Secondary Structure Of Human Serum Albumin Research Articles

Molecular Insights into the Conformational and Binding Behaviors of Human Serum Albumin Induced by Surface-Active Ionic Liquids.

Extensive research has been carried out to investigate the stability and function of human serum albumin (HSA) when exposed to surface-active ionic liquids (SAILs) with different head groups (imidazolium, morpholinium, and pyridinium) and alkyl chain lengths (ranging from decyl to tetradecyl). Analysis of the protein fluorescence spectra indicates noticeable changes in the secondary structure of HSA with varying concentrations of all SAILs tested. Helicity calculations based on the Fourier transform infrared (FTIR) data show that HSA becomes more organized at the micellar concentration of SAILs, leading to an increased protein activity at this level. Small-angle neutron scattering (SANS) data confirm the formation of a bead-necklace structure between the SAILs and HSA. Atomistic molecular dynamics (MD) simulation results identify several hotspots on the protein surface for interaction with SAIL, which results in the modulation of protein conformational fluctuation and stability. Furthermore, fluorescence resonance energy transfer (FRET) experiments with the intramolecular charge transfer (ICT) probe trans-ethyl p-(dimethylamino) cinnamate (EDAC) demonstrate that higher alkyl chain lengths and SAIL concentrations result in a significantly increased energy transfer efficiency. The findings of this study provide a detailed molecular-level understanding of how the protein structure and function are affected by the presence of SAILs, with potential implications for a wide range of applications involving protein-SAIL composite systems.

The mechanism of interaction between tri-para-cresyl phosphate and human serum protein: a multispectroscopic and in-silico study

Organophosphate flame retardants (OPFRs) pose the significant risks to the environment and human health and have become a serious public health issue. Tricresyl phosphates (TCPs), a group of aryl OPFRs, exhibit neurotoxicity and endocrine disrupting toxicity. However, the binding mechanisms between TCPs and human serum albumin (HSA) remain unknown. In this study, through fluorescence and ultraviolet-visible (UV-vis) absorption spectroscopy, molecular docking and molecular dynamics (MD), tri-para-cresyl phosphate (TpCP) was selected to explore potential interactions between HSA and TCPs. The results of the fluorescence spectroscopy demonstrated that a decrease the fluorescence intensity of HSA and a blue shift were observed with the increasing concentrations of TpCP. The binding constant (Ka) was 2.575 × 104 L/mol, 4.701 × 104 L/mol, 5.684 × 104 L/mol and 9.482 × 104 L/mol at 293 K, 298 K, 303 K, and 310 K, respectively. The fluorescence process between HSA and TpCP involved a mix of static and dynamic quenching mechanism. The gibbs free energy (ΔG0) of HSA-TpCP system was -24.452, -25.907, 27.363, and 29.401 kJ/mol at 293 K, 298 K, 303 K, and 310 K, respectively, suggesting that the HSA-TpCP reaction was spontaneous. The enthalpy change (ΔH0) and thermodynamic entropy change (ΔS0) of the HSA-TpCP system were 291.08 J/K mol and 60.83 kJ/mol, respectively, indicating that hydrophobic force was the major driving forces in the HSA-TpCP complex. Furthermore, multispectral analysis also revealed that TpCP could alter the microenvironment of tryptophan residue and the secondary structure of HSA and bind with the active site I of HSA. Molecular docking and MD simulations confirmed that TpCP could spontaneously form a stable complex with HSA, which was consistent with the fluorescence experimental results. This study provides novel insights into the mechanisms of underlying the transportation and distribution of OFPRs in humans.

