Structure Of Human Serum Albumin Research Articles

Role of surface charge on the interaction between carbon nanodots and human serum albumin

Carbon nanodots (Cdots) have aroused widespread concerns in the field of biomedical applications. In order to achieve better implications of behavior of Cdots in the biological environment, an array of spectroscopic, electrochemical and calorimetric techniques were performed to study the interaction of Cdots possessing different charges with human serum albumin (HSA) in physiological condition. Two polymer, polyethylene glycol (PEG) and polyetherimide (PEI), were applied to passivate the bare Cdots to achieve the Cdots with different surface charge, namely negatively charged PEG Cdots and positively charged PEI Cdots. The fluorescence of HSA was obviously quenched by both Cdots in a charge-independent behavior through a dynamic collision mechanism. Moreover, the association affinity of PEG Cdots or PEI Cdots bound to HSA was very close to each other. In addition, PEG Cdots with diverse content exhibited little effects on the secondary structure of HSA while only high content of PEI Cdots induced obvious conformation perturbation of HSA. The electrostatic forces dominate the association between HSA and PEI Cdots while the association of PEG Cdots to HSA is initiated by hydrophobic and van der Waals forces. Furthermore, the results of isothermal titration calorimetry revealed that both the interaction was driven by favorable entropy and enthalpy, which confirmed that these association processes are thermodynamically spontaneous. Finally, the sites marker competitive experiment showed that the association sites of Cdots with HSA exhibit a charge dependent manner, namely PEG Cdots effectively occupy the site I of HSA while the association sites of PEI Cdots are mainly located in site II.

Binding Studies of Andrographolide with Human Serum Albumin: Molecular Docking, Chromatographic and Spectroscopic Studies.

Human serum albumin acts as a carrier protein to a variety of drugs and aids their transport. Andrographis paniculata, a herbal plant has been used as a source of traditional medicine in the Asian countries. Among the various constituents of this plant, andrographolide is the most active and is being used from centuries in the treatment of many chronic and infectious diseases. The present study was designed to evaluate the interaction and binding affinity of andrographolide with HSA, by molecular docking, chromatographic and spectral studies. Andrographolide was docked with crystal structure of human serum albumin (1AO6) using Auto Dock Vina software and the interactions were analyzed by a visualizing software py- MOL. For further characterization and confirmation, andrographolide (3x10-5 M) and HSA (0.001, 0.005, 0.01, 0.02, 0.04 M) sample mixtures were incubated at 37°C for 3h in a metabolic shaker, followed by centrifugation. The supernatant and the filtrate were analyzed by UV spectroscopy, HPLC, CD and FTIR spectral analysis. The docking studies revealed that andrographolide interacted with HSA and formed hydrogen bonds with Trp 214, Arg 218 and Lys 444 amino acid residues. The UV spectral analysis revealed a decrease in the absorption peak of HSA due to its interaction with andrographolide. A new peak was observed at retention time 7.45 min by HPLC analysis and the Bmax was found to be 7.5 ± 0.4 mg protein with a Kd value of 1.89 mM, indicating interaction of andrographolide with HSA. The CD spectra results suggested, a marginal decrease in the negative ellipticity without any significant shift in peak, indicating the stabilization of the HSA-andrographolide complex. The FTIR analysis of the andrographolide-HSA mixture showed a peak at wave number 1637 cm-1 (a shift of amide I groups from 1646 cm-1) and 1016 cm-1 which corresponded to the ligand, confirming the complex formation. The molecular docking studies demonstrated the interactions of andrographolide to the crystal structure of HSA. The chromatographic and spectroscopic analysis confirmed the binding of andrographolide with HSA and their complex formation. Overall the present studies conclude the binding of andrographolide to HSA protein, favoring its pharmacokinetics.

