IIA Of Human Serum Albumin Research Articles

Comprehensive investigations about the binding interaction of acesulfame with human serum albumin.

In this work, the binding interaction of an artificial sweetener, acesulfame (ACS) with human serum albumin (HSA) are investigated at the molecular level by using spectral methods and molecular modeling. ACS has the ability to induce static quenching of the intrinsic fluorescence of HSA by a complex formed between HSA and ACS through weak multi-noncovalent forces including hydrophobic, hydrogen bond and van der Waals forces. ACS enters subdomain IIA of HSA to induce the tertiary structure changes of HSA and decreased the hydrophobicity of protein. In addition, ACS binding does not obviously alter the secondary structure of HSA. This study is hoped to provide some crucial information for further investigations of the biosafety of sweetener.

Interactions of Ionophoric Polyphenols with Human Serum Albumin

The distribution of a drug is determined, at least in part, by its interactions with serum proteins. Human serum albumin (HSA), the most abundant blood plasma protein, serves as the most common mode of transport for drugs to their target. In our previous work, we have synthesized and studied important characteristics of a series of ionophoric polyphenols as potential anti‐Alzheimer’s disease agents. As part of our ongoing investigations on the biological activity of these compounds, we are now exploring possible transport mechanisms. In our current work, the interactions of the ionophoric polyphenols with HSA were studied via in vitro and in silico methods. In line with in vitro studies, the interaction of the ionophoric polyphenols with HSA were studied by fluorescence and circular dichroism (CD) spectroscopies to obtain binding affinities, bimolecular quenching constants, theoretical number of binding sites and HSA secondary structural changes. Moreover, in line with in silico studies, a preferred mode of binding was predicted by molecular docking and the predicted systems were subject to a 5 ns MD simulation; consequently, RMSD studies were performed to attest for stability of the systems, MM/GBSA binding free energies were calculated to correlate with experimental binding affinities and per‐residue energy decomposition analyses were carried out to analyze residues critical to binding. Using resveratrol, a polyphenolic compound which has demonstrated strong neuroprotective and anti‐Alzheimer disease properties, as a control, in vitro results showed the formation of adducts (static quenching), one theoretical binding site, binding constants (Ka) ranging 104 to 106 M−1 and only slight secondary structure modifications between HSA and the ionophoric polyphenols. Further, in silico results revealed the ionophoric polyphenols and resveratrol favorably binding subdomain IIA of HSA, forming critical interactions to Trp 214 and Asp451. RMSD studies showed the HSA‐IIA system plateauing after a short time indicating stable binding events; in addition, a Pearson correlation coefficient of R=0.80 between the experimental binding affinity and computational binding free energies showed a strong correlation between in vitro and in silico results. Overall, our results seem to indicate that there is a ionophoric polyphenol‐serum albumin interaction, which could have a potential impact on the use of ionophoric polyphenols as therapeutics for Alzheimer’s disease.Support or Funding InformationThis research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE‐AC02‐05CH11231.

Exploring the combination characteristics of lumefantrine, an antimalarial drug and human serum albumin through spectroscopic and molecular docking studies

Binding of lumefantrine (LUM), an antimalarial drug to human serum albumin (HSA), the main carrier protein in human blood circulation was investigated using fluorescence quenching titration, UV–vis absorption and circular dichroism (CD) spectroscopy as well as molecular docking. LUM-induced quenching of the protein (HSA) fluorescence was characterized as static quenching, as revealed by the decrease in the value of the Stern-Volmer quenching constant, Ksv with increasing temperature, thus suggesting LUM-HSA complex formation. This was also confirmed from the UV–vis absorption spectral results. Values of the association constant, Ka for LUM–HSA interaction were found to be within the range, 7.27–5.01 × 104 M−1 at three different temperatures, i.e. 288 K, 298 K and 308 K, which indicated moderate binding affinity between LUM and HSA. The LUM–HSA complex was stabilized by hydrophobic interactions, H-bonds, as well as van der Waals forces, as predicted from the thermodynamic data (ΔS = +50.34 J mol−1 K−1 and ΔH = −12.3 kJ mol−1) of the binding reaction. Far-UV and near-UV CD spectral results demonstrated smaller changes in both secondary and tertiary structures of HSA upon LUM binding, while three-dimensional fluorescence spectra suggested alterations in the microenvironment around protein fluorophores (Trp and Tyr). LUM binding to HSA offered stability to the protein against thermal stress. Competitive drug displacement results designated Sudlow’s Site I, located in subdomain IIA of HSA as the preferred binding site of LUM on HSA, which was well supported by molecular docking analysis.Communicated by Ramaswamy H. Sarma

