Molecular interaction of cationic gemini surfactant with bovine serum albumin: A spectroscopic and molecular docking study

Herein, we report the effect of N,N′-bis(dodecyloxycarbonylmethyl)-N,N,N′,N′-tetramethyl-1,2-ethanediammonium dibromide (dodecyl betainate gemini or DBG) on the structure and function of bovine serum albumin (BSA) by using fluorescence, time resolved fluorescence, circular dichroism and dynamic light scattering techniques. The Stern–Volmer quenching constants K_SV and the corresponding thermodynamic parameters viz ΔH, ΔG and ΔS have been estimated by the fluorescence quenching method. The results indicated that DBG binds spontaneously with BSA through hydrophobic interaction. Time resolved fluorescence data show that the quenching follows the static mechanism pathway. It can be seen from far-UV CD spectra that the α-helical network of BSA is disrupted and its content increases from 71% to 79% at lower concentrations which again decreases to 38% at higher concentration. DLS measurements suggested that hydrodynamic radius (R_h) decreases in the presence of 30 and 40 μM of DBG while it increases when the concentration of DBG was 70 and 100 μM. The molecular docking study indicated that DBG is embedded into subdomain IIA of BSA and binds with the R-914, R-195 and R-217 residues by hydrogen bonding and by hydrophobic interaction.     

Spectroscopy and docking simulations of the interaction between lochnericine and bovine serum albumin

Lochnericine (LOC) is a component of Voacanga africana, which is a type of traditional medical food in Africa widely used for treating diseases. In this article, the interaction between LOC and bovine serum albumin (BSA) was studied by fluorescence spectroscopy. Furthermore, Fourier transform infrared (FTIR), Raman and circular dichroism (CD) were used to investigate the structural changes of BSA. The experimental results consistently indicated that LOC changed the secondary structure of BSA. Three structure‐similar components were used to study the interference experiments. The molecular modeling results showed that LOC could bind within not only sites I and II, but also bind the cavity of subdomain IB. Copyright © 2014 John Wiley & Sons, Ltd.     

The interaction between N-n-undecyl-N'-(sodium p-aminobenzenesulfonate) thiourea and serum albumin studied using various spectroscopies and the molecular modeling method

The preparation and characteristics of N-n-undecyl-N'-(sodium-p-aminobenzenesulfonate) thiourea (UPT), a new water-soluble reagent with a saturated fatty hydrocarbon group, were described. The interactions of UPT with bovine serum albumin (BSA) and human serum albumin (HSA) were studied using fluorescence spectroscopy in combination with ultraviolet (UV) absorption spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and the molecular modeling method. UPT exhibited a strong ability to quench the intrinsic fluorescence of both BSA and HSA through a static quenching procedure. The binding constants of UPT and BSA or HSA were determined at different temperatures based on the relevant fluorescence data. The binding sites were obtained and the acting force was suggested to be mainly hydrophobic interaction, which was consistent with the result of the molecular modeling study, and there were also a number of hydrogen bonds between UPT and HSA. The results of determination of the proteins in bovine serum or human serum by this method were very close to those obtained by using Coomassie Brilliant Blue G-250 colorimetry. A practical method was proposed for the determination of UPT in bovine serum or human serum samples with satisfactory results.     

Interactions between bovine serum albumin and gemini surfactant alkanediyl-alpha, omega-bis(dimethyldodecyl-ammonium bromide)

Interactions between bovine serum albumin (BSA) and cationic gemini surfactant alkanediyl-alpha,omega-bis(dimethyldodecyl-ammonium bromide) (12-n-12, n=3, 4, 6) in aqueous solution have been investigated by measuring fluorescence, UV-vis transmittance, dynamic lighting scattering, and circular dichroism. Compared to a traditional surfactant dodecyltrimethylammonium bromide (DTAB), 12-n-12 interacts with BSA more strongly. With increasing concentration, 12-n-12 first binds specifically onto BSA leading to the unfolding and aggregation of BSA, and the decrease in alpha-helix content; and then forms micelle-like complexes along the unfolded BSA chains. A gemini surfactant with a longer spacer has a larger effect on BSA unfolding due to a stronger hydrophobic interaction.     

