Conformational Changes Of Bovine Serum Albumin Research Articles

Insight into the interaction of isochroman with bovine serum albumin: extensive experimental and computational investigations

The way therapeutic compounds interact with serum protein provides valuable information on their pharmacokinetics, toxicity, effectiveness, and even their structural-related information. Isochroman (IC) is a phytochemical compound obtained from the leaves of Olea europea plant. The derivatives of IC have various pharmacological properties including antidepressants, antihistamines, antiinflammation, anticonvulsants, appetite depressants, etc. The binding of small molecules to bovine serum albumin (BSA) is useful to ensure their efficacy. Thus, in this study, we have found out the binding mode of IC with BSA using several spectroscopic and in silico studies. UV and fluorescence spectroscopy suggested the complex formation between IC and BSA with a binding constant of 103 M−1. IC resulted in fluorescence quenching in BSA through static mechanism. The microenvironmental and conformational changes in BSA were confirmed using synchronous and three-dimensional studies. Site marker experiment revealed the IC binding in site-III of BSA. The influence of vitamins, metals and β-cyclodextrin (β-CD) on binding constant of IC–BSA complex was also examined. Circular dichroism spectra showed that α-helical of BSA decreased upon interaction with IC. Computational and experimental results were complimentary with one another and assisted in determining the binding sites, nature of bonds and amino acids included in the IC–BSA complex formation. Communicated by Ramaswamy H. Sarma

Evaluating binding and interaction of selected pesticides with serum albumin proteins by Raman, 1H NMR, mass spectrometry and molecular dynamics simulation

Addressing the acute pesticide poisoning and toxicity to humans, is a global challenge of top priority. Serum albumin is the most abundant plasma protein, capable of binding with herbicide and pesticide residues. This study reports multifaceted approaches for in-depth and robust investigation of the molecular interactions of selected pesticides, including propanil (PPL), bromoxynil (BXL), metolachlor (MLR) and glyphosate (GPE) with bovine serum albumin (BSA) proteins using experimental (Raman and FTIR spectroscopy, native mass spectrometry and high field 1H NMR), molecular dynamics (MD) simulation and principal component analysis (PCA). The binding of pesticides with BSA resulted in BSA amide I and amide II Raman spectral shifts. PCA of Raman spectra of serum-pesticide complexes showed the grouping of pesticides on the score plot based on the similarities and differences in pesticides’ chemical structures. Native mass spectrometry results revealed strong adduct formation of the pesticides with the protein. The observed changes in chemical shifts, peak broadening or peak disappearance of characteristic proton signals of the pesticides, indicated altered chemical environments due to binding BSA-pesticides interactions. The results of MD simulation conducted for over 500 ns revealed strong pesticides interaction with LEU197, LEU218, LEU237, TRP213, SER286 and ILE289 residues to the site I of BSA. Free energy landscapes provided insights into the conformational changes in BSA on the binding of pesticides. Overall, the experimental and computational results are in consonant and indicate the binding of pesticides into the site I and site II (sub-domain IIA) of the BSA via hydrogen bonding, non-covalent and hydrophobic interactions. Communicated by Ramaswamy H. Sarma

Exploring Multifunctional Response of Ca10(PO4)6(OH)2-K0.5Na0.5NbO3 Ceramic Composite for Biomedical Applications.

