Structure Of Human Serum Albumin Research Articles

Thermodynamics of benzoquinone-induced conformational changes in nucleic acids and human serum albumin

Biological macromolecules such as proteins, nucleic acids, carbohydrates and lipids, play a crucial role in biochemical and molecular processes. Thus, the study of the structure-function relationship of biomolecules in presence of ligands is an important aspect of structural biology. The current communication describes the chemico-biological interaction between benzene metabolite para-benzoquinone (BQ) with B-form of nucleic acids (B-DNA) and human serum albumin (HSA). The binding ability of HSA towards bromocresol green (BCG) was significantly suppressed when exposed to increasing concentrations of BQ in the presence of various physiological buffers. Further, the native fluorescence of HSA was drastically reduced and the secondary structures of HSA were significantly compromised with increasing concentrations of BQ. In vitro and in silico studies also revealed that BQ binds to domains I and II of HSA and thus altering the conformation of HSA which may potentially affect plasma osmotic pressure, as well as the binding and transport of numerous endogenous and exogenous molecules. Similarly, BQ interacts directly to the GC region of B-DNA particularly in the minor groove which was also assessed by computational docking studies. Isothermal titration calorimetry data suggest higher binding affinity of BQ towards DNA than HSA. Various spectroscopic observations also suggest that BQ binds to DNA preferably in the minor grooves. Thus, the results revealed that BQ may play a key role in inducing mutagenicity, either by formation of adducts on GC regions or by accelerating oxidative damage to biomacromolecules through chemico-biological interactions.

Shedding light on the molecular interaction between the Hepatitis B virus inhibitor, clevudine, and human serum albumin: Thermodynamic, spectroscopic, microscopic, and in silico analyses

The molecular interaction between clevudine (CLV), a hepatitis B virus inhibitor, and human serum albumin (HSA), the major transporter in plasma, was investigated via fluorescence, UV–vis absorption, circular dichroism (CD), atomic force microscopy (AFM), and molecular modelling approaches. A steady reduction in the Stern-Volmer quenching constant (Ksv) with increasing temperature endorsed the static mode of the protein fluorescence quenching upon CLV addition, thus confirming CLV-HSA complex formation. This finding was supported by alteration in the UV–vis absorption spectrum of HSA upon CLV addition, higher value (>10 10 M−1 s−1) of the bimolecular quenching rate constant (kq), along with swelling of the HSA molecule in the presence of CLV, as revealed by AFM. Fluorescence quenching titration established a weak binding affinity from the values of the binding constant (Ka=8.65-11.20×103 M−1) at various temperatures (290, 300, 310 and 315 K) for the CLV-HSA system. According to the thermodynamic data (ΔS = +51.89 J mol−1 K−1 and ΔH = −7.69 KJmol−1) of the binding reaction, hydrophobic interactions, hydrogen bonds, and van der Waals forces stabilized the CLV-HSA complex. Lesser changes in both secondary and tertiary structures of HSA upon CLV binding were ratified from the far-UV and the near-UV CD spectral results. In addition, the microenvironment around HSA’s Trp and Tyr residues was also altered, as deduced from three-dimensional fluorescence spectra. The protein showed some resistance against thermal stress in the presence of CLV. The binding site of CLV in subdomain IIA (Site I) of HSA was identified by competitive displacement and molecular docking findings.

An AIE luminogen self-assembled nanoprobe for efficient monitoring of the concentration and structural transition of human serum albumin

Monitoring the content and structural transition of human serum albumin (HSA) is valuable for diagnosing hypoalbuminemia and albuminuria and elucidating its transport function, respectively. Herein, we developed a multifunctional and efficient nanoprobe based on the self-assembly of an amphiphilic aggregation-induced emission luminogen, TPNN, for HSA detection and structure monitoring. TPNN molecules formed loose self-assembly in aqueous media and emitted faint fluorescence due to vigorous intramolecular motion. In the presence of HSA, a remarkable fluorescence enhancement accompanied by dissociation of TPNN assembly was observed due to the site-specific binding of TPNN to the middle long-narrow pocket of HSA. This binding blocked the intramolecular motion while producing a sensitive, selective, fast and stable fluorescence turn-on response to HSA, making TPNN assembly suitable for the HSA assay. TPNN assemblies also showed superior selectivity to HSA than bovine serum albumin (BSA) due to the distinct binding modes, and enabled us to distinguish the two homologous proteins. Furthermore, the generated TPNN-HSA complex underwent stepwise fluorescence quenching in the presence of protein denaturants and proteases, which revealed the process and kinetics of HSA unfolding and cleavage. TPNN assembly provides a powerful tool for accurate quantification of HSA in serum and urine and real-time monitoring of HSA structural transition.

