Biophysical Studies on the Interactions of a Classic Mitochondrial Uncoupler with Bovine Serum Albumin by Spectroscopic, Isothermal Titration Calorimetric and Molecular Modeling Methods

Lactoferrin-Chitosan Composite Hydrogels Induced by Microbial Transglutaminase: Potential Delivery Systems for Thermosensitive Bioactive Substances

In this work, lactoferrin (LF)-chitosan (CS) composite hydrogels with good loading capacity of thermosensitive bioactive substances were successfully obtained by microbial transglutaminase (MTG)-induced cross-linking. We evaluated the rheological, textural, and microstructural characteristics of the composite hydrogels under different conditions. The results demonstrated that the concentrations of LF and CS as well as the amount of MTG could regulate the textural properties, rheological properties, and water holding capability. The results of FTIR and fluorescence spectroscopy indicated that the main interactions within the composite gel were hydrogen and isopeptide bonds. Additionally, in vitro digestion simulation results verified that riboflavin kept stable in stomach due to the protection of LF-CS composite hydrogels and was released in small intestine. These results suggested that thermosensitive bioactive substance could be encapsulated and delivered by the LF-CS composite hydrogel, which could be applied in lots of potential applications in functional food as a new material.

Synergistic effects of microbial transglutaminase and apple pectin on the gelation properties of pea protein isolate and its application to probiotic encapsulation

The low gelation capacity of pea protein isolate (PPI) limits their use in food industry. Therefore, microbial transglutaminase (MTG) and apple pectin (AP) were combined to modify PPI to enhance its gelling characteristics, and the mechanism of MTG-induced PPI-AP composite gel generation was investigated. PPI (10 wt%) could not form a gel at 40 °C, while MTG-treated PPI (10 wt%) formed a self-supporting gel at 40 °C. Subsequently, the addition of AP further promoted the crosslinking of PPI and significantly improved the water holding capacity, rheology, and strength of PPI gels, which was attributed to both hydrogen and isopeptide bonds in the composite gel. Additionally, the PPI-AP composite gel showed excellent protection ability, and the survival rate of probiotics could reach over 90%, which could be used as an effective delivery system. This study verified that MTG and AP were efficient in enhancing the functional quality of PPI gels.

Interaction of bovine serum albumin with ellagic acid and urolithins A and B: Insights from surface plasmon resonance, fluorescence, and molecular docking techniques

Human serum albumin (HSA) shows the sequence homology and structural similarity with bovine serum albumin (BSA). Therefore, here, the interaction of natural phenolic antioxidants, ellagic acid (ELA), and its derivatives-urolithins A (ULA) and B (ULB)-with BSA was investigated. The results of surface plasmon resonance (SPR) indicated a high affinity of ELA, ULA, and ULB to BSA, with KD value < 1 × 10-6 M. The KD values of binding of the studied compounds to BSA increased with temperature, revealing a reduction in affinity with an increase in temperature. Fluorescence data showed that the quenching of BSA by tested compounds occurred via a static quenching. However, the affinity of ELA for BSA was higher than that of ULA and ULB, which may be because of the presence of a large number of hydroxyl groups in its structure. The assessment of the antioxidant activity of BSA and BSA-ELA/ULA/ULB complexes using the DPPH assay indicated that the DPPH scavenging activity of BSA increased after complex formation with ELA/ULA/ULB in the following order: BSA-ELA > BSA-ULA > BSA-ULB > BSA, which was due to their structural differences. The results of the docking analysis were in agreement with the experimental results.