Unravelling the interaction of glipizide with human serum albumin using various spectroscopic techniques and molecular dynamics studies

Glipizide is known to stimulate insulin secretion by β-cells of the pancreas. It is a second-generation sulfonylurea drug used in the management of type 2 diabetes. The shorter biological half-life makes it a suitable candidate to be designed as a controlled release formulation. Human serum albumin (HSA), a major plasma protein plays a crucial role in the transportation of drugs, hormones, fatty acids, and many other molecules and determines their physiological fate and biodistribution. In this study, the interaction of glipizide with HSA was investigated under physiological conditions using multi-spectroscopic techniques corroborated with molecular docking and dynamics approach. It was found that glipizide integrates to HSA with a binding constant in the order of 105 M−1. The mode of fluorescence quenching by glipizide is static in nature with one binding site. Glipizide preferentially interacts with sub-domain IIA of HSA and their complexion is thermodynamically favorable. This interaction results in the loss of α-helical content of HSA. The energy transfer efficiency from HSA to glipizide was found to be 26.72%. In silico molecular docking and simulation studies ratified in vitro findings and revealed that hydrogen bonds and hydrophobic interactions are accountable for glipizide-HSA complex formation.Communicated by Ramaswamy H. Sarma

Study of HSA interactions with arachidonic acid using spectroscopic methods revealing molecular dynamics of HSA-AA interactions.

The interaction between human serum albumin (HSA) and arachidonic acid (AA) as an unsaturated fatty acid were investigated in the present study using methods including UV-VIS spectrophotometry, fluorescence and circular dichroism (CD) spectroscopy, lifetime measurements, fluorescence anisotropy measurements and visual molecular dynamics (MD). The thermodynamic parameters were assessed from HSA thermal and chemical denaturation in the presence and absence of AA. From the thermal denaturation, the Tm and ΔG˚(298K) magnitudes obtained were 327.7 K and 88 kJ/mol, respectively, for HSA alone, and 323.4 K and 85 kJ/mol, respectively, following treatment with a 10 µM AA concentration. The same manner of reduction in Gibbs free energy as a criterion of protein stability was achieved during chemical denaturation by urea in the presence of AA. The present study investigates HSA binding nature through MD approaches, and the results indicated that the binding affinity of AA to the subdomain IIA of HSA is greater compared with that of subdomain IIIA. Although the HSA regular secondary structure evaluation by CD exhibited a minor change following incubation with AA, its tertiary structure revealed an observable fluctuation. Thus, it appears that the interaction between AA and HSA requires minor instability and partial structural changes.

Exploring the interactions of a Tb(III)-quercetin complex with serum albumins (HSA and BSA): spectroscopic and molecular docking studies.

Serum albumins (human serum albumin (HSA) and bovine serum albumin (BSA), two main circulatory proteins), are globular and monomeric macromolecules in plasma that transport many drugs and compounds. In the present study, we investigated the interactions of the Tb(III)-quercetin (Tb-QUE) complex with HSA and BSA using common spectroscopic techniques and a molecular docking study. Fluorescence data revealed that the inherent fluorescence emission of HSA and BSA was markedly quenched by the Tb-QUE complex through a static quenching mechanism, confirming stable complex formation (a ground-state association) between albumins and Tb-QUE. Binding and thermodynamic parameters were obtained from the fluorescence spectra and the related equations at different temperatures under biological conditions. The binding constants (Kb ) were calculated to be 0.8547 × 103 M-1 for HSA and 0.1363 × 103 M-1 for BSA at 298 K. Also, the number of binding sites (n) of the HSA/BSA-Tb-QUE systems was obtained to be approximately 1. Thermodynamic data calculations along with molecular docking results indicated that electrostatic interactions have a main role in the binding process of the Tb-QUE complex with HSA/BSA. Furthermore, molecular docking outputs revealed that the Tb-QUE complex has high affinity to bind to subdomain IIA of HSA and BSA. Binding distances (r) between HSA-Tb-QUE and BSA-Tb-QUE systems were also calculated using the Forster (fluorescence resonance energy transfer) method. It is expected that this study will provide a pathway for designing new compounds with multiple beneficial effects on human health from the phenolic compounds family such as the Tb-QUE complex.