This study focuses on investigating the intriguing properties of Ca10(PO4)6(OH)2 (HAP)-K0.5Na0.5NbO3 (KNN) bioceramic composites, seeking to elucidate the relationship between their structural, electrical, biological, and optical behavior. The article begins with a close inspection of the O 1s spectra of the specimens obtained from X-ray photoelectron spectroscopy (XPS). The spectra reveal the peak related to lattice oxygen, O vacancy and the surface adsorbed O. The formed O vacancy strongly influences the changes in lattice parameters as observed from the X-ray diffraction (XRD) patterns. The frequency variation of the dielectric response for the composites in the radio frequency (RF) regime has electrical polarization effective for biomedical applications. Nyquist plots along with equivalent RC circuits further confirm that those electrical responses are mainly contributed from the grain boundaries. Adsorption dynamics of protein on the ceramic surface are investigated using bovine serum albumin (BSA), which established the major role of electrostatic interaction. Surface charge and O vacancies are modeled to understand the adsorption of protein and a linear correlation is reported. The role of O vacancies in modulating adsorption dynamics adds a new dimension to this study. The conformational change of BSA has also been considered by constructing the secondary structure following the protein-ceramic interaction. Excitingly, the composites are also found to be fluorescent active, a courtesy of the defects and vacancies leading to electron-hole recombination in the forbidden region. These promising properties envision an exciting future for HAP-KNN composites, especially in the domain of bioimaging and bone-tissue engineering.

Simultaneous binding characterization of different chromium speciation to serum albumin.

The binding process between three species of chromium and serum albumin (SA) was investigated, as well as the interaction between K2Cr2O7 and bovine serum albumin (BSA) under coexistence of different chromium forms. CrCl3, K2Cr2O7 and Crpic bound to SA spontaneously through Van der Waals force, and their binding constants were 103-104M-1 at 298K, respectively. K2Cr2O7 and Crpic both had strong binding affinity for BSA, and significantly affected the secondary structure of BSA and the microenvironment surrounding amino acid residues. Chromium exhibited a greater fluorescence quenching constant towards HSA than toward BSA, and K2Cr2O7 induced greater conformational changes in human serum albumin (HSA) than in BSA. A weak binding of CrCl3 to BSA had no significant effect on the binding affinity of K2Cr2O7 to BSA. K2Cr2O7 and BSA have a greater binding affinity when coexisting with Crpic, and K2Cr2O7 induces a greater conformational change in BSA.

Preparation and characterization of nanocarriers based on polysaccharides from Lentinus edodes and bovine serum albumin and its photoprotection of resveratrol against UV radiation

In this work, biopolymer nanomaterials were prepared by electrostatic complexation and thermal treatment using the medicinal and edible homologous polysaccharides from Lentinus edodes (LEP) and bovine serum albumin (BSA). The hydrodynamic radius, PDI and zeta potential of the LEP-BSA nanocarriers (NCs) were 125.3 ± 1.2 nm, 0.206 ± 0.007 and − 25.3 ± 0.7 mV, respectively. SEM images of LEP-BSA NCs further demonstrated their uniform morphology. UV–vis, fluorescence and FTIR spectra revealed that LEP interacted successfully with BSA. And the presence of LEP caused the conformational change of BSA, which was confirmed by FTIR spectroscopy. The LEP-BSA NCs maintained good stability in long-term storage at different temperatures and kept integrity at neutral or slightly higher pH conditions. In vitro hemolysis and cytotoxicity experiments were performed to verify the biocompatibility of the LEP-BSA NCs. Furthermore, the ability of LEP-BSA NCs to encapsulate bioactive compounds was proved by the successful encapsulation of resveratrol and the photoprotection of resveratrol. This work will be applied to other polysaccharide-protein systems with unique activities to prepare multi-functional stimuli-responsive nanomaterials for better applications in food production and biopharmaceuticals.

Molecular interactions and binding dynamics of Alpelisib with serum albumins: insights from multi-spectroscopic techniques and molecular docking

Alpelisib (ALP) is a potent anti-cancer drug showing promising activity against advanced breast cancers. Hence, profound understanding of its binding dynamics within the physiological system is vital. Herein, we have investigated interaction of ALP with human serum albumin (HSA) and bovine serum albumin (BSA) using spectroscopic techniques like absorption, fluorescence, time-resolved, synchronous and 3D-fluorescence, FRET, FT-IR, CD, and molecular docking studies. The intrinsic fluorescence of both BSA and HSA quenched significantly by ALP with an appreciable red shift in its emission maxima. Stern-Volmer analysis showed increase in Ksv with temperature indicating involvement of dynamic quenching process. This was further validated by no significant change in absorption spectrum of BSA and HSA (at 280 nm) upon ALP interaction, and by results of fluorescence time-resolved lifetime studies. ALP exhibited moderately strong binding affinity with BSA (of the order 106 M−1) and HSA (of the order 105 M−1), and the major forces accountable for stabilizing the interactions are hydrophobic forces. Competitive drug binding experiments and molecular docking suggested that ALP binds to site I in subdomain IIA of BSA and HSA. The Förster distance r was found to be less than 8 nm and 0.5 Ro < r < 1.5 Ro which suggests possible energy transfer between donors BSA/HSA and acceptor ALP. Synchronous and 3D-fluoresecnce, FT-IR and CD studies indicated that ALP induces conformational changes of BSA and HSA upon interaction. Communicated by Ramaswamy H. Sarma