Spectral demonstration of structural transitions in albumins

Several spectral methods (UV absorbance, fluorescent and FTIR spectroscopy) were applied to reveal the alterations in the secondary and tertiary structures of human serum albumin (HSA) in water solutions under various conditions (pH, protein concentration, ethanol and n-propanol addition). The structural transitions well known for defatted HSA at 1.5 < pH < 13 are observed for HSA in a complex with long-chain fatty acids in the molar ratio about 1:1. The changes of HSA ζ-potential during the protein isomerizations induced by the variation of pH are traced. It is shown that HSA does not completely lose its secondary structure at extreme alkaline or acidic solutions, which indicates that at these conditions HSA takes the “molten globule” conformation. A comparison of aggregation processes of HSA and ovalbumin in neutral water and 0.15 M NaCl solutions reveals that OVA aggregation is preceded by a partially denaturated state of the protein, whereas an intermediates of HSA aggregates are close to the native state of the protein. The aliphatic alcohols disturb the tertiary structure of HSA, but stabilize its secondary structure. This effect increases with the rise of the alcohol hydrophobicity.

Binding behavior of trelagliptin and human serum albumin: Molecular docking, dynamical simulation, and multi-spectroscopy

This study aims to investigate the interaction mechanism of a hypoglycemic agent, trelagliptin (TLP), and human serum albumin (HSA) through computer simulation and assisted spectroscopy methods. Computer simulation including molecular docking and molecular dynamics analysis was conducted under physiological conditions. Molecular docking results indicate that TLP bound to HSA at site I, and the binding behavior was mainly governed by hydrophobic force. Competitive experiments further verified the theoretical conclusion from molecular docking. Molecular dynamics simulation revealed that TLP indeed stably bound to site I of HSA in the hydrophobic subdomain IIA. Moreover, TLP presented a certain effect on the structural compactness of HSA. In molecular dynamics simulation, hydrogen bonds appeared, which suggested the reliability and stability of the combination. The binding energy of the stable phase is around −250 kJ/mol. Fluorescence quenching studies and time-resolved fluorescence analysis indicated that the evident fluorescence quenching phenomenon of HSA could be due to TLP binding initiated by static quenching mechanism. The binding constants (Ka) of the complex were found to be around 104 via fluorescence data, and the calculated thermodynamic parameters indicated that hydrophobic force played major role in the binding of TLP to HSA. Synchronous fluorescence and three-dimensional fluorescence results demonstrated that TLP slightly disturbed the microenvironment of amino residues. Circular dichroism spectra showed that TLP affected the secondary structure of HSA. The theoretical and experimental results showed excellent agreement.

A comparative study of binding properties of different coumarin-based compounds with human serum albumin

We have disclosed the impact of different coumarin-based compounds (3-(furan-2-yl)-6-methyl-2H-chromen-2-one (FM) and 6-chloro-3-(furan-2-yl)-2H-chromen-2-one) (CM)) on the change of human serum albumin's structure in vitro. The fluorescence experiments demonstrated that the HSA native fluorescence intensity was more reduced by CM than FM followed a static mode. We found the binding constants for FM and CM are 1.289 × 105 M−1 and 6.375 × 105 M−1, respectively, suggesting the much stronger binding affinity of CM to HSA than FM. Thermodynamic analysis showed the hydrophobic interaction between these coumarin-based compounds and HSA were clearly important. Moreover, a series of spectral methods were used to provide more details about the FM/CM-induced conformational changes of HSA. Finally, we used molecular docking set up a new HSA-FM/CM model to predict the possible binding sites.

Characterization of the binding of a novel antitumor drug ibrutinib with human serum albumin: Insights from spectroscopic, calorimetric and docking studies