The interaction of folate-modified Bletilla striata polysaccharide-based micelle with bovine serum albumin

We fabricated an amphiphilic folate-modified Bletilla striata polysaccharide (FA-BSP-SA) copolymer that exhibited good biocompatibility and superior antitumor effects. This study investigated the affinity between FA-BSP-SA and bovine serum albumin (BSA) via multispetroscopic approaches. Changes in the morphology and particle size showed that FA-BSP-SA formed a blurry "protein corona". Stern-Volmer equation demonstrated that FA-BSP-SA micelles decreased the fluorescence of BSA via static quenching. The measurement results of thermodynamic parameters (entropy change, enthalpy change, and Gibbs free energy) suggested that the binding between FA-BSP-SA and BSA was spontaneous in which Van der Waals forces and hydrogen bonding played major roles. The results from synchronous fluorescence, circular dichroism, and UV spectra also revealed that BSA conformation was slightly altered by decreasing α-helical contents. In addition, the antitumor effects in vitro of Dox@FA-BSP-SA micelles and the cellular uptake behavior of micelles in 4T1 cells were decreased after incubating with BSA.

Exploring The Interactions of a Natural Gamma-Oryzanol with Human Serum Albumin: Surface Plasmon Resonance, Fluorescence, and Molecular Modeling Studies

γ-oryzanol (ORY) is the vital bioactive compound, which is a mixture of ferulic acid ester and plant sterols. In the present work, the binding of ORY to human serum albumin (HSA) was investigated at the molecular level using fluorescence spectroscopy and surface plasmon resonance (SPR) as well as molecular modeling studies. Based on the fluorescence data analysis, ORY can form a non-fluorescent complex with HSA and induce static quenching of the emission intensity of HSA. Also, the high value of K _SV (34.69 × 10⁴ M^-1) confirmed a high sensitivity of HSA toward ORY. The real-time monitoring of the binding of ORY to HSA was carried out using the SPR technique. The small K _D value (1.23 × 10^-6 M) calculated by SPR analysis indicated a high affinity of ORY toward HSA. The molecular modeling studies confirmed that ORY has only one binding site on HSA and binds HSA in a cavity between subdomain IIA and IIIA.

Thermodynamic Implications and Time Evolution of the Interactions of Near-Infrared PbS Quantum Dots with Human Serum Albumin

Near-infrared (NIR)-emitting PbS quantum dots (QDs) are endowed with good stability, high quantum yield, and long lifetime in the body, so they are promising agents in biological imaging. They quickly form the so-called "protein corona" through nonspecific adsorption with proteins in biological fluids once upon exposure to the biological system. Here, PbS QDs and human serum albumin (HSA) were selected as the model system. Fluorescence quenching spectroscopic studies indicated a static quenching process caused by the addition of PbS QDs, which was corroborated by the UV-vis absorption spectroscopy and fluorescence lifetime. Thermodynamic parameters were obtained by the fluorescence quenching method. The enthalpy change and entropy change were well correlated with the "enthalpy-entropy compensation" (EEC) equation summarized in this work. The slope (α = 1.08) and the intercept (TΔS ₀ = 34.44 kJ mol^-1) indicated that the interaction resembled a protein-protein association. The both negative signs of enthalpy change and entropy change were elucidated by a proposed "two-step association-interaction" (TSAI) model. Agarose gel electrophoresis (AGE) and dynamic light scattering (DLS) showed that the binding ratio was roughly 2:1 (HSA/QDs), resembling sandwich-like structures. Furthermore, the secondary structure of HSA depended on the concentration of added QDs and the incubation time. The results preliminarily uncovered the physicochemical properties of QDs in the presence of proteins and elucidated the role of time evolution. These will inspire us to make the fluorescent QDs more biocompatible and use them in a proper way.

Poziotinib and bovine serum albumin binding characterization and influence of quercetin, rutin, naringenin and sinapic acid on their binding interaction

Serum albumin is the major transporter protein present in systemic circulation and the ability to transport ligands can be influenced in presence of other ligands. This interaction can influence the pharmacodynamic and pharmacokinetic property of certain ligands. Spectroscopic and molecular docking studies were conducted to understand the poziotinib binding interaction to bovine serum albumin (BSA). Further, influence of different flavonoids (quercetin, rutin, naringenin and sinapic acid) on displacing poziotinib from BSA binding sites was also studied. The BSA and poziotinib followed a static quenching mechanism as the Stern-Volmer constant showed decrease (7.6 × 10⁴-6.0 × 10⁴) when the temperature increased from 298 K to 310 K. The BSA and poziotinib interaction was spontaneous and enthalpy driven. Involvement of Van der Waals forces and hydrogen bonding in the binding interaction was suggested on the basis of thermodynamic study results. Conformational changes were suggested in the BSA on its interaction with poziotinib based on fluorescence experimental data. The binding constant for BSA-poziotinib showed a maximum decrease in presence of quercetin followed by naringenin, rutin and sinapic acid respectively. Site displacement studies suggested binding of poziotinib site I of BSA.