Cycloplatinated(II) Derivatives of Mercaptopurine Capable of Binding Interactions with HSA/DNA.

In this study, two new bis-cyclometalated Pt(II) complexes, [Pt(C^N)(S^N)] [S^N = deprotonated 6-mercaptopurine (6-MP) and C^N = deprotonated 2-phenylpyridine (ppy), 2a; C^N = deprotonated benzo[h]quinoline (bhq), 2b], are synthesized by the reaction of [PtR(SMe2)(C^N)] (R = Me or p-MeC6H4) with 1 equiv of 6-mercaptopurine (6-HMP) at room temperature. The complexes are fully characterized using 1H and 13C NMR spectroscopies, electrospray ionization mass spectrometry, and elemental analysis. Biomolecular interaction of complex 2a with human serum albumin (HSA) is studied by fluorescence, UV-vis, and circular dichroism (CD) spectroscopies. The binding constants (Kb) and number of binding sites (n) are evaluated using the Stern-Volmer equation. The intrinsic fluorescence of protein is quenched by a static quenching mechanism, with a binding constant of Kb ∼ 105 reflecting a high affinity of complex 2a for HSA. The thermodynamic parameters (ΔH°, ΔG°, and ΔS°) indicate that the interaction is a spontaneous process and hydrophobic forces play a main role in the reaction. The displacement experiments demonstrate that the reactive binding sites of HSA to complex 2a are mainly located within its hydrophobic cavity in subdomain IIA (site I). Synchronous fluorescence spectra reveal that complex 2a affected the microenvironment of tryptophan-214 residues in subdomain IIA of HSA. In the case of interaction of complex 2b and HSA, because of overlapping of the emission spectra of complex 2b with HSA, chemometric approaches are applied. The results indicate significant interaction between the tryptophan residue of HSA and complex 2b. Moreover, the binding of Pt(II) complexes 2a and 2b causes a reduction of the α-helix content of HSA, as obtained by far-UV CD spectroscopy. The average binding distance (r) between Pt(II) complexes and HSA is obtained by Förster's resonance energy-transfer theory. Also, a molecular docking simulation reveals that π-π-stacking and hydrophobic interactions between these complexes and HSA are significant. Furthermore, the interactions of platinum complexes, 2, with calf-thymus DNA (CT-DNA) are investigated. The UV-vis results and ethidium bromide competitive studies support an intercalative interaction of both Pt(II) complexes with DNA. The new complexes 2 are also screened for anticancer activities. The results show that complexes 2 exhibit significant anticancer activity against the K562 (chronic myelogenous leukemia) cell line.

Interaction characterization of 5−hydroxymethyl−2−furaldehyde with human serum albumin: Binding characteristics, conformational change and mechanism

5−Hydroxymethyl−2−furaldehyde (5-HMF) is a kind of by-product produced in food processing, which may cause latent hazard to human health. Here, the interaction of 5-HMF with human serum albumin (HSA) was studied by multi-spectroscopic methods, multivariate curve resolution-alternating least squares (MCR−ALS) and molecular docking. The formation of 5-HMF−HSA complex was confirmed by MCR−ALS. The fluorescence quenching mechanism of HSA by 5-HMF was static, and their binding constant was 5.25 × 104 L mol−1 at 298 K, the binding site of 5-HMF was located in subdomain IIA of HSA. The main forces of the interaction were hydrogen bonds and van der Waals forces. The molecular docking showed that three hydrogen bonds were formed between –CH2OH of 5-HMF and Lys106, Pro147 and Gln29 of HSA. The synchronous fluorescence, three-dimensional fluorescence and circular dichroism spectra showed that 5-HMF induced a structural shrinkage of HSA. Fluorescence phase diagram ascertained that the HSA conformational change was in accordance with all-or-none model. Moreover, the presence of the food nutrients (vitamin C, chlorogenic acid and phloretin) weakened the binding of 5-HMF with HSA. This study is helpful to understand the hazard mechanism of 5-HMF to human body and provides new strategies to reduce the hazard of 5-HMF.

