Quenching of the intrinsic fluorescence of bovine serum albumin by phenylfluorone-Mo(VI) complex as a probe

In this paper, the binding characteristics of bovine serum albumin (BSA) and phenylfluorone (PF)-molybdenum (Mo(VI)) complex have been studied by fluorophotometry. The binding constants are calculated at different temperatures. The binding distance and the energy transfer efficiency between PF-Mo(VI) complex and protein are obtained on the basis of the theory of Forster energy transfer. DeltaH and DeltaS are calculated to be -7.11 kJ mol-1 and 70.30 J mol-1 K-1, which indicate that electrostatic force plays major role in the interaction of PF-Mo(VI) complex and BSA. The experimental results show that BSA and PF-Mo(VI) complex have strong interactions and the mechanism of quenching belongs to static quenching.     

Elucidating the molecular interaction of sinigrin,a potent anticancer glucosinolate from cruciferous vegetables with bovine serum albumin: effect of methylglyoxal modification

The present study employed the spectroscopic techniques, i.e. fluorescence, and circular dichroism (CD) and the molecular docking approach to investigate the mechanism of interaction of a potent anticancer glucosinolate, sinigrin (SIN), with bovine serum albumin (BSA). SIN binding to BSA resulted in the quenching of intrinsic fluorescence, and the analysis of results revealed the presence of static quenching mechanism. Based on the results, it was evident that the interaction of SIN with BSA was mainly stabilized by hydrogen bonding. Results from CD analysis revealed that the binding of SIN does not induce significant conformational changes in BSA. Molecular docking studies showed that four hydrogen bonds stabilize the binding of SIN in the site I of BSA with a binding energy of ?6.2 kcal mol^?1. These findings will not only provide insights about the mechanism of interaction of sinigrin but also showed the effect of methylglyoxal-mediated glycation on ligand binding with BSA.     

In vitro study on binding interaction of quinapril with bovine serum albumin (BSA) using multi-spectroscopic and molecular docking methods

The binding interaction between quinapril (QNPL) and bovine serum albumin (BSA) in vitro has been investigated using UV absorption spectroscopy, steady-state fluorescence spectroscopic, synchronous fluorescence spectroscopy, 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and molecular docking methods for obtaining the binding information of QNPL with BSA. The experimental results confirm that the quenching mechanism of the intrinsic fluorescence of BSA induced by QNPL is static quenching based on the decrease in the quenching constants of BSA in the presence of QNPL with the increase in temperature and the quenching rates of BSA larger than 10¹⁰ L mol^?1 s^?1, indicating forming QNPL–BSA complex through the intermolecular binding interaction. The binding constant for the QNPL–BSA complex is in the order of 10⁵ M^?1, indicating there is stronger binding interaction of QNPL with BSA. The analysis of thermodynamic parameters together with molecular docking study reveal that the main binding forces in the binding process of QNPL with BSA are van der Waal’s forces and hydrogen bonding interaction. And, the binding interaction of BSA with QNPL is an enthalpy-driven process. Based on Förster resonance energy transfer, the binding distance between QNPL and BSA is calculated to be 2.76 nm. The results of the competitive binding experiments and molecular docking confirm that QNPL binds to sub-domain IIA (site I) of BSA. It is confirmed there is a slight change in the conformation of BSA after binding QNPL, but BSA still retains its secondary structure α-helicity.     

