Resveratrol Interferes with an Early Step in the Fibrillization Pathway of Human Lysozyme and Modulates it towards Less-Toxic, Off-Pathway Aggregates

Furosemide Derails Human Lysozyme Fibrillation by Interacting with Aggregation Hot Spots: A Biophysical Comprehension

Kidney-associated human lysozyme amyloidosis leads to renal impairments;thus, patients are often prescribed furosemide. Based on this fact, the effect of furosemide on induced human lysozyme fibrillation, in vitro, is evaluated by spectroscopic, calorimetric, computational, and cellular-based assays/methods. Results show that furosemide increases the lag phase and decreases the apparent rate of aggregation of human lysozyme, thereby decelerating the nucleation phase and amyloid fibril formation, as confirmed by the decrease in the level of Thioflavin-T fluorescence. Fewer entities of hydrodynamic radii of ∼171 nm instead of amyloid fibrils (∼412 nm) are detected in human lysozyme in the presence of furosemide by dynamic light scattering. Moreover, furosemide decreases the extent of conversion of the α/β structure of human lysozyme into a predominant β-sheet. The isothermal titration calorimetry established that furosemide forms a complex with human lysozyme, which was also confirmed through fluorescence quenching and computational studies. Also, human lysozyme lytic activity is inhibited competitively by furosemide due to the involvement of amino acid residues of the active site in catalysis, as well as complex formation. Conclusively, furosemide interacts with Gln58, Ile59, Asn60, Ala108, and Trp109 of aggregation-prone regions 2 and 4 of human lysozyme, thereby masking its sites of aggregation and generating only lower-order entities that are less toxic to red blood cells than the fibrils. Thus, furosemide slows the progression of amyloid fibrillation in human lysozyme.

Cyclic-NDGA Effectively Inhibits Human γ-Synuclein Fibrillation, Forms Nontoxic Off-Pathway Species, and Disintegrates Preformed Mature Fibrils

Parkinson's disease arises from protein misfolding, aggregation, and fibrillation and is characterized by LB (Lewy body) deposits, which contain the protein α-synuclein (α-syn) as their major component. Another synuclein, γ-synuclein (γ-syn), coexists with α-syn in Lewy bodies and is also implicated in various types of cancers, especially breast cancer. It is known to seed α-syn fibrillation after its oxidation at methionine residue, thereby contributing in synucleinopathy. Despite its involvement in synucleinopathy, the search for small molecule inhibitors and modulators of γ-syn fibrillation remains largely unexplored. This work reveals the modulatory properties of cyclic-nordihydroguaiaretic acid (cNDGA), a natural polyphenol, on the structural and aggregational properties of human γ-syn employing various biophysical and structural tools, namely, thioflavin T (ThT) fluorescence, Rayleigh light scattering, 8-anilinonaphthalene-1-sulfonic acid binding, far-UV circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR) spectroscopy, atomic force microscopy, ITC, molecular docking, and MTT-toxicity assay. cNDGA was observed to modulate the fibrillation of γ-syn to form off-pathway amorphous species that are nontoxic in nature at as low as 75 μM concentration. The modulation is dependent on oxidizing conditions, with cNDGA weakly interacting (Kd ∼10-5 M) with the residues at the N-terminal of γ-syn protein as investigated by isothermal titration calorimetry and molecular docking, respectively. Increasing cNDGA concentration results in an increased recovery of monomeric γ-syn as shown by sodium dodecyl sulfate and native-polyacrylamide gel electrophoresis. The retention of native structural properties of γ-syn in the presence of cNDGA was further confirmed by far-UV CD and FTIR. In addition, cNDGA is most effective in suppression of fibrillation when added at the beginning of the fibrillation kinetics and is also capable of disintegrating the preformed mature fibrils. These findings could, therefore, pave the ways for further exploring cNDGA as a potential therapeutic against γ-synucleinopathies.

