Interaction and esterase activity of albumin serums with orphenadrine: A spectroscopic and computational approach

Interaction studies of cannabidiol with human serum albumin by surface plasmon resonance, spectroscopy, and molecular docking

The binding interaction of cannabidiol (CBD) and human serum albumin (HSA) under physiological blood pH conditions (pH 7.4) was conducted by surface plasmon resonance (SPR), fluorescence spectroscopy, UV-Visible spectrophotometry, and molecular docking. The responses from SPR measurement increased with the increase in CBD concentration until equilibrium was reached at the equilibrium dissociation constant (KD) of 9.8 × 10-4 M. The results from fluorescence and UV-Visible spectroscopy showed that CBD bound to HSA at one site in a spontaneous manner to form protein-CBD complexes. The quenching process involved both static and dynamic mechanisms while the static mechanism contributed predominantly to the binding between CBD and albumin. The binding constants estimated from the fluorescence studies were from 0.16 × 103 to 8.10 × 103 M-1, which were calculated at different temperature conditions using Stern-Volmer plots. The thermodynamic parameters demonstrated that the binding interaction was a spontaneous reaction as Gibbs free energy had negative values (ΔG = -12.57 to -23.20 kJ.mol-1). Positive ΔH and ΔS values (ΔH = 2.46 × 105 J.mol-1 and ΔS = 869.81 J.mol-1K-1) indicated that the hydrophobic force was the major binding interaction. Finally, confirmation of the type and extent of interaction was provided using UV-spectroscopy and molecular docking studies. The outcomes of this study are expected to serve as a platform to conduct future studies on binding interactions and toxicological research of CBD.Communicated by Ramaswamy H. Sarma.

Exploring the binding mechanism and esterase-like activity of human serum albumin with levofloxacin and its choline based conjugates: A biophysical approach

Human serum albumin (HSA) effectively binds to compounds having different molecular weight and thus facilitates their distribution in the living organisms. Thus, the binding interactions between a potential antibacterial drug (levofloxacin) and synthesized choline based levofloxacinate conjugates with HSA have been explored. The binding efficacy and mechanism were explored by utilizing different spectroscopic techniques; UV-Visible, steady state fluorescence, time resolved fluorescence and esterase-like activity. The interactions between the ligands and protein were electrostatic as well as hydrophobic in nature. The influence of different ligands having different alkyl chain shows quenching of the fluorescence emission of HSA. The spontaneous binding/quenching of HSA with ligands was static in nature, validated by steady state and time resolved fluorescence spectroscopy. Also, the impact of these ligands on the conformation of the native HSA structure was evaluated by using circular dichroism spectroscopy. In combination to the structural change study, the native protein functionality was observed (in terms of 'esterase-like activity') which has been found to be on lower side due to ligand binding. Further, we have performed the reverse study to check the impact of HSA on the fluorescent fluoroquinolone drug. The current study may prove helpful in elucidating the chemico-biological interactions which may prove useful in the pharmaceuticals, pharmacology, and different biochemistry fields.

Analytical Aspects of ANSA-BSA Association: A Thermodynamic and Conformational Approach

Many studies have demonstrated the manner in which ANS interacts with bovine serum albumin (BSA), although they are limited by the extremely low solubility of dye. The present study demonstrates the binding of ANSA dye with BSA, and since this dye can easily replace ANS, it not only simplifies research but also improves sensor accuracy for serum albumin. A combination of calorimetry and spectroscopy has been employed to establish the thermodynamic signatures associated with the interaction of ANSA with the protein and the consequent conformational changes in the latter. The results of differential scanning calorimetry reveal that when the concentration of ANSA in solution is increased, the thermal stability of the protein increases substantially. The fluorescence data demonstrated a decrease in the binding affinity of ANSA with the protein when pH increased but was unable to identify a change in the mode of interaction of the ligand. ITC has demonstrated that the mode of interaction between ANSA and the protein varies from a single set of binding sites at pH 5 and 7.4 to a sequential binding site at pH 10, emphasizing the potential relevance of protein conformational changes. TCSPC experiments suggested a dynamic type in the presence of ANSA. Molecular docking studies suggest that ANSA molecules are able to find ionic centers in the hydrophobic pockets of BSA. The findings further imply that given its ease of use in experiments, ANSA may be a useful probe for tracking the presence of serum albumin and partially folded protein states.

