Binding of naringin and naringenin with hen egg white lysozyme: A spectroscopic investigation and molecular docking study

Exploring the interaction of a potent anti-cancer drug Selumetinib with bovine serum albumin: Spectral and computational attributes

The binding of drugs to plasma proteins determines its fate within the physiological system, hence profound understanding of its interaction within the bloodstream is important to understand its pharmacodynamics and pharmacokinetics and thereby its therapeutic potential. In this regard, our work delineates the mechanism of interaction of Selumetinib (SEL), a potent anti-cancer drug showing excellent effect against multiple solid tumors, with plasma protein bovine serum albumin (BSA), using methods such as absorption, steady-state fluorescence, time-resolved, fluorescence resonance energy transfer, Fourier transform infrared spectra (FTIR), circular dichroism (CD), synchronous and 3D-fluorescence, salt fluorescence, molecular docking and molecular dynamic simulations. The BSA fluorescence intensity was quenched with increasing concentration of SEL which indicates interactions of SEL with BSA. Stern-Volmer quenching analysis and lifetime studies indicate the involvement of dynamic quenching. However, some contributions from the static quenching mechanism could not be ruled out unambiguously. The association constant was found to be 5.34 × 105 M-1 and it has a single binding site. The Förster distance (r) indicated probable energy transmission between the BSA and SEL. The positive entropy changes and enthalpy change indicate that the main interacting forces are hydrophobic forces, also evidenced by the results of molecular modeling studies. Conformation change in protein framework was revealed from FTIR, synchronous and 3D fluorescence and CD studies. Competitive binding experiments as well as docking studies suggest that SEL attaches itself to site I (subdomain IIA) of BSA where warfarin binds. Molecular dynamic simulations indicate the stability of the SEL-BSA complex. The association energy between BSA and SEL is affected in the presence of different metals differently.

Thermodynamic and functional changes of alpha-chymotrypsin after interaction with gallic acid

In the present study, the interaction mechanism between gallic acid (GA) and α-Chymotrypsin (α-CT) was investigated by employing a series ofspectroscopic methods, computational docking and molecular dynamic (MD) simulation. Fluorescence spectra analysis indicated the formation of a stable complex between GA and α-CT, where the quenching of the fluorescence emission was predominantly characterized by a static mechanism. TheCA obtained binding constants for the α-CT-GA complex were in the order of 103 M-1, indicating the moderate binding affinity of GA for α-CT. The corresponding CD findings showed that the interaction between GA and α-CT resulted in an alteration of the protein's secondary structure. The findings of the enzyme activity investigation clearly showed that the presence of GA led to a notable decline in the enzymatic activity of α-CT, highlighting GA's function as an effective inhibitor for α-CT. The molecular docking simulations revealed the optimal binding site for the GA molecule within the α-CT structure and MD simulations confirmed the stability of the α-CT-GA complex. This research expands our comprehension regarding the behavior of enzymes in the presence of small-molecule ligands and opens avenues for food safety.

Probing the toxic effect of chlorpyrifos as an environmental pollutant on the structure and biological activity of lysozyme under physiological conditions

The pervasive use of pesticides like chlorpyrifos (CPY) has been associated with deleterious effects on biomolecules, posing significant risks to environmental integrity, public health, and overall ecosystem equilibrium. Accordingly, in this study, we investigated the potential binding interaction between the well-conserved enzyme, lysozyme (LSZ), and CPY through various spectroscopic techniques and molecular modeling. The UV-vis absorption and fluorescence experiments confirmed the complex formation and static quenching of the intrinsic fluorescence intensity. LSZ revealed a singular binding site for CPY, with binding constants around 105 M-1 across different temperature ranges. Analysis of thermodynamic parameters showed the spontaneous nature of the complexation process, while also revealing the pivotal role of hydrophobic interactions in stabilizing the LSZ-CPY system. According to circular dichroism and Fourier transform infrared studies, CPY binding changed the secondary structure of LSZ by boosting α-helix presence and reducing the levels of β-sheet and β-turn content. Further, CPY decreased the stability and activity of LSZ. Computational docking delineated the specific and highly preferred binding site of CPY within the structure of LSZ. Molecular dynamic simulation indicated the enduring stability of the LSZ/CPY complex and revealed structural modifications in the LSZ after binding with CPY. This research provides a detailed understanding of the intermolecular dynamics between CPY and LSZ, concurrently elucidating the molecular-level implications for the potential hazards of pesticides in the natural environment.