Intermolecular interaction of fosinopril with bovine serum albumin (BSA): The multi‐spectroscopic and computational investigation

The intermolecular interaction of fosinopril, an angiotensin converting enzyme inhibitor with bovine serum albumin (BSA), has been investigated in physiological buffer (pH 7.4) by multi‐spectroscopic methods and molecular docking technique. The results obtained from fluorescence and UV absorption spectroscopy revealed that the fluorescence quenching mechanism of BSA induced by fosinopril was mediated by the combined dynamic and static quenching, and the static quenching was dominant in this system. The binding constant, K_b, value was found to lie between 2.69 × 10³ and 9.55 × 10³ M^?1 at experimental temperatures (293, 298, 303, and 308 K), implying the low or intermediate binding affinity between fosinopril and BSA. Competitive binding experiments with site markers (phenylbutazone and diazepam) suggested that fosinopril preferentially bound to the site I in sub‐domain IIA on BSA, as evidenced by molecular docking analysis. The negative sign for enthalpy change (ΔH⁰) and entropy change (ΔS⁰) indicated that van der Waals force and hydrogen bonds played important roles in the fosinopril‐BSA interaction, and 8‐anilino‐1‐naphthalenesulfonate binding assay experiments offered evidence of the involvements of hydrophobic interactions. Moreover, spectroscopic results (synchronous fluorescence, 3‐dimensional fluorescence, and Fourier transform infrared spectroscopy) indicated a slight conformational change in BSA upon fosinopril interaction.     

Characterization of the interaction between reserpine and bovine serum albumin: spectroscopic approaches

The characteristics of the interaction between reserpine and bovine serum albumin (BSA) were studied by fluorescence, UV-vis absorption and Fourier transform infrared (FT-IR) spectroscopy. Spectroscopic analysis revealed that fluorescence quenching of BSA by reserpine was through a static quenching procedure. The binding constant K(A) of reserpine with BSA at 293, 301 and 309 K was 1.63, 1.78 and 2.35 x 10(5) moL(-1) L respectively, which indicated degree of binding force between reserpine and BSA. There was one binding site between reserpine and BSA. The entropy and enthalpy changes were positive, indicating that interaction of reserpine and BSA was driven mainly by hydrophobic forces. The average binding distance between the donor (BSA) and the acceptor (reserpine) was about 3.84 nm based on the Forster non-radiation energy transfer theory. Results of synchronous fluorescence and FT-IR spectra indicated that the conformation and microenvironment of BSA were changed by the binding of reserpine. The results may provide important insights into the physiological activity of reserpine.     

Determination on the binding of chlortetracycline to bovine serum albumin using spectroscopic methods

In this work, the interaction of chlortetracycline with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking. Results indicated that chlortetracycline quenches BSA fluorescence mainly by a static quenching mechanism. The quenching constants (K_SV) were obtained as 5.64 × 10⁴, 4.49 × 10^4/, and 3.44 × 10^4/ M_?1 at 283, 295, and 307 K, respectively. The thermodynamic parameters of enthalpy change Δ H°, entropy change Δ S°, and free energy change Δ G° were ?5.12 × 10^4/ J mol?1, ?97.6 J mol?1 K?1, and ?2.24 × 10^4/ J mol?1 (295 K), respectively. The association constant (K_A) and the number of binding sites (n) were 9.41 × 10^3/ M?1 and 0.86, respectively. The analysis results suggested that the interaction was spontaneous, and van der Waals force and hydrogen‐bonding interactions played key roles in the reaction process. In addition, CD spectra proved secondary structure alteration of BSA in the presence of chlortetracycline. © 2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 26:331–336, 2012; View this article online at wileyonlinelibrary.com . DOI 10:1002/jbt.21424     

Spectroscopic and molecular docking studies on interaction of two Schiff base complexes with bovine serum albumin

Abstract

This study was designed to examine interaction of two ternary copper (II) Schiff base complexes with bovine serum albumin (BSA), using spectroscopic and molecular docking techniques. The fluorescence quenching measurements revealed that the quenching mechanism was static and the binding site of both Schiff bases to BSA was singular. Förster energy transfer measurements, synchronous fluorescence spectroscopy, and docking study showed both Schiff bases bind to the Trp residues of BSA in short distances. Docking study showed that both Schiff base molecules bind with BSA by forming several hydrogen and van der Waals bonds. In addition, molecular docking study indicated that Schiff base A and Schiff base B were located within the binding pocket of subdomain IB and subdomain IIA of BSA, respectively. Results of Fourier transform-infrared spectroscopy demonstrated that bovine serum albumin interacts with both Schiff bases and the secondary structure of BSA was changed.