Conformational changes and location of BSA upon immobilization on zeolitic imidazolate frameworks

The location and the conformational changes of proteins/enzymes immobilized within Metal Organic Frameworks (MOFs) are still poorly investigated and understood. Bovine serum albumin (BSA), used as a model protein, was immobilized within two different zeolitic imidazolate frameworks (ZIF-zni and ZIF-8). Pristine ZIFs and BSA@ZIFs were characterized by X-ray diffraction, small-angle X-ray scattering, scanning electron microscopy, confocal laser scanning microscopy, thermogravimetric analysis, micro-FTIR and confocal Raman spectroscopy to characterize MOFs structure and the protein location in the materials. Moreover, the secondary structure and conformation changes of BSA after immobilization on both ZIFs were studied with FTIR. BSA is located both in the inner and on the outer surface of MOFs, forming domains that span from the micro- to the nanoscale. BSA crystallinity (β-sheets + α-helices) increases up to 25 % and 40 % due to immobilization within ZIF-zni and ZIF-8, respectively, with a consequent reduction of β-turns.

Insights into the interaction between the kusaginin and bovine serum albumin: Multi-spectroscopic techniques and computational approaches.

Kusaginin, as a phenylethanoid glycoside, which has exhibited wide antioxidant and antimicrobial properties. The molecular mechanism underlying the broad biological activities of kusaginin has not yet been well documented. In this paper, the interaction of kusaginin with bovine serum albumin (BSA) has been explored by fluorescence spectra, UV-vis absorption spectra, and circular dichroism (CD) spectra along with computational approaches. The fluorescence experiments showed that kusaginin could strongly quench the intrinsic fluorescence of BSA through both dynamic and static quenching mechanisms. The thermodynamic analysis suggested that hydrophobic force was the main force in stabilizing the BSA-kusaginin complex. In addition, conformation changes of BSA were observed from three-dimensional and synchronous fluorescence spectra, UV spectra, and CD spectra under experimental conditions. All these experimental results have been complemented and validated by the molecular docking and dynamic simulation studies, which revealed that kusaginin was bound on the hydrophobic cavity in subdomain IIA of BSA and formed a stable BSA-kusaginin complex. Finally, density functional theory (DFT) calculation further implied that hydrogen bonds also support stabilizing the BSA-kusaginin complex. This research may aid in understanding the pharmacological characteristics of kusaginin and provide a vital reference modeling for the design of analogues drugs.

Influence of amino acids on alkaline pH induced partially folded molten globule like intermediate of bovine serum albumin: Conformational and thermodynamic insights

Partially folded states of proteins can misfold or aggregate leading to various neurodegenerative diseases or disorders. Therefore stabilization of the partially folded states of proteins towards native conformation is important. Here, we investigate the effects of glycine, l-alanine, DL- α – aminobutyric acid, l-lysine, l-leucine and l-valine on the stability of molten globule like partially folded state of bovine serum albumin (BSA) at pH 11.2. We report the changes in the Trp microenvironment of the BSA at pH 11.2 by these amino acids. Except for l-leucine and l-valine, the other four amino acids impart thermal stabilization to partially folded MG like intermediate of BSA at pH 11.2. CD spectroscopy is employed to analyse tertiary conformation of BSA. We perform the ITC to study the interaction of BSA with these amino acids at pH 11.2. The spectroscopic in combination with calorimetric observations have enabled monitoring amino acid-induced conformational changes in BSA at pH 11.2 suggesting their osmolyte behavior. The results suggest significance of preferential hydration of partially folded proteins and the stability offered by the amino acids.