The potential impact of 6PPD and its oxidation product 6PPD-quinone on human health: A case study on their interaction with human serum albumin

6PPD and its oxidation product, 6PPD-quinone have garnered widespread attention due to their adverse effects on aquatic ecosystems and human health, and are recognized as emerging pollutants. In this study, we investigated the interaction mechanism between 6PPD/6PPD-quinone and human serum albumin (HSA) through various experiments. Experimental findings reveal that the IC50 values of 6PPD-quinone and 6PPD against HEK293T cells were 11.78 and 40.04 μM, respectively. Additionally, the cytotoxicity of these compounds was regulated by HSA, displaying an inverse correlation with their binding affinity to HSA. Furthermore, 6PPD/6PPD-quinone can spontaneously insert into site I on HSA, forming a binary complex that induces changes in the secondary structure of HSA. However, their effects on the esterase-like activity of HSA exhibit a dichotomy. While 6PPD activates the esterase-like activity of HSA, 6PPD-quinone inhibits it. Molecular docking analyses reveal that both 6PPD and 6PPD-quinone interact with many amino acid residues on HSA, including TRP214, ARG222, ARG218, ALA291, PHE211. The π electrons on the benzene rings of 6PPD/6PPD-quinone play pivotal roles in maintaining the stability of complexes. Moreover, the stronger binding affinity observed between 6PPD and HSA compared to 6PPD-quinone, may be attributed to the larger negative surface potential of 6PPD.

Biological activity and biomolecule interaction of pyridyl thiazole derivative and its copper complex

This article discusses the synthesis of pyridyl thiazole derivative (PT) and its copper complex (PTC − Pyridyl Thiazole Copper Complex) for studies related to biological activities and biomolecule interaction. Synthesized compounds were characterized, and their biological activities were tested. The metal complex, PTC exhibited positive antibacterial and anticancer activity. The complex PTC inhibited MCF-7 cells at IC50 of 516 µg/mL as compared to the ligand PT which showed IC50 of 868 µg/mL. The PT ligand showed inhibition of S. aureus with a minimum inhibitory concentration (MIC) of 50 µg/mL. While PTC exhibited inhibition against both S. aureus and E. coli organisms with MIC of 50 µg/mL and 150 µg/mL respectively. The binding interaction of two important biomolecules such as Human Serum Albumin (HSA) and Deoxyribonucleic acid (DNA) with both free ligand and metal complex were studied to determine the type and nature of reaction and forces involved in the process. The Ksv values obtained from fluorescence experiments to determine the interaction of PT/PTC with HSA illustrated a static quenching mechanism. Circular dichroism analysis showed minor changes in α-helix percentage, suggesting a lesser influence of these compounds on the secondary structure of HSA. Molecular docking demonstrated a binding pose for PTC with ΔG = −7.51 kcal/mol, supporting the experimental findings in this study. PTC showed more strong interaction with DNA compared to the ligand. Results obtained depict that the PTC complex may have the potential to be used in cancer treatments and antibacterial applications.

Spectroscopic investigation and structural simulation in human serum albumin with hydroxychloroquine/Silybum marianum and a possible potential COVID-19 drug candidate.

In this study, the interaction between human serum albumin (HSA) and the hydroxychloroquine/Silybum marianum (HCQ/SM) mixture was investigated using various techniques. The observed high binding constant (Kb) and Stern-Volmer quenching constant (KSV) indicate a strong binding affinity between the HCQ/SM mixture and HSA. The circular dichroism (CD) analysis revealed that HCQ/SM induced conformational changes in the secondary structure of HSA, leading to a decrease in the α-helical content. UV-Vis analysis exhibited a slight redshift, indicating that the HCQ/SM mixture could adapt to the flexible structure of HSA. The experimental results demonstrated the significant conformational changes in HSA upon binding with HCQ/SM. Theoretical studies were carried out using molecular dynamics simulation via the Gromacs simulation package to explore insights into the drug interaction with HSA-binding sites. Furthermore, molecular docking studies demonstrated that HCQ/SM-HSA exhibited favorable docking scores with the receptor (5FUZ), suggesting a potential therapeutic relevance in combating COVID-19 with a value of -6.24 kcal mol-1. HCQ/SM exhibited stronger interaction with both SARS-CoV-2 virus main proteases compared to favipiravir. Ultimately, the experimental data and molecular docking analysis presented in this research offer valuable insights into the pharmaceutical and biological properties of HCQ/SM mixtures when interacting with serum albumin.

