Spectroscopic studies of interaction between CuO nanoparticles and bovine serum albumin

Recently, the great interests in manufacturing and application of metal oxide nanoparticles in commercial and industrial products have led to focus on the potential impact of these particles on biomacromolecules. In the present study, the interaction of copper oxide (CuO) nanoparticles with bovine serum albumin (BSA) was studied by spectroscopic techniques. The zeta potential value for BSA and CuO nanoparticles with average diameter of around 50 nm at concentration of 10 μM in the deionized (DI) water were ?5.8 and ?22.5 mV, respectively. Circular dichroism studies did not show any changes in the content of secondary structure of the protein after CuO nanoparticles interaction. Fluorescence data revealed that the fluorescence quenching of BSA by CuO nanoparticles was the result of the formed complex of CuO nanoparticles – BSA. Binding constants and other thermodynamic parameters were determined at three different temperatures. The hydrogen bond interactions are the predominant intermolecular forces to stabilize the CuO nanoparticle – BSA complex. This study provides important insight into the interaction of CuO nanoparticles with proteins, which may be of importance for further application of these nanoparticles in biomedical applications.     

Interaction of iron nanoparticles with nervous system: an in vitro study

Nanoparticles (NPs) are one of the interesting and widely studying issues mainly because of their particular physico-chemical features and broad applications in the field of biomedical sciences, such as diagnosis and drug delivery. In this study, the interaction of iron nanoparticles (Fe–NPs) with Tau protein and PC12 cell, as potential nervous system models, was investigated with a range of techniques including dynamic light scattering, intrinsic fluorescence spectroscopy, circular dichroism, [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium-bromid] assay, and acridine orange/ethidium bromide (AO/EB) dual staining method. An inverse correlation between Stern and Volmer constant (K_SV) and temperature indicated a probable static quenching mechanism occurred between Tau protein and Fe–NPs. The number of binding site (n = 0.86) showed that there is almost one binding site of Fe–NP per protein. The negative values of ?H (?53.21 kJ/mol) and T?S (?42.44 kJ/mol) revealed that Fe–NPs interacts with Tau protein with dominate role of hydrogen bonds and van der Waals interactions and this interaction was spontaneous (?G = ?10.77 kJ/mol). Also, Fe–NPs stabilized the random coil structure of Tau protein. Moreover, Fe–NPs reduced PC12 cells viability by fragmentation of DNA in an apoptotic manner. In conclusion, induced conformational changes of Tau protein and cytotoxicity of PC12 cells by Fe–NP were revealed to be in a concentration and time-dependent manner.     

Elucidating the interaction of Spathodea campanulata leaf extracts mediated potential bactericidal gold nanoparticles with human serum albumin: spectroscopic analysis

Nanomaterials in different form have been thoroughly used in the area of pharmaceutics and medicine for drug delivery. The large scale of nanoparticles (NPs) synthesis from plant extract is much safe, cheap and eco-friendly. Here, we demonstrated a new, one-step, ultra-fast biosynthesis of gold nanoparticles (sc-AuNPs, 19.54?nm) by using aqueous Spathodea campanulata leaf extracts as a reducing and capping agent. And also, we presented the synthesis of citrate capped gold nanoparticles (cit-AuNPs) of approximately same size (19.66?nm). These two NPs were characterized by UV-Visible, dynamic light scattering, transmission electron microscope and energy dispersive X-ray spectroscopy. Fourier transform infrared spectroscopy confirmed that the functional groups like OH, NH, OH of COOH and CO were contributed in the sc-AuNPs formation. The negative zeta potential (?20.5, ?22.8?mV) established the stability and dispersion of the sc- and cit-AuNPs. The anti-bacterial activity of the sc- and cit-AuNPs were checked against Escherichia coli (DH5-Alpha). Minimum inhibitory concentration was 2.4 and 3.0?nM, respectively for sc- and cit-AuNPs. The interaction study of the sc-AuNPs/cit-AuNPs-human serum albumin (HSA) system was done by UV-Visible absorbance, fluorescence, circular dichroism, time resolved fluorescence spectroscopy and the measurement of zeta potential. Absorbance, three dimensional fluorescence, synchronous fluorescence and circular dichroism spectroscopy showed a minor conformational change of HSA upon interaction with the sc-AuNPs compared to cit-AuNPs. The present comparative study will advance our knowledge about the binding mode, mechanism and conformational change of the protein upon interaction with green synthesized sc-AuNPs and cit-AuNPs.

