Interaction of inosine with human serum albumin as determined by NMR relaxation data and fluorescence methodology

Synthesis, anti-browning effect and mechanism research of kojic acid-coumarin derivatives as anti-tyrosinase inhibitors

Thirteen kojic acid-coumarin derivatives were synthesized using the principle of molecular hybridization, and their structures were characterized by 1H NMR, 13C NMR, and HRMS. In vitro enzyme inhibition experiments showed that all newly synthesized derivatives have excellent inhibition of tyrosinase (TYR) activity. As a mixed inhibitor, compound 6f has the strongest activity, with an IC50 value of 0.88 ± 0.10 µM. Multispectral experiments have confirmed that the mode of action of compound 6f on TYR was static quenching. In addition, compound 6f formed a new complex with TYR, which increased the hydrophobicity of the enzyme microenvironment, reduced the content of the α-helix in the enzyme, and changed the secondary structure. The experimental results showed that compound 6f effectively inhibited the browning of lotus root slices and had low cytotoxicity. Therefore, compound 6f is believed to have great development potential as a TYR inhibitor in the food industry.

Deciphering the binding mode and structural perturbations in floxuridine-human serum albumin complexation with spectroscopic, microscopic, and computational techniques

The binding mode of antineoplastic antimetabolite, floxuridine (FUDR), with human serum albumin (HSA), the leading carrier in blood circulation, was ascertained using multi-spectroscopic, microscopic, and computational techniques. A static fluorescence quenching was established due to decreased Ksv values with rising temperatures, suggesting FUDR-HSA complexation. UV-vis absorption spectral results also supported this conclusion. The binding constant, Ka values, were found within 9.7-7.9 × 103 M-1 at 290, 300, and 310 K, demonstrating a moderate binding affinity for the FUDR-HSA system. Thermodynamic data (ΔS = +46.35 J.mol-1.K-1 and ΔH = -8.77 kJ.mol-1) predicted the nature of stabilizing forces (hydrogen-bonds, hydrophobic, and van der Waals interactions) for the FUDR-HSA complex. Circular dichroism spectra displayed a minor disruption in the protein's 2° and 3° structures. At the same time, atomic force microscopy images proved variations in the FUDR-HSA surface morphology, confirming its complex formation. The protein's microenvironment around Trp/Tyr residues was also modified, as judged by 3-D fluorescence spectra. FUDR-bound HSA showed better resistance against thermal stress. As disclosed from ligand displacement studies, the FUDR binding site was placed in subdomain IIA (Site I). Further, the molecular docking analysis corroborated the competing displacement studies. Molecular dynamics evaluations revealed that the complex achieved equilibrium during simulations, confirming the FUDR-HSA complex's stability.

Preparation, Multispectroscopic Characterization, and Stability Analysis of Monascus Red Pigments-Whey Protein Isolate Complex

Monascus red pigments (MRPs) are mainly used as natural food colorants; however, their application is limited due to their poor stability. To expand their areas of application, we investigated the binding constants and capacity of MRPs to whey protein isolate (WPI) and whey protein hydrolysate (WPH) and calculated the surface hydrophobicities of WPI and WPH. MRPs were combined with WPI and WPH at a hydrolysis degree (DH) of 0.5% to form the complexes (DH = 0.0%) and (DH = 0.5%), respectively. Subsequently, the structural characteristics of complex (DH = 0.5%) and WPI were characterized and the color retention rates of both complexes and MRPs were investigated under different pretreatment conditions. The results showed that the maximum binding constant of WPI with MRPs was 0.670 ± 0.06 U-1 and the maximum binding capacity was 180 U/g. Furthermore, the thermal degradation of complex (DH = 0.0%), complex (DH = 0.5%), and MRPs in a water bath at 50-100 °C followed a first-order kinetic model. Thus, the interaction of WPI with MRPs could alter the protein conformation of WPI and effectively protect the stability of MRPs.