A comprehensive investigation of the interactions of human serum albumin with polymeric and hybrid nanoparticles.

Nanoparticles (NPs) engineered as drug delivery systems continue to make breakthroughs as they offer numerous advantages over free therapeutics. However, the poor understanding of the interplay between the NPs and biomolecules, especially blood proteins, obstructs NP translation to clinics. Nano-bio interactions determine the NPs' in vivo fate, efficacy and immunotoxicity, potentially altering protein function. To fulfill the growing need to investigate nano-bio interactions, this study provides a systematic understanding of two key aspects: (i) protein corona (PC) formation and (ii) NP-induced modifications on protein's structure and stability. A methodology was developed by combining orthogonal techniques to analyze both quantitative and qualitative aspects of nano-bio interactions, using human serum albumin (HSA) as a model protein. Protein quantification via liquid chromatography-mass spectrometry, and capillary zone electrophoresis (CZE) clarified adsorbed protein quantity and stability. CZE further unveiled qualitative insights into HSA forms (native, glycated HSA and cysteinylated), while synchrotron radiation circular dichroism enabled analyzing HSA's secondary structure and thermal stability. Comparative investigations of NP cores (organic vs. hybrid), and shells (with or without polyethylene glycol (PEG)) revealed pivotal factors influencing nano-bio interactions. Polymeric NPs based on poly(lactic-co-glycolic acid) (PLGA) and hybrid NPs based on metal-organic frameworks (nanoMOFs) presented distinct HSA adsorption profiles. PLGA NPs had protein-repelling properties while inducing structural modifications on HSA. In contrast, HSA exhibited a high affinity for nanoMOFs forming a PC altering thereby the protein structure. A shielding effect was gained through PEGylation for both types of NPs, avoiding the PC formation as well as the alteration of unbound HSA structure.

Polymers as candidates for broad‐spectrum antivirals—in vitro inhibition of Zika virus with sodium polyanethole sulfonate

AbstractZika virus (ZIKV), belonging to the family of flaviviruses, is an emerging mosquito‐borne pathogen causing microcephaly and other congenital abnormalities in newborns as well as various neurologic pathologies in adults. The climate change and the lifestyle of current societies, involving global mobility, result in a rapid broadening of ZIKV geographic distribution. There are no vaccines or drugs available to protect against or cure the diseases caused by that virus. Our in vitro studies have demonstrated that sodium polyanethole sulfonate (PASNa), a degradable polymer used in various biomedical applications, acts as an efficient ZIKV inhibitor, both in animal and human cells. The mechanistic studies indicated that PASNa bound to the ZIKV particles thus hindering their attachment to the host cells and also interfered in the late steps of viral replication. PASNa is characterized by very low cytotoxicity and its antiviral activity can be achieved at a concentration much lower than that at which its anticoagulant activity has to be considered. Isothermal titration calorimetry (ITC) studies have shown that the interaction of PASNa with human serum albumin (HSA), the most abundant blood protein, is the endothermic, entropy‐driven process resulting in the formation of stoichiometric (1:1) PASNa‐HSA complexes with a hydrodynamic diameter of 8.8 ± 0.8 nm and zeta potential (ζ) equal to −21.3 mV. The analysis of CD spectra indicated that PASNa did not significantly affect the HSA secondary structure on binding to that protein.

