Separate and simultaneous binding effects through a non-cooperative behavior between cyclophosphamide hydrochloride and fluoxymesterone upon interaction with human serum albumin: multi-spectroscopic and molecular modeling approaches

Exploring high hydrostatic pressure effects on anthocyanin binding to serum albumin and food-derived transferrins

This study investigated the effects of high hydrostatic pressure (HHP) on the binding interactions of cyanindin-3-O-glucoside (C3G) to bovine serum albumin, human serum albumin (HSA), bovine lactoferrin, and ovotransferrin. Fluorescence quenching revealed that HHP reduced C3G-binding affinity to HSA, while having a largely unaffected role for the other proteins. Notably, pretreating HSA at 500 MPa significantly increased its dissociation constant with C3G from 24.7 to 34.3 μM. Spectroscopic techniques suggested that HSA underwent relatively pronounced tertiary structural alterations after HHP treatments. The C3G-HSA binding mechanisms under pressure were further analyzed through molecular dynamics simulation. The localized structural changes in HSA under pressure might weaken its interaction with C3G, particularly polar interactions such as hydrogen bonds and electrostatic forces, consequently leading to a decreased binding affinity. Overall, the importance of pressure-induced structural alterations in proteins influencing their binding with anthocyanins was highlighted, contributing to optimizing HHP processing for anthocyanin-based products.

Electrostatic interactions mediated defibrillation of β-lactoglobulin fibrils using Keggin Polyoxometalates

The whey protein β-lactoglobulin (βLG) forms fibrils similar to the amyloid fibrils in the neurodegenerative diseases due to its higher predisposition of β-sheets. This study shed light on the understanding different inorganic Keggin polyoxometalates (POMs) interaction with the protein βLG fibrils. POMs such as Phosphomolybdic acid (PMA), silicomolybdic acid (SMA), tungstosilicic acid (TSA), and phosphotungstic acid (PTA) were used due to their inherent higher anionic charges. The interaction studies were monitored with fluorescence spectra and Thioflavin T assay for both the βLG monomers and the fibrils initially to elucidate the binding ability of the POMs. The binding of POMs and βLG is also demonstrated by molecular docking studies. Zeta potential studies showed the electrostatic mediated higher interactions of the POMs with the protein fibrils. Isothermal titration calorimetry (ITC) studies showed that the molybdenum containing POMs have higher affinity to the protein fibrils than the tungsten. This study could help understanding formation of food grade protein fibrils which have profound importance in food industries.

Effects of myricetin and its derivatives on nonenzymatic glycation: A mechanism study based on proteomic modification and fluorescence spectroscopy analysis

Myricetin and its derivatives, myricitrin and dihydromyricetin, are flavonoids widely presented in foods and phytomedicine that possess tremendous health potential. In this study, we compared the antiglycation activity of myricetin and its derivatives, then investigated the underlying mechanism using proteomic modification and fluorescence spectroscopy analysis. All three compounds exhibited thorough inhibition on nonenzymatic glycation process, with the inhibitory effects on AGEs reaching 85% at 40 μmol/L. They effectively protected bovine serum albumin (BSA) structure by inhibiting protein oxidation, preventing the conversion from α-helix to β-sheet, and reducing amyloid-like cross-β structure formation. Among the three compounds, myricetin showed a predominant antiglycation activity. Proteomic analysis identified the early glycated sites that were protected by myricetin, including lysine K235, 256, 336, 421, 420, 489, etc. Additionally, fluorescence spectroscopy revealed spontaneous interactions between BSA and myricetin. Overall, myricetin holds promise as an antiglycation agent in both the food and drug industries.

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.

Biosensor Detection of COVID-19 in Lung Cancer: Hedgehog and Mucin Signaling Insights

Coronavirus disease 2019 is a global pandemic, particularly affecting individuals with pre-existing lung conditions and potentially leading to pulmonary fibrosis. Age and healthcare system limitations further amplify susceptibility to both diseases, especially in low- and middle-income countries. The intricate relationship between Coronavirus disease 2019 and lung cancer highlights their clinical implications and the potential for early detection through biosensor techniques involving hedgehog and mucin signaling. This study highlights the connection between Coronavirus disease 2019 and lung cancer, focusing on the mucosa, angiotensin- altering enzyme 2 receptors, and their impact on the immune system. It details the inflammatory mechanisms triggered by Coronavirus disease 2019, which can result in pulmonary fibrosis and influence the cancer microenvironment. Various cytokines like Interleukins-6 and Tumor Necrosis Factor-alpha are examined for their roles in both diseases. Moreover, the review delves into the Hedgehog signaling pathways and their significance in lung cancer, particularly their influence on embryonic cell proliferation and tissue integrity. Mucin signaling is another vital aspect, highlighting the diverse mucin expression patterns in respiratory epithelial tissues and their potential as biomarkers. The review concludes with insights into diagnostic imaging techniques like chest computed tomography, Positron Emission Tomography and Computed Tomography, and Magnetic Resonance Imaging for early lung cancer detection, emphasizing the crucial role of biosensors in identifying specific biomarkers for early disease detection. This review provides a comprehensive overview of the clinical impact of Coronavirus disease 2019 on lung cancer patients and the potential for biosensors utilizing hedgehog and mucin signaling for early detection. It underscores the ongoing need for research and innovation to address these critical healthcare challenges.