Communicated by Ramaswamy H. Sarma     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction between lisinopril and bovine serum albumin

To further understand the mode of action and pharmacokinetics of lisinopril, the binding interaction of lisinopril with bovine serum albumin (BSA) under imitated physiological conditions (pH 7.4) was investigated using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD) and molecular docking methods. The results showed that the fluorescence quenching of BSA near 338 nm resulted from the formation of a lisinopril–BSA complex. The number of binding sites (n) for lisinopril binding on subdomain IIIA (site II) of BSA and the binding constant were ~ 1 and 2.04 × 10⁴ M^–1, respectively, at 310 K. The binding of lisinopril to BSA induced a slight change in the conformation of BSA, which retained its α‐helical structure. However, the binding of lisinopril with BSA was spontaneous and the main interaction forces involved were van der Waal's force and hydrogen bonding interaction as shown by the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ for the binding of lisinopril with BSA. It was concluded from the molecular docking results that the flexibility of lisinopril also played an important role in increasing the stability of the lisinopril–BSA complex. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation of new indole derivatives of bovine serum albumin using spectroscopic and molecular docking techniques

We investigated the interaction of two derivatives of bis (indolyl) methane with bovine serum albumin (BSA) using spectroscopic and molecular docking calculations. Fluorescence quenching measurements revealed that the quenching mechanism was static. F?rster energy transfer measurements, synchronous fluorescence spectroscopy and docking studies demonstrated that both bis(indolyl)methanes bound to the Trp residues of BSA. The docking study confirmed that both bis(indolyl)methanes form hydrogen bonds and van der Waals interactions with BSA. Our molecular docking study indicated that the compounds are located within the binding pocket of subdomains IIB and IB of BSA. Fourier transform infrared spectroscopy demonstrated that both bis(indolyl)methane derivatives can interact with BSA and can affect the secondary structure of BSA.     

Underlying molecular interaction of bovine serum albumin and linezolid: a biophysical outlook

Linezolid, one of the reserve antibiotic of oxazolidinone class has wide range of antimicrobial activity. Here we have conducted a fundamental study concerning the dynamics of its interaction with bovine serum albumin (BSA), and the post binding modification of the later by employing different spectroscopic (absorption, fluorescence and circular dichroism (CD) spectroscopy) and molecular docking tools. Gradual quenching of the tryptophan (Trp) fluorescence upon addition of linezolid to BSA confirms their interaction. Analysis of fluorescence quenching at different temperature indicates that the interaction is made by static complex formation and the BSA has one binding site for the drug. The negative Gibbs energy change (ΔG⁰), and positive values of enthalpy change (ΔH⁰) and entropy change (ΔS⁰) strongly suggest that it is an entropy driven spontaneous and endothermic reaction. The reaction involves hydrophobic pocket of the protein, which is further stabilized by hydrogen bonding and electrostatic interactions as evidenced from 8-anilino-1-napthalene sulfonic acid, sucrose and NaCl binding studies. These findings also support the molecular docking study using AutoDock 4.2. The influence of this interaction on the secondary structure of the protein is negligible as evidenced by CD spectroscopy. So, from these findings, we conclude that linezolid interacts with BSA in 1:1 ratio through hydrophobic, hydrogen bonding and ionic interactions, and this may not affect the secondary structure of the protein.     