Computer aided therapeutic tripeptide design, in alleviating the pathogenic proclivities of nocuous α-synuclein fibrils

Parkinson's disorder (PD) exacerbates neuronal degeneration of motor nerves, thereby effectuating uncoordinated movements and tremors. Aberrant alpha-synuclein (α-syn) is culpable of triggering PD, wherein cytotoxic amyloid aggregates of α-syn get deposited in motor neurons to instigate neuro-degeneration. Amyloid aggregates, typically rich in beta sheets are cardinal targets to mitigate their neurotoxic effects. In this analysis, owing to their interaction specificity, we formulated an efficacious tripeptide out of the aggregation-prone region of α-syn protein. With the help of a proficient computational pipeline, systematic peptide shortening and an adept molecular simulation platform, we formulated a tripeptide, VAV from α-syn structure based hexapeptide KISVRV. Indeed, the VAV tripeptide was able to effectively mitigate the α-syn amyloid fibrils' dynamic rate of beta-sheet formation. Additional trajectory analyses of the VAV- α-syn complex indicated that, upon its dynamic interaction, VAV efficiently altered the distinct pathogenic structural dynamics of α-syn, further advocating its potential in alleviating aberrant α-syn's amyloidogenic proclivities. Consistent findings from various computational analyses have led us to surmise that VAV could potentially re-alter the pathogenic conformational orientation of α-syn, essential to mitigate its cytotoxicity. Hence, VAV tripeptide could be an efficacious therapeutic candidate to efficiently ameliorate aberrant α-syn amyloid mediated neurotoxicity, eventually attenuating the nocuous effects of PD.Communicated by Ramaswamy H. Sarma.

Effect of artificial sweetener saccharin on lysozyme aggregation: A combined spectroscopic and in silico approach

The use of saccharin in food products attracts much attention as it involves the risk of lethal allergies and many protein aggregation diseases. However, its role in protein aggregation has not been explored to date. This study embodies the effect of artificial sweeteners on HEWL in the absence and presence of commonly available natural products such as curcumin and EGCG. Various techniques have been used to characterize the protein interaction, such as steady-state emission and time-resolved fluorescence, FTIR, gel electrophoresis, TEM, and molecular docking. Steady-state and time-resolved studies revealed the binding strength and concomitant effect of saccharin on HEWL protein. Kinetic measurements revealed that saccharin causes significant enhancement of HEWL aggregation with a considerable reduction in lag phase time i.e. from 37 hr to 08 hr. Whereas in the presence of natural products, the effect of saccharin on HEWL aggregation was significantly reduced specifically in the case of curcumin. The result obtained in the fluorescence experiment were also supported by the gel electrophoresis technique and morphological images taken by TEM. The rapid change in the secondary structure of the protein in the presence of saccharin was confirmed by the FTIR spectroscopy technique. This study is instrumental in understanding the effect of saccharin on protein aggregation and the role of commonly available natural products in curbing its effect.

A quinoline alkaloid potentially modulates the amyloidogenic structural transitions of the biofilm scaffolding small basic protein

Bacterial biofilm formation by communities of opportunistic bacterial pathogens like Staphylococcus epidermidis is regarded as the primary virulence mechanism facilitating the spread of detrimental nosocomial and implant-associated infections. An 18-kDa small basic protein (Sbp) and its amyloid fibrils account for strengthening the biofilm architecture and scaffolding the S. epidermidis biofilm matrix. Our study reports systematic analysis of the amyloidogenic structural transitions of Sbp and predicts the amyloid core of the protein which may trigger misfolding and aggregation. Herein, we report the novel amyloid inhibitory potential of Camptothecin, a quinoline alkaloid which binds stably to Sbp monomers and redirects the formation of unstructured regions further destabilizing the protein. Molecular dynamics simulations reveal that Camptothecin averts β-sheet transitions, interrupts with electrostatic interactions and disrupts the intermolecular hydrophobic associations between the exposed hydrophobic amyloidogenic regions of Sbp. Collectively, our study puts forward the first report detailing the heteromolecular associations and amyloid modulatory effects of Camptothecin which may serve as a structural scaffold for the tailored designing of novel drugs targeting the S. epidermidis biofilm matrix.Communicated by Ramaswamy H. Sarma.