Elucidation of binding mechanism of stigmasterol with human serum albumin: a biophysical and molecular dynamics simulation approach

In the present study, we have analyzed the interaction of a phytochemical, stigmasterol (Stig), with human serum albumin (HSA) under physiological conditions using fluorescence quenching, circular dichroism and molecular modeling methods. Cytotoxic studies with Stig in mouse macrophages (RAW 246.7) and HeLa cell lines showed anti-inflammatory and anti-cancer properties. Further, the intrinsic fluorescence of HSA was quenched by Stig, which was considered a static quenching mechanism. The site-specific marker experiments revealed that Stig binds to the IIIA subdomain of HSA with a binding constant of K_Stig=1.8 ± 0.03 × 10⁵ M^-1 and free energy of -7.26 ± 0.031 Kcal/mol. The secondary structure of HSA was partially unfolded after binding of Stig, which indicates an alteration in the microenvironment of the protein binding site. Molecular docking experiments found that Stig binds strongly with HSA at the IIIA domain of the hydrophobic pocket with one hydrogen bond. The rigidity of the protein-Stig complex and free energies were analyzed by molecular dynamic simulation (MDS) for 100 ns, where the HSA-Stig was stabilized after 40 ns. MDS studies revealed that HSA does not significantly change the secondary structure when it binds with Stig, which is in agreement with the circular dichroism data. Overall, the results obtained gave qualitative and quantitative insight into the binding interaction between HSA and Stig, which is essential in understanding the latter as a therapeutic molecule.Communicated by Ramaswamy H. Sarma.

Insight on the microscopic binding mechanism of bisphenol compounds (BPs) with transthyretin (TTR) based on multi-spectroscopic methods and computational simulations

Thyroid hormones are involved in numerous physiological processes as regulators of metabolism, regulating organ growth, and mental state. Bisphenol compounds (BPs) are recognized as chemicals that interfere with endocrine balance. Because BPs have a similar structure to thyroxine, they can compete for binding to thyroid protein and disrupt the normal physiological activity of the thyroid system. In this study, three typical bisphenol compounds were selected to explore the interaction between BPs and TTR by computer simulations and multi-spectroscopic methods. The results revealed that BPs quenched the endogenous fluorescence of TTR via the combination of static quenching and non-radiative energy transfer, and the van der Waals forces and hydrogen bonding played a synergistic role in the binding process of BPs and TTR. Furthermore, the three-dimensional fluorescence spectroscopy, UV-vis spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, which were employed to determine the conformation of protein, revealed that binding of BPs with TTR could induce conformational changes in TTR. In addition, the binding sites and the residues surrounding the BPs within the TTR were determined through molecular docking and molecular dynamics simulation. Therefore, this work provides new insights into the interaction between BPs and TTR to evaluate the potential toxicity of BPs.

Nobiletin, a hexamethoxyflavonoid from citrus pomace, attenuates G1 cell cycle arrest and apoptosis in hypoxia-induced human trophoblast cells of JEG-3 and BeWo via regulating the p53 signaling pathway

Background

Hypoxia is associated with abnormal cell apoptosis in trophoblast cells, which causes fetal growth restriction and related placental pathologies. Few effective methods for the prevention and treatment of placenta-related diseases exist. Natural products and functional foods have always been a rich source of potential anti-apoptotic drugs. Nobiletin (NOB), a hexamethoxyflavonoid derived from the citrus pomace, shows an anti-apoptotic activity, which is a non-toxic constituent of dietary phytochemicals approved by the Food and Drug Administration. However, their effects on hypoxia-induced human trophoblast cells have not been fully studied.

Objective

The aim of this study was to investigate the protective effects of NOB on hypoxia-induced apoptosis of human trophoblast JEG-3 and BeWo cells, and their underlying mechanisms.

Design

First, the protective effect of NOB on hypoxia-induced apoptosis of JEG-3 and BeWo cells was studied. Cell viability and membrane integrity were determined by CCK-8 assay and lactate dehydrogenase activity, respectively. Real Time Quantitative PCR (RT-qPCR) and Western blot analysis were used to detect the mRNA and protein levels of HIF1α. Propidium iodide (PI)-labeled flow cytometry was used to detect cell cycle distribution. Cell apoptosis was detected by flow cytometry with Annexin V-FITC and PI double staining, and the expression of apoptosis marker protein cl-PARP was detected by Western blot analysis. Then, the molecular mechanism of NOB against apoptosis was investigated. Computer molecular docking and dynamics were used to simulate the interaction between NOB and p53 protein, and this interaction was verified in vitro by Ultraviolet and visible spectrum (UV-visible spectroscopy), fluorescence spectroscopy and circular dichroism. Furthermore, the changes in the expression of p53 signaling pathway genes and proteins were detected by RT-qPCR and Western blot analysis, respectively.

