Subdomain IIA Research Articles

The presence of NSAIDs may affect the binding capacity of serum albumin to the natural products hymecromone and umbelliferone

The natural products 7-hydroxycoumarin (7HC) and 7-hydroxy-4-methylcoumarin (7H4MC), known as umbelliferone and hymecromone, respectively, are one of the simplest structural examples from coumarin's family, showing several biological activities. Bovine serum albumin (BSA) is the main model protein used in laboratory experiments to characterize the biophysical capacity of potential drugs to be carried until the target in the bloodstream. Thus, the interaction BSA:7HC and BSA:7H4MC was biophysically characterized by circular dichroism (CD), steady-state, and time-resolved fluorescence techniques combined with molecular docking calculations via cross-docking approach to better correlate with the biological medium. There is a ground-state association BSA:7HC/7H4MC, and the presence of the methyl group in the coumarin core did not change the binding affinity and trend to BSA significantly. However, comparing the obtained data with those reported to benzo-α-pyrone there is evidence that the incorporation of the hydroxyl group in the aromatic ring A of the coumarin core improves the binding affinity to albumin around 10-folds and changes the binding site from subdomain IIA to IIIA or IB. In addition, the presence of other drugs, e.g., naproxen or ketoprofen, might interfere with the binding capacity of 7HC and 7H4MC, resulting in perturbations on the residence time of some clinically used drugs in the bloodstream.

Nonlinear van't Hoff Behavior in the Interaction of Two Water-Soluble Porphyrins with Bovine Serum Albumin (BSA).

Thermodynamic analysis of the binding process of water-soluble negatively charged meso-tetrakis(p-sulfonatophenyl) (TPPS4) and positively charged meso-tetrakis(4-methylpyridyl) (TMPyP) porphyrins with bovine serum albumin (BSA) at different temperatures was carried out based on the data of BSA quenching fluorescence by porphyrins. The comparison of binding constants (K b) shows that negatively charged TPPS4 possesses higher affinity to BSA than positively charged TMPyP. Thermodynamic characteristics of the binding process were obtained in accordance with the van't Hoff theory by processing nonlinear dependences of ln K b on inverse absolute temperature within the framework of two models: taking into account the dependence or independence of the change in the standard heat capacity (ΔC 0) on temperature. A comparison of thermodynamic characteristics with the data obtained from the Förster fluorescence quenching theory and with literature data leads to the conclusion that TPPS4 is bound to the Sudlow I site (subdomain IIA), while TMPyP is bound to the Heme site (between the subdomains IA and IB). The analysis of ΔC 0 changes with temperature demonstrates that binding of TPPS4 promotes hydration of nonpolar groups in the protein, which increases with the increase of temperature, while binding of TMPyP decreases the hydration of polar groups of the protein, the effect increasing with rising temperature. The obtained information may be useful for elucidating the mechanisms of interaction of porphyrins with albumins and the effect of this interaction upon the effectiveness of porphyrins in photodynamic therapy and in fluorescence diagnostics of cancer.

Assessment of the binding mechanism of ergothioneine to human serum albumin: Multi-spectroscopy, molecular docking and molecular dynamic simulation

