Molecular interaction of human serum albumin with paracetamol: Spectroscopic and molecular modeling studies

The interaction between paracetamol and human serum albumin (HSA) under physiological conditions has been investigated by fluorescence, circular dichroism (CD) and docking. Fluorescence data revealed that the fluorescence quenching of HSA by paracetamol was the result of the formed complex of HSA–paracetamol, and the binding constant (K_a) and binding number obtained is 1.3 × 10⁴ at 298 K and 2, respectively for the primary binding site. Circular dichorism spectra showed the induced conformational changes in HSA by the binding of paracetamol. Moreover, protein–ligand docking study indicated that paracetamols (two paracetamols bind to HSA) bind to residues located in the subdomain IIIA.     

Binding of daunorubicin to human serum albumin using molecular modeling and its analytical application

This study was designed to examine the interaction of daunorubicin with human serum albumin (HSA) for the first time by fluorescence spectroscopy in combination with UV absorption and molecular modeling under simulative physiological conditions. The quenching mechanism was suggested to be static quenching according to the fluorescence measurement and the linearity of Scatchard plot indicated that daunorubicin bound to a single class of binding sites on HSA. The thermodynamic parameters, enthalpy change (DeltaH) and entropy change (DeltaS) were calculated to be -16.13 kJ/mol and 27.86 J/(molK), according to the Vant'Hoff equation. These data suggested that hydrophobic interaction was the predominant intermolecular forces stabilizing the complex, which was in good agreement with the results of molecular modeling study. In addition, the effects of common ions on the binding constant of daunorubicin-HSA complex were also discussed at room temperature. Moreover, the synchronous fluorescence technique was successfully employed to determine the total proteins in serum, urine and saliva samples at room temperature under the optimum conditions with a wide linear range and satisfactory results.     

Spectroscopic studies of the interaction between hypocrellin B and human serum albumin

Previous work has proved that hypocrellin B (HB) binds to human serum albumin (HSA) at a specific site instead of distributed randomly on the surface of a protein. In the current work, further investigation by using bilirubin as a site I marker indicates that HB can compete for the same site with bilirubin, suggesting that the HB binding site is located at sub-domain IIA (site I) of HSA. Moreover, bound to HSA, the HB fluorescence was found to be pH sensitive in physiological range (pH 6.0-8.0). The increasing of binding constant of HB to HSA in the pH range 6-8 also indicates that the N<-->B transition modulates the microenvironment changes of the binding site and influences considerably the binding between HB and HSA. Furthermore, picosecond time-resolved fluorescence spectra of HB-HSA complex in PBS indicate an additional short-lived component compared to that for HB in benzene, which may be assigned to the process of electron transfer from Trp-214 to HB.     

Spectroscopic and molecular modeling studies on the binding of the flavonoid luteolin and human serum albumin

Luteolin (LUT) is a polyphenolic compound, found in a variety of fruits, vegetables, and seeds, which has a variety of pharmacological properties. In the present contribution, binding of LUT to human serum albumin (HSA), the most abundant carrier protein in the blood, was investigated with the aim of describing the binding mode and parameters of the interaction. The application of circular dichroism, UV‐Vis absorption, fluorescence, Raman and surface‐enhanced Raman scattering spectroscopy combined with molecular modeling afforded a clear picture of the association mode of LUT to HSA. Specific interactions with protein amino acids were evidenced. LUT was found to be associated in subdomain IIA where an interaction with Trp‐214 is established. Hydrophobic and electrostatic interactions are the major acting forces in the binding of LUT to HSA. The HSA conformations were slightly altered by the drug complexation with reduction of α‐helix and increase of β‐turns structures, suggesting a partial protein unfolding. Also the configuration of at least two disulfide bridges were altered. Furthermore, the study of molecular modeling afforded the binding geometry. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 917–927, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Spectroscopic studies of interaction between CuO nanoparticles and bovine serum albumin

Recently, the great interests in manufacturing and application of metal oxide nanoparticles in commercial and industrial products have led to focus on the potential impact of these particles on biomacromolecules. In the present study, the interaction of copper oxide (CuO) nanoparticles with bovine serum albumin (BSA) was studied by spectroscopic techniques. The zeta potential value for BSA and CuO nanoparticles with average diameter of around 50 nm at concentration of 10 μM in the deionized (DI) water were ?5.8 and ?22.5 mV, respectively. Circular dichroism studies did not show any changes in the content of secondary structure of the protein after CuO nanoparticles interaction. Fluorescence data revealed that the fluorescence quenching of BSA by CuO nanoparticles was the result of the formed complex of CuO nanoparticles – BSA. Binding constants and other thermodynamic parameters were determined at three different temperatures. The hydrogen bond interactions are the predominant intermolecular forces to stabilize the CuO nanoparticle – BSA complex. This study provides important insight into the interaction of CuO nanoparticles with proteins, which may be of importance for further application of these nanoparticles in biomedical applications.     

