Sodium dodecyl sulphate modulates the fibrillation of human serum albumin in a dose-dependent manner and impacts the PC12 cells retraction

Intrinsic mechanisms for the inhibition effect of graphene oxide on the catalysis activity of alpha amylase

Comprehending the interactions between graphene oxide (GO) and enzymes is critical for understanding the toxicities of GO. In this study, the inherent interactions of GO with α-amylase as a typical enzyme, and the impacts of GO on the conformation and biological activities of α-amylase were systematically investigated. The results reveal that GO formed ground-state complex with α-amylase primarily via hydrogen bonding and van der Waals interactions, thus quenching the intrinsic fluorescence of the protein statically. Particularly, the strong interactions altered the microenvironment of tyrosine and tryptophan residues, caused rearrangement of polypeptide structure, and reduced the contents of α-helices and β-sheets, thus changing the conformational structure of α-amylase. According to molecular docking results, GO binds with the amino acid residues (i.e., His299, Asp300, and His305) of α-amylase mainly through hydrogen bonding, which is in accordance with in vitro incubation experiments. As a consequence, the ability of α-amylase to catalyze starch hydrolysis into glucose was depressed by GO, suggesting that GO might cause dysfunction of α-amylase. This study discloses the intrinsic binding mechanisms of GO with α-amylase and provides novel insights into the adverse effects of GO as it enters organisms.

Effect of ligands with different affinity on albumin fibril formation

The effect of binding of several ligands to bovine serum albumin on the kinetics of fibril formation at denaturing conditions is studied. The considered ligands are clinical drugs with different binding constants to albumin: relatively strong binders (naproxen, ibuprofen, warfarin with 10⁵ to 10⁷ binding constant values) and weak binders (isoniazid, ranitidine with 10³ to 10⁴ binding constant values). The data of thioflavin fluorescence binding assay, Congo red binding assay, and circular dichroism spectroscopy indicate ligand concentration-dependent suppression of fibril formation in the presence of strong binders and no effects in the presence of weak binders. Analysis of kinetic curves shows no induction lag associated with fibril nucleation and the first-order kinetics of fibril formation with respect to albumin concentration for all the studied systems. Using DSC method, the fractions of unfolded albumin at incubation temperature were determined for each albumin-ligand system and ligand concentration. Their magnitudes ranging from 0 to 1 correlate with the initial rates of fibril formation and with equilibrium concentrations of fibrils formed in the system after incubation for at least 120 min. The results indicate that fibrils are formed from partially or completely denatured albumin form with the rate proportional to the fraction of this form. Strong albumin binders act as thermodynamic inhibitors of fibrillation shifting the unfolding equilibrium to the side of the native ligand-bound protein.

Mechanisms of amyloid proteins aggregation and their inhibition by antibodies, small molecule inhibitors, nano-particles and nano-bodies

Protein misfolding and aggregation can be induced by a wide variety of factors, such as dominant disease-associated mutations, changes in the environmental conditions (pH, temperature, ionic strength, protein concentration, exposure to transition metal ions, exposure to toxins, posttranslational modifications including glycation, phosphorylation, and sulfation). Misfolded intermediates interact with similar intermediates and progressively form dimers, oligomers, protofibrils, and fibrils. In amyloidoses, fibrillar aggregates are deposited in the tissues either as intracellular inclusion or extracellular plaques (amyloid). When such proteinaceous deposit occurs in the neuronal cells, it initiates degeneration of neurons and consequently resulting in the manifestation of various neurodegenerative diseases. Several different types of molecules have been designed and tested both in vitro and in vivo to evaluate their anti-amyloidogenic efficacies. For instance, the native structure of a protein associated with amyloidosis could be stabilized by ligands, antibodies could be used to remove plaques, oligomer-specific antibody A11 could be used to remove oligomers, or prefibrillar aggregates could be removed by affibodies. Keeping the above views in mind, in this review we have discussed protein misfolding and aggregation, mechanisms of protein aggregation, factors responsible for aggregations, and strategies for aggregation inhibition.

Influence of micelles on protein's denaturation

To evaluate the role of micelles for protein-surfactant interaction, we have studied the binding modes of serum albumin proteins (human (HSA) and rabbit (RSA)) with anionic-surfactant, sodium dodecyl sulfate (SDS) by using UV-visible, fluorescence, circular dichroism, fluorescence lifetime, atomic force microscopy (AFM) techniques. The study performed with three different pHs (below (4.0), at (4.7), and above (7.0) isoelectric point). Hydrocarbon chain of the surfactant, dominant role of hydrophobic forces and electrostatic interactions helped in polar interaction on protein on binding surfaces. The change above and below the critical micelle concentration (CMC) in fluorescence spectra was due to polarity of the microenvironment. The CD spectra different binding aspects as below CMC and above CMC, explain about folding and unfolding in secondary structure. Surfactant's binding induces fluctuations in the microenvironment of aromatic amino acid's residues of both proteins at different pHs. AFM images clarify the structural changes in both proteins (HSA & RSA). AFM images also indicate some different interesting conformational and structural changes in both proteins below/above the CMC of the surfactant. The molecular docking studies indicate the binding energy -4.8 kcal mol^-1 and -4.7 kcal mol^-1 for HSA-SDS and RSA-SDS, respectively. Structural changes can be seen above and below the CMC.