Application of Infrared Free-Electron Laser Irradiation of Protein Complexes Binding to Salen-Type Schiff Base Zn(II) Complexes Using Secondary Conformational Changes in the Proteins for the Treatment of Alzheimer’s Disease

Alzheimer’s disease causes the destruction of cranial nerve cells and is said to be caused by neuronal cell death due to the accumulation of amyloid-β protein. One method for the treatment of Alzheimer’s disease is to reduce the toxicity of the amyloid beta protein. Among the possibilities is to reduce toxicity by changing the secondary structure of the protein. In this study, the secondary structure of the protein was verified by binding a zinc complex to the protein and irradiating it with an infrared free-electron laser (IR-FEL). By binding Salen-Type zinc complexes to human serum albumin (HSA) and irradiating it with IR-FEL, structural changes were observed in the α-helix and β-sheet, the secondary structure of HSA. In addition to researching the possibility of binding zinc complexes to small proteins, docking simulations were examined. GOLD docking simulations showed that it is possible to bind zinc complexes to lysozyme (Lyz), a small protein. These results suggest that binding zinc complexes to amyloid-β and inducing a secondary conformational change through IR-FEL irradiation could be used for the treatment of Alzheimer’s disease by making the complexes lose their toxicity.

Deciphering the binding mechanism of gingerol molecules with plasma proteins: implications for drug delivery and therapeutic potential

Ginger is a highly valued herb, renowned globally for its rich content of phenolic compounds. It has been traditionally used to treat various health conditions such as cardiovascular diseases, digestive issues, migraines, Alzheimer’s disease, tumor reduction and chronic inflammation. Despite its potential medicinal applications, the therapeutic effectiveness of ginger is hindered by its limited availability and low plasma concentration levels. In this study, we explored the interaction of ginger’s primary phenolic compounds, specifically 6-gingerol (6 G), 8-gingerol (8 G) and 10-gingerol (10 G), with plasma proteins which are human serum albumin (HSA) and α-1-acid glycoprotein (AGP). These two plasma proteins significantly influence drug distribution and disposition as they are key binding sites for most drugs. Fluorescence emission spectra indicated strong binding of 6, 8 and 10 G with HSA, with binding constants of 2.03 ± 0.01 × 104 M−1, 4.20 ± 0.01 × 104 M−1 and 6.03 ± 0.01 × 106 M−1, respectively. However, the binding of gingerols with AGP was found to be negligible. Molecular displacement by site-specific probes and molecular docking analyses revealed that gingerols bind at the IIA domain, with stability provided by hydrogen bonds, van der Waals forces, conventional hydrogen bonds, carbon-hydrogen bonds, alkyl and Pi–alkyl interactions. Further, the partial unfolding of the protein was observed upon binding the gingerol compound with HSA. In addition, molecular dynamic simulations demonstrated that gingerols remained stable in the subdomain IIA over 100 ns. This stability, coupled with Molecular Mechanics Generalized Born Surface Area indicating free energies of −43.765, −57.504 and −66.69 kcal/mol for 6, 8 and 10 G, respectively, reinforces the robust binding potential of these compounds. Circular dichroism studies suggested that the interaction of gingerols leads to the minimal transformation of HSA secondary structure, with the pattern being 10 G > 8 G > 6 G, a finding further substantiated by root mean square deviation and root mean square fluctuation fluctuations. These results propose that HSA has a stronger affinity to gingerols than AGP, which could have significant implications on the therapeutic circulating levels of gingerols. Communicated by Ramaswamy H. Sarma

Aggregation and cytotoxicity of food additive dye (Azorubine)-albumin adducts: a multi-spectroscopic, microscopic and computational analysis

