Binding Sites Of Bovine Serum Albumin Research Articles

Albumin-induced circular dichroism in Congo red: Applications for studies of amyloid-like fibril aggregates and binding sites

Congo red (CR), one of the most commonly used dyes for the identification of amyloid fibril aggregates, is also a ligand of native bovine serum albumin (BSA). Induced circular dichroism (ICD) is a phenomenon observed when a chiral compound induces chirality in an achiral one. Here, we study the spectral properties and analytical applications of ICD in Congo red provoked by its interaction with BSA. The complex BSA:CR displays a strong ICD spectrum with a positive band at 412nm and two negative bands at 356 and 490nm. The use of site I and site II albumin ligands as warfarin and ibuprofen, respectively, provoked different alterations in the Congo red ICD spectrum. The BSA binding sites were modified by oxidation and the ICD signal was sensitive to this alteration. The thermal treatment of the BSA:CR complex (30–90°C) was monitored by ICD at 490nm and showed a sigmoidal pattern typical of phase transition in proteins. The altered ICD spectrum is consistent with the formation of amyloid-like fibril aggregates in BSA, which was confirmed by thioflavin T and Rayleigh scattering assays. In conclusion, the ICD provoked by the binding of Congo red to albumin may represent a new spectroscopic technique for studying alterations in the structure of albumin regarding its binding sites and the formation of amyloid aggregates.

Assessment of the europium(III) binding sites on albumin using fluorescence spectroscopy.

Intrinsic fluorescence quenching of bovine serum albumin (BSA) and europium(III) luminescence in BSA complexes were investigated. The number of BSA binding sites (n) and equilibrium constant (Keq) values were determined from both measurements provided qualitatively different results. While the modified Stern-Volmer relation for BSA fluorescence quenching gave n = 1 at pH 4.5 and pH 6, two sets of binding sites were determined from Eu(3+) luminescence with n1 = 2, n2 = 4 at pH 6 and n1 = 1, n2 = 2 at pH 4.5. The model explaining the discrepancy between the results obtained by these fluorescent approaches was suggested, and the limitations in application of the "log-log" Stern-Volmer plots in analysis of binding processes were discussed.

Spectroscopic studies on the interactions of bovine serum albumin with alkyl sulfate gemini surfactants

Protein–surfactant interactions carry greater importance in a number of process and industries. However, most researches mainly focused on the interactions of protein with traditional surfactants such as sodium dodecyl sulfate, and the researches on gemini surfactants, a new generation of surfactants, with proteins are relatively limited. The present study aimed to explore the interactions of bovine serum albumin (BSA) with four alkyl sulfate gemini surfactants (designated as C12CnC12, where n is the spacer carbon number of 3, 4, 6 and 10) using fluorescence spectroscopy, circular dichroism (CD) and dynamic light scattering (DLS). Results showed that the spacer length had an important influence on the binding of gemini surfactants to BSA. The binding of C12C3C12 and C12C4C12 to BSA at low surfactant concentrations showed an enhancement of fluorescence, which was contrary to the effect of gemini surfactant with a longer spacer (n=6 and 10) to BSA. CD experiments showed that C12CnC12 could play two opposite roles when they interacted with BSA. At low C12CnC12/BSA molar ratios, C12CnC12 could stabilize the secondary structure of BSA, while C12CnC12 could mainly act as denaturants at higher molar ratios. The micropolarities of C12CnC12–BSA complexes were lower than the corresponding free gemini micelles. The hydrodynamic radii of the C12CnC12–BSA complexes were also measured and discussed. Further studies using molecular modeling are recommended to obtain detailed information about the binding sites of BSA, which are mainly influenced by alkyl sulfate gemini surfactants with different spacer length.

