Deciphering the interactions of phytochemicals with ovalbumin, the major food allergen from egg white: spectroscopic and computational studies.

Ovalbumin (OVA), the major component of egg white, has been used as a model carrier protein to study the interaction of four bioactive phytochemicals 6-hydroxyflavone, chrysin, naringin, and naringenin. A static quenching mechanism was primarily associated with the complexation of the flavonoids with OVA. Hydrophobic forces play a major part in the stability of the complexes. The structural changes within the protein in response to flavonoid binding revealed a decrease in OVA's α-helical content. The hypothesized binding site for flavonoids in OVA overlaps with one or more immunoglobulin E-binding epitopes that may have some effect in the immunoglobulin E response pathway. The flavonoids remain in the same binding site throughout the simulation time and impart protein stability by forming different noncovalent interactions. This study presents comprehensive information about the interaction of the flavonoids with OVA and the associated structural variations after the binding, which might help researchers better comprehend similar medication pharmacodynamics and provide critical information for future therapeutic development.

Molecular recognition of two bioactive coumarin derivatives 7-hydroxycoumarin and 4-methyl-7-hydroxycoumarin by hen egg white lysozyme: Exploring the binding mechanism, thermodynamic parameters and structural changes using multispectroscopic and computational approaches.

Multispectroscopic and computational methods of exploring the interaction between a carrier protein and therapeutic compounds provide a preliminary investigation into establishing the efficacy of such compounds. Here, two coumarin derivatives, 7-hydroxycoumarin (7-HC) and 4-methyl-7-hydroxycoumarin (4-Me-7-HC), were selected to carry out numerous biophysical interaction studies with a model carrier protein, hen egg white lysozyme (HEWL). Fluorescence spectroscopy studies conducted between HEWL and 7-HC/4-Me-7-HC revealed the binding constants (Kb) were in the range of 104 M-1, indicating a moderate nature of binding. The quenching mechanism observed during complexation process was an unusual static quenching due to the effect of temperature on the rate constant. Thermodynamic parameters revealed a positive ΔH and ΔS for HEWL-7-HC/4-Me-7-HC, indicating hydrophobic forces played a dominant role in the interaction process. FRET studies suggested a possible non-radiative energy transfer from the donor (HEWL) to the acceptor (coumarins). Molecular docking studies revealed the interaction of 7-HC/4-Me-7-HC with intrinsic fluorophores, Trp63 and Trp108, Trp108 being an essential residue for binding as proven by molecular dynamic (MD) simulation. MD simulation studies also indicated conformational stability gained by HEWL upon interaction with 7-HC and 4-Me-7-HC. The microenvironment surrounding the Trp residues showed a significant Stoke's shift on carrying out 3-D fluorescence. CD studies revealed a decrease in the alpha helical content of HEWL upon interacting with the ligands. Enzymatic assay conducted for HEWL in the presence of 7-HC/4-Me-7-HC saw an increase in the activity of HEWL, suggesting a change in structural conformation and stability of the protein, altering its activity.Communicated by Ramaswamy H. Sarma.

Biocompatible silver nanoparticles: An investigation into their protein binding efficacies, anti-bacterial effects and cell cytotoxicity studies.

Green synthesis of silver nanoparticles (AgNPs) has garnered tremendous interest as conventional methods include the use and production of toxic chemicals, products, by-products and reagents. In this regard, the synthesis of AgNPs using green tea (GT) extract and two of its components, (-)-epigallocatechin gallate (EGCG) and (+)-catechin (Ct) as capping/stabilizing agents, is reported. The synthesized AgNPs showed antibacterial activity against the bacterial strains Staphylococcus aureus and Escherichia coli, along with anticancer activity against HeLa cells. After administering nanoparticles to the body, they come in contact with proteins and results in the formation of a protein corona; hence we studied the interactions of these biocompatible AgNPs with hen egg white lysozyme (HEWL) as a carrier protein. Static quenching mechanism was accountable for the quenching of HEWL fluorescence by the AgNPs. The binding constant (K b) was found to be higher for EGCG-AgNPs ((2.309 ± 0.018) × 104 M-1) than for GT-AgNPs and Ct-AgNPs towards HEWL. EGCG-AgNPs increased the polarity near the binding site while Ct-AgNPs caused the opposite effect, but GT-AgNPs had no such observable effects. Circular dichroism studies indicated that the AgNPs had no such appreciable impact on the secondary structure of HEWL. The key findings of this research included the synthesis of AgNPs using GT extract and its constituent polyphenols, and showed significant antibacterial, anticancer and protein-binding properties. The -OH groups of the polyphenols drive the in situ capping/stabilization of the AgNPs during synthesis, which might offer new opportunities having implications for nanomedicine and nanodiagnostics.

Inhibition of huntingtin aggregation by its N-terminal 17-residue peptide and its analogs.

The N-terminal 17-residue stretch of huntingtin (httN17) folds into an amphipathic α-helix. The httN17-harboring polyQ peptides form oligomers that are mediated via the assembly of the httN17 α-helices. The oligomerization results in higher local concentration of the polyglutamine (polyQ) region, thereby facilitating amyloid formation. The httN17 co-assembles with the httN17-harbouring polyQ peptides, thereby reducing the local polyQ concentration, and consequently inhibiting aggregation. This study presents the aggregation inhibition of the exon I region of pathogenic huntingtin by httN17 and its analogs. The C-terminal amidation of httN17 is found to be essential for activity. The httN17 peptides with free amino terminus and the acetylated amino terminus possess comparable activity. The httN17 analog, wherein the Leu7 and Ala10 are substituted with 2-aminoisobutyric acid residues, exhibits significantly higher activity than the native httN17.