Analysis of Binding Modes between Three Perfluorosulfonates and GPER Based on Computational Simulation and Multiple Spectral Methods

Perfluorinated compounds (PFCs) belong to a significant category of global environmental pollutants. Investigating the toxicological effects of PFCs within biological systems is of critical significance in various disciplines such as life sciences, environmental science, chemistry, and ecotoxicology. In this study, under simulated human physiological conditions (pH = 7.4), a combination of multiple spectroscopic techniques and computational simulations was employed to investigate the impact of perfluorinated compounds (PFCs) on the G protein-coupled estrogen receptor (GPER). Additionally, the research focused on exploring the binding modes and toxicological mechanisms between PFCs and GPER at the molecular level. All three perfluorinated sulfonic acids (PFSAs) can induce quenching of GPER fluorescence through static quenching and non-radiative energy transfer. Steady-state fluorescence calculations at different temperatures revealed apparent binding constants in the order of 106, confirming a strong binding affinity between the three PFSAs and GPER. Molecular docking studies indicated that the binding sites of PFSAs are located within the largest hydrophobic cavity in the head region of GPER, where they can engage in hydrogen bonding and hydrophobic interactions with amino acid residues within the cavity. Fourier transform infrared spectroscopy, three-dimensional fluorescence, and molecular dynamics simulations collectively indicate that proteins become more stable upon binding with small molecules. There is an overall increase in hydrophobicity, and alterations in the secondary structure of the protein are observed. This study deepens the comprehension of the effects of PFCs on the endocrine system, aiding in evaluating their potential impact on human health. It provides a basis for policy-making and environmental management while also offering insights for developing new pollution monitoring methods and drug therapies.

3-Acyl-4-Pyranone as a Lysine Residue-Selective Bioconjugation Reagent for Peptide and Protein Modification

Chemoselective protein modification plays extremely important roles in various biological, medical, and pharmaceutical investigations. Mimicking the mechanism of the chemoselective reaction between natural azaphilones and primary amines, this work successfully simplified the azaphilone scaffold into much simpler 3-acyl-4-pyranones. Examinations confirmed that these slim-size mimics perfectly kept the unique reactivity for selective conjugation with the primary amines including lysine residues of peptides and proteins. The newly developed pyranone tool presents remarkably increased aqueous solubility and compatible second-order rate constant by comparison with the original azaphilone. Additional advantages also include the ease of biorthogonal combinative use with a copper-catalyzed azide-alkyne Click reaction, which was conveniently applied to decorate lysozyme with neutral-, positive- and negative-charged functionalities in parallel. Moderate-degree modification of lysozyme with positively charged quaternary ammoniums was revealed to increase the enzymatic activities.

Unravelling the molecular interactions of phenyl isothiocyanate and benzoyl isothiocyanate with human lysozyme: Biophysical and computational analyses

Phenyl isothiocyanate and benzoyl isothiocyanate are the phytochemicals present in the Brassicaceae family. They have antibacterial, antiapoptotic and antifungal properties. Protein-small molecule interaction studies are done to assess the changes in structure, dynamics, and functions of protein and to decipher the binding mechanism. This study is based on the comparative binding of PT and BT with human lysozyme using in vitro and computational techniques. UV, fluorescence emission, and FRET spectra gave insight into the complex formation, quenching mechanism, and binding parameters. Both PT and BT quenched the intrinsic fluorescence of Lyz by a static quenching mechanism. Synchronous, 3D fluorescence and CD spectroscopy substantiated conformational and microenvironmental alterations in the Lyz. The metal ions and β-cyclodextrin had a pronounced effect on the binding strength of Lyz-PT and Lyz-BT complexes. Accessible surface area analysis was determined to characterise the amino acid residue packing. Molecular docking further validated the wet lab experimental results.

Structural alterations and inhibition of lysozyme activity upon binding interaction with rotenone: Insights from spectroscopic investigations and molecular dynamics simulation

The pervasive employment of pesticides such as rotenone on a global scale represents a substantial hazard to human health through direct exposure. Therefore, exploring the interactions between such compounds and body macromolecules such as proteins is crucial in comprehending the underlying mechanisms of their detrimental effects. The present study aims to delve into the molecular interaction between rotenone and lysozyme by employing spectroscopic techniques along with Molecular dynamics (MD) simulation in mimicked physiological conditions. The binding interaction resulted in a fluorescence quenching characterized by both dynamic and static mechanisms, with static quenching playing a prominent role in governing this phenomenon. The analysis of thermodynamic parameters indicated that hydrophobic interactions primarily governed the spontaneous bonding process. FT-IR and circular dichroism findings revealed structural alternations of lysozyme upon complexation with rotenone. Also, complexation with rotenone declined the biological activity of lysozyme, thus rotenone could be considered an enzyme inhibitor. Further, the binding interaction substantially decreased the thermal stability of lysozyme. Molecular docking studies showed the binding location and the key residues interacting with rotenone. The findings of the spectroscopic investigations were confirmed and accurately supported by MD simulation studies.