Ergothioneine (EGT) has attracted great attention due to its extremely potent antioxidant properties, universally acknowledged as ‘longevity vitamin’. In order to comprehensive understanding of its pharmacodynamics and pharmacokinetics, the binding mechanism of EGT with human serum albumin (HSA) was clarified by cutting-edged multi-spectroscopic approaches and in silico molecular docking coupled with molecular dynamic simulation. Our fluorescence quenching results revealed that the binding of EGT to HSA was in a static quenching mode validated by the descending Stern–Volmer constant (Ksv) values (2.82, 2.36, 1.48 × 104 L mol−1) and biomolecular quenching rate constant (Kq) values (2.82, 2.36, 1.48 × 1012 L mol−1) at 298 K, 305 K, and 310 K, respectively. van’t Hoff criterion revealed the combination of EGT with HSA was a spontaneous exothermic process (ΔG = −24.16 kJ mol−1) via hydrogen bonding and van der Waals force interactions (ΔH = −60.25 kJ mol−1, ΔS = −129.44 J mol−1 K−1) at 310 K. The analysis of UV–vis absorption spectrum, synchronous fluorescence spectrum, three-dimensional fluorescence spectrum and circular dichroism indicated the addition of EGT affected the microenvironment of Trp214 and rearranged the structure of HSA. The binding replacement assay interpreted their binding site was near the subdomain IIA of HSA (Sudlow’s site I), which was intuitively exhibited by molecular docking. In addition of obvious van der Wall forces, attractive charge and Pi-alkyl interactions, the chiral betaine group (N+(CH3+)3) in the side chain of EGT was inclined to form hydrogen bonds with Lys199, Ser287 and Arg257 in the hydrophobic cavity of albumin. Moreover, the dynamic simulation reinforced the equilibrium and stability of formed docking complex by four indicators (RMSD, RMSF, Rg, SASA) within 100 ns.

Insights into the Binding of Metadoxine with Bovine Serum Albumin: A Multi-Spectroscopic Investigation Combined with Molecular Docking.

Metadoxine, also known as pyruvate dehydrogenase activator, is a small molecule drug that has been used in the treatment of various medical conditions. Bovine serum albumin is a commonly studied protein that serves as a plasmatic for understanding protein-drug interactions due to its abundance. This research suggests that metadoxine can bind to bovine serum albumin with moderate affinity, leading to an alteration in the secondary structure of the protein, which may also influence the protein's stability and function, which could provide a comprehensive understanding of the interaction at a molecular level. In this study, a variety of methodologies wereused to determine various thermodynamic parameters. The study uses UV-visible, Fluorescence, Fourier-transform infrared, Circular dichroism spectroscopy, and Molecular docking to analyze the interaction between bovine serum albumin and metadoxine, providing thermodynamic parameters for understanding the protein structure and its binding. The binding of metadoxine with bovine serum albumin, causes a hyperchromic shift. In fluorescence spectroscopy, the value of the Stern Volmer increases constantly with an increase in temperature, suggesting a stronger interaction between the Metadoxine and the Bovine serum albumin, leading to dynamic quenching. Additionally, Fourier-transform infrared and circular dichroism indicated a reduction in the secondary structure of Bovine serum albumin. The interactions between metadoxine and bovine serum albumin, cause hyperchromic shift revealed by UV-visible spectroscopy, whereas in Fluorescence spectroscopy, the value of the Stern Volmer constant increases with an increase in temperature, suggesting a stronger interaction between the MD and the BSA, leading to dynamic quenching. Additionally, Fourier-transform infrared and circular dichroism spectroscopy indicated a reduction in the secondary structure of the protein, as evidenced by the shifting of the amide II band and leading to a slight decrease in the αhelix content. The molecular docking shows that metadoxine was docked in the subdomain IIA binding pocket of BSA.

Mechanistic insights into the interaction of anxiolytic drugs with human serum albumin in a ternary system utilizing spectroscopic and molecular modeling approaches

In recent years, buspirone has been co-administered with sertraline to resolve sexual disorders caused by sertraline. Therefore, the present study was conducted to investigate the interaction effect of two antidepressants and anxiolytic drugs, sertraline and buspirone, on human serum albumin (HSA) using spectroscopic and molecular docking techniques. Fluorescence emission spectroscopy and molecular docking were used to calculate the binding affinity and determine the best binding sites for these two drugs. Additionally, UV-visible and circular dichroism spectroscopy were performed to investigate the effect of these drugs on the conformational changes of HSA. The results showed that both drugs have a strong ability to quench the fluorescence of HSA through a static mechanism, and cause structural changes in HSA. It was also found that binding of sertraline and buspirone to HSA is spontaneous (ΔG° <) and hydrophobic interactions, van der Waals forces and hydrogen bonds play a significant role in these interactions in the ternary system. In addition, molecular docking data showed that both drugs bind with high affinity to the Trp residue in subdomain IIA. The binding constants (Kb) for (HSA-SRH)-BSH and (HSA-BSH)-SRH were equal to 6.30 and 3.99, respectively, at 298 K. This study demonstrates that the presence of the second drug (buspirone/sertraline) affects the interaction and binding affinity of the first drug (sertraline/buspirone) to human serum albumin.

