Conformational Changes Of Human Serum Albumin Research Articles

Human serum albumin–malathion complex study in the presence of silver nanoparticles at different sizes by multi spectroscopic techniques

The binding of malathion to human serum albumin (HSA) in the presence of silver nanoparticles (AgNPs) was investigated for the first time by multiple spectroscopic methods such as fluorescence quenching, fluorescence resonance energy transfer (FRET), circular dichroism, red-edge excitation shift (REES), synchronous fluorescence and three dimensional fluorescence spectroscopy under physiological conditions .The results indicated that binding of malathion to HSA induced fluorescence quenching through static mechanism. The number of binding sites was calculated by double logarithmic equation. Changes in the micro-environment of the fluorophore residues were also probed by synchronous fluorescence spectroscopy and REES. Changes of secondary structure of HSA in HSA–malathion complex was verified by circular dichroism approach in the presence of AgNPs that showed the electrostatic interaction changes in the protein structure. The binding average distance (r) between the donor (HSA) and the acceptor (malathion) was measured and found to be 1.63 nm according to the Forster’s theory of non-radiation energy transfer which was <7 nm confirmed the existence of static quenching in the presence of AgNPs. The conformational changes of HSA by three-dimensional fluorescence spectroscopy were studied. By comparing the resonance light scattering in the binary and ternary systems, we could estimate the effect of AgNPs on the precipitation of the malathion on the HSA. Generally we have discussed the toxicity reduction effect of malathion in food industrial by the results of spectroscopy techniques.

BINDING STUDIES OF VALGANCICLOVIR TO HUMAN SERUM ALBUMIN BY MULTISPECTROSCOPIC TECHNIQUES

Objective: The aim of the present study was to investigate the mode and mechanism of interactions involved towards binding of valganciclovir (VGC) with Human Serum Albumin (HSA) by spectroscopic and molecular modeling studies which can be extrapolated for the ten folds increase of bioavailability over its prodrug galanciclovir.Methods: Herein we employed fluorescence spectroscopy for evaluating the binding constant value, site of interaction and changes in the microenvironment of HSA fluorophores. Circular dichroism (CD) and UV-Visible spectroscopy is used for conformational changes of HSA in the event of binding of valaganciclovir. These experimental studies were further corroborated with molecular modeling studies.Results: Considerable quenching of fluorescence intensities of fluorophores in the presence of VGC showed that VGC interacts with HSA strongly with a binding constant of 4.11x104 M-1 with a free energy change of-6.26 Kcal/mol. Synchronous fluorescence and CD studies show that the microenvironment and confirmation of HSA are slightly altered in the presence of VGC. Though site marker experiments does not give any clue for identification of site, molecular docking studies showed that VGC binds to site IB of HSA.Conclusion: The weaker dominant electrostatic interactions with minor contributions of hydrophobic interactions of VGC with HSA at site IB (catalytic domain) might be the probable reason for the relative increase of hydrolysis of VGC to galanciclovir. And moderate binding constant value with HSA implies that HSA can be able to transport VGC under physiological conditions.

Stereoselective interactions of lactic acid enantiomers with HSA: Spectroscopy and docking application

Lactic acid enantiomers, normally found in fermented food, are absorbed into the blood and interact with plasma carrier protein human serum albumin (HSA). Unveiling the effect on the function and structure of HSA during chiral interaction can give a better understanding of the different distribution activities of the two enantiomers. Multi-spectroscopic methods and molecular modelling techniques are used to study the interactions between lactic acid enantiomers and HSA. Time-resolved and steady-state fluorescence spectra manifest that the fluorescence quenching mechanism is mainly static in type, due to complex formation. Binding interactions, deduced by thermodynamic calculation, agree with the docking prediction. Docking results and kinetic constants represent chiral-recognizing discriminations consistently. The bindings of lactic acid enantiomers lead to some microenvironmental and slight conformational changes of HSA as shown by circular dichroism (CD), synchronous and three-dimensional fluorescence spectra. This investigation may yield useful information about the possible toxicity risk of lactic acid enantiomers to human health.