Effects of different levels of inosine-5'-monophosphate (5'-IMP) supplementation on the growth performance and meat quality of finishing pigs (75 to 100 kg)

This study aimed to assess the effects of dietary supplementation of inosine-5'-monophosphate (5'-IMP) on energy efficiency, growth performance, carcass characteristics, meat quality, oxidative status, and biochemical profile of blood plasma in finishing pigs. Fifty-four crossbred castrated male pigs were distributed in a randomized block design consisting of nine blocks, with six treatments per block and one animal per treatment per block. Experimental diets were as follows: positive control diet (PC, 3300 kcal ME/kg), negative control diet (NC, 3200 kcal ME/kg), and four diets prepared by supplementing the NC diet with 0.050%, 0.100%, 0.150%, or 0.200% 5'-IMP. Based on regression analysis, supplementation with 0.129% 5'-IMP increased average daily weight gain (1.30 kg). Backfat thickness, pH45minutes and redness of m. Longissimus Lumborum (LL) increased linearly with 5'-IMP supplementation level. Drip loss and pH at 24 h post-slaughter had a quadratic response to 5'-IMP supplementation. It is concluded that 5'-IMP supplementation positively influenced growth performance, carcass characteristics and LL meat quality in finishing barrows.

In vitro interaction of organophosphate metabolites with bovine serum albumin: A comparative 1H NMR, fluorescence and molecular docking analysis

Since the exposure of organophosphate pesticides are known to cause severe health consequences, it is important to understand the molecular interaction of these pesticides metabolites with vital biomolecules, especially with the proteins. Here, considering bovine serum albumin (BSA) as a model protein, we have examined its interaction with two selected organophosphate metabolites, 3,5,6-trichloro-2-pyridinol (TCPy) and paraoxon methyl (PM). TCPy and PM are resultant metabolites of two most widely used organophosphate pesticides chlorpyrifos and parathion respectively. ¹H NMR line broadening, selective spin-lattice relaxation rate measurements, saturation transfer difference (STD) NMR of both TCPy and PM were carried out in the presence and absence of BSA. The obtained values of the affinity index (A), binding constants (K_a) and thermodynamic parameters indicated strong organophosphates-BSA interaction. Further, fluorescence quenching data on TCPy-BSA and PM-BSA interactions strongly supported the NMR results, besides providing the stoichiometry of these complexes. Molecular docking analysis unraveled viable, strong hydrogen bonds and electrostatic interactions in TCPy-BSA and PM-BSA complexes. This study also revealed substantial time-dependent changes in the ¹H NMR intensity of PM in the presence of BSA, which suggests faster degradation of PM with increasing protein concentration during protein-metabolite interactions. The hydrolysis is attributed to the esterase-like action of BSA. The result provides key insights into the direct interaction of the organophosphate metabolites with a biologically important carrier protein, serum albumin.

Probing the binding mechanism of capecitabine to human serum albumin using spectrometric methods, molecular modeling, and chemometrics approach

Capecitabine as a prodrug of 5-Fluorouracil plays an important role in the treatment of breast and gastrointestinal cancers. Herein, in view of the importance of this drug in chemotherapy, interaction mechanism between Capecitabine (CAP) and human serum albumin (HSA) as a major transport protein in the blood circulatory system has been investigated by using a combination of spectroscopic and molecular modeling methods. The fluorescence spectroscopic results revealed that capecitabine could effectively quench the intrinsic fluorescence of HSA through a static quenching mechanism. Evaluation of the thermodynamic parameters suggested that the binding process was spontaneous while hydrogen bonds and van der Waals forces played a major role in this interaction. The value of the binding constant (K_b = 1.820 × 10⁴) suggested a moderate binding affinity between CAP and HSA which implies its easy diffusion from the circulatory system to the target tissue. The efficiency of energy transfer and the binding distance between the donor (HSA) and acceptor (CAP) were determined according to forster theory of nonradiation energy transfer as 0.410 and 4.135 nm, respectively. Furthermore, UV-Vis spectroscopic results confirmed that the interaction was occurred between HSA and CAP and caused conformational and micro-environmental changes of HSA during the interaction. Multivariate curve resolution-alternating least square (MCR-ALS) methodology as an efficient chemometric tool was used to separate the overlapped spectra of the species. The MCR-ALS result was exploited to estimate the stoichiometry of interaction and to provide concentration and structural information about HSA-CAP interactions. Molecular docking studies suggested that CAP binds mainly to the subdomain IIA of HSA, which were compatible with those obtained by experimental data. Finally, molecular dynamics simulation (MD) was performed on the best docked complex by considering the permanence and flexibility of HSA-CAP complex in the binding site. MD result showed that CAP could steadily bind to HSA in the site I based on the formation of hydrogen bond and π-π stacking interaction in addition to hydrophobic force.