Protein and peptide misfolding is a central factor in the formation of pathological aggregates and fibrils linked to disorders like Alzheimer’s and Parkinson’s diseases. Therefore, it’s essential to understand how food additives, particularly Azorubine, affect protein structures and their ability to induce aggregation. In this study, human serum albumin (HSA) was used as a model protein to investigate the binding and conformational changes caused by azorubine, a common food and drink colorant. The research revealed that azorubine destabilized the conformation of HSA at both physiological (pH 7.4) and acidic (pH 3.5) conditions. The loss of tryptophan fluorescence in HSA suggested significant structural alterations, particularly around aromatic residues. Far UV-CD analysis demonstrated disruptions in HSA's secondary structure, with a notable reduction in α-helical structures at pH 7.4. At pH 3.5, Azorubine induced even more extensive perturbations, resulting in a random coil conformation at higher azorubine concentrations. The study also investigated aggregation phenomena through turbidity measurements, RLS analysis, and TEM imaging. At pH 3.5, larger insoluble aggregates formed, while at pH 7.4, only conformational changes occurred without aggregate formation. Cytotoxicity assessments on neuroblastoma (SH-SY5Y) cells highlighted the concentration-dependent toxicity of albumin aggregates. Molecular dynamics simulations reaffirmed the stable interaction between azorubine and HSA. This research provides valuable insights into the mechanisms by which azorubine influences protein conformations. To further advance our understanding and contribute to the broader knowledge in this area, several future directions can be considered such as exploring other proteins, studying dose-response relationship, gaining mechanistic insights, biological relevance, toxicity assessment, identifying alternative food colorants, and mitigation strategies to prevent adverse effects of azorubine on serum proteins.Communicated by Ramaswamy H. Sarma

Unveiling the molecular interactions between alkyl imidazolium ionic liquids and human serum albumin: Implications for toxicological significance

Alkyl imidazolium-based ionic liquids (ILs) are promising for diverse industrial applications; however, their growing prevalence has raised concerns regarding human exposure and potential health implications. A critical aspect to be clarified to address the adverse health effects associated with ILs exposure is their binding mode to human serum albumin (HSA). In this study, we delved into the binding interactions between three alkyl imidazolium ILs (1-hexyl-3-methyl-imidazolium (C6[MIM]), 1-ethyl-3-methyl-imidazolium chloride (C8[MIM]) and 1-decyl-3-methyl-imidazolium (C10[MIM]) and human serum albumins (HSAs) using a comprehensive approach encompassing molecular docking and multi-spectroscopy (UV–visible, Fluorescence, Circular Dichroism, FTIR). Furthermore, for the first time, we developed an ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) approach time to quantify plasma protein binding rates. Our results revealed that the ILs primarily bind to the hydrophobic cavity of HSA through hydrogen bonding and van der Waals forces, forming stable complexes via static quenching. This affected HSA's secondary structure, reducing α-helical content, particularly around specific residues. Equilibrium dialysis and ultrafiltration coupled with UPLC-MS/MS analysis showed modest plasma protein binding rates (17.84%–31.85%) for the three ILs, with no significant influence from alkyl chain effects or concentration relationship. Lower plasma protein binding rates can affect bioavailability and distribution of ILs, potentially influencing their toxicity. These findings provide critical insights into the potential toxicological implications at the molecular level, thereby contributing to continuous efforts to evaluate the risk profiles and ensure the safe utilization of these compounds.

Investigation on the interactions of contaminant triclosan with human serum albumin: Spectroscopic and molecular docking studies

Triclosan (TCS) is an extensively distributed environmental contaminant that can have impacts on ecosystems and human health. This study employed both in vitro experiments and computer simulations to assess the interaction between TCS and human serum albumin (HSA) at the molecular level. The formation of the HSA-TCS complex was a spontaneous process, maintained by strong affinity (Ka > 105) due to hydrogen bonds and van der Waals forces. TCS binding to the I site of HSA led to an increase in hydrophobicity around the Trp-residue and altered the structure of the peptide chain backbone. CD spectroscopy revealed alterations in the secondary structure of HSA, including decreased α-helical content and increased disorder, in the presence of TCS. Moreover, the esterase activity in HSA was inhibited by TCS as an anticompetitive inhibitor. Molecular docking studies identified TCS tightly embedded at site I of HSA, with binding facilitated through hydrogen bonds and hydrophobic interactions. Molecular dynamics simulations highlighted the significant energy contributions of Trp214 and Lys199 residues, directly involved in the formation of the HSA-TCS complex. Additionally, the presence of TCS enhanced the compactness of the HSA structure. Therefore, new insights into toxicological studies of other contaminants can be proposed based on these results of TCS.

