Subdomain IIIA Research Articles

Toxicity Study and Binding Analysis of Newly Synthesized Antifungal N-(4-aryl/cyclohexyl)-2-(pyridine-4-yl carbonyl) hydrazinecarbothioamide Derivative with Bovine Serum Albumin

The presence of the p-aryl/cyclohexyl ring in the N-(4-aryl/cyclohexyl)-2-(pyridine-4-yl carbonyl) hydrazine carbothioamide derivative (2C) is reported to enhance the antifungal properties when compared to those of itraconazole. Serum albumins present in plasma bind and transport ligands, including pharmaceuticals. This study explored 2C interactions with BSA using spectroscopic methods such as fluorescence and UV-visible spectroscopy. In order to acquire a deeper comprehension of how BSA interacts with binding pockets, a molecular docking study was carried out. The fluorescence of BSA was quenched by 2C via a static quenching mechanism since a decrease in quenching constants was observed from 1.27 × 105 to 1.14 × 105. Thermodynamic parameters indicated hydrogen and van der Waals forces responsible for the BSA-2C complex formation with binding constants ranging between 2.91 × 105 and 1.29 × 105, which suggest a strong binding interaction. Site marker studies displayed that 2C binds to BSA's subdomains IIA and IIIA. Molecular docking studies were conducted to further comprehend the molecular mechanism of the BSA-2C interaction. The toxicity of 2C was predicted by Derek Nexus software. Human and mammalian carcinogenicity and skin sensitivity predictions were associated with a reasoning level of equivocal, inferring 2C to be a potential drug candidate.

Biophysical and molecular modelling analysis of the binding of β-resorcylic acid with bovine serum albumin

The bovine serum albumin (BSA) is a model carrier protein that transports and deposits the various endogenous and exogenous ligands in the body. β-resorcylic acid (BR) is a phyto-phenolic molecule mainly used in the food industry because of its antibacterial, flavouring and preservative nature. The interactions of small ligand molecules with proteins are of great importance for researchers from the pharmacology perspective. This article explains the mechanism of binding of BR with BSA with the help of multi-spectroscopic approaches and molecular modelling. The UV absorption and fluorescence spectroscopy affirmed the formation of BSA-BR complex. The thermodynamic studies confirmed the nature of the reaction to be spontaneous and exothermic, and the stabilisation of the complex by van der Waals interactions and hydrogen bonding. The energy transfer was found to occur with a high probability. BR induced the microenvironmental and conformational alterations BSA as revealed by synchronous spectra, 3D fluorescence maps, circular dichroism (CD), resonance-enhanced Rayleigh scattering (RRS), red edge excitation shift ( REES) and Fourier transform infrared (FT-IR). The β-cyclodextrin (β-cd), metals and vitamins largely influenced the BR-BSA binding strength. Competitive displacement assays further elucidated the BR binds to BSA at subdomain IIIA (site II). Molecular docking and simulations computationally validated the results of the wet lab experiments. • The BSA-BR complex was affirmed with 1:1 binding stoichiometry and quenching in static mode. • The binding reaction was spontaneous and exothermic, involving van der Waals forces and hydrogen bonding. • The binding strength was found to change in the presence of metal ions, vitamins and β-cd. • BR binds with BSA near subdomain IIIA (site II). • BR induced minor changes in the conformation and microenvironment in BSA.

Spectroscopic and computational study of the interaction of Pt(II) pyrrole-imine chelates with human serum albumin.

