Sodium louroyl sarcosinate (sarkosyl) modulate amyloid fibril formation in hen egg white lysozyme (HEWL) at alkaline pH: a molecular insight study

Interaction of gallium, indium, and vanadyl curcumin complexes with hen egg-white lysozyme (HEWL): Mechanistic aspects and evaluation of antiamyloidogenic activity

Many proteins and peptides can aggregate into amyloid fibrils with high-ordered and cross-β rich structure characteristics. Amyloid deposition is a common feature of neurodegenerative diseases called amyloidosis. Various natural polyphenolic compounds such as curcumin exhibited antiamyloidogenic activities, but less researches were focused on the metal complexes of these compounds. In this study, the inhibitory effects of gallium curcumin (Ga(cur)3), indium curcumin (In(cur)3), and vanadyl curcumin (VO(cur)2) on the amyloid fibrillation of hen egg white lysozyme (HEWL) have been investigated. Moreover, the details of binding interactions of these metal complexes with HEWL have been explored. The results of fluorescence quenching analyses revealed that In(cur)3 and VO(cur)2 have much higher binding affinities than Ga(cur)3 toward HEWL. The interactions of these metal complexes were accompanied by partial conformational changes in the tertiary structure of HEWL. The kinetic curves of the fibrillation process demonstrated that In(cur)3 and VO(cur)2 have higher inhibitory effects than Ga(cur)3 on the amyloid fibrillation of HEWL. The strength of binding to HEWL is completely in accordance with inhibitory activities of these metal complexes of curcumin.

Role of salts and solvents on the defibrillation of food dye "sunset yellow" induced hen egg white lysozyme amyloid fibrils

Several food dyes are known to induce amyloid fibrillation when interacting with proteins. Here, we studied the role of sunset yellow (SY) in the amyloid fibrillation of hen egg white lysozyme (HEWL) and characterized the changes using spectroscopy techniques. Turbidity results showed that SY dye induces aggregation in HEWL in concentrations dependent manner. The aggregation induced by SY dye is kinetically very fast, no lag phase was detected, and the kinetics process follows an isodesmic kinetics pathway. The SY-dye induce aggregates have cross-β secondary structure confirmed by far-UV CD measurements. The effect of salts and solvents was also seen on SY-induced aggregates. Turbidity, far-UV CD, and kinetics results suggest that certain concentrations of NaCl and (NH₄)₂SO₄ solubilize the SY-induce amyloid fibrils, but (NH₄)₂SO₄ is more effective. Similarly, solvents are also solubilized the SY-induces HEWL amyloid fibrillation but the order of defibrillation is as follows: Isopropanol> ethanol > methanol which signified that isopropanol is more effective than other solvents. The salts and solvents data suggest that the electrostatic, as well as hydrophobic interaction, is responsible for SY-induced amyloid fibrillation. These conformational changes should be examined, more seriously for the purpose of food safety.

Lysozyme amyloid fibril: Regulation, application, hazard analysis, and future perspectives

Self-assembly of misfolded proteins into ordered fibrillar aggregates known as amyloid results in various human diseases. However, more and more proteins, whether in human body or in food, have been found to be able to form amyloid fibrils with in-depth researches. As a model protein for amyloid research, lysozyme has always been the focus of research in various fields. Firstly, the formation mechanisms of amyloid fibrils are discussed concisely. Researches on the regulation of lysozyme amyloid fibrils are helpful to find suitable therapeutic drugs and unfriendly substances. And this review article summarizes a number of exogenous substances including small molecules, nanoparticles, macromolecules, and polymers. Small molecules are mainly connected to lysozyme through hydrophobic interaction, electrostatic interaction, π-π interaction, van der Waals force and hydrogen bond. Nanoparticles inhibit the formation of amyloid fibers by stabilizing lysozyme and fixing β-sheet. Besides, the applications of lysozyme amyloid fibrils in food-related fields are considered furtherly due to outstanding physical and mechanical properties. Nevertheless, the potential health threats are still worthy of our attention. Finally, we also give suggestions and opinions on the future research direction of lysozyme amyloid fibrils.

Imidazolium-based ionic liquids with increasing alkyl chain length of cations decrease the stability and fibrillation propensity of lysozyme

Imidazolium ionic liquids with longer alkyl side chains show a larger destabilization effect on lysozyme. Increased hydrophobicity of the IL increases its binding affinity and inhibits the fibril formation of lysozyme.

Elevated temperatures accelerate the formation of toxic amyloid fibrils of hen egg-white lysozyme