Investigation on the site-selective binding of bovine serum albumin by erlotinib hydrochloride

The purpose of this study was to investigate the site-selective binding of erlotinib hydrochloride (ET), a targeted anticancer drug, to bovine serum albumin (BSA) through 1H NMR, spectroscopic, thermodynamic, and molecular modeling methods. The fluorescence quenching of BSA by ET was a result of the formation of BSA–ET complex with high binding affinity. The site marker competition study combined with isothermal titration calorimetry experiment revealed that ET binds to site II of BSA mainly through hydrogen bond and van der Waals force. Molecular docking was further applied to define the specific binding site of ET to BSA. The conformation of BSA was changed in the presence of ET, revealed by synchronous fluorescence, circular dichroism, and three-dimensional fluorescence spectroscopy results. Further, NMR analysis of the complex revealed that the binding capacity contributed by the aromatic protons in the binding site of BSA might be greater than the aliphatic protons. An animated interactive 3D complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:26

Analysis of the molecular interactions and complexation of chloroquine with bovine serum albumin

Pharmacokinetic parameters, drug bioavailability, and biological activities depend on the mechanisms of interaction with serum albumin. In this study, the binding properties as well as mechanisms of interaction of chloroquine with bovine serum albumin (BSA) were investigated. The binding of chloroquine with BSA was carried out using a microcalorimetric approach. The mechanism of binding, the number of binding molecules as well as changes of BSA upon complexation with chloroquine were investigated. The binding isotherms indicated a variable number of binding sites of chloroquine on one molecule of BSA. At lower temperatures, larger numbers of binding sites were available for chloroquine, these decrease by increasing the temperature. The binding constant of chloroquine with BSA varied from 9.4×10³ M⁻¹ at 25°C to 5.7×10³ M⁻¹ at 40°C. Chloroquine showed temperature-dependent binding affinity, with stronger affinity at lower temperature. By increasing the temperature, from 25°C to 40°C, the binding affinity was decreased by approximately 60% of its value. Chloroquine showed weak binding affinity with BSA. The weak binding affinity of chloroquine with BSA is important in determining the drug-drug interactions at the binding sites of BSA. The presence of stronger binding ligands, e.g., chloramphenicol, tetracyclines or diclofenac, can compete with chloroquine for its binding sites, and therefore lowers its serum albumin binding. This study will be helpful in understanding the binding properties of mechanisms of interaction of chloroquine with BSA.

Displacement Reaction Using Ibuprofen in a Mixture of Bioactive Imidazole Derivative and Bovine Serum Albumin—a Fluorescence Quenching Study

The mutual interaction of imidazole derivative (PIPP) with bovine serum albumin (BSA) was investigated using photoluminescent studies. The fluorescence quenching mechanism of BSA by PIPP was analyzed and the binding constant was calculated. The binding distance between PIPP and BSA was obtained based on the theory of Forester's non-radiation energy transfer. Displacement experiments were performed by using ibuprofen to identify PIPP binding site in BSA. The effect of some common ions on the binding constant between PIPP and BSA was also examined.

Adsorptive membranes for bilirubin removal

In this study, we employed ethylene vinyl alcohol (EVAL) adsorptive membranes with bovine serum albumin (BSA) as bioligand for affinity supports for bilirubin (BR) retention. Microfiltration membranes were prepared from ternary or quaternary water/(1-octanol)/DMSO/EVAL systems. To obtain active binding sites for BSA, the EVAL membranes were either chemically functionalized in aqueous and organic medium and by plasma dischargement or physically activated by entrapping of active particles. Static BR removal was determined for all EVAL-BSA membranes. BR retentions relevant for human plasma were gained for the mixed adsorber membranes and additionally investigated in the dynamic mode.

Spectrophotometric and Kinetic Studies on the Binding of the Bioflavonoid Quercetin to Bovine Serum Albumin