Three bis(pyrrolide-imine) Pt(II) chelates were synthesised and characterized with different bridging alkyl groups, specifically 2-hydroxypropyl (1), 2,2-dimethylpropyl (2), and 1,2-(S,S)-(+)-cyclohexyl (3). Novel compounds 1 and 2 were analysed by single-crystal X-ray diffraction (space group P1̄). The asymmetric unit of 1 comprises three independent molecules linked by hydrogen bonds involving the OH groups, forming a trimeric supramolecular structure. The Pt(II) chelates were reacted with human serum albumin (HSA) to investigate how the ligand bound to the Pt(II) ion influences the compound's affinity for HSA. Fluorescence quenching data obtained for native HSA and HSA bound to site-specific probes (warfarin, subdomain IIA; ibuprofen, subdomain IIIA) indicated that the three Pt(II) chelates bind close enough (within ∼30 Å) to Trp-214 to quench its intrinsic fluorescence. The bimolecular quenching constant (kq) was 103-104 -fold higher than the maximum diffusion-controlled collision constant in water (1010 M s-1) at 310 K, while the affinity constants, Ka, ranged from ∼5 × 103 to ∼5 × 105 at 310 K, and followed the order 1 > 3 > 2. The reactions of 1 and 3 with HSA were enthalpically driven, while that for 2 was entropically driven. Macromolecular docking simulations (Glide XP) and binding site specificity assays employing site-specific probes and UV-vis CD spectroscopy indicated that 1 and 2 target Sudlow's site II in subdomain IIIA, minimally perturbing the tertiary structure of the protein. Well-resolved induced CD signals from 1 and 2 bound to HSA in subdomain IIIA were adequately simulated by hybrid QM:MM TD-DFT methods. We conclude that the structure of the bis(pyrrolide-imine) Pt(II) chelate measurably affects its uptake by HSA without detectable decomposition or demetallation. Such compounds could thus serve as metallodrug candidates capable of utilising an HSA-mediated cellular uptake pathway.

Effects of different fatty acid ligands on the host-guest interaction of astaxanthin-bovine serum albumin: Thermodynamical analysis, binding site identification, and in vivo antioxidant evaluation

The multi-ligand binding properties of proteins make the introduction of small-molecule ligands an effective approach through which to improve the biological functions of protein-based carriers. In this study, the effect of fatty acids (FAs) as functional ligands on the self-assembly of astaxanthin (ASTA) and bovine serum albumin (BSA) and the in vivo antioxidant properties of their ternary ligand complexes were investigated. As the seven common dietary FAs, lauric acid (LAA), palmitic acid (PA), stearic acid (SA), oleic acid (OA), linoleic acid (LA), arachidonic acid (AA) and docosahexaenoic acid (DHA) were selected. The results indicated that, with the exception of DHA, six of these FAs were able to change the conformation of BSA while simultaneously improving its hydrophilicity. The introduction of FA ligands did not affect the binding mode (static quenching) or the type of intermolecular forces (hydrogen bonding and van der Waals forces) between ASTA and BSA. However, the involvement of FA ligands could cause the dominant binding domain of ASTA in BSA to migrate from the initial subdomain IIIA (site II) to subdomain IIA (site I). Simultaneously, the altered binding affinity between ASTA and BSA was also observed, and the effect of unsaturated FAs (except DHA) was more pronounced than that of saturated ones. As expected, compared with the ASTA-BSA binary complexes, the ASTA-FA-BSA terpolymer performed an increased total antioxidant capacity in vivo as well as an improved antioxidant protein expression. This study provides a new strategy for the efficient delivery of carotenoids using proteins and function ligands. • Different FA ligands altered the conformation of BSA to different degrees. • The effect of different FA ligands on the hydrophilicity of BSA was variable. • The FA ligands did not affect the binding mode between astaxanthin and BSA. • The FA ligands changed the dominant binding domain of astaxanthin in BSA. • The FA ligands improved the in vivo anti-oxidative activity of astaxanthin.

Molecular spectroscopic and docking analysis of the interaction of fluorescent thiadicarbocyanine dye with biomolecule bovine serum albumin

Binding studies of the water-soluble thiadicarbocyanine dye 3,3’-diethylthiadicarbocyanine acetate (DTC) with bovine serum albumin (BSA) were examined under physiological conditions using spectroscopic techniques like fluorescence, UV-Visible, circular dichroism (CD), FT-IR and molecular docking methods. Compiled experimental results envisage that DTC quench the fluorescence intensity of BSA. The increasing binding constants (K) were found to be in the order of 103 Mol−1 as a function of temperature, as calculated from the fluorescence quenching data. The quenching mechanism, thermodynamic parameters (ΔH0, ΔS0 and ΔG0) and the number of binding sites have been explored. CD values showed that the secondary structure of the BSA has been altered upon binding to DTC. Displacement experiments were carried out with different site probes to find out the binding site of DTC on BSA and it was found that binding interaction at site II of sub-domain IIIA. The interference of common metal ions on the interaction of DTC with BSA has also been studied. The experimental data exhibit that DTC interacts with BSA by hydrophobic forces. The experimental findings from BSA binding studies were validated by using in silico molecular docking technique. The results of the investigations were accurately supported by studies on molecular docking. The optimal shape of the molecular probe demonstrated the affinity as a free binding energy release of −7.37 Kcal/mol. The present research report endeavors to the approachable nature of water-soluble DTC dye and paves way for targeted biological interactions. Communicated by Ramaswamy H. Sarma