Using fluorescence and circular dichroism (CD) spectroscopy to investigate the interaction between di-n-butyl phthalate and bovine serum albumin

The interaction between di-n-butyl phthalate (DBP) and bovine serum albumin (BSA) in physiological Tris-HCl buffer at pH 7.4 was investigated by fluorescence quenching technique. By analyzing the fluorescence spectrum and intensity, it was observed that the DBP had a strong ability to quench the intrinsic fluorescence of BSA through a static quenching procedure. The binding constants K and the number of binding sites n of DBP with BSA were calculated to be 0.11 × 102 L·mol−1 and 0.52 at 298 K, respectively. The thermodynamic parameters of enthalpy change (ΔH) and entropy change (ΔS) were also calculated to be positive showing that hydrophobic forces might play a major role in the binding of DBP to BSA. The binding process was spontaneous in which Gibbs free energy change (ΔG) was negative. The distance (r) between the donor (BSA) and acceptor (DBP) was calculated to be 2.02 nm based on Forster’s non-radiative energy transfer theory, which indicated that the energy transfer from BSA to DBP occurs with a high possibility. The synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectra showed that the binding of di-n-butyl phthalate to BSA induced conformational changes in BSA. The interaction between DBP and BSA can help researchers better understand the nature of poisons and serve people in the right way with first aid and detoxification.

Exploring the mode of binding between butylated hydroxyanisole with bovine serum albumin: Multispectroscopic and molecular docking study

Considering the harm of BHA on humans, thorough research of the effect of BHA on the structure of serum albumin is necessary. The binding mechanisms of BHA with bovine serum albumin (BSA) and the effects of other three food additives (butylated hydroxytoluene, benzoic acid and citric acid) on BHA-BSA system were researched by multispectroscopy and molecular docking. The fluorescence quenching experiment results showed that the fluorescence quenching mechanism of BSA by BHA was static quenching. The binding constant ((5.70 ± 0.38) × 103 M−1 at 298 K) and thermodynamic parameters (ΔH = 110.8 ± 2.91 kJ·mol−1 and ΔS = 443.3 ± 9.30 J·mol−1·K−1) indicated that BHA and BSA formed a relatively stable complex through hydrophobic interaction. Three-dimensional fluorescence spectra confirmed the conformation changes of BSA due to the binding of BHA. Site marker competitive experiments and molecular docking proved that BHA could bind BSA into site I in subdomain IIA. The results of molecular docking showed that BHA formed hydrophobic interactions with amino acid residues (Ala290, Leu237, Leu259, Ile263 and Ile289). The presence of other food additives weakened the binding of BHA to BSA.

Pistacia lentiscus by-product as a promising source of phenolic compounds and carotenoids: Purification, biological potential and binding properties

The hydro-distilled leaves of Pistacia lentiscus are considered as an agricultural residue and of no commercial value yet. In this study, chromatographic purification of a methanolic fraction of P. lentiscus L. (lentisk) distilled leaves yielded pure compounds, including Quercitrin (QUE) and Loliolid (LOL) which are characterized, for the first time, in the lentisk leaves’ residue. The inhibitory potential of QUE and LOL was investigated against tyrosinase and acetylcholinesterase activities using enzymatic assays and lysozyme fibrillation through Thioflavin-T fluorescence assay. Their binding mode to Bovine Serum Albumin (BSA) was also assessed by several spectroscopic analyses. Results show that QUE was more potent to inhibit enzyme activity than LOL. Besides, the Thioflavin-T assay confirmed that only QUE was able to block the fibril formation at a concentration of 25 μg/mL. Furthermore, the BSA quenching mechanism by QUE and LOL is a static process with conformational changes in BSA. Interestingly, our findings may provide novel insights into the potentiality of lentisk to be used as a bioresource for the generation of Quercitrin and Loliolid which can be commercially exploited in the field of cosmeceuticals and nutraceuticals.

