Affinity of rosmarinic acid to human serum albumin and its effect on protein conformation stability

A novel synergistic inhibition mechanism of pancreatic lipase by 2-mercaptobenzothiazole and stearic acid migrants from dairy contact rubbers

This study explores the inhibitory effects of two migrants-2-mercaptobenzothiazole (MBT) and stearic acid-from dairy rubber contact materials on pancreatic lipase (PL). Enzyme assays showed significant, dose-dependent inhibition, with stearic acid being more potent. MBT and stearic acid exhibited reversible inhibition, with MBT acting competitively and stearic acid non-competitively. Fluorescence spectroscopy and circular dichroism indicated conformational changes in PL upon binding, while molecular docking confirmed specific interactions at the active site (MBT) and near it (stearic acid). Binding affinities for MBT-PL and stearic acid-PL complexes were - 24.90 and - 20.23 kJ/mol, respectively. High concentrations of both compounds exhibited synergistic inhibition, potentially affecting lipid digestion in dairy products. This study highlights the influence of rubber-derived migrants on PL activity and suggests limiting their use in food contact materials to safeguard dairy nutritional quality.

Potential Antidiabetic Activity of Nordihydroguaiaretic Acid: An Insight into Its Inhibitory Mechanisms on Carbohydrate-Hydrolyzing Enzymes, the Binding Behaviors with Enzymes, and In Vivo Antihyperglycemic Effect

The inhibitory mechanisms and binding behaviors of nordihydroguaiaretic acid (NDGA) to α-glucosidase/α-amylase were investigated by in vitro multispectroscopic methods and in silico modeling technique. The results demonstrated that NDGA reversibly and uncompetitively inhibited α-glucosidase, exhibiting stronger inhibition than acarbose, while it displayed noncompetitive inhibition against α-amylase. Additionally, NDGA could spontaneously bind to α-glucosidase/α-amylase mainly through hydrogen bonds and hydrophobic forces, thus altering the spatial structure of enzymes and reducing their catalytic activity. The presence of crowding reagents/polysaccharides/undigested milk proteins would decrease the inhibitory ability of NDGA, whereas fatty acids exhibited the opposite phenomenon on α-glucosidase. Furthermore, the antidiabetic activity of NDGA in vivo was evaluated using the diabetic Drosophila model induced by a high-sugar diet. It was found that NDGA significantly reduced the glucose levels of diabetic Drosophila. These findings suggested that NDGA was a potential inhibitor of α-glucosidase/α-amylase and could be used as a nutritional adjuvant to prevent diabetes.

Inhibition of coreopsin against α-amylase/α-glucosidase and synergy with acarbose

Coreopsin is a flavonoid from Coreopsis tinctoria. The inhibition of coreopsin and synergy with acarbose against α-amylase (PPA) or α-glucosidase (SCG) were explored. As a result, coreopsin exhibited stronger inhibition on PPA/SCG than that of acarbose. Combination of coreopsin (4.11 μM) with acarbose (132.77 μM) had significant synergistic effect on PPA, while combination of coreopsin (5.76 μM) and acarbose (121.7 μM) had significant synergy on SCG. Coreopsin, acarbose and acarbose-coreopsin inhibited PPA in mixed-type mode. Acarbose competitively inhibited SCG, whereas coreopsin and acarbose-coreopsin inhibited SCG in mixed-type mode. Fluorescence analysis conformed that coreopsin could synergize with acarbose by increasing the binding ability of acarbose to PPA/SCG. Compared with acarbose or coreopsin, acarbose-coreopsin complexes resulted in more conformational changes of PPA/SCG, revealing that the complexes had stronger inhibitory ability than acarbose or coreopsin alone. The detail binding information of coreopsin, acarbose or acarbose-coreopsin to PPA /SCG was revealed by computer simulation.

Spontaneous interactions between typical antibiotics and soil enzyme: Insights from multi-spectroscopic approaches, XPS technology, molecular modeling, and joint toxic actions

A large amount of antibiotics enters the soil environment and accumulates therein as individuals and mixtures, threatening the soil safety. However, there is little information regarding the influence of single and mixed antibiotics on key soil proteins at molecular level. In this study, setting sulfadiazine (SD) and tetracycline hydrochloride (TC) as the representative antibiotics, the interactions between these agents and α-amylase (an important hydrolase in soil carbon cycle) were investigated through multi-spectroscopic approaches, X-ray photoelectron spectrometry, and molecular modeling. It was found that both SD and TC spontaneously bound to α-amylase with 1:1 stoichiometry mainly via forming stable chemical bonds. The interactions altered the polarity of aromatic amino acids, protein backbone, secondary structure, hydrophobicity and activity of α-amylase. The SD-TC mixtures were designed based on the direct equipartition ray to comprehensively characterize the possible concentration distribution, and interactive effects indicated that the mixtures antagonistically impacted α-amylase. These findings reveal the binding characteristics between α-amylase and typical antibiotics, which probably influence the ecological functions of α-amylase in soil. This study clarifies the potential harm of antibiotics on soil functional enzyme, which is significant for the environmental risk assessment of antibiotics and their mixtures.

Unraveling the interaction mechanism between orphan drug Nitisinone and bovine serum albumin through spectroscopic and in silico approaches

The interaction between Nitisinone (NTBC) and bovine serum albumin (BSA) as the transport protein in a circulating system was investigated for the first time utilizing various analytical (UV-Vis spectrophotometry, fluorescence spectroscopy, dynamic light scattering, and differential scanning calorimetry) and computational (molecular docking and molecular dynamics simulations) methods. The BSA fluorescence intensity was quenched upon interaction with NTBC, and the quenching mechanism was observed as static. The interaction between NTBC and BSA was examined at 288 K, 298 K, and 308 K where the binding constants were found to be 1.44 × 105 ± 0.22 M-1, 5.18 × 104 ± 0.20 M-1, and 3.02 × 104 ± 0.22 M-1 respectively, suggesting an intermediate binding affinity between NTBC and BSA. Changes in the microenvironment surrounding tryptophan and tyrosine residues of BSA were elucidated using 3-D fluorescence spectroscopy. Thermodynamic studies revealed the calculated values of ΔH =  - 54.34 ± 5 kJ/mol and ΔS =  - 0.0908 ± 0.24 kJ/mol K-1, indicating the involvement of van der Waals forces and hydrogen bonds in the interaction between NTBC and BSA. Moreover, the interaction's spontaneous nature was evidenced by negative ΔG values across all temperatures. Using dynamic light scattering, it was observed that higher NTBC concentrations led to a gradual rise in hydrodynamic diameter and notable aggregation of the NTBC-BSA complex. Moreover, changing signal values and shifted peaks of BSA, NTBC, and complex in differential scanning calorimetry curves, meant there were molecular interactions between the NTBC and BSA. In silico approaches also elucidated how NTBC binds to active sites on BSA, further supporting other findings. Moreover, molecular docking studies offer a more profound insight into the changing dynamics of hydrophobic, hydrogen, and halogen bonding involved in stabilizing the NTBC-BSA complex.