Characterization of Climbazole–Bovine serum albumin interaction by experimental and in silico approaches

Interactive association of an antifungal drug, climbazole (CBZ) with the carrier protein in bovine circulation, bovine serum albumin (BSA) was explored by fluorescence and absorption spectroscopy along with in silico techniques. The fluorescence and absorption spectral alterations of the protein upon addition of CBZ affirmed the complex foration between CBZ and BSA. The inverse temperature dependence behaviour of the KSV values as well as the hyperchromic result of the protein’s absorption signals characterized CBZ-triggered quenching of BSA fluorescence as the static quenching. A weak binding affinity (Ka = 3.12–1.90-× 103 M−1) was reported towards the CBZ−BSA association process. Interpretation of thermodynamic data (entropy change = +14.68 J mol−1 K−1 and enthalpy change = –15.07 kJ mol−1) and in silico analyses anticipated that hydrophobic forces, van der Waals forces and hydrogen bonds were the key intermolecular forces in the complex stabilization. Inclusion of CBZ to BSA produced microenvironmental perturbations around Tyr and Trp residues, and also significantly defended temperature-induced destabilization of BSA. The binding locus of CBZ was detected in the proximity of Sudlow’s sites I (subdomain IIA) and II (subdomain IIIA) of BSA, exhibiting greater preference towards site II, as revealed by competitive site-marker displacement investigations and in silico analysis. The stability of the CBZ–BSA complex was further validated by the molecular dynamics simulation assessments.

Fluorescence signal switching of novel pyrenyl probe for the detection of bovine serum albumin

In this study, a specific recognition element tagged with a fluorescent dye was developed for the detection of binding interaction with bovine serum albumin (BSA). A novel pyrenyl probe, ibuprofen-1-pyrenemethylamide (Py-IB), was designed and synthesized by attaching ibuprofen to the pyrenyl chromophore. The ibuprofen-derived pyrenyl probe caused switching of emissive signals of Py-IB from pyrene excimer to excited monomer upon binding to BSA. This switching behavior of Py-IB was not observed upon its binding to other tested proteins, such as lysozyme or lactoglobulin, indicating high selectivity and sensitivity of Py-IB to BSA. Visual detection under UV light of Py-IB/BSA solution showed the switching back from the monomer form to the excimer form in the presence of ibuprofen, indicating the binding competition of ibuprofen at Py-IB binding site. Photocleavage of BSA by Py-IB was achieved by activation of Py-IB/BSA solution with light at 346 nm, in the presence of cobalt (III) hexamine trichloride (CoHA) as an electron acceptor. Two new product bands were observed, and the cleavage site possibly occurred between Arg409 – Tyr410. Molecular docking study revealed a Py-IB binding site at subdomain IIIA on BSA, which confirmed the results from competitive study, with the lowest binding free energy of −10.17 kcal/mol. The studies showed that Py-IB was located in close proximity to hydrophobic residues in the binding pocket. The fluorescence signal switching of ligand upon binding to its target protein can be an easy way and very useful for monitoring ligand-biomolecular interaction.

Effects of Heme Site (FA1) Ligands Bilirubin, Biliverdin, Hemin, and Methyl Orange on the Albumin Binding of Site I Marker Warfarin: Complex Allosteric Interactions.

