Effect of surfactants on preformed fibrils of human serum albumin

Reducing the assemblies of amyloid-beta multimers by sodium dodecyl sulfate surfactant at concentrations lower than critical micelle concentration: molecular dynamics simulation exploration

Amyloid-β peptide, the predominant proteinaceous component of senile plaques, is responsible for the incidence of Alzheimer's disease (AD), an age-associated neurodegenerative disorder. Specifically, the amyloid-β(1-42) (Aβ1-42) isoform, known for its high toxicity, is the predominant biomarker for the preliminary diagnosis of AD. The aggregation of the Aβ1-42 peptides can be affected by the components of the cellular medium through changing their structures and molecular interactions. In this study, we investigated the effect of sodium dodecyl sulfate (SDS) at much lower concentrations than the critical micelle concentration (CMC) on Aβ1-42 aggregation. For this purpose, we studied mono-, di-, tri- and tetramers of Aβ1-42 peptide in two different concentrations of SDS molecules (10 and 40 molecules) using a 300 ns molecular dynamics simulation for each system. The distance between the center of mass (COM) of Aβ1-42 peptides confirms that an increase in the number of SDS molecules decreases their aggregation probability due to greater interaction with SDS molecules. Besides, the less compactness parameter reveals the reduced aggregation probability of Aβ1-42 peptides. Based on the energetic FEL landscapes, SDS molecules with the concentration closer to the CMC are an effective inhibitory agent to prevent the formation of Aβ1-42 fibrils. Also, the aggregation direction of the peptide pairs can be predicted by determining the direction of the accumulation-deterrent forces.Communicated by Ramaswamy H. Sarma.

Insights into the remarkable attenuation of hen egg white lysozyme amyloid fibril formation mediated by biogenic gold nanoparticles stabilized by quercetin-functionalized tara gum

Aberrant protein misfolding and/or aggregation and fibrillation has been linked to the pathogenesis of several debilitating chronic diseases including Alzheimer's and Parkinson's disease. Inhibiting protein amyloidogenesis has been proposed as a viable strategy to prevent or ameliorate associated disorders. Herein, we investigated the anti-amyloidogenic properties of biogenic gold nanoparticles (QTG-GNP) prepared via a simple green chemistry route and stabilized by quercetin-functionalized tara gum (QTG). The synthesized QTG-GNP was extensively characterized for its physicochemical attributes via UV-visible spectroscopy, TEM, FESEM, EDX, DLS/Zeta potential, FTIR, RAMAN, XRD, XPS, and TGA analyses, as well as for its biological properties. The results revealed that small-sized (5.01 ± 1.17 nm), well-dispersed, highly stable and round-shaped biogenic gold nanoparticles were successfully synthesized at room temperature with QTG as the sole reductant /stabilizer. Importantly, QTG-GNP demonstrated potent anti-aggregation and fibrillation inhibitory effects against amyloidogenic hen egg white lysozyme (HEWL). Also, QTG-GNP was able to dissociate pre-formed HEWL amyloid fibrils. Furthermore, the constructed nanoparticles exhibited potent anti-radical activities against DPPH and ABTS⁺ and were cytocompatible with mouse L929 fibroblast cells. On the basis of these findings, it was established that QTG-GNP holds strong prospects for further development as an agent for countering protein aggregation and associated disease conditions.

Potential of tetradecyltrimethylammonium bromide in preventing fibrillation/aggregation of lysozyme: biophysical studies

A key step in the prevention of neurodegenerative disorders is to inhibit protein aggregation or fibrillation process. Functionality recognition is an essential strategy in developing effective therapeutics in addressing the treatment of amyloidosis. Here, we have focused on an approach based on structure-property energetics correlation associated with tetradecyltrimethylammonium bromide (TTAB), a cationic surfactant that acts as an inhibitor targeting different stages of hen egg-white lysozyme fibrillation. Characterization of amyloid fibrils and the inhibitory capability of 16 mM TTAB surfactant on fibrillation were investigated with the calorimetric, spectroscopic and microscopic techniques. ThT binding fluorescence studies inferred that micellar TTAB exerts its maximum inhibitory effect against amyloid fibrillation than monomer TTAB. The TEM measurements also confirmed complete absence of amyloid fibrils at micellar TTAB. At the same time, the transformation of β-sheet to α-helix under the action of TTAB was confirmed by the Far-UV CD spectroscopy. Although there have been some reports suggesting that cationic surfactants can induce aggregation in proteins, this work suggests that polar interactions between head groups of TTAB and amyloid fibrils are the predominant factors that cause retardation in fibrillation by interrupting/disturbing the intermolecular hydrogen bond of β-sheets. The present finding has explored the knowledge-based details in developing efficient potent inhibitors and provides a platform to treat diseases associated with protein misfolding.Communicated by Ramaswamy H. Sarma.

Amyloid Disassembly: What Can We Learn from Chaperones?