Polyphenol-solubility alters amyloid fibril formation of α-synuclein

Amyloid fibril formation is associated with various amyloidoses, including neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Amyloid fibrils form above the solubility of amyloidogenic proteins or peptides upon breaking supersaturation, followed by a nucleation and elongation mechanism, which is similar to the crystallization of solutes. Many additives, including salts, detergents, and natural compounds, promote or inhibit amyloid formation. However, the underlying mechanisms of the opposing effects are unclear. We examined the effects of two polyphenols, that is, epigallocatechin gallate (EGCG) and kaempferol-7─O─glycoside (KG), with high and low solubilities, respectively, on the amyloid formation of α-synuclein (αSN). EGCG and KG inhibited and promoted amyloid formation of αSN, respectively, when monitored by thioflavin T (ThT) fluorescence or transmission electron microscopy (TEM). Nuclear magnetic resonance (NMR) analysis revealed that, although interactions of αSN with soluble EGCG increased the solubility of αSN, thus inhibiting amyloid formation, interactions of αSN with insoluble KG reduced the solubility of αSN, thereby promoting amyloid formation. Our study suggests that opposing effects of polyphenols on amyloid formation of proteins and peptides can be interpreted based on the solubility of polyphenols.

Scutellarin inhibits the uninduced and metal-induced aggregation of α-Synuclein and disaggregates preformed fibrils: implications for Parkinson's disease

The aggregation of the protein alpha synuclein (α-Syn), a known contributor in Parkinson's disease (PD) pathogenesis is triggered by transition metal ions through occupational exposure and disrupted metal ion homeostasis. Naturally occurring small molecules such as polyphenols have emerged as promising inhibitors of α-Syn fibrillation and toxicity and could be potential therapeutic agents against PD. Here, using an array of biophysical tools combined with cellular assays, we demonstrate that the novel polyphenolic compound scutellarin efficiently inhibits the uninduced and metal-induced fibrillation of α-Syn by acting at the nucleation stage and stabilizes a partially folded intermediate of α-Syn to form SDS-resistant, higher-order oligomers (∼680 kDa) and also disaggregates preformed fibrils of α-Syn into similar type of higher-order oligomers. ANS binding assay, fluorescence lifetime measurements and cell-toxicity experiments reveal scutellarin-generated oligomers as compact, low hydrophobicity structures with modulated surface properties and significantly reduced cytotoxicity than the fibrillation intermediates of α-Syn control. Fluorescence spectroscopy and isothermal titration calorimetry establish the binding between scutellarin and α-Syn to be non-covalent in nature and of moderate affinity (Ka ∼ 105 M−1). Molecular docking approaches suggest binding of scutellarin to the residues present in the NAC region and C-terminus of monomeric α-Syn and the C-terminal residues of fibrillar α-Syn, demonstrating inhibition of fibrillation upon binding to these residues and possible stabilization of the autoinhibitory conformation of α-Syn. These findings reveal interesting insights into the mechanism of scutellarin action and establish it as an efficient modulator of uninduced as well as metal-induced α-Syn fibrillation and toxicity.

In Vitro Prion Amplification Methodology for Inhibitor Screening

Prion (PrP^C) is an endogenous protein found mainly in the nervous system, and its misfolded isoform (PrP^Sc) is associated with a group of neurodegenerative disorders known as transmissible spongiform encephalopathies, or simply prion diseases. The PrP^Sc isoform shows an intriguing ability to self-perpetuate, acting as template for PrP^C misfolding and consequent aggregation. Aggregation in vitro and in vivo follows a fibrillation processes that is associated with neurodegeneration. Therefore, it is important to investigate and understand the molecular mechanisms involved in this process; such understanding also allows investigation of the action of possible candidate molecules to inhibit this process. Here, we highlight useful in vitro methodologies and analyses that were developed using PrP as a protein model but that, as other amyloid proteins also exhibit the same behavior, may be applied to understand other "prion-like" diseases such as Alzheimer's and Parkinson's disease.