Results

Hypoxia treatment resulted in a decreased cell viability and cell membrane integrity in JEG-3 and BeWo cell lines, and an increased expression of HIF1α, cell cycle arrest in the G1 phase, and massive cell apoptosis, which were alleviated after NOB treatment. Molecular docking and dynamics simulations found that NOB spontaneously bonded to human p53 protein, leading to the change of protein conformation. The intermolecular interaction between NOB and human p53 protein was further confirmed by UV-visible spectroscopy, fluorescence spectroscopy and circular dichroism. After the treatment of 100 μM NOB, a down-regulation of mRNA and protein levels of p53 and p21 and an up-regulation of BCL2/BAX mRNA and protein ratio were observed in JEG-3 cells; however, there was also a down-regulation of mRNA and protein levels observed for p53 and p21 in BeWo cells after the treatment of NOB. The BCL2/BAX ratio of BeWo cells did not change after the treatment of 100 μM NOB.

Conclusion

NOB attenuated hypoxia-induced apoptosis in JEG-3 and BeWo cell lines and might be a potential functional ingredient to prevent pregnancy-related diseases caused by hypoxia-induced apoptosis. These findings would also suggest the exploration and utilization of citrus resources, and the development of citrus industry.

Characterizing the Binding of Angiotensin Converting Enzyme I Inhibitory Peptide to Human Hemoglobin: Influence of Electromagnetic Fields

Background:

Drug-protein complexes is one of the crucial factors when analyzing the pharmacokinetics and pharmacodynamics of a drug because they can affect the excretion, distribution, metabolism and interaction with target tissues.

Objectives:

The aim of this study was to investigate the interaction of human hemoglobin (Hb) and angiotensin I converting enzyme inhibitory peptide (ACEIP) in the absence and presence of different- frequency electromagnetic fields (EMF).

Methods:

Various spectroscopic methods like fluorescence spectroscopy, ultraviolet, circular dichroism and conductometry techniques were applied to investigate Hb-ACEIP interaction in the absence and presence of EMF.

Result:

The presented spectroscopic studies indicated that EMF changed the interaction between Hb and ACEIP. The a-helix content of Hb decreased upon binding to ACEIP and conductivity of the solution enhanced upon binding. Based on Stern-Volmer equations, it could be stated that the Hb-ACEIP affinity was higher in the presence of EMF.

Conclusion:

It can be concluded that for patients who use the drug to control blood pressure, a low-frequency electromagnetic field would have a positive effect on the uptake of the drug.

Probing the interaction of a coumarin-di(2-picolyl)amine hybrid drug-like molecular entity with human serum albumin: Multiple spectroscopic and molecular modeling techniques

HSA is an important plasma protein responsible for transport of drug molecules. Coumarin derivatives play critical role as anticancer, antidiabetic and antiparkinson agents. In our lab we have synthesized coumarin-based pharmacophore, di(2-picolyl)amine-3(bromoacetyl) coumarin (ligand-L) endowed with anticancer activity. Anticancer agents binding mode of HSA provides valuable pharmacological information and is a structural guidance in synthesizing new drugs with greater efficacy. Thus, binding mechanism of ligand-L with HSA was explored using spectroscopic and molecular docking techniques. UV-Vis spectroscopy demonstrates hyperchromism in the absorbance spectra of HSA on addition of ligand-L suggesting interaction of ligand-L with HSA. Fluorescence spectroscopy indicates quenching in the fluorescence of HSA in the presence of ligand-L confirming the complex formation and this binding follows static mechanism. Steady state fluorescence spectroscopy revealed high binding affinity between ligand-L and HSA with a 1:1 stoichiometry. Thermodynamic parameters obtained by ITC suggest that the interaction between ligand-L and HSA is mainly driven by van der Waals forces and hydrogen bonds, and the negative value of ΔG is an indication of spontaneous binding process. Competitive binding and molecular docking experiments showed that the binding site of ligand-L mainly resides in sub-domain IIA of HSA. CD experiments revealed no significant conformational changes in the secondary structure of HSA on binding of ligand-L. We also found that esterase-like activity of HSA was not affected by ligand-L. In conclusion, this study demonstrates binding mechanism of ligand-L with HSA, and the binding did not induce conformational changes in HSA. This study is likely to provide better understanding of transport and delivery of ligand-L via HSA. Overall, it will provide insights into pharmacokinetic properties of ligand-L and designing new ligand-L based derivatives with greater efficacy.