Ibrutinib (IBR) is a novel Bruton's tyrosine kinase inhibitor and shows good efficacy for several B-cell malignancies. In the current study, the molecular mechanism of the interaction between IBR and the transport protein human serum albumin (HSA) was ascertained by spectroscopic, calorimetric, and docking studies. Detailed investigations on affinity parameter, binding model, conformational change, and site selectivity were implemented by receptor-based and ligand-based analysis. An unusual fluorescence co-quenching (mutual quenching) was observed in the binding of IBR to HSA, followed by a static mechanism. Fluorescence spectroscopy and isothermal titration calorimetry indicated that the binding affinity was at 104 M−1 level and electrostatic interactions and hydrophobic forces contributed the interaction. UV–vis and 3D fluorescence spectroscopy suggested the conformational changes of HSA after binding with IBR. Fourier transform infrared and circular dichroism spectroscopy further verified the variation in the secondary structure of HSA. Site-markers competition and molecular docking confirmed that IBR preferably binds to HSA at the cysteine-rich region of Sudlow's site I (subdomain IIA). This study systematically clarified the binding process of the novel antitumor drug with the functional biomacromolecule for the first time. The findings are helpful for IBR pharmacological assessment and can provide valuable reference for other tinib-type drugs.

Metal-catalyzed oxidation of human serum albumin does not alter the interactive binding to the two principal drug binding sites

It is well known that various physiological factors such as pH, endogenous substances or post-translational modifications can affect the conformational state of human serum albumin (HSA). In a previous study, we reported that both pH- and long chain fatty acid-induced conformational changes can alter the interactive binding of ligands to the two principal binding sites of HSA, namely, site I and site II. In the present study, the effect of metal-catalyzed oxidation (MCO) caused by ascorbate/oxygen/trace metals on HSA structure and the interactive binding between dansyl-L-asparagine (DNSA; a site I ligand) and ibuprofen (a site II ligand) at pH 6.5 was investigated. MCO was accompanied by a time-dependent increase in carbonyl content in HSA, suggesting that the HSA was being oxidized. In addition, The MCO of HSA was accompanied by a change in net charge to a more negative charge and a decrease in thermal stability. SDS-PAGE patterns and α-helical contents of the oxidized HSAs were similar to those of native HSA, indicating that the HSA had not been extensively structurally modified by MCO. MCO also caused a selective decrease in ibuprofen binding. In spite of the changes in the HSA structure and ligand that bind to site II, no change in the interactive binding between DNSA and ibuprofen was observed. These data indicated that amino acid residues in site II are preferentially oxidized by MCO, whereas the spatial relationship between sites I and II (e.g. the distance between sites), the flexibility or space of each binding site are not altered. The present findings provide insights into the structural characteristics of oxidized HSA, and drug binding and drug-drug interactions on oxidized HSA.

Spectroscopic studies of human serum albumin exposed to Fe3O4 magnetic nanoparticles coated with sodium oleate: Secondary and tertiary structure, fibrillation, and important functional properties

The structural and functional properties of human serum albumin (HSA) exposed to Fe3O4 magnetic nanoparticles coated with sodium oleate (SOMNPs) were examined by various spectroscopy methods. The results of dynamic light scattering (DLS) indicated the formation of the HSA-SOMNPs complex, referred to as the protein corona. It was found that SOMNPs could quench the intrinsic and synchronous fluorescence of HSA by a static quenching mechanism as evident from time-resolved fluorescence spectroscopy, and could also interfere with the hydrophobic areas of HSA. The values of Ksv, Kb and n were found to be 3.441 × 108 M−1, 7.49 × 108 M−1 and 1.043 at 310 K, respectively. The negative values of ΔH0 (−76.56 kJ mol−1) and ΔS0 (−74.37 J mol−1 K−1) suggested hydrogen bond and Van der Waal's force were the predominant intermolecular forces between the complexes. By following Fluorescence resonance energy transfer (FRET) theory, R0 and r were calculated to be 2.01 nm and 2.26 nm, respectively, which indicated the possibility of energy transfer. Besides, SOMNPs only slightly increased the α-helical content of HSA, and the negative charge of SOMNPs helped to stabilize the secondary structure of HSA. Furthermore, SOMNPs had no significant impact on the formation of HSA fibrillation. The HSA bound to SOMNPs showed higher affinity to copper ions and its drug binding sites Ⅰ and Ⅲ were affected. In addition, SOMNPs also decreased the number of free sulfhydryl groups in HSA and thus reduced its antioxidant property.

Interactions between tetrahydroisoindoline-1,3-dione derivatives and human serum albumin via multiple spectroscopy techniques.