Study on the interaction of the bromodomain inhibitor JQ1 with human serum albumin by spectroscopic and molecular docking studies

The present study examined the interaction of the bromodomain inhibitor/anti-cancer drug JQ1 with human serum albumin (HSA) by spectroscopic and molecular docking methods. Spectroscopic analysis of the fluorescence emission quenching at different temperatures and UV-vis spectroscopy revealed that the quenching mechanism of human serum albumin by JQ1 was static in nature. The quenching data was analyzed using Stern-Volmer equation. JQ1 was bound to HSA at only one site with a binding constant of 3.5 × 104 mol L−1 at 293 K. The binding site of JQ1 in HSA was identified as subdomain IIA in site I, predominantly interacting with Trp-214 residue present at the site I revealed by the site binding experiment. van't Hoff equation was applied to calculate thermodynamic parameters like enthalpy change (∆H°) -29.9 kJ/mol and entropy change (∆S°) +0.09 J/mol K at a temperature of 293 K. The negative value of ∆H° and positive ∆S° suggest the involvement of hydrogen bond and hydrophobic interactions as the predominant binding forces. Circular dichroism spectroscopy revealed that JQ1 induced a slight change in the secondary structure of HSA by reducing the percentage of α-helical content from 56.34% to 56.12%. Molecular docking studies showed that JQ1 majorly interacts with the amino acid residues present in the active site of site I through different types of interactions, including polar, hydrogen bond, electrostatic and hydrophobic interactions.

Synthesis and Antitumor Activity of a GSH Inert Bisphosphonate Platinum (II) Complex

Osteosarcoma is a highly aggressive neoplasm. Traditional platinum chemotherapeutic agents for osteosarcoma inevitably have acquired drug resistance and serious side effects, which have limited their utility. To slow down the reaction of platinum drugs with glutathione (GSH) is a strategy to overcome the resistance of platinum chemotherapeutic agents. Herein, the unique design of a GSH inert bisphosphonate platinum complex cis-{di(amino)platinum[tetraethyl 2,2-bis(2-pyridinylmethyl)methylidene-1,1-bisphosphonate]} (DBPP) is reported. MTT assay demonstrates that DBPP showed moderate inhibition towards human osteosarcoma cell line U2OS cells. The cytostatic action of DBPP is related to conformational conversion from B-DNA to A-DNA and the unwinding of pUC19 DNA. DBPP could also destroy the tertiary structure of human serum albumin (HSA). Notably, 31P NMR and 1H NMR indicate that DBPP can hardly chelate with GSH, which could overcome the GSH-induced side effects. We envision that this unique design of the platinum complex would open up new ways to overcome GSH-induced resistance.

Insight into the binding of alpha-linolenic acid (ALA) on human serum albumin using spectroscopic and molecular dynamics (MD) studies

Alpha-linolenic acid (ALA) is one of the necessary fatty acids for the human body. It is a precursor for synthesizing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The consumption of ALA as an anti-inflammatory factor plays a significant role in preventing cardiovascular diseases. The current study was investigated to evaluate the binding affinity and molecular interactions between human serum albumin (HSA) with ALA through spectroscopic and computational studies. In the existence of ALA, the absorbance of HSA is reduced, confirming the development of the HSA-ALA complex. The fluorescence spectroscopic data implied that the quenching mechanism for HSA-ALA interaction was static mode. The negative values of ΔH° and ΔS° indicated that hydrogen bonding and van der Waals are the predominant intermolecular forces in the complex between HSA and ALA. The binding of ALA induces changes in the structure of HSA, which were revealed by far-UV circular dichroism (CD). The reduction of root mean square deviation (RMSD) after binding to ALA proved the stability of the structure of HSA in the presence of ALA. The results of the esterase activity of HSA presented that ALA competitively binds with HSA. This study demonstrated the importance of ALA in medicine and emphasized its main pharmacological significance.