Characterization of the interaction between nitrofurazone and human serum albumin by spectroscopic and molecular modeling methods

The interaction of nitrofurazone (NF) and human serum albumin (HSA) has been studied by fluorescence spectroscopy, FT-IR spectroscopy and molecular modeling methods. The results showed that the fluorescence of HSA was quenched by NF in a static quenching mechanism. Thermodynamic parameters revealed that hydrogen bonds and van der Waals force played the major role during the interaction. The calculated binding distance (r) indicated that the non-radioactive energy transfer came into being in the interaction between NF and HSA. HSA had a single class of binding site at Sudlow' site I in subdomain IIA for NF, which was verified by the displacement experiment. The molecular modeling study further confirmed the specific binding sites of NF on HSA, such as the interaction between N11 and N14 of NF with Lue 283 and Ser 287 predominately through hydrogen bonds. Three-dimensional fluorescence spectra indicated that the polarity around the tryptophan residues decreased and the conformation of HSA changed after adding NF. FT-IR spectra showed that NF could induce the polypeptides of HSA unfolding because it changed α-helix and β-sheet into β-turn and random structure of HSA.     

Spectroscopic and molecular docking studies on the interaction between N‐acetyl cysteine and bovine serum albumin

The interaction between N‐acetyl cysteine (NAC) and bovine serum albumin (BSA) was investigated by UV–vis, fluorescence spectroscopy, and molecular docking methods. Fluorescence study at three different temperatures indicated that the fluorescence intensity of BSA was reduced upon the addition of NAC by the static quenching mechanism. Binding constant (K_b) and the number of binding sites (n) were determined. The binding constant for the interaction of NAC and BSA was in the order of 10³ M^?1, and the number of binding sites was obtained to be equal to 1. Enthalpy (ΔH), entropy (ΔS), and Gibb's free energy (ΔG) as thermodynamic values were also achieved by van't Hoff equation. Hydrogen bonding and van der Waals force were the major intermolecular forces in the interaction process and it was spontaneous. Finally, the binding mode and the binding sites were clarified using molecular docking which were in good agreement with the results of spectroscopy experiments. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 638–645, 2015.     

Spectroscopic and molecular modeling studies of the interaction between morin and polyamidoamine dendrimer

Interactions between the polyamidoamine (PAMAM) dendrimer and drug molecules are of interest for their potential biomedical applications. The goal of this work is to examine the interaction of PAMAM‐C₁₂ 25% dendrimer with morin. The ultraviolet–visible, fluorescence spectroscopic methods as well as molecular modeling were used to analyze drug‐binding mode, binding constants and binding sites, etc. The experimental data showed that the binding constant of morin‐PAMAM‐C₁₂ 25% is about 10⁵ L/mol. The interaction of morin with PAMAM‐C₁₂ 25% is mainly driven by the hydrophobic, electrostatic, hydrogen bonds and van der Waals forces. There are mainly three classes of binding site of morin at the interface of PAMAM‐C₁₂ 25%. These results provided some useful information for self‐assembling and disassembling the PAMAM dendrimer as well as efficient drug delivery and therapeutic applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectroscopic studies on the interaction of riboflavin with bovine serum albumin