This work investigates the binding of the bioflavonoid, quercetin, to bovine serum albumin (BSA) by spectrophotometric techniques involving both the conventional and stopped-flow methods. Both the neutral and negatively-charged forms of quercetin bound to BSA with a red shift in the maximal absorption. At high pH values, quercetin was rapidly degraded in an oxygen-dependent process, but this decomposition was substantially slower when the flavonoid was bound to BSA. At pH 7.4, the difference spectrum of quercetin with and without BSA was maximal at 425 nm; this wavelength can be conveniently used to monitor the extent and speed of binding. Spectrophotometric studies with a range of equimolar mixtures of quercetin and BSA at pH 7.4 suggest the binding was maximal when the concentration was 10 microM. It is postulated that the binding site of BSA for quercetin was less available at higher protein concentrations, perhaps because of conformational change or self-association. The rate of spectrophotometric change when quercetin bound to BSA was fairly slow; the process was not quite complete within 45 seconds and was biphasic. When a pre-mixed equimolar mixture of BSA and quercetin was diluted with an equal volume of the buffer, there was a surprising further increase in absorbance at 425 nm (rather than the fall anticipated if the binary complex were to dissociate). It is concluded that, upon dilution, the effective concentration of BSA's binding site increased, providing more scope for quercetin to bind.

Thermodynamics of binding of cadmium to bovine serum albumin

The binding isotherm of Cd 2+ ion to bovine serum albumin (BSA) has been investigated by microcalorimetry at 310.15 K and pH 7.0. The thermodynamic parameters of the binding reaction have been determined, and the stoichiometry of the complex is 2:1, indicating that there exist two identical binding sites of BSA with Cd 2+ ion. The value of Δ r H m Θ is −28.4±1.7 kJ mol −1 , the free energy of binding Δ r G m Θ is −25.2 kJ mol −1 , and the entropy of binding Δ r S m Θ is −10.3 J mol −1 K −1 . The negative Δ r H m Θ and Δ r S m Θ values are observed for the binding reaction of Cd 2+ ion and BSA, suggesting that the binding reaction is mainly enthalpy-driven and the entropy is unfavorable for it.

Serum Albumin Binds β- and α-Monoolein In Vitro

We investigated the interaction of bovine serum albumin (BSA) and monoolein (MO) and estimated the number of BSA binding sites for the alpha- and beta-isomers of MO. The turbidity of increasing concentrations of aqueous dispersions of alpha-MO and beta-MO in the presence and absence of BSA was measured in triplicate by absorption spectrophotometry. Aqueous dispersions of [13C(1)]MO and [13C(1)]MO/BSA mixtures at molar ratios of 1:1, 3:1 and 5:1 were analyzed in duplicate by [13C]nuclear magnetic resonance (NMR) at pH 7.4 and 36 degrees C. BSA bound significantly more beta-MO than alpha-MO at 15 min: 5.4 +/- 0.42 and 3.3 +/- 0.60 mol MO/mol BSA, respectively (P: < 0.05). [13C]NMR spectra of the 1:1 molar ratio of [13C(1)]MO /BSA exhibited a single carbonyl peak at 175.19 ppm, whereas spectra of 3:1 and 5:1 molar ratios exhibited three peaks between 172 and 174 (ppm), each distinct from carbonyl resonances of either [13C(1)]MO dispersed in water, 176.72 (ppm) or BSA alone. The intensities of individual peaks, but not their chemical shift values, varied between 3:1 and 5:1 molar ratios, indicating that BSA has at least three MO binding sites and may bind up to five molecules of MO per molecule. This study confirms that serum albumin binds MO in vitro and supports the theory that albumin transports monoglycerides produced by lipoprotein lipase hydrolysis of triglyceride.

Evidence of sex hormone binding globulin binding sites in the medial preoptic area and hypothalamus.

We have demonstrated a high density of both radiolabeled progesterone and estradiol conjugated to bovine serum albumin binding sites in the medial preoptic area and hypothalamus. Infusions of sex hormone binding globulin into the medial preoptic area of rats increased their female sexual receptivity similarly to the effect of estradiol conjugated to bovine serum albumin, suggesting sex hormone binding globulin acts at binding sites for estradiol conjugated to bovine serum albumin. In this study sex hormone binding globulin was used to displace radiolabeled progesterone conjugated to bovine serum albumin from plasma membrane fractions from the medial preoptic area-anterior hypothalamus and medial basal hypothalamus of ovariectomized rats injected with either 5 microg estradiol benzoate or sesame oil vehicle. We found that sex hormone binding displaced radiolabeled progesterone conjugated to bovine serum albumin in both areas and that in vivo estradiol treatment greatly increased the relative displacement by sex hormone binding globulin in the medial preoptic area-anterior hypothalamus. We interpret these data as indicating the presence of sex hormone binding globulin receptors in brain plasma membranes and further suggest that endogenous steroid conditions may alter these receptors.

