Deciphering the interaction of procaine with bovine serum albumin and elucidation of binding site: A multi spectroscopic and molecular docking study

In-Vitro Study of the Binding of Atorvastatin with Adenine using Multi-Spectroscopic Approaches

Atorvastatin-an oral lipid regulating drug is a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), which is the rate determining enzyme for cholesterol synthesis. Adenine is a purine nucleobase that is found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) to generate genetic information. The binding mechanism of atorvastatin and adenine was studied for the first time utilizing various techniques, including UV-visible spectrophotometry, spectrofluorimetry, synchronous fluorescence spectroscopy (SF), Fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET), and metal ion complexation. The fluorescence spectra of the complex indicated that atorvastatin is bound to adenine via hydrophobic interaction through a spontaneous binding process, and the fluorescence quenching mechanism was found to be static quenching with a binding constant of 1.4893 × 104 Lmol-1 at 298 K. Various temperature settings were used to investigate thermodynamic characteristics, such as binding forces, binding constants, and the number of binding sites. The interaction parameters, including the standard enthalpy change (ΔHο) and standard entropy change (ΔSο) were calculated using Van't Hoff's equation to be 42.82 kJmol-1 and 208.9 Jmol-1K-1, respectively. The findings demonstrated that the adenine- atorvastatin binding was endothermic. Furthermore, the results of the experiments revealed that some metal ions (K+, Ca+2, Co+2, Cu+2, and Al+3) facilitate the binding interaction between atorvastatin and adenine. Slight changes are observed in the FTIR spectra of adenine, indicating the binding interaction between adenine and atorvastatin.

Investigating the binding interaction of quinoline yellow with bovine serum albumin and anti-amyloidogenic behavior of ferulic acid on QY-induced BSA fibrils

Protein aggregation induces profound changes in the structure along with the conformation of the protein, and is responsible for the pathogenesis of a number of neurodegenerative conditions such as Huntington's, Creutzfeldt-Jacob, Type II diabetes mellitus, Alzheimer's, etc. Numerous multi-spectroscopic approaches and in-silico experiments were utilized to investigate BSA's biomolecular interaction and aggregation in the presence of quinoline yellow. The present research investigation evaluated the interaction of BSA with the food colorant (QY) at two different pH (7.4 and 2.0). The development of the BSA-QY complex was established with UV visible and fluorescence spectroscopy. The quenching of fluorescence upon the interaction of BSA with QY revealed the static nature of quenching mechanism. The Kb value obtained from our result is 4. 54 × 10-4 M-1. The results from the competitive site marker study infer that quinoline yellow is binding with the sub-domain IB of bovine serum albumin, specifically on site III. Three-dimensional fluorescence and synchronous fluorescence spectroscopy were applied for monitoring the alterations in the microenvironment of BSA upon the addition of quinoline yellow. The results from turbidity and RLS studies showed that higher concentrations of QY (80-400 µM) triggered bovine serum albumin (BSA) aggregation at pH 2.0. At pH 7.4, QY couldn't manage to trigger bovine serum albumin aggregation, perhaps because of the repulsion between negatively charged dye (QY) and anionic bovine serum albumin. The results from far-UV CD, Congo Red, and scanning electron microscopy implicate that the QY-induced aggregates exhibit amyloid fibril-like structures. Molecular docking results revealed that hydrophobic interactions, hydrogen bonding, and Pi-Sulfur interactions contribute to QY-induced aggregation of BSA. Further, the amyloid inhibitory potential of ferulic acid (FA), a phenolic acid on QY-induced aggregation of BSA, has also been assessed. The QY-induced amyloid fibrils are FA-soluble, as confirmed by turbidity, RLS, and far-UV CD studies. Far-UV CD results showed that FA retains α helix and inhibits cross β sheet formation when the BSA samples were pre-incubated with increasing concentrations of FA (0-500 µM). Our findings conclude that QY dye successfully stimulates BSA aggregation, but ferulic acid inhibits QY-induced aggregation of BSA. Thus, FA can serve as a therapeutic agent and can help in the treatment of various amyloid-related conditions.

Comparison of Non-Covalent and Covalent Interactions between Lactoferrin and Chlorogenic Acid

Adding polyphenols to improve the absorption of functional proteins has become a hot topic. Chlorogenic acid is a natural plant polyphenol with anti-inflammatory, antioxidant, and anticancer properties. Bovine lactoferrin is known for its immunomodulatory, anticancer, antibacterial, and iron-chelating properties. Therefore, the non-covalent binding of chlorogenic acid (CA) and bovine lactoferrin (BLF) with different concentrations under neutral conditions was studied. CA was grafted onto lactoferrin molecules by laccase catalysis, free radical grafting, and alkali treatment. The formation mechanism of non-covalent and covalent complexes of CA-BLF was analyzed by experimental test and theoretical prediction. Compared with the control BLF, the secondary structure of BLF in the non-covalent complex was rearranged and unfolded to provide more active sites, the tertiary structure of the covalent conjugate was changed, and the amino group of the protein participated in the covalent reaction. After adding CA, the covalent conjugates have better functional activity. These lactoferrin-polyphenol couplings can carry various bioactive compounds to create milk-based delivery systems for encapsulation.