Multifaceted analysis of bempedoic acid binding to subdomain IIA of human serum albumin

The molecular association between bempedoic acid (BAC) and the major blood plasma transporter, human serum albumin (HSA), was investigated using molecular docking, molecular dynamics (MD) simulation, isothermal titration calorimetry (ITC), atomic force microscopy (AFM), and spectroscopic techniques. During the docking and MD simulation investigations, it was observed that BAC interacted with subdomain IIA (Site I) of HSA through hydrogen bonds and hydrophobic interactions. This interaction ensured the stability of the complex throughout the duration of 100 ns. The observed enhancement in the fluorescence intensity of HSA after BAC inclusion and the swelling of HSA generated by BAC in the AFM data also suggested the formation of a complex between BAC and HSA. The BAC demonstrated a moderate affinity towards HSA, with a binding constant (Ka) of 1.21 ± 0.05 × 105M−1 at 300 K. Notable modifications in the secondary and tertiary structures of the protein, as well as changes in the protein's Tyr/Trp surroundings, were observed using circular dichroism and three-dimensional fluorescence spectra when the protein was attached to BAC. Insightful information regarding molecular interactions that regulate the stability of the BAC-HSA complex is provided by these investigations.

A comprehensive investigation of the nano-[Cu2-(DIP)2-EA] effects on HSA through spectroscopic procedures and computer simulations

In this research, the toxicity of nano-[Cu2-(DIP)2-EA], a metal nano-complex consisting of ellagic acid and bathophenanthroline ligands, on human serum albumin (HSA) at a protein level was investigated. Molecular docking simulations and spectral analyses were conducted in a simulated physiological environment at pH 7.4 to explore the interaction of nano-[Cu2-(DIP)2-EA] with HSA. The results represented an increase in albumin absorption upon exposure to nano-[Cu2-(DIP)2-EA], demonstrating significant interaction between the two compounds. Steady-state and time-resolved fluorescence measurements pointed out that nano-[Cu2-(DIP)2-EA] induced static quenching of the albumin's intrinsic fluorescence with a high binding affinity of approximately 106 mol/L in a 1:1 interaction ratio. The thermodynamic variables clarified that binding of nano-[Cu2-(DIP)2-EA] to albumin occurs spontaneously and primarily driven by van der Waals interactions and H-bonds. The results of the computer simulations and the binding displacement experiments utilizing the site markers warfarin and ibuprofen revealed that nano-[Cu2-(DIP)2-EA] binds to site I within the subdomain IIA of albumin. Circular dichroism analysis elaborated that nano-[Cu2-(DIP)2-EA] slightly perturbed the microenvironment around of tryptophan residues and diminished the α-helix structure stability to a negligible amount.

Metal complexes containing vitamin B6-based scaffold as potential DNA/BSA-binding agents inducing apoptosis in hepatocarcinoma (HepG2) cells.