Theabrownin/whey protein isolate complex coacervate strengthens C2C12 cell proliferation via modulation of energy metabolism and mitochondrial apoptosis

Theabrownin (TB)-whey protein isolate (WPI) complex coacervates (TW) were firstly prepared to investigate the regulatory effects on skeletal muscle. The binding of TB to WPI reached saturation with the strongest electrostatic interaction at the ratio of 10:1. The formation of TW was driven by electrostatic interactions with the aid of hydrogen bonding and hydrophobic interactions, and the digestion behavior of TW was investigated based on in vitro gastrointestinal and CaCO2 cell models. The regulatory effect of TW on muscle cells was investigated by C2C12 cell assay. Cell cycle analysis showed that TW promoted the transition of skeletal muscle cells from proliferative state to differentiated state. Immunofluorescence and gene expression revealed that TW positively regulated myogenic regulatory factors, contributing to myofiber formation. Moreover, TW activated the intracellular TCA cycling and oxidative phosphorylation, providing energy for skeletal muscle regeneration and repair. Mechanistically, TW inhibited the release of cytochrome C from mitochondria to cytoplasm through the Bcl-2/Cytochrome C/Cleaved-Caspase-3 pathway, exhibiting a protective effect on skeletal muscle cells. In the future, the molecular mechanism of TW enhancing skeletal muscle function should be validated through aging animal models and clinical trials and expand its therapeutic application for muscle health in functional food and dietary supplements.

Binding characteristics and conformational changes in alpha-2-macroglobulin by the dietary flavanone naringenin: biophysical and computational approach

In the present study, we investigated the interaction of alpha-2-macroglobulin (α2M) with naringenin using multi-spectroscopic, molecular docking, and molecular simulation approaches to identify the functional changes and structural variations in the α2M structure. Our study suggests that naringenin compromised α2M anti-proteinase activity. The results of absorption spectroscopy and fluorescence measurement showed that naringenin-α2M formed a complex with a binding constant of (kb)∼104, indicative of moderate binding. The value of ΔG° in the binding indicates the process to be spontaneous and the major force responsible to be hydrophobic interaction. The findings of FRET reveal the binding distance between naringenin and the amino acids of α2M was 2.82 nm. The secondary structural analysis of α2M with naringenin using multi-spectroscopic methods like synchronous fluorescence, red-edge excitation shift (REES), FTIR, and CD spectra further confirmed the significant conformational alterations in the protein. Molecular docking approach reveals the interactions between naringenin and α2M to be hydrogen bonds, van der Waals forces, and pi interactions, which considerably favour and stabilise the binding. Molecular dynamics modelling simulations also supported the steady binding with the least RMSD deviations. Our study suggests that naringenin interacts with α2M to alter its confirmation and compromise its activity.Communicated by Ramaswamy H. Sarma.

Comprehending the inhibition mechanism of indole-based bis-acylhydrazone compounds on α-glucosidase: Spectral and theoretical approaches

Indole-based bis-acylhydrazone compounds can inhibit the activity of α-glucosidase and control the concentration of blood glucose. In this paper, the characteristics of three indole-based bis-acylhydrazone compounds with different inhibitory activities of α-glucosidase as well as the interaction with α-glucosidase were studied by experiments and computational simulation techniques. Enzyme kinetic and spectral experiments showed that the indole-based bis-acylhydrazone compounds were able to inhibit enzyme activity through mixed inhibition dominated by competitive inhibition, and during the binding reaction, indole-based bis-acylhydrazone compounds can quench the intrinsic fluorescence of α-glucosidase through static quenching and an aggregation of the indole-based bis-acylhydrazone with α-glucosidase produces a stable complex with a molar ratio of 1:1, and the combination of indole-based bis-acylhydrazone compounds could lead to slight change in the conformation of α-glucosidase. The theoretical simulation demonstrated that the stability of the complex systems was positively correlated with the inhibitory activity of indole-based bis-acylhydrazone compounds, and the indole-based bis-acylhydrazone compounds occupied the active site in the multi-ligand system, resulting in a significant decrease in the binding ability of starch to active amino acids. These results suggested that indole-based bis-acylhydrazone compound was expected to be a new type of α-glucosidase inhibitor.

Exploring the binding behavior mechanism of vitamin B12 to α-Casein and β-Casein: multi-spectroscopy and molecular dynamic approaches

The aim of this study was to investigate the behavior interaction of α-Casein-B12 and β-Casein-B12 complexes as binary systems through the methods of multiple spectroscopic, zeta potential, calorimetric, and molecular dynamics (MD) simulation. Fluorescence spectroscopy denoted the role ofB12as a quencher in both cases of α-Casein and β-Casein fluorescence intensities, which also verifies the existence of interactions. The quenching constants of α-Casein-B12 and β-Casein-B12 complexes at 298 K in the first set of binding sites were 2.89 × 104 and 4.41 × 104 M-1, while the constants of second set of binding sites were 8.56 × 104 and 1.58 × 105 M-1, respectively. The data of synchronized fluorescence spectroscopy at Δλ = 60 nm were indicative of the closer location of β-Casein-B12 complex to the Tyr residues. Additionally, the binding distance between B12 and the Trp residues of α-Casein and β-Casein were obtained in accordance to the Förster's theory of nonradioactive energy transfer to be 1.95 nm and 1.85 nm, respectively. Relatively, the RLS results demonstrated the production of larger particles in both systems, while the outcomes of zeta potential confirmed the formation of α-Casein-B12 and β-Casein-B12 complexes and approved the existence of electrostatic interactions. We also evaluated the thermodynamic parameters by considering the fluorescence data at three varying temperatures. According to the nonlinear Stern-Volmer plots of α-Casein and β-Casein in the presence of B12 in binary systems, the two sets of binding sites indicated the detection of two types of interaction behaviors. Time-resolved fluorescence results revealed that the fluorescence quenching of complexes are static mechanism. Furthermore, the outcomes of circular dichroism (CD) represented the occurrence of conformational changes in α-Casein and β-Casein upon their binding to B12 as the binary system. The experimental results that were obtained throughout the binding of α-Casein-B12 and β-Casein-B12 complexes were confirmed by molecular modeling.Communicated by Ramaswamy H. Sarma.