Molecular characterization of the effects of Ganoderma Lucidum polysaccharides on the structure and activity of bovine serum albumin

The investigation about polysaccharides-protein system is attributed to numerous very important applications for pharmaceutical, food, chemical and other industries. In the present work, multi-spectral methods and molecular docking were used to analyze the molecular interactions of polysaccharides from Ganoderma Lucidum (GLP) with bovine serum albumin (BSA). The nonenzymatic glucosylation, fibrillation, thermal stability, and structure information of GLP-BSA system were also studied. The results showed that the formation of GLP-BSA complex by mainly hydrogen-bonding forces resulted in the conformational changes of protein. GLP acted as a stabilizer to increase the thermal stability of BSA solution having a novel and more stable conformational state during the thermal denaturation process. 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence spectral results suggested that there exist some intermediate state which has low binding ability with ANS in the presence of GLP. The presence of GLP caused a decrease in the formation of beta sheet structures with a lower rate. The fluorescence spectra of BSA glycosylated by GLP confirmed the formation of covalent bonds between BSA and GLP through the Maillard reaction which was also confirmed by using thermogravimetric (TGA) and Fourier transform infrared (FTIR) analysis. In addition, BSA still maintains the esterase-like good activity in the presence of GLP. These results provide a basis for screening the molecular interactions of polysaccharides with protein from the perspective of important food active ingredients.

Impact of the alkyl chain length on binding of imidazolium-based ionic liquids to bovine serum albumin

The effects of six imidazolium-based ionic liquids (ILs) with different alkyl chain length ([C_nMim]Cl, n=2, 4, 6, 8, 10, 12) on the structure and functions of bovine serum albumin (BSA) were studied by multi-spectral methods and molecular docking. ILs with the longer alkyl chain length have the stronger binding interaction with BSA and the greater conformational damage to protein. The effects of ILs on the functional properties of BSA were further studied by the determination of non-enzyme esterase activity, β-fibrosis and other properties of BSA. The thermal stability of BSA was reduced, the rate of the formation of beta sheet structures of BSA was lowered, and the esterase-like activity of BSA were decreased with the increase of ILs concentration. Simultaneous molecular modeling technique revealed the favorable binding sites of ILs on protein. The hydrophobic force and polar interactions were the mainly binding forces of them. The calculated results are in a good agreement with the spectroscopic experiments. These studies on the impact of the alkyl chain length on binding of imidazolium-based ionic liquids to BSA are of great significance for understanding and developing the application of ionic liquid in life and physiological system.

Inhibition of Amyloid Aggregation of Bovine Serum Albumin by Sodium Dodecyl Sulfate at Submicellar Concentrations

Sodium dodecyl sulfate (SDS), as an anionic surfactant, can induce protein conformational changes. Recent investigations demonstrated different effects of SDS on protein amyloid aggregation. In the present study, the effect of SDS on amyloid aggregation of bovine serum albumin (BSA) was evaluated. BSA transformed to β-sheet-rich amyloid aggregates upon incubation at pH 7.4 and 65°C, as demonstrated by thioflavin T fluorescence, circular dichroism, and transmission electron microscopy. SDS at submicellar concentrations inhibited BSA amyloid aggregation with IC₅₀ of 47.5 µM. The inhibitory effects of structural analogs of SDS on amyloid aggregation of BSA were determined to explore the structure-activity relationship, with results suggesting that both anionic and alkyl moieties of SDS were critical, and that an alkyl moiety with chain length ≥10 carbon atoms was essential to amyloid inhibition. We attributed the inhibitory effect of SDS on BSA amyloid aggregation to interactions between the detergent molecule and the fatty acid binding sites on BSA. The bound SDS stabilized BSA, thereby inhibiting protein transformation to amyloid aggregates. This study reports for the first time that the inhibitory effect of SDS on albumin fibrillation is closely related to its alkyl structure. Moreover, the specific binding of SDS to albumin is the main driving force in amyloid inhibition. This study not only provides fresh insight into the role of SDS in amyloid aggregation of serum albumin, but also suggests rational design of novel anti-amyloidogenic reagents based on specific-binding ligands.