A ligand (HL) was synthesized from the pyridoxal hydrochloride (vitamin B6 form) and 1-(2-Aminoethyl)piperidine in one single step. The metal complexes [Zn(L)(Bpy)]NO3 (1), [Cu(L)(Bpy)]NO3 (2), and [Co(L)(Bpy)]NO3 (3) were prepared by tethering HL and 2,2'-bipyridine. The synthesized HL and metal complexes 1-3 were thoroughly characterized using spectroscopic techniques such as 1H NMR, 13C NMR, FTIR, EI-MS, molar conductance, and magnetic moment, in addition to CHN elemental analysis. The geometry of complexes was square pyramidal around the metal ions {Zn(II), Cu(II), and Co(II)}. The interaction of ligand and metal complexes with DNA and BSA macromolecules was accomplished by UV-Vis absorption and fluorescence spectroscopy in vitro. The hyperchromism in band at 303-325 with no shift supports the groove binding with some partial intercalation in grooves. Similarly, in BSA-binding studies, complex 2 shows greater binding potential in the hydrophobic core probably near the Trp-212 in the subdomain IIA. Furthermore, complex 2 shows excellent cytotoxicity on HepG2 cancer cells with IC50 = 25.0 ± 0.45µM. The detailed analysis by cell-cycle studies shows cell arrest at the G2/M phase. The type of cell death was authenticated by an annexin V-FTIC dual staining experiment that reveals maximum death by apoptosis together with non-specific necrosis.

Linamarin Binding to Human Serum Albumin. A Spectroscopic and Molecular Docking Approach

AbstractThe interaction between linamarin (LIN), a cyanogenic glycoside, and human serum albumin (HSA) was studied by multiple spectroscopic techniques and molecular docking simulation. All measurements were performed under physiological conditions. The obtained results (including the binding constants, effective quenching constant and a number of binding sites) showed that the complex of HSA‐LIN is formed. The values of Stern‐Volmer constants (6.70×103, 5.53×103 and 1.95×103) indicate that fluorescence quenching of HSA was static. Results of site marker experiments showed that the binding site of LIN is mainly located in site I (subdomain IIA) of HSA. The thermodynamic parameters showed that binding process occurs spontaneously through hydrophobic interactions. Molecular docking results are in good agreement with experimental data. Furthermore, computational results revealed LIN binds in the cavity of TRP 214, that is, subdomain IIA (site I) of HSA. This comprehensive study provides a deeper insight into ligand binding in HSA which may be useful in drug design and pharmacology.

A Biophysical Study of Molecular Interaction of Tucatinib with Bovine Serum Albumin

AbstractA profound understanding of the binding dynamics of drugs with plasma proteins is highly important as it determines its therapeutical potential. Herein, we have investigated the molecular interaction of Tucatinib (TUC), a novel, primitive and highly selective drug for treatment of HER2+ advanced unresectable breast cancer, with bovine serum albumin (BSA) using multi‐pronged spectroscopic techniques and molecular docking. TUC considerably quenched the intrinsic fluorescence of BSA via static quenching mechanism, and it binds to the hydrophobic cleft of subdomain IIA of BSA with a moderate binding affinity. The thermodynamic analysis revealed the major interplay of van der Waals forces and hydrogen bonding interactions in stabilising the binding. The Förster distance ‘r’ signifies feasible energy transfer between BSA and TUC. The conformational analyses indicate some alterations in the protein secondary structure as a consequence of some changes in the protein polar environment due to complex formation. The experimental results are supported by docking analyses.

Cytotoxic and genotoxic effects of tert-butylhydroquinone, butylated hydroxyanisole and propyl gallate as synthetic food antioxidants.

Synthetic food antioxidants such as tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), and propyl gallate (PG) have been extensively utilized in different food industries because of their high protectant activities to stop food spoilage and remove foodborne diseases in humans and animals. It would be emphasized that increasing the intake of antioxidants through intracellular may lead to cyto/genotoxicity, and their complex formation with biological molecules eventually accelerate the progress of various diseases like multiple sclerosis, diabetes, neurological disorders, cardiac vascular disease, cancer, etc. Therefore, their toxicity is one of the challenging subjects due to their extensive use in food-related industries. TBHQ, BHA, and PG antioxidants have cytotoxic, genotoxic, and carcinogenic effects if absorbed in high doses through the gastrointestinal tract. Thermodynamic parameters presented that the hydrophobic bind plays a key role in the complexation of the TBHQ, BHA, and PG with albumin. The molecular modeling results showed that subdomain IIA plays a vital role in the interaction of TBHQ and BHA with albumin. To comprehend the mechanisms of the cyto/genotoxicity effects of these food antioxidants and conformational alterations of albumin macromolecule, we aim to overview numerous types of research that evaluated the cyto/genotoxicity effects of these antioxidants using several procedures.