Spectroscopic and photochemical properties of Malachite Green noncovalently bound to bovine serum albumin

The noncovalent binding of the cationic triarylmethane dye Malachite Green (MG+) to bovine serum albumin (BSA) was investigated using fluorescence and UV-vis spectroscopy. The results indicate that the BSA binding sites are very effective in hindering fast nonradiative relaxation processes that occur via rotational motion of the aromatic rings of this triarylmethane. As a result, pronounced increases in both fluorescence yield and dye photoreactivity were observed upon protein binding. The 532 nm laser-induced photobleaching of protein-bound MG+ yields leuco malachite green and 4-dimethylaminobenzophenone as major reaction photoproducts. Based on the nature of these products, the first step of the bleaching process is postulated to be an electron or hydrogen atom transfer from the protein to the dye moiety.

High resolution of DL-tryptophan at high flow rates using a bovine serum albumin-multilayered porous hollow-fiber membrane.

We describe a bovine serum albumin (BSA)-multilayer-adsorbed porous hollow-fiber membrane as a stationary phase that enables chiral separations at a high resolution and high rate. Epoxy-group-containing graft chains were uniformly immobilized on the surface of pores throughout a porous hollow-fiber membrane by radiation-induced graft polymerization. Subsequently, a diethylamino group as an anion-exchange moiety was introduced to the graft chains, which caused the chains to expand toward the interior of the pores due to mutual electrostatic repulsion. The expanding polymer chains provided multilayer binding sites for BSA as a chiral selector. BSA with a degree of multilayer binding of 4 specifically recognized L-tryptophan with a separation factor of 6.6 during permeation by a mobile phase (Tris-HC1 buffer) injected with a racemic solution of DL-tryptophan through the BSA-multilayered porous membrane. In addition, the separation factor was constant irrespective of flow rates of the mobile phase because of negligible diffusional mass-transfer resistance of tryptophan to BSA multilayered by the graft chains.

Detailed Investigation of 2-(p-Toluidinyl)naphthalene-6-Sulfonate (TNS) Binding to Bovine Serum Albumin (BSA) by Steady-State and Time-Resolved Fluorescence Spectroscopy

The complexation of 2-( p-toluidinyl)naphthalene-6-sulfonate (TNS) to the hydrophobic sites of bovine serum albumin (BSA) and the effects of quencher and denaturant were studied by steady-state and dynamic fluorescence spectroscopy. Experimental results show that there are multiple sites in BSA which bind TNS. Fluorescence decay kinetics of BSA-bound TNS were recovered by multifrequency phase-modulation measurements and analyzed by a global analysis scheme. For all the cases, a distributed lifetime model best fits the experimental data—a result of the dynamical nature of BSA/TNS association and of the multiple binding sites in BSA. In addition to the distributed species, a short, discrete component exists, arising from unbound or free TNS. The recovered Stern-Volmer quenching constant for acrylamide from the lifetime data is consistent with the steady-state results. The denaturant, urea, decreases significantly the pre-exponential factor for protein-bound TNS, but affects the center lifetime and the distribution width only at high urea concentrations. The perturbation of probe molecules on the three-dimensional conformation of proteins and the effects of complex (TNS-BSA) age were also studied.

