogen bonding forces played a dominant role in the binding of ECG to tyrosinase, affecting the binding affinity of l-dopa to tyrosinase, leading to a decrease in tyrosinase activity. Molecular dynamics analysis indicated that ECG led to the stretching of the basic framework structure of tyrosinase and slightly influenced the microenvironment of amino acid residues. The research might provide new perspectives on the inhibition mechanism of epicatechin gallate on tyrosinase and a theoretical basis for the prevention and treatment of pigmented skin diseases and anti-browning of catechin as a food supplement.

Ferulic acid (FA), a phenolic acid widely occurring in nature, has attracted extensive attention because of its biological activity. Ovalbumin (OVA) is a commonly used carrier protein. The mechanism of FA binding with OVA was investigated by utilizing a variety of spectral analyses, accompanied by computer simulation.It was discovered that the fluorescence quenching mechanism of OVA by FA was a static mode as a result of the formation of an FA-OVA complex, which was verified by the concentration distributions and pure spectrum of the constituents decomposed from the high overlap spectrum signals using multivariate curve resolution-alternate least squares algorithm. Hydrogen bonds and Van der Waals forces drove the formation of FA-OVA complex with a binding constant of 1.69 × 10The study may supply the theoretical basis for the design of FA transport system using OVA as carrier protein to improve the instability and low bioavailability of FA. © 2021 Society of Chemical Industry.

Glutenin has limited applicability in food industry due to poor water solubility and emulsifying properties. In this study, the physicochemical properties of glutenin were improved by combined treatments of alkaline pH-shifting or acidic pH with heating. The surface morphology, structure and physicochemical properties were measured during the modification process of glutenin. Results showed that the smaller square clusters and regular tubular fibrils were observed in modified glutenin and the α-helix proportion of the treated glutenin was finally increased to 59.90 ± 0.01%. Compared with untreated glutenin, the combined treatments of pH-shifting with heating as well as fibrillation process increased the solubility of glutenin by 21.3 and 3.5 times, respectively. Moreover, the treated glutenin showed excellent emulsifying stability (EAI: 50.84 ± 0.51 m

AIMS AND OBJECTIVES To investigate the feasibility of using peripheral perfusion index (PPI) to monitor acute limb ischaemia (ALI) in newborns after catheterisations. BACKGROUND ALI is common complication of neonatal peripheral artery cannulation. It is important to address as soon as the early signs of ALI. PPI could aid in noninvasive evaluation of distal extremity perfusion in an effort to notify risk of potential ischaemic injury from catheterisations. DESIGN A nested case-control study. METHODS Clinical information of newborns who had been admitted to the Neonatal Intensive Care Unit of Jiangxi Provincial Children's Hospital and had received peripheral artery cannulation from January 2018 to January 2020 was prospectively collected. Transcutaneous blood oxygen saturation (TcSO2 ), PPI and delta-PPI (ΔPPI1; the difference in PPI values of the two arms. ΔPPI2; difference in the PPI values before and after cannulation) were recorded. We used STROBE checklist as an EQUATOR in this study. RESULTS A total of 25 newborns with ALI were included in the study. These were then paired with 100 newborns without ALI. The PPI and TcSO2 of the cannulated limb were significantly lower in the ALI group than in the non-ALI (NALI) group (p

Isoeugenol, a natural phenolic compound in plant essential oils, is known to have many biological and pharmacological properties. In the present work, the interaction of isoeugenol with calf thymus DNA (ctDNA) and its protective effect on DNA oxidative damage were investigated by multispectroscopic techniques, viscosity measurements, gel electrophoresis studies and molecular simulation. Analyses of ultraviolet-visible (UV–vis) absorption and fluorescence spectra indicated that isoeugenol could bind to ctDNA with a binding constant on the order of 103 L mol−1, which was mainly driven by hydrogen bonding and van der Waals forces. The results from the viscosity measurements, competitive displacement studies and circular dichroism (CD) analysis indicated that the binding of isoeugenol to ctDNA was in the groove mode and that the A–T base pairs in the minor grooves of ctDNA were the main binding sites for isoeugenol, which was supported by molecular docking analyses. In addition, isoeugenol was found to show a protective effect against hydroxyl-induced DNA damage, which may be explained by its good antioxidant activity. These findings may improve the understanding of the mechanism of interaction between isoeugenol and ctDNA and provide a theoretical basis for the development of isoeugenol in the food and drug industry.