Human serum albumin (HSA) is the most abundant plasma protein in circulation. The three most important drug-binding sites on HSA are Sudlow's Site I (subdomain IIA), Sudlow's Site II (subdomain IIIA), and Heme site (subdomain IB). Heme site and Site I are allosterically coupled; therefore, their ligands may be able to allosterically modulate the binding affinity of each other. In this study, the effects of four Heme site ligands (bilirubin, biliverdin, hemin, and methyl orange) on the interaction of the Site I ligand warfarin with HSA were tested, employing fluorescence spectroscopic, ultrafiltration, and ultracentrifugation studies. Our major results/conclusions are the following. (1) Quenching studies indicated no relevant interaction, while the other fluorescent model used suggested that each Heme site ligand strongly decreases the albumin binding of warfarin. (2) Ultrafiltration and ultracentrifugation studies demonstrated the complex modulation of warfarin-HSA interaction by the different Heme site markers; for example, bilirubin strongly decreased while methyl orange considerably increased the bound fraction of warfarin. (3) Fluorescence spectroscopic studies showed misleading results in these diligand-albumin interactions. (4) Different Heme site ligands can increase or decrease the albumin binding of warfarin and the outcome can even be concentration dependent (e.g., biliverdin and hemin).

Molecular interactions between bovine serum albumin (BSA) and trihalophenol: Insights from spectroscopic, calorimetric and molecular modeling studies

The issue of disinfection byproducts (DBPs) in the water has received critical attention due to the health effects on humans. In the water environment, interactions between bovine serum albumins (BSA), the most abundant water-soluble protein, and DBPs unavoidably occur. In this study, comparative binding interactions of two aromatic DBPs − 2,4,6-trichlorophenol (TCP) and 2,4,6-tribromophenol (TBP) with BSA were investigated systematically utilizing fluorescence spectrometry, UV absorption spectrometry, isothermal titration calorimetry and molecular docking approach. The fluorescence quenching results indicated that TCP/TBP could quench the endogenous fluorescence of BSA through static quenching mechanisms, and TBP showed a more substantial quenching effect. The binding constants were determined for TCP-BSA (3.638 × 105 L/mol, 303 K) and TBP-BSA (6.394 × 105 L/mol, 303 K) complexes, with TBP showing higher binding affinity than TCP. The thermodynamic study and docking analysis suggested that hydrogen bonding and van der Waals forces were the primary interaction forces. Both of TCP and TBP were located in the subdomain IIIA of BSA, and TBP could form more stable complex than TCP. The results of the present study contributed valuable information on the environmental behaviors of halophenols in water environment from perspectives of binding with BSA.

Investigation of the Interaction between Human Serum Albumin and Branched Short-Chain Perfluoroalkyl Compounds.

The current trend dealing with the production of per- and polyfluoroalkyl substances (PFASs) involves the shifting toward branched short-chain fluorinated compounds known as new-generation PFASs. A key aspect to be clarified, to address the adverse health effects associated with the exposure to PFASs, is their binding mode to human serum albumin (hSA), the most abundant protein in plasma. In this study, we investigated the interaction between hSA and two representative branched short-chain PFASs, namely, HPFO-DA and C6O4. In-solution studies revealed that both compounds bind hSA with affinities and stoichiometries lower than that of the legacy long-chain perfluoroalkyl compound PFOA. Competition experiments using hSA-binding drugs with known site-selectivity revealed that both HPFO-DA and C6O4 bound to pockets located in subdomain IIIA. The crystal structure of hSA in complex with HPFO-DA unveiled the presence of two binding sites. The characterization and direct comparison of hSA interactions with new-generation PFASs may be key elements for the understanding of the toxicological impact of these compounds.

Elucidation of the binding mechanism of astragaloside IV derivative with human serum albumin and its cardiotoxicity in zebrafish embryos.