Surface plasmon resonance, fluorescence, and molecular docking studies of bovine serum albumin interactions with natural coumarin diversin

In the present study the binding of diversin (DIV), a prenylated coumarin isolated from Ferula diversivittata, to bovine serum albumin (BSA) was investigated using surface plasmon resonance (SPR), spectrofluorimetry, and molecular docking approaches. Following the activation of carboxylic groups, via NHS/EDC, BSA was immobilized on the carboxymethyl dextran (CMD) hydrogel coated Au sensor, and was used for real-time monitoring of the interactions between DIV and BSA. K_D value of DIV binding to BSA increased with increasing temperature, confirmed that the affinity between BSA and DIV decreases with rising temperature. In addition, the fluorescence and synchronous fluorescence spectroscopic data revealed that the intrinsic emission intensity of BSA was quenched via a dynamic mechanism. In addition, the micro-region around BSA tyrosine residue was changed upon interaction with DIV. The thermodynamic parameter findings suggested that the hydrophobic interactions were dominant in the binding and formation of the BSA and DIV complex. The molecular docking outputs indicated that there is only one binding site on BSA for DIV, in agreement with experimental data, and DIV bind BSA in subdomain IB.

Responses of catalase and superoxide dismutase to low-dose quantum dots on molecular and cellular levels

With the wider application of cadmium-containing quantum dots (Cd-QDs) in biomedical fields, it is easier for people to be exposed. Studies have suggested that Cd-QDs could release cadmium ion and induce oxidative effects due to the disruption of redox equilibrium. Antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD), play an important role in organisms to resist the negative impact of exogenous substances. Molecular mechanisms of antioxidant enzymes with Cd-QDs remain unclear, however. In this study, structural and functional changes of CAT and SOD have been investigated under low dose Cd-QDs exposure. Cell viability, malondialdehyde (MDA) level, CAT and SOD activities were influenced by Cd-QDs in hepatocytes of mice. To further investigate the responses of CAT and SOD to Cd-QDs, multiple spectroscopic, calorimetric and activity measurements were carried out. Similar interaction patterns were observed that result in interaction force, structural and functional changes: Cd-QDs combine with CAT and SOD through hydrophobic forces; Intrinsic fluorescence of proteins was statically quenched by Cd-QDs and new complexes were formed; Also, the skeleton and secondary structure (with α-helix decrease) of CAT and SOD was influenced. Taken together, we suggest that Cd-QDs chosen in this study induce oxidative stress effects to hepatocytes but have not caused serious oxidative stress damage at concentrations below 10 μg/mL. MPA-CdSe/ZnS QDs caused the lowest level of oxidative stress which is associated with the induction of antioxidant proteins. This paper presents responses of CAT and SOD to low-dose Cd-QDs, and provides a reference for evaluating health damages caused by Cd-QDs.

Physicochemical stability and antioxidant activity of soy protein/pectin/tea polyphenol ternary nanoparticles obtained by photocatalysis

The ternary nanoparticles were fabricated by soy protein, pectin and tea polyphenol through photocatalysis. The particulate characteristics, including particle size, polydispersity index, and zeta potential were monitored for ternary nanoparticles formed under different photocatalysis time. Photocatalysis was favorable to form ternary nanoparticles with moderate particle size (310-370 nm), uniform distribution, spherical shape, and improved antioxidant activity. It was found that the fluorescence intensity of soy protein decreased with the increase in photocatalysis time in the ternary nanoparticles. Far-UV circular dichroism results indicated that increasing photocatalysis time could alter the secondary structure of soy protein with an increase in the proportion of β-sheet and β-turn structure at the cost of unordered coil and α-helix structure. According to FT-IR results, photocatalysis time could also modulate the conjugation between pectin and soy protein. In addition, photocatalysis could increase the binding affinities among the components, leading to better environmental stability of the ternary nanoparticles. The ternary nanoparticles in this study could be used as a good alternative to understand and consequently improve the physicochemical stability in food, pharmaceutical, and cosmetic matrices.