Investigation of the binding behavior of bioactive 7-methoxyflavone to human serum albumin by coupling multi-spectroscopic with computational approaches

The natural flavonoids with bioactivity as secondary plant metabolites are mostly found in fruits, vegetables, tea and herbs, the distribution and bioavailability of which in vivo depends on the interaction and successive binding with carrier proteins in the systemic circulation. In this paper, the binding behavior of bioactive 7-methoxyflavone (7-MF) with human serum albumin (HSA) was studied with the aid of the combination of multi-spectroscopic methods, molecular docking and molecular dynamic simulation.The results of multi-spectroscopic experiments revealed that 7-MF interacted with HSA predominantly via fluorescence static quenching and the microenvironment around the fluorophore Trp residues in HSA became more hydrophilicity with the binding of 7-MF.Thermodynamic analysis demonstrated that hydrogen bonds and van der Waals forces played a dominant role in stabilizing the HSA-7-MF complex. Moreover, the docking experiment and molecular dynamic simulation further confirmed that 7-MF could enter the active cavity of HSA and caused more stable conformation and change of secondary structure of HSA through forming hydrogen bond. The exploration of the mechanism of 7-MF binding to HSA lights a new avenue to understand the stability, transport and distribution of 7-MF and 7-MF may hold great potential to be extended as a promising alternative of dietary supplements or pharmaceutical agents.

Investigation of structural changes in human serum albumin after binding with elaidic acid

Elaidic acid (EA) is an unsaturated trans-fatty acid and one of the most important fatty acids obtained from solidifying vegetable oils. The increase in the consumption of EA is associated with rise and decline of LDL-cholesterol and HDL-cholesterol levels, respectively. It activates pro-inflammatory markers in the body and increases heart stroke and cardiovascular diseases. In this study, to understand the impact of EA in humans, we investigated the molecular interaction between EA and human serum albumin (HSA) and its binding affinity using spectroscopic, molecular dynamics (MD), and molecular docking techniques. According to fluorescence quenching experiments, EA could quench the inherent fluorescence of HSA via a static quenching mechanism. The thermodynamic characteristics of EA binding on HSA demonstrated hydrogen bonds and Van der Waals forces within the interaction, which matched molecular docking results. Further, the negative amount of ΔG° indicated the spontaneous binding of HSA to EA. Based on Förster's resonance energy transfer, the spatial distance between EA and HSA was 3.493 nm. The far-UV circular dichroism spectrum showed the decrease in the contents of the β-sheet and α-helix in the HSA structure. According to the RMSF data, the HSA structure's flexibility was diminished. The molecular dynamic simulation and spectroscopic studies also indicated that the binding interactions altered the milieu of the Trp chromophore and HSA structures. All experimental data could be matched with molecular dynamics simulation.

Strategies for Therapeutic Amelioration of Aberrant Plasma Zn2+ Handling in Thrombotic Disease: Targeting Fatty Acid/Serum Albumin-Mediated Effects.

The initiation, maintenance and regulation of blood coagulation is inexorably linked to the actions of Zn2+ in blood plasma. Zn2+ interacts with a variety of haemostatic proteins in the bloodstream including fibrinogen, histidine-rich glycoprotein (HRG) and high molecular weight kininogen (HMWK) to regulate haemostasis. The availability of Zn2+ to bind such proteins is controlled by human serum albumin (HSA), which binds 70–85% of plasma Zn2+ under basal conditions. HSA also binds and transports non-esterified fatty acids (NEFAs). Upon NEFA binding, there is a change in the structure of HSA which leads to a reduction in its affinity for Zn2+. This enables other plasma proteins to better compete for binding of Zn2+. In diseases where elevated plasma NEFA concentrations are a feature, such as obesity and diabetes, there is a concurrent increase in hypercoagulability. Evidence indicates that NEFA-induced perturbation of Zn2+-binding by HSA may contribute to the thrombotic complications frequently observed in these pathophysiological conditions. This review highlights potential interventions, both pharmaceutical and non-pharmaceutical that may be employed to combat this dysregulation. Lifestyle and dietary changes have been shown to reduce plasma NEFA concentrations. Furthermore, drugs that influence NEFA levels such as statins and fibrates may be useful in this context. In severely obese patients, more invasive therapies such as bariatric surgery may be useful. Finally, other potential treatments such as chelation therapies, use of cholesteryl transfer protein (CETP) inhibitors, lipase inhibitors, fatty acid inhibitors and other treatments are highlighted, which with additional research and appropriate clinical trials, could prove useful in the treatment and management of thrombotic disease through amelioration of plasma Zn2+ dysregulation in high-risk individuals.