Molecular insight into binding behavior of caffeine with lactoferrin: Spectroscopic, molecular docking, and simulation study

The majority of bioactive substances in the human diet come from polyphenols. Here, we use spectroscopy, molecular docking, molecular dynamics simulations, and in vitro digestion to look at the relationship between caffeine (CAF) and bovine lactoferrin (BLF). The correlation analysis of the CAF-BLF fluorescence quenching process revealed that the reaction was spontaneous and that the CAF-BLF fluorescence quenching process may have been static. The predominant intrinsic binding forces were hydrogen bonds and van der Waals forces, which were also supported by molecular docking and molecular dynamics simulations. Through Fourier infrared and circular dichroism spectroscopy experiments, it was found that CAF changed the secondary structure of BLF and might bind to the hydrophobic amino acids of BLF. Compared with BLF, CAF-BLF showed inhibitory effects on digestion in simulated in vitro digestion. It will be helpful to better understand the interaction between CAF and BLF and provide the basis for the development of innovative dairy products.

Non-Steroidal Anti-Inflammatory Drug Effect on the Binding of Plasma Protein with Antibiotic Drug Ceftazidime: Spectroscopic and In Silico Investigation

The coexistence of ceftazidime, which is a popular third-generation of cephalosporin antibiotic, with ubiquitous paracetamol or acetaminophen, is very likely because the latter is given to the patients to reduce fever due to bacterial infection along with an antibiotic such as the former. Therefore, in this study, we investigated the detailed binding of ceftazidime with plasma protein, human serum albumin (HSA), in the absence and presence of paracetamol using spectroscopic techniques such as fluorescence, UV-visible, and circular dichroism, along with in silico methods such as molecular docking, molecular dynamics simulations, and MM/PBSA-based binding free energy analysis. The basic idea of the interaction was attained by using UV-visible spectroscopy. Further, fluorescence spectroscopy revealed that there was a fair interaction between ceftazidime and HSA, and the mechanism of the quenching was a dynamic one, i.e., the quenching constant increased with increasing temperature. The interaction was, primarily, reinforced by hydrophobic forces, which resulted in the partial unfolding of the protein. Low concentrations of paracetamol were ineffective in affecting the binding of ceftazidime with has; although, a decrease in the quenching and binding constants was observed in the presence of high concentrations of the former. Competitive binding site experiments using warfarin and ibuprofen as site markers revealed that ceftazidime neither binds at drug site 1 or at drug site 2, articulating another binding site, which was confirmed by molecular docking simulations.

Spectroscopic studies on noncovalent binding of nicotinamide-modified BRCA1 (856-871) analogs to calf thymus DNA

Various peptide drugs have entered the market with the development of molecular biology. Peptide drugs are used for treat diseases such as diabetes, breast cancer, and HIV infection. In this study, three nicotinamide-modified peptides were synthesized by modifying the N-terminus of BRCA1 (856-871, Y856R, K862Y, R866W) peptide with three nicotinic acid derivatives using solid-phase peptide synthesis. The results of calf thymus DNA (ctDNA) binding activity indicated that binding constants of BRCA1 (856-871, Y856R, K862Y, R866W) (P0) and three nicotinamide-modified peptides (P1, P2, and P3) to ctDNA were 1.89 × 10³, 2.97 × 10⁴, 7.61 × 10⁴, and 8.09 × 10⁴ L·mol^-1, respectively. The binding affinity of the modified peptides was superior to that of BRCA1 (856-871, Y856R, K862Y, R866W). ΔH^θ < 0 and ΔS^θ < 0 indicated that van der Waals force and hydrogen bond contributed most to peptide-ctDNA binding. Results obtained by Circular dichroism (CD) indicated that peptide binding interaction led to conformational changes in ctDNA. Ultraviolet-visible (UV) spectroscopy, ethidium bromide (EB) competition experiments, DNA melting experiments, and viscosity measurements verified that peptides interacted with ctDNA via groove binding. Ionic strength experiments manifested that electrostatic binding was also involved in peptide-ctDNA binding.

Insights on the in-vitro binding interaction between donepezil and bovine serum albumin

In this work, the binding mechanism between donepezil (DNP) and bovine serum albumin (BSA) was established using several techniques, including fluorimetry, UV- spectrophotometry, synchronous fluorimetry (SF), fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET) besides molecular docking study. The fluorescence quenching mechanism of DNP-BSA binding was a combined dynamic and static quenching. The thermodynamic parameters, binding forces, binding constant, and the number of binding sites were determined using a different range of temperature settings. Van't Hoff's equation was used to calculate the reaction parameters, including enthalpy change (ΔH^ο) and entropy change (ΔS^ο). The results pointed out that the DNP-BSA binding was endothermic. It was shown that the stability of the drug-protein system was predominantly due to the intermolecular hydrophobic forces. Additionally, the site probing method revealed that subdomain IIA (Site I) is where DNP and BSA's binding occurs. This was validated using a molecular docking study with the most stable DNP configuration. This study might help to understand DNP's pharmacokinetics profile and toxicity as well as provides crucial information for its safe use and avoiding its toxicity.

