Structural modulation of insulin by hydrophobic and hydrophilic molecules.

In the bloodstream, insulin interacts with various kinds of molecules, which can alter its structure and modulate its function. In this work, we have synthesized two molecules having extremely hydrophilic and hydrophobic side chains. The effects of hydrophilic and hydrophobic molecules on the binding with insulin have been investigated through a multi-spectroscopic approach. We found that hydrophilic molecules have a slightly higher binding affinity towards insulin. Insulin can bind with the hydrophilic molecules as it binds glucose. The high insulin binding affinity of a hydrophobic molecule indicates its dual nature. The hydrophobic molecule binds at the hydrophobic pocket of the insulin surface, where hydrophilic molecules interact at the polar surface of the insulin. Such binding with the hydrophobic molecule perturbs strongly the secondary structure of the insulin much more in comparison to hydrophilic molecules. Therefore, the stability of insulin decreases in the presence of hydrophobic molecules.

Correction: Coumarin derivatives inhibit the aggregation of ß-lactoglobulin.

[This corrects the article DOI: 10.1039/D2RA01029A.].

Coumarin derivatives inhibit the aggregation of ß-lactoglobulin.

The binding of a small molecule to a protein through non-covalent interactions mainly depends on its size and electronic environment. Such binding can change the stability of the three dimensional protein structure which sometimes may destabilize it to accelerate or to inhibit protein aggregation. Coumarin is a widely used fluorescent dye with several biological applications. Different substituents (electron-donating and electron-withdrawing) at different positions of the coumarin moiety can influence its molecular volume, physical and chemical properties. Here we investigate the effect of such substituents of coumarin on the aggregation of a model protein, beta-lactoglobulin (ß-lg) through a multi spectroscopic approach. It was observed that coumarin methyl ester with an 8-hydroxyl group can inhibit the ß-lg aggregation. This compound can bind the hydrophobic site of beta-lactoglobulin and stabilize a particular protein conformation through the formation of hydrogen bond and hydrophobic interactions. Thus a properly designed compound can inhibit protein-protein interactions through protein-small molecule interactions. Other coumarinoid compounds also are effective in the prevention of thermal aggregation of ß-lg.

Modulation of amyloid fibrillation of bovine ß-lactoglobulin by selective methionine oxidation.

Deposition of oxidation-modified proteins during normal aging and oxidative stress are directly associated with systemic amyloidoses. Methionine (Met) is believed to be one of the most readily oxidisable amino acid residues of protein. Bovine beta-lactoglobulin (ß-lg), a model globular whey protein, has been presented as a subsequent paradigm for studies on protein aggregation and amyloid formation. Herein, we investigated the effect of t-butyl hydroperoxide (tBHP)-induced oxidation on structure, compactness and fibrillation propensity of ß-lg at physiological pH. Notably, whey protein modification, specifically Met residues, plays an important role in the dairy industry during milk processing and lowering nutritional value and ultimately affecting their technological properties. Several bio-physical studies revealed enhanced structural flexibility and aggregation propensity of oxidised ß-lg in a temperature dependent manner. A molecular docking study is used to predict possible interactions with tBHP and infers selective oxidation of methionine residues at 7, 24 and 107 positions. From our studies, it can be corroborated that specific orientations of Met residues directs the formation of a partially unfolded state susceptible to fibrillation with possible different cytotoxic effects. Our studies have greater implications in deciphering the underlying mechanism of different whey proteins encountering oxidative stress. Our findings are also important to elucidate the understanding of oxidation induced amyloid fibrillation of protein which may constitute a new route to pave the way for a modulatory role of oxidatively stressed proteins in neurological disorders.

Silver nanoparticle modulates the aggregation of beta-lactoglobulin and induces to form rod-like aggregates.

Silver nanoparticles (SNPs) have been increasingly used in medicines and biomaterials as a drug carriers and diagnostic or therapeutic material due to their smaller size, large surface area and cell penetration ability. Here we report the preparation of SNPs of diameter 10 ±â€¯3 nm by using silver nitrate and sodium borohydride and the interaction of synthesized SNPs with our model protein ß-lactoglobulin (ß-lg) in 10 mM phosphate buffer at pH 7.5 after thermal exposure at 75 °C. Heat exposed ß-lg forms amyloidal fibrillar aggregates whereas this protein aggregates adopt rod-like shape instead of fibrillar structure in presence of SNP under the same conditions. Size of the synthesized SNPs is confirmed by UV-Visible spectroscopy, SEM and TEM. Interactions and subsequent formation of molecular assembly of heat stressed ß-lg with SNP were investigated using Th-T assay and ANS binding assay, DLS, RLS, CD, FT-IR, SEM, TEM. Docking study parallely also support the experimental findings.