Organic acid treatments on citrus insoluble dietary fibers and the corresponding effects on starch in vitro digestion

Three environmentally friendly organic acids, acetic acid, citric acid and oxalic acid, were used to treat citrus insoluble dietary fiber (CIDF) in present study, aiming to explore the changes in structural properties as well as their inhibitory effects on starch digestion. The results showed that organic acid treatment significantly reduced the particle size of all three CIDFs, with rougher and folded surfaces, improved crystallinity and thermal stability. During in vitro digestion, it was found that organic acid treatment could increase the particle size and viscosity of digestion, and also effectively enhance the inhibitory ability of α-glucosidase activity, resulting in a further blockage of starch digestion. The starch digestion in oxalic acid-treated group (with 3 wt% addition) was significantly reduced by 18.72 % compared to blank group and 9.05 % compared to untreated. These findings provide evidence of the potential of organic acid-treated insoluble dietary fiber as a functional food.

Inhibition of α-glucosidase activity and intestinal glucose transport to assess the in vivo anti-hyperglycemic potential of dodecyl-acylated phlorizin and polydatin derivatives

A diet containing natural active compounds that can inhibit the hydrolytic activity of α-glucosidase on carbohydrates and intestinal glucose absorption is an effective means of controlling postprandial hyperglycemia. Phlorizin and polydatin as phenolic glycosides have a high affinity for the catalytic site of α-glucosidase, but exhibited unsatisfactory competitive inhibitory capacity, with an IC50 of 0.97 and >2 mM, respectively. However, dodecyl-acylated derivatives of phlorizin and polydatin exerted α-glucosidase inhibitory capacity, with an IC50 of 55.10 and 70.95 μM, respectively, which were greatly enhanced and much stronger than that of acarbose with an IC50 of 2.46 mM. The SPR assay suggested the high affinity of dodecyl phlorizin and dodecyl polydatin to α-glucosidase with equilibrium dissociation constant (KD) values of 12.0 and 7.9 μM, respectively. Both dodecyl phlorizin and dodecyl polydatin reduced the catalytic ability of α-glucosidase by reversible noncompetitive and uncompetitive mixed inhibition, which bind noncovalently to the allosteric site 2 through hydrogen bonds and hydrophobic interactions, thereby inducing the secondary structure unfolding and intrinsic fluorescence quenching of α-glucosidase. Confocal microscopy detection visually showed significant inhibitory effects on FITC-labeled glucose uptake in intestinal Caco-2 cells by phlorizin, polydatin, dodecyl phlorizin and dodecyl polydatin. In addition, based on the differentiated Caco-2 cell monolayer model, dodecyl phlorizin and dodecyl polydatin suppressed intestinal glucose transport more effectively than phlorizin and polydatin, suggesting that they were promising in vivo hypoglycemic active compounds.

Bovine serum albumin-liposome stabilized high oil-phase emulsion: Effect of liposome ratio on interface properties and stability

This study aimed to solve the issue of poor lipophilicity of natural bovine serum albumin (BSA) by combining with liposomes (Lips) to stabilize high oil-phase emulsions (HOPEs). The interaction between BSA and Lips was mainly driven by hydrophobic forces, followed by hydrogen bonding. The secondary structure and tertiary structure of BSA were characterized and indicated that the addition of Lips promoted the structural expansion of BSA exposing the hydrophobic groups inside. Interfacial adsorption behaviours were assessed through dynamic interfacial tension, three-phase contact angle, and quartz crystal microbalance with dissipation. These results indicated that BSA-Lips crosslinking improved wettability, promoting adsorption and rearrangement at the oil-water interface, thereby resulting in a dense interfacial layer. The emulsifying efficacy of BSA-stabilized HOPEs also displayed a distinct Lips dependency. Varying the BSA-to-Lips ratio transformed their consistency from flowing to semi-solid, reinforcing the gel network. Under optimal conditions (BSA: Lips = 1:1), the droplet size of BSA-Lips stabilized HOPEs reached a minimum with a highly uniform distribution. Moreover, a 1:1 BSA to Lips ensured outstanding storage, thermal, and centrifugal stability for the HOPEs. This work provides valuable references for the interaction between protein and Lips, guiding the development of highly stable HOPEs stabilizers.

Simultaneous binding characterization of different chromium speciation to serum albumin

The binding process between three species of chromium and serum albumin (SA) was investigated, as well as the interaction between K2Cr2O7 and bovine serum albumin (BSA) under coexistence of different chromium forms. CrCl3, K2Cr2O7 and Crpic bound to SA spontaneously through Van der Waals force, and their binding constants were 103-104 M-1 at 298 K, respectively. K2Cr2O7 and Crpic both had strong binding affinity for BSA, and significantly affected the secondary structure of BSA and the microenvironment surrounding amino acid residues. Chromium exhibited a greater fluorescence quenching constant towards HSA than toward BSA, and K2Cr2O7 induced greater conformational changes in human serum albumin (HSA) than in BSA. A weak binding of CrCl3 to BSA had no significant effect on the binding affinity of K2Cr2O7 to BSA. K2Cr2O7 and BSA have a greater binding affinity when coexisting with Crpic, and K2Cr2O7 induces a greater conformational change in BSA.