Spectroscopic investigation of the effects of aqueous-phase prepared CdTe quantum dots on protein hemoglobin at the molecular level

3-Mercaptopropionic Acid-modified CdTe quantum dots (QDs) were synthesized and characterized by infrared, fluorescence, and ultraviolet-visible absorption spectra and Nano-ZetaSizer measurements. Then the interaction between QDs and hemoglobin was studied to investigate the effects of QDs on the structure and function of hemoglobin by using a variety of spectroscopy methods and isothermal titration calorimetry. The results showed van der Waals forces and hydrogen bonding predominantly played major roles in the binding. The intrinsic fluorescence of hemoglobin was quenched with changes to the microenvironment of tyrosine and tryptophan residues and complex conformational changes of hemoglobin were induced with the loosening and unfolding skeleton. However, the heme in hemoglobin was still stable, indicating that the main physiological function of hemoglobin might not be significantly inhibited. This study will provide a new strategy to study the biological toxicity of QDs at the molecular level.

Spectroscopic and molecular modeling study on the separate and simultaneous bindings of alprazolam and fluoxetine hydrochloride to human serum albumin (HSA): with the aim of the drug interactions probing

The objective of the present research is to study the interaction of separate and simultaneous of alprazolam (ALP) and fluoxetine hydrochloride (FLX) with human serum albumin (HSA) in phosphate buffer (pH 7.4) using different kinds of spectroscopic, cyclic voltammetry and molecular modeling techniques. The absorbance spectra of protein, drugs and protein-drug showed complex formation between the drugs and HSA. Fluorescence analysis demonstrated that ALP and FLX could quench the fluorescence spectrum of HSA and demonstrated the conformational change of HSA in the presence of both drugs. Also, fluorescence quenching mechanism of HSA-drug complexes both separately and simultaneously was suggested as static quenching. The analysis of UV absorption data and the fluorescence quenching of HSA in the binary and ternary systems showed that FLX decreased the binding affinity between ALP and HSA. On the contrary, ALP increased the binding affinity of FLX and HSA. The results of synchronous fluorescence and three-dimensional fluorescence spectra indicated that the binding of drugs to HSA would modify the microenvironment around the Trp and Tyr residues and the conformation of HSA. The distances between Trp residue and the binding sites of the drugs were estimated according to the Förster theory, and it was demonstrated that non-radiative energy transfer from HSA to the drugs occurred with a high probability. Moreover, according to CV measurements, the decrease of peak current in the cyclic voltammogram of the both drugs in the presence of HSA revealed that they interacted with albumin and binding constants were calculated for binary systems which were in agreement with the binding constants obtained from UV absorption and fluorescence spectroscopy. The prediction of the best binding sites of ALP and FLX in binary and ternary systems in molecular modeling approach was done using of Gibbs free energy.

Binding mechanism of tauroursodeoxycholic acid to human serum albumin: insights from NMR relaxation and docking simulations

Binding patterns and structure–affinity relationship of tauroursodeoxycholic acid with human serum albumin were established by NMR methodology and docking simulations.

Study of the structure-activity relationship of flavonoids based on their interaction with human serum albumin

The influence of functional groups on the interaction has been studied detailed here; fluorescence quenching degrees and the conformation change are considered through multiple methods; molecular docking has been introduced to verify related results.

pH-driven encapsulation of curcumin in self-assembled casein nanoparticles for enhanced dispersibility and bioactivity