Correlations between the binding of neoglycoproteins, bovine serum albumin (BSA) and lectins in 10 to 13-day-old mouse embryos

In the present work we compared the appearance of carbohydrate binding sites for mannose, maltose, sialic acid and N-acetyl-glucosamine in the 11 to 13-day-old mouse embryo with the appearance of BSA and lectin binding sites. The carbohydrate-binding sites were localized with FITC-coupled neoglycoproteins, synthesized by chemical glycosylation of bovine serum albumin (BSA). These localizations were compared with binding of the FITC-labelled unglycosylated BSA. Furthermore the localizations of neoglycoprotein and BSA binding sites were correlated with binding of the FITC-labelled lectins WGA, RCA I and Con A. Initial appearance of neoglycoprotein binding sites occurred in the lens capsule of the 13 day old mouse embryo. Binding sites for the unglycosylated BSA appeared earlier, i.e. already in the 12-day-old embryo, in the basement membranes of the choroid plexus and the lung bud and lectin binding sites were seen in these structures in the 11-day-old embryo. The staining of the basement membrane and the lens capsule for BSA binding sites in the 12-and 13-day-old embryos correspond to WGA binding to these membranes. From these results we concluded that 1) specific carbohydrates which are probably involved in embryonic development appear much earlier in the embryo than the endogenous lectins which are able to react with these carbohydrates and 2) BSA is a protein which like WGA probably binds N-acetylglucosamine or sialic acid moieties.

ESR studies of stearic acid binding to bovine serum albumin

The ESR spectra of a series of chain-labelled doxyl stearic acids (5-, 7-, 12- and 16-DSA) and doxyl methyl stearates (5-, 7-, 12- and 16-DMS) bound to the high-affinity binding sites of bovine serum albumin (BSA) have been analyzed using nonlinear least-squares fitting of slow-motional ESR simulation. The motional analysis reveals that the rotational diffusion of these stearates around the axis perpendicular to the long hydrocarbon chain is greatly hindered, suggesting that they are held tightly in a channel of the protein. Comparison of the isotropic hyperfine splitting, A 0, among each series shows that 5- and 16-DSA and 16-DMS have larger A 0 values than the other spin labels. In addition, labels at the 16-C position of both DSA and DMS exhibit significantly increased motion relative to the other positions. These observations suggest that the channel starts at 5-C of the chain and ends somewhere between 13-C and 15-C, leading to an estimate of 11 ± 1 A ̊ for the lenght of the channel. The methyl stearate lables exhibit significantly faster rotation around the chain axis than the analogous stearic acid labels, suggesting a double hydrogen-bonding mechanism for fatty acid binding to BSA. The ability of the acid to form two hydrogen bonds apparently fixes it more rigidly in the protein preventing rotation about either single hydrogen bond. A double-hydrogen bonding mechanism is most consistent with the formation of a salt bridge between the negatively charged carboxylate of the acid and either a positively charged guanidino group of arginine, or the positively charged ω-amino groups of two lysine residues. An ESR study of the pH dependence of DSA binding indicates that salt bridge formation with lysine is responsible for at least some of the long chain fatty acid binding sites of BSA.

Plasma protein binding and endothelial enzyme interactions in the lung

The influence of plasma albumin binding of the synthetic angiotensin-converting enzyme (ACE) substrate [3H]benzoyl-phenylalanyl-alanyl-proline (BPAP) on BPAP hydrolysis by pulmonary endothelial ACE was studied in isolated rabbit lungs perfused with a salt solution containing either 5% bovine serum albumin (BSA) or 5% dextran. The single-pass indicator-dilution method was used to measure the fraction (M) of [3H]BPAP hydrolyzed. Lung M was greater with albumin-free perfusate than when BSA was present. M decreased as the time (ti) that the BPAP was in contact with the BSA before reaching the lung was increased, suggesting that some BSA binding sites for BPAP were not in equilibrium during bolus transit through the lungs. The M vs. ti data were correlated using a model incorporating both rapid and slow binding kinetics of BPAP and BSA. For the slow BPAP-BSA interaction, the dissociation rate constant was approximately 0.015 s-1, and the fraction of the BPAP bound to these slowly equilibrating sites at equilibrium was approximately 22%. The results indicate that transient plasma protein binding kinetics can affect lung BPAP hydrolysis.