Copper-flavonoid family of complexes involved in alkaline phosphatase activation

The flavonoid naringenin and a family of naringenin derivative Cu(II) complexes having phenanthroline-based second ligands were selected to study alkaline phosphatase activation. This enzyme plays a critical role in tissue formation, increasing the inorganic phosphate formation, favoring mineralization, and being essential to producing bone mineralization. The effects of those compounds on the function and structure of the enzyme were evaluated by kinetic measurements, fluorescence, FTIR, and UV-Vis spectroscopies. The results showed that naringenin did not affect alkaline phosphatase activity, having a value of the Michaelis-Menten-constant close to the enzyme (Km = 3.07 × 10-6). The binary complex, Cu(II)-naringenin, and the ternary complex Cu(II)-naringenin-phenanthroline behaved as an enzyme activator in all the concentrations range used in this study. Those complexes increased in c.a. 1.9% the catalytic efficiency concerning enzyme and naringenin. The ternary complex Cu(II)-naringenin-bathophenanthroline, provokes an activator mixed effect, dependent on the substrate concentrations. The different kinetic behavior can be correlated with different conformational changes observed under the interaction with ALP. Fluorescence experiments showed a raising of the binding constant with temperature. FTIR determinations showed that the complex with bathophenanthroline modifies the ALP structure but maintains the helical structure. The other copper complexes provoked a structural unfolding, decreasing the α-helix content. None of them affect the dephosphorylation enzyme ability. Even though the interactions and structural modifications on ALP are different, it is evident that the presence of copper favors enzymatic activity. The observed electrostatic interactions probably benefit the dissociation of the bound phosphate. The results suggest potential biological applications for the studied compounds.

Interaction and binding mechanism of cyanidin-3-O-glucoside to lysozyme in varying pH conditions: Multi-spectroscopic, molecular docking and molecular dynamics simulation approaches

Due to pH sensitivity, the interaction between lysozyme and cyanidin-3-O-glucoside was investigated at pH 3.0 and 7.4 via multi-spectroscopic approaches, with additional molecular docking and molecular dynamics simulation (MD). Binding with cyanidin-3-O-glucoside, the enhanced UV spectra and the reduced the α-helicity of lysozyme were both more significant at pH 7.4 than that at pH 3.0 (p < 0.05), corresponding to Fourier transform infrared spectroscopy (FTIR) study. Fluorescence quenching indicated the static mode was major at pH 3.0 with a part dynamic mode at pH 7.4 with a significantly high of Ks at 310 K (p < 0.05), corresponding to their MD. An instantaneous conformation of lysozyme was observed during C3G addition at pH 7.4 in fluorescence phase diagram. Cyanidin-3-O-glucoside derivatives bind with lysozyme at a common site via hydrogen-bond and π-π interactions in molecular docking and tryptophan played a potential role in the interaction based on the MD.

Digital Database of Absorption Spectra of Diverse Flavonoids Enables Structural Comparisons and Quantitative Evaluations

Flavonoids play diverse roles in plants, comprise a non-negligible fraction of net primary photosynthetic production, and impart beneficial effects in human health from a plant-based diet. Absorption spectroscopy is an essential tool for quantitation of flavonoids isolated from complex plant extracts. The absorption spectra of flavonoids typically consist of two major bands, band I (300-380 nm) and band II (240-295 nm), where the former engenders a yellow color; in some flavonoids the absorption tails to 400-450 nm. The absorption spectra of 177 flavonoids and analogues of natural or synthetic origin have been assembled, including molar absorption coefficients (109 from the literature, 68 measured here). The spectral data are in digital form and can be viewed and accessed at http://www.photochemcad.com. The database enables comparison of the absorption spectral features of 12 distinct types of flavonoids including flavan-3-ols (e.g., catechin, epigallocatechin), flavanones (e.g., hesperidin, naringin), 3-hydroxyflavanones (e.g., taxifolin, silybin), isoflavones (e.g., daidzein, genistein), flavones (e.g., diosmin, luteolin), and flavonols (e.g., fisetin, myricetin). The structural features that give rise to shifts in wavelength and intensity are delineated. The availability of digital absorption spectra for diverse flavonoids facilitates analysis and quantitation of these valuable plant secondary metabolites. Four examples are provided of calculations─multicomponent analysis, solar ultraviolet photoprotection, sun protection factor (SPF), and Förster resonance energy transfer (FRET)─for which the spectra and accompanying molar absorption coefficients are sine qua non.