Protein aggregation and subsequent accumulation of insoluble amyloid fibrils with cross-β structure is an intrinsic characteristic of amyloid diseases, i.e., amyloidoses. Amyloid formation involves a series of on-pathway and off-pathway protein aggregation events, leading to mature insoluble fibrils that eventually accumulate in multiple tissues. In this cascade of events, soluble oligomeric species are formed, which are among the most cytotoxic molecular entities along the amyloid cascade. The direct or indirect action of these amyloid soluble oligomers and amyloid protofibrils and fibrils in several tissues and organs lead to cell death in some cases and organ disfunction in general. There are dozens of different proteins and peptides causing multiple amyloid pathologies, chief among them Alzheimer's, Parkinson's, Huntington's, and several other neurodegenerative diseases. Amyloid fibril disassembly is among the disease-modifying therapeutic strategies being pursued to overcome amyloid pathologies. The clearance of preformed amyloids and consequently the arresting of the progression of organ deterioration may increase patient survival and quality of life. In this review, we compiled from the literature many examples of chemical and biochemical agents able to disaggregate preformed amyloids, which have been classified as molecular chaperones, chemical chaperones, and pharmacological chaperones. We focused on their mode of action, chemical structure, interactions with the fibrillar structures, morphology and toxicity of the disaggregation products, and the potential use of disaggregation agents as a treatment option in amyloidosis.

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.

Dielectric and Mechanical Properties of CTAB-Modified Natural Rubber Latex-Cement Composites

Cetyl trimethyl ammonium bromide (CTAB)-modified natural rubber latex/Portland cement paste (CTAB + NL/PC) composites were fabricated by varying the NL/cement and CTAB/cement ratios to improve the elastic property of PC. The stability and workability of the CTAB-modified NL particles in the PC matrix were significantly improved. The microstructure and dielectric property analyses of PC, CTAB/PC, NL/PC, and (CTAB + NL)/PC composites were performed to describe the interaction mechanism between the CTAB-modified NL and PC. The portlandite phase in PC was reduced by incorporating CTAB + NL. Although the tensile strength of NL/PC was significantly increased, its compressive strength also greatly decreased by ~40.3%. The tensile and compressive strengths of CTAB/PC were not significantly improved. Notably, the tensile strength of (CTAB + NL)/PC was significantly increased compared to those of PC, CTAB/PC, and NL/PC, while the depreciated compressive strength was only 18.7%. The optimized compressive–tensile performance of (CTAB + NL)/PC was equal to that of PC. The dielectric constants of NL/PC, CTAB/PC, and (CTAB + NL)/PC were reduced due to the low dielectric constant of NL and the ability of CTAB to capture negative charges in the PC matrix, leading to a reduction in the negative surface charges and hence the interfacial polarization. This result was confirmed by the decreased loss tangent in a low-frequency range, which is usually reduced by decreasing the free charges. This work provides a comprehensive guideline for significantly improving the elastic property of PC while retaining a high compressive strength.

Investigation on conformational variation and fibrillation of human serum albumin affected by molybdenum disulfide quantum dots

In this work, binding interaction between molybdenum disulfide quantum dots (MoS₂ QDs) and human serum albumin (HSA) was researched deeply to dissect the conformational variation and fibrillation of HSA affected by MoS₂ QDs. The results revealed that MoS₂ QDs bound strongly with HSA with molar ratio of 1:1 under the joint actions of hydrogen bond and van der Waals force, leading to the static fluorescence quenching of HSA. MoS₂ QDs caused the secondary structure transition of HSA from α-helix stepwise to β-turn, β-sheet, and random coil gradually. MoS₂ QDs reduced both the molar enthalpy change and the melting temperature of HSA, reducing the thermal stability of HSA significantly. It is worth noting that MoS₂ QDs inhibited the fibrillation process of HSA according to the reduced hydrophobic environment and the disturbance of disulfide bonds in HSA network structure. These results reveal the precise binding mechanism of MoS₂ QDs with HSA at molecular level, providing indispensable information for the potential application of MoS₂ QDs in biological fields.

Protein Handshake on the Nanoscale: How Albumin and Hemoglobin Self-Assemble into Nanohybrid Fibers

Creating and establishing proof of hybrid protein nanofibers (hPNFs), i.e., PNFs that contain more than one protein, is a currently unsolved challenge in bioinspired materials science. Such hPNFs could serve as universal building blocks for the bottom-up preparation of functional materials with bespoke properties. Here, inspired by the protein assemblies occurring in nature, we introduce hPNFs created via a facile self-assembly route and composed of human serum albumin (HSA) and human hemoglobin (HGB) proteins. Our circular dichroism results shed light on the mechanism of the proteins' self-assembly into hybrid nanofibers, which is driven by electrostatic/hydrophobic interactions between similar amino acid sequences (protein handshake) exposed to ethanol-triggered protein denaturation. Based on nanoscale characterization with tip-enhanced Raman spectroscopy (TERS) and immunogold labeling, our results demonstrate the existence and heterogenic nature of the hPNFs and reveal the high HSA/HGB composition ratio, which is attributed to the fast self-assembling kinetics of HSA. The self-assembled hPNFs with a high aspect ratio of over 100 can potentially serve as biocompatible units to create larger bioactive structures, devices, and sensors.