Exploring the interaction of sesamol as an antilung cancer compound with albumin through spectroscopic and bioinformatic analyses and the mechanism of anticancer effect

Sesamol has moved into biomedical research in recent years. However, its interactions with blood proteins and cancer cells have not been fully explored. Therefore, we aimed to investigate the interaction of sesamol with human serum albumin (HSA), A549 human nonsmall cell lung cancer (NSCLC) cell line, and Raw 264.7 macrophage. The interaction of HSA with sesamol was explored via application of fluorescence and circular dichroism (CD) spectroscopy studies as well as molecular docking analysis. Then, the cytotoxic effects of sesamol on A549 lung cancer cells and Raw 264.7 macrophages were evaluated by qPCR analysis. It was found that sesamol spontaneously (ΔG˚=-45.89 kJ/mol) binds with HSA having a high affinity (log K b = 8.05, n = 1.70, T = 298 K ) and form a static complex trough contribution of hydrogen bonds and van der Waals interactions (ΔH˚=-409.43 kJ/mol, TΔS˚=-363.54 kJ/mol) which was supported by molecular docking study. Furthermore, by using CD and synchronous fluorescence spectroscopy analyses it was found that sesamol induced some minor secondary and tertiary structural changes, respectively in HSA structure. Cellular assays displayed that sesamol triggered selective cytotoxicity against A549 lung cancer cells through regulation of intrinsic apoptosis pathway mediated by mitigation of mitochondrial membrane potential, elevation of ROS generation, downregulation of Bax, and up regulation of caspase-9, −3. In conclusion, it was found that sesamol could show high affinity with HSA and mediate intrinsic apoptosis pathway through ROS generation in the A549 lung cancer cell lines. These data indicate that the biochemical and anticancer mechanisms of sesamol can be further investigated in future studies to integrate it in the biomedical platforms.

Exploring the binding mechanism and adverse toxic effects of chiral phenothrin to human serum albumin: Based on multi-spectroscopy, biochemical and computational approach

To understand the binding mechanism of a mixture of chiral phenothrin with human serum albumin (HSA), we used multi-spectroscopy, including steady-state fluorescence spectroscopic titration, three-dimensional fluorescence spectroscopy, circular dichroism, and FTIR spectra to explore the precise interactions between the complex. Based on the modified Stern–Volmer equation, the binding constant (Ka) was calculated under three temperatures, which revealed that phenothrin interacts with HSA through a static quenching mechanism. The thermodynamic parameters including enthalpy change (ΔH) and entropy change (ΔS) were determined by fitting the experimental data with van’t Hoff equation, which indicates that electrostatic force and hydrogen bonds dominate the interplay in the phenothrin-HSA complex. Circular dichroism and FTIR showed the addition of phenothrin changed the secondary structure of proteins, in which the α-helicity decreased from 52.37% in free HSA to 50.02%. The esterase-like activity was reduced with the increase of phenothrin concentration, which may be attributed to the perturbated senior structure of HSA. Competitive displacement experiments confirmed that phenothrin inserted into the subdomain IIA (site I) of HSA. Several computational approaches such as molecular docking, frontier molecular orbital analysis, and electrostatic potential analysis were utilized to probe into the binding mode of the phenothrin-HSA complex. The binding behaviors of the chiral phenothrin mixture differed during the complexation. In conclusion, both the experimental and theoretical investigations provide useful information for better understanding and reducing the potential deleterious effects of the chiral phenothrin mixture on human long-term physio-pathological status.

Molecular Insight into the Binding of Astilbin with Human Serum Albumin and Its Effect on Antioxidant Characteristics of Astilbin.

Astilbin is a dihydroflavonol glycoside identified in many natural plants and functional food with promising biological activities which is used as an antioxidant in the pharmaceutical and food fields. This work investigated the interaction between astilbin and human serum albumin (HSA) and their effects on the antioxidant activity of astilbin by multi-spectroscopic and molecular modeling studies. The experimental results show that astilbin quenches the fluorescence emission of HSA through a static quenching mechanism. Astilbin and HSA prefer to bind at the Site Ⅰ position, which is mainly maintained by electrostatic force, hydrophobic and hydrogen bonding interactions. Multi-spectroscopic and MD results indicate that the secondary structure of HSA could be changed because of the interaction of astilbin with HSA. DPPH radical scavenging assay shows that the presence of HSA reduces the antioxidant capacity of astilbin. The explication of astilbin–HSA binding mechanism will provide insights into clinical use and resource development of astilbin in food and pharmaceutical industries.

