Troger's Base Molecular Scaffolds in Dicarboxylic Acid Recognition

Artificial receptors (1−5) have been designed and synthesized from simple precursors. The chain length selectivity studies of dicarboxylic acids within the cavities of new fluorescent Troger's base molecular frameworks (1−3) have been carried out with a critical examination of their role of rigidity as well as flexibility in selective binding in comparison to receptor 5. The chiral resolution of the racemic Troger's base receptors (1 and 2) by chiral recognition with (+)- camphoric acid using hydrogen-bonding interactions has been studied

Fibrillation of Human Serum Albumin Differentially Affected by Asp‑, Arg‑, and Tyr-Capped Gold Nanoparticles

Fibrillation of proteins is associated with a number of debilitating diseases, including various neurodegenerative disorders. Prevention of the protein fibrillation process is therefore of immense importance. We investigated the effect of amino acid-capped AuNPs on the prevention of the fibrillation process of human serum albumin (HSA), a model protein. Amino acid-capped AuNPs of varying sizes and agglomeration extents were synthesized under physiological conditions. The AuNPs were characterized by their characteristic surface plasmon resonance (SPR), and their interactions with HSA were investigated through emission spectroscopy in addition to circular dichroism (CD) spectral analyses. Fluorescence lifetime imaging (FLIM) as well as transmission electron microscopy (TEM) were used to observe the fibrillar network. Thermodynamic and kinetic analyses from CD and fluorescence emission spectra provided insights into the fibrillation pathway adopted by HSA in the presence of capped AuNPs. Kinetics of the fibrillation pathway followed by ThT fluorescence emission confirmed the sigmoidal nature of the process. The highest cooperativity was observed in the case of Asp-AuNPs with HSA. This was in accordance with the ΔG value obtained from the CD spectral analyses, where Arg-AuNPs with HSA showed the highest positive ΔG value and Asp-AuNPs with HSA showed the most negative ΔG value. The study provides information about the potential use of conjugate AuNPs to monitor the fibrillation process in proteins

Effect of Silica Nanoparticles on the Amyloid Fibrillation of Lysozyme

Protein fibrils are regarded as undesired products as these are associated with numerous neuro- and non-neurodegenerative disorders. Increasing evidence suggests that the mechanism of fibrillation involves the formation of various oligomeric intermediates, which are known to be more toxic than mature fibrils. Here, we report the impact of synthesized silica nanoparticles (SiNPs) of diameters ∼52 nm on the aggregation behavior of hen egg white lysozyme (HEWL) under heat and acidic conditions. Congo red as well as ThT binding assays and AFM imaging studies indicate that SiNPs trigger the amyloid formation of HEWL in a dose-dependent manner. ThT kinetic studies and FTIR studies suggest that the fibrillation kinetics does not involve the formation of toxic oligomeric intermediates at higher concentrations of SiNPs. By measuring fluorescence lifetime values of the bound ThT, SiNP-induced fibrillation of HEWL can easily be realized. CD spectroscopic studies indicate that native HEWL becomes unfolded upon incubation under the experimental conditions and is rapidly converted into the β-sheet-rich fibrillar aggregates in the presence of SiNPs with increasing concentrations. It has been further revealed that fibrillar aggregates formed at higher concentrations of SiNPs preferably adopt an antiparallel β-sheet configuration. The enhanced fibrillation in the presence of SiNPs is likely because of preferential adsorption of the non-amyloidogenic regions of HEWL, resulting in the exposure of the aggregation-prone regions of HEWL toward the solvent. The study will provide deeper insights into the evolution of oligomer-free fibrillation that can be useful to demonstrate the underlying mechanism of amyloid fibrillation

Complexation With Human Serum Albumin Facilitates Sustained Release of Morin From Polylactic-Co-Glycolic Acid Nanoparticles

Understanding the interaction of proteins with nanoparticles has become an important area of research in biomedical and pharmaceutical fields. Morin is a flavonol which shows several properties including antioxidant, anticancer, and anti-inflammatory activities. However, the major limitation is its poor aqueous solubility. Therefore, morin-loaded polylactic-<i>co</i>-glycolic acid (PLGA) nanoparticles (MPNPs) were prepared to improve the solubility of morin. The resulting MPNPs were characterized by spectroscopic and microscopic techniques. The nanoparticles were spherical with an average size of 237 ± 17 nm. UV–visible, fluorescence, and circular dichroism (CD) spectroscopy were employed to study the interaction of the MPNPs with human serum albumin (HSA). Our study revealed that a static fluorescence quenching mechanism was involved in the interaction between HSA and MPNPs. Hydrophobic interactions also play an important role in stabilizing the HSA-MPNP complex. CD results suggest that there is an alteration of the secondary structure of HSA in the presence of MPNPs. MPNPs exhibit antioxidant properties which are supported by the DPPH assay. We have further checked the effect of HSA on the antioxidant property of morin and MPNPs. HSA binding with MPNPs was also found to influence the <i>in vitro</i> release property of morin from MPNPs wherein a delayed release response is observed

Inhibition of Human Serum Albumin Fibrillation by Two-Dimensional Nanoparticles

The formation and deposition of amyloid fibrils have been linked to the pathogenesis of numerous debilitating neurodegenerative disorders. Serum albumins serve as good model proteins for understanding the molecular mechanisms of protein aggregation and fibril formation. Graphene-based nanotherapeutics appear to be promising candidates for designing inhibitors of protein fibrillation. The inhibitory effect of graphene oxide (GO) nanoparticles on the fibrillation of human serum albumin (HSA) in an in vitro mixed solvent system has been investigated. The methods used include ThT fluorescence, ANS binding, Trp fluorescence, circular dichroism, fluorescence microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. It was observed that GO inhibits HSA fibrillation and forms agglomerates with β-sheet rich prefibrillar species. Binding of GO prevents the formation of mature fibrils with characteristic cross-β sheet but does not promote refolding to the native state