The mechanism of interaction of riboflavin (RF) with bovine serum albumin (BSA) using fluorometric and circular dichroism (CD) methods has been reported. The association constant (K) for RF-BSA binding shows that the interaction is non-covalent in nature. Stern-Volmer analysis of fluorescence quenching data shows that the fraction of fluorophore (BSA) accessible to the quencher (RF) is close to unity, indicating that both tryptophan residues of BSA are involved in the interaction. The high magnitude of rate constant for quenching kq (10(13) M(-1) s(-1) indicates that RF binding site is in close proximity to tryptophan residue of BSA. Thermodynamic parameters obtained from data at different temperatures showed that the binding of RF to BSA predominantly involves the formation of hydrophobic bonds. Binding studies in the presence of a hydrophobic probe 8-anilino-1-naphthalene sulphonic acid, sodium salt (ANS) showed that RF and ANS do not share common sites in BSA. The small decrease in critical micellar concentration of anionic surfactant, sodium dodecyl sulphate in the presence of RF shows that ionic character of RF also contributes to binding and is not solubilized inside the micelle. Significant decrease in concentration of free RF has been observed in the presence of paracetamol. The CD spectrum shows the binding of RF leads to a change in the alpha helical structure of BSA.     

Spectroscopic study of the interaction between lycopene and bovine serum albumin

The interaction of lycopene with bovine serum albumin (BSA) in aqueous solution was studied by fluorescence quenching, three‐dimensional fluorescence and circular dichroism spectroscopy. The data showed that the fluorescence of BSA was quenched by lycopene at different temperatures through a dynamic mechanism. The evaluation of three‐dimensional fluorescence spectra revealed a conformational modification of BSA induced by coupling with lycopene and an increase in protein diameter as a consequence of the ligand–protein interaction. Moreover, the information obtained from evaluation of the effect of lycopene on BSA conformation by circular dichroism strongly supported the existence of a slight unfolding of BSA induced by coupling to lycopene. Copyright © 2012 John Wiley & Sons, Ltd.     

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     

Spectroscopic studies on the comparative interaction of cationic single-chain and gemini surfactants with human serum albumin

To gain insights into the comparative effect of single-chain/gemini surfactants on proteins and the possible implications, the interaction of human serum albumin (HSA) with cationic single-chain surfactant cetyltrimethylammonium bromide (CTAB) and its gemini counterpart bis(cetyldimethylammonium)butane dibromide with spacer -(CH(2))(4)- (designated as G4) using turbidity measurements, far-UV and near-UV circular dichroism (CD), intrinsic fluorescence and extrinsic fluorescence spectroscopy at pH 7.0 are reported in this contribution. A decrease of 33.5% alpha-helical content at 22.5 microM G4 was monitored compared to a 15% decrease at 2,250 microM CTAB. Against a 3.5% increase at 11,250 microM CTAB, a rise of 21.1% in the alpha-helical content was observed 375 microM G4. The result is related to the stronger electrostatic and hydrophobic forces in G4, owing to the presence of two charged headgroups and two hydrophobic hydrocarbon tails that make it to bind strongly to the protein compared to its single chain counterpart, CTAB, resulting in larger unfolding. The stabilization at higher concentrations is attributed to the highly hydrophobic microdomain of the G4 aggregates formed at such concentrations. The results of the multi-technique approach are consistent with the fact that the gemini surfactants are more efficient than their conventional single-chain counterparts and hence may be used more effectively in the renaturation of proteins produced in the genetically engineered cells via the artificial chaperone protocol, as solubilizing agents to recover proteins from insoluble inclusion bodies and in drug delivery.     

Spectroscopic and molecular modeling approaches to investigate the binding of proton pump inhibitors to human serum albumin

The interaction between two proton pump inhibitors viz., omeprazole (OME) and esomeprazole (EPZ) with human serum albumin (HSA) was studied by fluorescence, absorption, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR), voltammetry, and molecular modeling approaches. The Stern–Volmer quenching constants (K_sv) for OME-HSA and EPZ-HSA systems obtained at different temperatures revealed that both OME and EPZ quenched the intensity of HSA through dynamic mode of quenching mechanism. The binding constants of OME-HSA and EPZ-HSA increased with temperature, indicating the increased stability of these systems at higher temperatures. Thermodynamic parameters viz., ?H^°, ?S^°, and ?G^° were determined for both systems. These values revealed that both systems were stabilized by hydrophobic forces. The competitive displacement and molecular docking studies suggested that OME/EPZ was bound to Sudlow’s site I in subdomain IIA in HSA. The extent of energy transfer from HSA to OME/EPZ and the distance of separation in tryptophan (Trp214) Trp214-OME and Trp214-EPZ was determined based on the theory of fluorescence resonance energy transfer. UV absorption, 3D fluorescence, and CD studies indicated that the binding of OME/EPZ to HSA has induced micro environmental changes around the protein which resulted changes in its secondary structure.     