Communicated by Ramaswamy H. Sarma     

Probing the interaction of anticancer drug temsirolimus with human serum albumin: molecular docking and spectroscopic insight

The binding interaction between temsirolimus, an important antirenal cancer drug, and HSA, an important carrier protein was scrutinized making use of UV and fluorescence spectroscopy. Hyper chromaticity observed in UV spectroscopy in the presence of temsirolimus as compared to free HSA suggests the formation of complex between HSA and temsirolimus. Fluorescence quenching experiments clearly showed quenching in the fluorescence of HSA in the presence of temsirolimus confirming the complex formation and also confirmed that static mode of interaction is operative for this binding process. Binding constant values obtained through UV and fluorescence spectroscopy reveal strong interaction; temsirolimus binds to HSA at 298 K with a binding constant of 2.9 × 10⁴ M^?1implying the strength of interaction. The negative Gibbs free energy obtained through Isothermal titration calorimetry as well as quenching experiments suggests that binding process is spontaneous. Molecular docking further provides an insight of various residues that are involved in this binding process; showing the binding energy to be -12.9 kcal/mol. CD spectroscopy was retorted to analyze changes in secondary structure of HSA; increased intensity in presence of temsirolimus showing changes in secondary structure of HSA induced by temsirolimus. This study is of importance as it provides an insight into the binding mechanism of an important antirenal cancer drug with an important carrier protein. Once temsirolimus binds to HSA, it changes conformation of HSA which in turn can alter the functionality of this important carrier protein and this altered functionality of HSA can be highlighted in variety of diseases.     

Ceramide influences neurite outgrowth and neuroblastoma cell apoptosis regulated by novel protein kinase C isoforms

We have previously seen that protein kinase C (PKC) epsilon induces neurite outgrowth and that PKCdelta and PKCtheta elicit apoptosis in neuroblastoma cells. In this study we investigate the effects of cell-permeable C(2)-ceramide on these events in SK-N-BE(2) neuroblastoma cells. C(2)-ceramide abolishes neurite formation induced by overexpression of PKCepsilon and, in cells overexpressing PKCdelta or PKCtheta, ceramide treatment leads to apoptosis. Exposure to C(2)-ceramide also suppressed neurite outgrowth induced by retinoic acid, but ceramide did not abrogate neurite induction by treatment with the ROCK inhibitor Y-27632, demonstrating that C(2)-ceramide is not a general inhibitor of neurite outgrowth. The neurite-suppressing effect occurs independently of cell-death. Furthermore, C(2)-ceramide relocated PKCepsilon and the isolated regulatory domain of PKCepsilon from the cytosol to the perinuclear region. In contrast, neither the localization of PKCdelta nor of PKCtheta was affected by C(2)-ceramide. Taken together, the data indicate that the neurite-inhibiting effect of C(2)-ceramide treatment may be caused by a re-localization of PKCepsilon and thus identify a functional consequence of ceramide effects on PKCepsilon localization.     

Probing the conformational changes and peroxidase-like activity of cytochrome c upon interaction with iron nanoparticles