A ratiometric nanoprobe based on silver nanoclusters and carbon dots for the fluorescent detection of biothiols

Ratiometric fluorescent probes could eliminate the influence from experimental factors and improve the detection accuracy. In this article, a ratiometric nanoprobe was constructed based on silver nanoclusters (AgNCs) with nitrogen-doped carbon dots (NCDs) and used for the detection of biothiols. The fluorescence peak of AgNCs was observed at 650nm with excitation wavelength at 370nm. In order to construct the ratiometric fluorescent probe, NCDs with the excitation and emission wavelengths at 370nm and 450nm were selected. After adding AgNCs, the fluorescence of NCDs was quenched. The mechanism of the fluorescence quenching was studied by fluorescence, UV-Vis absorption and the fluorescence lifetime spectra. The results indicated that the quenching could be ascribed to the inner filter effect (IFE). With the addition of biothiols, the fluorescence of AgNCs at 650nm decreased due to the breakdown of AgNCs, and the fluorescence of NCDs at 450nm recovered accordingly. Thus, the relationship between the ratio of the fluorescence intensities (I₄₅₀/I₆₅₀) and biothiol concentration was used to establish the determination method for biothiols. Cysteine (Cys) was taken as the model of biothiols, and the working curve for Cys was I₄₅₀/I₆₅₀=0.60C_Cys-1.86 (C_Cys: μmol/L) with the detection limit of 0.14μmol/L (S/N=3). Then, the method was used for the detection of Cys in human urine and serum samples with satisfactory accuracy and recovery ratios. Furthermore, the probe could be applied for the visual semi-quantitative determination of Cys by naked eyes.

Ultrasound-assisted interaction between chlorin-e6 and human serum albumin: pH dependence, singlet oxygen production, and formulation effect

The interaction between chlorin e6 (Ce6) and human serum albumin (HSA) in the presence and absence of ultrasound have been investigated by ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. Ce6 is found to bind strongly to HSA at or near physiological pH conditions, but the strength of the binding is significantly weakened at lower pHs. The intrinsic fluorescence of HSA is incrementally quenched with increasing concentration of Ce6, and the quenching is enhanced after exposure to high-frequency ultrasound. Our experimental results suggest that Ce6-induced sonodynamic oxidation of HSA is mainly mediated by singlet oxygen. The formulation of Ce6 by high molecular weight polyvinylpyrrolidone (PVP) increased its stability in aqueous solutions and its quantum yield of singlet oxygen under ultrasound irradiation.

The mechanism and conformational changes of polybrominated diphenyl ethers to TTR by fluorescence spectroscopy, molecular simulation, and quantum chemistry

Free energy contribution of amino acid LYS (B and D chains) and PDBEs was analyzed combining quantum chemistry and molecular modeling.

Decrease of the affinity of theophylline bind to serum proteins induced by flavonoids and their synergies on protein conformation

In this study, the single and simultaneous interactions of theophylline and flavonoids with human serum albumin (HSA) were studied by multi-spectroscopic and molecular docking approaches. The influences of flavonoids on the binding constant (K_b) and the binding distance (r) of theophylline bind to HSA were determined and the changes of HSA conformation caused by the synergies of theophylline and flavonoids were investigated. Because theophylline, rutin and baicalin are all bond to the same binding site, the competitive bind of theophylline and flavonoids to HSA leads to the reduction of the K_a value of theophylline binding to HSA. The addition of rutin and baicalin can increase the value of r of theophylline binding to HSA, which further confirm the existence of the competitive bind of theophylline and flavonoids to HSA. Additionally, the results of synchronous fluorescence, three-dimensional fluorescence and circular dichroism spectra indicate that the presence of rutin and baicalin can give rise to the further changes of HSA conformation. These results suggest that the intake of flavonoid-rich food and beverages can increase the serum concentrations of theophylline and induce a high incidence of toxic symptom in clinic.

Fluorescence quenching study on the interaction of ferroferric oxide nanoparticles with bovine serum albumin

Fluorescence quenching was used to study the potential interaction mechanism of Bovine serum albumin (BSA) with either hydrophilic ferroferric oxide (Fe₃O₄) nanoparticles (NPs) or hydrophobic Fe₃O₄ NPs. The experimental results indicated the mechanism between BSA and hydrophilic Fe₃O₄ NPs was static quenching and the one between BSA and hydrophobic Fe₃O₄ NPs was dynamic process that was drove by Förster's resonance energy transfer (FRET). And the binding parameters for the interaction of BSA with either hydrophilic or hydrophobic Fe₃O₄ NPs were calculated by using the fluorescence quenching measurement. The binding constant (K_A) values of hydrophilic Fe₃O₄ NPs were 8518.73±23.35 (at 298K), 1190.31±15.41 (at 306K) and 321.97±8.57 (at 313K), respectively. The thermodynamic analysis implied that the intermolecular forces between BSA and hydrophilic Fe₃O₄ NPs were Van der Waals interaction or hydrogen bond, because the values of ΔH and ΔS between them were negative. While the one of BSA and hydrophobic Fe₃O₄ NPs involved hydrophobic forces, owing to the positive ΔH and ΔS between them. But they were all enthalpy-driven and exothermic, since their ΔG values were all negative. Synchronous fluorescence spectroscopy suggested that the conformation of tryptophan residue of BSA was changed in the presence of hydrophilic Fe₃O₄ NPs or hydrophobic Fe₃O₄ NPs, because the position of the maximum emission wavelength had a discernible red shift.