Structure and energetics of serum protein complex of tea adulterant dye Bismarck brown Y using experimental and computational methods

Tea, a widely consumed aromatic beverage, is often adulterated with dyes such as Bismarck brown Y (C.I. 21000) (BBY), Prussian blue, and Plumbago, which pose potential health risks. The objective of this study is to analyze how the food dye BBY interacts with serum protein, bovine serum albumin (BSA). This study investigated the BBY-BSA interaction at the molecular level. Fluorescence spectroscopy results showed that the quenching of BSA by BBY is carried out by dynamic quenching mechanism. The displacement assay and molecular docking studies revealed that BBY binds at the flavanone binding site of BSA with hydrophobic interactions. Circular Dichroism results indicate the structural stability of the protein upon BBY binding. Molecular dynamics simulations demonstrated the stability of the complex in a dynamic solvent system, and quantum mechanics calculations showed slight conformational changes of the diaminophenyl ring due to increased hydrophobic interaction. The energetics of gas phase optimized and stable MD structures of BBY indicated similar values which further confirmed that the conformational changes were minor, and it also exhibited a moderate binding with BSA as shown by the MM/PBSA results. This study enhances our understanding of the molecular-level interactions between BBY and BSA, emphasizing the critical role of hydrophobic interactions.

Synthesis, biological evaluation and action mechanism of 7H-[1,2,4] triazolo [3,4-b] [1,3,4] thiadiazine-phenylhydrazone derivatives as α-glucosidase inhibitors

In our work, several 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-phenylhydrazone derivatives as α-glucosidase inhibitors (α-GIs) were synthesized and characterized by 1H NMR, 13C NMR, and HRMS spectrum. Then, their bio-activity against the α-glucosidase (α-Glu) was further evaluated. Among them, almost all compounds displayed better bio-activity with IC50 from 31.23 ± 0.89 to 213.50 ± 4.19 μM than acarbose (IC50 = 700.20 ± 10.55 μM). In particular, compound 5o showed the best potency to inhibit α-Glu in a mixed manner. Moreover, the action mechanisms of 5o were further clarified including fluorescence quenching, circular dichroism spectra, three-dimensional fluorescence spectra, molecular docking, etc. All mechanism studies revealed that 5o could arouse the changed secondary structure of α-Glu to hinder enzyme catalytic activity. It was observed from an in vivo study that 5o of 20 mg/kg could significantly decrease by 24.45 % postprandial blood glucose in mice vs. the control. Meanwhile, 5o had low drug-drug interaction potential and was likely to be an orally active compound. Moreover, 5o was observed to be no obvious cytotoxicity to HEK-293 cells. In summary, compound 5o exhibited one potential to be further applied as an antidiabetic drug.

Utilizing bio-affinity ultrafiltration combined with UHPLC Q-Exactive Plus Orbitrap HRMS to detect potential α-glucosidase inhibitors in Oxalis corniculate L

Oxalis corniculate L. (O. corniculate) was used to treat diabetes in Chinese folk as a popular tea drink. In this work, 31 compounds from O. corniculate were screened and identified as potential α-Glucosidase inhibitors (α-GIs). Among them, 6 compounds displayed stronger inhibitory activity than acarbose (IC50 = 212.9 ± 5.98 μg/mL). Especially, the most effective compounds quercetin (Qu, IC50 = 4.70 ± 0.40 μg/mL) and luteolin (Lu, IC50 = 15.72 ± 0.75 μg/mL) inhibited α-Glu in competitive and mixed manners, respectively. Moreover, fluorescence quenching, circular dichroism (CD), and molecular docking study revealed that they can arouse the changes in the secondary structure and hydrophobic micro-environment of the enzyme mainly through a hydrophobic binding. Furthermore, it was observed that oral administration of Qu (20 mg/kg) can significantly reduce postprandial blood glucose (PBG) levels in mice vs. the control group. To sum up, the above research confirmed that O. corniculate could prevent and treat postprandial hyperglycemia as a good tea drink, and the plant was an excellent source to obtain natural α-GIs.

Understanding molecular interaction between thermally modified β-lactoglobulin and curcumin by multi-spectroscopic techniques and molecular dynamics simulation

This study elucidated the binding of curcumin (CUR) onto preliminary thermally modified β-lactoglobulin (β-LG). β-LG at pH 8.1 was heated at 75 °C, 80 °C and 85 °C for 10 min to construct denatured proteins (β-LG75, β-LG80, β-LG85). Steady and time-resolved fluorescence studies uncovered that CUR quenched proteins in simultaneous static and dynamic mode. Pre-heating β-LG improved its binding with CUR and the strongest affinity occurred in β-LG80. Fluorescence resonance energy transfer (FRET) analysis indicated that binding distance between CUR and β-LG80 was the smallest and energy transfer was the most efficient. β-LG80 had the highest surface hydrophobicity. Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimeter (DSC) confirmed that CUR transferred from crystal to amorphous state after association with protein and revealed the contribution of hydrogen bonds. Combination of β-LG80 with CUR retained the antioxidant capacity of each component. Molecular dynamics simulation demonstrated enhanced hydrophobic solvent accessible surface area of β-LG80 compared with native protein. Data obtained from this study may provide useful information for comprehensively understanding the ability of β-lactoglobulin to bind hydrophobic substances under different environmental conditions like high temperature and alkaline medium.

Contribution of process-induced molten-globule state formation in duck liver protein to the enhanced binding ability of (E,E)-2,4-heptadienal

BACKGROUND

Extracted proteins of alternative animal origin tend to present strong off-flavor perception due to physicochemical interactions of coextracted off-flavor compounds with proteins. To investigate the relationship between absorption behaviors of volatile aromas and the processes-induced variations in protein microstructures and molecular conformations, duck liver protein isolate (DLp) was subjected to heating (65/100 °C, 15 min) and ultra-high pressure (UHP, 100-500 MPa/10 min, 28 °C) treatments to obtain differential unfolded protein states.

RESULTS

Heat and UHP treatments induced the unfolding of DLp to varied degrees, as revealed by fluorescence spectroscopy, ultraviolet-visible absorption, circular dichroism spectra and surface hydrophobicity measurements. Two types of heating-denatured states with varied unfolding degrees were obtained, while UHP at both levels of 100/500 MPa caused partial unfolding of DLp and the presence of a molten-globule state, which significantly enhanced the binding affinity between DLp and (E,E)-2,4-heptadienal. In particular, significantly modified secondary structures of DLp were observed in heating-denatured samples. Excessive denaturing and unfolding degrees resulted in no significant changes in the absorption behavior of the volatile ligand, as characterized by observations of fluorescence quenching and analysis of headspace concentrations.