In Vitro Study of the Interaction between Ochratoxin A and Human Serum Albumin by Spectroscopic and Molecular Docking Methods

AbstractOchratoxin A (OA) is a mycotoxin that has a potential risk to human health due to its nephrotoxic, immunotoxic and carcinogenic effects. For these reasons the interaction of ochratoxin A with human serum albumin (HSA) was investigated in physiological media by various techniques such as UV‐Vis, fluorescence (FL), circular dichroism (CD), attenuated total reflection (ATR), differential scanning calorimetry (DSC), atomic force microscopy (AFM) and molecular docking study via Auto Dock‐vina software. The fluorescence intensity of tryptophan in HSA was strongly quenched in the present of OA and the quenching constants and binding constant were valued 108 M−1 and 1.04 M−1, respectively. The CD spectra showed alteration in the secondary structure of HSA in the presence of ochratoxin by reducing the regular alpha helical structure and increasing the beta‐sheet structure. By increasing the concentration of OA to 1.25 μM, the intensity of absorption spectrum at 282 nm was increased, indicating the strong interaction of OA and HSA. The enthalpies of these molecular interaction calculated from DSC analysis indicate OA interaction with HAS is exothermic. The docking calculations showed that the amino acids of Lys190, ASP187, LYS519, ARG186 and ARG428 were interacted with OA by hydrogen bonding.

The effect of novel tyrosine-modified polyethyleneimines on human albumin structure – Thermodynamic and spectroscopic study

The interaction of proteins with nanoparticle components are crucial for the evaluation of nanoparticle function, toxicity and biodistribution. Polyethyleneimines (PEIs) with defined tyrosine modifications are a class of novel polymers designed for improved siRNA delivery. Their interactions with biomacromolecules are still poorly described. This paper analyzes the interaction of different tyrosine-modified PEIs with human serum albumin as the most abundant serum protein. The ability of tyrosine modified, linear or branched PEIs to bind human serum albumin (HSA) was analyzed and further characterized. The interaction with hydrophobic parts of protein were studied using 1- nilinonaphthalene-8-sulfonic acid (ANS) and changes in the HSA secondary structure were evaluated using circular dichroism (CD). Complex formation and sizes were studied by transmission electron microscopy (TEM) and dynamic light scattering methods (DLS). We demonstrate that tyrosine modified PEIs are able to bind human serum albumin. Based on thermodynamic studies, van der Waals interaction, H-bonding and hydrophobic interactions are determined as main molecular forces involved in complex formation. Analysis of secondary structures revealed that the polymers decreased α-helix content, while increasing levels of randomly folded structures. Complex formation was confirmed by TEM and DLS. These findings are crucial for understanding polymer-protein interactions and the properties of nanoparticles.

Detailed Experimental and In Silico Investigation of Indomethacin Binding with Human Serum Albumin Considering Primary and Secondary Binding Sites

The interaction of indomethacin with human serum albumin (HSA) has been studied here considering the primary and secondary binding sites. The Stern-Volmer plots were linear in the lower concentration range of indomethacin while a downward curvature was observed in the higher concentration range, suggesting the presence of more than one binding site for indomethacin inside HSA due to which the microenvironment of the fluorophore changed slightly and some of its fraction was not accessible to the quencher. The Stern-Volmer quenching constants (KSV) for the primary and secondary sites were calculated from the two linear portions of the Stern-Volmer plots. There was around a two-fold decrease in the quenching constants for the low-affinity site as compared to the primary binding site. The interaction takes place via a static quenching mechanism and the KSV decreases at both primary and secondary sites upon increasing the temperature. The binding constants were also evaluated, which show strong binding at the primary site and fair binding at the secondary site. The binding was thermodynamically favorable with the liberation of heat and the ordering of the system. In principle, hydrogen bonding and Van der Waals forces were involved in the binding at the primary site while the low-affinity site interacted through hydrophobic forces only. The competitive binding was also evaluated using warfarin, ibuprofen, hemin, and a warfarin + hemin combination as site markers. The binding profile remained unchanged in the presence of ibuprofen, whereas it decreased in the presence of both warfarin and hemin with a straight line in the Stern-Volmer plots. The reduction in the binding was at a maximum when both warfarin and hemin were present simultaneously with the downward curvature in the Stern-Volmer plots at higher concentrations of indomethacin. The secondary structure of HSA also changes slightly in the presence of higher concentrations of indomethacin. Molecular dynamics simulations were performed at the primary and secondary binding sites of HSA which are drug site 1 (located in the subdomain IIA of the protein) and the hemin binding site (located in subdomain IB), respectively. From the results obtained from molecular docking and MD simulation, the indomethacin molecule showed more binding affinity towards drug site 1 followed by the other two sites.