Some tetrahydroisoindoline-1,3-dione derivatives (TDDs) possess potent herbicidal activity. To assess possible impacts of TDDs on humans, the interactions between TDDs and human serum albumin (HSA) were evaluated with steady-state and time-resolved fluorescence spectroscopy, synchronous fluorescence spectroscopy, Fourier transform-infrared spectroscopy, and circular dichroism spectroscopy. The thermodynamic data obtained at temperatures of 298, 307, and 316K indicate that TDDs spontaneously bind to HSA and thus form a TDD-HSA complex. The conformation and secondary structure of HSA are changed, and the intrinsic fluorescence of HSA is statically quenched by TDDs. Moreover, the TDD-HSA complex is formed primarily through electrostatic interactions and has only one binding site on HSA. A competitive ligand-binding assay revealed that site II (subdomain IIIA) displays the greatest affinity for TDDs. In addition, an acute toxicity bioassay showed no zebrafish mortality upon exposure to 4000μgL-1 of TDDs. This work is helpful for understanding interactions between TDDs and HSA.

Understanding the mode of binding mechanism of doripenem to human serum albumin: Spectroscopic and molecular docking approaches.

The infections caused by multidrug resistant bacteria are widely treated with carabapenem antibiotics as a drug of choice, and human serum albumin (HSA) plays a vital role in binding with drugs and affecting its rate of delivery and efficacy. So, we have initiated this study to characterize the mechanism of doripenem binding and to locate its site of binding on HSA by using spectroscopic and docking approaches. The binding of doripenem leads to alteration of the environment surrounding Trp-214 residue of HSA as observed by UV spectroscopic study. Fluorescence spectroscopic study revealed considerable interaction and complex formation of doripenem and HSA as indicated by Ksv and Kq values of the order of 104 M-1 and 1012 M-1 s-1 , respectively. Furthermore, doripenem quenches the fluorescence of HSA spontaneously on a single binding site with binding constant of the order of 103 M-1 , through an exothermic process. Van der Waals forces and hydrogen bonding are the major forces operating to stabilize HSA-doripenem complex. Circular dichroism spectroscopic study showed changes in the structure of HSA upon doripenem binding. Drug displacement and molecular docking studies revealed that the binding site of doripenem on HSA is located on subdomain IB and III A. This study concludes that, due to significant interaction of doripenem on either subdomain IB or IIIA of HSA, the availability of doripenem on the target site may be compromised. Hence, there is a possibility of unavailability of threshold amount of drug to be reached to the target; consequently, resistance may develop in the bacterial population.

Redox responsive curcumin-loaded human serum albumin nanoparticles: Preparation, characterization and in vitro evaluation

The purpose of this study was to fabricate redox-responsive human serum albumin (HSA) nanoparticles (NPs) through self-assembly of HSA molecules for incorporation of curcumin (CCM) as a hydrophobic drug molecule. The structural changes of HSA in self-assembly process of nanoparticle formation were investigated using fluorescence, UV–vis, circular dichroism spectroscopy and X-ray diffraction. Spectroscopy data show changes in secondary and tertiary structures of HSA in the process of nanoparticle formation, which can be indicative of the interaction of the hydrophobic drug with HSA molecules. Unlike free CCM, nanoparticulate curcumin is readily dispersed in aqueous medium. Furthermore, self-assembled HSA-CCM NPs release CCM in an environment imitating the intracellular environment with the trigger of acidic pH and redox potential. The in vitro release studies showed that at pH7.4 only 26% CCM was released from CCM-loaded HSA NPs in 48h. However, the release of CCM was significantly accelerated in the presence of 10mM glutathione (GSH) at pH7.4 or pH5.5, in which 57% and 70% of CCM was released, respectively. The incorporation of CCM in HSA nanoparticles enhanced the cellular uptake of CCM in comparison with free CCM results in higher anticancer efficacy against MCF-7 cells.