Herein, the interaction of iron nanoparticle (Fe-NP) with cytochrome c (Cyt c) was investigated, and a range of techniques such as dynamic light scattering (DLS), zeta potential measurements, static and synchronous fluorescence spectroscopy, near and far circular dichroism (CD) spectroscopy, and ultraviolet–visible (UV–vis) spectroscopy were used to analyze the interaction between Cyt c and Fe-NP. DLS and zeta potential measurements showed that the values of hydrodynamic radius and charge distribution of Fe-NP are 83.95 ± 3.7 nm and 4.5 ± .8 mV, respectively. The fluorescence spectroscopy results demonstrated that the binding of Fe-NP with Cyt c is mediated by hydrogen bonds and van der Waals interactions. Also Fe-NP induced conformational changes in Cyt c and reduced the melting temperature value of Cyt c from 79.18 to 71.33°C. CD experiments of interaction between Fe-NP and Cyt c revealed that the secondary structure of Cyt c with the dominant α-helix structures remained unchanged whereas the tertiary structure and heme position of Cyt c are subjected to remarkable changes. Absorption spectroscopy at 695 nm revealed that Fe-NP considerably disrupt the Fe…S(Met80) bond. In addition, the UV–vis experiment showed the peroxidase-like activity of Cyt c upon interaction with Fe-NP. Hence, the data indicate the Fe-NP results in unfolding of Cyt c and subsequent peroxidase-like activity of denatured species. It was concluded that a comprehensive study of the interaction of Fe-NP with biological system is a crucial step for their potential application as intracellular delivery carriers and medicinal agents.     

Positive Charges on Lysine Residues of the Extrinsic 18 kDa Protein Are Important to Its Electrostatic Interaction with Spinach Photosystem Ⅱ Membranes

To determine the contribution of charged amino acids to binding with the photosystem II complex （PSII）, the amino or carboxyl groups of the extrinsic 18 kDa protein were modified with N- succinimidyl propionate （NSP） or glycine methyl ester （GME） in the presence of a water-soluble carbodiimide, respectively. Based on isoelectric point shift, 4-10 and 10-14 amino groups were modified in the presence of 2 and 4 mM NSP, respectively. Similarly, 3-4 carboxyl groups were modified by reaction with 100 mM GME. Neutralization of negatively charged carboxyl groups with GME did not alter the binding activity of the extrinsic 18 kDa protein. However, the NSP-modified 18 kDa protein, in which the positively charged amino groups had been modified to uncharged methyl esters, failed to bind with the PSII membrane in the presence of the extrinsic 23 kDa protein. This defect can not be attributed to structural or conformational alterations imposed by chemical modification, as the fluorescence and circular dichroism spectra among native, GME- and NSP-modified extrinsic 18 kDa proteins were similar. Thus, we have concluded that the positive charges of lysyl residues in the extrinsic 18 kDa protein are important for its interaction with PSII membranes in the presence of the extrinsic 23 kDa protein. Furthermore, it was found that the negative charges of carboxyl groups of this protein did not participate in binding with the extrinsic 23 kDa protein associated with PSII membranes.     

Green synthesis of silver nanoparticles using Pongamia pinnata seed: Characterization,antibacterial property,and spectroscopic investigation of interaction with human serum albumin

In recent years, green synthesized nanoparticles from plant extract have drawn a great interest due to their prospective nanomedicinal application. This study investigates a proficient, safer, and sustainable way for the preparation of AgNPs using medicinal plant Pongamia pinnata (family: Leguminoseae, species: Pinnata ) seeds extract without using any external reducing and stabilizing agent. Both ultraviolet‐visible spectrum at λ_max = 439 nm and energy dispersive X‐ray spectra proof the formation of AgNPs. An average diameter of the AgNPs was 16.4 nm as revealed from transmission electron microscope. Hydrodynamic size (d  = ~19.6 nm) was determined by dynamic light scattering (DLS). Zeta potential of AgNPs was found to be −23.7 mV, which supports its dispersion and stability. Fourier transform infrared study revealed that the O ─ H, C ═ O, and C‐O‐C groups were responsible for the formation of AgNPs. The antibacterial activity of the synthesized AgNPs was checked against Escherichia coli ATCC 25922. AgNPs at its LD₅₀ dose exhibited synergistic effect with ampicillin. Because protein‐AgNPs association greatly affects its adsorption, distribution, and functionality and can also influence the functions of biomolecules. So in order to understand the adsorption and bioavailability, we investigated by fluorescence, ultraviolet‐visible, and circular dichroism spectroscopic methods the interaction of synthesized AgNPs toward human serum albumin. The binding affinity and binding sites of human serum albumin toward AgNPs were measured by using the fluorescence quenching data. The circular dichroism spectroscopic results revealed that there was a negligible change of α‐helical content in their native structure. Overall, these AgNPs show versatile biological activities and may be applied in the field of nanomedicine.     

