Amine Group Surface-Functionalized Carbon Quantum Dots Exhibit Anti-amyloidogenic Effects Towards Hen Egg White Lysozyme by Inducing Formation of Nontoxic Spherical Aggregates

The tendency of polypeptide chains to deviate from their conventional protein folding pathway and instead get trapped as off-pathway intermediates, has been a matter of great concern. These off-pathway intermediates eventually lead to the formation of insoluble, ordered fibrillar aggregates called amyloids, which are responsible for a host of neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Type II diabetes. In spite of extensive research, development of an effective therapeutic strategy against amyloidosis still remains elusive. In recent times, carbon quantum dots (CQD) have grabbed the attention of researchers against amyloidogenesis due to their ease of preparation, aqueous soluble nature, unique optical properties, high surface to volume ratio, physio-chemical properties, semi-conducting nature and mainly biocompatible. In the current study, we have reported an easy-to-prepare procedure for synthesis of amine group surface functionalized CQDs from commonly available kitchen spices with anti-oxidant properties. The as-synthesized CQDs were evaluated for their anti-amyloidogenic properties towards Hen Egg White Lysozyme (HEWL). Our results clearly show that the surfaced functionalized CQDs were able to interact with HEWL, thereby forming a stable complex, which was resistant towards amyloid formation and instead lead to the formation of non-toxic globular aggregates.

Inhibitory effects of carbon quantum dots towards hen egg white lysozyme amyloidogenesis through formation of a stable protein complex

Proteins, under certain circumstances such as defective quality control mechanism, mutations and altered environmental conditions, undergo misfolding and assemble into highly ordered beta-sheet structured fibrillar aggregates called amyloid fibrils. Formation of amyloid is seen in most of the protein linked degenerative diseases like Alzheimer's disease, Parkinson's disease, Huntington's disease, Type II diabetes mellitus and many more. Amyloid fibril forms via intermediate state(s), and is known to follow a nucleated condensation polymerization mechanism. Though extensive research is being carried out towards finding a therapeutic solution to the amyloidosis, an effective treatment to these diseases still remains elusive and also the mechanism of amyloidogenesis largely remains unclear. In recent times, carbon quantum dots (CQDs) are gaining the attention of researchers due to their semi-conductive nature, excellent physio-chemical properties, high surface to volume ratio, optical properties and mainly bio-compatibility. In the current study, we have synthesized CQDs from commonly available kitchen spice mix and explored their role in amyloidogenesis using hen egg white lysozyme (HEWL) as a model protein. The results clearly demonstrate the amyloid inhibitory as well as disaggregation potential of CQD by forming a stable complex with HEWL and thereby increasing the energy barrier for the aggregation process.

Solid-state packing dictates the unexpected solubility of aromatic peptides

The understanding and prediction of the solubility of biomolecules, even of the simplest ones, reflect an open question and unmet need. Short aromatic tripeptides are among the most highly aggregative biomolecules. However, in marked contrast, Ala-Phe-Ala (AFA) was surprisingly found to be non-aggregative and could be solubilized at millimolar concentrations. Here, aiming to uncover the underlying molecular basis of its high solubility, we explore in detail the solubility, aggregation propensity, and atomic-level structure of the tripeptide. We demonstrate an unexpectedly high water solubility of AFA reaching 672 mM, two orders of magnitude higher than reported previously. The single crystal structure reveals an anti-parallel β sheet conformation devoid of any aromatic interactions. This study provides clear mechanistic insight into the structural basis of solubility and suggests a simple and feasible tool for its estimation, bearing implications for design of peptide drugs, peptides materials, and advancement of peptide nanotechnology.