Probing the binding mechanism of capecitabine to human serum albumin using spectrometric methods, molecular modeling, and chemometrics approach

Capecitabine as a prodrug of 5-Fluorouracil plays an important role in the treatment of breast and gastrointestinal cancers. Herein, in view of the importance of this drug in chemotherapy, interaction mechanism between Capecitabine (CAP) and human serum albumin (HSA) as a major transport protein in the blood circulatory system has been investigated by using a combination of spectroscopic and molecular modeling methods. The fluorescence spectroscopic results revealed that capecitabine could effectively quench the intrinsic fluorescence of HSA through a static quenching mechanism. Evaluation of the thermodynamic parameters suggested that the binding process was spontaneous while hydrogen bonds and van der Waals forces played a major role in this interaction. The value of the binding constant (Kb = 1.820 × 104) suggested a moderate binding affinity between CAP and HSA which implies its easy diffusion from the circulatory system to the target tissue. The efficiency of energy transfer and the binding distance between the donor (HSA) and acceptor (CAP) were determined according to forster theory of nonradiation energy transfer as 0.410 and 4.135 nm, respectively. Furthermore, UV–Vis spectroscopic results confirmed that the interaction was occurred between HSA and CAP and caused conformational and micro-environmental changes of HSA during the interaction. Multivariate curve resolution-alternating least square (MCR-ALS) methodology as an efficient chemometric tool was used to separate the overlapped spectra of the species. The MCR-ALS result was exploited to estimate the stoichiometry of interaction and to provide concentration and structural information about HSA-CAP interactions. Molecular docking studies suggested that CAP binds mainly to the subdomain IIA of HSA, which were compatible with those obtained by experimental data. Finally, molecular dynamics simulation (MD) was performed on the best docked complex by considering the permanence and flexibility of HSA-CAP complex in the binding site. MD result showed that CAP could steadily bind to HSA in the site I based on the formation of hydrogen bond and π-π stacking interaction in addition to hydrophobic force.

Spectroscopic and cytotoxicity studies on the combined interaction of (-)-epigallocatechin-3-gallate and anthracycline drugs with human serum albumin.

The interactions of (-)-epigallocatechin-3-Gallate (EGCG) and anthracycline drugs (doxorubicin, DOX and epirubicin, EPI) alone or in combination with human serum albumin (HSA) under physiological condition were studied by fluorescence spectroscopy, UV-vis absorption spectroscopy, circular dichroism (CD) spectroscopy, and dynamic light scattering (DLS). The cytotoxic activity of the single drug, combined drugs, and their complexes with HSA against human cervical cancer HeLa cell line was determined by MTT assay. Fluorescence quenching result and difference spectra of UV absorption revealed the formation of static complex between EGCG, DOX, or EPI and HSA. The binding of EGCG with HSA was driven by both enthalpy and entropy while the binding of DOX or EPI was mainly entropy driven. The nature of binding was expounded based on the effect of sodium chloride, tetrabutylammonium bromide, and sucrose which interfere in electrostatic, hydrophobic, and hydrogen bonding interactions, respectively. Site marker competitive experiments combined with synchronous fluorescence spectra showed that these three ligands mainly bound to subdomain IIA of HSA and were closer to tryptophan residues. In EGCG + DOX/EPI + HSA ternary system, the effect of one drug on the binding ability of another drug was discussed. The influences of the individual and combined binding of EGCG and DOX/EPI on the secondary structure and particle size of HSA were investigated by CD spectroscopy and DLS, respectively. Moreover, the synergistic cytotoxicity of EGCG and DOX/EPI as well as their complexes with HSA were discussed. Obtained results would provide beneficial information on the combination of EGCG and anthracyclines in clinic.

Synthesis of (E)-Ethyl-4-(2-(furan-2-ylmethylene)hydrazinyl)benzoate, crystal structure, and studies of its interactions with human serum albumin by spectroscopic fluorescence and molecular docking methods.