Synthesis and Characterization of Metal Complexes [M(L)(Im)]NO3, In Vitro DNA/BSA Binding Behavior and Cytotoxicity on HepG2 Cancer Cells

AbstractA new ligand (HL) was prepared from heterocyclic 8‐Hydroxy‐2‐quinolinecarboxaldehyde and 2‐Aminobenzophenone in one pot synthesis. The metal complexes of the types [Zn(L)(Im)]NO3 (1), [Cu(L)(Im)]NO3 (2) and [Co(L)(Im)]NO3 (3) were prepared by adopting HL and Imidazole under refluxing conditions. The HL and complexes 1–3, were characterized by CHN elemental analysis and spectroscopic methods 1H NMR, 13C NMR, FT‐IR, ToF Mass. The spectroscopic studies suggest square pyramidal geometry in all complexes. The interaction of ligand and complexes with DNA and BSA was conducted by UV‐vis absorption and fluorescence spectroscopy. The Kb value of 2.17×104 M−1 for complex 2 is the highest depicting its greater binding propensity with DNA. Similarly, in BSA binding studies, complex 2 shows greater binding potential in the hydrophobic core probably near the Trp 212 in the subdomain IIA. Furthermore, the complex 2 shows excellent cytotoxicity on HepG2 cancer cells with IC50=74.05±0.69 μM. In the cell cycle analysis of HepG2 cells, it has been observed that complex 2 arrests the cell proliferation in the G1/S phase. Annexin V‐based flow cytometry analysis further indicated 6‐fold apoptotic cell death by complex 2 in the experiment along with non‐specific necrosis cell death.

Multi-spectral and docking assessments to explore the combination of an antiviral drug, entecavir with bovine serum albumin

Molecular interaction of entecavir (ETV) with the transport protein, albumin from bovine serum (BSA) was explored through multispectral and molecular docking approaches. The BSA fluorescence was appreciably quenched upon ETV binding and the quenching nature was static. The ETV–BSA complexation and the static quenching process were further reiterated using UV–visible absorption spectra. The binding constant (Ka) values of the complex were found as 1.47 × 104–4.0 × 103 M−1, which depicting a modarate binding strength in the ETV–BSA complexation. The experimental outcomes verified that the stable complexation was primarily influenced by hydrophobic interactions, hydrogen bonds and van der Waals forces. Synchronous and 3-D fluorescence spectral results demonstrated that ETV had significant impact on the hydrophobicity and polarity of the molecular environment near Tyr and Trp residues. Competitive site-markers displacement (with warfarin and ketoprofen) results discovered the suitable binding locus of ETV at site I in BSA. The molecular docking assessments also revealed that ETV formed hydrogen bonds and hydrophobic interactions with BSA, predominantly binding to site I (sub-domain IIA) of BSA.

Mechanism understanding of PIKfyve inhibitor YM201636 with human serum albumin: Insights from molecular modeling and multiple spectroscopic techniques.

YM201636 is the potent PIKfyve inhibitor that is being actively investigated for liver cancer efficacy. In this study, computer simulations and experiments were conducted to investigate the interaction mechanism between YM201636 and the transport protein HSA. Results indicated that YM201636 is stably bound between the subdomains IIA and IIIA of HSA, supported by site marker displacement experiments. YM201636 quenched the endogenous fluorescence of HSA by static quenching since a decrease in quenching constants was observed from 7.74 to 2.39 × 104 M-1. UV-vis and time-resolved fluorescence spectroscopy confirmed the YM201636-HSA complex formation and this binding followed a static mechanism. Thermodynamic parameters ΔG, ΔH, and ΔS obtained negative values suggesting the binding was a spontaneous process driven by Van der Waals interactions and hydrogen binding. Binding constants ranged between 5.71 and 0.33 × 104 M-1, which demonstrated a moderately strong affinity of YM201636 to HSA. CD, synchronous, and 3D fluorescence spectroscopy revealed that YM201636 showed a slight change in secondary structure. The increase of Kapp and a decrease of PSH with YM201636 addition showed that YM201636 changed the surface hydrophobicity of HSA. The research provides reasonable models helping us further understand the transportation and distribution of YM201636 when it absorbs into the blood circulatory system.