Characterization of the interaction between 2′-deoxyuridine and human serum albumin

The binding of 2′-deoxyuridine to human serum albumin (HSA) was investigated by fluorescence spectroscopy in combination with molecular modeling under simulation of physiological conditions. The quenching mechanism was suggested to be static according to the fluorescence measurement. The thermodynamic parameters: enthalpy change (ΔH) and entropy change (ΔS) were calculated to be −18.87 kJ/mol and 24.00 J/(mol K) according to the Vant’Hoff equation. These data suggest that hydrophobic interactions are the predominant intermolecular forces stabilizing the complex. Experimental results are in agreement with the results obtained by molecular modeling study. In addition, the effects of common ions on the binding constants were also studied at room temperature.     

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.     

Mutational analysis of the interaction between albumin-binding domain from streptococcal protein G and human serum albumin

Streptococcal protein G (SpG) is a bacterial cell surface receptor exhibiting affinity to both human immunoglobulin (IgG) and human serum albumin (HSA). Interestingly, the serum albumin and immunoglobulin-binding activities have been shown to reside at functionally and structurally separated receptor domains. The binding domain of the HSA-binding part has been shown to be a 46-residue triple alpha-helical structure, but the binding site to HSA has not yet been determined. Here, we have investigated the precise binding region of this bacterial receptor by protein engineering applying an alanine-scanning procedure followed by binding studies by surface plasmon resonance (SPR). The secondary structure as well as the HSA binding of the resulting albumin-binding domain (ABD) variants were analyzed using circular dichroism (CD) and affinity blotting. The analysis shows that the HSA binding involves residues mainly in the second alpha-helix.     

Spectroscopic analysis of the binding interaction between tinidazole and bovine serum albumin (BSA)

The interaction between bovine serum albumin (BSA) and tinidazole (Tindamax; 1) in aqueous solution was investigated in detail by means of UV/VIS and fluorescence spectroscopy, as well as through resonance light-scattering (RLS) spectroscopy. The apparent binding constant and number of binding sites were determined at three different temperatures, as well as the average binding distances between 1 and the nearest amino acid residue(s) of BSA, as analyzed by means of F?rster's theory of non-radiation energy transfer. Compound 1 was found to quench the inner fluorescence of BSA by forming a tight 1:1 aggregate, based on both static quenching and non-radiation energy transfer. The entropy change upon complexation was positive, and the enthalpy change was negative, indicating that the observed spontaneous binding is mainly driven by electrostatic interactions.     

Investigation of interaction between human serum albumin and N6-(2-hydroxyethyl)-adenosine by fluorescence spectroscopy and molecular modelling.

The interaction between human serum albumin (HSA) and N(6)-(2-hydroxyethyl)-adenosine (HEA) was investigated using fluorescence spectroscopy in combination with UV absorption spectroscopy for the first time. The results of spectroscopic measurements suggested that the hydrophobic interaction was the predominant intermolecular force stabilizing the complex, which was in good agreement with the results of molecular modelling study. The enthalpy change (DeltaH) and the entropy change (DeltaS) were calculated, according to the Van't Hoff equation, to be -24.05 kJ/mol and 30.23 J/mol/K, respectively. The effects of common ions on the binding constant of the HEA-HSA complex at room temperature were also investigated.     

Studies on the interaction between vincamine and human serum albumin: a spectroscopic approach

The interaction between vincamine (VCM) and human serum albumin (HSA) has been studied using a fluorescence quenching technique in combination with UV/vis absorption spectroscopy, Fourier transform infrared (FT–IR) spectroscopy, circular dichroism (CD) spectroscopy and molecular modeling under conditions similar to human physiological conditions. VCM effectively quenched the intrinsic fluorescence of HSA via static quenching. The binding constants were calculated from the fluorescence data. Thermodynamic analysis by Van't Hoff equation revealed enthalpy change (ΔH) and entropy change (ΔS) were ?4.57 kJ/mol and 76.26 J/mol/K, respectively, which indicated that the binding process was spontaneous and the hydrophobic interaction was the predominant force. The distance r between the donor (HSA) and acceptor (VCM) was obtained according to the Förster's theory of non‐radiative energy transfer and found to be 4.41 nm. Metal ions, viz., Na⁺, K⁺, Li⁺, Ni²⁺, Ca²⁺, Zn²⁺ and Al³⁺ were found to influence binding of the drug to protein. The 3D fluorescence, FT–IR and CD spectral results revealed changes in the secondary structure of the protein upon interaction with VCM. Furthermore, molecular modeling indicated that VCM could bind to the subdomain IIA (site I) of HSA. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

A spectroscopic and molecular dynamic approach on the interaction between ionic liquid type gemini surfactant and human serum albumin