Deciphering the interactions of phytochemicals with ovalbumin, the major food allergen from egg white: spectroscopic and computational studies

Ovalbumin (OVA), the major component of egg white, has been used as a model carrier protein to study the interaction of four bioactive phytochemicals 6-hydroxyflavone, chrysin, naringin, and naringenin. A static quenching mechanism was primarily associated with the complexation of the flavonoids with OVA. Hydrophobic forces play a major part in the stability of the complexes. The structural changes within the protein in response to flavonoid binding revealed a decrease in OVA's α-helical content. The hypothesized binding site for flavonoids in OVA overlaps with one or more immunoglobulin E-binding epitopes that may have some effect in the immunoglobulin E response pathway. The flavonoids remain in the same binding site throughout the simulation time and impart protein stability by forming different noncovalent interactions. This study presents comprehensive information about the interaction of the flavonoids with OVA and the associated structural variations after the binding, which might help researchers better comprehend similar medication pharmacodynamics and provide critical information for future therapeutic development.

Molecular mechanism of two functional protein structure changes under 2,3-butanedione-induced oxidative stress and apoptosis effects in the hepatocytes

Food security has become closely watched with the occurrence of a series of food safety incidents in recent years. The widespread adoption of 2,3-butanedione (BUT), as a food additive, is an unpreventable significant risk factor to food security. Based on this, mouse hepatocyte AML-12 cells and two functional proteins (bovine serum albumin and lysozyme) were utilized as targeted receptors to study the adverse effects of BUT at the cellular and molecular levels. Results suggested that BUT could disrupt the redox balance of AML-12 cells, reducing glutathione (GSH) activity fell to 87.18 %, which cannot offset the production of reactive oxygen species (ROS). Meanwhile, the increasement of lipid peroxidation and malondialdehyde (MDA) levels were observed. The mitochondrial membrane function was also abnormal due to the excessive accumulation of ROS and eventually leads to cell apoptosis and death. At the molecular level, the exposure of BUT could alter the skeleton and secondary structure of bovine serum albumin (BSA) and lysozyme (LYZ), and it could statically quench the intrinsic fluorescence of proteins. The combined experiments confirmed proved the potentially toxic effects of BUT accumulation on the detoxification organ, providing theoretical support for the liver diseases caused by BUT exposure, and a reference for the risk assessment of occupational exposure of BUT.

Study on the interaction between nimodipine and five proteinases and the effects of naringin and vitamin C on these interactions by spectroscopic and molecular docking methods

The interaction mechanisms of nimodipine with pepsin, trypsin, α-chymotrypsin, lysozyme and human serum albumin were investigated by multispectral and molecular docking methods. Vitamin C and naringin were the main active components of grapefruit juice, and nimodipine was the typical drug that interacts with this juice. Fluorescence spectroscopy was used to study the interaction of nimodipine with five proteinases (pepsin, trypsin, α-chymotrypsin, lysozyme and human serum albumin) and the effects of vitamin C and naringin on these interactions. The fluorescence quenching results showed that nimodipine can quench the intrinsic fluorescence of these five proteinases by a static quenching procedure. Nimodipine binds to pepsin and α-chymotrypsin, through hydrogen bonding and van der Waals forces, whereas it binds to trypsin, lysozyme and human serum albumin mainly by hydrophobic interactions. The microenvironment of the five proteinases changed. The probability of nonradiative energy transfer between the five proteinases and nimodipine was high. Both vitamin C and naringin reduced the binding constant of nimodipine to the four proteinases (except α-chymotrypsin) and might increase the concentration of free nimodipine. Thus, vitamin C or naringin in fruits or foods could increase the blood concentration of free nimodipine and perhaps a reduction in nimodipine dose was needed.

The effect of putrescine on the lysozyme activity and structure: Spectroscopic approaches and molecular dynamic simulation

The present research addressed the influence of polyamine (putrescine) on the compound as well as function of lysozyme; accordingly, UV- Visible, fluorescence spectroscopy and simulation method were applied to fulfill this goal. Lysozyme's structural variability was examined at various putrescine ‌concentrations; also, the putrescine binding to lysozyme was addressed using spectrofluorescence, circular dichroism (CD) and UV-Vis measurements. The obtained results indicated that with raising the putrescine concentration, the intrinsic quenching fluorescence of lysozyme was decreased based on the static mechanism. Analysis of thermodynamic parameters also indicated that van der Waals as well as hydrogen bond forces served a fundamental role in determining the resulting stability; this was in agreement with modeling studies. Measurement of UV absorption spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy also demonstrated that lysozyme's second and tertiary structures were altered in a putrescine concentration-dependent manner. Putrescine inhibited lysozyme's enzymatic activity, displaying its affinity with the lysozyme's active site. Further, molecular simulation conducted revealed that putrescine could have spontaneous binding to lysozyme, changing its structure, thus further emphasizing the experimental results.