Homology modeling of human serum paraoxonase1 and its molecular interaction studies with aspirin and cefazolin

Human serum paraoxonase1 (HuPON1) belongs to the family of A-esterases (EC.3.1.8.1). It is associated with HDL particle and prevents atherosclerosis by cleaving lipid hydroperoxides and other proatherogenic molecules of oxidized low density lipoproteins (LDL). Since the precise structure of HuPON1 is not yet available, the structure-function relationship between HuPON1 and activators/inhibitors is still unknown. Therefore, a theoretical model of HuPON1 was generated using homology modelling and precise molecular interactions of an activator aspirin and an inhibitor cefazolin with PON1 were studied using Autodock software. The ligand binding residues were found to be similar to the predicted active site residues. Both cefazolin and aspirin were found to dock in the vicinity of the predicted active sites of PON1; cefazolin bound at residues N166, S193 and Y71, while aspirin at residues N309, I310 and L311. Binding region in the PON1 by prediction (3D2GO server) and docking studies provide useful insight into mechanism of substrate and inhibitor binding to the enzyme active site.     

Spectroscopic investigation on the interaction of J-aggregate with human serum albumin

The interactions of three cyanine dyes, which exhibit different meso substituent in polymethine chain, with human serum albumin (HSA) have been investigated by the means of absorption, fluorescence and circular dichroism (CD) spectra. In phosphate buffer solution (PBS), the mentioned dyes exist not as isolated monomers but rather in the formation of J-aggregation. In the presence of HSA, the absorption and fluorescence emission spectra indicated that the J-aggregation was decomposed to monomer because of the strong affinity between dye molecules and HSA. Besides the association of cyanine dyes with HSA, binding to HSA gave rise to the J-aggregation CD signals. The meso substituent in the polymethine plays an important role in the interaction of HSA and the J-aggregation. Spectral studies showed that the dye bound with HSA in a 1:1 formation. The apparent constant (K(a)) value was roughly identified by analysis of the corresponding fluorescence data at various HSA concentrations. The higher affinity of the molecule with meso phenyl towards HSA with respect to molecules with meso ethyl or methyl can be attributed to the arrangement of molecules in J-aggregation and the hydrophobic force between the molecules and HSA.     

Binding of hydroxylated polybrominated diphenyl ethers with human serum albumin: Spectroscopic characterization and molecular modeling

Three hydroxylated polybrominated diphenyl ethers (OH‐PBDEs), 3‐OH‐BDE‐47, 5‐OH‐BDE‐47, and 6‐OH‐BDE‐47, were selected to investigate the interactions between OH‐PBDEs with human serum albumin (HSA) under physiological conditions. The observed fluorescence quenching can be attributed to the formation of complexes between HSA and OH‐PBDEs. The thermodynamic parameters at different temperatures indicate that the binding was caused by hydrophobic forces and hydrogen bonds. Molecular modeling and three‐dimensional fluorescence spectrum showed conformational and microenvironmental changes in HSA. Circular dichroism analysis showed that the addition of OH‐PBDEs changed the conformation of HSA with a minor reduction in α‐helix content and increase in β‐sheet content. Furthermore, binding distance r between the donor (HSA) and acceptor (three OH‐PBDEs) calculated using Förster's nonradiative energy transfer theory was <7 nm; therefore, the quenching mechanisms for the binding between HSA and OH‐PBDEs involve static quenching and energy transfer. Combined with molecular dynamics simulations, the binding free energies (ΔG _bind ) were calculated using molecular mechanics/Poisson ? Boltzmann surface area method, and the crucial residues in HSA were identified.     

A study on the interaction between 5-Methyluridine and human serum albumin using fluorescence quenching method and molecular modeling

This work was designed to study the interaction between 5-Methyluridine and human serum albumin (HSA) under simulative physiological conditions using fluorescence spectroscopy in combination with molecular modeling technique for the first time. Static quenching was suggested by the fluorescence measurement. The binding constants (K) were calculated according to the relevant fluorescence data at different conditions including temperature. Thermodynamic parameter, different conditions including temperature to determine enthalpy change and entropy change, indicating the hydrophobic force played a major role in the binding interaction between 5-Methyluridine and HSA. The experimental result was in correspondence with molecular modeling theory.     