New Synthetic Quinoline (Qui) Derivatives as Novel Antioxidants and Potential HSA's Antioxidant Activity Modulators-Spectroscopic Studies.

The antioxidant activity of drugs, as well as the influence of drugs on the activity of endogenous antioxidant mechanisms in the human body is of great importance for the course of the disease and the treatment process. Due to the need to search for new therapeutic methods, the study of newly synthesized substances with potential therapeutic activity is necessary. This study aimed to designate some properties and characteristic parameters of new, synthetic quinoline three derivatives-1-methyl-3-allylthio-4-(4'-methylphenylamino)quinolinium bromide (Qui1), 1-methyl-3-allylthio-4-(3'-hydroxyphenylamino)quinolinium bromide (Qui2) as well as 1-methyl-3-allylthio-4-(4'-hydroxyphenylamino)quinolinium bromide (Qui3), including their antioxidant properties, as well as to analyse their activity as the potential modulators of Human Serum Albumin (HSA) antioxidant activity. In order to achieve the goal of the study, spectroscopic methods such as UV-Vis and circular dichroism (CD) spectroscopy have been used and based on the obtained data only slight and probably some surface interaction of quinoline derivatives (Qui1-Qui3) with HSA have been observed. The effect of Qui1-Qui3 on the HSA secondary structure was also insignificant. All analysed quinine derivatives have antioxidant activity against ABTS cation radical, in turn against DPPH radical, only Qui3 has noticeable antioxidant potential. The highest reduction potential by Qui3 as well as (Qui3 + HSA)complex has been shown. Qui3 mixed with HSA has mostly the synergistic effect against DPPH, ABTS and FRAP, while Qui1 and Qui2 in the presence of HSA mostly have a synergistic and additive effect towards ABTS, respectively. Based on the obtained results it can be concluded that Qui2 and Qui3 can be considered potential modulators of HSA antioxidant activity.

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.

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.

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.

An insight into the interaction between Indisulam and human serum albumin: Spectroscopic method, computer simulation and in vitro cytotoxicity assay

Indisulam (IDM) is a sulfanilamide anticancer agent and has been identified as a molecular glue recently. It shows potential for novel therapies development and brings more hope for curing human diseases. The affinity between molecular glues and plasma protein makes it significant to understand the characteristics of such substances. Therefore, the interaction between IDM and human serum albumin (HSA) was explored through solvent experiments, computer simulation experiments, enzyme kinetics experiments, and cell viability assay. The results revealed that IDM and HSA spontaneously formed stable binary complex with the binding constant of the order 105 M−1. IDM inserted in the site I of HSA, resulting the change in HSA secondary structure. And π electrons in IDM’s benzene rings, as well as van der Waals forces and the H-bond, all helped to stabilize the HSA-IDM complex. The results of molecular dynamic simulation (MD) corresponded with the results from solvent experiment well. For instance, there were approximately 1–5 H-bonds between IDM and HSA. Lys199 and Arg218 were crucial energy contributors in the binding process. The esterase-like activity experiment confirmed that IDM inhibited the catalytic activity of HSA. In addition, cell experiment revealed that serum albumin can significantly reduce the cytotoxicity of IDM towards human embryonic kidney 293T (HEK293T) cells.