Evaluation of pH change effects on the HSA folding and its drug binding characteristics, a computational biology investigation.

The binding of therapeutics to human serum albumin (HSA), which is an abundant protein in plasma poses a major challenge in drug discovery. Although HSA has several binding pockets, the binding site I on D2 and binding site II on D3 are the main binding pockets of HSA. To date, a few experiments have been conducted to examine the effects of the potential of hydrogen (pH) changes on HSA attributes. In the present investigation, the effect of acidic (pH7.1) and basic states (pH7.7) on HSA structure and its drug binding potency were examined in comparison with the physiological state (pH 7.4). For this purpose, molecular dynamics (MD), free energy landscape (FEL), principal component analysis (PCA), probability distribution function (PDF), tunnel-cavity investigation, secondary structure analysis, docking study, and free energy investigation were employed to investigate the effect of pH changes on the structural characteristics of HSA at the atomic level. The results obtained from this study revealed the significant effect of pH alterations on the secondary and tertiary structure of HSA. In addition, HSA stability and its drug binding ability can be severely affected following pH changes. Given that pH change frequently occurs in various diseases such as cancer, diabetes, and kidney failure, therefore, pharmaceutical companies should allocate specific consideration to this subject throughout their drug design experiments.

Interaction of fungal lipase with potential phytotherapeutics.

Interaction of thymol, carvacrol and linalool with fungal lipase and Human Serum Albumin (HSA) have been investigated employing UV-Vis spectroscopy Fluorescence and Circular dichroism spectroscopy (CD) along with docking studies. Thymol, carvacrol and linalool displayed approximately 50% inhibition at 1.5 mmol/litre concentrations using para-nitrophenyl palmitate (pNPP). UV-Vis spectroscopy give evidence of the formation of lipase-linalool, lipase-carvacrol and lipase—thymol complex at the ground state. Three molecules also showed complex formation with HSA at the ground state. Fluorescence spectroscopy shows strong binding of lipase to thymol (Ka of 2.6 x 109 M-1) as compared to carvacrol (4.66 x 107 M-1) and linalool (5.3 x 103 M-1). Number of binding sites showing stoichiometry of association process on lipase is found to be 2.52 (thymol) compared to 2.04 (carvacrol) and 1.12 (linalool). Secondary structure analysis by CD spectroscopy results, following 24 hours incubation at 25°C, with thymol, carvacrol and linalool revealed decrease in negative ellipticity for lipase indicating loss in helical structure as compared with the native protein. The lowering in negative ellipticity was in the order of thymol > carvacrol > linalool. Fluorescence spectra following binding of all three molecules with HSA caused blue shift which suggests the compaction of the HSA structure. Association constant of thymol and HSA is 9.6 x 108 M-1 which along with ‘n’ value of 2.41 suggests strong association and stable complex formation, association constant for carvacrol and linalool was in range of 107 and 103 respectively. Docking results give further insight into strong binding of thymol, carvacrol and linalool with lipase having free energy of binding as -7.1 kcal/mol, -5.0 kcal/mol and -5.2 kcal/mol respectively. To conclude, fungal lipases can be attractive target for controlling their growth and pathogenicity. Employing UV-Vis, Fluorescence and Circular dichroism spectroscopy we have shown that thymol, carvacrol and linalool strongly bind and disrupt structure of fungal lipase, these three phytochemicals also bind well with HSA. Based on disruption of lipase structure and its binding nature with HSA, we concluded thymol as a best anti-lipase molecule among three molecules tested. Results of Fluorescence and CD spectroscopy taken together suggests that thymol and carvacrol are profound disrupter of lipase structure.