Radioprotective effect of nanoceria and magnetic flower-like iron oxide microparticles on gamma radiation-induced damage in BSA protein

<abstract><sec> <title>Purpose</title> Gamma radiation at therapeutic doses can cause conformation changes in proteins and consequently damage cells/tissues associated with the initiation of several pathological disorders. In this study, serum albumin, the most abundant protein in plasma, was chosen as the protein sample. </sec><sec> <title>Methods and Materials</title> Bovine serum albumin (BSA) was exposed to gamma radiation at a therapeutic dose (3 Gy) in the absence and presence of Ceria nanoparticles (CNPs) and flower-like Fe₃O₄ microparticles (FIOMPs). The conformational changes in BSA including primary, secondary, tertiary structures were then studied by UV-Vis, circular dichroism (CD), and fluorescence spectroscopy, respectively. </sec><sec> <title>Results</title> The primary structure of gamma-irradiated BSA (IR-BSA) was conserved, whereas the secondary and tertiary structures were considerably changed. IR-BSA showed α-helix to β-sheet and random coil structure transition along with reduced fluorescence emission intensity compared to non-irradiated native BSA. Both CNPs and FIOMPs could inhibit the secondary and tertiary structural changes in IR-BSA by scavenging the reactive oxygen species produced during the radiolysis of water. </sec><sec> <title>Conclusions</title> The radioprotective property of CNPs arises from enzyme mimetic activities (catalase, superoxide dismutase, and peroxidase) and their antioxidant capability against hydroxyl radicals. In case of FIOMPs, the radioprotective property is attributed to catalase mimetic activity (CAT), and a porous structure leading to increased ROS recombination with each other in the same radiolytic track, and subsequently decreased encounters with BSA. The latter mechanism of restricting ROS migration seems to be more dominant for FIOMPs. Both CNPs/FIOMPs themselves at low concentrations do not show a significant effect on the native protein conformation. These findings indicate that the proposed NPs/MPs can be good candidates for developing strong nano-radioprotectors. </sec></abstract>

A spectroscopic insight into the interaction of chromene 1,2,4-oxadiazole-based compounds with bovine serum albumin

Four synthesized 2H-chromene-based 1,2,4-oxadiazole compounds (6a-6d) were studied for binding with bovine serum albumin (BSA) by different spectroscopic and thermodynamic analyses. A molecular docking program was used to find out the possible binding sites and binding affinity of 2H-chromene based 1,2,4-oxadiazole compounds with bovine serum albumin (BSA). The intrinsic fluorescence of BSA was quenched by these compounds through static quenching mechanism, and the estimated binding constant (Kb) value was found to be 1.5 × 103–10 × 103. The conformational changes of BSA were monitored by circular dichroism analysis, and it was observed that BSA is structurally stable in the presence of these compounds. The thermodynamic results indicated that the interaction process is spontaneous and the binding between oxadiazole compounds and BSA is mainly driven by hydrogen bonding and van der Waals forces. This study would be helpful to understand the biological benefits of oxadiazole-based compounds as well as the nature of interactions with biomolecules.

Investigation on the interaction of brazilin with bovine serum albumin using multi-spectroscopic and computational methods: Exploring the binding mechanism and inhibitory effect on amyloid aggregation