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

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

Investigations of interaction mechanism and conformational variation of serum albumin affected by artemisinin and dihydroartemisinin

In this work, binding interactions of artemisinin (ART) and dihydroartemisinin (DHA) with human serum albumin (HSA) and bovine serum albumin (BSA) were investigated thoroughly to illustrate the conformational variation of serum albumin. Experimental results indicated that ART and DHA bound strongly with the site I of serum albumins via hydrogen bond (H-bond) and van der Waals force and subsequently statically quenched the intrinsic fluorescence of serum albumins through concentration-dependent manner. The quenching abilities of two drugs on the intrinsic fluorescence of HSA were much higher than the quenching abilities of two drugs on the intrinsic fluorescence of BSA. Both ART and DHA, especially DHA, caused the conformational variation of serum albumins and reduced the α-helix structure content of serum albumins. DHA with hydrophilic hydroxyl group bound with HSA more strongly, suggesting the important roles of the chemical polarity and the hydrophilicity during the binding interactions of two drugs with serum albumins. These results reveal the molecular understanding of binding interactions between ART derivatives and serum albumins, providing vital information for the future application of ART derivatives in biological and clinical areas.

Exploration of the binding between cuminol and bovine serum albumin through spectroscopic, molecular docking and molecular dynamics methods

Cuminol (4-Isopropylbenzyl alcohol), found in the essential oils of several plant sources, is an important constituent of several cosmetics formulations. The interaction of cuminol with model plasma protein bovine serum albumin was studied in this paper. The experimental studies were mainly carried out using fluorescence spectrophotometry aided with UV visible and CD spectroscopies. Intrinsic fluorescence measurements showed that there was a weak binding between cuminol and BSA. The mechanism of binding involved static quenching with around 1:1 binding. The binding was chiefly supported by hydrophobic forces although a little contribution of hydrogen bonding was also found in the interaction and the values of enthalpy change were negative with positive entropy change. The secondary structure of BSA didn't change significantly in presence of low concentrations of cuminol, however, partial unfolding of the former taken place when the concentration of the latter increased. Molecular docking analyses showed cuminol binds at the intersection of subdomains IIA and IIIA, i.e. its binding site is in between Sudlow sites I and II. Molecular dynamics simulations results have shown that BSA forms a stable complex with cuminol and the structure of the former didn't change much in presence of later. Communicated by Ramaswamy H. Sarma.

Horizontal comparison of "red or blue shift" and binding energy of six fluoroquinolones: Fluorescence quenching mechanism, theoretical calculation and molecular modeling method

In this article, the interaction between six fluoroquinolones (FQs) and bovine serum albumin (BSA) was initially studied at 298 K, 303 K and 310 K respectively under simulated physiological conditions by fluorescence spectroscopy. At the same time, the sub-structural domains on BSA that may bind to FQs were investigated by molecular docking simulation technique. A combination of quantitative and qualitative approaches was used in the analysis of the binding constants, binding sites and corresponding thermodynamic parameters in the interaction system, it was found that FQs forms a complex with BSA and undergoes static quenching, which is the main cause of fluorescence quenching. The results indicated that hydrogen bonds, Van der Waals force and electrostatic interaction were the main binding forces between the complexes, it also showed that these six fluoroquinolones mainly bound to the IIA and IIIA structural domains of BSA, while DANO and SARA may be more toxic than other antibiotics. Based on Foster's non-radiative energy transfer theory, the binding distance between FQs and BSA was calculated to be less than 7 nm, indicating the existence of energy transfer between small molecule drugs and proteins. Synchronous fluorescence and UV-Vis absorption spectroscopy further confirmed that FQs can alter the secondary conformational change of BSA. Lomefloxacin has a different effect from the other five fluoroquinolone antibiotics because it causes a decrease in polarity and an increase in hydrophobicity around tryptophan residues, while the other five FQs have the opposite effect. Together, the study of FQs-BSA is of great significance to elucidate the pharmacokinetics and pharmacodynamics of FQs.

Exploring the molecular interaction of mebendazole with bovine serum albumin using multi-spectroscopic approaches and molecular docking

This article presents the binding interaction between mebendazole (MBZ) and bovine serum albumin. The interaction has been studied using different techniques, such as fluorescence quenching spectroscopy, UV–visible spectroscopy, synchronous fluorescence spectroscopy, fourier transform infrared, and fluorescence resonance energy transfer in addition to molecular docking. Results from Stern Volmer equation stated that the quenching for MBZ-BSA binding was static. The fluorescence quenching spectroscopic study was performed at three temperature settings. The binding constant (k_q), the number of binding sites (n), thermodynamic parameters (ΔH^ο, ΔS^ο and ΔG^ο), and binding forces were determined. The results exhibited that the interaction was endothermic. It was revealed that intermolecular hydrophobic forces led to the stabilization of the drug-protein system. Using the site marker technique, the binding between MBZ and BSA was found to be located at subdomain IIA (site I). This was furtherly approved using the molecular docking technique with the most stable MBZ configuration. This research may aid in understanding the pharmacokinetics and toxicity of MBZ and give fundamental data for its safe usage to avoid its toxicity.