Morphological Effects of CuO Nanostructures on Fibrillation of Human Serum Albumin

The influence of different morphologies of nanostructures on amyloid fibrillation has been investigated by monitoring the fibrillation of human serum albumin (HSA) in the presence of rod-, sphere-, flower-, and star-shaped copper oxide (CuO) nanostructures. The different morphologies of CuO have been synthesized from an aqueous solution-based precipitation method using various organic acids, viz., acetic acid, citric acid, and tartaric acid. The fibrillation process of HSA has been examined using various biophysical techniques, e.g., Thioflavin T fluorescence, Congo red binding studies through UV spectroscopy, circular dichroism spectroscopy, and fluorescence microscopy. The monolayer protein coverage on the CuO nanostructures has been established through DLS studies, and the well-fitted Langmuir isotherm model has been used to interpret the differential adsorption behavior of HSA molecules on the CuO nanostructures. The nanostar-shaped CuO, by virtue of their higher specific surface area (94.45 m² g^-1), presence of high indexed facets {211} and high positive surface charge potential (+16.2 mV at pH 7.0) was found to show the highest adsorption of the HSA monomers and thus was more competent to inhibit the formation of HSA fibrils compared to the other nanostructures of CuO.

Direct Evidence of Intrinsic Blue Fluorescence from Oligomeric Interfaces of Human Serum Albumin

The molecular origin behind the concentration-dependent intrinsic blue fluorescence of human serum albumin (HSA) is not known yet. This unusual blue fluorescence is believed to be a characteristic feature of amyloid-like fibrils of protein/peptide and originates due to the delocalization of peptide bond electrons through the extended hydrogen bond networks of cross-β-sheet structure. Herein, by combining the results of spectroscopy, size exclusion chromatography, native gel electrophoresis, and confocal microscopy, we have shown that the intrinsic blue fluorescence of HSA exclusively originates from oligomeric interfaces devoid of any amyloid-like fibrillar structure. Our study suggests that this low energy fluorescence band is not due to any particular residue/sequence, but rather it is a common feature of self-assembled peptide bonds. The present findings of intrinsic blue fluorescence from oligomeric interfaces pave the way for future applications of this unique visual phenomenon for early stage detection of various protein aggregation related human diseases.

Prion like behavior of HSA-hydroxylated MWCNT interface

Carbon nanotubes (CNTs) with unique and outstanding properties were expected to revolutionize various aspects of the biomedical sector. Interaction studies of proteins with functionalized CNTs would shed light on their toxicological aspects upon entering the human body. Hyperchromicity of the UV-Visible spectra and declining fluorescence potential of HSA on interaction with CNTs suggested ground state complex to exist between them. Synchronous and 3D spectral features of CNT-HSA system proposed their possible binding site to occur nearby Trp and Tyr residues. FTIR and FT-Raman spectra showed a shift in the amide band region that proportionate the possible alteration to occur in the alpha-helical structures. CD far and near spectra showed loss of alpha-helical structures and shift in the Trp position of the polypeptide backbone. CNT's UV and FTIR band showed shift on interaction with HSA, which conveys the possible aggregation of CNTs in the presence of protein. The promoting role of CNTs against HSA fibril formation has been confirmed by spectroscopic and microscopic evaluations. Secondary conformational changes, besides the existence of increased beta-sheet structures of HSA amyloid fibrils, remain similar to the amyloid behavior of Prion protein. Hence, HSA fibril-CNT interface predominates the possible mechanism for several amyloid-related disorders concerning their toxic accumulations in the body.

Inhibition of fibrillation of human serum albumin through interaction with chitosan-based biocompatible silver nanoparticles

Electrostatic interaction of chitosan-based silver nanoparticles with human serum albumin leads to inhibition of fibrillogenesis.

Insight into the co-solvent induced conformational changes and aggregation of bovine β-lactoglobulin

Many proteins form ordered irreversible aggregates called amyloid fibrils which are responsible for several neurodegenerative diseases. β-lactoglobulin (β-lg), an important globular milk protein, self-assembles to form amyloid-like fibrils on heating at low pH. The present study investigated the effects of two commonly used organic solvents acetonitrile (MeCN) and antimicrobial preservative benzyl alcohol (BA) on the conformation and self-assembly of β-lg at ambient condition. Both MeCN and BA induced a concentration-dependent conformational change showing exposure of hydrophobic patches, loss of tertiary structure and higher α-helical structure at moderate concentrations. In the presence of 50-80% (v/v) MeCN and 1.5-3% (v/v) BA further structural transitions from α-helical to non-native β-sheet structure were observed with a molten globule-like intermediate at 70% MeCN. These non-native β-sheet structures have high tendency to form aggregates. The formation of β-lg self-assembly was confirmed by Thioflavin T studies, Congo red assay, Rayleigh scattering and dynamic light scattering analysis. Transmission electron microscopy studies showed amyloid fibril formation in both MeCN and BA. Our results showed that BA enhances the unfolding and self-assembly of β-lg at much lower concentration than MeCN. Thus solvent composition forces the protein to achieve the non-native structures which are responsible for protein aggregation.