Japanese encephalitis virus (JEV) is a flavivirus transmitted by mosquitoes that causes severe encephalitis in humans and animals. It has been suggested that AXL, a transmembrane protein, can promote the replication of various flaviviruses, such as dengue (DENV), Zika (ZIKV), and West Nile (WNV) viruses. However, the effect of AXL on JEV infection has not yet been determined. In the present study, we demonstrate that AXL is down-regulated after JEV infection in the late stage. JEV NS2B-3 protein specifically interacted with AXL, and promoted AXL degradation through the ubiquitin–proteasome pathway. AXL-degradation increased cell apoptosis by disrupting phosphatidylinositol 3-kinase (PI3K)/Akt signal transduction. In addition, the degradation of AXL promoted JEV release to supernatant, whereas the virus in the cell lysates decreased. The supplementation of AXL ligand Gas6 inhibited the JEV-mediated degradation of AXL. Altogether, we discover a new function of NS2B-3 during the process of JEV replication, and provide a new insight into the interactions between JEV and cell hosts. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12250-021-00442-3.

The Japanese encephalitis serogroup of the neurogenic Flavivirus has a specific feature that expresses a non-structural protein NS1′ produced through a programmed -1 ribosomal frameshifting (-1 PRF). Herein, C19orf66, a novel member of interferon-stimulated gene (ISG) products, exhibited significant activity of antagonizing Japanese encephalitis virus (JEV) infection. Overexpression of C19orf66 in 293T cells significantly inhibited JEV replication, while knock-down of endogenous C19orf66 in HeLa cells and A549 cells significantly increased virus replication. Notably, C19orf66 had an inhibitory effect on frameshift production of JEV NS1′. The inhibition was more significant when C19orf66 and JEV NS1-NS2A were co-expressed in the 293T cells. Both C19orf66-209 and C19orf66-Zinc(mut) did not significantly change the NS1′ to NS1 ratio and had weaker antiviral effects than C19orf66. Similarly, C19orf66-209 and C19orf66-Zinc(mut) had no significant effect on the expression of the JEV NS3 protein, whose expression was down-regulated by C19orf66 via the lysosome-dependent pathway. These findings suggest that C19orf66 may possess at least two different mechanisms of antagonizing JEV infection. This study identified C19orf66 as a novel interferon-stimulated gene product that can inhibit JEV replication by targeting -1 PRF and the NS3 protein. The study provides baseline information for the future development of broad-spectrum antiviral agents against JEV. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12250-021-00423-6.

4-Octylphenol (OP) is an environmental estrogen that can enter organisms through the food chain and cause various toxic effects. Here, the interaction between OP and human serum albumin (HSA) was explored through multipectral, molecular docking and dynamics simulation. The results showed that OP and HSA formed a ground state complex through a static quenching mechanism, and the interaction was spontaneously driven by hydrogen bonds and hydrophobic interaction forces. The binding constant at different temperatures was measured to be on the order of 105 L mol-1. Site competition experiments suggested that OP interacted with amino acid residues Lys195, Cy245 and Cys246 located at the Sudlow site I of HSA, resulting in a more stretched protein peptide. The presence of OP increased the surface hydrophobicity of HSA, and reduced the content of α-helix in HSA by 3.4%. FT-IR spectra showed that OP interacted with the C=O and C-H groups of the polypeptide backbone. Molecular docking demonstrated that OP mainly bound to Site I of HSA and hydrogen bonds participated in the interaction. In addition, molecular dynamics simulations further explored the stability and dynamic behavior of the OP-HSA complex through RMSD, RMSF, SASA and Rg.

Inhibition of tyrosinase activity contributes to the control of food browning and skin pigmentation diseases. Herein, the inhibitory mechanism of epigallocatechin-3-gallate (EGCG) and gallocatechin gallate (GCG) on tyrosinase were investigated. Both EGCG and GCG inhibited tyrosinase in a mixed manner with the IC50 values of 39.4 ± 0.54 μM and 36.8 ± 0.21 μM, and showed a synergism with their combination, while EGCG and GCG combined with kojic acid (IC50 = 19.2 ± 0.26 μM) exhibited antagonism and additive effect, respectively. EGCG and GCG interacted with tyrosinase mainly by hydrogen bonding and hydrophobic interactions and induced a looser conformation of tyrosinase. Molecular docking indicated that EGCG and GCG bound to the active center of tyrosinase and interacted with copper ions and key amino acid residues. Molecular dynamics simulation further characterized the structure and property of EGCG/GCG–tyrosinase complex. This study provides novel insights into the mechanism of catechins as tyrosinase inhibitors.