Molecular interaction study of an anticancer drug, ponatinib with human serum albumin using spectroscopic and molecular docking methods

Binding of a potent anticancer agent, ponatinib (PTB) to human serum albumin (HSA), main ligand transporter in blood plasma was analyzed with several spectral techniques such as fluorescence, absorption and circular dichroism along with molecular docking studies. Decrease in the K_SV value with increasing temperature pointed towards PTB-induced quenching as the static quenching, thus affirming complexation between PTB and HSA. An intermediate binding affinity was found to stabilize the PTB-HSA complex, as suggested by the K_a value. Thermodynamic analysis of the binding phenomenon revealed participation of hydrophobic and van der Waals interactions along with hydrogen bonds, which was also supported by molecular docking analysis. Changes in both secondary and tertiary structures as well as in the microenvironment around Trp and Tyr residues of HSA were anticipated upon PTB binding to the protein, as manifested from circular dichroism and three-dimensional fluorescence spectra, respectively. Binding of PTB to HSA led to protein's thermal stabilization. Competitive ligand displacement experiments using different site markers such as warfarin, indomethacin and ketoprofen disclosed the binding site of PTB as Sudlow's site I in HSA, which was further confirmed by molecular docking analysis.

Preparation, characterization and comparison of biological potency in two new Zn(II) and Pd(II) complexes of butanedione monoxime derivatives

A novel Schiff base ligand (2-iminothiophenol-2,3-butanedione monoxime, ITBM) and its complexes with Pd(II) and Zn(II) metal ions ([M(ITBM)₂]Cl₂) were synthesized and characterized in the present study. The formulated complexes were evaluated for in vitro antioxidant activity as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH^•). According to the results, antioxidant activity of Pd complex (IC₅₀=36 mg L^-1) was more effective than that of Zn(II) complex (IC₅₀=72 mg L^-1). Biophysical techniques along with computational modeling were employed to examine the binding of these complexes with human serum albumin (HSA) as the model protein. The trial findings revealed an interaction between Schiff base complexes and HSA with a modest binding affinity [K_b=6.31(±0.11)×10⁴ M^-1 for Zn(II) complex and 0.71(±0.05)×10⁴ M^-1 for Pd(II) complex at 310 K]. An intense fluorescence quenching of protein through a static quenching mechanism was occurred due to the binding of both complexes to HSA. Hydrogen bonds and van der Waals forces in both examined systems were the main stabilizing forces in the development of drug-protein complex. Based on far-UV-CD observations, the content of α-helical structure in the protein was reduced through induction by both complexes. Analysis of protein-ligand docking demonstrated binding of the two Schiff base complexes to residues placed in the IIA subdomain of HSA. In addition, Zn complex with HSA showed a stronger binding ability than that of Pd complex.Communicated by Ramaswamy H. Sarma.

Binding behavior of trelagliptin and human serum albumin: Molecular docking, dynamical simulation, and multi-spectroscopy

This study aims to investigate the interaction mechanism of a hypoglycemic agent, trelagliptin (TLP), and human serum albumin (HSA) through computer simulation and assisted spectroscopy methods. Computer simulation including molecular docking and molecular dynamics analysis was conducted under physiological conditions. Molecular docking results indicate that TLP bound to HSA at site I, and the binding behavior was mainly governed by hydrophobic force. Competitive experiments further verified the theoretical conclusion from molecular docking. Molecular dynamics simulation revealed that TLP indeed stably bound to site I of HSA in the hydrophobic subdomain IIA. Moreover, TLP presented a certain effect on the structural compactness of HSA. In molecular dynamics simulation, hydrogen bonds appeared, which suggested the reliability and stability of the combination. The binding energy of the stable phase is around -250 kJ/mol. Fluorescence quenching studies and time-resolved fluorescence analysis indicated that the evident fluorescence quenching phenomenon of HSA could be due to TLP binding initiated by static quenching mechanism. The binding constants (K_a) of the complex were found to be around 10⁴ via fluorescence data, and the calculated thermodynamic parameters indicated that hydrophobic force played major role in the binding of TLP to HSA. Synchronous fluorescence and three-dimensional fluorescence results demonstrated that TLP slightly disturbed the microenvironment of amino residues. Circular dichroism spectra showed that TLP affected the secondary structure of HSA. The theoretical and experimental results showed excellent agreement.