A Survey of Gasoline Ameliorator, Methyl-Tert-Butyl Ether (MTBE) on Bovine Serum Albumin: A Spectroscopy and Molecular Dynamic Simulation Study

Background

Methyl-Tert-Butyl Ether (MTBE) as a gasoline modifier is frequently added to fuels and used in plenty of worldwide applications. MTBE biodegradation in groundwater occurs slowly and produces water miscibility; therefore, it causes diverse environmental and human health concerns.

Objectives

The interaction of MTBE with bovine serum albumin (BSA) as a model protein at physiological conditions is investigated to illustrate the possible interactions of MTBE with the body's proteins.

Materials and Methods

Uv-visible, fluorescence, circular dichroism (CD) spectroscopy methods, and molecular modeling were used to analyze the MTBE's effect on BSA structure and dynamics. The constant protein concentration and various MTBE contents were used for possible interactions.

Results

The protein structural analysis shows that MTBE binds to BSA via positive enthalpy and entropy via hydrophobic interactions. Molecular docking shows the participation of several amino acids in the MTBE-BSA interaction. The CD spectroscopy results show that the BSA structure was not changed in the MTBE concentrations utilized in the study. Molecular dynamics (MD) simulation results suggest that MTBE can slightly change protein structure in the last 50ns.

Conclusion

Comparing experimental and MD simulation results demonstrated that the BSA secondary structure was maintained in the low concentration of the MTBE. The entropy and enthalpy parameters asserted the hydrophobic interaction was the major force in the interaction between the BSA and MTBE.

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

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

Experimental and Computational Investigation on the Interaction of Anticancer Drug Gemcitabine with Human Plasma Protein: Effect of Copresence of Ibuprofen on the Binding

The interaction of common anticancer drug gemcitabine with human serum albumin (HSA) has been studied in detail. The effect of an omnipresent nonsteroidal anti-inflammatory drug ibuprofen was also seen on the binding of HSA and gemcitabine. A slight hyperchromic shift in the difference UV-visible absorption spectra of HSA on the addition of gemcitabine gave a primary idea of the possible complex formation between them. The inner filter effect, which happens due to the significant absorbance of the ligand at the excitation and/or emission wavelengths, played an important role in the observed fluorescence quenching of HSA by gemcitabine that can be understood by comparing the observed and corrected fluorescence intensities obtained at λ_ex = 280 nm and 295 nm. Gemcitabine showed weak interaction with HSA, which took place via a dynamic quenching mechanism with 1:1 cooperative binding between them. Secondary structural analysis, based on circular dichroism (CD) spectroscopy, showed that low concentrations of gemcitabine did not affect the native structure of protein; however, higher concentrations affected it slightly with partial unfolding. For understanding the binding site of gemcitabine within HSA, both experimental (using site markers, warfarin and ibuprofen) as well as computational methods were employed, which revealed that the gemcitabine binding site is located between the interface of subdomain IIA and IIB within the close proximity of the warfarin site (drug site 1). The effect of ibuprofen on the binding was further elaborated because of the possibility of its coexistence with gemcitabine in the prescription given to the cancer patients, and it was noticed that, ibuprofen, even present in high amounts, did not affect the binding efficacy of gemcitabine with HSA. DFT analyses of various conformers of gemcitabine obtained from its docking with various structures of HSA (free and bounded with site markers), show that the stability of the gemcitabine molecule increased slightly after binding with ibuprofen-complexed HSA. Both experimental as well as computational results were in good agreement with each other.

Complexation mechanism between 20(R, S)-ginsenoside Rh1 and serum albumin: Multi-spectroscopy, in vitro cytotoxicity, and in silico investigations