LS-102 is a new derivative of astragaloside IV (AGS IV) that has been shown to possess potentially significant cardioprotective effects. However, there are no reports concerning its interaction with human serum albumin (HSA) and toxicology in vertebrates. The present investigation was undertaken to characterize the interaction of AGS IV and LS-102 with HSA using equilibrium dialysis and UHPLC-MS/MS methods, along with computational methods. Notably, the effects of AGS IV and LS-102 were studied in vivo using the zebrafish embryo model. Markers related to embryonic cardiotoxicity and thrombosis were evaluated. We showed that the plasma protein binding rate of AGS IV (94.04%–97.42%) was significantly higher than that of LS-102 (66.90%–69.35%). Through site marker competitive experiments and molecular docking, we found that AGS IV and LS-102 were located at the interface of subdomains IIA and IIIA, but the site I might be the primary binding site. Molecular dynamics revealed that AGS IV showed a higher binding free energy mainly due to the stronger hydrophobic and hydrogen bonding interactions. Moreover, the secondary structure implied no obvious effect on the protein structure and conformation during the binding of LS-102. LS-102 significantly ameliorated the astramizole-induced heart rate slowing, increased SV-BA spacing, and prevented arachidonic acid-induced thrombosis in zebrafish. To our knowledge, we are the first to reveal that LS-102 binds to HSA with reversible and moderate affinity, indicating its easy diffusion from the circulatory system to the target tissue, thereby providing significant insights into its pharmacokinetic and pharmacodynamic properties when spread in the human body. Our results also provide a reference for the rational clinical application of LS-102 in the cardiovascular field.

Spectrofluorometric and computational approaches for the interaction studies of aclonifen and bifenox with human serum albumin

Interaction of two broadly used herbicides, aclonifen (ACF) and bifenox (BIF) with the major transporter in human circulation, human serum albumin (HSA) were examined using fluorescence and absorption spectral measurements combined with in silico analyses. Assessment of the fluorescence and absorption spectral results affirmed the complexation between ACF/BIF and HSA. Increase in the KSV value with temperature characterized the ACF/BIF-induced quenching of the protein fluorescence as dynamic quenching. The moderate binding affinities (Kf = 1.74×104 – 1.95×106 M−1 for ACF–HSA complex; Kf = 2.00×103 – 1.02×106 M−1 for BIF–HSA complex) were pointed out between ACF/BIF and HSA, showing a relatively higher binding constant values with increasing temperatures. Quantitative evaluation of thermodynamic data (ΔS = +0.86 kJ mol−1 K−1 and ΔH = +225.43 kJ mol−1 for ACF–HSA complex; ΔS = +1.11 kJ mol−1 K−1 and ΔH = +304.63 kJ mol−1 for BIF–HSA complex) predicted the contribution of hydrophobic interactions in the ACF–HSA and BIF–HSA association processes, which were well supported by our molecular docking results. In silico analyses were made to acquire insight details into the ACF and BIF binding to HSA at the binding sites and suggested the locations of ACF and BIF binding sites as both subdomain IIA (site I) and subdomain IIIA (site II) of HSA, showing more preference toward site I.

Potential toxic effects of sulfonamides antibiotics: Molecular modeling, multiple-spectroscopy techniques and density functional theory calculations

Sulfonamide antibiotics (SAs) are widely used in medicine, animal husbandry and aquaculture, and excessive intake of SAs may pose potential toxicity to organisms. The toxicological mechanisms of two classical SAs, sulfamerazine (SMR) and sulfamethoxazole (SMT), were investigated by molecular docking, DFT and multi-spectroscopic techniques using HSA and BSA as model proteins. The quenching of HSA/BSA endogenous fluorescence by SMR was higher than that by SMT due to the stronger binding effect of the pyrimidine ring on HSA/BSA compared to the oxazole ring, and that result was consistent with that predicted by DFT calculations. Thermodynamic parameters show that the binding of SAs to HSA/BSA is an exothermic process that proceeds spontaneously (ΔG < 0). Marker competition experiments illustrate that the binding site of SMR/SMT on serum albumin is located in subdomain IIIA. The combination of SAs and HSA/BSA is mainly realized by hydrogen bond and hydrophobic interaction, and the concept is also supported by molecular modeling. The reduced α-helix content of HSA/BSA induced by SMR/SMT indicates a greater stretching of the protein α-helix structure of the SMR/SMT-HSA/BSA. The results could provide useful toxicological information on the hazards of SAs in response to growing concern that SAs may pose a toxic threat to organisms.