Non-enzymatic glycation of human serum albumin modulates its binding efficacy towards bioactive flavonoid chrysin: A detailed study using multi-spectroscopic and computational methods.

The non-enzymatic glycation of plasma proteins by reducing sugars have important consequences on the conformational and functional properties of protein. The formation of advanced glycation end products (AGEs) is responsible for cell death and other pathological conditions. We have synthesized the glycated human serum albumin (gHSA) and characterized the same by using differential spectroscopic measurements. The aim of the present study is to determine the effect of glycation on the binding of human serum albumin (HSA) with bioactive flavonoid chrysin, which possesses anti-cancer, anti-inflammatory and anti-oxidant activities. The interaction of chrysin with HSA and gHSA was studied using multi-spectroscopic, molecular docking and molecular dynamics (MD) simulation techniques. Chrysin quenched the intrinsic fluorescence of both HSA and gHSA by static quenching mechanism. The value of the binding constant (Kb) for the interaction of HSA-chrysin complex (4.779 ± 0.623 × 105 M-1 at 300 K) was found to be higher than that of gHSA-chrysin complex (2.206 ± 0.234 × 105 M-1 at 300 K). Hence, non-enzymatic glycation of HSA significantly reduced its binding affinity towards chrysin. The % α-helicity of HSA was found to get enhanced upon binding with chrysin, and minimal changes were observed for the gHSA-chrysin complex. Site marker probe studies indicated that chrysin binds to subdomain IIA and IIIA of both HSA and gHSA. The results from molecular docking and MD simulation studies correlated well with the experimental findings. Electrostatic interactions followed by hydrogen bonding and hydrophobic interactions played major roles in the binding process. These observations may have some useful insights into the field of pharmaceutics.

Amyloids and their untapped potential as hydrogelators.

Amyloid fibrils are cross-ß-sheet-rich fibrous aggregates. They were originally identified as disease-associated protein/peptide deposits. The cross-ß motif was consequently labelled as an alien and pathogenic fold. Subsequent research revealed that the fibrillar aggregates were benign, and the cytotoxicity in the amyloid diseases was attributed to the pre-fibrillar structures. Research in the past two decades has identified the native functional amyloids in organisms ranging from bacteria to human. The amyloid-like fibrils, therefore, are not necessarily pathogenic, and the cross-ß motif is very much native. This premise makes way for the amyloids to be used as biocompatible materials. Many naturally occurring amyloidogenic proteins/peptides or their fragments have been reported in the literature to form hydrogels. Hydrogels constitute one of the most interesting classes of soft materials that find application in diverse fields such as environmental, electronic, and biomedical engineering. Applications of hydrogels in medicine are particularly extensive. Among various classes of peptides that form hydrogels, the potential of amyloids is largely untapped. In this review, we have attempted to compile the literature on amyloid hydrogels and discuss their potential applications.

The ß-turn-supporting motif in the polyglutamine binding peptide QBP1 is essential for inhibiting huntingtin aggregation.

Aggregation of polyglutamine proteins is a hallmark of several neurodegenerative diseases. The 11-residue polyglutamine binding peptide Ac-SNWKWWPGIFD-am, known as QBP1, inhibits polyglutamine aggregation. Besides, a minimal 8-residue stretch in the QBP1 peptide (Ac-WKWWPGIF-am) is reported in the literature to retain this activity. Both peptides harbor a Pro-Gly dipeptide motif, a feature characteristic of potential ß-turn regions. Here, we investigated whether the presence of this ß-turn motif is necessary for the inhibition of huntingtin aggregation, a polyglutamine protein implicated in Huntington's disease. Using single amino acid substitutions to generate analogs that could support, introduce, or eliminate the ß-turn, we show that the turn-supporting motif is essential for QBP1-mediated inhibition of huntingtin aggregation.

Aromatic-rich C-terminal region of LCI is a potent antimicrobial peptide in itself.

LCI is a 47-residue antimicrobial peptide produced by Bacillus subtilis. The peptide displays potent activity against plant pathogens, Xanthomonas and Pseudomonas. The peptide takes a compact 3-dimensional structure characterized by a four-stranded ß-sheet. The peptide is unusually rich in aromatic residues; 10 of the 47 residues are aromatic and 8 of them lie in the C-terminal region, LCI22-47. Here we report the antimicrobial activity of this C-terminal region against Gram-positive and Gram-negative bacteria. The C-terminal-amidated peptide displays potent activity against E. coli, methicillin and gentamicin-resistant S. aureus, and Xanthomonas oryzae pv. oryzae with lethal concentrations ≤4 µM. Membrane-binding assays indicate preferential binding to the negatively-charged lipids. The peptide permeabilizes the outer-membrane of E. coli indicating membrane-permeabilization as one of the mechanisms of killing. Interestingly, however, no inner-membrane permeabilization was observed, indicating that the membrane-permeabilization may not be the sole mechanism of action.