Free and active concentration of drug in the blood plays a vital role in the disease treatment. Binding of drug to serum albumin, an important transport protein in plasma, usually improves its aqueous solubility, stability and bioactivity. Brazilin (Bra) is a natural compound extracted from Caesalpinia sappan with numerous pharmacological applications, while the behavior of Bra in circulatory system is still unknown. Therefore, in the present work, we firstly examined the interaction of Bra with bovine serum albumin (BSA) using various spectroscopic and computer simulation techniques. The static quenching mechanism and moderate binding affinity (2.18 × 104 M−1 at 298 K) were obtained through fluorescence spectroscopic measurement. Thermodynamic analysis results indicated that hydrophobic interactions and hydrogen bonds played a major role in the binding process. Site marker competitive experiments and molecular simulation suggested that the probable Bra-binding position was located in subdomain IIA of BSA. UV–vis absorption, circular dichroism (CD) and dynamic light scattering (DLS) experiments suggested the conformational changes of BSA induced by Bra. Additionally, the potential of Bra to inhibit the formation of amyloid fibrils, in vitro, has also been analyzed. Thioflavin T (ThT) binding, 8-anilino-1-naphthalenesulfonic acid (ANS) binding, Congo red binding, DLS, CD, fluorescence microscopic image, atomic force microscopy (AFM), size-exclusion chromatography (SEC) and native gel-electrophoresis methods were used, and all confirmed the anti-amyloidogenic behavior of Bra. In short, our findings have provided some important insights into the binding mechanism of Bra with BSA, and would be helpful in designing suitable agents against amyloid diseases.

Spectroscopic and molecular modelling study of binding mechanism of bovine serum albumin with phosmet.

Phosmet exerts its neurotoxicity by inhibiting acetylcholinesterase that catalyzes the degradation of acetylcholine (a neurotransmitter). Serum proteins are known to influence the biodistribution of various endogenous and exogenous compounds. In the present study, the binding interactions of phosmet with bovine serum albumin (BSA) was investigated to determine the free concentration of phosmet for its neurotoxicity. The binding mechanism was studied using fluorescence, UV-Vis absorption spectroscopy, circular dichroism (CD), and molecular docking techniques. UV-Vis absorption data showed an increase in absorbance of BSA upon binding with phosmet with a slight red-shift in the peak around 280nm. Intrinsic fluorescence of BSA was quenched in the presence of phosmet. The quenching was observed to be inversely correlated to the temperature that indicated the formation of ground state non-fluorescent complex (static quenching). Binding constant values and n values for the binding of phosmet with BSA at three different temperatures confirmed non-covalent binding interactions with a single set of equivalent binding sites. Thermodynamic parameters ∆G (-137.40±3.58kJmol-1); ΔH (-16.33±5.28kJmol-1) and ΔS(-469±12.45kJmol-1) confirmed that the binding was spontaneous and non-covalent interactions like electrostatic, hydrogen bonding and van der Waals forces played an important role in the binding. The CD data indicated the conformational change in BSA upon binding with phosmet which resulted in a change in the melting temperature. Molecular docking presented the binding model for BSA-phosmet complex and displayed that non-covalent interactions played a significant role in the binding mechanism.

Investigating the biomolecular interactions between model proteins and glycine betaine surfactant with reference to the stabilization of emulsions and antimicrobial properties

Binding effect and interaction of 2-pentadecanoyloxymethyl)trimethylammonium bromide (DMGM-14) with bovine serum albumin (BSA) and hen egg white lysozyme (HEWL) were systematically investigated by the fluorescence spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC), surface tension analysis, and molecular docking studies. The emulsion properties and particle size distribution of surfactant/protein complexes containing sunflower oil were studied using static light scattering and confocal laser scanning microscopy (CLSM). The fluorescence spectroscopy and ITC analysis confirmed the complexes formation of DMGM-14 with BSA and HEWL which was also verified by surface tension measurements. CD results explained the conformational changes in BSA and HEWL upon DMGM-14 complexation. Molecular docking study provides insight into the binding of DMGM-14 into the specific sites of BSA and HEWL. Besides, the studies drew a detailed picture on the emulsification properties of DMGM-14 with BSA and HEWL. In addition, the in vitro experiment revealed a broad antibacterial spectrum of DMGM-14 and DMGM-14/HEWL complex including activity against Gram-positive and Gram-negative bacteria. In conclusion, the present study revealed that the interaction between DMGM-14 with BSA and HEWL is important for the pharmaceutical, biological, and food products.