Insight into the interaction of isochroman with bovine serum albumin: extensive experimental and computational investigations

The way therapeutic compounds interact with serum protein provides valuable information on their pharmacokinetics, toxicity, effectiveness, and even their structural-related information. Isochroman (IC) is a phytochemical compound obtained from the leaves of Olea europea plant. The derivatives of IC have various pharmacological properties including antidepressants, antihistamines, antiinflammation, anticonvulsants, appetite depressants, etc. The binding of small molecules to bovine serum albumin (BSA) is useful to ensure their efficacy. Thus, in this study, we have found out the binding mode of IC with BSA using several spectroscopic and in silico studies. UV and fluorescence spectroscopy suggested the complex formation between IC and BSA with a binding constant of 103 M-1. IC resulted in fluorescence quenching in BSA through static mechanism. The microenvironmental and conformational changes in BSA were confirmed using synchronous and three-dimensional studies. Site marker experiment revealed the IC binding in site-III of BSA. The influence of vitamins, metals and β-cyclodextrin (β-CD) on binding constant of IC-BSA complex was also examined. Circular dichroism spectra showed that α-helical of BSA decreased upon interaction with IC. Computational and experimental results were complimentary with one another and assisted in determining the binding sites, nature of bonds and amino acids included in the IC-BSA complex formation.Communicated by Ramaswamy H. Sarma.

Mechanistic Insights into the Binding of Boar Salivary Pheromones and Putative Molecule with Receptor Proteins: A Comparative Computational Approach

Precise estrus detection in sows is pivotal in increasing the productivity within the pork industry. Sows in estrus exhibit exclusive behaviors when exposed to either a live boar or the steroid pheromones androstenone and androstenol. Recently, a study employing solid-phase microextraction-gas chromatography-mass spectrometry has identified a novel salivary molecule in boars, known as quinoline. This finding has intriguing implications as a synthetic mixture of androstenone, androstenol, and quinoline induces estrus behaviors in sows. Nevertheless, the precise pheromonal characteristics of quinoline remain elusive. In this study, we validate and compare the binding efficiency of androstenone, androstenol, and quinoline with porcine olfactory receptor proteins (odorant-binding protein [OBP], pheromaxein, salivary lipocalin [SAL], and Von Ebner's gland protein [VEGP]) using molecular docking and molecular dynamics simulations. All protein-ligand complexes demonstrated stability, as evidenced by the root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), radius of gyration (Rg), solvent-accessible surface area (SASA), and hydrogen-bond (H-bond) plots. Furthermore, quinoline displayed higher binding efficiency with OBP, measured at -85.456 ± 8.268 kJ/mol, compared to androstenone and androstenol, as determined by molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) calculations. Conversely, quinoline exhibited a lower binding efficacy when interacting with SAL, pheromaxein, and VEGP compared to androstenone and androstenol. These findings, in part, suggest the binding possibility of quinoline with carrier proteins and warrant further investigation to support the role of quinoline in porcine chemical communication.

Inhibition of toll-like receptor 4 activation by apigenin and chrysin via competition for sites and conformational changes

The activation of toll-like receptor 4 (TLR4) signaling is crucial for initiating and coordinating the immune response against infections, and is proved as a vital target for inflammatory diseases. Herein, TLR4 with sufficient amount and functional activity was generated by heterologous expression and used to investigate the mechanism of apigenin (Api)/chrysin (Chr) inhibition of TLR4 activation. The results demonstrated that Api/Chr exhibited a strong fluorescence quenching effect through a static quenching and a high binding affinity (Ka > 105 L·mol-1) with TLR4, indicating the potential of Api/Chr as a TLR4 inhibitor. Additionally, the binding of Api/Chr induced a loose and unstable conformation of TLR4 with evidence like the decreased hydrophobicity of the tryptophan microenvironment, decreased α-helix content and increased free sulfhydryl content, resulting in reduced stability of the TLR4. The computer simulations revealed that Api/Chr occupied the myeloid differentiation factor 2 (MD-2) binding region, preventing MD-2 from binding to TLR4. Furthermore, the accuracy of the binding site between Api/Chr and TLR4 was confirmed through genetic mutations. Overall, the mechanism by which Api/Chr inhibited TLR4 activation was elucidated at the macroscopic and molecular levels, providing the worthful information concerning the future therapeutic application of Api/Chr as a natural TLR4 inhibitor.

Exploring the effect of surfactants on the interactions of manganese dioxide nanoparticles with biomolecules