Interactions of three berberine mid-chain fatty acid salts with bovine serum albumin (BSA): Spectroscopic analysis and molecular docking

In this paper, the interaction of three berberine mid-chain fatty acid salts ([BBR][FAs]), viz. berberine caproate ([BBR][CAP]), berberine heptylate ([BBR][HEP]) and berberine octoate ([BBR][OCT]), with bovine serum albumin (BSA) was studied by means of UV–visible absorption spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FT-IR) and molecular docking techniques. Fluorescence experiments revealed that three berberine salts quench the fluorescence of BSA by static quenching mechanism resulted from a stable [BBR][FAs]-BSA complex formation. The stoichiometric numbers of [BBR][FAs]-BSA complexes were found to be 1:1. Synchronous and three-dimensional fluorescence spectra as well as FT-IR demonstrated that the binding of [BBR][FAs] altered the microenvironment and conformation of BSA. The binding average distance from [BBR][FAs] to BSA (3.2–3.5 nm) was determined according to Förster energy transfer theory. Site probe investigation showed that [BBR][FAs] bound to BSA active site I (sub-domain IIA). The binding promotes the esterase-like activity of BSA. The molecular docking results confirmed the fluorescence competition findings and provided the type of binding forces. Furthermore, the relationship between the anionic chain length of [BBR][FAs] and the interaction was explored, and the positive correlation was found.

Evidence of Hyperglycemic Levels Improving the Binding Capacity between Human Serum Albumin and the Antihypertensive Drug Hydrochlorothiazide

Cardiovascular diseases (CVDs), especially arterial hypertension, stand as prominent contributors to global mortality. Regrettably, individuals with diabetes encounter a two-fold increase in the risk of mortality associated with CVDs. Hydrochlorothiazide (HCTZ) represents a primary intervention for hypertension, particularly in diabetic patients. Nevertheless, there has not yet been a comprehensive assessment of the biophysical characteristics regarding the impact of glucose levels on its binding affinity with human serum albumin (HSA). Thus, the present work reports the interactive profile of HSA/HCTZ in nonglycemic, normoglycemic (80 mg/dL), and hyperglycemic (320 mg/dL) conditions by time-resolved fluorescence, saturation transfer difference–nuclear magnetic resonance (STD-NMR), and surface plasmon resonance (SPR). There was a moderate ground state association of HSA/HCTZ with subdomain IIA that was affected in the presence of different glucose levels. The hyperglycemic condition decreased the binding affinity of HCTZ to subdomain IIA and increased the possibility of subdomain IB also being considered as a secondary binding site due to cooperativity and/or alterations in the protein’s structure. Overall, the glucose level under hyperglycemic conditions led to the cavities being more likely to receive more ligands, offering insights into the necessity of glucose control in the human bloodstream to not impact the residence time (pharmacokinetic profile) and pharmacotherapeutic potential of HCTZ.