4–Octylphenol is an endocrine disruptor, belonging to environmental estrogens. It can be enriched in the human body through the food chain and may harm human health. Herein, we used a variety of spectroscopic techniques, molecular docking, and gel electrophoresis to study the interaction of 4–octylphenol and ctDNA. It was found that the mechanism of ctDNA quenching the endogenous fluorescence of 4–octylphenol was static quenching, and formed a complex. The negative enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) have shown that 4–octylphenol and ctDNA spontaneously bind together under the action of hydrogen bonds and van der Waal's force. Viscosity, melting temperature and iodide quenching experiments showed that 4–octylphenol acted on the groove of ctDNA. Insignificant change in circular dichromism spectra further confirmed this binding mode. The binding sites and groups for 4–octylphenol and ctDNA interaction were identified by molecular docking. Gel electrophoresis found that 4–octylphenol at high concentrations caused DNA cleavage. Above findings may lay a theoretical foundation for understanding the toxicity mechanism of 4–octylphenol.

Suppression of xanthine oxidase (XO) may contribute to control hyperuricemia and gout. In this study, baicalein and baicalin, two dietary flavones, were found to inhibit the formation of uric acid and generation of superoxide anion (O2−) catalysed by XO through interaction with primary amino acid residues located in flavin adenine dinucleotides center of XO. Baicalein or baicalin binding to XO mainly facilitated by hydrophobic interactions and hydrogen bonds resulted in more compact of XO structure. The concentration profiles and pure spectra of the components extracted from highly overlapping spectral signal by multivariate curve resolution–alternating least squares chemometrics algorithm confirmed the formation of complexes and monitored the reaction kinetics process between XO and these flavones. Furthermore, the isobolographic analysis found that baicalein or baicalin exhibited a moderate synergy on the inhibition of XO when it combined with allopurinol as well as the joint use of baicalein and baicalin.

The postprandial hyperglycemia of diabetic patients is associated with a-amylase and a-glucosidase, searching safer enzyme inhibitors and deciphering their inhibition mechanism are important. In this study, gallocatechin gallate (GCG) was found to exert strong inhibition on α-amylase and α-glucosidase in the mixed-type and non-competitive manners, respectively. GCG could bind with α-amylase and α-glucosidase to form the complexes, which induced conformational changes of the two carbohydrate digestive enzymes. Docking analysis verified that GCG interacted with pivotal amino acids within the active site of α-amylase, while it bound to a site close to the active site of α-glucosidase, which might affect active site, causing declines in a-amylase and α-glucosidase activities. Moreover, the combination of GCG with acarbose increased the inhibition of α-amylase and α-glucosidase and reduced the dosage of acarbose. This study may provide theoretical basis for designing novel functional foods of GCG for the prevention and treatment of diabetes.

Betulinic acid (BA), an important pentacyclic triterpene widely distributed in many foods, possesses high antidiabetic activity. In this study, BA was found to exhibit stronger inhibition of α-glucosidase than acarbose with an IC50 value of (1.06 ± 0.02) × 10–5 mol L–1 in a mixed-type manner. BA bound with α-glucosidase to form a BA−α-glucosidase complex, resulting in a more compact structure of the enzyme. The obtained concentrations and spectra profiles of the components resolved by the multivariate-curve resolution–alternating least-squares confirmed the formation of the BA−α-glucosidase complex. Molecular docking showed that BA tightly bound to the active cavity of α-glucosidase, which might hinder the entrance of the substrate leading to a decline in enzyme activity. The chemical modification of α-glucosidase verified the results of the computer simulation that the order of importance of the four amino acid residues in the binding process was His > Tyr > Lys > Arg.