Interactions of manganese dioxide nanoparticles (MnO2 NPs) with vital biomolecules namely deoxyribonucleic acid (DNA) and serum albumin (BSA) have been studied in association with different surfactants by using fluorescence (steady state, synchronous and 3D), UV-visible, resonance light scattering (RLS), dynamic light scattering (DLS), and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The esterase activity of serum albumin was tested in associations with MnO2 NPs and surfactants. The antioxidant potential of prepared NPs was also evaluated (DPPH method). Gel electrophoresis was carried out to analyze the effect of MnO2 NPs and surfactants on DNA. Presence of CTAB, Tween 20, DTAB and Tween 80 enhanced nanoparticle-protein binding. Tween 20 based nanoparticle systems showed long-term stability and biocompatibility. The quenching of BSA fluorescence emission in presence of MnO2 NPs alone and along with Tween 20 revealed stronger association of nanoparticles with proteins. Enhancement in the esterase activity (BSA) was observed in the presence of Tween 20. Furthermore, radical scavenging activity showed highest antioxidant potential in presence of Tween 20. The enthalpy and entropy assessment for protein-NPs association showed the predominance of Vander Waals interactions and hydrogen bonding. The synchronous fluorescence analysis highlighted the involvement of tryptophan (Trp) in the MnO2 NPs-protein interactions. The study evaluates the influence of surfactant on the associations of MnO2 NPs with the essential biomolecules. The findings can be crucially utilized in designing biocompatible MnO2 formulations for long term applications.Communicated by Ramaswamy H. Sarma.

Elucidating the significance of molecular interaction between sulphur doped zinc oxide nanoparticles and serum albumin using multispectroscopic approach

Ingenious nanomaterials with improved biocompatibility and multifunctional properties are gaining vital significance in biomedical applications, including advanced drug delivery and nanotheranostics. In a biological system, these nanoparticles interact with serum proteins forming a dynamic corona that affects their biological or toxicological properties producing undesirable effects. Thus, the current study focuses on the synthesis of sulphur-doped zinc oxide nanoparticles (ZnO/S NPs) and characterizing their mechanism of interaction with serum proteins using multispectroscopic approach. ZnO/S NPs were synthesized by employing a co-precipitation approach and characterized using various analytical techniques. The results of interaction studies demonstrated that ZnO/S NPs interact with serum albumins via the static quenching process. Analysis of thermodynamic parameters (ΔG, ΔH and ΔS) revealed that the binding process is spontaneous, exothermic and van der Waals force or hydrogen bonding plays a major role. The interaction of ZnO/S NPs with tyrosine residue in bovine serum albumin was established by synchronous fluorescence spectroscopy. In addition, the results of UV-visible, circular dichroism, Fourier transform infrared, Forster's resonance energy transfer theory and dynamic light scattering spectroscopic studies revealed that the ZnO/S NPs interact with albumin by inducing the conformational changes in secondary structure and reducing the α-helix content.

Investigation on the binding behavior of human α1-acid glycoprotein with Janus Kinase inhibitor baricitinib: Multi-spectroscopic and molecular simulation methodologies

Baricitinib is a Janus Kinase (JAK) inhibitor that is primarily used to treat moderately to severely active rheumatoid arthritis in adults and has recently been reported for the treatment of patients with severe COVID-19. This paper describes the investigation of the binding behavior of baricitinib to human α1-acid glycoprotein (HAG) employing a variety of spectroscopic techniques, molecular docking and dynamics simulations. Baricitinib can quench the fluorescence from amino acids in HAG through a mix of dynamic and static quenching, according to steady-state fluorescence and UV spectra observations, but it is mainly static quenching at low concentration. The binding constant (K_b) of baricitinib to HAG at 298 K was at the level of 10⁴ M^-1, indicating a moderate affinity of baricitinib to HAG. Hydrogen bonding and hydrophobic interactions conducted the main effect, according to thermodynamic characteristics, competition studies between ANS and sucrose, and molecular dynamics simulations. For the change in HAG conformation, the results of multiple spectra showed that baricitinib was able to alter the secondary structure of HAG as well as increase the polarity of the microenvironment around the Trp amino acid. Furthermore, the binding behavior of baricitinib to HAG was investigated by molecular docking and molecular dynamics simulations, which validated experimental results. Also explored is the influence of K⁺, Co²⁺, Ni²⁺, Ca²⁺, Fe³⁺, Zn²⁺, Mg²⁺ and Cu²⁺plasma on binding affinity.

Synthetic Transformation of 2-{2-Fluoro[1,1'-biphenyl]-4-yl} Propanoic Acid into Hydrazide-Hydrazone Derivatives: In Vitro Urease Inhibition and In Silico Study

In the present study, 28 acyl hydrazones (4-31) of flurbiprofen were synthesized in good to excellent yield by reacting different aromatic aldehydes with the commercially available drug flurbiprofen. The compounds were deduced with the help of different spectroscopic techniques like ¹H-NMR and HREI-MS and finally evaluated for in vitro urease inhibitory activity. All of the synthesized products demonstrated good inhibitory activities in the range of IC₅₀ = 18.92 ± 0.61 to 90.75 ± 7.71 μM as compared to standard thiourea (IC₅₀ = 21.14 ± 0.42 μM). Compound 30 was found to be the most active among the series better than the standard thiourea. A structure-activity relationship (SAR) study revealed that the presence of electron-donating groups on the phenyl ring plays a prominent role in the inhibition of the urease enzyme. Moreover, in silico molecular modeling analysis was carried out to study the effect of substituents in synthesized derivatives on the binding interactions with the urease enzyme.