Human serum albumin adsorption on cellulose nanocrystal: A spectroscopy and molecular dynamics simulation research

Cellulose nanocrystal (CNC) is a relatively new natural nanoparticle derived from plants. Several biomedical applications are envisioned for CNC. Although its safety upon systemic administration is still questionable, it may serve as a worthy substrate for the adsorption of blood proteins in ex vivo settings for diagnostic purposes. The interaction between CNC and Human serum albumin (HSA) may influence both structure and function of other adsorbed proteins on the CNC surface. Herein, molecular dynamics (MD) simulation and circular dichroism spectroscopy (CD) were utilized to study the conformational changes of HSA in the presence and absence of the CNC. The secondary structure study results show that the HSA structure was conserved during the interaction. Fluorescence spectroscopy indicates that the CNC has a quenching property on the intrinsic fluorescence of HSA. Furthermore, increasing CNC concentrations led to a blue shift in the HSA fluorescence emission at 344 nm. The Gibbs free energy demonstrated the HSA and CNC interaction is spontaneous; the MMPBSA outcomes also approved that electrostatic and van der Waals (vdW) interactions were the major forces in the HSA-CNC complex. The results of this study shed light on the adsorption of HSA on CNC and the nature of their interactions.

Alterations in the conformation and function of human serum albumin induced by the binding of methyl hydrogen phthalate

Phthalate esters (PAEs) are widely used as plasticizer components in production. Methyl hydrogen phthalate (MHP) is a metabolite of dimethyl phthalate (DMP, a kind of PAEs), and its toxic residues accumulate in the nature and can enter the human body. Here, the interaction between MHP and human serum albumin (HSA) was probed by using multi-spectral, computer simulations, and biochemical techniques. The results showed that MHP was spontaneously embedded in site I of HSA to form a complex by H-bonds and van der Waals forces (ΔH < 0, ΔS < 0). The binding constant (Ka) of the HSA-MHP system was 1.136 ± 0.026 × 104 M−1 (298 K). The combination of MHP produced conformational variations of HSA, as shown by the 3D fluorescence spectrum, CD spectra, and molecular dynamics simulation. Additionally, molecular docking indicated that MHP was surrounded by multiple residues, such as Lys199, Leu203, Phe206, and Trp214. Specifically, Lys199 and Trp214 exerted a crucial effect on the interaction of HSA and MHP. The residues with important energy contribution were mostly located in site I. The ASA values of the aromatic amino acids of HSA changed after combining with MHP. The Rg and SASA values of HSA increased after adding MHP, suggesting that the structure of HSA was less compact. Moreover, the esterase-like activity of HSA increased after adding MHP to HSA, indicating that MHP may disturb the normal physiological activities in the human body. This study was helpful to understand the biological function of MHP and provided some insights for its side effect in the human body.

Macromolecular Crowding-Induced Unusual Liquid-Liquid Phase Separation of Human Serum Albumin via Soft Protein-Protein Interactions.

Macromolecular crowding has a profound impact on the conformational dynamics and intermolecular interactions of biological macromolecules. In this context, the role of inert synthetic crowders in the protein-protein interactions of globular proteins is poorly understood. Here, using native human serum albumin (HSA) under physiological conditions, we show that macromolecular crowding induces liquid-liquid phase separation (LLPS) via liquid-like membrane-less droplet formation in a concentration- and time-dependent manner. Circular dichroism measurements reveal significant alteration in the secondary structure of HSA inside the droplet during aging. In contrast, at a high protein concentration, a liquid-to-solid-like phase transition has been observed upon maturation. Our findings reveal that the LLPS of HSA is mainly driven by enthalpically controlled intermolecular protein-protein interactions via hydrophobic contacts involving aromatic and/or nonaromatic residues. Moreover, modulation of LLPS of HSA has been demonstrated upon denaturation and ligand binding. This study highlights the importance of soft protein-protein interactions of globular proteins in a crowded cellular environment in driving the LLPS.

Spectroscopic and Molecular Docking Investigation on the Interaction of Cumin Components with Plasma Protein: Assessment of the Comparative Interactions of Aldehyde and Alcohol with Human Serum Albumin.