Distinguishing the transitions of fluorescence spectra of tryptophan-134 and 213 in BSA induced by bindings of UV filters, oxybenzone-3, and avobenzone

Abstract Oxybenzone-3 (OBZ) and avobenzone (ABZ), commercially available ultraviolet-light filters for sunscreens, are known to induce photosensitizing allergy as an adverse effect, similar to an analgesic ketoprofen (KTP) due to their benzophenone moiety. The present study focused on OBZ and ABZ's protein binding compared to the related analgesics, KTP, diclofenac (DCF), and ibuprofen (IBP). The bovine serum albumin (BSA) was used as a protein model, measuring the fluorescent spectral peak shifts (i) and Stern–Volmer analysis (i) of its intrinsic tryptophans. Moreover, their adsorption types (iii) were verified using the singular value decomposition (SVD) computation of fluorescence spectra. For (i), (ii), and (iii), KTP and DCF caused a no-shift peak, an ordinary dynamic quenching, and a simple Langmuir adsorption. We found OBZ exhibiting (i) red-shift and (ii) including static quenching, ABZ suggesting (i) blue-shift and (iii) binding to multiple bind sites, and IBP indicating (i) blue-shift and (iii) multivalent bindings. Integrating the results, it can be understood that OBZ interacts with subdomain IA (around W134) in BSA, while ABZ interacts with subdomain IIA (around W213) in BSA. Moreover, IBP is bound to BSA with a cooperative effect, certified by Hill's plot. OBZ and ABZ had their individual binding sites on a protein, suggesting the exchange between OBZ and ABZ might reduce their own adverse effect. The present study verified the effectiveness of the SVD computation in distinguishing the details of the adsorption manner of ligands around the intrinsic fluorescent probes.

Structural and mechanistic insights into the transport of aristolochic acids and their active metabolites by human serum albumin

Aristolochic acids I and II (AA-I/II) are carcinogenic principles of Aristolochia plants, which have been employed in traditional medicinal practices and discovered as food contaminants. While the deleterious effects of AAs are broadly acknowledged, there is a dearth of information to define the mechanisms underlying their carcinogenicity. Following bioactivation in the liver, N-hydroxyaristolactam and N-sulfonyloxyaristolactam metabolites are transported via circulation and elicit carcinogenic effects by reacting with cellular DNA. In this study, we apply DNA adduct analysis, X-ray crystallography, isothermal titration calorimetry (ITC) and fluorescence quenching to investigate the role of human serum albumin (HSA) in modulating AA carcinogenicity. We find that HSA extends the half-life and reactivity of N-sulfonyloxyaristolactam-I with DNA, thereby protecting activated AAs from heterolysis. Applying novel pooled plasma HSA crystallization methods, we report high-resolution structures of myristic acid-enriched HSA (HSAMYR) and its AA complexes (HSAMYR/AA-I and HSAMYR/AA-II) at 1.9 Å resolution. Whereas AA-I is located within HSA subdomain IB, AA-II occupies subdomains IIA and IB. ITC binding profiles reveal two distinct AA sites in both complexes with association constants of 1.5 and 0.5 · 106 M-1 for HSA/AA-I versus 8.4 and 9.0 · 105 M-1 for HSA/AA-II. Fluorescence quenching of the HSA Trp214 suggests variable impacts of fatty acids on ligand binding affinities. Collectively, our structural and thermodynamic characterizations yield significant insights into AA binding, transport, toxicity, and potential allostery, critical determinants for elucidating the mechanistic roles of HSA in modulating AA carcinogenicity.

Evaluating the biomolecular interaction between delamanid/formulations and human serum albumin by fluorescence, CD spectroscopy and SPR: Effects on protein conformation, kinetic and thermodynamic parameters