Investigation of the interaction of a polyamine-modified flavonoid with bovine serum albumin (BSA) by spectroscopic methods and molecular simulation

The interaction between BSA and compound 1 was studied by UV–vis, fluorescence and circular dichroism spectroscopy under physiological conditions (pH = 7.4). Molecular docking and molecular dynamics analyses were also performed. The results showed that compound 1 could bind to BSA. When compound 1 bound to BSA, there were a series of changes in the spectral properties of BSA, which were an enhancement effect of the UV–Vis spectrum of BSA, fluorescence quenching and a weak conformational change in the CD spectrum. The results of the fluorescence experiments at 298, 303 and 310 K showed that fluorescence quenching caused by the addition of compound 1 to BSA was generally static quenching accompanied by a dynamic quenching process, which was shown by the quenching constants of 2.010 × 104 L∙M−1, 1.850 × 104 L∙M−1, and 1.970 × 104 L∙M−1 at the three different temperatures, respectively. From the obtained binding constants and thermodynamic parameters, it was found that hydrophobic forces played an important role in the binding process of 1 to BSA. The results of synchronous fluorescence and three-dimensional fluorescence showed that compound 1 caused a weak conformational change in BSA. Docking results showed that compound 1 was located at binding site II of bovine serum albumin protease. In addition, the flavonoid moiety of compound 1 contributes to the hydrophobic binding of compound 1 to BSA. The results of molecular dynamics, including the root-mean-square deviation (RMSD) and RMS fluctuation (RMSF) values, showed that the binding of compound 1 to BSA did not cause a significant conformational change in BSA.

Synthesis of two novel pyrazolo[1,5-a]pyrimidine compounds with antibacterial activity and biophysical insights into their interactions with plasma protein.

Two novel water-soluble pyrazolo[1,5-a]pyrimidine derivatives, 5-chloro-7-(4-methyl-piperazin -1-yl)-pyrazolo[1,5-a]pyrimidine (CMPS) and N'-(5-chloro-pyrazolo[1,5-a]pyrimidin-7-yl)-N,N-dimethyl -propane-1,3-diamine (NCPS), were synthesized and characterized with antibacterial activity. Then, the interactions of these compounds with bovine serum albumin (BSA) were studied by fluorescence, time-resolved fluorescence, circular dichroism (CD) spectroscopy and molecular docking. The results indicate that both CMPS and NCPS could effectively quench the intrinsic fluorescence of BSA via a static quenching process. The energy transfer from BSA to CMPS and NCPS may occur with high probability. Both CMPS and NCPS bind in the site I of BSA. The hydrophobic force and hydrogen bonds play major roles in the complex formation. Binding constants for both systems show that the affinity of CMPS binding to BSA is stronger than that of NCPS. The results of three-dimensional fluorescence and CD spectra reveal that the binding of CMPS and NCPS to BSA can induce conformational changes of BSA, and the influence of CMPS is slightly stronger than that of NCPS.

Synthesis of a novel p-hydroxycinnamic amide and its interaction with bovine serum albumin

A novel p-hydroxycinnamic amides ((E)-4-(3-((4-(N-(5-methoxy-pyrimidin-2-yl) sulfamoyl) phenyl)amino)-3-oxoprop-1-en-1-yl)phenyl acetate (MSAP) was synthesized and confirmed by 1H NMR, 13CNMR ESI-MS, elemental analysis and single-crystal X-ray diffraction analysis. The crystal structure of the complex is monoclinic system and space group is P21/c. The interactions between MSAP and bovine serum albumin (BSA) was investigated with fluorescence and UV–Vis spectral analysis and molecular simulation. According to the fluorescence quenching calculation, the corresponding thermodynamic parameters (ΔH, ΔG and ΔS etc.), bimolecular quenching rate constant (kq), apparent quenching constants (Ksv) and binding sites number (n) were calculated. The distances (r) between BSA and its derivatives were obtained according to Foster’s non-radioactive energy transfer theory. Conformational changes in BSA were observed from synchronous fluorescence spectra. Furthermore, the site marker competitive experiments indicated that the binding of compounds to BSA primarily took place in site I (sub-domain IIA).