Urea-Appended Amino Acid To Vitalize Yeast Growth, Enhance Fermentation, and Promote Ethanol Production

The development of sustainable protocols for enhancing the production of ethanol is highly important for its utilization in automotive transportation and energy sector. Up to 15% ethanol can blend with diesel to make e-diesel that can be used in fuel compression ignition engine. Urea-modified amino acids can be used as a very good vitalizer for yeast (Saccharomyces cerevisiae, Baker's yeast (ATCC 204508)) growth and thus promote ethanol production. A simple, one-step, room-temperature synthetic procedure has been developed for urea-appended α-amino acids from amino acid by treatment with KCNO. Single-crystal X-ray studies confirm the successful synthesis and molecular structures of the urea-appended α-amino acids. Out of 20 urea-appended amino acids, Arg-, Pro-, His-, and Gln-containing compounds promote yeast growth significantly after 12 h at pH 6.8 and 38 °C. These compounds are nontoxic. The urea-appended Arg shows 2-fold increase of yeast growth. However, urea-appended m-aminobenzoic acid and p-aminobenzoic acid inhibit yeast growth. NMR experiments confirmed the enhanced production of ethanol by glucose fermentation in the presence of 2.5 μmol urea-appended Arg. Not only glucose but also commercially available sugars and feedstock of the starch slurry drained out after boiling of rice exhibit significant enhancement of ethanol production under same conditions.

Conditions Governing Food Protein Amyloid Fibril Formation-Part I: Egg and Cereal Proteins

Conditions including heating mode, time, temperature, pH, moisture and protein concentration, shear, and the presence of alcohols, chaotropic/reducing agents, enzymes, and/or salt influence amyloid fibril (AF) formation as they can affect the accessibility of amino acid sequences prone to aggregate. As some conditions applied on model protein resemble conditions in food processing unit operations, we here hypothesize that food processing can lead to formation of protein AFs with a compact cross β-sheet structure. This paper reviews conditions and food constituents that affect amyloid fibrillation of egg and cereal proteins. While egg and cereal proteins often coexist in food products, their impact on each other's fibrillation remains unknown. Hen egg ovalbumin and lysozyme form AFs when subjected to moderate heating at acidic pH separately. AFs can also be formed at higher pH, especially in the presence of alcohols or chaotropic/reducing agents. Tryptic wheat gluten digests can form fibrillar structures at neutral pH and maize and rice proteins do so in aqueous ethanol or at acidic pH, respectively.

Modifications of amino acids using arenediazonium salts

Aryl transfer reactions from arenediazonium salts have started to make their impact in chemical biology with initial forays in the arena of arylative modifications and bio-conjugations of amino acids, peptides and proteins.

1-(2-aminophenyl)-1H-1,2,3-triazole-4-carboxylic acid: activity against Gram-positive and Gram-negative pathogens including Vibrio cholerae

We report a new synthetic aromatic ε-amino acid containing a triazole moiety with antimicrobial potential against Gram-positive, Gram-negative and pathogenic bacteria including Vibrio cholerae. Structure-property relationship studies revealed that all the functional groups are essential to enhance the antimicrobial activity. The 1-(2-aminophenyl)-1H-1,2,3-triazole-4-carboxylic acid was synthesized by click chemistry. From X-ray crystallography, the amino acid adopts a kink-like structure where the phenyl and triazole rings are perpendicular to each other and the amine and acid groups maintain an angle of 60°. The agar diffusion test shows that the amino acid has significant antibacterial activity. The liquid culture test exhibits that the minimum inhibitory concentration (MIC) value for Bacillus subtilis and Vibrio cholerae is 59.5 µg ml-1. FE-SEM experiments were performed to study the morphological changes of bacterial shape after treatment with compound 1. The antimicrobial activity of the amino acid was further studied by DNA binding and degradation study, protein binding, dye-binding assay and morphological analysis. Moreover, the amino acid does not have any harmful effect on eukaryotes.

Synthesis and structural investigation of 2-aminomethyl-3-(4-methoxy-phenyl)-propionic acid containing a peptide analogue of the amyloidogenic AS(6–7) sequence: inhibition of fibril formation

The incorporation of a β-amino acid, namely 2-aminomethyl-3-(4-methoxy-phenyl)-propionic acid, inhibits amyloid-like fibril formation.