The interaction of the important plasma protein, human serum albumin (HSA), with two monoterpenes found in cumin oil, i.e., cuminaldehyde (4-isopropylbenzaldehyde) and cuminol (4-isopropylbenzyl alcohol), was studied in this paper. Both experimental and computational methods were utilized to understand the mechanism of binding. The UV absorption profile of HSA changes in the presence of both cuminaldehyde and cuminol, due to the interaction between HSA with both monoterpenes. The intrinsic fluorescence intensity of HSA was also quenched on the sequential addition of both ligands, due to change in the microenvironment of the fluorophore present in the former. Quenching of HSA by cuminaldehyde was much higher in comparison to that in the presence of cuminol. Fluorescence quenching data were analyzed using modified Stern-Volmer and Lineweaver-Burk methods, which suggested that the binding mechanism was of a static type for both ligands. In both cases, the binding was favored by the domination of hydrophobic as well as hydrogen bonding/Van der Waals forces. Both ligands partially unfolded the secondary structure of HSA, although the effect of cuminaldehyde was more pronounced, as compared to cuminol. The preferred binding site of cuminaldehyde and cuminol inside HSA was also the same; namely, drug binding site 1, located in subdomain IIA. The study showed that cuminaldehyde binds strongly with albumin as compared to its alcohol counterpart, which is due to the more hydrophobic nature of the former.

A “traffic jam” of (+)-catechin caused by hyperglycemia — The interaction between (+)-catechin and human serum albumin (HSA) in high glucose environment

(+)-catechin is an active natural substance for hyperglycemia. However, HSA may be affected by high blood glucose, which alters HSA in the secondary structure to affect the combination of (+)-catechin and HSA, resulting in a “traffic jam” of (+)-catechin in the body. In this study, the effect of glucose on the binding between (+)-catechin and HSA was studied by multiple analysis techniques. It was found that glucose could not alter the static quenching of (+)-catechin-HSA. Electrostatic force played an important role through thermodynamics parameters. The binding constants were 4.956 × 105 mol⋅L-1, ΔH° = –33.6 kJ⋅mol−1, and ΔS° = 99.68 J⋅mol−1⋅K−1 in the glucose-free environment and the binding constants were 4.602 × 104 mol⋅L-1, ΔH° = −20.4 kJ⋅mol−1 and ΔS° = 57.7 J⋅mol−1⋅K−1 in the glucose environment at 298 K. We found that the binding sites of (+)-catechin in two environments were site II through the probe test. 3D fluorescence and CD experiments indicated the addition of (+)-catechin changed the secondary structure of HSA. Besides, molecular docking manifested that glucose could affect the combine of HSA and (+)-catechin. (+)-catechin had weaker binding to HSA in the glucose environment, which was different from the combination of (+)-catechin and HSA alone. The dosage of (+)-catechin for diabetic patients should be reduced because the concentration of free (+)-catechin would increase in the body. This study had a certain guiding significance for the medication of diabetic patients.

Investigation of Pazopanib and Human Serum Albumin Interaction Using Spectroscopic and Molecular Docking Approaches

Pazopanib (PAZ), a tyrosine kinase inhibitor, is used to treat advanced renal cell carcinoma (RCC) and advanced soft tissue sarcoma (STS). The FDA approved PAZ for RCC in 2009 and for STS in 2012. The antitumor activity of pazopanib, according to the degree of inhibition, shows different results depending on the dose. Renal cell carcinoma is the most sensitive carcinoma to pazopanib, with 77% inhibition at the 10 mg/kg dose. Clinical studies have shown 53% to 65% inhibition in carcinomas such as breast carcinoma, prostate carcinoma, and melanoma. Plasma proteins such as human serum albumin (HSA) have a critical role in transporting and storing bioactive components. This feature of HSA is very important for the development of cancer therapy. Here, we investigated the interaction between PAZ and HSA to evaluate their binding strength, binding types, and conformational change in HSA. We used spectroscopic methods to assess the drug–protein interaction. Fluorescence measurements revealed that the interaction of PAZ with HSA occurred via the static quenching mechanism. The calculated binding number and binding constants were 1.041 and 1.436 × 106 M−1, respectively, at 298.15 K based on fluorescence screening. The high binding constant and calculated Gibbs free energy at different temperatures showed spontaneous and strong binding. Circular dichroism measurements showed that the α-helix structure of HSA was retained as the secondary structure, with a slight reduction in its percentage after adding PAZ. Furthermore, molecular modeling studies suggested that the docking score of PAZ is higher than those of bicalutamide and ibuprofen, the drugs that were chosen as model competitors against PAZ. Accordingly, PAZ was found to replace bicalutamide and ibuprofen on the HSA binding site, which was also confirmed by UV absorption spectroscopy.