Stereoselective interactions of lactic acid enantiomers with HSA: Spectroscopy and docking application

Mechanistic insights into betanin-protein interactions: Structural and thermal stability enhancement by non-covalent binding with animal- and plant-derived proteins

This study evaluated animal- and plant-derived proteins (whey protein isolate, ovalbumin, soy protein isolate, pea protein) for enhancing betanin's thermal stability. Protein-betanin complex formation was confirmed via particle size, SEM, and UV-Vis spectroscopy. Multi-spectroscopy and molecular dynamics simulations revealed static quenching dominated WPI/ovalbumin-betanin interactions, driven by hydrogen bonds and van der Waals forces, evidenced by negative ΔH0, ΔS0, and ΔG0 values, indicating spontaneous, exothermic binding. Reduced free amino groups, intrinsic tryptophan fluorescence, surface hydrophobicity, and α-helix content, alongside increased β-sheet structures, highlighted the roles of hydrophobic and electrostatic interactions. These forces unfolded proteins, altered tryptophan microenvironments, and stabilized complexes. Findings provide mechanistic insights into betanin stabilization and demonstrate the potential of diverse proteins as effective carriers, broadening betanin's application scope in food and pharmaceuticals.

Assessment of exposure to Phenanthrene: Insight in to the in vivo, in vitro, and in silico techniques

Organic pollutants have become a serious environmental concern due to improper use of agricultural chemicals, mining activities, and large volumes of urban waste discharge. Organic pollutants have emerged as a significant ecological issue because of the misuse of agricultural chemicals, mining operations, and the substantial discharge of urban waste. Phenanthrene (PHE), a polycyclic aromatic hydrocarbon (PAH), has various industrial applications such as dyes, plastics, pesticides, explosives, and drugs. In this study, to estimate the Human serum albumin (HAS) binding and liver cytotoxicity of PHE, the in vivo, in vitro, and in silico investigation was applied. The results show that the interaction between PHE and HSA can be done, spontaneously. The in vivo study demonstrated that both low- and high doses of PAH led to a decrease in hepatocytes and sinusoid volumes and an upward trend in blood vessels compared to the control group. The total measured biochemical factors except for HDL showed an increase in both doses of PAH compared to controls. The serum level of HDL in Phe-treated rats was markedly decreased compared to control rats.

Inquiry lipaseoring the mechanism of pancreatic lipase inhibition by isovitexin based on multispectral method and enzyme inhibition assay

Isovitexin is a main natural flavonoid component in various plants. Currently, the inhibitory effect of isovitexin on pancreatic lipase (PL) and its mechanism have not been elucidated yet. In the present study, we investigated the inhibitory effect of isovitexin on PL, as well as its interaction mechanism, using enzyme inhibition methods, spectroscopic analysis, and molecular simulations. Results showed that isovitexin possessed significant PL inhibitory activity, with IC50 values of 0.26 ± 0.02 mM. The interaction between isovitexin and PL was dominated by static quenching, and mainly through hydrogen bonding and hydrophobic interaction forces. Analysis of fluorescence spectroscopy confirmed that isovitexin binding altered the conformation of the PL. Circular dichroism (CD) spectrum indicated that isovitexin altered the secondary structure of PL by decreasing the α-helix content and increasing the β-fold content. Molecular simulations further characterize the conformational changes produced by the interaction between isovitexin with PL. The performed study may provide a new insight into the inhibitory mechanism of isovitexin as a novel PL inhibitor.

Studies on the binding of wedelolactone to human serum albumin with multi-spectroscopic analysis, molecular docking and molecular dynamic simulation

Wedelolactone (WEL) is a small molecule compound isolated from Eclipta prostrate L., which has been reported to possess various biological activities such as anti-hepatotoxicity, anti-hypertension, anti-tumour, anti-phospholipase A2 and detoxification activity against snake venom. In the present study, we investigated the interaction of WEL with human serum albumin (HSA) using simultaneous fluorescence, UV-visible spectroscopy, 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), molecular docking technique and molecular dynamics simulation. We found that the interaction between HSA and WEL can exhibit a static fluorescence burst mechanism, and the binding process is essentially spontaneous, with the main forces manifested as hydrogen bonding, van der Waals force and electrostatic interactions. Competitive binding and molecular docking studies showed that WEL preferentially bound to HSA in substructural region IIA (site I); molecular dynamics simulations showed that HSA interacted with WEL to form a stable complex, which also induced conformational changes in HSA. The study of the interaction between WEL and HSA can provide a reference for a more in-depth study of the pharmacodynamic mechanism of WEL and its further development and utilisation.