The interactions of imidazolium bashed ionic liquid-type cationic gemini surfactant ([C₁₂-4-C₁₂im]Br₂) with HSA were studied by fluorescence, time-resolved fluorescence, UV-visible, circular dichroism, molecular docking and molecular dynamic simulation methods. The results showed that the [C₁₂-4-C₁₂im]Br₂ quenched the fluorescence of HSA through dynamic quenching mechanism as confirmed by time-resolved spectroscopy. The Stern–Volmer quenching constant (K_sv) and relevant thermodynamic parameters such as enthalpy change (ΔH), Gibbs free energy change (ΔG) and entropy change (ΔS) for interaction system were calculated at different temperatures. The results revealed that hydrophobic forces played a major role in the interactions process. The results of synchronous fluorescence, UV-visible and CD spectra demonstrated that the binding of [C₁₂-4-C₁₂im]Br₂ with HSA induces conformational changes in HSA. Inquisitively, the molecular dynamics study contribute towards understanding the effect of binding of [C₁₂-4-C₁₂im]Br₂ on HSA to interpret the conformational change in HSA upon binding in aqueous solution. Moreover, the molecular modelling results show the possible binding sites in the interaction system.     

The investigation of the interaction between orientin and bovine serum albumin by spectroscopic analysis

In this paper, the interaction between orientin and bovine serum albumin (BSA) was examined using fluorescence and absorbance spectroscopy. The analysis of the quenching mechanism was done using Stern–Volmer plots which exhibit upward (positive) deviation. A linear response to orientin was shown in the concentration range between 3 and 50 μM. The experimental results showed the presence of a static quenching process between orientin and BSA. The thermodynamic parameters ΔH, ΔS and ΔG were also calculated and suggested that the hydrophobic and electrostatic interactions played an important role in the interaction between orientin and BSA. Furthermore, the distances between BSA and orientin were determined according to Förster non‐radiation energy transfer theory. In addition, the results of the synchronous fluorescence obtained indicated that the binding of orientin with BSA could affect conformation in BSA. Copyright © 2013 John Wiley & Sons, Ltd.     

Doxorubicin hinders DNA condensation promoted by the protein bovine serum albumin (BSA)

In this work, we have studied the interaction between the anticancer drug doxorubicin (doxo) and condensed DNA, using optical tweezers. To perform this task, we use the protein bovine serum albumin (BSA) in the working buffer to mimic two key conditions present in the real intracellular environment: the condensed state of the DNA and the abundant presence of charged macromolecules in the surrounding medium. In particular, we have found that, when doxo is previously intercalated in disperse DNA, the drug hinders the DNA condensation process upon the addition of BSA in the buffer. On the other hand, when bare DNA is firstly condensed by BSA, doxo is capable to intercalate and to unfold the DNA condensates at relatively high concentrations. In addition, a specific interaction between BSA and doxo was verified, which significantly changes the chemical equilibrium of the DNA–doxo interaction. Finally, the presence of BSA in the buffer stabilizes the double‐helix structure of the DNA–doxo complexes, preventing partial DNA denaturation induced by the stretching forces.     

Studies on the interaction between Oxaprozin-E and bovine serum albumin by spectroscopic methods

The interaction between Oxaprozin-E and bovine serum albumin (BSA) was studied by spectroscopic methods including fluorescence and UV–vis absorption spectroscopy. The quenching mechanism of fluorescence of BSA by Oxaprozin-E was discussed to be a dynamic quenching procedure. The number of binding sites n and apparent binding constant K was measured by fluorescence quenching method. The thermodynamics parameter ΔH, ΔG, ΔS were calculated. The results indicate the binding reaction was mainly entropy-driven and hydrophobic forces played major role in the binding reaction. The distance r between donor (BSA) and acceptor (Oxaprozin-E) was obtained according to Förster theory of non-radioactive energy transfer.     

Cytotoxic palladium(II) complexes of 8-aminoquinoline derivatives and the interaction with human serum albumin

Palladium(II) complexes are potential antitumor metallodrugs for their chemical resemblance to platinum(II) complexes. Two palladium(II) complexes (1 and 2) in the formula of [PdLⁿCl] [L¹ = N-(tert-butoxycarbonyl)-l-methionine-N′-8-quinolylamide, L² = L-alanine-N′-8-quinolylamide] have been synthesized accordingly. The structures of the complexes were fully characterized by X-ray crystallography. The palladium(II) center in 1 is coordinated by two N atoms and an S atom from L¹ with one chloride anion as the leaving group; while that in 2 is coordinated by three N atoms from L² with one chloride anion as the leaving group. The interaction between complex 1 and human serum albumin (HSA) has been investigated using fluorescence and circular dichroism spectroscopies. The complex seems to react with HSA chiefly through hydrophobic and electrostatic interactions, and it does not alter the α-helical nature of HSA. The cytotoxicity of these complexes has been tested against the human cervical cancer (HeLa), human mammary cancer (MCF-7), and human lung cancer (A-549) cell lines. Complex 1 displays a cytotoxic activity comparable to that of cisplatin, but complex 2 is less active than cisplatin.     