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 (K_a) 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.

A multi-spectroscopic and computational simulations study to delineate the interaction between antimalarial drug hydroxychloroquine and human serum albumin

Hydroxychloroquine (HCQ), a quinoline based medicine is commonly used to treat malaria and autoimmune diseases such as rheumatoid arthritis. Since, human serum albumin (HSA) serves as excipient for vaccines or therapeutic protein drugs, it is important to understand the effect of HCQ on the structural stability of HSA. In this study, the binding mechanism of HCQ and their effect on stability of HSA have been studied using various spectroscopic techniques and molecular dynamic simulation. The UV-VIS results confirmed the strong binding of HCQ with HSA. The calculated thermodynamics parameters confirmed that binding is spontaneous in nature and van der Waals forces and hydrogen bonding are involved in the binding system which is also confirmed by molecular docking results. The steady-state fluorescence confirms the static quenching mechanism in the interaction system, which was further validated by time-resolved fluorescence. The synchronous fluorescence confirmed the more abrupt binding of HCQ with tryptophan residue of HSA compared to Tyr residue of HSA. Isothermal titration calorimetry (ITC) was done to validate the thermodynamics parameters of HSA-HCQ complex in one experiment, supporting the values obtained from the spectroscopic techniques. The circular dichroism (CD) demonstrated that the HCQ affected the secondary structure of HSA protein by reducing their α-helical content. The docking and molecular dynamic simulation results further helped in understanding the effect of HCQ on conformational changes of HSA. Overall, present work defined the physicochemical properties and interaction mechanism of HCQ with HSA that have extensively been elucidated by both in vitro and in silico approaches.

Chebulinic and chebulagic acid binding with serum proteins: biophysical and molecular docking approach

Chebulinic acid (CHN) and chebulagic acid (CHG) have been known for centuries for their anti-cancer, anti-diabetes, HIV and anti-inflammatory properties. In this study, the interaction of these phytochemicals CHN/CHG, with the two major transport proteins for various drugs, human serum albumin (HSA) and α-1-acid glycoprotein (AGP), was unraveled by using several spectroscopic techniques and computational methods. The binding of CHN/CHG quenches the HSA/AGP fluorescence intensities, and also these phytochemicals are bound strongly to HSA/AGP proteins. An apparent decrease in fluorescence intensities of CHN/CHG-HSA and CHN/CHG-AGP complex showed the static mode of fluorescence quenching. Furthermore, the intrinsic fluorescence and using site-specific markers ibuprofen competing with these molecules, thereby replacing it in the binding site of subdomain IIIA. The computational methods substantiated the experimental findings, revealing that CHN interacted with Lys414A, Glu492A, Glu492A and Lys413A residues of subdomain IIIA of HSA and for CHG showed the interaction with Lys545A and Lys413A residues of subdomain IIIA of HSA. Fluorescence and surface plasmon resonance data unveiled a previously unreported binding event between CHN/CHG and HSA; the determined binding affinities of both compounds were slightly higher for HSA than AGP. A change in functionality of protein confirmed the esterase-like activity of HSA in the presence of CHG/CHN upon binding with CHG/CHN. Displacement and circular dichroism (CD) experiments analysis showed that the two CHN/CHG and binding specifically to IIIA subdomain on HSA results in the conformational changes in the HSA. Thus, CD revealed a few conformational changes in HSA due to CHN/CHG. The binding of these two phytochemicals to the plasma proteins would give a path to develop new inspired drug molecules for chronic diseases.Communicated by Ramaswamy H. Sarma.

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.

Visible-Light-Prompted Synthesis and Binding Studies of 5,6-Dihydroimidazo[2,1-b]thiazoles with BSA and DNA Using Biophysical and Computational Methods

Fused heterocyclic systems containing a bridgehead nitrogen atom have emerged as imperative pharmacophores in the design and development of new drugs. Among these heterocyclic moieties, the imidazothiazole scaffold has long been used in medicinal chemistry for the treatment of various diseases. In this study, we have established a simplistic and environmentally safe regioselective protocol for the synthesis of 5,6-dihydroimidazo[2,1-b]thiazole derivatives from easily available reactants. The reaction proceeds through in situ formation of the α-bromodiketones ensuing trap with imidazolidine-2-thione to provide these versatile bicyclic heterocycles in excellent yields. The synthesized compounds were screened through the molecular docking approach for the most stable complex formation with bovine serum albumin (BSA) and calf thymus deoxyribonucleic acid (ctDNA). The selected compound was further studied using ex vivo binding studies, which revealed moderate interactions with BSA and ctDNA. The binding studies were performed using biophysical approaches including UV-visible spectroscopy, steady-state fluorescence, circular dichroism (CD), and viscosity parameters.