The formation of amyloid fibrils is critical for neurodegenerative diseases. Some physiochemical conditions can promote the conversion of proteins from soluble globular shapes into insoluble well‐organized amyloid fibrils. The aim of this study was to investigate the effect of temperatures on amyloid fibrils formation in vitro using the protein model of hen egg‐white lysozyme (HEWL). The HEWL fibrils were prepared at temperatures of 37, 45, 50 and 57°C in glycine solution of pH 2.2. Under transmission electron microscopy, we found the well‐organized HEWL amyloid fibrils at temperatures of 45, 50 and 57°C after 10 days of incubation. Thioflavin T and Congo red florescence assays confirmed that the formation and growth of HEWL fibrils displayed a temperature‐dependent increase, and 57°C produced the most amounts. Meanwhile, the surface hydrophobicity of aggregates was greatly increased by ANS binding assay, and β‐sheet contents by circular dichroism analysis were increased by 17.8%, 22.0% and 34.9%, respectively. Furthermore, the HEWL fibrils formed at 57°C caused significant cytotoxicity in SH‐SY5Y cells after 48 hr exposure, and the cell viability determined by MTT assay was decreased, with 81.35 ± 0.29% for 1 μM, 61.45 ± 2.62% for 2 μM, and 11.58 ± 0.39% (p < .01) for 3 μM. Nuclear staining results also confirmed the apoptosis features. These results suggest that the elevated temperatures could accelerate protein unfolding of the native structure and formation of toxic amyloid fibrils, which can improve understanding the mechanisms of the unfolding and misfolding process of prion protein.

Effect of cetyltrimethylammonium bromide (CTAB) on the conformation of a hen egg white lysozyme: A spectroscopic and molecular docking study

The interactions between cetyltrimethylammonium bromide (CTAB) and hen egg white lysozymes (HEWL) was carried out to investigate protein-surfactant interaction mechanisms while both exist in the overall same charged state. The interactions between CTAB and the HEWL were examined with circular dichroism (CD), dynamic light scattering (DLS), fluorescence spectroscopy, and computational docking at a pH9.0 at room temperature. The far-UV CD and fluorescence results revealed that CTAB at concentrations from 0.15 to 10.0mM influenced the secondary as well as the tertiary structure of HEWL. The secondary structure of the HEWL was retained, while the tertiary structure of the HEWL was disrupted in the CTAB-treated samples at pH9.0. The hydrodynamic radii of the HEWL were also expanded in the presence of CTAB. Molecular docking studies showed that CTAB formed one electrostatic and four hydrophobic interactions, as well as one carbon hydrogen bond with HEWL. The data obtained from spectroscopic and computational studies demonstrated that the positively charged head and 18‑carbon alkyl chain of the CTAB interacted through weak electrostatic and strong hydrophobic interactions.

Inhibitory effect of silibinin on Amadori-albumin in diabetes mellitus: A multi-spectroscopic and biochemical approach

Due to increased understanding of the damaging effects of glycation process, it is highly desirable to manage this process effectively either by prevention or by managing the consequences of glycation preferentially at early stage. The use of potential naturally occurring compounds as anti-glycating agents may provide an effective approach to control the development and progression of diabetic associated complications. In the present study, human serum albumin (albumin) was co-incubated with glucose and different concentrations of silibinin. Silibinin was demonstrated to possess anti-glycation activity. We found that silibinin inhibits glucoseinduced glycation at an early stage. We analyzed the effect of silibinin on albumin structure and its biochemical properties at early stage of glycation through various biophysical and biochemical techniques. Nitro blue tertazolium assay results showed that fructosamine formation was reduced in the presence of silibinin. UV-visible spectra results showed decrease in the absorbance with increasing concentrations of silibinin towards native albumin absorbance. Fluorescence results showed that the intensity was increased with increasing the silibinin concentrations as compared to Amadori-albumin. In addition, Far-UV CD spectra demonstrated some restoration of α-helicity when albumin was incubated with glucose in the presence of silibinin. Moreover, silibinin caused significant reduction in carbonyl contents with concomitant increase in free thiol, lysine and arginine residues. The anti-glycation activity of silibinin was concentration-dependent. From all the observations, we can conclude that silibinin might be acting as an obstacle in the binding of glucose with albumin and thus preventing the glycation induced changes in albumin. Silibinin may be effective in delaying glycation mediated pathologies in diabetic individuals.

Interaction of a dimeric carbocyanine dye aggregate with bovine serum albumin in non-aggregated and aggregated forms

The interaction of fluorescent dyes with serum proteins has garnered significant interest owing to potential for non-covalent labeling and imaging applications. In this work, dimeric benzothiazole-based trimethine cyanine dyes are synthesized and their interaction with bovine serum albumin studied. The dimeric cyanine dyes mainly exist as H-dimers and H-aggregates in aqueous solution. A combination of absorbance, fluorescence, circular dichroism spectroscopy and atomic force and fluorescence microscopy indicate the formation of dye-BSA complexes. Binding of one of the dimeric dyes on BSA with a K_a of 1.49×10⁵M^-1 results in disruption of dye self-aggregates and unfolding of the dyes into the monomeric or open conformation. Fluorescence enhancement experienced by the dimeric dyes upon interaction with BSA is superior to that registered by Thioflavin T. Surfactant SDS has been used to further tune the self-aggregation of the dimeric dye resulting in a 200-fold fluorescence enhancement in presence of BSA. Interaction of a dimeric dye with BSA under conditions favoring protein aggregation is found to result in faster dye binding and the resulting fluorescence enhancement is easily visualized by fluorescence microscopy. The interaction of a dimeric cyanine dye aggregate with BSA is promising for non-covalent labeling applications in sharp contrast to the monomeric dye counterpart.

Interaction of anticancer drug pinostrobin with lysozyme: a biophysical and molecular docking approach

Communicated by Ramaswamy H. Sarma.