A comparative study of the interaction of naringenin with lysozyme by multi-spectroscopic methods, activity comparisons, and molecular modeling procedures

The present study applied steady-state fluorescence, UV-Vis spectrophotometry, molecular docking studies, and circular dichroism (CD) to investigate the interaction of naringenin with lysozyme in an aqueous medium. The UV-Vis measurement indicated the changes in lysozyme secondary and tertiary structure change as a function of the concentration of naringenin. Naringenin could be used to turn the static quenching mechanism into the intrinsic fluorescence of lysozyme. The negative amount of Gibbs free energy (ΔG°) suggested that the binding operation was spontaneous. Fluorescence studies also demonstrated the changes occurring in the Trp microenvironment upon the concatenation into lysozyme. Analysis of thermodynamic parameters also revealed that hydrophobic forces played a fundamental role in determining the complex stability; this was consistent with the previous modeling studies. Circular dichroism also suggested that the alpha-helicity of lysozyme was enhanced as ligand was bound. Naringenin inhibited lysozyme enzymatic activity, displaying its affinity with the lysozyme active site. Further, molecular docking studies demonstrated that naringenin could bind to both residues essential for catalytic activity in the proximity of Trp 62 and Trp 63.

Fabrication of food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a dihydromyricetin and lysozyme mixture

This study evaluated the feasibility of fabricating food-grade HIPEs using a dihydromyricetin and lysozyme mixture. The effects of the oil phase volume fraction (φ), composition (lysozyme:dihydromyricetin, k), and addition amount (w) of the mixture on the formation and properties of the HIPEs were analyzed. Then, the interactions of dihydromyricetin and lysozyme were investigated. The results indicated that when w was 0.4%, HIPEs with φ value of 90% could be obtained. Furthermore, the k also affected the microstructure, mechanical properties, oil oxidation, and lutein protection ability of the HIPEs. However, the presence of dihydromyricetin did not affect lysozyme activity. Both isothermal titration calorimetry and molecular simulations proved that they did not form a typical host-guest complex. But, dihydromyricetin could absorb on the lysozyme surface. Therefore, we speculated that lysozyme and dihydromyricetin particles could overlap and form a 3D network structure to stabilize the HIPEs, which was consistent with the microstructure observations.

Exploring the interactions of naringenin and naringin with trypsin and pepsin: Experimental and computational modeling approaches

Naringenin and naringin are two natural compounds with important health benefits, whether as food or drug. It is necessary to study the interactions between naringenin/naringin and digestive proteases, such as trypsin and pepsin. In this study, the bindings of naringenin and naringin to trypsin and pepsin were investigated using multi-spectroscopy analysis and computational modeling approaches. Fluorescence experiments indicate that both naringenin and naringin can quench the intrinsic fluorescence of trypsin/pepsin via static quenching mechanism. Naringin binds trypsin/pepsin in a more firmly way than naringenin. Thermodynamic analysis reveals that the interactions of naringenin/naringin and trypsin/pepsin are synergistically driven by enthalpy and entropy, and the major driving forces are hydrophobic, electrostatic interactions and hydrogen bonding. Synchronous fluorescence spectroscopy, circular dichroism spectroscopy and FT-IR show that naringenin/naringin may induce microenvironmental and conformational changes of trypsin and pepsin. Molecular docking reveals that naringenin binds in the close vicinity of the active site (Ser-195) of trypsin and Asp-32 (the catalytic activity of pepsin) appears in naringin-pepsin system. The direct interactions between naringenin or naringin and catalytic amino acid residues will inhibit the catalytic activity of trypsin and pepsin, respectively. The results of molecular dynamic simulation validate the reliability of the docking results.

Structural Compactness in Hen Egg White Lysozyme Induced by Bisphenol S: A Spectroscopic and Molecular Dynamics Simulation Approach

The endocrine disrupting compound Bisphenol and its analogues are widely used in food packaging products and can cause serious health hazards. The protein, Lysozyme (Lyz), showing anti-microbial properties, is used as a "natural" food and dairy preservative. Herein, we explored the interaction between Lyz and Bisphenol S (BPS) by multi-spectroscopic and theoretical approaches. Lyz interacts with BPS through static quenching, where hydrophobic force governed the underlying interaction. Molecular docking results reveal that tryptophan plays a vital role in binding, corroborated well with near UV-CD studies. A decrease in the radius of gyration (from 1.43 nm to 1.35 nm) of Lyz substantiates the compactness of the protein conformation owing to such an interaction. This structural alteration experienced by Lyz may alter its functional properties as a food preservative. Consequently, this can degrade the quality of the food products and thereby lead to severe health issues.