5−Hydroxymethyl−2−furaldehyde (5-HMF) in dairy food products generated via Maillard reaction may bring health risks. Herein, the interaction of 5-HMF with β-casein (β-CN) and its influences on the structure and function of β-CN were investigated. 5-HMF was found to quench the inherent fluorescence of β-CN by a static mode and the binding constant was in the order of magnitude of 104 L mol−1. Thermodynamic analysis indicated that hydrophobic forces played the major role in the interaction. The results of synchronous and three-dimensional fluorescence revealed that 5-HMF changed the microenvironment of tyrosine and tryptophan residues and interfered the stability of the polypeptide backbone structure in β-CN. Molecular docking revealed that 5-HMF bound to the hydrophobic cavity of β-CN mainly interacting with the amino acid residues Pro196, Val155, Leu163, Phe157 and Leu192. The binding of 5-HMF with β-CN caused partial unfolding of β-CN conformation, resulting in the increase in surface hydrophobicity and emulsifiability, and decrease in emulsification stability of β-CN, thereby reducing the solubility of β-CN. The study might facilitate the comprehensive understanding of 5-HMF affecting the structure and functional properties of β-CN.

The inhibition of pancreatic lipase by apigenin, a natural dietary flavonoid, was investigated by various spectroscopic techniques and computational simulation. The results showed that apigenin reversibly inhibited pancreatic lipase activity in a competitive manner with an IC50 value of 0.45 ± 0.03 mM, and its combination with orlistat showed a synergistic effect. Formation of a complex between apigenin and pancreatic lipase driven by hydrogen bonds resulted in the fluorescence quenching of the enzyme through a static manner. The binding constant of apigenin with the enzyme was (5.47 ± 0.01) × 104 L mol−1 at 298 K, and the kinetic process of their interaction was characterized by the resolved concentration profiles and pure spectra of different components from the multivariate curve resolution-alternating least squares algorithm. The inhibition of pancreatic lipase by apigenin was mainly attributed to the tighter structure of the enzyme and the interaction between apigenin and the amino acid residues in the active center of the enzyme to prevent the substrate from being oxidized, as demonstrated by the analysis of circular dichroism spectra and molecular docking. Molecular dynamics simulation further characterized the binding conformation and property of apigenin-pancreatic lipase complex. This study provides novel insights into the mechanism of apigenin as pancreatic lipase inhibitor and the development of apigenin as an anti-obesity nutrient.

In this study, the interaction between di-(2-ethylhexyl) phthalate (DEHP) and calf thymus DNA (ctDNA) was investigated by a combination of multispectroscopic methods, chemometrics algorithm, cyclic voltammetry and molecular simulation. The concentration profiles of the components obtained from resolving the UV–vis absorption data by multivariate curve resolution–alternating least-squares (MCR–ALS) provided a basic evidence for the formation of DEHP–ctDNA complex. Furthermore, the groove binding of DEHP to ctDNA was evidenced by the results from iodide quenching effect, single-stranded DNA quenching effect, melting studies, viscosity measurements and cyclic voltammetry. The binding constant of the complex was in the order of magnitudes of 104 L mol−1, and hydrophobic forces were inferred to drive the binding process. Analysis of Fourier transform infrared spectra suggested that DEHP preferentially bound to A–T rich region of ctDNA in the minor groove, and these results further confirmed by molecular docking. The circular dichroism spectra indicated that DEHP induced a decrease in base stacking degree and an increase in right-handed helicity of ctDNA, but did not cause a significant damage in DNA. This study may improve the understanding of interaction between DEHP and ctDNA and help evaluate the toxicological effect of DEHP.

A modified biuret method suitable for protein determination of corn-based products was developed by introducing a combination of an alkaline reagent with sodium dodecyl sulfate (reagent A) and heat treatments. The method was tested on seven corn-based samples. The results showed mostly good agreement (P>0.05) as compared to the Kjeldahl values. The proposed method was found to enhance the accuracy of prediction on zein content using bovine serum albumin as standard. Reagent A and sample treatment were proved to effectively improve protein solubilization for the thermally-dried corn-based products, e.g. corn gluten meal. The absorbance was stable for at least 1-h. Moreover, the whole measurement of protein content only needs 15-20min more than the traditional biuret assay, and can be performed in batches. The findings suggest that the proposed method could be a timesaving alternative for routine protein analyses in corn processing factories.