CONCLUSION

Defining process-induced conformational transition behavior of matrix proteins could be a promising strategy to regulate food flavor attributes and, particularly, to produce DLp coextracted with limited off-flavor components by modifying their interaction during extraction processes. © 2023 Society of Chemical Industry.

Food Antioxidants and Their Interaction with Human Proteins

Common to all biological systems and living organisms are molecular interactions, which may lead to specific physiological events. Most often, a cascade of events occurs, establishing an equilibrium between possibly competing and/or synergistic processes. Biochemical pathways that sustain life depend on multiple intrinsic and extrinsic factors contributing to aging and/or diseases. This article deals with food antioxidants and human proteins from the circulation, their interaction, their effect on the structure, properties, and function of antioxidant-bound proteins, and the possible impact of complex formation on antioxidants. An overview of studies examining interactions between individual antioxidant compounds and major blood proteins is presented with findings. Investigating antioxidant/protein interactions at the level of the human organism and determining antioxidant distribution between proteins and involvement in the particular physiological role is a very complex and challenging task. However, by knowing the role of a particular protein in certain pathology or aging, and the effect exerted by a particular antioxidant bound to it, it is possible to recommend specific food intake or resistance to it to improve the condition or slow down the process.

Probing the interaction between niobium pentoxide nanoparticles and serum albumin proteins by Spectroscopic approaches

Nanoparticles (NPs) can directly or indirectly enter into the body because of their small size; then they tend to alter the conformation and function of proteins upon interaction with them. Thus, it is crucial to understand the impact of NPs in a biological medium. Recently, niobium pentoxide nanoparticles (Nb2O5 NPs) are finding increasing applications in the biological system, for example, bone tissue and dental material, matrix for biosensing of proteins, etc. In all such applications, the Nb2O5 NP interacts with proteins and other biomolecules. Hence, the study of such interactions is of considerable importance. Here in this work, we present the impact of Nb2O5 NP on the structure, stability and activity of blood proteins, bovine serum albumin (BSA) and human serum albumin (HSA) by means of various spectroscopic approaches. Steady-state fluorescence studies indicated that intrinsic fluorescence intensities of both serum albumin proteins got quenched upon their interaction with NP. The nature of the quenching was elucidated by time-resolved fluorescence and absorption measurements. Using circular dichroism (CD) and synchronous fluorescence spectroscopy (SFS), the structural perturbations of the protein molecules after interaction with NP were investigated. Moreover, the role of temperature on protein stability upon complexation with NP was also explored. In addition, the effect of NP on protein functionality was probed by esterase-like activity assays.Communicated by Ramaswamy H. Sarma.

A comprehensive insight into the effects of caffeic acid (CA) on pepsin: Multi-spectroscopy and MD simulations methods

The interaction between caffeic acid (CA) and pepsin was investigated using multi-spectroscopy approaches and molecular dynamic simulations (MDS). The effects of CA on the structure, stability, and activity of pepsin were studied. Fluorescence emission spectra and UV-vis absorption peaks all represented the static quenching mechanism of pepsin by CA. Moreover, the fluorescence spectra displayed that the interaction of CA exposed the tryptophan chromophores of pepsin to a more hydrophilic micro-environment. Consistent with the simulation results, thermodynamic parameters revealed that CA was bound to pepsin with a high binding affinity. The Van der Waals force and Hydrogen bond interaction were the dominant driving forces during the binding process. The circular dichroism (CD) spectroscopy analysis showed that the CA binding to pepsin decreased the contents of α-Helix and Random Coil but increased the content of β-sheet in the pepsin structure. Accordingly, MD simulations confirmed all the experimental results. As a result, CA is considered an inhibitor with adverse effects on pepsin activity.

Investigations on the binding properties of hydroxylated polybrominated diphenyl ethers with lysozyme using the multispectral techniques and molecular modeling

As a kind of phenolic chemical with endocrine disrupting potency, hydroxylated polybrominated diphenyl ethers (OH-PBDEs) cause a latent threat to human health from their residue in the environment. Their binding efficiency with lysozyme (LYSO) was studied by molecular simulation combined with fluorescence, UV-vis absorption and circular dichroism (CD), so as to assess their toxicity at the molecular level. Molecular docking data indicate that van der Waals force is the principal interaction force between OH-PBDEs and LYSO. The binding site for 5'-OH-BDE-25 in LYSO is ascertained as the active site, which interaction with the TRP63 and TRP108 residues of LYSO to take shape a strong face-to-face stacked rank (F-shaped). Both 4'-OH-BDE-99 and 3'-OH-BDE-154 display a certain degree of deviation from the active site. Nevertheless, their F-shaped interaction with TRP63 conduce to bind LYSO and stabilize the docking conformation. Combined with dynamics simulation and spectral analysis, the secondary structure of LYSO can be induced by the three kinds of OH-PBDEs. CD spectrum shows that the combination of LYSO and OH-PBDEs will make α- Helix content increased. The combination of OH-PBDEs and LYSO touch upon a static quenching mechanism as a result of steady state fluorescence. The energy decomposition analysis exhibited that LYSO-OH-PBDEs binding site was stable by van der Waals and hydrophobic interaction. As enzyme activity experiments demonstrate that OH-PBDEs can inhibit the activity of LYSO, which is helpful to clarify the molecular toxicity mechanism of OH-PBDEs.

Modulating the structure of lamb myofibrillar protein gel influenced by psyllium husk powder at different NaCl concentrations: Effect of intermolecular interactions

In this study, a strategy involving psyllium husk powder (PHP) was proposed to alleviate the textural deterioration of protein gels under low-sodium conditions. Results revealed that myofibrillar protein (MP) in 0.3 M NaCl could accommodate more PHP to achieve better gels properties compared with that of 0.6 M NaCl. The 3 % addition of PHP could lessen the textural deterioration of gels at 0.3 M NaCl because of the insertion of PHP into the hydrophobic cavity of MP. Consequently, the reduction in protein viscoelasticity and the thermal stability of the head and tail of myosin improved. α-Helix structures unfolded, intermolecular forces formed, and proteins aggregated. Molecular docking predicted hydrogen bonds and hydrophobic interactions as the main forces to stabilize the conformation of composites. Experiments further verified that hydrophobic interactions and disulfide bonds were the main forces that stabilized the structure of MP-PHP composite gels.