The poor water solubility and bioactivity of lipophilic phytochemicals can be potentially improved by delivery systems. In this study, a low-cost, low-energy, and organic solvent-free encapsulation technology was studied by utilizing the pH-dependent solubility properties of curcumin and self-assembly properties of sodium caseinate (NaCas). Curcumin was deprotonated and dissolved, while NaCas was dissociated at pH 12 and 21 °C for 30 min. The subsequent neutralization enabled the encapsulation of curcumin in self-assembled casein nanoparticles. The degradation of curcumin under encapsulation conditions was negligible based on visible light and nuclear magnetic resonance spectroscopy. The dissociation of NaCas at pH 12 and reassociation after neutralization were confirmed using dynamic light scattering and analytical ultracentrifugation. The curcumin encapsulated in casein nanoparticles showed significantly improved anti-proliferation activity against human colorectal and pancreatic cancer cells. The studied encapsulation method is promising to utilize lipophilic compounds in food or pharmaceutical industries.

Development of morin-conjugated Au nanoparticles: exploring the interaction efficiency with BSA using spectroscopic methods

In order to enhance its interaction efficiency with biomacromolecules for the usage as a therapeutic agent, we have conjugated morin, an antioxidant activity and anti-tumor drug, with citrate-coated Au nanoparticles (M-C-AuNPs). M-C-AuNPs were prepared by reducing chloroauric acid using trisodium citrate in the boiling condition, and the resulted M-C-AuNPs were characterized by UV-vis absorption spectroscopy, Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. In this article, UV-vis absorption spectroscopy in combination with fluorescence spectroscopy, and circular dichroism (CD) spectroscopy were employed to investigate the interactions between M-C-AuNPs and bovine serum albumin (BSA), C-AuNPs and BSA in a phosphate buffer at pH 7.4. By comparing the quenching constant KSV, effective quenching constant Ka, binding constant Kb and the number of binding sites n, it is clearly suggested that M-C-AuNPs could enhance the binding force of morin with BSA, which would pave the way for the design of nanotherapeutic agents with improved functionality.

Thymol nanoencapsulated by sodium caseinate: physical and antilisterial properties

In this work, thymol was encapsulated in sodium caseinate using high shear homogenization. The transparent dispersion at neutral pH was stable for 30 days at room temperature as determined by dynamic light scattering and atomic force microscopy, which agreed with high ζ potential of nanoparticles. The slightly decreased particle dimension during storage indicates the absence of Ostwald ripening. When molecular binding was studied by fluorescence spectroscopy, thymol was observed to bind with tyrosine and possibly other amino acid residues away from tryptophan of caseins. At pH 4.6 (isoelectric point of caseins), the stabilization of thymol nanoparticles against aggregation was enabled by soluble soybean polysaccharide, resulting from the combined electrostatic and steric repulsions. The encapsulated thymol showed the significantly improved antilisterial activity in milk with different fat levels when compared to thymol crystals, resulting from the quicker mixing and increased solubility in the milk serum. The transparent thymol nanodispersions have promising applications to improve microbiological safety and quality of foods.

Exploring the site-selective binding of jatrorrhizine to human serum albumin: spectroscopic and molecular modeling approaches

This paper exploring the site-selective binding of jatrorrhizine to human serum albumin (HSA) under physiological conditions (pH=7.4). The investigation was carried out using fluorescence spectroscopy, UV-vis spectroscopy, and molecular modeling. The results of fluorescence quenching and UV-vis absorption spectra experiments indicated the formation of the complex of HSA-jatrorrhizine. Binding parameters calculating from Stern-Volmer method and Scatchard method were calculated at 298, 304 and 310 K, with the corresponding thermodynamic parameters ΔG, ΔH and ΔS as well. Binding parameters calculating from Stern-Volmer method and Scatchard method showed that jatrorrhizine bind to HSA with the binding affinities of the order 10(4) L mol(-1). The thermodynamic parameters studies revealed that the binding was characterized by negative enthalpy and positive entropy changes and the electrostatic interactions play a major role for jatrorrhizine-HSA association. Site marker competitive displacement experiments and molecular modeling calculation demonstrating that jatrorrhizine is mainly located within the hydrophobic pocket of the subdomain IIIA of HSA. Furthermore, the synchronous fluorescence spectra suggested that the association between jatrorrhizine and HSA changed molecular conformation of HSA.