Insights on the interaction mechanism of exemestane to three digestive enzymes by multi-spectroscopy and molecular docking

Exemestane is an irreversible steroidal aromatase inhibitor, typically used to treat breast cancer. As an anti-tumor drug, exemestane has more obvious side effects on the gastrointestinal tract. The purpose of this work is to investigate the combination of exemestane with three important digestive enzymes including pepsin (Pep), trypsin (Try) and α-Chymotrypsin (α-ChT) so as to analyze the mechanism of the gastrointestinal adverse effects causing by exemestane binding. Enzyme activity experiment showed that the enzyme activity of Pep was decreased in the presence of exemestane. Fluorescence spectra revealed that exemestane formed stable complexes with digestive enzymes, and the quenching mechanism of drug-digestive enzymes interaction were all static quenching. The binding constants of Pep, Try and α-ChT at 298 K were 2.34 × 10⁵, 1.45 × 10⁵, and 2.05 × 10⁵ M^-1, respectively. Synchronous fluorescence and 3D fluorescence spectroscopy showed that the conformation of exemestane was slightly changed after combining with digestive enzymes, and non-radiative energy transfer occurred. Circular dichroism results indicated that exemestane could change the secondary structure of digestive enzymes via increase the α-helix content and decrease in the β-sheet content. Thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) revealed that exemestane interacted with α-ChT through electrostatic force, and the binding force with Pep and Try was van der Waals interactions and hydrogen, which was basically consistent with the molecular docking results.

Study of the noncovalent interactions between phenolic acid and lysozyme by cold spray ionization mass spectrometry (CSI-MS), multi-spectroscopic and molecular docking approaches

Elucidating the recognition mechanisms of the noncovalent interactions between pharmaceutical molecules and proteins is important for understanding drug delivery in vivo, and for the further rapid screening of clinical drug candidates and biomarkers. In this work, a strategy based on cold spray ionization mass spectrometry (CSI-MS), combined with fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and molecular docking methods, was developed and applied to the study of the noncovalent interactions between phenolic acid and lysozyme (Lys). Based on the real characterization of noncovalent complex, the detailed binding parameters, as well as the protein conformational changes and specific binding sites could be obtained. CSI-MS and tandem mass spectrometry (MS/MS) technique were used to investigate the phenolic acid-Lys complexes and the structure-affinity relationship, and to assess their structural composition and gas phase stability. The binding affinity was obtained by direct and indirect MS methods. The fluorescence spectra showed that the intrinsic fluorescence quenching of Lys in solution was a static quenching mechanism caused by complex formation, which supported the MS results. The CD and FTIR spectra revealed that phenolic acid changed the secondary structure of Lys and increased the α-helix content, indicating an increase in the tryptophan (W) hydrophobicity near the protein binding site resulting in a conformational alteration of the protein. In addition, molecular docking studies were performed to investigate the binding sites and binding modes of phenolic acid on Lys. This strategy can more comprehensively and truly characterize the noncovalent interactions and can guide further research on the interactions of phenolic acid with other proteins.

Comparative study on the interaction of oxyresveratrol and piceatannol with trypsin and lysozyme: binding ability, activity and stability

Natural polyphenols showing a variety of beneficial effects will interact with multiple proteases after administration. The interactions of oxyresveratrol and piceatannol with trypsin and lysozyme were investigated using fluorescence spectroscopy, UV-vis absorption spectroscopy, circular dichroism spectroscopy, differential scanning calorimetry and molecular docking. Fluorescence quenching results and UV-vis absorption difference spectra revealed that the quenching process was a static mode initiated by ground-state complex formation. The different binding ability of oxyresveratrol and piceatannol with trypsin and lysozyme was discussed based on their different molecular structures. Moreover, the major driving force for the binding process was elucidated as hydrogen bonding and van der Waals forces by the negative enthalpy and entropy changes. Synchronous fluorescence, three-dimensional fluorescence and circular dichroism spectral analysis suggested that the binding of oxyresveratrol and piceatannol to trypsin and lysozyme induced some microenvironmental and conformational changes of the two enzymes. The thermal stability of the enzymes in the presence of polyphenols was studied based on the change in melting temperature by differential scanning calorimetry. The above experimental results were validated by the protein-ligand docking studies which showed the location of the two ligands in the enzymes and the surrounding amino acid residues. Furthermore, enzyme activity assays indicated that the enzymatic activity of trypsin and lysozyme was inhibited by oxyresveratrol and piceatannol. The effect of trypsin and lysozyme on the antioxidant activity and stability of oxyresveratrol and piceatannol was also investigated. In conclusion, the comparative study on the interaction of oxyresveratrol and piceatannol with trypsin and lysozyme showed that the positions of hydroxyl groups of the polyphenols had an important influence on their interaction with enzymes and their antioxidant activity and stability as well as the enzyme activities. The obtained results are expected to provide a theoretical basis for the application of polyphenols in functional foods and pharmaceuticals.