A novel hydrazone, (E)-Ethyl-4-(2-(furan-2-ylmethylene)hydrazinyl)benzoate (EFHB), has been synthesized and characterized by FT-IR, NMR and Mass spectroscopy, and X-ray diffraction; compound crystallized as translucent light yellow thin plates. EFHB was studied for their binding to human serum albumin (HSA) using the fluorescence quench titration method. Molecular docking was also performed to get a more detailed insight into their interaction with HSA at the binding site. Addition of this hydrazone to HSA produced significant fluorescence quenching and splitting of emission spectra of HSA through static quenching mechanism with binding constants of about 104 M-1 at 292.15, 298.15, 304.15 and 310.15 K. According to the synchronous fluorescence, tryptophan and tyrosine residues of the protein are most perturbed by the binding process. Thermodynamic parameters ΔG, ΔH, and ΔS were got and the main sort of acting force between EFHB and HSA was studied. Results of molecular docking have shown that EFHB binds to subdomain IIA of HSA mainly by hydrophobic interaction, energy binding are in good agreement with those obtained by fluorescence study (ΔGthe = -7.32 ± 0.09 kcal mol-1 and ΔGexp = -6.76 ± 0.03 kcal mol-1).

Maslinic acid conjugate with 7-amino-4-methylcoumarin as probe to monitor the temperature dependent conformational changes of human serum albumin by FRET.

Synthesis, characterization and spectroscopic investigation of maslinic acid labeled with fluorescent 7-amino-4-methylcoumarin is reported. It was found that the coumarin-maslinic derivative (MaCo) forms an excellent fluorescence resonance energy transfer (FRET) pair with the tryptophan (Trp) residue of human serum albumin (HSA). This feature allowed for monitoring HSA conformational alterations by measuring the distance between donor (Trp) and acceptor (MaCo) through Förster energy transfer mechanism. Displacement experiments confirmed that MaCo binds to subdomain IIA of HSA with independence of temperature. It was observed that, in the temperature range 35-45 °C, the fluorescence emission maximum of HSA-MaCo complex decreased, whereas in the range 45 °C-65 °C, an increment was detected. The concomitant change in the polarity of environment surrounding Trp was confirmed by red edge excitation shift experiments. Thermal denaturation of HSA was followed by time-resolved fluorescence spectroscopy. Average lifetime of Trp residue decreased with temperature due to the increment of solvent collisions and changes in the solvent exposure of Trp. To discriminate the importance of each effect, lifetime of N-Acetyl-L-tryptophanamide (NATA) at different temperatures was measured. Circular dichroism (CD) studies confirmed the loss of secondary structure of HSA with increasing temperature and showed a different trend in the conformational transformation below and above 45 °C, in agreement with steady-state and time-resolved fluorescence experiments.

Novel tetradentate Schiff base zinc(II) complex as a potential antioxidant and cancer chemotherapeutic agent: Insights from the photophysical and computational approach

In this study a new N4 Schiff base ligand (SB) was synthesized via condensation reaction of 3,4-diaminobenzophenone with diacetyl monoxime in 1:2 M ratio. Moreover, the synthesization and characterization of its zinc (II) complex was carried out through elemental analysis, FT-IR, 1H NMR, UV–Vis spectroscopies and molar conductance. Afterwards we scrutinized the above obtained complex to determine its potential anticancer activity against MCF-7 cell line through MTT test, reducing the viable cell numbers to 11% of the control samples after exposure for 72 h. In order to specify its in vitro antioxidant activity, the Zn(II) complex was evaluated, as a radical scavenger, versus 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH). Data obtained from the above assay revealed that Zn(II) complex demonstrated limited (IC50 = 239.5 mg L−1) antioxidant activity in comparison with ascorbic acid. For the purpose of investigating the complex-model proteins binding, human serum albumin (HSA) and β-lactoglobulin (β-LG), we used biophysical methods and molecular modeling. Experimental results showed that the two systems demonstrated identical interactions (hydrogen bonding and Van der Waals forces). But the β-LG demonstrated a much firmer binding affinity to Zn(II) complex than HSA (Kb ∼ 0.67 (±0.10) × 104 M−1 for HSA-Zn complex and 6.45 (±0.15) × 104 M−1 for β-LG-Zn complex). According to the molecular modeling analysis, the Zn(II) complex develops bonds to the remnants that exist in the subdomain IIA of HSA and site A of β-LG.