Calmodulin binds to a tubulin binding site of the microtubule-associated protein tau

Previous studies have demonstrated that the microtubule - associated proteins MAP-2 and tau interact selectively with common binding domains on tubulin defined by the low-homology segments a (430–441) and (422–434). It has been also indicated that the synthetic peptide VRSKIGSTENLKHQPGGG corresponding to the first tau repetitive sequence represents a tubulin binding domain on tau. The present studies show that the calcium-binding protein calmodulin interacts with a tubulin binding site on tau defined by the second repetitive sequence VTSKCGSLGNIHHKPGGG. It was shown that both tubulin and calmodulin bind to tau peptide-Sepharose affinity column. Binding of calmodulin occurs in the presence of 1 mM Ca 2+ and it can be eluted from the column with 4 mM EGTA. These findings provide new insights into the regulation of microtubule assembly, since Ca 2+/calmodulin inhibition of tubulin polymerization into microtubules could be mediated by the direct binding of calmodulin to tau, thus preventing the interaction of this latter protein with tubulin.     

Study of the interaction between DNP and DIDS with human hemoglobin as binary and ternary systems: spectroscopic and molecular modeling investigation

The combination of several drugs is necessary, especially during long-term therapy. A competitive binding of the drugs can cause a decrease in the amount of drugs actually bound to the protein and increase the biologically active fraction of the drug. Here, the interaction between 4,4′-Diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS) and 2,4-Dinitrophenol (DNP) with Hemoglobin (Hb) was investigated by different spectroscopic and molecular modeling techniques. Fluorescence analysis was used to estimate the effect of the DIDS and DNP on Hb as well as to define the binding properties of binary and ternary complexes. The distance r between donor and acceptor was obtained by the FRET and found to be 2.25 and 2.13 nm for DIDS and DNP in binary and 2.08 and 2.07 nm for (Hb–DNP) DIDS and (Hb–DIDS) DNP complexes in ternary systems, respectively. Time-resolved fluorescence spectroscopy confirmed static quenching for Hb in the presence of DIDS and DNP in both systems. Furthermore, an increase in ellipticity values of Hb upon interaction with DIDS and DNP showed secondary structural changes of protein that determine to disrupt of hydrogen bonds and electrostatic interactions. Our results showed that the Hb destabilize in the presence of DIDS and DNP. Molecular modeling of the possible binding sites of DIDS and DNP in binary and ternary systems in Hb confirmed the experimental results.     

Evidence of the production of silver nanoparticles via pretreatment of Phoma sp.3.2883 with silver nitrate

AIMS: The objective was to demonstrate the size of silver particles produced by the filamentous fungus Phoma sp.3.2883 via adsorption and accumulation, and to confirm that this silver was in a reduced state. METHODS AND RESULTS: Mycelium was freeze-dried and then shake-cultured in a silver nitrate solution. It was found that up to 13.4 mg of silver was produced per gram of dry mycelium via atomic absorption spectrometer (AAS) analysis. The silver particles adsorbed on the mycelium were observed and measured under transmission electron microscope and their estimated size was 71.06 +/- 3.46 nm. Further examination of the particles via X-ray photoelectron spectroscope confirmed that the adsorbed silver particle had been reduced. CONCLUSION: The frozen mycelium of Phoma sp3.2883 has the potential for use in silver nanoparticle production. SIGNIFICANCE AND IMPACT OF THE STUDY: Silver nanoparticles could be used in the oil industry as an important catalyst and in the field of human medicine as a bactericide. The fungus Phoma sp3.2883 is a potential biosorbent that could be used for the production of these silver nanoparticles, and may also be useful in waste detoxification and in silver recovery programmes.     