Elucidation of energetics and mode of recognition of green tea polyphenols by human serum albumin

Green tea is rich in several polyphenols which has many beneficial biological effects. We have done a detailed qualitative and quantitative study on binding of two polyphenol (−)-epicatechin (EC) and (−)-epigallocatechin-3-gallate (EGCG) with human serum albumin (HSA) by using a combination of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), steady-state fluorescence, and circular dichroism spectroscopies. The binding constants obtained from isothermal titration calorimetry for EC-HSA and EGCG-HSA complexes are (2.09 ± 0.08) × 104 and (1.84 ± 0.30) × 105, respectively. The effects of ionic strength and additives of polar and non-polar characters indicate contribution of a mix of ionic, hydrogen bonding and hydrophobic interactions in the polyphenol-HSA association process. The 3D fluorescence analysis and circular dichroism (CD) studies reveal that the complexation of EGCG induces significant conformational change in HSA. The DSC results also show that the binding of EGCG is stronger compared to that of EC and provides quantitative information on the effect of these polyphenols on the thermal stability of HSA. Such studies play a crucial role in understanding the mechanism of drug-protein interactions and optimization of various binding parameters for successful drug delivery.

Spectroscopic analysis, docking and molecular dynamics simulation of the interaction of cinnamaldehyde with human serum albumin

Human serum albumin (HSA) is one of the blood plasma proteins, which plays an important role in the transportation of various natural and pharmaceutical compounds in the body. Cinnamaldehyde is the main component of cinnamon extract which has several medicinal properties. In this study, the conformational changes of HSA in the presence of cinnamaldehyde were investigated by UV–Vis, fluorescence and FT-IR spectroscopic methods and the binding parameters of cinnamaldehyde to HSA were determined. The binding site and driving forces of this interaction were calculated using molecular docking softwares. On the other hand, molecular dynamics simulations were also performed with the GROMACS program package. Using the results of the intrinsic fluorescence spectroscopy data, binding constant of 1.14 × 104 M−1 and number of binding sites 0.883 was obtained. FT-IR measurements have shown that the secondary structure of the protein have been changed by the interaction of cinnamaldehyde with HSA. The free energy of binding (ΔG°) and binding constant (Ka) obtained from the intrinsic fluorescence results were − 5.54 kcal mol−1 and 1.14 × 104 M−1 respectively, which is in good agreement with molecular docking results. On the other hand, the molecular docking calculations showed that cinnamaldehyde binding site is located in the IA subdomain of HSA. Spectroscopy, molecular docking and MD simulations methods showed that the cinnamaldehyde is bound to the HSA protein and hydrogen bonding and hydrophobic forces play the most important role in this interaction. Excellent agreement was found between the experimental and theoretical results.

Characterization of the binding of a novel antitumor drug ibrutinib with human serum albumin: Insights from spectroscopic, calorimetric and docking studies

Ibrutinib (IBR) is a novel Bruton's tyrosine kinase inhibitor and shows good efficacy for several B-cell malignancies. In the current study, the molecular mechanism of the interaction between IBR and the transport protein human serum albumin (HSA) was ascertained by spectroscopic, calorimetric, and docking studies. Detailed investigations on affinity parameter, binding model, conformational change, and site selectivity were implemented by receptor-based and ligand-based analysis. An unusual fluorescence co-quenching (mutual quenching) was observed in the binding of IBR to HSA, followed by a static mechanism. Fluorescence spectroscopy and isothermal titration calorimetry indicated that the binding affinity was at 104 M−1 level and electrostatic interactions and hydrophobic forces contributed the interaction. UV–vis and 3D fluorescence spectroscopy suggested the conformational changes of HSA after binding with IBR. Fourier transform infrared and circular dichroism spectroscopy further verified the variation in the secondary structure of HSA. Site-markers competition and molecular docking confirmed that IBR preferably binds to HSA at the cysteine-rich region of Sudlow's site I (subdomain IIA). This study systematically clarified the binding process of the novel antitumor drug with the functional biomacromolecule for the first time. The findings are helpful for IBR pharmacological assessment and can provide valuable reference for other tinib-type drugs.