Molecular docking and experimental investigation of new indole derivative cyclooxygenase inhibitor to probe its binding mechanism with bovine serum albumin

The indole derivative 2-(5-methoxy-2-methyl-1H-indol-3-yl)-N'-[(E)-(3-nitrophenyl) methylidene]acetohydrazide (IND) was synthesized for its therapeutic potential to inhibit cyclooxygenase (COX)-II. Binding if IND to bovine serum albumin (BSA) was investigated was because most drugs bind to serum albumin in-vivo. Fluorescence, UV–vis spectrophotometry and molecular modeling methodologies were employed for studying the interaction mechanism. The intrinsic fluorescence of BSA was quenched by BSA and the quenching mechanism involved was static quenching. The binding constants between IND and BSA at the three studied temperatures (298, 301 and 306 K) were 1.09 × 10⁵, 4.36 × 10⁴ and 1.23 × 10⁴ L mol⁻¹ respectively. The most likely site for binding IND to BSA was Site I (subdomain IIA). The analysis of thermodynamic parameter revealed the involvement of hydrogen bonding and van der Waals forces in the IND-BSA interaction. Synchronous fluorescence spectroscopic (SFS) and UV–vis spectrophotometric studies suggested conformational change in BSA molecule post interaction to IND. Molecular docking and the experimental results corroborated one another. The study can prove as an insight for future IND drug development.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction of enalapril with bovine serum albumin

The binding interaction between bovine serum albumin (BSA) and enalapril (ENPL) at the imitated physiological conditions (pH = 7.4) was investigated using UV–vis absorption spectroscopy (UV–vis), fluorescence emission spectroscopy (FES), synchronous fluorescence spectroscopy (SFS), Fourier transform infrared spectroscopy (FT‐IR), circular dichroism (CD) and molecular docking methods. It can be deduced from the experimental results from the steady‐state fluorescence spectroscopic titration that the intrinsic BSA fluorescence quenching mechanism induced by ENPL is static quenching, based on the decrease in the BSA quenching constants in the presence of ENPL with increase in temperature and BSA quenching rates >10¹⁰ L mol^?1 sec^?1. This result indicates that the ENPL–BSA complex is formed through an intermolecular interaction of ENPL with BSA. The main bonding forces for interaction of BSA and ENPL are van der Waal's forces and hydrogen bonding interaction based on negative values of Gibbs free energy change (ΔG ⁰), enthalpic change (ΔH ⁰) and entropic change (ΔS ⁰). The binding of ENPL with BSA is an enthalpy‐driven process due to |ΔH °| > |T ΔS °| in the binding process. The results of competitive binding experiments and molecular docking confirm that ENPL binds in BSA sub‐domain IIA (site I) and results in a slight change in BSA conformation, but BSA still retains its α‐helical secondary structure.     

Characterization of intermolecular interaction between cyanidin‐3‐glucoside and bovine serum albumin: Spectroscopic and molecular docking methods

The intermolecular interaction between cyanidin‐3‐glucoside (Cy‐3‐G) and bovine serum albumin (BSA) was investigated using fluorescence, circular dichroism and molecular docking methods. The experimental results revealed that the fluorescence quenching of BSA at 338 nm by Cy‐3‐G resulted from the formation of Cy‐3‐G–BSA complex. The number of binding sites (n) for Cy‐3‐G binding on BSA was approximately equal to 1. The experimental and molecular docking results revealed that after binding Cy‐3‐G to BSA, Cy‐3‐G is closer to the Tyr residue than the Trp residue, the secondary structure of BSA almost not change, the binding process of Cy‐3‐G with BSA is spontaneous, and Cy‐3‐G can be inserted into the hydrophobic cavity of BSA (site II′) in the binding process of Cy‐3‐G with BSA. Moreover, based on the sign and magnitude of the enthalpy and entropy changes (ΔH⁰ = – 29.64 kcal/mol and ΔS⁰ = – 69.51 cal/mol K) and the molecular docking results, it can be suggested that the main interaction forces of Cy‐3‐G with BSA are Van der Waals and hydrogen bonding interactions. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigations on the interactions of DiAmsar with serum albumins: Insights from spectroscopic and molecular docking techniques