Multi-spectroscopic and molecular modeling studies of interaction between two different angiotensin I converting enzyme inhibitory peptides from gluten hydrolysate and human serum albumin

The present study was carried out to characterize Angiotensin-converting enzyme (ACE) inhibitory peptides which are released from the trypsin hydrolysate of wheat gluten protein. The binding of two inhibitory peptide (P₄ and P₆) to human serum albumin (HSA) under physiological conditions has been investigated by multi-spectroscopic in combination with molecular modeling techniques. Time-resolved and quenching fluorescence spectroscopies results revealed that the quenching of HSA fluorescence by P₄ and P₆ in the binary and ternary systems caused HSA-peptides complexes formation. The results indicated that both peptides quenched the fluorescence intensity of HSA through a static mechanism. The binding affinities and number of binding sites were obtained for the HSA-peptides complexes. The circular dichroism (CD) data revealed that the presence of both peptides increased the α-helix content of HSA and induced the remarkable folding of the polypeptide of the protein. Therefore, the CD data determined that the protein structure has been stabilized in the percent of ACE inhibitory peptides in binary and ternary systems. The binding distances between HSA and both peptides were estimated by the Forster theory, and it was revealed that nonradiative energy transfer from HSA to peptides occurred with a high probability. ITC experiments reveal that, in the absence and presence of P₆, the dominant forces are electrostatic in binary and ternary systems. Furthermore, molecular modeling studies confirmed the experimental results. Molecular modeling investigation suggested that P₄ bound to the site IA and IIA of HSA in binary and ternary systems, respectively. This study on the interaction of peptides with HSA should prove helpful for realizing the distribution and transportation of food compliments and drugs in vivo, elucidating the action mechanism and dynamics of food compliments and drugs at the molecular level. It should moreover be of great use for understanding the pharmacokinetic and pharmacodynamic mechanism of the food compliments and drugs.     

Interaction of human serum albumin with 10-hydroxycamptothecin: spectroscopic and molecular modeling studies

In this work, fluorescence spectroscopy in combination with circular dichroism spectroscopy and molecular modeling was employed to investigate the binding of 10-hydroxycamptothecin (HCPT) to human serum albumin (HSA) under simulative physiological conditions. The experiment results showed that the fluorescence quenching of HSA by HCPT was a result of the formation of HCPT–HSA complex. The corresponding association constants (K _a) between HCPT and HSA at four different temperatures were determined according to the modified Stern–Volmer equation. The results of thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrogen bonds and van der Waals forces played major roles for HCPT–HSA association. Site marker competitive displacement experiment indicated that the binding of HCPT to HSA primarily took place in sub-domain IIA (site I). Molecular docking study further confirmed the binding mode and the binding site obtained by fluorescence and site marker competitive experiments. The conformational investigation showed that the presence of HCPT decreased the α-helical content of HSA and induced the slight unfolding of the polypeptides of protein, which confirmed some micro-environmental and conformational changes of HSA molecules.     

Molecular interactions of isoxazolcurcumin with human serum albumin: spectroscopic and molecular modeling studies

Curcumin is a nontoxic natural product with diverse pharmacological potencies. We report the interaction of a potent synthetic derivative of curcumin, isoxazolcurcumin (IOC) with human serum albumin (HSA) using various biophysical methods. The observed fluorescence quenching of HSA by IOC is due to a complex formation by a static quenching process with a quenching constant of the order of 10(5) M(-1). The binding affinity and the number of binding sites were obtained from a Scatchard analysis. Thermodynamics reveals that the interaction is entropy driven with predominantly hydrophobic forces. From the observed F?rster-type fluorescence resonance energy transfer (FRET), the donor (Trp 214 in HSA) to acceptor (IOC) distance is calculated to be 3.2 nm. The conformational changes of HSA due to the interaction were investigated qualitatively from synchronous fluorescence spectra along with a quantitative estimation of the secondary structure from Fourier Transform Infrared (FTIR) and circular dichroism (CD) spectroscopies. Molecular docking studies were performed to obtain information on the possible residues involved in the interaction process, and changes in accessible surface area of the interacting residues were calculated. The preferred binding site of IOC was analyzed by ligand displacement experiments with 1-anilino-8-naphthalenesulfonate (ANS) and warfarin-bound HSA.