Delamanid is an anti-tuberculosis drug used for the treatment of drug-resistant tuberculosis. Since delamanid has a high protein bound potential, even patients with low albumin levels should experience high and rapid delamanid clearance. However, the interaction between delamanid and albumin should be better controlled to optimize drug efficacy. This study was designed to evaluate the binding characteristics of delamanid to human serum albumin (HSA) using various methods: fluorescence spectroscopy, circular dichroism (CD), surface plasmon resonance (SPR), and molecular docking simulation. The fluorescence emission band without any shift indicated the interaction was not affected by the polarity of the fluorophore microenvironment. The reduction of fluorescence intensity at 344 nm was proportional to the increment of delamanid concentration as a fluorescence quencher. UV-absorbance measurement at the maximum wavelength (λmax, 280 nm) was evaluated using inner filter effect correction. The HSA conformation change was explained by the intermolecular energy transfer between delamanid and HSA during complex formation. The study, which was conducted at temperatures of 298 K, 303 K, and 310 K, revealed a static quenching mechanism that correlated with a decreased of bimolecular quenching rate constant (kq) and binding constant (Ka) at increased temperatures. The Ka was 1.75–3.16 × 104 M−1 with a specific binding site with stoichiometry 1:1. The negative enthalpy change, negative entropy change, and negative Gibbs free energy change demonstrated an exothermic-spontaneous reaction while van der Waals forces and hydrogen bonds played a vital role in the binding. The molecular displacement approach and molecular docking confirmed that the binding occurred mainly in subdomain IIA, which is a hydrophobic pocket of HSA, with a theoretical binding free energy of −9.33 kcal/mol. SPR exhibited a real time negative sensorgram that resulted from deviation of the reflex angle due to ligand delamanid-HSA complex forming. The binding occurred spontaneously after delamanid was presented to the HSA surface. The SPR mathematical fitting model revealed that the association rate constant (kon) was 2.62 × 108 s−1M−1 and the dissociation rate constant (koff) was 5.65 × 10−3 s−1. The complexes were performed with an association constant (KA) of 4.64 × 1010 M−1 and the dissociation constant (KD) of 2.15 × 10−11 M. The binding constant indicated high binding affinity and high stability of the complex in an equilibrium. Modified CD spectra revealed that conformation of the HSA structure was altered by the presence of delamanid during preparation of the proliposomes that led to the reduction of secondary structure stabilization. This was indicated by the percentage decrease of α-helix. These findings are beneficial to understanding delamanid-HSA binding characteristics as well as the drug administration regimen.

Spectroscopic and in silico characterization of the interaction between synthetic 2-substituted-naphtho-1,4-quinones and human serum albumin

The intermolecular interaction between 2-(N-phenyl-N-methyl)aminonaphtho-1,4-quinone (1) and 2-(4-N-methylaminophenyl)naphtho-1,4-quinone (2) and human serum albumin (HSA) was investigated using spectroscopic techniques combined with in silico calculations via molecular docking. Steady-state titration of HSA fluorescence by 1 and 2 (λexc 295 nm) in PBS at 305, 310, and 315 K, as well as studies employing time-resolved fluorescence emission, demonstrated that the HSA:1 and HSA:2 interaction occurs through a static quenching mechanism. The Stern-Volmer constant (Ksv) values, (1.56 ± 0.08) and (3.05 ± 0.10) × 104 L/mol at 310 K for HSA:1 and HSA:2, respectively, indicate a moderate binding affinity. Van't Hoff plots showed that HSA:1 and HSA:2 interactions are spontaneous (negative ΔGo) with a hydrophobic character (ΔSo value of 0.00707 ± 0.00106 and 0.0392 ± 0.0062 kJ/mol K for HSA:1 and HSA:2, respectively) and specific electrostatic interactions (ΔHo value of –22.7 ± 3.3 and −14.4 ± 1.9 kJ/mol for HSA:1 and HSA:2, respectively). Synchronous fluorescence results showed significant perturbation in the microenvironment of the tryptophan residue (Trp-214). Circular dichroism indicated that after interaction with naphthoquinones 1 and 2, the HSA structure remains predominantly in the α-helix form. Finally, molecular docking revealed the formation of hydrophobic, electrostatic, and hydrogen bond interactions with the surrounding amino acid residues in subdomain IIA of HSA, which contains the Trp-214 residue, validated with the experimental drug-displacement assays. Overall, spectroscopic and in silico characterization of HSA:1 and HSA:2 might reflect in a low half-life in the human bloodstream, indicating the necessity of methods to improve the bioavailability, e.g., studies on the type of administration (oral versus intravenous).