Methylglyoxal induced glycation and aggregation of human serum albumin: Biochemical and biophysical approach

Serum protein glycation and formation of advanced glycation end products (AGEs) correlates with many diseases viz. diabetes signifying the importance of studying the glycation pattern of serum proteins. In our present study, methylglyoxal was investigated for its effect on the structure of human serum albumin (HSA); exploring the formation of AGEs and aggregates of HSA. The analytical tools employed includes intrinsic and extrinsic fluorescence, UV spectroscopy, far UV circular dichroism, Thioflavin T fluorescence, congo red binding, polyacrylamide gel electrophoresis (PAGE). UV and fluorescence spectroscopy revealed the structural transition of native HSA evident by new peaks and increased absorbance in UV spectra and quenched fluorescence in the presence of MG. Far UV CD spectroscopy revealed MG induced secondary structural alteration evident by reduced α-helical content. AGEs formation was confirmed by AGEs specific fluorescence. Increased ThT fluorescence and CR absorbance of 10mM MG incubated HSA suggests that glycated HSA results in the formation of aggregates of HSA. SEM and TEM were reported to have an insight of these aggregates. Molecular docking was also utilized to see site specific interaction of MG-HSA. This study is clinically significant as HSA is a clinically relevant protein which plays a crucial role in many diseases.

Isorenieratene interaction with human serum albumin: Multi-spectroscopic analyses and docking simulation

Isorenierantene was reported to be an aromatic carotenoid and has become a food ingredient, mainly from smear cheese, which possesses special antioxidant ability and significant photoprotective effect. In this paper, the interaction of isorenieratene with human serum albumin (HSA) was explored and compared with that of nonaromatic carotenoids using multi-spectroscopic methods and docking simulations. The results suggested isorenieratene could bind to HSA through a static quenching mechanism. The binding processes were spontaneous and exothermic, and the binding between isorenieratene and HSA was mainly driven by hydrophobic forces and electrostatic attraction. Synchronous fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and surface-enhanced Raman scattering (SERS) experiments showed isorenieratene may change the secondary structure of HSA and the micro-environment of its amino acids. Additionally, isorenieratene showed higher stability during the binding process than did nonaromatic carotenoids. Docking simulation indicated isorenieratene may bind to HSA at site II.

Biophysical and immunological characterization of 2-dRib modified HSA and its implications in diabetes mellitus

Glycoxidation of protein may lead to develop diabetes. In the present study, different concentrations of 2-deoxy d-ribose (2-dRib) were used to modify human serum albumin (HSA). Nitro Blue Tetrazolium (NBT) assay results showed that yield of the fructosamine content was directly proportional to the concentration of 2-dRib. UV and fluorescence spectroscopy results showed an increment in hyperchromicity and decrease in fluorescence intensity of 2-dRib modified HSA as compared to native HSA. Further secondary structural changes were confirmed by UV-circular dichroism (UV-CD) and Fourier transform infrared spectroscopy (FT-IR). To evaluate the immunogenicity of 2-dRib modified HSA, rabbits were immunized with native and 2-dRib modified HSA. Modified HSA sera showed high antibodies titre as compared to native HSA. Moreover, the binding affinity of native and modified HSA with diabetic patient's sera has been evaluated by direct binding ELISA. It was found that diabetic patient's sera showed high binding affinity with the modified HSA as compared to native HSA. On the basis of above findings, it can be concluded that 2-dRib is a potential glycating agent that can cause alteration in HSA structure and make HSA more immunogenic that might play a role in onset and progression of diabetes mellitus and its complications.