Systematic investigation of the toxicity interaction of ZnSe@ZnS QDs on BSA by spectroscopic and microcalorimetry techniques

The interaction of ZnSe@ZnS quantum dots (QDs) and bovine serum albumin (BSA) was investigated by means of fluorescence (FL) spectrometry, circular dichroism (CD) spectra, and isothermal titration calorimetry (ITC). The fluorescence intensity of BSA decreased regularly with the increasing of QDs concentration. The decrease of BSA fluorescence intensity was proved to be a kind of static quenching. CD results show the helicity of BSA decreased from 38.04% to 26.51% with the addition of QDs, which suggests a stronger structural change that is related to a low degree of surface coverage. And also, both ion strength and pH value could affect the interaction between BSA and QDs, suggesting that both the static electronic attraction and H-bond contribute to the interaction between BSA and QDs. The thermodynamics of interaction between BSA and QDs were calculated from ITC data. Both enthalpy and entropy changes were favorable for the interaction in Tris-buffer, while only enthalpy change was favorable for the interaction in NaCl or HCl solution.

Applications of isothermal titration calorimetry in pure and applied research--survey of the literature from 2010

Isothermal titration calorimetry (ITC) is a biophysical technique for measuring the formation and dissociation of molecular complexes and has become an invaluable tool in many branches of science from cell biology to food chemistry. By measuring the heat absorbed or released during bond formation, ITC provides accurate, rapid, and label-free measurement of the thermodynamics of molecular interactions. In this review, we survey the recent literature reporting the use of ITC and have highlighted a number of interesting studies that provide a flavour of the diverse systems to which ITC can be applied. These include measurements of protein-protein and protein-membrane interactions required for macromolecular assembly, analysis of enzyme kinetics, experimental validation of molecular dynamics simulations, and even in manufacturing applications such as food science. Some highlights include studies of the biological complex formed by Staphylococcus aureus enterotoxin C3 and the murine T-cell receptor, the mechanism of membrane association of the Parkinson's disease-associated protein α-synuclein, and the role of non-specific tannin-protein interactions in the quality of different beverages. Recent developments in automation are overcoming limitations on throughput imposed by previous manual procedures and promise to greatly extend usefulness of ITC in the future. We also attempt to impart some practical advice for getting the most out of ITC data for those researchers less familiar with the method.

Separate and simultaneous binding effects through a non-cooperative behavior between cyclophosphamide hydrochloride and fluoxymesterone upon interaction with human serum albumin: multi-spectroscopic and molecular modeling approaches

This study was designed to examine the interaction of two anti-breast cancer drugs, i.e., fluoxymesterone (FLU) and cyclophosphamide (CYC), with human serum albumin (HSA) using different kinds of spectroscopic, zeta potential and molecular modeling techniques under imitated physiological conditions. The RLS technique was utilized to investigate the effect of the two anticancer drugs on changes of the protein conformation, both separately and simultaneously. Our study suggested that the enhancement in RLS intensity was attributed to the formation of a new complex between the two drugs and the protein. Both drugs demonstrated a powerful ability to quench the fluorescence of HSA, and the fluorescence quenching action was much stronger when the two drugs coexisted. The quenching mechanism was suggested to be static as confirmed by time-resolved fluorescence spectroscopy results. The effect of both drugs on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy. Our results revealed that the fluorescence quenching of HSA originated from the Trp and Tyr residues, and demonstrated a conformational change of HSA with the addition of both drugs. The binding distances between HSA and the drugs were estimated by the Förster theory, and it was revealed that nonradiative energy transfer from HSA to both drugs occurred with a high probability. According to CD measurements, the influence of both drugs on the secondary structure of HSA in aqueous solutions was also investigated and illustrated that the α-helix content of HSA decreased with increasing drug concentration in both systems. Moreover, the zeta-potential experiments revealed that both drugs induced conformational changes on HSA. Docking studies were also performed and demonstrated that a reduction of the binding affinity between the drugs and HSA occurred in the presence of both drugs.