Study of pyridoxamine against glycation and reactive oxygen species production in human serum albumin as model protein: An in vitro & ex vivo approach

Hyperglycaemia is considered to be a driving factor for advanced glycated end products (AGEs). Inhibiting the process of glycation play an important role in reducing the diabetes related complications. We have explored the glucose mediated glycation and antiglycation activity of pyridoxamine using human serum albumin (HSA). Protein was incubated with glucose for 28 days at physiological temperature to achieve glycation. Antiglycation activity was assessed by the estimation of carbonyl content, free lysine and AGE specific fluorescence. Molecular docking was used to study the interaction of pyridoxamine with HSA and to get a detailed understanding of binding sites and binding energy. Glycation was reduced by pyridoxamine to commendable levels which was evident by the quantification of free lysine and carbonyl content. Pyridoxamine treatment also prevented the loss in secondary structure induced by glycation. It has also emerged as the quencher of reactive oxygen species which lead to the protection of DNA from oxidative damage. Pyridoxamine was found to be located at subdomain IIA of HSA with binding energy of −5.6 kcal/mol. These results are high points in the antiglycation activity of pyridoxamine. Its antioxidant nature and antiglycation activity are proof of its potential in preventing disease progression in diabetes.

Inhibition of advanced glycation end products by isoferulic acid and its free radical scavenging capacity: An in vitro and molecular docking study

Non-enzymatic glycation and Oxidation of some essential biological macromolecules are paramount in the pathogenesis of various diseases including diabetes and atherosclerosis. Hyperglycemia plays a key role in the pathological process of diabetic complications by progressive accumulation of advanced glycation end products (AGEs) in body tissues. Formation of AGEs as a result of protein glycation is followed by an increased free radical activity that additionally contributes towards the bio-macromolecular damage. The present study aimed to evaluate the free radical scavenging and antiglycation capacity of isoferulic acid (IFA). The free radical scavenging activity of IFA was measured using DPPH, FRAP, and metal chelating assays. IFA showed effective reducing power, free radical scavenging activity and metal chelation activity in concentration dependent manner. The antiglycation activity of IFA was studied using various spectroscopic techniques. The obtained results were validated with free amino, sulfhydryl group, carbonyl content and AGEs formation. Secondary structural alterations were monitored using circular dichroism, morphology of aggregates was analyzed using transmission electron microscopy. Molecular docking reveals the possible binding location of IFA with in the sub-domain IIA of human serum albumin (HSA).

Interaction between quinoline yellow and human serum albumin: spectroscopic, chemometric and molecular docking studies.

Quinoline yellow (QY), a synthetic colourant widely used in the food industry, has caused extensive concerns because of its potentially harmful effects on human health. In the present work, the interactions between QY and human serum albumin (HSA) were characterized by multiple spectroscopic methods, a chemometric algorithm, and molecular modelling studies. The concentration profiles and pure spectra obtained for the components (QY, HSA and QY-HSA complex) from analyses of the expanded UV-visible absorption data matrices by multivariate curve resolution alternating least squares confirmed the QY-HSA interaction process. QY quenched the fluorescence of HSA through formation of a QY-HSA complex that was stabilized by moderate affinity. Hydrophobic forces and hydrogen bonding play major roles in the binding of QY to HSA. Site-specific marker-induced displacement results suggest that QY binds to subdomain IIA of HSA. This was corroborated by the molecular docking results. Decreases in HSA surface hydrophobicity and free sulfhydryl group content indicate that QY causes a contraction of the peptide strand in HSA, hiding the hydrophobic patches of the protein. Analyses by UV-visible absorption, circular dichroism, and three-dimensional fluorescence spectroscopy found that QY causes microenvironmental perturbations around the fluorophores and secondary structure changes in HSA. This work shows that QY binds to HSA, affecting its structural and functional properties, and provides new insights into the binding mechanism and a comprehensive understanding of the toxicity of QY to biological processes. © 2018 Society of Chemical Industry.

Chemometrics-assisted investigation of interactions of Tasmar with human serum albumin at a glassy carbon disk: Application to electrochemical biosensing of electro-inactive serum albumin