Dihydromyricetin (DMY), a natural flavonoid, was found to effectively inhibit tyrosinase activity in a mixed-type manner with an IC50 value of (3.66 ± 0.14) × 10-5 mol L-1. DMY combined with the dietary vitamin D3 at lower concentrations exhibited a synergistic effect on the inhibition of tyrosinase. The formation of a DMY-tyrosinase complex led to fluorescence quenching and conformational changes of tyrosinase, which was driven mainly by hydrophobic interactions and hydrogen bonds. The molecular simulation further found that DMY inserted into the active pocket of tyrosinase interacted with amino acid residues Tyr78, His85, and Ala323, occupying the catalytic center of tyrosinase to hinder entrance of the substrate, leading to the inhibition of tyrosinase. This study may provide a scientific foundation for screening effective tyrosinase inhibitors.

Porous organosilica monoliths have attracted much attention from both the academic and industrial fields due to their porous structure, excellent mechanical property and easily functionalized surface. A new mercapto-functionalized silicone monolith from a precursor mixture containing methyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyl(dimethoxy)methylsilane prepared via a two-step acid/base hydrolysis&ndash, polycondensation process was reported. Silane precursor ratios and surfactant type were varied to control the networks of porous monolithic gels. Gold nanoparticles were loaded onto the surface of the porous organosilica monolith (POM). Versatile characterization techniques were utilized to investigate the properties of the synthesized materials with and without gold nanoparticles. Scanning electron microscopy was used to investigate the morphology of the as-synthesized porous monolith materials. Fourier transform infrared spectroscopy was applied to confirm the surface chemistry. 29Si nuclear magnetic resonance was used to investigate the hydrolysis and polycondensation of organosilane precursors. Transmission electron microscopy was carried out to prove the existence of well-dispersed gold nanoparticles on the porous materials. Ultraviolet&ndash, visible spectroscopy was utilized to evaluate the high catalytic performance of the as-synthesized Au/POM particles

Background The suppression of α-glucosidase activity to retard glucose absorption is an important therapy for type-2 diabetes. Corosolic acid (CRA) is a potential antidiabetic component in many plant-based foods and herbs. In this study, the interplay mechanism between α-glucosidase and corosolic acid was investigated by several methods, including three-dimensional fluorescence spectra, circular dichroism spectra, and molecular simulation. Results Corosolic acid significantly inhibited α-glucosidase reversibly in an uncompetitive manner and its IC50 value was 1.35 × 10-5 mol L-1 . A combination of CRA with myricetin exerted a weak synergy against α-glucosidase. The intrinsic fluorescence of α-glucosidase was quenched via a static quenching course and the binding constant was 3.47 × 103 L mol-1 at 298 K. The binding of CRA to α-glucosidase was mainly driven by hydrophobic forces and resulted in a partial extension of the protein polypeptide chain with a loss of α-helix content. The molecular simulation illustrated that CRA bound to the entrance part of the active center of α-glucosidase and interacted with the amino acid residues Ser157, Arg442, Phe303, Arg315, Tyr158, and Gln353, which could hinder the release of substrate and catalytic reaction product, eventually suppressing the catalytic activity of α-glucosidase. Conclusions These results may suggest new insights into corosolic acid from food sources as a potential α-glucosidase inhibitor that could better control diabetes. © 2019 Society of Chemical Industry.

Protein glycation can produce the advanced glycation end products (AGEs), which has a potential health risk due to its relevance with diabetic complications. Searching for potent inhibitors to suppress hyperglycemia-induced protein glycation is of great significance. Here, we probed the anti-glycation potential of epicatechin gallate (ECG), an important ingredient of green tea, by spectroscopy and chromatography supplemented by molecular docking. It was found that ECG suppressed the carbonylation and the formation of amyloid cross-β structures of bovine serum albumin (BSA) as well as the generation of AGEs in BSA–fructose model by 65.6%, 73.7% and 87.0%, resepctively. A combination of ECG with epigallocatechin gallate (EGCG) at molar ratios from 0.5:1 to 2:1 exhibited the interactive effects on AGEs formation from moderate antagonism to synergy. Moreover, ECG at 44.2 μg/mL showed a trapping efficiency of 81.6% for the important precursor methylglyoxal (MGO) of AGEs within 24 h, and the formed ECG–mono-MGO and ECG–di-MGO adducts were verified by LC–QqQ–MS analysis. The inhibitory effect of ECG on the protein glycation may be due to its MGO trapping and the specific binding with certain amino acid residues of BSA. These findings may provide the theoretical basis for the development of ECG as an inhibitor of protein glycation.