Deciphering the effect of hydrophobicity on protein binding interaction in cobalt(II) complexes by multispectroscopic and computational methods

In the present work, we report the synthesis, characterization of two cobalt complexes (1 and 2) and their HSA binding studies by multispectroscopic methods. Hirshfeld surfaces analysis and fingerprint plot analysis were carried out to identify intermolecular interactions viz., N-H···O, O-H···O and C-H···O linkages in crystal framework of the complexes. Density functional theory (DFT) studies were carried out to ascertain the electronic structure and molecular geometry of the complexes 1 and 2, and determine the localization of HOMO and LUMO in the complexes. A comparative in vitro interaction study of complex 1 and 2 with human serum albumin protein was carried out by employing UV-vis, fluorescence, circular dichroism, FTIR and molecular docking techniques. Interestingly, the HSA binding affinity of complex 2 was found to be more than complex 1 which was evidenced from the higher binding constant values owing to its strong hydrophobic topology. Further, a significant conformational change in microenvironment of HSA was noticed upon binding with complexes 1 and 2, nevertheless more perturbations were noticed in presence of complex 1. Molecular docking studies were carried out to validate the spectroscopic results and ascertain the preferential binding mode of complexes at the specific target site of HSA.Communicated by Ramaswamy H. Sarma.

Inhibitory Effects against Alpha-Amylase of an Enriched Polyphenol Extract from Pericarp of Mangosteen (Garcinia mangostana)

The pericarp of mangosteen, a by-product of the mangosteen, is rich in polyphenols. In this study, an efficient and environmentally friendly method for preparative enrichment of polyphenols from mangosteen pericarp (MPPs) was developed, and the inhibitory effects on starch digestion were also evaluated. It was found that the optimal extract method of MPPs was at a solid to solvent ratio of 1:50 g/mL, pH of 2, and at 80 °C for 2 h. The IC₅₀ of MPPs for α-amylase was 0.28 mg/mL. Based on the fluorescence quenching results, we presumed that MPPs could alter the natural structure of α-amylase, resulting in inhibitory activity on α-amylase. In addition, MPPs significantly reduced the blood glucose peak and AUC of glucose responses in rats after ingestion of the starch solution. Taken together, MPPs may have the potential as a functional supplement for blood glucose control and diabetes prevention.

Interaction of Carbon Dots from Grilled Spanish Mackerel with Human Serum Albumin, γ-Globulin and Fibrinogen

The potential biological effects of food-borne carbon dots (FCDs) generated during food heating procedures on human health has received great attention. The FCDs will be inevitably exposed to blood proteins along with our daily diet to produce unknown biological effects. In this study, the interaction between FCDs extracted from grilled Spanish mackerel and three main types of human plasma proteins including human serum albumin (HSA), human γ-globulin (HGG) and human fibrinogen (HF) was reported. It was found that the grilled Spanish mackerel FCDs could affect the morphology, size and surface electrical properties of the three proteins. The interaction between the FCDs and proteins had different effects on the secondary structure of the three proteins through a static mechanism. The tested HSA, HGG, and HF could adsorb FCDs to reach saturation state within 0.5 min after the adsorption happened. The binding affinity of the FCDs to the plasma proteins was sorted as follows: HF > HGG > HSA. The results of FCDs interacted with plasma proteins provided useful information in the assessment of the safety of FCDs in our daily diet.

Inhibition Mechanism of α-Amylase/α-Glucosidase by Silibinin, Its Synergism with Acarbose, and the Effect of Milk Proteins

As a natural flavonolignan, silibinin is reported to possess multiple biological activities, while the inhibitory potential of silibinin on carbohydrate-hydrolyzing enzymes is still unclear. Therefore, in this study, the inhibitory effect and underlying mechanism of silibinin against α-amylase/α-glucosidase were investigated. The results indicated that silibinin showed a strong inhibitory efficiency against α-amylase/α-glucosidase in noncompetitive manners and exhibited synergistic inhibition against α-glucosidase with acarbose. However, interestingly, the inhibitory effect of silibinin was significantly hindered in various milk protein-rich environments, but this phenomenon disappeared after simulated gastrointestinal digestion of milk proteins in vitro. Furthermore, silibinin could combine with the inactive site of α-amylase/α-glucosidase and change the microenvironment and secondary structure of the enzymes, thereby influencing the catalytic efficiency of enzymes. This research suggested that silibinin could be used as a novel carbohydrate-hydrolyzing enzyme inhibitor, and milk beverages rich in silibinin had the potential for further application in antidiabetic dietary or medicine.

Static quenching upon adduct formation: a treatment without shortcuts and approximations

Luminescence quenching is a process exploited in transversal applications in science and technology and it has been studied for a long time. The luminescence quenching mechanisms are typically distinguished in dynamic (collisional) and static, which can require different quantitative treatments. This is particularly important - and finds broad and interdisciplinary application - when the static quenching is caused by the formation of an adduct between the luminophore - at the ground state - and the quencher. Due to its nature, this case should be treated starting from the well-known law of mass action although, in specific conditions, general equations can be conveniently reduced to simpler ones. A proper application of simplified equations, though, can be tricky, with frequent oversimplifications taking to severe errors in the interpretation of the photophysical data. This tutorial review aims to (i) identify the precise working conditions for the application of the simplified equations of static quenching and to (ii) provide general equations for broadest versatility and applicability. The latter equations can be used even beyond the sole case of pure quenching, i.e., in the cases of partial quenching and even luminescence turn-on. Finally, we illustrate different applications of the equations via a critical discussion of examples in the field of sensing, supramolecular chemistry and nanotechnology.

Nanocomplexes of curcumin and glycated bovine serum albumin: The formation mechanism and effect of glycation on their physicochemical properties

Bovine serum albumin (BSA) and BSA-glucose conjugates (GBSAⅠ and GBSAⅠI) with different extent of glycation were complexed with curcumin (CUR). The formation mechanism of BSA/GBSA-CUR complexes and the effect of glycation on their physicochemical properties were investigated. Fluorescence quenching and FTIR analysis indicated that the BSA/GBSA-CUR nanocomplexes were formed mainly by hydrophobic interactions. XRD analysis demonstrated that CUR was present in an amorphous state in the nanocomplexes. BSA with a greater extent of glycation (BSA < GBSAⅠ<GBSAⅠI) displayed a higher binding affinity for CUR. The highest CUR encapsulation efficiency (86.77%) and loading capacity (7.81 mg/g) were obtained in the GBSAⅠI-CUR nanocomplex. The zeta-potential varied from -17.45 to -27.65 mV, depending on the extent of glycation. Furthermore, the physicochemical stability of BSA/GBSA-CUR nanocomplexes increased with the increasing extent of glycation of BSA. Thus, the obtained GBSAⅠI have the potential to become new delivery carriers for encapsulating hydrophobic food components.