Spectroscopic study on the interaction of bovine serum albumin with zinc(II) phthalocyanine

The interaction between the photosensitive antitumour drug, 2(3),9(10),16(17),23(24)‐tetra‐(((2‐aminoethylamino)methyl)phenoxy)phthalocyaninato‐zinc(II) (ZnPc) and bovine serum albumin (BSA) has been investigated using various spectroscopic methods. This work may provide some useful information for understanding the interaction mechanism of anticancer drug–albumin binding and gain insight into the biological activity and metabolism of the drug in blood. Based on analysis of the fluorescence spectra, ZnPc could quench the intrinsic fluorescence of BSA and the quenching mechanism was static by forming a ground state complex. Meanwhile, the Stern–Volmer quenching constant (K_SV), binding constant (K_b), number of binding sites (n) and thermodynamic parameters were obtained. Results showed that the interaction of ZnPc with BSA occurred spontaneously via hydrogen bond and van der Waal's force. According to Foster's non‐radioactive energy transfer theory, the energy transfer from BSA to ZnPc occurred with high possibility. Synchronous fluorescence and circular dichroism (CD) spectra also demonstrated that ZnPc induced the secondary structure of and conformation changes in BSA, especially α helix. Copyright © 2015 John Wiley & Sons, Ltd.     

Probing into the binding interaction between medroxyprogesterone acetate and bovine serum albumin (BSA): spectroscopic and molecular docking methods

To further understand the mechanism of action and pharmacokinetics of medroxyprogesterone acetate (MPA), the binding interaction of MPA with bovine serum albumin (BSA) under simulated physiological conditions (pH 7.4) was studied using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, circular dichroism and molecular docking methods. The experimental results reveal that the fluorescence of BSA quenches due to the formation of MPA–BSA complex. The number of binding sites (n) and the binding constant for MPA–BSA complex are ~1 and 4.6 × 10³ M^?1 at 310 K, respectively. However, it can be concluded that the binding process of MPA with BSA is spontaneous and the main interaction forces between MPA and BSA are van der Waals force and hydrogen bonding interaction due to the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ in the binding process of MPA with BSA. MPA prefers binding on the hydrophobic cavity in subdomain IIIA (site II′′) of BSA resulting in a slight change in the conformation of BSA, but BSA retaining the α‐helix structure. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of the interaction between ofloxacin and human serum albumin by spectroscopic methods

The binding of ofloxacin (OFLX) to human serum albumin (HSA) was investigated by fluorescence and circular dichroism (CD) techniques. The binding parameters have been evaluated by a fluorescence quenching method. Competitive binding measurements were performed in the presence of warfarin and ibuprofen and suggest binding to the warfarin site I of HSA. The distance r between donor (HSA) and acceptor (OFLX) was estimated according to the Forster's theory of non‐radiatiative energy transfer. CD spectra revealed that the binding of OFLX to HSA induced conformational changes in HSA. Molecular docking was performed and shows that for the lowest energy complex OFLX is located in site I of HSA, which correlate to the competitive binding experiments. Copyright © 2011 John Wiley & Sons, Ltd.     

A method of chemiluminescence coupled with ultrafiltration for investigating the interaction between ibuprofen and human serum albumin

In acidic media, ibuprofen substantially enhanced the weak chemiluminescence (CL) produced by sodium sulfite and potassium permanganate. The increased signals were linearly correlated with ibuprofen concentrations ranging from 1.2 × 10^‐3 to 4.8 μM, with a detection limit of 4.8 × 10^‐4 μM. Two ultrafiltration (UF) membranes were used to construct a unit for trapping 0.15 and 0.75 μM human serum albumin (HSA) and coupled online with the CL system. At low HSA concentrations, the numbers of bound molecules per binding site were calculated to be 0.9 for Sudlow site I and 6.2 for Sudlow site II. The association constants on these binding sites were 5.9 × 10⁵ and 3.4 × 10⁴ M^‐1, respectively. Our CL–UF protocol presents a rapid and sensitive method for studies on drug–protein interaction. Copyright © 2012 John Wiley & Sons, Ltd.