Probing binding mode between sodium acid pyrophosphate and albumin: multi-spectroscopic and molecular docking analysis

Sodium acid pyrophosphate (SAPP) food additive is widely used as a preservative, bulking agent, chelating agent, emulsifier and pH regulator. It is also used as an improver of color and water retention capacity in the processing of various types of seafood, canned food, cooked meat and flour products. For the first time, we evaluated the SAPP interaction with bovine serum albumin (BSA) using spectroscopic methods including UV-Vis absorption, fluorescence spectroscopy, and surface plasmon resonance, and docking analysis to understand the mechanisms of complex formation and binding. The fluorescence intensity of BSA reduces when titrated with various concentrations of SAPP by forming a complex with BSA via a static quenching mechanism. The binding constant between BSA and SAPP decreased from 123,300 to 15,800 (M-1) with rising temperature, which indicates a decrement in complex formation owing to the interaction of SAPP with BSA. A negative ΔG° value means that SAPP binds spontaneously to BSA at all temperatures, and both ΔH° and ΔS° negative values indicate that hydrogen bonds (H-bonding) and van der Waals forces are the primary forces involved in the binding processes. The UV-Vis spectrum of BSA reduced upon increasing SAPP concentrations due to forming a new ground state complex between SAPP and BSA. Molecular docking study shows that residues Arg256, Ser259, Ser286, Ile 289 and Ala 290 play an important role in SAPP binding process to site I (subdomain IIA) of BSA through H-bonding and van der Waals forces, which is supported by the thermodynamic study.Communicated by Ramaswamy H. Sarma.

Influence of Endogenous Substances on Site-II to Site-I Displacement of Diclofenac Bound to Albumin in the Aqueous Humor of Patients with Cataract

Diclofenac instillation is useful in preventing intraoperative miosis and macular edema caused by postoperative inflammation in cataract surgery; however, optimum efficacy is not attained when the instilled diclofenac strongly binds to albumin in patients' aqueous humor. Therefore, a method that inhibits diclofenac binding and increases the concentration of its free fraction is needed. We conducted a basic study regarding the effects of inhibitors on the binding of instilled diclofenac to albumin and endogenous substances in aqueous humor. Aqueous humor samples from 16 patients were pooled together for analysis. The free fraction of diclofenac was measured using ultrafiltration methods in various experiments with pooled and mimic aqueous humor. Free fraction of diclofenac, a site II drug, in pooled aqueous humor was 0.363 ± 0.013. The binding of diclofenac in the presence of phenylbutazone (PB), a site I inhibitor, was significantly inhibited (free fraction = 0.496 ± 0.013); however, no significant inhibition by ibuprofen, a site II inhibitor, (free fraction = 0.379 ± 0.004), was observed. The unexpected result was due to free fatty acids (FFAs; palmitic acid (PA)) and L-tryptophan (Trp). The inhibition of diclofenac binding by PB in the mimic aqueous humor containing these endogenous substances revealed significant binding inhibition in the presence of PA and Trp. Diclofenac is strongly rebound from site II to site I in the presence of FFAs and Trp in the aqueous humor because FFAs and Trp induce a conformational change in albumin. Therefore, PB significantly inhibits the binding of diclofenac to albumin.

Spectroscopic and molecular docking study of three kinds of cinnamic acid interaction with pepsin