Spectroscopic and molecular docking studies for the binding and interaction aspects of curcumin-cysteine conjugate and rosmarinic acid with human telomeric G-quadruplex DNA

The binding and interaction aspects of potential anticancer ligands like: curcumin-cysteine (CC) and rosmarinic acid (RA) with human telomeric G-quadruplex DNA, a novel anticancer target, have been probed by spectroscopic and molecular docking approach. The circular dichroism study unravels the conformational switching from mixed hybrid to parallel structure for the short sequence of human telomeric G-quadruplex structure in the presence of both the ligands. Further a good correlation for binding affinity has been established from the emission and absorption binding spectrum analysis. Further our spectroscopic and molecular docking studies have suggested that the CC having better binding capability than RA to human telomeric G-quadruplex. The presence of L-cysteine moiety in CC ligand is responsible factor for its binding via both minor as well as major groove of human telomeric G-quadruplex DNA where-as RA binds only via minor groove of telomeric G-DNA.

Binding and drug displacement study of colchicine and bovine serum albumin in presence of azithromycin using multispectroscopic techniques and molecular dynamic simulation

The binding and displacement interaction of colchicine and azithromycin to the model transport protein bovine serum albumin (BSA) was evaluated in this study. Azithromycin, a macrolide antibiotic, has antiviral properties and hence, has been used concomitantly with hydroxychloroquine against SARS-CoV-2. Colchicine, a natural plant product is used to treat and prevent acute gout flares. Some macrolide antibiotics are reported to have fatal drug-drug interactions with colchicine. The displacement interaction between colchicine and azithromycin on binding to BSA was evaluated using spectroscopic techniques, molecular docking and molecular dynamic simulation studies. The binding constant recorded for the binary system BSA-colchicine was 7.44 × 104 whereas, the binding constant for the ternary system BSA-colchicine in presence of azithromycin was 7.38 × 104 and were similar. Azithromycin didn't bind to BSA neither did it interfere in binding of colchicine. The results from molecular docking studies also led to a similar conclusion that azithromycin didn't interfere in the binding of colchicine to BSA. These findings are important since there is possibility of serious adverse event with co-administration of colchicine and azithromycin in patients with underlying gouty arthritis and these patients need to be continuously monitored for colchicine toxicity.

Magnetic reduced graphene oxide as a nano-vehicle for loading and delivery of curcumin

Magnetic nanoparticles have been widely used in the field of nanomedicine as drug delivery vehicles for targeted imaging-guided and controlled drug uptake and release actions. In this work, the loading of curcumin on Fe₃O₄/rGO nanocomposites and their interaction mechanism were investigated by multispectral methods including resonance light scattering (RLS), atomic force microscopy (AFM), circular dichroism (CD) and Fourier transform infrared (FT-IR). Results revealed that the drug loading was a complex process which is not governed by a simple adsorption. The interactions of vitro human serum albumin (HSA) with free curcumin and/or curcumin-Fe₃O₄/rGO complex have been studied. Outcomes from the fluorescence quenching showed that the binding constant of curcumin to HSA increased significantly in the presence of Fe₃O₄/rGO, confirming the enhanced effect of Fe₃O₄/rGO besides its low toxicity towards HSA. Findings from this work verified that Fe₃O₄/rGO nanocomposite has a promising potential as a good drug loading carrier that can be used and broad range of therapies.

The noncovalent conjugations of human serum albumin (HSA) with MS/AK and the effect on anti-oxidant capacity as well as anti-glycation activity of Monascus yellow pigments

Monascin (MS) and ankaflavin (AK), as typical yellow lipid-soluble pigments identified from Monascus-fermented products, have been confirmed to possess diverse biological activities such as anti-oxidation, reversing diabetes, and anti-atherosclerosis, and have received increasing attention in recent years. Certainly Monascus-fermented product with a high content of MS/AK is also a concern. The current work explored interactions between MS/AK and human serum albumin (HSA) as well as their influence on the anti-oxidant properties of MS/AK. Moreover, the anti-glycation potential of Monascus-fermented products rich in MS and AK (denoted as Mps) was assessed. The results showed that the fluorescence emission of HSA was quenched by MS/AK through a static quenching mechanism, and MS-HSA and AK-HSA complexes were mainly formed by van der Waals forces and hydrophobic interactions, but AK showed a higher binding affinity than MS. Although the DPPH radical-scavenging abilities of MS-HSA and AK-HSA complexes declined, Mps significantly reduced the formation of fructosamine, α-dicarbonyl compounds and advanced glycation end products (AGEs) in the in vitro glycation model (HSA-glucose). Notably, approximately 80% of fluorescent-AGEs were suppressed by Mps at a concentration of 0.95 mg mL^-1, while aminoguanidine (AG, a reference standard) caused only 65% decrease at the same concentration. Although radical scavenging and metal chelating activities could justify the observed anti-glycation activity of Mps, in-depth research on the structures of other functional compounds present in Mps except MS/AK and reaction mechanisms should be performed. Overall, the present study proved that Mps would be promising sources of food-based anti-glycation agents because of their superior inhibitory effect on AGEs.