Interaction mechanism of olaparib binding to human serum albumin investigated with NMR relaxation data and computational methods

The interaction mechanism between olaparib (OLA) and human serum albumin (HSA) has been investigated using experimental and computational techniques. An NMR relaxation approach based on the analysis of proton selective and non-selective spin-lattice relaxation rates at different temperatures can provide quantitative information about the affinity index and the thermodynamic equilibrium constant of the OLA-HSA system. The affinity index and the thermodynamic equilibrium constant decreased as temperature increased, indicating that the interactions between OLA and HSA could be weakened as temperature increased. Molecular docking and dynamics simulations revealed that OLA stably bound to subdomain II (site 1), and OLA could induce the conformational and micro-environmental changes in HSA. CD results suggested that α-helix content decreased after OLA was added, demonstrating that OLA affected the secondary structure of HSA.

Interactions between tetrahydroisoindoline-1,3-dione derivatives and human serum albumin via multiple spectroscopy techniques

Some tetrahydroisoindoline-1,3-dione derivatives (TDDs) possess potent herbicidal activity. To assess possible impacts of TDDs on humans, the interactions between TDDs and human serum albumin (HSA) were evaluated with steady-state and time-resolved fluorescence spectroscopy, synchronous fluorescence spectroscopy, Fourier transform-infrared spectroscopy, and circular dichroism spectroscopy. The thermodynamic data obtained at temperatures of 298, 307, and 316 K indicate that TDDs spontaneously bind to HSA and thus form a TDD-HSA complex. The conformation and secondary structure of HSA are changed, and the intrinsic fluorescence of HSA is statically quenched by TDDs. Moreover, the TDD-HSA complex is formed primarily through electrostatic interactions and has only one binding site on HSA. A competitive ligand-binding assay revealed that site II (subdomain IIIA) displays the greatest affinity for TDDs. In addition, an acute toxicity bioassay showed no zebrafish mortality upon exposure to 4000 μg L^-1 of TDDs. This work is helpful for understanding interactions between TDDs and HSA.

Biophysical and computational characterization of vandetanib-lysozyme interaction

Interaction of an anticancer drug, vandetanib (VDB) with a ligand transporter, lysozyme (LYZ) was explored using multispectroscopic techniques, such as fluorescence, absorption and circular dichroism along with computational analysis. Fluorescence data and absorption results confirmed VDB-LYZ complexation. VDB-induced quenching was characterized as static quenching based on inverse correlation of K_SV with temperature as well as k_q values. The complex was characterized by the weak binding constant (K_a=4.96-3.14×10³M^-1). Thermodynamic data (ΔS=+12.82Jmol^-1K^-1; ΔH=-16.73kJmol^-1) of VDB-LYZ interaction revealed participation of hydrophobic and van der Waals forces along with hydrogen bonds in VDB-LYZ complexation. Microenvironmental perturbations around tryptophan and tyrosine residues as well as secondary and tertiary structural alterations in LYZ upon addition of VDB were evident from the 3-D fluorescence, far- and near-UV CD spectral analyses, respectively. Interestingly, addition of VDB to LYZ significantly increased protein's thermostability. Molecular docking results suggested the location of VDB binding site near the LYZ active site while molecular dynamics simulation results suggested stability of VDB-LYZ complex. Presence of Mg²⁺, Ba²⁺ and Zn²⁺ was found to interfere with VDB-LYZ interaction.

Comprehensive insight into the binding of sunitinib, a multi-targeted anticancer drug to human serum albumin

Binding studies between a multi-targeted anticancer drug, sunitinib (SU) and human serum albumin (HSA) were made using fluorescence, UV-vis absorption, circular dichroism (CD) and molecular docking analysis. Both fluorescence quenching data and UV-vis absorption results suggested formation of SU-HSA complex. Moderate binding affinity between SU and HSA was evident from the value of the binding constant (3.04×10⁴M^-1), obtained at 298K. Involvement of hydrophobic interactions and hydrogen bonds as the leading intermolecular forces in the formation of SU-HSA complex was predicted from the thermodynamic data of the binding reaction. These results were in good agreement with the molecular docking analysis. Microenvironmental perturbations around Tyr and Trp residues as well as secondary and tertiary structural changes in HSA upon SU binding were evident from the three-dimensional fluorescence and circular dichroism results. SU binding to HSA also improved the thermal stability of the protein. Competitive displacement results and molecular docking analysis revealed the binding locus of SU to HSA in subdomain IIA (Sudlow's site I). The influence of a few common ions on the binding constant of SU-HSA complex was also noticed.

Investigation on the interaction of antibacterial drug moxifloxacin hydrochloride with human serum albumin using multi-spectroscopic approaches, molecular docking and dynamical simulation

Investigating the interactions of moxifloxacin hydrochloride with human serum albuminviamulti-spectroscopic approaches, molecular docking and dynamical simulation.