Comparison of interactions between human serum albumin and silver nanoparticles of different sizes using spectroscopic methods

Three different sizes (15.9 ± 2.1 nm, 26.4 ± 3.2 nm and 39.8 ± 4.0 nm, respectively) of citrate‐coated silver nanoparticles (SNPs) have been synthesized and characterized. The interactions of the synthesized SNPs with human serum albumin (HSA) at physiological pH have been systematically studied by UV‐vis absorption spectroscopy, fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The results indicate that the SNPs can bind to HSA with high affinity and quench the intrinsic fluorescence of HSA. The binding constants and quenching rate constants were calculated. The apparent association constants (K_app) values are 2.14 × 10⁴ M^–1 for 15.9 nm SNP, 1.65 × 10⁴ M^–1 for 26.4 nm SNP and 1.37 × 10⁴ M^–1 for 39.8 nm SNP, respectively. The values of binding constant obtained from the fluorescence quenching data match well with that determined from the absorption spectral changes. These results suggest that the smaller SNPs have stronger interactions to HSA than the larger ones at the same concentrations. Synchronous fluorescence, three‐dimensional fluorescence and CD spectroscopy studies show that the synthesized SNPs can induce slight conformational changes in HSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Phosphorylation of tau at Ser214 mediates its interaction with 14-3-3 protein: implications for the mechanism of tau aggregation

The microtubule associated protein tau is a major component of neurofibrillary tangles in Alzheimer disease brain, however the neuropathological processes behind the formation of neurofibrillary tangles are still unclear. Previously, 14-3-3 proteins were reported to bind with tau. 14-3-3 Proteins usually bind their targets through specific serine/threonine –phosphorylated motifs. Therefore, the interaction of tau with 14-3-3 mediated by phosphorylation was investigated. In this study, we show that the phosphorylation of tau by either protein kinase A (PKA) or protein kinase B (PKB) enhances the binding of tau with 14-3-3 in vitro . The affinity between tau and 14-3-3 is increased 12- to 14-fold by phosphorylation as determined by real time surface plasmon resonance studies. Mutational analyses revealed that Ser214 is critical for the phosphorylation-mediated interaction of tau with 14-3-3. Finally, in vitro aggregation assays demonstrated that phosphorylation by PKA/PKB inhibits the formation of aggregates/filaments of tau induced by 14-3-3. As the phosphorylation at Ser214 is up-regulated in fetal brain, tau's interaction with 14-3-3 may have a significant role in the organization of the microtubule cytoskeleton in development. Also as the phosphorylation at Ser214 is up-regulated in Alzheimer's disease brain, tau's interaction with 14-3-3 might be involved in the pathology of this disease.     

Insight into the interaction of benzothiazole tethered triazole analogues with human serum albumin: Spectroscopy and molecular docking approaches

The interaction of four benzothiazole tethered triazole analogues (MS43, MS70, MS71, and MS78) with human serum albumin (HSA) was investigated using various spectroscopic techniques (ultraviolet–visible (UV–vis) light absorption, fluorescence, circular dichroism (CD), molecular docking and density functional theory (DFT) studies). Fluorescence quenching constants (~10¹²) revealed a static mode of quenching and binding constants (K_b ~10⁴) indicating the strong affinity of these analogues for HSA. Further alteration in the secondary structure of HSA in the presence of these analogues was also confirmed by far UV–CD spectroscopy. The intensity loss in CD studied at 222 nm indicated an increase in random coil/β‐sheet conformations in the protein. Binding energy values (MS71 (?9.3 kcal mol^?1), MS78 (?8.02 kcal mol^?1), MS70 (?7.16 kcal mol^?1) and MS43 (?6.81 kcal mol^?1)) obtained from molecular docking revealed binding of these analogues with HSA. Molecular docking and DFT studies validated the experimental results, as these four analogues bind with HSA at site II through hydrogen bonding and hydrophobic interactions.     