Molecular interaction of 2,4-diacetylphloroglucinol (DAPG) with human serum albumin (HSA): The spectroscopic, calorimetric and computational investigation

Drug molecule interaction with human serum albumin (HSA) affects the distribution and elimination of the drug. The compound, 2,4-diacetylphloroglucinol (DAPG) has been known for its antimicrobial, antiviral, antihelminthic and anticancer properties. However, its interaction with HSA is not yet reported. In this study, the interaction between HSA and DAPG was investigated through steady-state fluorescence, time-resolved fluorescence (TRF), circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopy, isothermal titration calorimetry (ITC), molecular docking and molecular dynamics simulation (MDS). Fluorescence spectroscopy results showed the strong quenching of intrinsic fluorescence of HSA due to interaction with DAPG, through dynamic quenching mechanism. The compound bound to HSA with reversible and moderate affinity which explained its easy diffusion from circulatory system to target tissue. The thermodynamic parameters from fluorescence spectroscopic data clearly revealed the contribution of hydrophobic forces but, the role of hydrogen bonds was not negligible according to the ITC studies. The interaction was exothermic and spontaneous in nature. Binding with DAPG reduced the helical content of protein suggesting the unfolding of HSA. Site marker fluorescence experiments revealed the change in binding constant of DAPG in the presence of site I (warfarin) but not site II marker (ibuprofen) which confirmed that the DAPG bound to site I. ITC experiments also supported this as site I marker could not bind to HSA-DAPG complex while site II marker was accommodated in the complex. In silico studies further showed the lowest binding affinity and more stability of DAPG in site I than in site II. Thus the data presented in this study confirms the binding of DAPG to the site I of HSA which may help in further understanding of pharmacokinetic properties of DAPG.

Spectroscopic studies of the interaction mechanisms between mono-caffeoylquinic acids and transferrin

Transferrin (Tf) is an important protein responsible for circulating and transporting iron into cytoplasm. Tf can be taken into cells through endocytosis mediated by Tf receptor, which usually overexpresses in cancer cells. The Tf-Tf receptor pathway opens a possible avenue for novel targeted cancer therapy by utilizing Tf-binding active compounds. Among which, anti-cancer active caffeoylquinic acids (CQAs) were recently found to be promising Tf-binders by our group. For better understanding the anti-cancer activities of CQAs, it is important to unveil the binding mechanisms between CQAs and Tf. In this study, the fluorescence quenching, surface plasmon resonance (SPR), circular dichroism (CD) and molecular docking were used to investigate the interactions between CQA and Tf. The results showed that the calculated apparent association constants of interactions between 1-, 3-, 4- and 5-CQA and Tf at 298K were 7.97×10⁵M^-1, 4.36×10⁷M^-1, 6.58×10⁵M^-1 and 4.42×10⁶M^-1, respectively. The thermodynamic parameters indicated that the interaction between 1-, 3-, 5-CQA and Tf is due to H-bonding, and electrostatic interactions were likely involved in the binding of 4-CQA and Tf. The CD results indicated that bindings of 1-CQA, 4-CQA and 5-CQA with Tf resulted in more stretched β-turn and random coil translated from β-sheet. In contrast, 3-CQA led to more stable a-helix conformation. Molecular docking studies of CQAs with Tf further displayed that CQAs were able to interact with residues near Fe³⁺ binding site. The spectroscopic studies revealed the action mechanisms, thermodynamics and interacting forces between CQAs and Tf, and thus are helpful for future design and discovery of Tf-binders for targeted cancer therapy applying Tf-Tf receptor pathway.

Interaction between 8-methoxypsoralen and trypsin: Monitoring by spectroscopic, chemometrics and molecular docking approaches

8-Methoxypsoralen (8-MOP) is a naturally occurring furanocoumarin with various biological activities. However, there is little information on the binding mechanism of 8-MOP with trypsin. Here, the interaction between 8-MOP and trypsin in vitro was determined by multi-spectroscopic methods combined with the multivariate curve resolution-alternating least squares (MCR-ALS) chemometrics approach. An expanded UV-vis spectral data matrix was analysed by MCR-ALS, the concentration profiles and pure spectra for the three reaction species (trypsin, 8-MOP and 8-MOP-trypsin) were obtained to monitor the interaction between 8-MOP and trypsin. The fluorescence data suggested that a static type of quenching mechanism occurred in the binding of 8-MOP to trypsin. Hydrophobic interaction dominated the formation of the 8-MOP-trypsin complex on account of the positive enthalpy and entropy changes, and trypsin had one high affinity binding site for 8-MOP with a binding constant of 3.81×10⁴Lmol^-1 at 298K. Analysis of three dimensional fluorescence, UV-vis absorption and circular dichroism spectra indicated that the addition of 8-MOP induced the rearrangement of the polypeptides carbonyl hydrogen-bonding network and the conformational changes in trypsin. The molecular docking predicted that 8-MOP interacted with the catalytic residues His57, Asp102 and Ser195 in trypsin. The binding patterns and trypsin conformational changes may result in the inhibition of trypsin activity. This study has provided insights into the binding mechanism of 8-MOP with trypsin.