In this work, voltammetric data recorded by a glassy carbon electrode (GCE) was used to investigate the interactions of tolcapone (Tasmar, TAS) with human serum albumin (HSA) at the electrode surface. The recorded voltammetric data was also combined with spectroscopic data to construct an augmented data matrix which was analysed by multivariate curve resolution-alternating least squares (MCR-ALS) as an efficient chemometric tool to obtain more information about TAS-HSA interactions. The results of MCR-ALS confirmed formation of one complex species (HSA-TAS2) and application of MCR-BANDS to the results of MCR-ALS confirmed the absence of rotational ambiguities and existing unambiguous and reliable results. Binding of TAS to HSA was also modeled by molecular docking and the results showed that the TAS was bound to sub-domain IIA of HSA which were compatible with the ones obtained by recording experimental data. Hard-modeling of combined voltammetric and spectroscopic data by EQUISPEC helped us to compute binding constant of HSA-TAS2 complex species which was compatible with the binding constant value obtained by direct analysis of experimental data. Finally, a new electroanalytical method was developed based on TAS-HSA interactions for determination of HSA in two ranges of 0–541 nM and 541–1200 nM with a limit of detection of 0.04 nM and a sensitivity of 0.02 μA nM−1.

Effect of glycation on human serum albumin-zinc interaction: a biophysical study.

Zinc deficiency is common in diabetes. However, the cause of this phenomenon is largely unknown. 80% of the absorbed zinc is transported through the blood in association with human serum albumin (HSA). Under persistent hyperglycemia, HSA frequently undergoes non-enzymatic glycation which can affect its structure and metal-binding function. Hence, in this study, we have examined the interaction of zinc with native and glycated HSA. The protein samples were incubated either in the presence or in the absence of physiologically elevated glucose concentration for 21days. The samples were then analyzed for structural changes and zinc-binding ability using various spectrometric and calorimetric approaches. The study reveals changes in the three-dimensional structure of the protein upon glycation that cause local unfolding of the molecule. Most such regions are localized in subdomain IIA of HSA which plays a key role in zinc binding. This affects zinc interaction with HSA and could in part explain the perturbed zinc distribution in patients with hyperglycemia. The varying degree of HSA glycation in blood could explain the observed heterogeneity pertaining to zinc deficiency among people suffering from diabetes.

Diketo modification of curcumin affects its interaction with human serum albumin

Curcumin isoxazole (CI) and Curcumin pyrazole (CP), the diketo modified derivatives of Curcumin (CU) are metabolically more stable and are being explored for pharmacological properties. One of the requirements in such activities is their interaction with circulatory proteins like human serum albumin (HSA). To understand this, the interactions of CI and CP with HSA have been investigated employing absorption and fluorescence spectroscopy and the results are compared with that of CU. The respective binding constants of CP, CI and CU with HSA were estimated to be 9.3×105, 8.4×105 and 2.5×105M−1, which decreased with increasing salt concentration in the medium. The extent of decrease in the binding constant was the highest in CP followed by CI and CU. This revealed that along with hydrophobic interaction other binding modes like electrostatic interactions operate between CP/CI/CU with HSA. Fluorescence quenching studies of HSA with these compounds suggested that both static and dynamic quenching mechanisms operate, where the contribution of static quenching is higher for CP and CI than that for CU. From fluorescence resonance energy transfer studies, the binding site of CU, CI and CP was found to be in domain IIA of HSA. CU was found to bind in closer proximity with Trp214 as compared to CI and CP and the same was responsible for efficient energy transfer and the same was also established by fluorescence anisotropy measurements. Furthermore docking simulation complemented the experimental observation, where both electrostatic as well as hydrophobic interactions were indicated between HSA and CP, CI and CU. This study is useful in designing more stable CU derivatives having suitable binding properties with proteins like HSA.

Investigation on the interaction between nanocarriers and functional compounds of flavonoids

Studies have suggested that a diet rich in functional foods containing flavonoids provides benefits to human health for anti-inflammatory, antioxidant, antibacterial, and anticancer activities. These compounds are usually present in fruits, vegetables and beverages. Human Serum Albumin (HSA) is a predominant carrier protein in blood plasma. The exceptional capacity of HSA to interact with many molecules makes this protein an important regulator of intercellular fluxes. In this work, HSA was used as a model for the study of nanocarrier-flavonoid interaction. The flavonoids investigated were Rutin (RU) and Guaijaverin (GUA). For analytical studies a combination of steady-state fluorescence spectroscopy and molecular modelling calculations were employed. The fluorescence quenching results indicated that the flavonoids binding near residue Trp214, which is localized in the subdomain IIA of HSA. The quenching mechanism is static which indicates the formation of the HSA-flavonoid complexes. The Gibbs free energy changes of both complexes were negative which characterize spontaneous reactions. The molecular modelling results for binding of RU and GUA with HSA are in accordance with the fluorescence spectroscopy data.