Binding of Tolperisone Hydrochloride with Human Serum Albumin: Effects on the Conformation, Thermodynamics, and Activity of HSA

Tolperisone hydrochloride (TH) has muscle relaxant activity and has been widely used for several years in clinical practice to treat pathologically high skeletal muscle tone (spasticity) and related pains. The current study was designed to explore the binding efficacy of TH with human serum albumin (HSA) using multispectrscopic, calorimetric approach, FRET, esterase-like activity, and a molecular docking method. A reduction in fluorescence emission at 340 nm of HSA was attributed to fluorescence quenching by TH via a static quenching type. Binding constants ( Kb) were evaluated at different temperatures, and obtained Kb values were ∼104 M-1, which demonstrated moderately strong affinity of TH for HSA. A calculated negative Δ G° value indicated spontaneous binding of TH to HSA. Far-UV CD spectroscopy revealed that the α-helix content was increased after TH binding. The binding distance between donor and acceptor was calculated to be 2.11 nm based on Förster's resonance energy transfer theory. ITC results revealed TH interacted with HSA via hydrophobic interactions and hydrogen bonding. The thermal stability of HSA was studied using DSC, and results showed that in the presence of TH the structure of HSA was significantly more thermostable. The esterase-like activity of HSA showed fixed Vmax and increased Km suggesting that TH binds with HSA in a competitive manner. Furthermore, molecular docking results revealed TH binds in the cavity of HSA, that is, subdomain IIA (Sudlow site I), and that it hydrogen bonds with K199 and H242 of HSA. Binding studies of drugs with HSA are potentially useful for elucidating chemico-biological interactions that can be utilized in the drug design, pharmaceutical, pharmacology, and biochemistry fields. This extensive study provides additional insight of ligand binding and structural changes induced in HSA relevant to the biological activity of HSA in vivo.

Crystal structure analysis of human serum albumin complexed with sodium 4-phenylbutyrate

Sodium 4-phenylbutyrate (PB) is an orphan drug for the treatment of urea cycle disorders. It also inhibits the development of endoplasmic reticulum stress, the action of histone deacetylases and as a regulator of the hepatocanalicular transporter. PB is generally considered to have the potential for use in the treatment of the diseases such as cancer, neurodegenerative diseases and metabolic diseases. In a previous study, we reported that PB is primarily bound to human serum albumin (HSA) in plasma and its binding site is drug site 2. However, details of the binding mode of PB to HSA remain unknown. To address this issue, we examined the crystal structure of HSA with PB bound to it. The structure of the HSA–PB complex indicates that the binding mode of PB to HSA is quite similar to that for octanoate or drugs that bind to drug site 2, as opposed to that for other medium-chain length of fatty acids. These findings provide useful basic information related to drug–HSA interactions. Moreover, the information presented herein is valuable in terms of providing safe and efficient treatment and diagnosis in clinical settings.

Structural Changes of Human Serum Albumin (HSA) in Simulated Microgravity.

Nowadays, the biological effects of microgravity have been the subject of various experimental researches. Microgravity has been confirmed to affect biological systems. Furthermore, as a result of improvement in space technology for instance a manned mission to the moon, probabilities for human exposed to microgravity have incremented undoubtedly. The purpose of this study was to investigate the probable biological effects of microgravity on the human serum albumin (HSA) structure after 3 and 24 h exposure. It is worth mentioning that this is the first effort to investigate the structural alternations of HSA under simulated microgravity condition in biophysico-chemical terms thru different spectroscopic instruments. 2D clinostat was utilized for simulating microgravity. The UV-Vis, intrinsic and extrinsic fluorescence, dynamic light scattering (DLS) and circular dichroism (CD) spectra of 3.76 µM HSA in Tris-HCl buffer (pH 7.4, 0.1 M) and 3.76 µM HSA in Tris-HCl buffer (pH 7.4, 0.1 M) kept at simulated microgravity for 3 and 24h were verified. The UV-Visible, near-UV-CD and intrinsic fluorescence spectroscopy represented that microgravity can remarkably change the tertiary structure of HSA. Additionally, the ANS affinity for HSA incremented when the protein was exposed to simulate microgravity compared to unexposed HSA, which may possibly have appeared attributable to expansion of the structure of simulated HSA. Fluorescence quenching by acrylamide demonstrated higher stern-volmer constant for exposed HSA. The results of zeta potential and dynamic light scattering (DLS) experiments depicted that simulated microgravity cause raise in the surface charge and size of HSA. Far-UV CD data demonstrated that simulated microgravity did not perturb the secondary structures of the protein. Collectively, our results suggest that HSA after 24 h exposure to microgravity can exhibit a molten globule (MG) structure. This is the first report to demonstrate the molten globule state formation in microgravity condition. Results from this study could give knowledge to understand the role of gravity on protein folding process. In addition, this finding could help to find out safe limits for astronauts and space travelers and to develop adequate countermeasures against any harmful effects of microgravity.