A molecular bridge-like binding mode of buspirone to BSA: Multispectroscopic and molecular docking investigation

• Binding interaction of buspirone with BSA has been studied. • Flexibility of buspirone played a critical role in binding process to BSA with change in the structure. • Buspirone simultaneously bound on sub domain IIIA and IIA of BSA. • Fluorescence of BSA quenched by buspirone. • Molecular docking results were explained, conventional hydrogen bond, carbon-hydrogen bonds, van-der-Waals forces and alkyl interactions were found in BSA-Buspirone complex. The anxiolytic psychotropic drug buspirone from the azapirone class of tranquilizer treats seizures, panic disorder, and anxiety disorder. The buspirone's binding interaction to bovine serum albumin (BSA) was investigated using UV-visible, fluorescence spectroscoy with molecular docking methods. Findings are indicative that buspirone is bound simultaneously on two subdomains IIA and IIIA of albumin through conventional hydrogen bond, carbon-hydrogen bonds, van-der-Waals forces and alkyl interactions. The binding sites ( n ) and binding constant ( K b ) of the buspirone-BSA complex were about 2 and 1.64217×10 5 M −1 at 298 K. The buspirone binding to BSA was spontaneous and enthalpy-driven. The buspirone's binding interaction with BSA brings about a minor conformation change in BSA and apparent conformation change in buspirone, suggesting that the flexibility of buspirone also played a role in the cumulative stability of the buspirone-BSA complex.

Mitigation of ribose and glyoxal induced glycation, AGEs formation and aggregation of human serum albumin by citrus fruit phytochemicals naringin and naringenin: An insight into their mechanism of action

Human serum albumin (HSA) being the most prevalent protein in the plasma is extremely vulnerable to glycation. Two flavonoids naringin and naringenin were tested for their effects on the glyoxal and ribose-induced glycation, advanced glycation end products (AGEs) and fibril formation of HSA. The inhibition of the formation of AGEs in the presence of both flavonoids demonstrated their antiglycating properties. The presence of fibrillar aggregates in the glyoxal and ribose modified HSA were also decreased by naringin and naringenin. The explanation for naringenin's stronger antiglycating potential than naringin was further investigated by examining their interactions with HSA. H-bonding and other non-covalent interactions with flavonoids stabilize HSA. Interactions of lysine and arginine residues with flavonoids may prevent the residues from getting modified during glycation process. Naringenin bind to both subdomains IIA and IIIA of HSA, protecting more residues than naringin, which only binds to subdomain IIA, may describe the higher inhibitory activity of naringenin.

Binding of the B-Raf Inhibitors Dabrafenib and Vemurafenib to Human Serum Albumin: A Biophysical and Molecular Simulation Study.

Drug binding to human serum albumin (HSA) significantly affects in vivo drug transport and biological activity. To gain insight into the binding mechanism of the two B-Raf tyrosine kinase inhibitors dabrafenib and vemurafenib to HSA, in this work, we adopted a combined strategy based on fluorescence spectroscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and molecular simulations. Both anticancer drugs are found to bind spontaneously and with a 1:1 stoichiometry within the same binding pocket, located in Sudlow's site II (subdomain IIIA) of the protein with comparable affinity and without substantially perturbing the protein secondary structure. However, the nature of each drug-protein interactions is distinct: whereas the formation of the dabrafenib/HSA complex is more entropically driven, the formation of the alternative vemurafenib/HSA assembly is prevalently enthalpic in nature. Kinetic analysis also indicates that the association rate is similar for the two drugs, whereas the residence time of vemurafenib within the HSA binding pocket is somewhat higher than that determined for the alternative B-Raf inhibitor.

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

Effects of Myristate on the Induced Circular Dichroism Spectra of Aripiprazole Bound to Human Serum Albumin: A Structural-Chemical Investigation.