Comparison of the interaction between lactoferrin and isomeric drugs

The binding properties of pentacyclic triterpenoid isomeric drugs, i.e. ursolic acid (UA) and oleanolic acid (OA), to bovine lactoferrin (BLF) have been studied by molecule modeling, fluorescence spectroscopy, UV-visible absorbance spectroscopy and infrared spectroscopy (IR). Molecular docking, performed to reveal the possible binding mode or mechanism, suggested that hydrophobic interaction and hydrogen bonding play important roles to stabilize the complex. The results of spectroscopic measurements showed that the two isomeric drugs both strongly quenched the intrinsic fluorescence of BLF through a static quenching procedure although some differences between UA and OA binding strength and non-radiation energy transfer occurred within the molecules. The number of binding sites was 3.44 and 3.10 for UA and OA, respectively, and the efficiency of Förster energy transfer provided a distance of 0.77 and 1.21nm for UA and OA, respectively. The conformation transformation of BLF affected by the drugs conformed to the "all-or-none" pattern. In addition, the changes of the ratios of α-helices, β-sheets and β-turns of BLF during the process of the interaction were obtained. The results of the experiments in combination with the calculations showed that there are two modes of pentacyclic triterpenoid binding to BLF instead of one binding mode only governed by the principle of the lowest bonding energy.

Interactions of cephalexin with bovine serum albumin: displacement reaction and molecular docking

Introduction: The drug-plasma protein interaction is a fundamental issue in guessing and checking the serious drug side effects related with other drugs. The purpose of this research was to study the interaction of cephalexin with bovine serum albumin (BSA) and displacement reaction using site probes.

Methods: The interaction mechanism concerning cephalexin (CPL) with BSA was investigated using various spectroscopic methods and molecular modeling method. The binding sites number, n, apparent binding constant, K, and thermodynamic parameters, ΔG⁰, ΔH⁰, and ΔS⁰ were considered at different temperatures. To evaluate the experimental results, molecular docking modeling was calculated.

Results: The distance, r=1.156 nm between BSA and CPL were found in accordance with the Forster theory of non-radiation energy transfer (FRET) indicating energy transfer occurs between BSA and CPL. According to the binding parameters and ΔG⁰= negative values and ΔS⁰= 28.275 j mol^-1K^-1, a static quenching process is effective in the CPL-BSA interaction spontaneously. ΔG⁰ for the CPL-BSA complex obtained from the docking simulation is -28.99 kj mol^-1, which is close to experimental ΔG of binding, -21.349 kj mol^-1 that indicates a good agreement between the results of docking methods and experimental data.

Conclusion: The outcomes of spectroscopic methods revealed that the conformation of BSA changed during drug-BSA interaction. The results of FRET propose that CPL quenches the fluorescence of BSA by static quenching and FRET. The displacement study showed that phenylbutazon and ketoprofen displaced CPL, indicating that its binding site on albumin is site I and Gentamicin cannot be displaced from the binding site of CPL. All results of molecular docking method agreed with the results of experimental data.

Effect of peroxynitrite on human serum albumin: a multi technique approach

In this study, human serum albumin (HSA), the most abundant protein of blood plasma, was modified with varying concentrations of peroxynitrite. The peroxynitrite-induced changes in HSA was monitored by spectroscopy, SDS-PAGE, 1-anilinonaphthalene-8-sulfonic acid (ANS), thermal denaturation studies, and matrix-assisted laser desorption/inonization-time of flight mass spectrometry (MALDI-TOF MS). Aggregate formation was studied by thioflavin T binding and scanning electron microscopy (SEM). The results indicated formation of 3-nitrotyrosine, 6-nitrotryptophan, dityrosine, and carbonyls in modified samples and showed retarded mobility in SDS-polyacrylamide gel. Reduction in α-helicity and surface protein hydrophobicity confirmed the secondary and tertiary structure alterations in peroxynitrite-modified-HSA. Also, attachment of nitro group and increase in melting temperature was observed in modified sample. Furthermore, significant enhancement in the fluorescence intensity of ThT upon binding with peroxynitrite-modified-HSA and images under scanning electron microscope are suggestive of protein aggregation. It is, therefore, speculated that HSA modified by endogenously formed peroxynitrite might act as a trigger for nitration/aggregation and suggested the role of peroxynitrite-modified-HSA in SLE.

Conjugation of biogenic and synthetic polyamines with serum proteins: A comprehensive review

We have reviewed the conjugation of biogenic polyamines spermine (spm), spermidine (spmd) and synthetic polyamines 3,7,11,15-tetrazaheptadecane.4HCl (BE-333) and 3,7,11,15,19-pentazahenicosane.5HCl (BE-3333) with human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) in aqueous solution at physiological pH. The results of multiple spectroscopic methods and molecular modeling were analysed here and correlations between polyamine binding mode and protein structural changes were estabilished. Polyamine-protein bindings are mainly via hydrophilic and H-bonding contacts. BSA forms more stable conjugates than HSA and b-LG. Biogenic polyamines form more stable complexes than synthetic polyamines except in the case of b-LG, where the protein shows more hydrophobic character than HSA and BSA. The loading efficacies were 40-52%. Modeling showed the presence of several H-bonding systems, which stabilized polyamine-protein conjugates. Polyamine conjugation induced major alterations of serum protein conformations. The potential application of serum proteins in delivery of polyamines is evaluated here.