As rare ginsenosides, 20(R, S)-ginsenoside Rh1 [20(R, S)-Rh1] are isomers and have been reported to exhibit multiple biological effects. However, the application of 20(R, S)-Rh1 is still limited due to their poor solubilities and low bioavailabilities. Here, the complexation mechanism between 20(R, S)-Rh1 and serum albumin (SA) was explored by a combination of multi-spectroscopy and in silico investigations. Results of spectra experiments showed that 20(R, S)-Rh1 could form complexes with bovine serum albumin (BSA) and quench its intrinsic fluorescence. In addition, the influence of BSA on the anti-cancer activity of 20(R, S)-Rh1 was also evaluated in A549 cells. The result of the MTT assay indicated that anti-cancer activity of 20(R, S)-Rh1 was enhanced when combined with BSA. The results of molecular docking and dynamics simulation demonstrated that the subtle structural differences of 20(R, S)-Rh1 at the 20-carbon atom may be responsible for their different binding capacities and binding stabilities with human serum albumin. The cytotoxicity assay for 20(R, S)-Rh1 alone and their complexes with BSA demonstrated the enhancement effect of BSA for inhibition of cell proliferation. In conclusion, this work provided insight into the complexation mechanism between 20(R, S)-Rh1 and SA. PRACTICAL APPLICATION: The complexation mechanism between 20(R, S)-ginsenoside Rh1 [20(R, S)-Rh1] and serum albumin (SA) was explored by a combination of multi-spectroscopy and in silico investigations in this work. The cytotoxicity assay for 20(R, S)-Rh1 alone and their complexes with bovine serum albumin (BSA) demonstrates the enhancement effect of BSA for inhibition of cell proliferation. Hence, this work provided insight into the complexation mechanism between 20(R, S)-Rh1 and SA.

Profiling the interaction of a novel toxic pyruvate dehydrogenase kinase inhibitor with human serum albumin

To discover novel pyruvate dehydrogenase kinase (PDK) inhibitors, a new compound 2,2-dichloro-1-(4-((4-isopropylphenyl)amino)-3-nitrophenyl)ethan-1-one, namely XB-1 was identified, which inhibited PDK activity with a half maximal inhibitory concentration (IC₅₀) value of 337.0 nM, and reduced A549 cell proliferation with a half maximal effective concentration (EC₅₀) value of 330.0 nM. However, the compound appears to exhibit a negligible selectivity between cancer cell and normal one, indicating a potential toxicity existed for the compound. Herein, the interaction of the toxic XB-1 to human serum albumin (HSA) was firstly explored by spectroscopic approaches with the aim to reduce/avoid the toxicity of PDK inhibitors in the next hit-to-lead campaign. In detail, it was found that the XB-1 could effectively bind to HSA mainly via hydrogen bond interaction in PBS buffer (pH = 7.4, 10.0 mM), resulting in the formation of HSA-XB-1 complex. The negative value of ΔG showed that the binding of XB-1 to HSA is a spontaneous process. The result from site-selective binding assay suggested that the XB-1 bound to the site I of HSA by competing with warfarin, which was perfect in agreement with the molecular docking method. The results of this paper may offer a valuable theoretical basis to study the toxicity of biofunctional molecules and may offer thoughts about how to avoid/reduce toxicity for a small molecule.

Effect of local anesthetic drug procaine hydrochloride on the conformational stability of bovine hemoglobin: Multi-spectroscopic and computational approaches

The interaction between bovine hemoglobin (BHb) and local anesthetic drug procaine hydrochloride (PCH) was examined by spectroscopic and computational studies. Intrinsic fluorescence analysis explored the ground-state complex formation in the binding of PCH with BHb through static quenching mechanism. The binding constants (K_b) are 29.38 × 10³, 22.54 × 10³ and 17.99 × 10³ M^-1 at 288, 298 and 308 K, respectively, and the ratio of BHb:PCH was 1:1 in the interaction mechanism of PCH and BHb. The acquired thermodynamic parameters (ΔH⁰, ΔG⁰ and ΔS⁰) demonstrated that interaction mechanism is spontaneous and enthalpy driven. The van der Waals forces and hydrogen bonding have been played a predominant role in the binding mechanism. The UV-vis spectroscopy validates the ground-state complexation between PCH and BHb and the binding constant (K_b) has been evaluated utilizing Benesi-Hildebrand equation. Fluorescence resonance energy transfer (FRET) results have demonstrated that the distance between donor (BHb) and acceptor (PCH) is very short (2.34 nm) suggesting a significant probability to energy transfer from BHb to PCH. Synchronous fluorescence results revealed that the alteration in the micro-environment of Tyrosine (Tyr) is more than tryptophan (Trp) residues suggesting that PCH molecule is close to Tyr residue. The secondary structure alterations were confirmed by CD, 3-D fluorescence and FT-IR spectroscopic measurements. Moreover, computational analyses further corroborated that PCH molecules are closer to Tyr residues as compared to Trp residues of BHb during the interaction process. The BHb-PCH complexes may contribute to a deeper understanding of the metabolism of drug, blood circulation process and may help to illustrate the relationship between functions and structure of BHb.Communicated by Ramaswamy H. Sarma.

Noncovalent molecular interactions between antineoplastic drug gemcitabine and a carrier protein identified through spectroscopic and in silico methods

Herein we have studied the noncovalent molecular interactions between hen egg white lysozyme (HEWL) and the commonly employed antineoplastic drug gemcitabine through the cumulative implementation of spectroscopic techniques and in silico approaches. The formation of a complex between HEWL and gemcitabine was made evident by the differences between the UV-visible spectra of the protein and protein-gemcitabine complex. Fluorescence quenching of HEWL by gemcitabine was hardly detectable at room temperature, but it became prominent at higher temperatures. Very low values for the bimolecular quenching constant and the non-reciprocal dependence of quenching on temperature indicated that dynamic quenching was taking place. Analysis of experimental data indicated that the interaction was dominated by hydrophobic forces, while the results of a computational investigation suggested the concomitant contribution of hydrogen bonding. Gemcitabine binding induced modifications of the secondary structure of HEWL by slightly increasing the α-helical content of the protein. Finally, gemcitabine binding site was inferred to be located in HEWL big hydrophobic cavity.