β-Carboline Silver Compound Binding Studies with Human Serum Albumin: A Comprehensive Multispectroscopic Analysis and Molecular Modeling Study.

β-Carbolines (βCs) belong to the naturally occurring alkaloid family, derived from 9H-pyrido[3,4-b]indole, also known as norharmane (Hnor). Knowing the importance of the βCs alkaloid family in biological processes, a comprehensive binding study is reported of four Ag(I) compounds containing the ligand Hnor and having different counteranions, namely, NO3 −, ClO4 −, BF4 −, and PF6 −, with human serum albumin (HSA) as a model protein. Different approaches like UV-visible, fluorescence spectroscopy, circular dichroism (CD), and molecular docking studies have been used for this purpose. The fluorescence results establish that the phenomenon of binding of Ag(Hnor) complexes to HSA can be deduced from the static quenching mechanism. The results showed a significant binding propensity of the used Ag(I) compounds towards HSA. The role of the counteranion on the binding of Ag(I) compounds to HSA appeared to be remarkable. Compounds with (ClO4 −) and (NO3 −) were found to have the most efficient binding towards HSA as compared to BF4 −and PF6 −. Circular dichroism (CD) studies made clear that conformational changes in the secondary structure of HSA were induced by the presence of Ag(I) compounds. Also, the α-helical structure of HSA was found to get transformed into a β-sheeted structure. Interestingly, (ClO4 −) and (NO3 −) compounds were found to induce most substantial changes in the secondary structure of HSA. The outcome of this study may contribute to understanding the propensity of proteins involved in neurological diseases (such as Alzheimer's and Parkinson's diseases) to undergo a similar transition in the presence of Ag-β-carboline compounds.

Interaction mechanism of olaparib binding to human serum albumin investigated with NMR relaxation data and computational methods.

The interaction mechanism between olaparib (OLA) and human serum albumin (HSA) has been investigated using experimental and computational techniques. An NMR relaxation approach based on the analysis of proton selective and non-selective spin–lattice relaxation rates at different temperatures can provide quantitative information about the affinity index and the thermodynamic equilibrium constant of the OLA–HSA system. The affinity index and the thermodynamic equilibrium constant decreased as temperature increased, indicating that the interactions between OLA and HSA could be weakened as temperature increased. Molecular docking and dynamics simulations revealed that OLA stably bound to subdomain II (site 1), and OLA could induce the conformational and micro-environmental changes in HSA. CD results suggested that α-helix content decreased after OLA was added, demonstrating that OLA affected the secondary structure of HSA.

Biointeractions of Herbicide Atrazine with Human Serum Albumin: UV-Vis, Fluorescence and Circular Dichroism Approaches.

The herbicide atrazine is widely used across the globe, which is a great concern. To investigate its potential toxicity in the human body, human serum albumin (HSA) was selected as a model protein. The interaction between atrazine and HSA was investigated using steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-Vis spectroscopy, three-dimensional (3D) fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The intrinsic fluorescence of HSA was quenched by the atrazine through a static quenching mechanism. Fluorescence spectra at two excitation wavelengths (280 and 295 nm) showed that the fluorescence quenched in HSA was mainly contributed to by tryptophan residues. In addition, the atrazine bound to HSA, which induced changes in the conformation and secondary structure of HSA and caused an energy transfer. Thermodynamic parameters revealed that this binding is spontaneous. Moreover, electrostatic interactions play a major role in the combination of atrazine and HSA. One atrazine molecule can only bind to one HSA molecule to form a complex, and the atrazine molecule is bound at site II (subdomain IIIA) of HSA. This study furthers the understanding of the potential effects posed by atrazine on humans at the molecular level.