Synthesis, characterization and serum albumin binding studies of vitamin K3 derivatives

Synthesis, characterization and bovine serum albumin (BSA) binding properties of three derivatives of vitamin K3 have been described. Results of UV-Vis and fluorescence spectra indicate complexation between BSA and the ligands with conformational changes in protein, which is strongly supported by synchronous and three dimensional fluorescence studies. Addition of the ligands quenches the fluorescence of BSA which is accompanied by reduction in quantum yield (Ф) from 0.1010 to 0.0775-0.0986 range. Thermodynamic investigations reveal that hydrophobic interaction is the major binding force in the spontaneous binding of these ligands with BSA. The binding constants obtained depend on the substituent present in the quinone ring, which correlates linearly with the Taft's field substituent constant (σ_F). The results show that compound with strong electron withdrawing nitro-group forms relatively stronger complex with BSA than amino and thioglycolate substituted ones. Circular dichroism studies show that the α-helical content of the protein, upon complexation with the ligands, decreases in the case of amino and nitro substituted vitamin K3 while increases in thioglycolate substituted compound. Molecular docking studies indicated that the vitamin K3 derivatives are surrounded by hydrophobic residues of the BSA molecule, which is in good agreement with the results of fluorescence spectral and thermodynamic studies.

Albumin-coated SPIONs: an experimental and theoretical evaluation of protein conformation, binding affinity and competition with serum proteins

The variety of nanoparticles (NPs) used in biological applications is increasing and the study of their interaction with biological media is becoming more important. Proteins are commonly the first biomolecules that NPs encounter when they interact with biological systems either in vitro or in vivo. Among NPs, super-paramagnetic iron oxide nanoparticles (SPIONs) show great promise for medicine. In this work, we study in detail the formation, composition, and structure of a monolayer of bovine serum albumin (BSA) on SPIONs. We determine, both by molecular simulations and experimentally, that ten molecules of BSA form a monolayer around the outside of the SPIONs and their binding strength to the SPIONs is about 3.5 × 10(-4) M, ten times higher than the adsorption of fetal bovine serum (FBS) on the same SPIONs. We elucidate a strong electrostatic interaction between BSA and the SPIONs, although the secondary structure of the protein is not affected. We present data that supports the strong binding of the BSA monolayer on SPIONs and the properties of the BSA layer as a protein-resistant coating. We believe that a complete understanding of the behavior and morphology of BSA-SPIONs and how the protein interacts with SPIONs is crucial for improving NP surface design and expanding the potential applications of SPIONs in nanomedicine.

Cation-mediated optical resolution and anticancer activity of chiral polyoxometalates built from entirely achiral building blocks

We report the crystallization of homochiral polyoxometalate (POM) macroanions {CoSb6O4(H2O)3[Co(hmta)SbW8O31]3}15- (1, hmta = hexamethylenetetramine) via the counter cation-mediated chiral symmetry breaking and asymmetric autocatalytic processes. In the presence of low Co2+ concentrations both Δ- and Λ-enantiomers of 1 formed in the reaction, crystallizing into the racemic crystal rac-1. At a high Co2+ concentration, the polyoxoanion enantiomers showed a high level of chiral recognition via H-bonding interactions to crystallize into enantiopure crystals of Δ- or Λ-[Co(H2O)6{CoSb6O4(H2O)3[Co(hmta)SbW8O31]3}]13-. During crystallization, a microscale symmetry-breaking event and a nonlinear asymmetric autocatalysis process make the enantiomers crystallize in different batches, which provides an opportunity to isolate the homochiral bulk materials. The defined structures of the racemic and homochiral crystals thus provide a molecular-level illustration that H-bonding interactions are responsible for such high-level chiral recognition, in a process similar to the supramolecular chirality frequently observed in biology. These POM macroanions showed a high cytotoxicity against various cancer cells, particularly ovarian cancer cells. The antitumor activity of these compounds resulted at least in part from the activation of the apoptotic pathways, as shown by the flow cytometry, Annexin V staining, DNA ladder, and TUNEL assay, likely by blocking the cell cycle and complexing with proteins in cells. The POM macroanions reported herein provide promising and novel antitumor agents for the potential treatment of various cancers.