The adsorption of bovine blood proteins onto the surface of O-(carboxymethyl)chitin

Chitin was found to interact with bovine blood proteins and the affinities of these proteins for chitin tended to be decreased by the introduction of O-carboxymethyl (CM) groups onto the chitin surface, especially with fibrinogen. As the adsorption of blood proteins to the CM-chitin (d.s. 0.35) was assumed to follow an isothermal adsorption-curve, the adsorption coefficients were estimated by applying the Langmuir equation. Bovine serum albumin showed the highest affinity among the proteins applied in this experiment [ K BSA (bovine serum albumin); 20.0, K BγG (bovine gamma globulin); 1.96, K BF (bovine fibrinogen); 1.20]. The binding site of BSA for CM-chitin was assumed to be regulated not only by the cationic groups of BSA but also by other factors such as the recognition capacity of BSA to bind to GlcNAc residues in CM-chitin.

Interactions of myristic acid with bovine serum albumin: a 13C NMR study.

Interactions of myristic acid with bovine serum albumin were studied by 13C NMR spectroscopy at 50.3 MHz using 90% isotopically substituted [1-13C]-, [3-13C]-, and [14-13C]myristic acids, either individually or in a combination of all three with albumin. At pH 7.4, two or more resonances of different intensities were observed for each 13C-enriched myristic acid. Carboxyl and methylene C-3 resonances corresponding to the major myristic acid environment(s) exhibited pH-dependent chemical shift changes indicative of protonation below pH 6.7; in contrast, carboxyl groups in minor environments were resistant to protonation. 13C NMR spectra obtained as a function of the molar ratio of [3-13C]- and [14-13C]myristic acid to bovine serum albumin (from 0.7 to 5.6) revealed at least two narrow resonances for each carbon at all molar ratios. Thus, bovine serum albumin binding sites for myristic acid are heterogeneous with respect to titration behavior and with respect to the local magnetic environment at both the polar and the nonpolar ends of the fatty acid. The narrow resonances observed for the methylene and methyl carbons are inconsistent with complete immobilization of the protein-bound acid molecules. Together with spin- lattice relaxation times and nuclear Overhauser enhancements, the linewidth results indicate that bound myristic acid has internal motions that are rapid compared with overall protein tumbling and that the C-3 methylene carbon is more restricted than the terminal methyl carbon.

Interactions of the carboxyl group of oleic acid with bovine serum albumin: a 13C NMR study.

The interactions of the carboxyl group of oleic acid with bovine serum albumin (BSA) were studied by 13C NMR spectroscopy at 50.3 MHz using 90% isotopically substituted [1-13C]oleic acid. 13C NMR spectra were obtained as a function of the mole ratio of oleic acid to BSA (from 0.5-10.0) and, for selected mole ratios, as a function of pH (between pH 3.0 and 10.6) and temperature (between 15 and 55 degrees C and thermally denatured at 95 degrees C). Except for spectra of highly acidic (pH less than or equal to 3.9) and denatured samples, spectra of oleic acid/BSA complexes showed multiple narrow resonances from the oleic acid carboxyl carbon in a region (179-184 ppm) downfield from protein carbonyl and carboxyl carbon resonances. At low oleic acid/BSA ratios (0.5 and 1.0), at least two oleic acid carboxyl carbon peaks were observed; at high ratios (greater than or equal to 3.0), at least four peaks were present. The intensities of individual peaks, but not their chemical shifts, varied with the oleic acid/BSA ratio. The chemical shift of individual oleic acid peaks was invariant between pH 6.0 and 10.6; below pH 6.0, one of the oleic acid resonances exhibited an NMR titration curve with an apparent pKa of approximately 4. Thus, BSA binding sites for oleic acid are heterogeneous as monitored by the magnetic microenvironment of the oleic acid carboxyl carbon. The number of different oleic acid environments and the relative population of oleic acid molecules in these environments is dependent on the mole ratio of oleic acid/BSA. Our results suggested that the anionic form of oleic acid is bound to BSA at physiological pH and that the multiplicity of NMR peaks for [1-13C]oleic acid resulted from, at least in part, different electrostatic and hydrogen bonding interactions between the oleic acid carboxyl group and specific amino acid residues of BSA.