Investigations of the molecular interactions between nisoldipine and human serum albumin in vitro using multi-spectroscopy, electrochemistry and docking studies

Nisoldipine represents a compound with diverse pharmacological activities. The interaction between nisoldipine and human serum albumin (HSA) was investigated using various methods, including UV–vis, three-dimensional fluorescence, synchronous fluorescence, electrochemical methods and molecular docking. The decreased quenching constant upon increasing temperatures and UV–vis absorption difference spectrum revealed that there was a static quenching mechanism rather than a dynamic quenching mechanism in the interaction of nisoldipine with human serum albumin. The thermodynamic parameters demonstrated that the binding of nisoldipine to human serum albumin was spontaneous and hydrogen bonding, hydrophobic interactions as well as electrostatic interactions played major roles in the binding process. The binding distance was 2.31nm, indicating the presence of fluorescence energy transfer. Site marker competitive experiments and molecular docking demonstrated that the binding site of nisoldipine in human serum albumin was site I (subdomain IIA). In addition, three-dimensional fluorescence as well as synchronous fluorescence spectra suggested conformational changes of HSA due to the interaction with nisoldipine.

Probing the in vitro binding mechanism between human serum albumin and La 2 O 2 CO 3 nanoparticles

The interaction of La2O2CO3 nanoparticles (La NPs) with human serum albumin (HSA) has been studied. Analysis of the fluorescence quenching data of HSA using Stern–Volmer method showed that La NPs quenched HSA fluorescence in static quenching mode. Thermodynamic analysis indicated that hydrogen bonds and Van der Waals interactions play a major role for HSA–La NPs associations. Fluorescent displacement measurements confirmed that the primary binding site of La NPs was mainly located within site I (subdomain IIA) of HSA. The binding distance was calculated by using Forster resonance energy transfer theory. Also, the results of Fourier-transform infrared spectroscopy, circular dichroism, three-dimensional fluorescence and UV–visible measurements indicated that the binding of above La NPs to HSA may induce conformational and micro-environmental changes of protein. This study suggested that the conformational change of HSA was at secondary structure of it and the biological activity of this protein was changed in the present of La NPs.

Interaction between Saikosaponin D, Paeoniflorin, and Human Serum Albumin.

Saikosaponin D (SSD) and paeoniflorin (PF) are the major active constituents of Bupleuri Radix and Paeonia lactiflora Pall, respectively, and have been widely used in China to treat liver and other diseases for many centuries. We explored the binding of SSD/PF to human serum albumin (HSA) by using fluorospectrophotometry, circular dichroism (CD) and molecular docking. Both SSD and PF produced a conformational change in HSA. Fluorescence quenching was accompanied by a blue shift in the fluorescence spectra. Co-binding of PF and SSD also induced quenching and a conformational change in HSA. The Stern-Volmer equation showed that quenching was dominated by static quenching. The binding constant for ternary interaction was below that for binary interaction. Site-competitive experiments demonstrated that SSD/PF bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for the binary association. Also, there was energy transfer upon binary interaction. Molecular docking supported the experimental findings in conformation, binding sites and binding forces.

Human serum albumin interaction studies of a new copper(II) complex containing ceftobiprole drug using molecular modeling and multispectroscopic methods

A copper(II) complex containing the ceftobiprole drug and 1,10-phenanthroline (phen) has been synthesized and characterized by UV–vis, FT-IR and mass spectra, and elemental analysis. The binding interaction between [Cu(cef)(phen)Cl2] complex and human serum albumin (HSA) was investigated using absorption, fluorescence emission and circular dichroism spectroscopies, and molecular docking. Thermodynamic parameters (ΔH < 0 and ΔS < 0) indicated that the hydrogen bond and van der Waals interactions played main roles in the binding of complex [Cu(cef)(phen)Cl2] to HSA. The results of CD and UV–vis spectroscopy showed that the binding of [Cu(cef)(phen)Cl2] to HSA induces some conformational changes in HSA. Displacement experiments predicted that the binding of [Cu(cef)(phen)Cl2] complex to HSA is located within domain III, Sudlow’s site 2, and these observations were substantiated by molecular docking studies.