The effect of spermidine on the structure, kinetics and stability of proteinase K: spectroscopic and computational approaches

Polyamines (such as spermidine) are low molecular weight compounds which can be used as cosolvents in biological and industrial applications.

In vitro investigation of the interaction between the hepatitis C virus drug sofosbuvir and human serum albumin through 1H NMR, molecular docking, and spectroscopic analyses

The qualitative and quantitative investigation of sofosbuvir and HSA interaction provides a convictive explanation for its binding mechanism.

Exploring the thermodynamics and conformational aspects of nicotinic acid binding with bovine serum albumin: a detailed calorimetric, spectroscopic and molecular docking study

An attempt to obtain a physicochemical and conformational outlook on the binding interaction of vitamin B₃ (NA) with a model transport protein BSA using calorimetry, light scattering, molecular docking, and spectroscopic techniques.

Fluorescence resonance energy transfer for investigation of the interaction of Para Red with serum albumins

Para Red (PR) has been isolated from food additives, and shown to be toxic to humans. To facilitate examination of its toxicity, the interaction between PR and serum albumins (SA) was studied using fluorescence quenching and circular dichroism (CD) spectrophotometry. The experiments showed that the fluorescence intensity of serum albumins decreased with increasing concentrations of PR, which resulted from the binding of PR and SA. The binding constant, number of binding sites and thermodynamic parameters were calculated and hydrogen bond and van der Waals interactions were shown to play a key role in the binding process. Competition experiments indicated that PR mainly binds to Trp residues of SA within the site I. As the CD and three-dimensional spectra revealed, the addition of PR induced a conformational change in SA.

Monitoring the heat-induced structural changes of alkaline phosphatase by molecular modeling, fluorescence spectroscopy and inactivation kinetics investigations

The heat induced conformational changes of calf alkaline phosphatase (ALP) were analyzed using different methods, based on fluorescence spectroscopy, molecular modeling and inactivation studies. Experimental studies were conducted in buffer solution in the temperature range between 25 and 70 °C. Molecular dynamic (MD) simulation provided details on thermally induced changes in ALP structure, highlighting that heating favored the hydrophobic exposure and important alteration of the catalytic site above 60 °C. Additional information to MD data were obtained by using different fluorescence spectroscopy methods, which revealed a complex mechanism of thermal denaturation. Therefore, the emissive properties indicated an unfolding of ALP at temperatures below 60 °C, whereas at higher temperatures, the polypeptides chains fold leading to a higher exposure of Trp residues. In order to establish a structure-function relationship, the results were correlated with inactivation studies of ALP in buffer at pH 9.0. The inactivation data were fitted using a first-order kinetic model, resulting in an activation energy value of 207.26 ± 21.68 kJ · mol(-1).

Binding interaction of a prospective chemotherapeutic antibacterial drug with β-lactoglobulin: results and challenges

This Article reports a detailed characterization of the binding interaction of a potential chemotherapeutic antibacterial drug, norfloxacin (NOF), with the mammalian milk protein β-lactoglobulin (βLG). The thermodynamic parameters, ΔH, ΔS, and ΔG, for the binding phenomenon as-evaluated on the basis of van't Hoff relationship reveal the predominance of electrostatic/ionic interactions underlying the binding process. However, the drug-induced quenching of the intrinsic tryptophanyl fluorescence of the protein exhibits intriguing characteristics on Stern-Volmer analysis (displays an upward curvature instead of conforming to a linear regression). Thus, an extensive time-resolved fluorescence spectroscopic characterization of the quenching process has been undertaken in conjugation with temperature-dependent fluorescence quenching studies to unveil the actual quenching mechanism. The invariance of the fluorescence decay behavior of βLG as a function of the quencher (here NOF) concentration coupled with the commensurate dependence of the drug-protein binding constant (K) on temperature, the drug-induced fluorescence quenching of βLG is argued to proceed through static mechanism. This postulate is aided further support from absorption, fluorescence, and circular dichroism (CD) spectral studies. The present study also throws light on the important issue of drug-induced modification in the native protein conformation on the lexicon of CD, excitation-emission matrix spectroscopic techniques. Concurrently, the drug-protein interaction kinetics and the energy of activation of the process are also explored from stopped-flow fluorescence technique. The probable binding locus of NOF in βLG is investigated from AutoDock-based blind docking simulation.