In this work, under simulated physiological conditions (pH = 2.2, glycine hydrochloric acid buffer solution), the interactions of cinnamic acid (CA), m-hydroxycinnamic acid (m-CA) and p-hydroxycinnamic acid (p-CA) with pepsin were studied by fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared spectroscopy (FTIR), molecular docking and molecular dynamic simulation (MD). The spectrogram results showed that these three kinds of CA had a strong ability to quench the intrinsic fluorescence of pepsin, and the quenching effects were obvious with the increase of concentration of these three kinds of molecules. The quenching mechanism of CA, m-CA and p-CA on the fluorescence of pepsin was static quenching. In addition, a stable complex was formed between three kinds of CA with pepsin. Thermodynamic data and docking information suggested that three kinds of CA combine with pepsin were mainly driven by electrostatic force and hydrogen bond. The binding constant and the number of binding sites were determined. The interaction of CA, m-CA and p-CA with pepsin was spontaneous, and accompanied by non-radiative energy transfer. The results from CD, FTIR, UV-Vis and synchronous fluorescence spectra measurements manifested that the secondary structure of pepsin was changed by the binding of three kinds of CA. The β-sheet of pepsin increased after the interaction with three kinds of CA. The assay results of pepsin activity showed that three kinds of CA led to a decrease in pepsin activity within the investigated concentrations. Molecular docking investigation revealed the formation of polar hydrogen bonds as well as hydrophobic interactions between three kinds of CA with pepsin, and the ligand within the binding pocket of pepsin. MD results implied the formation of a stable complex between three kinds of CA and pepsin. The research suggested that cinnamic acid and its derivatives could be a potential effect on the structure and properties of digestive enzyme.

A novel water-soluble Cu(II) gluconate complex inhibits cancer cell growth by triggering apoptosis and ferroptosis related mechanisms

Metal copper complexes have attracted extensive attention as potential alternatives to platinum-based anticancer drugs due to their possible different modes of action. Herein, a new copper(II) gluconate complex, namely [Cu(DPQ)(Gluc)]·2H₂O (CuGluc, DPQ = pyrazino[2,3-f][1,10]phenanthroline), with good water-solubility and high anticancer activity was synthesized by using D-gluconic acid (Gluc-2H) as an auxiliary ligand. The complex was well characterized by single-crystal X-ray diffraction analysis, elemental analysis, molar conductivity, and Fourier transform infrared spectroscopy (FTIR). The DNA-binding experiments revealed that CuGluc was bound to DNA by intercalation with end-stacking binding. CuGluc could oxidatively cleave DNA, in which ¹O₂ and H₂O₂ were involved. In addition, CuGluc was bound to the IIA subdomain of human serum albumin (HSA) through hydrophobic interaction and hydrogen bonding, showing a good affinity for HSA. The complex showed superior anticancer activity toward several cancer cells than cisplatin in vitro. Further studies indicated that CuGluc caused apoptotic cell death in human liver cancer (HepG2) cells through elevated intracellular reactive oxygen species (ROS) levels, mitochondrial dysfunction, cell cycle arrest, and caspase activation. Interestingly, CuGluc also triggered the ferroptosis mechanism through lipid peroxide accumulation and inhibition of glutathione peroxidase 4 (GPX4) activity. More importantly, CuGluc significantly inhibited tumor growth in vivo, which may benefit from the combined effects of apoptosis and ferroptosis. This work provides a promising strategy to develop highly effective antitumor copper complexes by coordinating with the glucose metabolite D-gluconic acid and exploiting the synergistic effects of apoptosis and ferroptosis mechanisms.

Interaction Mechanism between α-Lactalbumin and Caffeic Acid: A Multispectroscopic and Molecular Docking Study

Caffeic acid (CA) is a phenolic acid found in a variety of foods. In this study, the interaction mechanism between α-lactalbumin (ALA) and CA was explored with the use of spectroscopic and computational techniques. The Stern-Volmer quenching constant data suggest a static mode of quenching between CA and ALA, depicting a gradual decrease in quenching constants with temperature rise. The binding constant, Gibbs free energy, enthalpy, and entropy values at 288, 298, and 310 K were calculated, and the obtained values suggest that the reaction is spontaneous and exothermic. Both in vitro and in silico studies show that hydrogen bonding is the dominant force in the CA-ALA interaction. Ser112 and Lys108 of ALA are predicted to form three hydrogen bonds with CA. The UV-visible spectroscopy measurements demonstrated that the absorbance peak A_280nm increased after addition of CA due to conformational change. The secondary structure of ALA was also slightly modified due to CA interaction. The circular dichroism (CD) studies showed that ALA gains more α-helical structure in response to increasing concentration of CA. The surface hydrophobicity of ALA is not changed in the presence of ethanol and CA. The present findings shown herein are helpful in understanding the binding mechanism of CA with whey proteins for the dairy processing industry and food nutrition security.