Assessment on the binding characteristics of residual marbofloxacin in animal-derived food to bovine/human serum albumin by spectroscopy and molecular modelling

To assess the toxicity of residual marbofloxacin from animal-derived food, the interaction characteristics of marbofloxacin to bovine/human serum albumins (BSA/HSA) were explored using spectroscopic methods combined with molecular modelling. According to fluorescence spectra and time-resolved fluorescence spectra measurements, quenching of BSA/HSA fluorescence induced by marbofloxacin was characterized as static quenching. A 1:1 ground-state complex of marbofloxacin to BSA/HSA was formed with binding constant (K_a ) 1.66 × 10⁴ /9.74 × 10³ M^-1 at 291 K. The location of marbofloxacin binding at site I within BSA/HSA was clarified by site marker competitive experiments. Molecular modelling demonstrated that the binding region for marbofloxacin to BSA and HSA were at site I with the lowest binding free energies of -22.86 and -21.60 kJ mol^-1 , respectively. Hydrogen bonds and van der Waals forces were dominantly involved in the spontaneous binding. Nonradiation energy transferred from BSA and HSA to marbofloxacin, due to the close distance (r₀ ) between marbofloxacin and Trp residues of BSA (4.28 nm) and HSA (3.34 nm). As explained by circular dichroism (CD) spectra, an increased BSA/HSA α-helix structure was observed after binding to marbofloxacin. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectra suggested that conformation of the two proteins was altered by marbofloxacin.

Investigation of the binding properties between levamlodipine and HSA based on MCR-ALS and computer modeling

Levamlodipine (LEE) is a drug commonly used for antihypertensive treatment in clinical therapy. The overlapping fluorescence spectra of LEE and human serum albumin (HSA) cause some trouble in analysis of interactions between them by using the classic fluorescence method. Here, the multivariate curve resolution-alternating least squares (MCR-ALS) approach was used to overcome this disadvantage. Meanwhile, the binding properties of LEE-HSA complex were then explored through computer modeling. The MCR-ALS results suggested that LEE-HSA complex was present in the mixture solution of LEE and HSA. This conclusion was then confirmed by the Stern-Volmer equation and time-resolved fluorescence experiment. The binding constant (K_a) was 2.139 × 10⁴ L·mol^-1 at 298 K. LEE was located close to the Trp-214 residue of HSA, with van der Waals forces and hydrogen bonding as main driving forces for this interaction. LEE can alter the conformation of HSA, in which the content of α-helix reduced from 57.2% to 52.3%. The Pi-Alkyl interactions contributed to maintaining the stability of the LEE-HSA complex. The results of molecular dynamics simulations showed that LEE-HSA complex was formed within 5 ns, and the particle size (R_g) of HSA was altered by the binding reaction. This study would promote better understanding of the transportation and distribution mechanisms of LEE in the human body.

Synthesis, Characterization, Photoluminescence, Molecular Docking and Bioactivity of Zinc (II) Compounds Based on Different Substituents

Six new zinc(II) complexes were prepared by the reaction of ZnBr₂ or ZnI₂ with 4′-(substituted-phenyl)-2,2′:6′,2′′-terpyridine compounds, bearing p-methylsulfonyl (L¹), p-methoxy (L²) and p-methyl (L³), which were characterized by elemental analysis, FT-IR, NMR and single crystal X-ray diffraction. The antiproliferative properties against Eca-109, A549 and Bel-7402 cell lines and the cytotoxicity test on RAW-264.7 of these compounds were monitored using a CCK-8 assay, and the studies indicate that the complexes show higher antiproliferative activities than cisplatin. The interactions of these complexes with CT-DNA and proteins (BSA) were studied by UV-Vis, circular dichroism (CD) and fluorescent spectroscopy, respectively. The results indicate that the interaction of these zinc(II) complexes with CT-DNA is achieved through intercalative binding, and their strong binding affinity to BSA is fulfilled through a static quenching mechanism. The simulation of the complexes with the CT-DNA fragment and BSA was studied by using molecular docking software. It further validates that the complexes interact with DNA through intercalative binding mode and that they have a strong interaction with BSA.