Study on the interaction of paeoniflorin with human serum albumin (HSA) by spectroscopic and molecular docking techniques

The interaction of paeoniflorin with human serum albumin (HSA) was investigated using fluorescence, UV–vis absorption, circular dichroism (CD) spectra and molecular docking techniques under simulative physiological conditions. The results clarified that the fluorescence quenching of HSA by paeoniflorin was a static quenching process and energy transfer as a result of a newly formed complex (1:1). Paeoniflorin spontaneously bound to HSA in site I (subdomain IIA), which was primarily driven by hydrophobic forces and hydrogen bonds (ΔH° = − 9.98 kJ mol−1, ΔS° = 28.18 J mol−1 K−1). The binding constant was calculated to be 1.909 × 103 L mol−1 at 288 K and it decreased with the increase of the temperature. The binding distance was estimated to be 1.74 nm at 288 K, showing the occurrence of fluorescence energy transfer. The results of CD and three-dimensional fluorescence spectra showed that paeoniflorin induced the conformational changes of HSA. Meanwhile, the study of molecular docking also indicated that paeoniflorin could bind to the site I of HSA mainly by hydrophobic and hydrogen bond interactions.

Study on the interaction of tussilagone with human serum albumin (HSA) by spectroscopic and molecular docking techniques

Tussilagone is a sesquiterpenoid which exhibits a variety of pharmacological activities. The interaction of tussilagone with human serum albumin (HSA) was investigated using fluorescence spectroscopy, UV–vis absorption, fluorescence probe experiments, synchronous fluorescence, circular dichroism (CD) spectra, three-dimensional spectra and molecular docking techniques under simulative physiological conditions. The results clarified that the fluorescence quenching of HSA by tussilagone was a static quenching process as a result of HSA-tussilagone (1:1) complex. Tussilagone spontaneously bound to HSA in site I (subdomain IIA), which was primarily driven by hydrophobic forces and hydrogen bonds (ΔH° = −13.89 kJ mol−1, ΔS° = 16.39 J mol−1 K−1). The binding constant was calculated to be 2.182 × 103 L mol−1 and the binding distance was estimated to be 2.07 nm at 291 K, showing the occurrence of fluorescence energy transfer. The results of CD, synchronous and three-dimensional fluorescence spectra all revealed that tussilagone induced the conformational changes of HSA. Meanwhile, the study of molecular docking also indicated that tussilagone could bind to the site I of HSA mainly by hydrophobic and hydrogen bond interactions.

Unraveling the thermodynamics, binding mechanism and conformational changes of HSA with chromolyn sodium: Multispecroscopy, isothermal titration calorimetry and molecular docking studies

Cromolyn sodium is an anti-allergic drug effective for treatment in asthma and allergic rhinitis. In this project, interaction of chromolyn sodium (CS) with human serum albumin (HSA) has been investigated by various techniques such as UV-vis, fluorescence, circular dichorism (CD), fourier transform infrared (FT-IR) spectroscopy, isothermal titration calorimetric (ITC) and molecular docking. The fluorescence quenching results revealed that there was static quenching mechanism in the interactions of CS with HSA. The binding constant (Kb), enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy change (ΔG°) were calculated. The negative values of TΔS° and ΔH° obtained from fluorescence spectroscopy and isothermal titration calorimetry, indicate that hydrogen bonding and van der Waal’s forces played major role in the binding process and the reaction is exothermic in nature. The binding constant (Kb) was found to be in the order of 104M−1 which depicts a good binding affinity of CS towards HSA. The conformational changes in the HSA due to interaction of CS were investigated from CD and FT-IR spectroscopy. The binding site of CS in HSA was sub-domain IIA as evident from site probing experiment and molecular docking studies.

Exploring the interaction between iron oxide nanoparticles (IONPs) and Human serum albumin (HSA): Spectroscopic and docking studies

The combination of the spectroscopic and molecular modeling methods was utilized to understand the iron (III) oxide nanoparticles (IONPs) interaction with Human serum albumin (HSA). Initial characterization of the IONPs using FTIR and FT-Raman techniques showed the bands corresponding to the FeO bonds at the low frequency region. Also, the XRD diffraction planes obtained confirms the magnetite phase of IONPs with the spinel structure. SEM-EDAX analysis showed the spherical morphology of the IONPs with weight percentage of iron metal constituents. Fluorescence and UV–Visible spectra of the HSA-IONPs complex dictated the quenching mechanism as static. Synchronous spectra found more affinity of IONPs against the Trp residues of HSA. 3D scan spectra added additional insight into the conformational changes of HSA on interaction with IONPs. CD spectra showed both the changes in the alpha helical contents and the Trp absorbance of the polypeptide backbone. Molecular docking result coherence with the spectroscopic findings in confirming the binding interaction between HSA and IONPs and showed the nearby amino acid residues including tyrosine.