Studies on the interaction between promethazine and human serum albumin in the presence of flavonoids by spectroscopic and molecular modeling techniques

Fluorescence, absorption, time-correlated single photon counting (TCSPC), and circular dichroism (CD) spectroscopic techniques as well as molecular modeling methods were used to study the binding characterization of promethazine (PMT) to human serum albumin (HSA) and the influence of flavonoids, rutin and baicalin, on their affinity. The results indicated that the fluorescence quenching mechanism of HSA by PMT is a static quenching due to the formation of complex. The reaction was spontaneous and mainly mediated by hydrogen bonds and hydrophobic interactions. The binding distance between the tryptophan residue of HSA and PMT is less than 8nm, which indicated that the energy transfer from the tryptophan residue of HSA to PMT occurred. The binding site of PMT on HSA was located in sites I and the presence of PMT can cause the conformational changes of HSA. There was the competitive binding to HSA between PMT and flavonoids because of the overlap of binding sites in HSA. The flavonoids could decrease the association constant and increase the binding distance. In addition, their synergistic effect can further change the conformation of HSA. The decrease in the affinities of PMT binding to HSA in the presence of flavonoids may lead to the increase of free drug in blood, which would affect the transportation or disposition of drug and evoke an adverse or toxic effect. Hence, rationalising dosage and diet regimens should be taken into account in clinical application of PMT.

Comparative study of the effects of the structurally similar flavonoids quercetin and taxifolin on the therapeutic behavior of alprazolam

After a meal rich in plant products, dietary flavonoids can be detected in plasma as serum albumin bound conjugates. Flavonoid–albumin binding is expected to control the bioavailability of drugs. In this study, the binding of alprazolam (ALP) and human serum albumin (HSA) has been investigated in the absence and presence of two flavonoids with similar structures, quercetin (QUER) and taxifolin (TAX), by means of fluorescence spectroscopy, chemometrics, and molecular dynamics simulation. Our results show that ALP has the ability to quench the intrinsic fluorescence of HSA. This quenching is affected by flavonoids. The presence of QUER and TAX decreased the quenching constants, binding constants, and equilibrium constants associated with ALP binding to HSA. The effect of ALP and both flavonoids on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy. Our results indicate a conformational change of HSA with the addition of ligands. The molecular dynamics study makes an important contribution to understanding the effect of the binding of ALP, QUER, and TAX on conformational changes of HSA and modification of its tertiary structure in the absence and presence of flavonoids. All of these results may have relevant consequences in rationalizing the interferences of common food and drugs.

Spectroscopic investigation on the sonodynamic damage to protein in the presence of eosine B

In this work, bovine serum albumin (BSA) and eosine B (EB) were selected as a model protein and sonosensitizer, respectively. The sonodynamic damage to protein in the presence of EB and its mechanism were studied by means of absorption and fluorescence spectra. The results indicated that the synergistic effects of ultrasound and EB can efficiently damage the BSA molecules, and the damage of protein could be mainly due to the generation of reactive oxygen species (ROS). The damage degree of protein increased with the increase of ultrasonic time and EB concentration because of the increased quantities of ROS. Hydroxyl free radical (OH) was the major mediators of the ultrasound-inducing proteins damage in the presence of EB. In addition, the quantities of ROS from the diphenylcarbazide (DPCI)-EB solutions and the DPCI-fluorescein (FS) solutions with or without ROS scavengers were contrasted, respectively. The results show that FS mainly produce OH, but the quantities of ROS in the presence of FS were lower than those of EB, which indicates that the nitro and bromine substituent groups on the benzene ring of FS increase the quantity of ROS, but do not change the kinds of ROS.

Binding studies of terbutaline sulfate to calf thymus DNA using multispectroscopic and molecular docking techniques

The interaction of terbutaline sulfate (TS) with calf thymus DNA (ctDNA) were investigated by fluorescence quenching, UV-vis absorption, viscosity measurements, ionic strength effect, DNA melting experiments and molecular docking. The binding constants (Ka) of TS to ctDNA were determined as 4.92×10(4), 1.26×10(4) and 1.16×10(4) L mol(-1) at 17, 27 and 37 °C, respectively. Stern-Volmer plots suggested that the quenching of fluorescence of TS by ctDNA was a static quenching. The absorption spectra of TS with ctDNA revealed a slight blue shift and hyperchromic effect. The relative viscosity ctDNA was hardly changed by TS, and melting temperature varied slightly. For the system of TS-ctDNA, the intensity of fluorescence decreased with the increase of ionic strength. Also, the Ka for TS-double stranded DNA (dsDNA) was clearly weaker than that for TS-single stranded DNA (ssDNA). All these results revealed that the binding mode of TS with ctDNA should be groove binding. The enthalpy change and entropy change suggested that van der Waals force or hydrogen bonds was a main binding force between TS and ctDNA. Furthermore, the quantum yield of TS was measured by comparing with the standard solution. Based on the Förster energy transference theory (FRET), the binding distance between the acceptor and donor was calculated. Molecular docking showed that TS was a minor groove binder of ctDNA and preferentially bound to A-T rich regions.