Glycation of human serum albumin alters its binding efficacy towards the dietary polyphenols: a comparative approach

<p>Diabetes is a major problem in the world. The proteins became modified during glycation after reacting with the reducing sugars (e.g. D-glucose) via non-enzymatic pathways. The glycated analogue of human serum albumin (HSA) has been characterized with the help of multi-spectroscopic methods. It has been observed that six glucose molecules can bind covalently to HSA under experimental condition. The binding affinity of the modified HSA towards the dietary polyphenols has been estimated using UV–vis and fluorescence spectroscopic techniques. The binding constant values of the ligands were found to decrease after the modification of HSA.</p> <p>The binding affinities (<i>K</i>_<i>b</i>) of the polyphenols decreased towards human serum albumin after its structural modification with D-glucose. Highest percentage decrease in the binding is observed for quercetin among all the polyphenols.</p

Fibrillation in Human Serum Albumin Is Enhanced in the Presence of Copper(II)

The aggregation process in proteins is governed by several factors such as temperature, pH, presence of electrolytes, denaturants, and metal ions. Here, we report the role of Cu(II) in inducing rapid fibrillation in human serum albumin. We have monitored this process via UV−vis spectroscopy, fluorescence spectroscopy, circular dichroism, ζ-potential measurements, electron paramagnetic resonance studies, fluorescence microscopy, and field emission scanning electron microscopy. Images show a fibrillar network of human serum albumin in the presence of Cu(II) in 60% ethanol incubated at 65 °C at physiological pH. All other studies also support the enhanced fibrillation in presence of Cu(II)

Exploring the Inhibitory and Antioxidant Effects of Fullerene and Fullerenol on Ribonuclease A

Fullerene–protein interaction studies have been a key topic of investigation in recent times, but the lower water solubility of fullerene somewhat limits its application in the biological system. In this work, we have compared the activities of fullerene and its water-soluble hydrated form, that is fullerenol, on ribonuclease A (RNase A) under physiological conditions (pH 7.4). The interaction studies of fullerene and fullerenol with protein suggest that the binding depends on the hydrophobic interactions between the protein and the ligand. In addition, fullerene and fullerenol slow down the ribonucleolytic activity of RNase A through noncompetitive and mixed types of inhibition, respectively. This precisely gives the idea about the ligand-binding sites in RNase A, which has further been explored using docking studies. Both these nanoparticles show a reduction in dityrosine formation in RNase A caused due to oxidative stress and also prevent RNase A dimer formation to different extents depending on their concentration

An investigation into the altered binding mode of green tea polyphenols with human serum albumin on complexation with copper

<div><p>Green tea is rich in several polyphenols, such as (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epigallocatechin-3-gallate (EGCG). The biological importance of these polyphenols led us to study the major polyphenol EGCG with human serum albumin (HSA) in an earlier study. In this report, we have compared the binding of ECG, EGC, and EGCG and the Cu(II) complexes of EGCG and ECG with HSA. We observe that the gallate moiety of the polyphenols plays a crucial role in determining the mode of interaction with HSA. The binding constants obtained for the different systems are 5.86 ± 0.72 × 10⁴ M⁻¹ (<i>K</i>_ECG-HSA), 4.22 ± 0.15 × 10⁴ M⁻¹ (<i>K</i>_{ECG-Cu(II)-HSA}), and 9.51 ± 0.31 × 10⁴ M⁻¹ (<i>K</i>_{EGCG-Cu(II)-HSA}) at 293 K. Thermodynamic parameters thus obtained suggest that apart from an initial hydrophobic association, van der Waals interactions and hydrogen bonding are the major interactions which held together the polyphenols and HSA. However, thermodynamic parameters obtained from the interactions of the copper complexes with HSA are indicative of the involvement of the hydrophobic forces. Circular dichroism and the Fourier transform infrared spectroscopic measurements reveal changes in α-helical content of HSA after binding with the ligands. Data obtained by fluorescence spectroscopy, displacement experiments along with the docking studies suggested that the ligands bind to the residues located in site 1 (subdomains IIA), whereas EGC, that lacks the gallate moiety, binds to the other hydrophobic site 2 (subdomain IIIA) of the protein.</p> </div

Effect of Functionalized Magnetic MnFe₂O₄ Nanoparticles on Fibrillation of Human Serum Albumin

Pathogenesis of amyloid-related diseases is related to nonnative folding of proteins with the formation of insoluble deposits in the extracellular space of various tissues. Having the unique properties of small size, large surface area, biodegradability, and relative nontoxicity, magnetic nanoparticles have drawn a lot of attention in biomedical applications. Herein, we demonstrate the effect of bare and differently functionalized magnetic MnFe₂O₄ nanoparticles on fibrillation of human serum albumin <i>in vitro</i>. The process has been monitored using Thioflavin T fluorescence, Congo red binding assay, circular dichroism, fluorescence microscopy, and transmission electron microscopy. From our experimental results, amine functionalized MnFe₂O₄ nanoparticles are found to inhibit formation of fibrils more effectively than bare ones, while carboxylated nanoparticles do not have a significant effect on fibrillation. This study has explored the prospects of using specific magnetic nanoparticles with appropriate modification to control self-assembly of proteins and may act as a precursor in therapeutic applications