Probing the toxic effect of quinoline to catalase and superoxide dismutase by multispectral method

Quinoline is a common nitrogen heterocyclic aromatic hydrocarbon with high water solubility. Studies have shown that quinoline can be teratogenic, carcinogenic and mutagenic. And Hepatocytes are the target cell of quinoline, which contain a large number of mitochondria and are related to cell function and the balance of reactive oxygen species (ROS). However, the research on the effect of quinoline on hepatocyte damage and anti-oxidation system is still unclear. Through the means of multispectral experiments, it is concluded that quinoline can affect the catalase (CAT) and superoxide dismutase (SOD), change their structure and affect their activity. The binding mode and binding site of quinoline to CAT/SOD were analyzed by isothermal calorimetric titration (ITC) and Molecular Operating Environment (MOE). In molecular docking simulation, the binding site of quinoline-CAT system is close to the active site, and affect the microenvironment of Tyr 357. This may be the reason why quinoline affects CAT activity and synchronous fluorescence (Δλ = 15 nm). This study demonstrated that quinoline has a great effect on CAT, which may affect the intracellular ROS balance and become a potential way to cause hepatocyte damage.

Use of chiral ionic liquid as additive for synergistic enantioseparation of basic drugs in capillary electrophoresis

This work presents a synergistic system for enantioseparation in capillary electrophoresis (CE) with a chiral ionic liquid (CIL) based on D-10-camphorsulfonic acid as additive and carboxymethyl-β-cyclodextrin (CM-β-CD) as the chiral selector. The proposed method showed excellent enantioseparation performance towards sixteen chiral drugs. In contrast to the single CM-β-CD system, the notably improved resolution (Rs) and selectivity factor (α) of model drugs were observed in synergistic system. Several key parameters such as CIL concentration, CM-β-CD concentration, buffer pH and separation voltage were investigated, after which Statistical Product and Service Solutions (SPSS) was used to prove the potential synergistic effect. The nuclear magnetic resonance (NMR) results further demonstrated the function of the CIL and the superiority of synergistic system. Finally, chiral impurity determination of chlorpheniramine maleate sample was successfully carried out using the established method.

Unveiling interaction mechanisms between myricitrin and human serum albumin: Insights from multi-spectroscopic, molecular docking and molecular dynamic simulation analyses

Myricitrin is a natural polyhydroxy flavonoid and is mainly derived from the bark and leaves of the Chinese Bayberry tree (Myrica rubra). It has different pharmacological activities, including antioxidative, anti-inflammatory, hypoglycemic, antiviral, liver protection and cholagogue properties, and may be added to foods, pharmaceuticals, and cosmetic products for antioxidant purposes. In this study, the interaction mechanism between myricitrin and human serum albumin (HSA) was investigated using spectroscopic methods, molecular docking techniques, and molecular dynamic simulations. We showed that the HSA/myricitrin interaction exhibited a static fluorescence quenching mechanism, and that binding processes were spontaneous in nature, with the main forces exemplified by hydrogen bonding, hydrophobic interactions, and electrostatic interactions. Fluorescence spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, synchronous fluorescence spectroscopy, three-dimensional (3D) fluorescence spectroscopy, micro-Fourier transform infrared spectroscopy (micro-FTIR), and circular dichroism (CD) spectroscopy showed that myricitrin binding altered the HSA conformation to some extent. Competitive binding and molecular docking studies showed that the preferred binding of myricitrin on HSA was in the sub-structural domain IIA (Site I); molecular dynamic simulations revealed that myricitrin interacted with HSA to produce a well stabilized complex, and it also generated a conformational change in HSA. The antioxidant capacity of the HSA-myricitrin complex was reduced when compared with free myricitrin. The identification of HSA-myricitrin binding mechanisms provides valuable insights for the application of myricitrin to the food and pharmaceutical industries.

Imaging human serum albumin behavior in process of PVOCs transportation in vivo: Spectroscopy analysis insight

Pomelo volatile organic compounds (PVOCs) are used as food additives to provide unique flavors, thus, and the possible effects of VOC binding to albumin should be considered. Headspace solid-phase microextraction with gas chromatography-mass spectrometry was used to fingerprints adsorption of PVOCs on human serum albumin (HSA). Spectral data and molecular modeling were used to establish a binding model between PVOCs and HSA. Twenty-one common components were identified, and dipentene, linalylacetate, and nootkatone were identified as characteristic components. Thermodynamic calculations showed that dipentene and linalylacetate bound to HSA via van der Waals forces and hydrophobic interactions, whereas nootkatone bound to HSA via van der Waals forces alone. Molecular modeling showed that the volatile components were all bound to the hydrophobic pocket of HSA site I. Our results provide a useful basis for quality evaluation of pomelo and explain the mechanism of interaction between PVOCs and HSA.