Enhancement of the binding affinity of methylene blue to site I in human serum albumin by cupric and ferric ions

In this work, the binding characteristics of methylene blue (MB) to human serum albumin (HSA) and the influence of Cu(2+) and Fe(3+) on the binding affinity of MB to HSA were investigated using fluorescence, absorption, circular dichroism (CD) spectroscopy and molecular modelling. The results of competitive binding experiments using the site probes ketoprofen and ibuprofen as specific markers suggested that MB was located in site I within sub-domain IIA of HSA. The molecular modelling results agreed with the results of competitive site marker experiments and the results of CD spectra indicated that the interaction between MB and HSA caused the conformational changes in HSA. The binding affinity of MB to HSA was enhanced but to a different extent in the presence of Cu(2+) and Fe(3+), respectively, which indicated that the influence of different metal ions varied. Enhancement of the binding affinity of MB to HSA in the presence of Cu(2+) is due to the formation of Cu(2+)-HSA complex leading to the conformational changes in HSA, whereas in the presence of Fe(3+), enhancement of the binding affinity is due to the greater stability of the Fe(3+)-HSA-MB complex compared with the MB-HSA complex.

Spectroscopic investigation on the food components-drug interaction: the influence of flavonoids on the affinity of nifedipine to human serum albumin

Nifedipine (NDP) is used extensively for the clinical treatment of a number of cardiovascular diseases. Herein, the interaction between human serum albumin (HSA) and NDP and the influence of flavonoids, rutin and baicalin, on their binding properties were investigated in vitro by means of fluorescence and absorption spectroscopy. The fluorescence of HSA was quenched remarkably by NDP and the quenching mechanism was considered as static quenching by forming a complex. The results of thermodynamic parameters indicate that both hydrogen bonds and hydrophobic interactions play the main role in the binding process and the binding process was spontaneous. The binding distance between the amino acid residue of HSA and NDP is 2.608 nm, which indicates that the energy transfer from HSA to NDP can occur with high probability. The decreased association constants and the increased binding distance of NDP binding to HSA in the presence of flavonoids were both due to their competitive binding to the site I of HSA. The results obtained from synchronous fluorescence and three-dimensional fluorescence spectra showed that the interaction between HSA and NDP caused the conformational changes of HSA and the synergism effects of NDP and flavonoids induced the further conformational changes of HSA.

Using gold nanoparticles as probe for detection of salmeterol xinafoate by resonance Rayleigh light scattering

The paper explores the method of determination of salmeterol xinafoate at nanogram level with gold nanoparticles (AuNPs) probe, to measure the intensity of resonance Rayleigh light scattering (RLS) by a common spectrofluorometer. The RLS intensity of salmeterol xinafoate was greatly enhanced by AuNPs, with the maximum scattering peak at 357 nm. The salmeterol xinafoate was determined basing on the binding of salmeterol xinafoate to AuNPs by electrostatic adsorption. Under the optimum conditions, the enhanced RLS intensity was directly proportional to the concentration of salmeterol xinafoate in the range of 0.054-6.038 μg mL(-1) with a good linear relationship (r=0.9928). The limit of detection (LOD) was 9.48 ng mL(-1). The interference tests were performed carefully. With the proposed method, the synthetic samples were analyzed satisfactorily, the recovery and RSD were 102.5-103.0% and 0.67-1.0% respectively.

Investigation of the interaction between quercetin and human serum albumin by multiple spectra, electrochemical impedance spectra and molecular modeling

Quercetin (Qu), a flavonoid compound, exists widely in the human diet and exhibits a variety of pharmacological activities. This work is aimed at studying the effect of Qu on the bioactive protein, human serum albumin (HSA) under simulated biophysical conditions. Multiple spectroscopic methods (including fluorescence and circular dichroism), electrochemical impedance spectra (EIS) and molecular modeling were employed to investigate the interaction between Qu and HSA. The fluorescence quenching and EIS experimental results showed that the fluorescence quenching of HSA was caused by formation of a Qu-HSA complex in the ground state, which belonged to the static quenching mechanism. Based on the calculated thermodynamic parameters, it concluded that the interaction was a spontaneous process and hydrogen bonds combined with van der Waal's forces played a major role in stabilizing the Qu-HSA complex. Molecular modeling results demonstrated that several amino acids participated in the binding process and the formed Qu-HSA complex was stabilized by H-bonding network at site I in sub-domain IIA, which was further confirmed by the site marker competitive experiments. The evidence from circular dichroism (CD) indicated that the secondary structure and microenvironment of HSA were changed. Alterations in the conformation of HSA were observed with a reduction in the amount of α helix from 59.9% (free HSA) to 56% (Qu-HSA complex), indicating a slight unfolding of the protein polypeptides.