Diamine‐sarcophagine (DiAmsar) binding to human serum albumin (HSA) and bovine serum albumin (BSA) was investigated under simulative physiological conditions. Fluorescence spectra in combination with Fourier transform infrared (FT‐IR), UV‐visible (UV–vis) spectroscopy, cyclic voltammetry (CV), and molecular docking method were used in the present work. Experimental results revealed that DiAmsar had an ability to quench the HSA and BSA intrinsic fluorescence through a static quenching mechanism. The Stern–Volmer quenching rate constant (K_sv) was calculated as 0.372 × 10³ M^‐1 and 0.640 × 10³ M^‐1 for HSA and BSA, respectively. Moreover, binding constants (K_a), number of binding sites (n) at different temperatures, binding distance (r), and thermodynamic parameters (?H°, ?S°, and ?G°) between DiAmsar and HSA (or BSA) were calculated. DiAmsar exhibited good binding propensity to HSA and BSA with relatively high binding constant values. The positive ?H° and ?S° values indicated that the hydrophobic interaction is main force in the binding of the DiAmsar to HSA (or BSA). Furthermore, molecular docking results revealed the possible binding site and the microenvironment around the bond. Copyright © 2014 John Wiley & Sons, Ltd.     

Binding of fexofenadine hydrochloride to bovine serum albumin: structural considerations by spectroscopic techniques and molecular docking

The binding interaction of peripheral H₁ receptor antagonist drug, fexofenadine hydrochloride to bovine serum albumin (BSA) is investigated by fluorescence spectroscopy in combination with UV-absorption spectroscopy under physiological conditions. The Stern–Volmer plots at different temperatures and the steady state fluorescence suggested a static type of interaction between fexofenadine and BSA. Binding constants were determined to provide a measure of the binding affinity between fexofenadine and BSA. It was found that BSA has one binding site for fexofenadine. On the basis of the competitive site marker experiments and thermodynamic results, it was considered that fexofenadine was primarily bound to the site I of BSA mainly by hydrogen bond and van der Waals force. Utilising Förster resonance energy transfer the distance, r between the donor, BSA and acceptor fexofenadine was obtained. Furthermore, the results of circular dichroism and synchronous fluorescence spectrum indicated that the secondary structure of BSA was changed in the presence of fexofenadine. Molecular docking was applied to further define the interaction of fexofenadine with BSA.     

Intermolecular interaction of nickel (ii) phthalocyanine tetrasulfonic acid tetrasodium salt with bovine serum albumin: A multi-technique study

The interaction of nickel (II) phthalocyanine tetrasulfonic acid tetrasodium salt with bovine serum albumin (BSA) has been investigated by combination of fluorescence, UV-vis absorption, Fourier transform infrared (FT-IR), and circular dichorism (CD) spectroscopies as well as through molecular docking. Fluorescence quenching and absorption spectra were investigated as a mean for estimating the binding parameters. Analysis of fluorescence quenching data at different temperatures was performed in order to specify the thermodynamics parameters for interactions of phthalocyanine complex with BSA. According to experimental data it was suggested that phthalocyanine had a significant binding affinity to BSA and the process was entropy driven. Based on the results of molecular docking it was indicated that the main active binding site for this phthalocyanine complex is site I in subdomain IIA of BSA. The results provide useful information for understanding the binding mechanism of anticancer drug-albumin and gives insight into the biological activity and metabolism of the drug in blood.     

Effect of quercetin on the amiloride–bovine serum albumin interaction using spectroscopic methods,molecular docking and chemometric approaches