Rosmarinic Acid-Human Pharmacokinetics and Health Benefits

Rosmarinic acid is a phenolic compound commonly found in the Lamiaceae (Labiateae) plant species. It is considered responsible for a wide spectrum of biological and pharmacological activities of plants containing this compound. The aim of the current review is to present the fate of rosmarinic acid inside the human body, explained through pharmacokinetic steps and to briefly present the health benefits of RA. Pharmacokinetics was at first studied in animal models, but several studies were conducted in humans as well. This compound can be applied topically, pulmonary, intranasally, and via intravenous infusion. However, peroral application is the main route of entry into the human body. Presumably, it is mainly metabolized by the gut microflora, providing simple, more easily absorbed phenolic units. Inside the body, the rosmarinic acid molecule undergoes structural changes, as well as conjugation reactions. Renal excretion represents the main path of elimination. Previously conducted studies reported no serious adverse effects of herbal remedies containing RA, as well as their positive effects on human health. In addition to in vitro studies, clinical investigations suggested its benefits in dermatological, allergic, and osteoarthritic disorders, as well as for improving cognitive performance and in metabolic syndrome treatment. Future studies should investigate the kinetics during long-term application in patients who would have potential benefits from RA usage. Pharmaceutical formulations designed to prevent the fast metabolism of RA and allow its penetration into other compartments of the human body are also interesting topics for future research.

Phosphorylation of myosin regulatory light chain at Ser17 regulates actomyosin dissociation

Phosphorylation of myosin regulatory light chain (MRLC) can regulate muscle contraction and thus affect actomyosin dissociation and meat quality. The objective of this study was to explore the mechanism by how MRLC phosphorylation regulates actomyosin dissociation and thus develop strategies for improving meat quality. Here, the phosphorylation status of MRLC was modulated by myosin light chain kinase and myosin light chain kinase inhibitor. MRLC phosphorylation at Ser17 decreased the kinetic energy and total energy of actomyosin, thus stabilized the structure, facilitating the interaction between myosin and actin; this was one possible way that MRLC phosphorylation at Ser17 negatively affects actomyosin dissociation. Moreover, MRLC phosphorylation at Ser17 was beneficial to the formation of ionic bonds, hydrogen bonds, and hydrophobic interaction between myosin and actin, and was the second possible way that MRLC phosphorylation at Ser17 negatively affects actomyosin dissociation.

Interaction between olanzapine and human serum albumin and effect of metal ions, caffeine and flavonoids on the binding: A spectroscopic study

In this study, the binding of olanzapine (OLZ) to human serum albumin (HSA) and the influence of metal ions (Ca²⁺, Mg²⁺, Cu²⁺, Zn²⁺, Fe³⁺), caffeine (CAF) and flavonoids (diosmin (DIO), catechin (CAT), quercetin (QUE)), on their affinity, was investigated by fluorescence spectroscopy and UV-vis absorption spectroscopy. Fluorescence experiments suggest that OLZ quench the fluorescence of HSA through the mixed quenching mechanism and non-radiation energy transferring as a result of the HSA-OLZ complex formation. OLZ spontaneously bind in the site I on HSA, and according to thermodynamic parameters, the reaction was spontaneous and mainly driven by hydrogen bonds and van der Waals interactions. The presence of Mⁿ⁺ ions, CAF, DIO and CAT decreased binding affinity between OLZ and HSA which indicates that they could compete against OLZ in the site I. Contrary, in the presence of QUE the binding affinity of the HSA-OLZ system enhanced, which may be explained by conformational changes in HSA (non-competitive interference).

A novel palladium(II) antitumor agent: Synthesis, characterization, DFT perspective, CT-DNA and BSA interaction studies via in-vitro and in-silico approaches

Since numerous people annually pass away due to cancer, research in this field is essential. Thus a newly made and water like palladium(II) complex of formula [Pd(phen)(acac)]NO3, where phen is 1,10-phenanthroline and acac is acetylacetonato ligand, has been synthesized by the reaction between [Pd(phen)(H2O)2](NO3)2 and sodium salt of acetylacetone in the molar ratio of 1:1. It has been structurally characterized via the methods such as conductivity measurement, elemental analysis and spectroscopic methods (FT-IR, UV-Vis and 1H NMR). The geometry optimization of this complex at the DFT level of theory reveals that Pd(II) atom is situated in a square-planar geometry. The complex has been screened for its antitumor activity against K562 cancer cells which demonstrated efficacious activity. The interaction of above palladium(II) complex with CT-DNA as a target molecule for antitumor agents and BSA as a transport protein was studies by a variety of techniques. The results of UV-Vis absorption and fluorescence emission indicated that the Pd(II) complex interacts with EB + CT-DNA through hydrophobic and with BSA by hydrogen bonding and van der Waals forces at very low concentrations. In these processes, the fluorescence quenching mechanism of both the macromolecules seems to be the combined dynamic and static. The interaction was further supported for CT-DNA by carrying out the gel electrophoresis and viscosity measurement and for BSA by the circular dichroism and Förster resonance energy transfer experiments. Furthermore, results of partition coefficient determination showed that the [Pd(phen)(acac)]NO3 complex is more lipophilic than that of cisplatin. Moreover, molecular docking simulation confirms the obtained results from experimental tests and reveals that the complex tends to be located at the intercalation site of DNA and Sudlow's site I of BSA.

In vivo and in vitro studies of Banhahoobak-tang tablets using UPLC-ESI-MS/MS with polarity switching

Banhahoobak-tang is the most prescribed herbal drug in East Asia when individuals experience sudden symptoms such as sore throat or neurological symptoms. The low toxicity and high in-vivo safety of this herbal medicine has made it more attractive to patients, and it has recently been formulated as tablets. In addition, Banhahoobak-tang tablets are registered as health insurance drugs in South Korea, and clinical prescriptions and demand are increasing. However, there are very few clinical trial data as well as very little accurate content analysis and results for Banhahoobak-tang tablets. The purpose of this study was to perform in-vitro and in-vivo studies on Banhahoobak-tang tablets, including content analysis, pharmacokinetics in humans, and plasma protein binding. For this study, a UPLC-ESI-MS/MS method with polarity switching was developed for simultaneous analysis of 18 components of Banhahoobak-tang. To separate the analytes, a C₈ reverse-phase column was used as the stationary phase, 0.1 % aqueous formic acid and acetonitrile as the mobile phase, and ionization and multiple reaction monitoring for quantification. The developed method was able to isolate and quantify the 18 components with good sensitivity and selectivity and was fully validated according to international analytical standards. Stability tests were also conducted on the analytes. Finally, the method was applied to in-vitro and in-vivo studies of Banhahoobak-tang tablets, and the tablet components were 52.49 ng/g to 91.00 μg/g on average. The detected components showed rapid oral absorption in humans as well as high plasma protein binding ratio overall. These results and methods can be useful not only for effectiveness and safety evaluation but also for quality control of Banhahoobak-tang tablets.