Study on the interaction between nimodipine and five proteinases and the effects of naringin and vitamin C on these interactions by spectroscopic and molecular docking methods

The interaction mechanisms of nimodipine with pepsin, trypsin, α-chymotrypsin, lysozyme and human serum albumin were investigated by multispectral and molecular docking methods. Vitamin C and naringin were the main active components of grapefruit juice, and nimodipine was the typical drug that interacts with this juice. Fluorescence spectroscopy was used to study the interaction of nimodipine with five proteinases (pepsin, trypsin, α-chymotrypsin, lysozyme and human serum albumin) and the effects of vitamin C and naringin on these interactions. The fluorescence quenching results showed that nimodipine can quench the intrinsic fluorescence of these five proteinases by a static quenching procedure. Nimodipine binds to pepsin and α-chymotrypsin, through hydrogen bonding and van der Waals forces, whereas it binds to trypsin, lysozyme and human serum albumin mainly by hydrophobic interactions. The microenvironment of the five proteinases changed. The probability of nonradiative energy transfer between the five proteinases and nimodipine was high. Both vitamin C and naringin reduced the binding constant of nimodipine to the four proteinases (except α-chymotrypsin) and might increase the concentration of free nimodipine. Thus, vitamin C or naringin in fruits or foods could increase the blood concentration of free nimodipine and perhaps a reduction in nimodipine dose was needed.

Study on the interaction between 2,6-dihydroxybenzoic acid nicotine salt and human serum albumin by multi-spectroscopy and molecular dynamics simulation

As a new form of nicotine introduction for novel tobacco products, the interaction of nicotine salt with biological macromolecules may differ from that of free nicotine and thus affect its transport and distribution in vivo. Hence, the mechanism underlying the interaction between 2,6-dihydroxybenzoic acid nicotine salt (DBN) and human serum albumin (HSA) was investigated by multi-spectroscopy, molecular docking, and dynamic simulation. Experiments on steady-state fluorescence and fluorescence lifetime revealed that the quenching mechanism of DBN and HSA was dynamic quenching, and binding constant was in the order of 10^4 L mol^-1. Thermodynamic parameters exhibited that the binding was a spontaneous process with hydrophobic forces as the main driving force. Fluorescence competition experiments revealed that DBN bound to site I of HSA IIA subdomain. According to the results of synchronous fluorescence, 3D fluorescence, FT-IR spectroscopy, circular dichroism (CD) spectroscopy, and molecular dynamics (MD) simulation, DBN did not affect the basic skeleton structure of HSA but changed the microenvironment around the amino acid residues. Computer simulations positively corroborated the experimental results. Moreover, DBN decreased the surface hydrophobicity and weakened the esterase-like activity of HSA, leading to the impaired function of the latter. This work provides important information for studying the interaction between DBN as a nicotine substitute and biological macromolecules and contributes to the further development and application of DBN.

Interactions of diclazuril enantiomers with serum albumins: Multi-spectroscopic and molecular docking approaches

In this work, multi-spectroscopic and molecular docking methods have been conducted in the investigation of enantioselective interactions between diclazuril enantiomers and human/bovine serum albumins (HSA/BSA). The binding constants between serum albumins (SAs) and diclazuril enantiomers revealed that SAs exhibited stronger binding affinity for (R)-diclazuril than (S)-enantiomer. In addition, the fluorescence quenching of SAs induced by diclazuril enantiomers was ascribed to static quenching mechanism, in which hydrogen bonds and Van der Waals forces were the main interactions. According to the thermodynamic study, binding of diclazuril enantiomers and SAs was an exothermic process driven by enthalpy change. Then, circular dichroism spectroscopy of SAs with diclazuril enantiomers revealed that the SAs conformation had changed in the presence of diclazuril. Moreover, molecular docking technology was applied in exploration of interactions between SAs and diclazuril enantiomers. The docking energy between SAs and (R)-diclazuril was larger than (S)-diclazuril, which indicated that the affinity of SAs with (R)-diclazuril was stronger than (S)-enantiomer. This work may provide valuable information for explaining differences in pharmacokinetics and residue elimination of diclazuril enantiomers in living organisms.