Osthole, a type of coumarin derivative, owns many biological functions, but the poor water solubility and low bioavailability limit its usage in food and pharmaceutical fields. β-Lactoglobulin (BLG) is a major protein in bovine milk whey which is usually used as a carrier of poorly soluble bioactive components. Researching the interaction between osthole and BLG can help us in understanding their binding mechanism and design an osthole delivery system using BLG as carrier protein to further promote the application of osthole in functional food and drug. Hence, this study was devoted to explore the binding properties of osthole with BLG and the effect on the protein structure by employing multispectroscopic approaches, chemometrics and molecular simulation studies. The results of the concentration profiles and pure spectra of the components resolved from highly overlapping spectral signals by the multivariate curve resolution−alternating least squares (MCR − ALS) algorithm verified the formation of an osthole−BLG complex. Moreover, osthole was found to strong quench the intrinsic fluorescence of BLG and the quenching mechanism was determined to be a static procedure. The binding constant of osthole with BLG at 298 K was (4.06 ± 0.03) × 104 L mol−1. Hydrophobic forces and hydrogen bonds played major roles in the binding process. The analysis of synchronous fluorescence, circular dichroism and Fourier transform infrared spectra found that the presence of osthole caused BLG structure compact and the change in the polarity and hydrophobicity of the microenvironment around Tyr residues of the protein. Modeling docking predicted that osthole bound to the hydrophobic cavity of BLG through stable hydrogen bonds primarily with the amino acid residues Lys75 and Thr76.

A highly sensitive, selective and simple method was proposed for colorimetric detection of ractopamine on the basis of the interaction between ractopamine and sulfanilic acid-modified gold-silver alloy nanoparticles (AuAgNPs). The AuAgNPs were prepared by the reduction of HAuCl

3-Indoleacetic acid (IAA), a broad-spectrum and efficient plant growth regulator, has been widely used in crop production. However, the accumulation of IAA in human body is potentially harmful to the human health. In this work, the binding properties of calf thymus DNA (ctDNA) with IAA and the impacts of IAA on ctDNA conformation were investigated through modern analysis techniques, including multispectroscopic methods, electrophoresis analysis and molecular docking. The results of fluorescence spectra analysis showed that ctDNA can cause significant fluorescence quenching of IAA in a static manner. The binding process was spontaneous and exothermic, which was mainly driven by van der Waals forces, and the binding constant was 5.58 × 103 L mol−1 at 25 °C. IAA bound to ctDNA via groove mode as revealed through iodine ion quenching assays, viscosity and melting temperature measurements. The molecular docking and Fourier transform infrared spectra intuitively displayed that IAA tended to bind to the G−C base-pairs of the minor grooves of ctDNA, but this binding did not lead to significant damage of DNA which was confirmed by the circular dichroism and gel electrophoresis analyses. These findings may provide novel insights into the toxic mechanism of IAA.

Galangin is a natural flavonol isolated from plants with potent biological activities. Galangin was found to significantly inhibit xanthine oxidase (XOD) activity in a competitive manner with the generation of superoxide radical (O 2 − ) in the enzyme catalysis, but galangin showed insignificant scavenging activity on 1,1-diphenyl-2-picryhydrazyl (DPPH) and O 2 – radicals. These results demonstrated that inhibition of O 2 – radical generation by galangin may be due to the competitive inhibition of uric acid formation by a ping-pong mechanism. XOD had one high affinity binding site for galangin with a binding constant of 3.60 × 10 4 L mol − 1 at 298 K. Hydrogen bond and hydrophobic interaction dominated the binding process on account of the negative enthalpy and positive entropy changes. The binding of galangin to XOD induced an increase in α-helix and random coil contents and a decrease in β-sheet and β-turn contents of XOD. Further molecular docking study validated that galangin can competitively bind to the site in the molybdenum atomic (Mo) domain, occupying the catalytic center to avoid the entrance of the substrate xanthine, resulting in the inhibition of XOD activity. These findings have provided new insights into the two-substrate kinetics of galangin on XOD and useful information for functional research of galangin in the treatment of gout and oxidative damage.