Spectroscopic and Molecular Docking Investigation on the Noncovalent Interaction of Lysozyme with Saffron Constituent "Safranal"

Owing to the various beneficial properties of the popular spice saffron, the interaction of safranal, a secondary metabolite of the former, with hen egg white lysozyme was investigated. The formation of a complex was evidenced by UV-visible spectroscopy. Fluorescence quenching experiments were also performed to understand the binding mechanism and to evaluate the forces involved in binding. The strong absorption of safranal in the range of excitation and emission wavelengths of lysozyme fluorescence required the correction of the inner filter effect for fluorescence spectra to obtain the apparent extent of binding. There was a considerable difference between the observed spectra and corrected spectra, and a similar observation was found in the case of synchronous fluorescence spectra. From the analysis of quenching data, it was found that the mechanism involved in quenching was static with 1:1 binding between them. The interaction was found to be driven, mainly, by hydrophobic forces and hydrogen bonding. Safranal had negligible impact on the secondary structure of lysozyme. The interaction was also studied by molecular docking, and the results were in good agreement with the results obtained experimentally. The binding site of safranal was in the big hydrophobic cavity of lysozyme. The amino acids involved in the interaction were Asp52, Ile58, Gln57, Asn59, Trp62, Trp63, Trp108, Ile98, Asp101, and Ala107.

Exploration of the binding between ellagic acid, a potentially risky food additive, and bovine serum albumin

Ellagic acid (EA), a natural plant polyphenol, is usually used as a functional additive in variety of health foods. However, the potential toxicity of EA to human health should be paid enough attention. To clarify its biological toxicity in vivo, this study explored the binding mechanism of EA with bovine serum albumin (BSA) by means of spectroscopic approaches and molecular docking insimulative physiological conditions. The results showed that the mixture of BSA with EA could spontaneously cause the formation of BSA-EA complex through electrostatic interaction under simulative physiological conditions (0.01 mol·L^-1Tris-HCl, 0.015 mol L^-1 NaCl, pH = 7.4). Molecular docking experiments revealed that EA was primarily bound to the hydrophobic pocket of the site I (subdomain IIA) of BSA. It has been reported that the binding of small functional molecules to serum albumins remarkably impacts their absorption, distribution, metabolism, and excretion features. Therefore, this study might be helpful for human to have an in-depth understanding of the biological effect of EA in vivo and guide human to take it safely and reasonably.

Interaction of repaglinide with bovine serum albumin: Spectroscopic and molecular docking approaches

Repaglinide (RPG) regulates the amount of glucose by stimulating the pancreas to release insulin in the blood. In view of its biological importance, we have examined the interaction between RPG and a model protein, bovine serum albumin (BSA) employing various spectroscopic, electrochemical and molecular docking methods. Fluorescence spectra of BSA were recorded in the presence and absence of RPG in phosphate buffer of pH 7.4. Fluorescence intensity of BSA was decreased upon the addition of increased concentrations of RPG, indicating the interaction between RPG and BSA. Stern-Volmer quenching analysis results revealed that RPG quenched the intensity of BSA through dynamic quenching mechanism. This was further confirmed from the time-resolved fluorescence measurements. The binding constant as calculated from the spectroscopic and voltammetric results was observed to be in the order of 10⁴ M⁻¹ at 298 K, suggesting the moderate binding affinity between RPG and BSA. Competitive experimental results revealed that the primary binding site for RPG on BSA was site II. Absorption and circular dichroism studies indicated the changes in the secondary structure of BSA upon its interaction with RPG. Molecular simulation studies pointed out that RPG was bound to BSA in the hydrophobic pocket of site II.

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Dynamic mode of quenching mechanism was noticed in RPG-BSA interaction.

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RPG was bound to BSA at the Sudlow’s site II and the resultant RPG-BSA complex was mainly stabilized by hydrophobic forces.

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The binding constant of RPG-BSA of the order of 10⁴ M⁻¹ at 298 K indicated the non-covalent interactions.

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Secondary structural changes in BSA upon binding to RPG were evident from absorption and circular dichroism studies.

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The influence of β-cyclodextrin and metal ions on RPG-BSA binding affinity was examined.

Fluorescent delivery vehicle containing cobalt oxide–umbelliferone nanoconjugate: DNA/protein interaction studies and anticancer activity on MF7 cancer cell line

Fluorescent labeling is limited to certain molecules and alters biomolecule functionality. A new class of nanomaterial with anticancer activity and fluorescence properties has been designed and prepared. This nanotherapeutic conjugate of natural molecules has a selective binding site in cancer cell lines. Natural drug umbelliferone was taken with cobalt metal ions in a one pot assembly in the presence of tannic acid which yields new fluorescent nanoparticles of umbelliferone cobalt oxide nanoconjugate. Umbelliferone has high fluorescent properties and also has coordination ability to bind with central metal ions. The nanoconjugate was synthesized and characterized by using TEM, EDX analysis, SEM, XRD, and FTIR spectroscopy. TEM shows that the average size of the particles formed with umbelliferone is ∼20 nm. The solubility of the drug nanoparticles in water showed compatibility with cancer cells and provided a favorable environment to investigate the mechanism of action on the MCF-7 cell line. The nanoconjugate is microcrystalline in nature and gives a clear suspension in water. The nanocobalt conjugate was loaded on TiO₂ nanoparticles by ultrasonication, and the solution was digested overnight. The conjugate of the drug with a TiO₂ drug carrier was stable in solution and maintained the nanostructure ∼34.6 nm. A comparative study with nano-vehicle TiO₂ and the nanoconjugate was performed. TiO₂ was used to compare the anti-cancer activity of the nanoconjugate at low dose in vitro. It was observed that the nanoconjugate with TiO₂ is capable of reaching the specific target like the TiO₂ nanoparticle and enhance the chemotherapeutic impact. Hence, the nanoconjugate can also be used like nano-TiO₂, as the drug and carrier. The ct-DNA and HSA protein binding studies were done and validated by docking studies.