The effects of myristate on the induced circular dichroism spectra of aripiprazole (ARP) bound to human serum albumin (HSA) were investigated. High concentrations of myristate reversed the Cotton effects induced in the ARP–HSA system. The observed ellipticities increased with increasing drug concentration up to an ARP-to-HSA molar ratio of 1:1 and then decreased, indicating that the extrinsic Cotton effects were generated by the binding of ARP molecules to the high- and low-affinity sites in HSA. The data for the concentration of free ARP show that myristate displaces ARP molecules from HSA. Moreover, the free fractions of ARP in the ARP–HSA–myristate system increased significantly when adding fusidic acid, a subdomain IB ligand. In the crystal structure of the ARP–HSA–myristate ternary complex, one ARP molecule is bound to subdomain IB, and the interaction between the carbonyl group of ARP and the aromatic ring of Tyr138 in subdomain IB is essential for binding to occur. Meanwhile, the ARP molecule in the ARP–HSA binary complex structure is bound only to subdomain IIIA. Consequently, the inversion in the extrinsic Cotton effects in the ARP–HSA system can be attributed to the modification of the geometry within the binding pocket, in addition to the transfer of ARP from subdomain IIIA to subdomain IB through the displacement as a result of the binding of myristate to subdomain IIIA.

Probing the potential toxicity by characterizing the binding mechanism of sodium dehydroacetate to human serum albumin.

Sodium dehydroacetate (DHA-S) is a common food additive, which can combine with serum proteins in the plasma, but the interaction mechanism between DHA-S and human serum albumin (HSA) is unclear. In this study, multiple spectroscopy techniques, isothermal titration calorimetry (ITC), molecular docking and esterase activity test were employed to investigate the interaction mechanism of DHA-S and HSA. A DHA-S-HSA complex was formed and the structure of HSA were altered by DHA-S. Since DHA-S changed the tight structure of the hydrophobic subdomain IIA where tryptophan (Trp) was placed, the hydrophobicity of the microenvironment of HSA was enhanced. With the addition of DHA-S, the skeleton structure of HSA became loose and the solvent shell on the HSA surface was destroyed. DHA-S altered the secondary structure of HSA, resulting in the decreased α-helix and increased β-sheet contents. The interaction was exothermic and spontaneous driven by van der Waals and hydrogen bonding. DHA-S inhibited the esterase activity of HSA. Molecular docking demonstrated that the binding site of DHA-S on HSA located at the cavity of subdomains IIA and IIIA, but the amino acids related to esterase activity of HSA were not in the binding pocket, indicating that the mechanism by which DHA-S inhibited HSA esterase activity was the change in protein structure. This study illustrated that DHA-S interacted with HSA and the structure and function of HSA were affected by DHA-S. This research could help to understand the toxicity of DHA-S and provide basic data for safe use of food additives. © 2021 Society of Chemical Industry.

Combined spectroscopic and computational approaches for the recognition of bioactive flavonoid 6-hydroxyflavone by human serum albumin: Effects of non-enzymatic glycation in the binding

Serum albumin's stability and function are influenced by several structural changes. Non-enzymatic glycation (NEG) is one of the mechanisms which impairs and changes the physiological function of serum albumins. Advanced glycation end products (AGEs) are produced in long-term hyperglycamia and are responsible for structural cell and tissue failures associated with a variety of health disorders. The objective of our study is to assess the consequences of NEG in the molecular recognition of bioactive flavonoid 6-hydroxyflavone by human serum albumin (HSA) using various spectroscopic and computational analyses. UV–visible study revealed the possibility of ground-state interaction of 6HF with HSA/glycated HSA (gHSA) and the presence of static quenching mechanism have been supported by the quenching parameters derived from fluorescence quenching studies at three temperatures (290, 300 and 310 K). Due to glycation-related modulations around the binding sites of HSA, 6HF's interaction with gHSA has higher binding constants than that with HSA. The negative ΔG° showed the spontaneous nature of binding. Positive ΔS° and negative ΔH° indicated that hydrogen bonding and hydrophobic interactions are responsible for the binding. The percentage α-helix of HSA raised in the presence of 6HF, while the effect on gHSA is minor. Site probe experiments revealed that 6HF occupies the binding sites in subdomain IIA and IIIA, but it prefers binding to subdomain IIIA of gHSA. The outcomes from the molecular docking and MD simulation also correlates with the experimental results. This study analyses the changes in the molecular recognition of 6HF by HSA after glycation, which may aid in the understanding of comparable drug pharmacodynamics and offer crucial information for future therapeutic development.