Paclitaxel inhibited lysozyme fibrillation by increasing colloidal stability through formation of "off-pathway" oligomers

Protein fibrillation is a challenging issue in medicine, causing many diseases, and an impediment to pharmaceutics and protein industry. Many chemicals, especially polyphenol compounds and aromatic small molecules, have been widely used as an effective strategy to combat protein fibril formation. Hence, understanding mechanisms of fibrillation inhibition and contributing forces in this process are significant. In this study, the inhibitory effect of paclitaxel on lysozyme fibrillation was investigated with respect to thermal and colloidal stability. Fibrillation was monitored with ThT fluorescence, circular dichroism, and AFM; paclitaxel-lysozyme interaction with isothermal titration calorimetry and docking; thermal and colloidal stability with differential scanning calorimetry and zeta-pulse, respectively. Paclitaxel inhibited lysozyme fibrillation, and interacted with lysozyme through hydrogen bonds and van der Waals' interactions. The viability of PC12 cells retrieved as a result of fibrillation inhibition by paclitaxel. Hydrophobic forces dominantly shielded the aggregation-prone region of lysozyme and suppressed the effective interactions between lysozyme monomers. Although paclitaxel did not affect lysozyme's thermal stability, it increased lysozyme's colloidal stability by either increasing the surface charge density or charge distribution on lysozyme. In conclusion, our results suggest a model for paclitaxel's inhibitory role through two complementary steps driving to "off-pathway" oligomer formation and attenuation of fibril formation.

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.

The severe impact of in vivo-like microfluidic flow and the influence of gemini surfactants on amyloid aggregation of hen egg white lysozyme

The formation of amyloid plaques is being intensively studied, as this process underlies severe human diseases, including Alzheimer's disease, and the exact mechanism of this specific aggregation has not been resolved yet.

The soluble recombinant N-terminal domain of HMW 1Dx5 and its aggregation behavior

This study seeks to clarify and determine the fundamental properties of N-terminal domain of high molecular weight glutenin subunits (HMW-GS) 1Dx5 (1Dx5-N). 1Dx5-N was expressed in E. coli and its solubility was measured by spectrophotometry. Effects of edible salts (NaCl, Na₂CO₃), disulfide bond reductant dithiothreitol (DTT) and hydrophobic interactions of denaturant sodium dodecyl sulfonate (SDS) on 1Dx5-N polymer were investigated by native polyacrylamide gelelectrophoresis (PAGE), nonreducing/reducing SDS-PAGE, intrinsic fluorescence, size exclusion chromatography (SEC), dynamic light scattering (DLS) and circular dichroism (CD). Results showed that 1Dx5-N formed a soluble aggregate in aqueous solutions by native-PAGE, clarifying the role of N-terminal of HMW-GS in the insolubility of the whole subunits. Meanwhile, the hydrophobic interaction was more potent in promoting the aggregation of 1Dx5-N in aqueous solutions from the results of SEC, DLS and CD. Edible salts, NaCl and Na₂CO₃, could improve the polymer formation of 1Dx5-N through disulfide bonds. Moreover, Na₂CO₃ at high concentrations (>200mM) greatly favored polymer formation by disulfide bonds, and it induced other types of cross-links between amino acids in 1Dx5-N according to nonreducing/reducing SDS-PAGE and fluorescence spectrum. Moreover, the formation of covalent bonds was reinforced by hydrophobic interactions between 1Dx5-N. Therefore, these results provide much novel information on the N-terminal domain of HMW-GS to facilitate the understanding of its functional properties in wheat flour.

Appearance of annular ring-like intermediates during amyloid fibril formation from human serum albumin

The self-assembly of proteins triggered by a conformational switch into highly ordered β-sheet rich amyloid fibrils has captivated burgeoning interest in recent years due to the involvement of amyloids in a variety of human diseases and a diverse range of biological functions. Here, we have investigated the mechanism of fibrillogenesis of human serum albumin (HSA), an all-α-helical protein, using an array of biophysical tools that include steady-state as well as time-resolved fluorescence, circular dichroism and Raman spectroscopy in conjunction with atomic force microscopy (AFM). Investigations into the temporal evolution of nanoscale morphology using AFM revealed the presence of ring-like intermediates that subsequently transformed into worm-like fibrils presumably by a ring-opening mechanism. Additionally, a multitude of morphologically-diverse oligomers were observed on the pathway to amyloid formation. Kinetic analysis using multiple structural probes in-tandem indicated that HSA amyloid assembly is a concerted process encompassing a major structural change that is primarily mediated by hydrophobic interactions between thermally-induced disordered segments originating in various domains. A slower growth kinetics of aggregates suggested that the protein structural reorganization is a prerequisite for fibril formation. Moreover, time-dependent Raman spectroscopic studies of HSA aggregation provided key molecular insights into the conformational transitions occurring within the protein amide backbone and at the residue-specific level. Our data revealed the emergence of conformationally-diverse disulfides as a consequence of structural reorganization and sequestration of tyrosines into the hydrophobic amyloid core comprising antiparallel cross β-sheets.