Toxicity of thimerosal in biological systems: Conformational changes in human hemoglobin, decrease of oxygen binding capacity, increase of protein glycation and amyloid's formation

Thimerosal (TH), an organomercurial compound, is used as a preservative in vaccines and cosmetics. Its interaction with human hemoglobin (Hb) was investigated under physiological conditions using biophysical and biological assays, aiming to evaluate hazardous effects. TH interacts spontaneously with Hb (stoichiometry 2:1, ligand-protein), preferably by electrostatic forces, with a binding constant of 1.41 × 10⁶ M^-1. Spectroscopic data allows to proposing that TH induces structural changes in Hg, through ethylmercury transfer to human Hb-Cys93 residues, forming thiosalicylic acid, which, in turn, interacts with the positive side of the amino acid in the Hb-HgEt adduct chain. As a consequence, inhibition of Hb-O₂ binding capacity up to 72% (human Hb), and 50% (human erythrocytes), was verified. Dose-dependent induction of TH forming advanced glycation end products (AGE) and protein aggregates (amyloids) was additionally observed. Finally, these results highlight the toxic potential of the use of TH in biological systems, with a consequent risk to human health.

Effect and Mechanism of Elaeagnus angustifolia Flower and Its Major Flavonoid Tiliroside on Inhibiting Non-enzymatic Glycosylation

This study aimed to evaluate the antiglycation ability of Elaeagnus angustifolia flower extract and to elucidate the mechanism with its major compound. The results indicated that E. angustifolia flower extract and its major compound tiliroside (24.2 mg/g of extract) exhibited excellent antiglycation ability with inhibition rates of 92.1 and 78.9% at 37.5 μg/mL, which are much higher than that of aminoguanidine (55.3% at 37.5 μg/mL). The stable tiliroside-ovalbumin (OVA) complexes were formed through a spontaneous exothermic progress in an equimolar manner, and hydrophobic interaction, hydrogen bond, and van der Waals forces were the major driving forces. Tiliroside could significantly ameliorate the conformation changes of OVA induced by the glycation reaction, quench its fluorescence by a static mechanism, and change the microenvironment adjacent to tryptophan and tyrosine. Molecular docking revealed that tiliroside inserted into the OVA hydrophobic pocket resulted in the formation of five hydrogen bonds. Orbitrap tandem mass spectrometry showed that tiliroside significantly suppressed the glycation of OVA, and the number of glycation sites was reduced from 9 to 5 after tiliroside was added. The above results indicated that E. angustifolia flowers and tiliroside have a good antiglycation effect and can be used as food additives to suppress the undesired glycation reaction during food processing.

Formation of the inclusion complex of water soluble fluorescent calix[4]arene and naringenin: solubility, cytotoxic effect and molecular modeling studies

Naringenin is considered as an important flavonoid in phytochemistry because of its important effect on cancer chemoprevention. Unfortunately its poor solubility has restricted its therapeutic applications. In this study, an efficient water-soluble fluorescent calix[4]arene (compound 5) was synthesized as host macromolecule to increase solubility and cytotoxicity in cancer cells of water-insoluble naringenin as well as to clarify localization of naringenin into the cells. Complex formed by host-guest interaction between compound 5 and naringenin was analyzed with UV-visible, fluorescence, FTIR spectroscopic techniques and molecular modeling studies. Stern-Volmer analysis showed binding constant value of K_sv 3.5 × 10⁷ M^-1 suggesting strong interaction between host and guest. Binding capacity shows 77% of naringenin was loaded on compound 5. Anticarcinogenic effects of naringenin complex were evaluated on human colorectal carcinoma cells (DLD-1) and it was found that 5-naringenin complex inhibits proliferation of DLD-1 cells 3.4-fold more compared to free naringenin. Fluorescence imaging studies show 5-naringenin complex was accumulated into the cytoplasm instead of the nucleus. Increased solubility and cytotoxicity of naringenin with fluorescent calix[4]arene makes it one of the potential candidates as a therapeutic enhancer. For deep understanding of host-guest interaction mechanisms, complementary multiscale molecular modeling studies were also carried out.Communicated by Ramaswamy H. Sarma.

Could Flavonoids Compete with Synthetic Azoles in Diminishing Candida albicans Infections? A Comparative Review Based on In Vitro Studies

Flavonoids are polyphenolic compounds with already confirmed various health benefits. This review will shed light on flavonoids as potential antifungals in Candida albicans infections. C. albicans is an opportunistic pathogen able to cause serious health issues due to numerous virulence factors amplifying its pathogenicity. One of the most important virulence factors is Candida ability to form biofilms which are highly resistant to the treatment of antifungal drugs; making diminishing of this pathogen even more challenging. This review will focus on current knowledge on individual flavonoid compounds having the potential to deal with C. albicans in vitro, with special turn on antibiofilm potential and insight into the mode of action, where available. Majority of the commercial drugs for the treatment of candidiasis belong to azole class, so the activity of flavonoids will be compared with the activity of newly synthetized azole compounds, as well as with azole drugs that are already on the market as official therapeutics. This literature review will provide pros and cons for pushing future research towards exploring novel synthetic azoles or further examination of a wide pallet of natural flavonoids.