The effect of quercetin flavonoid (QUE), on the binding interaction of antihypertensive drug, amiloride (AMI) with bovine serum albumin (BSA) was investigated in this study. Spectroscopic methods such as steady‐state, synchronous, three‐dimensional fluorescence, and circular dichroism spectroscopy were employed to study the interaction. Fluorescence data were analyzed using the Stern–Volmer equation and a static quenching process was found to be involved in the formation of AMI–BSA and QUE–BSA complexes and were in good agreement with the thermodynamic study. The thermodynamic parameters illustrated that the process is spontaneous and enthalpy driven. Hydrophobicity is acting as the primary force in the binding interaction. Fluorescence spectral data were resolved using a multivariate curve resolution‐alternating least squares method (MCR–ALS). Site marker and molecular docking studies confirmed the binding site of AMI on BSA, i.e. site II. The binding distance between amino acid of BSA and AMI was calculated and found to be 2.18 nm which indicated that energy transfer has occurred from an amino acid of BSA to AMI. The binding affinity of AMI to BSA was found to be reduced in the presence of QUE, which may lead to the poor distribution of AMI at the desired site.     

Spectroscopic,electrochemical and molecular docking studies of dothiepin and doxepin with bovine serum albumin and DNA base

The interaction of dothiepin (DOT) and doxepin (DOX) with bovine serum albumin (BSA) and a DNA base (adenine) was studied using UV–visible, fluorescence, attenuated total reflection–infra‐red (ATR‐IR), cyclic voltammetry and molecular docking methods. Strong fluorescence quenching was observed upon interaction of DOT and DOX with BSA/adenine and the mechanism suggested static quenching. Hydrophobic and hydrogen bonding interactions were the predominant intermolecular forces needed to stabilize the copolymer. Upon addition of the drugs: (i) the tautomeric equilibrium structure of the adenine was changed; and (ii) the oxidation and the reduction peaks of the adenine/BSA interaction shifted towards high and low potentials, respectively. In ATR‐IR, the band shift of amides I and II indicated a change in secondary structure of BSA upon binding to DOT and DOX drugs. The reduction in voltammetric current in the presence of BSA/adenine was attributed to slow diffusion of BSA/adenine binding with DOX/DOT. The docking method indicated that the drug moiety interacted with the BSA molecule. Copyright © 2016 John Wiley & Sons, Ltd.     

Molecular interactions of thymol with bovine serum albumin: Spectroscopic and molecular docking studies

Thymol is the main monoterpene phenol present in the essential oils which is used in the food industry as flavoring and preservative agent. In this study, the interaction of thymol with the concentration range of 1 to 6 μM and bovine serum albumin (BSA) at fixed concentration of 1 μM was investigated by fluorescence, UV‐vis, and molecular docking methods under physiological‐like condition. Fluorescence experiments were performed at 5 different temperatures, and the results showed that the fluorescence quenching of BSA by thymol was because of a static quenching mechanism. The obtained binding parameters, K, were in the order of 10⁴ M^?1, and the binding number, n, was approximately equal to unity indicating that there is 1 binding site for thymol on BSA. Calculated thermodynamic parameters for enthalpy (ΔH), entropy (ΔS), and Gibb's free energy (ΔG) showed that the reaction was spontaneous and hydrophobic interactions were the main forces in the binding of thymol to BSA. The results of UV‐vis spectroscopy and Arrhenius' theory showed the complex formation in the interaction of thymol and BSA. Negligible conformational changes in BSA by thymol were observed in fluorescence experiments, and the same results were also obtained from UV‐vis studies. Results of molecular docking indicated that the subdomain IA of BSA was the binding site for thymol.     

Study on the binding of cerium to bovine serum albumin

The interaction of Ce(3+) to bovine serum albumin (BSA) has been investigated mainly by fluorescence spectra, UV-vis absorption spectra, and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of BSA by Ce(3+) was a static quenching process, the binding constant is 6.70 × 10(5) , and the number of binding site is 1. The thermodynamic parameters (ΔH = -29.94 kJ mol(-1) , ΔG = -32.38 kJ mol(-1) , and ΔS = 8.05 J mol(-1) K(-1) ) indicate that electrostatic effect between the protein and the Ce(3+) is the main binding force. In addition, UV-vis, CD, and synchronous fluorescence results showed that the addition of Ce(3+) changed the conformation of BSA.