Probing the binding reaction of cytarabine to human serum albumin using multispectroscopic techniques with the aid of molecular docking

Cytarabine is a kind of chemotherapy medication. In the present study, the molecular interaction between cytarabine and human serum albumin (HSA) was investigated via fluorescence, UV–vis absorption, circular dichroism (CD) spectroscopy and molecular docking method under simulative physiological conditions. It was found that cytarabine could effectively quench the intrinsic fluorescence of HSA through a static quenching process. The apparent binding constants between drug and HSA at 288, 293 and 298K were estimated to be in the order of 103L·mol−1. The thermodynamic parameters ΔH°, ΔG°and ΔS° were calculated, in which the negative ΔG°suggested that the binding of cytarabine to HSA was spontaneous, moreover the negative ΔS°and negative ΔH°revealed that van der Waals force and hydrogen bonds were the major forces to stabilize the protein-cytarabine (1:1) complex. The competitive binding experiments showed that the primary binding site of cytarabine was located in the site I (subdomain IIA) of HSA. In addition, the binding distance was calculated to be 3.4nm according to the Förster no-radiation energy transfer theory. The analysis of CD and three-dimensional (3D) fluorescence spectra demonstrated that the binding of drug to HSA induced some conformational changes in HSA. The molecular docking study also led to the same conclusion obtained from the spectral results.

Analysis of binding properties and interaction of thiabendazole and its metabolite with human serum albumin via multiple spectroscopic methods

Thiabendazole (TBZ), which is oxidized into 5-hydroxythiabendazole (5-OH-TBZ) in vivo, is a commonly used food preservative. Interactions of TBZ and 5-OH-TBZ with human serum albumin (HSA) were comprehensively studied via multiple spectroscopic methods and molecular docking. This study focussed on the mechanistic and structural information on binding of TBZ and 5-OH-TBZ to HSA to evaluate the impact of the food additive on HSA. 1H NMR spectra of the two ligands showed the binding exists. ITC and fluorescence spectroscopy results revealed that TBZ was a stronger ligand, with a binding constant of 105l/mol and formed a more stable complex with HSA than did 5-OH-TBZ via electrostatic interaction. Spectroscopic results (UV–vis, FT-IR, and CD) showed that TBZ and 5-OH-TBZ caused conformational changes in HSA, in which α-helix and β-turn transformed into β-sheet, causing HSA structure to loosen. Docking programs showed that both TBZ and 5-OH-TBZ bound to HSA via IB.

Interactions of Three Chalcones with Human Serum Albumin Revealed by Spectroscopic Techniques.

Chalcones are the proverbial precursors of many naturally occurring compounds and possess a variety of biological activities and a broad spectrum of pharmacological properties. The interaction mechanism between three chalcones, 2',4',4-trihydroxyflavone (also called isoliquiritigenin, 2',4',4-triHC), 2',4'-dihydroxyflavone (2',4'-diHC), and 4-hydroxyflavone (4-HC) and human serum albumin (HSA) was investigated using fluorescence quenching, fluorescence enhancement and UV absorption spectra. The binding parameters of chalcone-HSA complexes were evaluated by fluorescence quenching measurements, and the results were consistent with those obtained from fluorescence enhancement methods. The binding affinities of three chalcones with HSA at pH 7.4 were ranked in the order (the binding constants in the range 0.28 - 2.39 × 105 L mol-1), 2',4',4-triHC > 2',4'-diHC > 4-HC, indicating that the three chalcones displayed tight affinities for HSA and the hydroxyl group in chalcones played a key role in their binding affinities with HSA. The results of the UV absorption and the fluorescence enhancement elucidated that the chalcones may lead to micro-environmental and conformational changes of HSA. The binding site of the chalcone 2',4',4-triHC on the HSA was explored by the spectroscopic properties of the 2',4',4-triHC-HSA complex at pH 7.4 and 3.5, and the results demonstrated that 2',4',4-triHC bound within the hydrophobic pockets of subdomain IIA of HSA, namely site I, and the electrostatic force and ionic interactions played a crucial role in the binding interaction between chalcones and protein. The obtained results provided scientific evidence for the binding property of the chalcones and protein, which would be helpful for development of novel drugs with the skeleton of chalcones.