Tau-fluvalinate (TFL) and flumethrin (FL), widely used in agriculture and a class of synthetic pyrethroid pesticides with a similar structure, may cause a potential security risk. Herein, the modes of binding in vitro of TFL and FL with calf thymus DNA (ctDNA) were characterized by fluorescence, UV-vis absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy with the aid of viscosity measurements, melting analyses and molecular docking studies. The fluorescence titration indicated that both TFL and FL bound to ctDNA forming complexes through hydrogen bonding and van der Waals forces. The binding constants of TFL and FL with ctDNA were in the range of 10(4)Lmol(-1), and FL exhibited a higher binding propensity than TFL. The iodide quenching effect, single/double-stranded DNA effects, and ctDNA melting and viscosity measurements demonstrated that the binding of both TFL and FL to ctDNA was groove mode. The FT-IR analyses suggested the A-T region of the minor groove of ctDNA as the preferential binding for TFL and FL, which was confirmed by the displacement assays with Hoechst 33258 probe, and the molecular docking visualized the specific binding. The changes in CD spectra indicated that both FL and TFL induced the perturbation on the base stacking and helicity of B-DNA, but the disturbance caused by FL was more obvious. Gel electrophoresis analyses indicated that both TFL and FL did not cause significant DNA cleavage. This study provides novel insights into the binding properties of TFL/FL with ctDNA and its toxic mechanisms.

As one of the most reactive dicarbonyl compounds, methylglyoxal (MGO) can react with protein to form advanced glycation end products (AGEs), then promoting the development of diabetic complications. Hence, it is significant for preventing protein glycation mediated by MGO. Here, the anti-glycation potential and mechanism of gallocatechin gallate (GCG) as an active ingredient of green tea were investigated. It was found that GCG exhibit good scavenging activities of O2.- and .OH radicals of lysine–MGO system by 92.9% and 15.6%, respectively. The inhibitions (%) of GCG at 354.0 μg/mL for AGEs, dityrosine and N-formylkynurenine in bovine serum albumin (BSA)–MGO system were 96.7%, 97.3% and 98.2%, respectively. GCG (17.8–354.0 μg/mL) trapped MGO in a dose-dependent manner, 82.5% of MGO was trapped and the trapping efficiency reached 46.6% within 12 h when the concentration of GCG was 354.0 μg/mL. Two GCG–mono-MGO adducts were found when the molar ratios of MGO to GCG were 1:3 and 1:6. The efficacy of GCG in recovering the amino groups content, tryptophan residues and hydrophobic pockets of BSA was weak. The binding constant between GCG and BSA was in the order of magnitude of 104 L/mol, and the simulation analysis showed that the GCG–BSA complex was stable. It was inferred that the molecular mechanism of GCG against protein glycation induced by MGO may be due to its scavenging activity of O2.- and .OH radicals, MGO trapping capability and BSA binding interaction. These results suggested that GCG may be a potential inhibitor of MGO-induced glycation and provide new insights into GCG as a dietary supplement in functional foods for ameliorating the diabetic complications of MGO-derived AGEs.

The binding characteristics of food antioxidant tert-butylhydroquinone (TBHQ) and its oxidation product tert-butylquinone (TBQ) with calf thymus DNA (ctDNA) in vitro were investigated using multispectroscopy, chemometrics, viscosity measurements, gel electrophoresis assays and molecular docking. Analysis of fluorescence spectra found that TBHQ and TBQ bound with ctDNA to form 1:1 complexes with the binding constant in the order of 104 L mol−1. The concentration profiles and the pure spectra for the components (TBHQ, TBQ, ctDNA and TBHQ– or TBQ–ctDNA complex) were obtained through analyzing the expanded ultraviolet-visible absorption data matrix by multivariate curve resolution–alternating least squares algorithm, which successfully monitored the binding process of TBHQ/TBQ with ctDNA. Fluorescence displacement, viscosity and molecular docking experiments showed that TBHQ bound to ctDNA through intercalation binding, while TBQ bound to the minor groove of ctDNA. The binding of TBHQ to ctDNA induced the conversion of DNA conformation from B-form to A-form, while TBQ caused a minor perturbation on the DNA conformation. Gel electrophoresis results indicated that the combination of TBHQ and Cu(II) could induce DNA damage. This study may contribute to understanding the binding mechanisms of TBHQ and TBQ with ctDNA and further evaluate the potential toxicological effects of TBHQ as a food additive.