Binding patterns and structure-affinity relationships of food azo dyes with lysozyme: a multitechnique approach

Food dyes serve to beguile consumers: they are often used to imitate the presence of healthful, colorful food produce such as fruits and vegetables. But considering the hurtful impact of these chemicals on the human body, it is time to thoroughly uncover the toxicity of these food dyes at the molecular level. In the present contribution, we have examined the molecular reactions of protein lysozyme with model food azo compound Color Index (C.I.) Acid Red 2 and its analogues C.I. Acid Orange 52, Solvent Yellow 2, and the core structure of azobenzene using a combination of biophysical methods at physiological conditions. Fluorescence, circular dichroism (CD), time-resolved fluorescence, UV-vis absorption as well as computer-aided molecular modeling were used to analyze food dye affinity, binding mode, energy transfer, and the effects of food dye complexation on lysozyme stability and conformation. Fluorescence emission spectra indicate complex formation at 10(-5) M dye concentration, and this corroborates time-resolved fluorescence results showing the diminution in the tryptophan (Trp) fluorescence mainly via a static type (KSV = 1.505 × 10(4) M(-1)) and Förster energy transfer. Structural analysis displayed the participation of several amino acid residues in food dye protein adducts, with hydrogen bonds, π-π and cation-π interactions, but the conformation of lysozyme was unchanged in the process, as derived from fluorescence emission, far-UV CD, and synchronous fluorescence spectra. The overall affinity of food dye is 10(4) M(-1) and there exists only one kind of binding domain in protein for food dye. These data are consistent with hydrophobic probe 8-anilino-1-naphthalenesulfonic acid (ANS) displacement, and molecular modeling manifesting the food dye binding patch was near to Trp-62 and Trp-63 residues of lysozyme. On the basis of the computational analyses, we determine that the type of substituent on the azobenzene structure has a powerful influence on the toxicity of food dyes. Results from this work testify that model protein, though an indirect method, provides a more comprehensive profile of the essence of toxicity evaluation of food dyes.

Spectroscopic studies on the interaction between tetrandrine and two serum albumins by chemometrics methods

The binding interactions of tetrandrine (TETD) with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated by spectroscopic methods. These experimental data were further analyzed using multivariate curve resolution-alternating least squares (MCR-ALS) method, and the concentration profiles and pure spectra for three species (BSA/HSA, TETD and TETD-BSA/HSA) existed in the interaction procedure, as well as, the apparent equilibrium constants Kapp were evaluated. The binding sites number n and the binding constants K were obtained at various temperatures. The binding distance between TETD and BSA/HSA was 1.455/1.451nm. The site markers competitive experiments indicated that TETD primarily bound to the tryptophan residue of BSA/HSA within site I. The thermodynamic parameters (ΔG, ΔH and ΔS) calculated on the basis of different temperatures revealed that the binding of TETD-BSA was mainly depended on the hydrophobic interaction strongly and electrostatic interaction, and yet the binding of TETD-HSA was strongly relied on the hydrophobic interaction. The results of synchronous fluorescence, 3D fluorescence and FT-IR spectra show that the conformation of proteins has altered in the presence of TETD. In addition, the effect of some common ions on the binding constants between TETD and proteins were also discussed.

A spectroscopic investigation on the interaction of a magnetic ferrofluid with a model plasma protein: effect on the conformation and activity of the protein

The understanding of the interaction of nanomaterials with relevant biological targets e.g., proteins is of paramount importance in biological and pharmaceutical fields of research. In a biological fluid, proteins can associate with nanomaterials which can subsequently exert a significant impact on the conformation and functionality of the protein. Here we report the binding interaction of a model plasma protein Bovine Serum Albumin (BSA) with a magnetic nanoparticle of mixed spinel origin (Ni(0.5)Zn(0.5)Fe(2)O(4), abbreviated as NZFO from now and onwards). The thermodynamic parameters (ΔH, ΔS and ΔG) for the protein-nanoparticle binding interaction have been evaluated from the van't Hoff equation to unveil that the binding interaction is enthalpically as well as entropically driven (ΔH < 0 and ΔS > 0), with an overall favorable Gibbs free energy change (ΔG < 0). Also the thermodynamic parameters delineate the predominant role of electrostatic interaction in the BSA-NZFO binding process. The results of temperature dependent fluorescence quenching and time-resolved fluorescence decay measurements indicate a static quenching mechanism in the present case. Steady-state absorption, synchronous fluorescence, three-dimensional (3D) fluorescence and circular dichroism (CD) spectroscopic techniques have been employed to unveil the conformational changes in BSA induced by the binding of NZFO. Disruption of the native conformation of the protein upon binding with NZFO is reflected through a reduced functionality (in terms of esterase activity) of the protein-NZFO conjugate system in comparison to the native protein. Based on the experimental findings the probable binding location of NZFO is argued to be the hydrophilic domain IB. This seems physically realizable since domain I of BSA is characterized by a net negative charge and hence can serve as a favorable binding site for NZFO carrying a positive surface charge. The key role of electrostatic forces in the BSA-NZFO interaction process is further substantiated from chemical denaturation study and measurement of the effect of ionic strength on the interaction process.