Synthesis, structural studies, interaction with DNA/HSA and antitumor evaluation of new Cu(ii) complexes containing 2-(1H-imidazol-2-yl)pyridine and amino acids

New Cu(ii) complexes with promising anticancer activity induce apoptosis in HepG2 cells through DNA damage and cytotoxic ROS-mediated mitochondrial dysfunction pathways.

Enantioresolution and Binding Affinity Studies on Human Serum Albumin: Recent Applications and Trends

The interaction between proteins and drugs or other bioactive compounds has been widely explored over the past years. Several methods for analysis of this phenomenon have been developed and improved. Nowadays, increasing attention is paid to innovative methods, such as high performance affinity liquid chromatography (HPALC) and affinity capillary electrophoresis (ACE), taking into account various advantages. Moreover, the development of separation methods for the analysis and resolution of chiral drugs has been an area of ongoing interest in analytical and medicinal chemistry research. In addition to bioaffinity binding studies, both HPALC and ACE al-low one to perform other type of analyses, namely, displacement studies and enantioseparation of racemic or enantiomeric mixtures. Actually, proteins used as chiral selectors in chromatographic and electrophoretic methods have unique enantioselective properties demonstrating suitability for the enantioseparation of a large variety of chiral drugs or other bioactive compounds. This review is mainly focused in chromatographic and electrophoretic methods using human serum albumin (HSA), the most abundant plasma protein, as chiral selector for binding affinity analysis and enantioresolution of drugs. For both analytical purposes, updated examples are presented to highlight recent applications and current trends.

Study of conformational and functional changes caused by binding of environmental pollutant tonalide to human serum albumin

Tonalide (AHTN) is a new category of pollutants with a wide range of potential environmental and organismal hazards due to its persistence and lipophilicity, and the safety evaluation of this pollutant under physiological condition is a pressing issue. This study investigated the mechanism of interaction between AHTN and human serum albumin (HSA) that is an important transporter in plasma using multiple spectroscopic, molecular docking, and dynamics simulation methods. The steady-state fluorescence and fluorescence lifetime experiments showed that AHTN quenches the inherent fluorescence of HSA through a static quenching mechanism. Thermodynamic parameters exhibited that the binding constant of AHTN and HSA is of the order of 10^{^4} L/mol, and the binding is a spontaneous process of moderate strength with hydrophobic forces as the main driving force. Site competition revealed that AHTN binds to site I of HSA IIA subdomain, which was evidenced by the molecular docking results. AHTN altered the HSA amino acid microenvironment and conformation can be derived from three-dimensional fluorescence, circular dichroism spectroscopy, and molecular dynamics simulation. The computer simulations corroborate the experimental results positively. Moreover, AHTN acted as a competitive inhibitor to weaken the esterase-like activity of HSA, leading to impaired function of HSA. Results suggest that interactions between AHTN and HSA may affect the normal structure and activities of the protein, this insight will be helpful to provide some basic information to further explore the potential hazards of AHTN in humans.

Multi-spectral techniques and molecular docking to investigation of the interaction between ferulic acid and pepsin

In this work, the interaction between ferulic acid (FA) and pepsin was explored by UV-visible absorption spectroscopy, fluorescence spectroscopy, synchronous fluorescence, circular dichroism (CD) spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and molecular docking. The results of fluorescence revealed that FA had a strong ability to quench the intrinsic fluorescence of pepsin through a static quenching procedure. The binding constant and the number of binding sites were determined. Thermodynamic dates and docking information suggest that FA combine with pepsin is mainly driven via electrostatic force. It also requires synergistic drive of hydrophobic and hydrogen bonding. The consequences from UV-Vis, synchronous, CD and FT-IR spectra measurements manifested that the secondary structure of pepsin was changed and the microenvironments of certain amino acid residues was modulated by the binding of FA. FA induced conformational changes in pepsin. The β-sheet, α-Helix, and Random fractions of pepsin increased and the β-turn decreased with the treatment of FA. In addition, analysis of pepsin activity assay measurements confirmed that FA reduced enzymatic activity of pepsin within the investigated concentrations. This work studied the inhibitory effects and revealed mechanisms of the interaction between FA and pepsin in vitro, and suggested that FA could be a potential component to affect the structure and properties of digestive enzyme.