Albumin binding and anticancer effect of magnesium oxide nanoparticles

BACKGROUND

Recently, nanomaterials have moved into biological and medicinal implementations like cancer therapy. Therefore, before clinical trials, their binding to plasma proteins like human serum albumin (HSA) and their cytotoxic effects against normal and cancer cell lines should be addressed.

METHODS

Herein, the interaction of magnesium oxide nanoparticles (MgO NPs) with HSA was studied by means of fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and docking studies. Afterwards, the cytotoxic impacts of MgO NPs on human leukemia cell line (K562) and peripheral blood mononucleated cells (PBMCs) were evaluated by MTT and flow cytometry assays to quantify reactive oxygen species (ROS) generation and apoptosis.

RESULTS

It was demonstrated that MgO NPs spontaneously form a static complex with HSA molecules through hydrophobic interactions. Docking study based on the size of NPs demonstrated that different linkages can be established between MgO NPs and HSA. The CD investigation explored that MgO NPs did not alter the secondary structure of HSA. Cellular studies revealed that MgO NPs induced cytotoxicity against K562 cell lines, whereas no adverse effects were detected on PBMCs up to optimum applied concentration of MgO NPs. It was exhibited that ROS production mediated by IC50 concentrations of MgO NPs caused apoptosis-associated cell death. The pre-incubation of K562 with ROS scavenger (curcumin) inhibited the impact of MgO NPs -based apoptosis on cell fate, revealing the upstream effect of ROS in our system.

CONCLUSION

In summary, MgO NPs may exhibit strong plasma distribution and mediate apoptosis by ROS induction in the cancer cell lines. These data demonstrate a safe aspect of MgO NPs on the proteins and normal cells and their application as a distinctive therapeutic approach in the cancer treatment.

Investigation of the effects of naringin on intestinal ischemia reperfusion model at the ultrastructural and biochemical level

We aimed to evaluate the ultrastructural effect of reversing cellular damage, occurring in rats due to ischemia-reperfusion (I/R) in the intestine, with naringin implementation through biochemical parameters. Rats were divided the sham/control, I/R and the naringin groups (n = 7). For I/R group, 120 min of ischemia and 120 min of reperfusion was applied to the superior mesenteric artery. In the naringin group, after 120 min, 50 mg/kg naringin was implemented, and then 120 min of reperfusion was applied. Morphological evaluation was performed via Chiu score and electron microscopy. The antioxidant parameters were examined. Chiu score in I/R (p < 0.01) and naringin (p < 0.05) groups were higher than the sham/control group. In ultrastructural level some irregularity were observed in I/R group. Although it decreased in the naringin group, the damage was observed to continue. Malondialdehyde (MDA) amount and Superoxide dismutase activity (SOD) in I/R group were higher in comparison to the sham/control group (p < 0.01), while glutathione peroxidase activity (Gpx) was found to be lower (p < 0.01). SOD (p < 0.05) and MDA (p < 0.01) were decreased by naringin group. Gpx was decreased in I/R group compared to sham/control group (p < 0.01) and elevated due to naringin administration (p < 0.05). Catalase activity was observed to decrease in the naringin group compared to control and I/R groups (p < 0.01). It was determined that naringin provided limited healing at the ultrastructural level but also effected recovery within antioxidant parameters.

Molecular recognition of bio-active flavonoids quercetin and rutin by bovine hemoglobin: an overview of the binding mechanism, thermodynamics and structural aspects through multi-spectroscopic and molecular dynamics simulation studies

The binding of two bio-active flavonoids, quercetin and rutin, with bovine hemoglobin (BHb) was investigated by multi-spectroscopic and computational (molecular docking and molecular dynamics simulation) studies. The two flavonoids were found to quench the intrinsic fluorescence of BHb through a static quenching mechanism. The binding constants at 288 K were observed to be (14.023 ± 0.73) × 104 M-1 and (7.848 ± 0.20) × 104 M-1, respectively for quercetin and rutin binding with BHb. Both rutin and quercetin were observed to increase the polarity around the Trp residues of BHb as indicated by synchronous and 3D spectral studies. No significant alterations in the secondary structural components of the protein were caused during the binding of the flavonoids as studied by CD and FTIR studies. The negative molar Gibbs free energies indicated the spontaneity of the interaction processes while the binding processes were characterized by a negative enthalpy change (ΔH) and a positive entropy change (ΔS). The possibility of energy transfer from the donor (BHb) to the acceptor molecules (flavonoids) was indicated by the FRET studies. According to the fluorescence studies, the flavonoids interact near to the β2-Trp37 residue of BHb. Excellent correlations with the experimental studies were observed from the molecular docking and molecular dynamics (MD) simulation studies. Further investigations established that these flavonoids are efficient in the inhibition of glucose mediated glycation of BHb.