Model of drug-nanoconjugate with DNA and HSA.

Evaluation of (ɳ6-p-cymene) ruthenium diclofenac complex as anticancer chemotherapeutic agent: interaction with biomolecules, cytotoxicity assays

The designing of metal-based anticancer therapeutic agents can be optimized in a better and rapid way if the ligands utilized have standalone properties. Therefore, even when the organometallic/coordination complex (i.e., metallodrug) gets dissociated in extreme conditions, the ligand can endorse its biological properties. Herein, we have synthesized and characterized ɳ⁶-p-cymene ruthenium diclofenac complex. Furthermore, the ruthenium complex interactions with human serum albumin (HSA) and ct-DNA have been studied using various spectroscopic studies viz., UV, fluorescence, and circular dichroism and exhibited a significant binding propensity. Furthermore, in vitro cytotoxicity assays were carried out against human breast cancer "MCF-7" cell line. The ɳ⁶-p-cymene ruthenium diclofenac complex registered significant cytotoxicity with an IC₅₀ value of ∼25.0 µM which is comparable to the standard drugs. The ɳ⁶-p-cymene ruthenium diclofenac complex was able to decrease the MCF-7 cell proliferation and induced significant levels of apoptosis with relatively low toxicity.

Spectroscopic and computational evaluation on the binding of safranal with human serum albumin: Role of inner filter effect in fluorescence spectral correction

For determining the pharmacological properties of medicinal compounds, their binding with serum albumins is very crucial. Herein, we have selected safranal, a major constituent of saffron which is known to retain a number of medicinal properties including antioxidant, anti-inflammatory, tumoricidal, anti-genotoxic, and anti-aging activities; and studied its mechanism of binding with human serum albumin at physiological pH using various spectroscopic methods along with computational approach using molecular docking. A change in the difference UV-visible spectrum of HSA in presence of safranal was found which is due to the complex formation. Owing to the strong absorption of safranal at the fluorescence excitation wavelength of HSA (295 nm) and in the whole range of emission, the fluorescence spectra of HSA in presence of safranal were corrected for the inner filter effect. After the correction the spectra were free from the safranal absorption effect and it was found that addition of safranal causes the quenching of HSA fluorescence and a blue shift of the emission maximum which are attributed to the binding of safranal to the protein and dominance of hydrophobic forces in the interaction, respectively. It was evident from the comparison of observed and corrected fluorescence spectra that before correction there was a large red shift while after correction appearance of blue shift was occurred. The involvement of hydrophobic interaction was also found from the extrinsic fluorescence measurements using ANS dye as well as from the analyzed thermodynamic parameters. Safranal was found to partially induce the secondary structure of HSA as construed from the CD measurements. The size of the HSA was also decreased as evident from the DLS and RLS measurements. Both site marker studies and molecular docking simulations suggested that the primary binding site of the safranal in the HSA is Sudlow's site 1 located in the subdomain IIA. Hydrophobic interaction provides the major contribution to the binding forces along with a little amount of hydrogen bonding.

Interactions of hemin with bovine serum albumin and human hemoglobin: A fluorescence quenching study

The binding interactions between hemin (Hmi) and bovine serum albumin (BSA) or human hemoglobin (HHb), respectively, have been examined in aqueous solution at pH=7.4, applying UV-vis absorption, as well as steady-state, synchronous and three-dimensional fluorescence spectra techniques. Representative results received for both BSA and HHb intrinsic fluorescence proceeding from the interactions with hemin suggest the formation of stacking non-covalent and non-fluorescent complexes in both the Hmi-BSA and Hmi-HHb systems, with highly possible concurrent formation of a coordinate bond between a group on the protein surface and the metal in Hmi molecule. All the values of calculated parameters, the binding, fluorescence quenching and bimolecular quenching rate constants point to the involvement of static quenching in both the systems studied. The blue shift in the synchronous fluorescence spectra imply the participation of both tryptophan and tyrosine residues in quenching of BSA and HHb intrinsic fluorescence. Depicted outcomes suggest that hemin is supposedly able to influence the physiological functions of BSA and HHb, the most important blood proteins, particularly in case of its overuse.

Comprehensive exploration of the anticancer activities of procaine and its binding with calf thymus DNA: a multi spectroscopic and molecular modelling study

DNA demethylating agent procaine binds at the minor groove of ct-DNA and increases the anticancer activity of doxorubicin.