Assessment of binding interaction dihydromyricetin and myricetin with bovine lactoferrin and effects on antioxidant activity

The binding interactions of bovine lactoferrin (BLF) with two flavonoids dihydromyricetin (DMY) and myricetin (MY) were investigated by the multi-spectroscopic, microscale thermophoresis (MST) techniques, molecular docking, and then their antioxidant activities were studied by detection of free radical scavenging activity against DPPH. Results of UV-vis and fluorescence spectroscopies showed that DMY/MY and BLF formed the ground state complex through the static quenching mechanism. Moreover, MY with more planar stereochemical structure had higher affinity for BLF than DMY with twisted stereochemical structure, according to the binding constant (K_b), free energy change (ΔG°), dissociation constant (K_d) and donor-acceptor distance (r). Thermodynamic parameters revealed that hydrogen bond and van der Waals force were major forces in the formation of BLF-DMY complex, while hydrophobic interactions played major roles in the formation of BLF-DMY complex. The circular dichroism (CD) study indicated that MY induced more conformational change in BLF than DMY. Furthermore, molecular modeling provided insights into the difference of binding interactions between BLF and two flavonoids. Finally, the radical scavenging activity assays indicated the presence of BLF delayed the decrease in antioxidant capacities of two flavonoids. These results were helpful to understand the binding mechanism and biological effects of non-covalent BLF-flavonoid interaction.

Potential ability of different types of cyclodextrins to modulate the interaction between bovine serum albumin and 1-hydroxypyrene

Hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) can bind with functional biomacromolecules and thus cause toxic effects in vivo. Four types of cyclodextrins (CDs) were selected to explore their potential ability to regulate the bindings between 1-hydroxypyrene (1-OHPyr) and bovine serum albumin (BSA) using multi-spectroscopic methods combined with molecular docking. The results showed that the four CDs caused varied modulating effects on the binding of BSA with 1-OHPyr, and the effects of γ-CD and (2-hydroxypropyl)-β-CD (HPCD) are the most significant. Specifically, γ-CD and HPCD could significantly reduce the binding affinity between 1-OHPyr and BSA, inhibit the micro-environmental changes of tryptophan residues, and slightly recover the helicity of BSA. The interactions and inclusion behavior of CDs with 1-OHPyr was the main reason why CDs could affect the binding of 1-OHPyr to BSA. The results indicated that γ-CD and HPCD might have potential application value in regulating the toxic effects of OH-PAHs.

Probing the Interaction between Human Serum Albumin and 9-Hydroxyphenanthrene: A Spectroscopic and Molecular Docking Study

9-Hydroxyphenanthrene (9-OHPhe), the representative hydroxyl metabolite of phenanthrene, has generated increasing concern as it is potentially hazardous to organisms. Herein, multispectroscopic and molecular docking techniques were applied to investigate the molecular interaction of human serum albumin (HSA) with 9-hydroxyphenanthrene (9-OHPhe) under simulated physiological conditions. Steady-state fluorescence and time-resolved fluorescence spectral analysis showed that 9-OHPhe quenched HSA fluorescence through a mixed static and dynamic process. HSA can bind with 9-OHPhe to form a 1:1 complex, with binding constants of 1.28 × 10⁵, 1.36 × 10⁵, and 1.26 × 10⁵ L·mol^-1 at 298.15, 303.15, and 308.15 K, respectively. The strong binding between HSA and 9-OHPhe is spontaneous and entropy-driven. Molecular docking indicated that the optimal binding site of 9-OHPhe with HSA was located in the IA subdomain of HSA. Thermodynamic analysis and molecular docking results suggested that hydrophobic interactions and hydrogen bond force dominated the binding process of HSA with 9-OHPhe. Specifically, 9-OHPhe formed hydrophobic interactions with LEU134, LEU139, ILE142, LEU154, PHE157, ALA158, and TYR161 and formed a 1.86 Å hydrogen bond with LEU135. Circular dichroism spectral analysis showed that the α-helical content of HSA decreased from 52.3 to 50.9% after adding 9-OHPhe with a ratio of 1:1. The obtained results are hoped to provide basic data for understanding the potential effects of the hydroxyl metabolites of PAHs on functional biomacromolecules.