Biophysical influence of isocarbophos on bovine serum albumin: spectroscopic probing

Isocarbophos (ICP) is a phosphorous pesticide with high toxicity. It has been detected in several kinds of food and therefore can enter human body. In this paper, spectroscopic approaches including three-dimensional fluorescence (3D-FL) spectroscopy, UV-visible absorption spectroscopy and circular dichroism (CD) spectroscopy were employed to explore the binding of ICP to bovine serum albumin (BSA) at simulated physiological conditions. It was found that the fluorescence quenching of BSA was caused by the formation of ICP-BSA complex at ground state and belonged to static quenching mechanism. The binding constants, the number of binding sites, enthalpy change (ΔH(θ)), Gibbs free energy change (ΔG(θ)) and entropy change (ΔS(θ)) were calculated at four different temperatures according to Scatchard model and thermodynamic equations. To identify the binding location, fluorescence probe techniques were used. The results showed that warfarin, an acknowledged site marker for BSA, could be partially replaced by ICP when ICP was added to warfarin-BSA systems, which demonstrated that ICP primarily bound on Sudlow's site I in domain IIA of BSA molecule. The distance r (3.06 nm) between donor (Trp-212) and acceptor (ICP) was obtained based on Förster's non-radiation fluorescence resonance energy transfer (FRET) theory. Furthermore, the CD spectral results indicated that the secondary structure of BSA was changed in presence of ICP. The study is helpful to evaluating the toxicology of ICP and understanding its effects on the function of protein during the blood transportation process.

Chemical composition, antioxidant and anticancer effects of the seeds and leaves of indigo (Polygonum tinctorium Ait.) plant

Seeds and leaves of indigo (Polygonum tinctorium Ait.) plant were investigated and compared with another medicinal plant named prolipid for their properties such as chemical composition, antioxidant, and anticancer effects by Fourier transform infrared, three-dimensional fluorescence spectroscopy, and electrospray ionization-MS in negative mode. It was found that polyphenols, flavonoids, and flavanols were significantly higher in prolipid (P<0.05), following by indigo mature leaves, immature leaves, and seeds. Methanol extract of mature indigo leaves in comparison with the ethyl acetate extract showed higher inhibition of proliferation. The interaction between polyphenol extracts of indigo mature leaves and BSA showed that indigo has a strong ability, as other widely used medicinal plants, to quench the intrinsic fluorescence of BSA by forming complexes. In conclusion, indigo mature leaves were compared with prolipid. High content of bioactive compounds, antioxidant, fluorescence, and antiproliferative properties of indigo justifies the use of this plant as a medicinal plant and a new source of antioxidants.

Morphological transition of the host-structure influences solvent-relaxation: a wavelength-selective fluorescence exploration through environment-sensitive intramolecular charge transfer photophysics

Here, we report the modulation of photo-induced intramolecular charge transfer (ICT) photophysics of N,N-dimethylaminonaphthyl-acrylo-nitrile (DMANAN) associated with sphere-to-rod structural transition of SDS micelles induced by increasing ionic strength of the medium. Emphasis is rendered on the exploration of solvent-relaxation associated with this transition on the basis of wavelength-selective fluorescence technique which includes monitoring of red-edge excitation shift (REES) and excitation/emission anisotropy profiles. Based on micropolarity determination and organization of solvent water around the probe microenvironment we argue that the present results advocate for rod-shaped micelles to be a better mimic for membrane bilayers than spherical micelles.