pH effects on the stability and dimerization of procaspase-3

pH-dependent conformational changes are known to occur in dimeric procaspase-3, and they have been shown to affect the rate of automaturation. We studied the equilibrium unfolding of procaspase-3(C163S) as a function of pH (between pH 8.5 and pH 4) in order to examine these changes in the context of folding and stability. The data show that the procaspase dimer undergoes a pH-dependent dissociation below pH 5, so that the protein is mostly monomeric at pH 4. Consistent with this, the dimer unfolds via a four-state process between pH 8.5 and pH 4.75, in which the native dimer isomerizes to a dimeric intermediate, and the dimeric intermediate dissociates to a monomer, which then unfolds. In contrast, a small protein concentration dependence was observed by circular dichroism, but not by fluorescence emission, at pH 4.5 and pH 4.2. There was no protein-concentration dependence to the data collected at pH 4. Overall, the results are consistent with the redistribution of the population of native dimer (N(2)) to dimeric intermediate (I(2)) to monomeric intermediate (I), as the pH is lowered so that at pH 4, the "native" ensemble resembles the monomeric intermediate (I) observed during unfolding at higher pH. An emerging picture of the monomeric procaspase is discussed. Procaspase-3 is most stable at pH approximately 7 (24-26 kcal/mol), and while the stability decreased with pH, it was observed that dimerization contributes the majority (>70%) of the conformational free energy.     

Probing the interaction of caffeic acid with ZnO nanoparticles

The binding of ZnO nanoparticles (NPs) and caffeic acid (CFA) was investigated using fluorescence quenching, UV/vis absorption spectrscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) at different temperatures. The study results indicated fluorescence quenching between ZnO NPs and CFA rationalized in terms of a static quenching mechanism or the formation of non‐fluorescent CFA–ZnO. From fluorescence quenching spectral analysis, the binding constant (K_a), number of binding sites (n) and thermodynamic properties were determined. Values of the quenching (K_SV) and binding (K_a) constants decrease with increasing temperature and the number of binding sites n = 2. The thermodynamic parameters determined using Van't Hoff equation indicated that binding occurs spontaneously involving the hydrogen bond, and van der Waal's forces played a major role in the reaction of ZnO NPs with CFA. The FTIR, TEM and DLS measurements also indicated differences in the structure, morphology and size of CFA, ZnO NPs and their corresponding CFA–ZnO. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of an ionic detergent on the natively unfolded beta-dystroglycan ectodomain and on its interaction with alpha-dystroglycan

Dystroglycan (DG) is an adhesion complex, expressed in a wide variety of tissues, formed by an extracellular and a transmembrane subunit, alpha-DG and beta-DG, respectively, interacting noncovalently. Recently, we have shown that the recombinant ectodomain of beta-DG, beta-DG(654-750), behaves as a natively unfolded protein, as it is able to bind the C-terminal domain of alpha-DG, while not displaying a defined structural organization. We monitored the effect of a commonly used denaturing agent, the anionic detergent sodium dodecylsulphate (SDS), on beta-DG(654-750) using a number of biophysical techniques. Very low concentrations of SDS (< or =2 mM) affect both tryptophan fluorescence and circular dichroism of beta-DG, and significantly perturb the interaction with the alpha-DG subunit as shown by solid-phase binding assays and fluorescence titrations in solution. This result confirms, as recently proposed for natively unfolded proteins, that beta-DG(654-750) exists in a native state, which is crucial to fulfill its biological function. Two-dimensional NMR analysis shows that SDS does not induce any evident conformational rearrangement within the ectodomain of beta-DG. Its first 70 amino acids, which show a lower degree of mobility, interact with the detergent, but this does not change the amount of secondary structure, whereas the highly flexible and mobile C-terminal region of beta-DG(654-750) remains largely unaffected, even at a very high SDS concentration (up to 50 mM). Our data indicate that SDS can be used as a useful tool for investigating natively unfolded proteins, and confirm that the beta-DG ectodomain is an interesting model system.     

Oligonucleotide-displaced organic monolayer-protected silver nanoparticles and enhanced luminescence of their salted aggregates

N-(2-mercaptopropionyl)glycine (tiopronin) monolayer-protected silver particles were partially displaced by single-stranded oligonucleotides through ligand exchanges. The oligonucleotide-displaced particles could be hybridized with complementary fluorophore-labeled oligonucleotides. Both the oligonucleotide-displaced and hybridized particles could be aggregated by electrostatic interactions with salt in buffer solution, and the aggregates displayed enhanced luminescence from fluorophores. This result suggests the possible application of surface-enhanced fluorescence from metallic nanoparticle aggregation for DNA detection.