Enantioselectivity in transplacental transfer of perfluoro-1-methylheptanesulfonate (1m-PFOS): Human biomonitoring and in silico study

Perfluorooctane sulfonates (PFOS) are one of the most prominent perfluoroalkyl contaminants in humans and wildlife. Currently, information regarding enantiomer-specific exposure to PFOS in humans through transplacental transfer is lacking. This study examined 32 matched maternal serum, cord serum and placenta samples collected from mother-infant pairs in Wuhan, China. The enantiomer fraction (EF) value of perfluoro-1-methylhptanesulfonate (1m-PFOS) was lower in cord sera (0.362 ± 0.062, n = 23) compared to maternal sera (0.422 ± 0.048, n = 21) and placenta (0.410 ± 0.060, n = 16). Evaluations of the difference between EF_1m-PFOS suggested enantioselective transplacental transfer of 1m-PFOS. In silico evaluation of the binding affinity of 1m-PFOS to human serum albumin (HSA) showed that the two 1m-PFOS enantiomers enantioselectively interacted with the HSA. This result hints the enantioselective carrier protein affinity may be a key factor for stereoselective 1m-PFOS transplacental transfer. The percentage of branched PFOS (%br-PFOS) and EF_1m-PFOS was correlated in maternal sera, but not in cord sera and placentas. These data indicated that %br-PFOS and EF_1m-PFOS may be less reliable in identifying PreFOS exposure when it comes to complex biological processes, such as transplacental transport. This study could expand our understanding of stereoselective placental contaminant transfer in humans.

Synthesis, X-ray structure, antiproliferative activity, interaction with HSA and docking studies of three novel mono and binuclear copper complexes containing the maltol ligand

The present study aims at synthesizing three new copper(ii) complexes of maltol in the presence of 1,10-phenanthroline-, 2,2′-bipyridine- and 4,4-dibromo-2,2′-bipyridine ligands.

Interaction of saffron carotenoids with catalase: in vitro, in vivo and molecular docking studies

The effects of saffron carotenoids, crocetin (Crt) and crocin (Cro) on the structure, function and kinetics of catalase (CAT) were investigated. Both Crt and Cro quenched the fluorescence emission of CAT through the dynamic mechanism, but Crt (Ksv= 8.1 × 10⁴ mol^-1) was more effective than Cro (Ksv= 0.6 × 10⁴ mol^-1) at 300 °K. The UV-vis and circular dichroism spectra showed conformational changes of CAT in the presence of both carotenoids, but with different degrees. Kinetic studies showed strong inhibition of CAT by Crt, while, different concentrations of Cro showed different effects. Our in vitro data showed that Crt treatment significantly (p = 0.002) reduced the CAT activity in MCF-7, up to 24 h. The in vivo results showed that both Crt and Cro significantly increased the CAT activity in the tumor (p = 0.000 for both), and liver (p = 0.000 and p = 0.026 for Crt and Cro, respectively) tissues of 4T1-induced breast cancer in BALB/c mice, after 4 weeks of treatment. These findings are consistent with the binding, thermodynamic and molecular docking data. In conclusion, Crt and Cro with some differences in the structure affect CAT structure, function and activity, but in a slightly different manner.Communicated by Ramaswamy H. Sarma.

Characterization of the interaction between carbon black and three important antioxidant proteins using multi spectroscopy and modeling simulations

A major user of carbon black is the pigment and dyes industry, where carbon black is incorporated into paints, inks, printers, and plastics. However, little is known about the mechanism underlying the toxicity of carbon black to antioxidant proteins. Carbon black can cause oxidative stress to organisms after they invade into the body. Antioxidant proteins play a key role in keeping the organism from nanoparticle-induced oxidative damage and tend to bind with nanoparticles immediately after their invading into the biological environment, so it is meaningful to elucidate the toxicity of nanoparticles on the antioxidant proteins. In this study, the toxicity of carbon black (SB100) on three different antioxidant proteins (TF (transferrin), SOD (superoxide dismutase), and LYZ (lysozyme)) were investigated. The multi-spectra studies indicated that SB100 interacted with these three proteins and changed their structure in different ways. SB100 changed the microenvironment of fluorophores in SOD and LYZ by quenching the fluorescence spectra of the two enzymes, while changed that of TF by increasing the fluorescence intensity of TF. SB100 changed the secondary structure of these three proteins by decreasing the α-helix content of TF and increasing that of SOD and LYZ. Moreover, SB100 changed the hydrophobicity of the three proteins in different ways as well. And SOD exhibits a more severe activity inhibition than LYZ after exposed to SB100. In summary, SB100 caused different structural and functional changes to these three antioxidant enzymes.