Domain-specific interactions between MLN8237 and human serum albumin estimated by STD and WaterLOGSY NMR, ITC, spectroscopic, and docking techniques

Alisertib (MLN8237) is an orally administered inhibitor of Aurora A kinase. This small-molecule inhibitor is under clinical or pre-clinical phase for the treatment of advanced malignancies. The present study provides a detailed characterization of the interaction of MLN8237 with a drug transport protein called human serum albumin (HSA). STD and WaterLOGSY nuclear magnetic resonance (NMR)-binding studies were conducted first to confirm the binding of MLN8237 to HSA. In the ligand orientation assay, the binding sites of MLN8237 were validated through two site-specific spy molecules (warfarin sodium and ibuprofen, which are two known site-selective probes) by using STD and WaterLOGSY NMR competition techniques. These competition experiments demonstrate that both spy molecules do not compete with MLN8237 for the specific binding site. The AutoDock-based blind docking study recognizes the hydrophobic subdomain IB of the protein as the probable binding site for MLN8237. Thermodynamic investigations by isothermal titration calorimetry (ITC) reveal that the non-covalent interaction between MLN8237 and HSA (binding constant was approximately 105 M−1) is driven mainly by favorable entropy and unfavorable enthalpy. In addition, synchronous fluorescence, circular dichroism (CD), and 3D fluorescence spectroscopy suggest that MLN8237 may induce conformational changes in HSA.

Exploring the mode of binding between food additive “butylated hydroxytoluene (BHT)” and human serum albumin: Spectroscopic as well as molecular docking study

Abstract Butylated hydroxytoluene (BHT) is a food additive and used as an antioxidant in food products. BHT also concerning several health risks such as cancer, asthma and behavioral disorder in children. Human serum albumin (HSA) is the main constituents of blood plasma and known as a carrier protein because it has a very strong ability to bind a variety of ligands. The binding of a drug or small molecules to serum albumin is a crucial determinant of its pharmacokinetic and pharmacodynamic profile. This study investigates the interaction between BHT and HSA at pH 7.4 using various spectroscopic techniques such as UV–visible absorption spectrophotometry, fluorescence quenching, circular dichroism (CD) and molecular docking. The interactions of BHT with human serum albumin in the UV–visible range of spectrum exhibits increased absorption peak at 280 nm that elevates with increasing concentrations of BHT. BHT was also found to quench the fluorescence of human serum albumin (HSA). However, the fluorescence quenching constant was decreased with increasing the temperature, indicating that the interaction between BHT and HSA takes place via the static quenching mechanism. The thermodynamic measurements indicated that both hydrogen and hydrophobic forces involved in the binding of BHT with HSA. Moreover, the negative ∆ G value showed that the binding process was spontaneous. Far-UV CD data suggested the marginal conformational changes in HSA due to BHT interactions. Furthermore, molecular docking study suggested that BHT interacted with HSA at domain III via hydrophobic interaction. Conclusively, spectroscopies, as well as computational analysis extend our understanding of BHT interaction with serum albumin, which has far reaching applications in the food industry.

A Study on the Binding of Loperamide to Human Serum Albumin Using Combination of Computational and Experimental Methods

In the present study, an attempt has been made to study the interaction of Loperamide, an drug used for treating symptoms or diarrhoea, with the most important transport protein, human serum albumin (HSA) employing UV-Vis, spectrofluorometric, FT-IR, Cyclic voltammetry, Electrochemical Impedance Spectroscopy and molecular modelling techniques. The results showed that binding of LOP to HSA caused strong fluorescence quenching of HSA through static quenching mechanism. The results of experimental and theoretical methods indicated that the binding of this drug to HSA induced slight conformational changes in HSA. Furthermore, the study of molecular modelling also showed that LOP could strongly bind to the site I (subdomain IIA) of HSA and hydrophobic interactions are the major forces in the stability of LOP-HSA complex.