Quinoline yellow (QY), a synthetic colourant widely used in the food industry, has caused extensive concerns because of its potentially harmful effects on human health. In the present work, the interactions between QY and human serum albumin (HSA) were characterized by multiple spectroscopic methods, a chemometric algorithm, and molecular modelling studies. RESULTS The concentration profiles and pure spectra obtained for the components (QY, HSA and QY?HSA complex) from analyses of the expanded UV-visible absorption data matrices by multivariate curve resolution alternating least squares confirmed the QY?HSA interaction process. QY quenched the fluorescence of HSA through formation of a QY?HSA complex that was stabilized by moderate affinity. Hydrophobic forces and hydrogen bonding play major roles in the binding of QY to HSA. Site-specific marker-induced displacement results suggest that QY binds to subdomain IIA of HSA. This was corroborated by the molecular docking results. Decreases in HSA surface hydrophobicity and free sulfhydryl group content indicate that QY causes a contraction of the peptide strand in HSA, hiding the hydrophobic patches of the protein. Analyses by UV-visible absorption, circular dichroism, and three-dimensional fluorescence spectroscopy found that QY causes microenvironmental perturbations around the fluorophores and secondary structure changes in HSA. CONCLUSION This work shows that QY binds to HSA, affecting its structural and functional properties, and provides new insights into the binding mechanism and a comprehensive understanding of the toxicity of QY to biological processes. ? 2018 Society of Chemical Industry

Chrysin, a bioactive flavonoid, was investigated for its potential to inhibit the activity of xanthine oxidase (XO), a key enzyme catalyzing xanthine to uric acid and finally causing gout. The kinetic analysis showed that chrysin possessed a strong inhibition on XO ability in a reversible competitive manner with IC50 value of (1.26±0.04)×10(-6)molL(-1). The results of fluorescence titrations indicated that chrysin bound to XO with high affinity, and the interaction was predominately driven by hydrogen bonds and van der Waals forces. Analysis of circular dichroism demonstrated that chrysin induced the conformational change of XO with increases in α-helix and β-sheet and reductions in β-turn and random coil structures. Molecular simulation revealed that chrysin interacted with the amino acid residues Leu648, Phe649, Glu802, Leu873, Ser876, Glu879, Arg880, Phe1009, Thr1010, Val1011 and Phe1013 located within the active cavity of XO. The mechanism of chrysin on XO activity may be the insertion of chrysin into the active site occupying the catalytic center of XO to avoid the entrance of xanthine and causing conformational changes in XO. Furthermore, the interaction assays indicated that chrysin and its structural analog apigenin exhibited an additive effect on inhibition of XO.

The characteristics of binding of 2-tert-butyl-4-methylphenol (TBMP), a synthetic phenolic antioxidant with hydroxypropyl-β-cyclodextrin (Hp-βCD) and calf thymus DNA (ctDNA) were investigated by multi-spectroscopic techniques and molecular simulation. The results indicated that TBMP preferred to form a 1:1 inclusion complex with Hp-βCD, with an inclusion constant of determined to be 7.15 × 10(3) L mol(-1). The intercalative mode of TBMP to ctDNA was supported by ctDNA melting temperature and relative viscosity studies, salt quenching effect, competitive binding with methylene blue and molecular modeling. The changes in Fourier transformed infrared (FT-IR) and circular dichroism (CD) spectra suggested that TBMP mainly bound to the G-C rich region with inducing a significant perturbation in B-like DNA structure. It was also found that Hp-βCD decreased the binding ability of TBMP with ctDNA, but did not affect the interactive mode between TBMP and ctDNA, and the formed inclusion complex of TBMP-Hp-βCD decomposed in the presence of ctDNA. This study may provide insights into the mechanism of binding of TBMP with ctDNA and the role of Hp-βCD in the TBMP-ctDNA interaction.

The flavonoid family has been reported to possess a high potential for inhibition of xanthine oxidase (XO). This study concerned the structural aspects of inhibitory activities and binding affinities of flavonoids as XO inhibitors. The result indicated that the hydrophobic interaction was important in the binding of flavonoids to XO, and the XO inhibitory ability increased generally with increasing affinities within the class of flavones and flavonols. The planar structure and the C2═C3 double bonds of flavonoids were advantageous for binding to XO and for XO inhibition. Both the hydroxylation on ring B and the substitution at C3 were unfavorable for XO inhibition more profoundly than their XO affinity. The methylation greatly reduced the inhibition (0.75-3.07 times) but hardly affected the affinity. The bulky sugar substitutions of flavonoids decreased the inhibition (1.69-1.99 times) and lowered the affinities (4.20-9.22 times) to different degrees depending on the conjunction site.