Self-assembly and Hydrogelation Properties of Peptides Derived from Peptic Cleavage of Aggregation-prone Regions of Ovalbumin

Self-Assembled Food Peptides: Recent Advances and Perspectives in Food and Health Applications

Self-assembling peptides are rapidly gaining attention as novel biomaterials for food and biomedical applications. Peptides self-assemble when triggered by physical or chemical factors due to their versatile physicochemical characteristics. Peptide self-assembly, when combined with the health-promoting bioactivity of peptides, can also result in a plethora of biofunctionalities of the biomaterials. This perspective highlights current developments in the use of food-derived self-assembling peptides as biomaterials, bioactive nutraceuticals, and potential dual functioning bioactive biomaterials. Also discussed are the challenges and opportunities in the use of self-assembling bioactive peptides in designing biocompatible, biostable, and bioavailable multipurpose biomaterials.

pH-Dependent Reversible Self-Assembly of β-Lactoglobulin-Derived Reducing Peptides

Peptide-based self-assembled nanostructures are emerging vehicles for nutrient delivery and interface engineering. The present study screened eight β-lactoglobulin (β-Lg) derived peptides and found that two reducing peptides [EQSLVCQCLV (EV-10) and VCQCLVR (VR-7)] demonstrated pH-dependent reversible fibrilization. EV-10 formed fibrils at pH 2.0 but became unordered aggregates at pH 7.0. VR-7 showed the opposite trend. Both peptides could undergo repetitive transitions between fibrils and unordered aggregates during consecutive pH-cycling. Fibrilization of both peptides was dominated by charges carried by N- and C-terminals. Both fibrils were characterized by a cross-β sheet structure where the β-sheet was arranged in an antiparallel manner. Fe3+ was reduced by Cys and EV-10 (pH 5.0 and 7.0) simultaneously upon mixing. In contrast, EV-10 fibrils released Fe3+ reducing capacity progressively, which were beneficial to long-term protection Fe2+. The EV-10 fibrils remained intact after simulated gastric digestion and finally dissociated after intestinal digestion. The results shed light on the mechanisms of fibrilization of β-Lg derived peptides. This study was beneficial to the rational design of smart pH-responsive materials for drug delivery and antioxidants for nutrients susceptible to oxidation.

Self-assembly and hydrogelation of a potential bioactive peptide derived from quinoa proteins

In this work the identification of peptides derived from quinoa proteins which could potentially self-assemble, and form hydrogels was carried out with TANGO, a statistical mechanical based algorithm that predicts β-aggregate propensity of peptides. Peptides with the highest aggregate propensity were subjected to gelling screening experiments from which the most promising bioactive peptide with sequence KIVLDSDDPLFGGF was selected. The self-assembling and hydrogelation properties of the C-terminal amidated peptide (KIVLDSDDPLFGGF-NH2) were studied. The effect of concentration, pH, and temperature on the secondary structure of the peptide were probed by circular dichroism (CD), while its nanostructure was studied by transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). Results revealed the existence of random coil, α-helix, twisted β-sheet, and well-defined β-sheet secondary structures, with a range of nanostructures including elongated fibrils and bundles, whose proportion was dependant on the peptide concentration, pH, or temperature. The self-assembly of the peptide is demonstrated to follow established models of amyloid formation, which describe the unfolded peptide transiting from an α-helix-containing intermediate into β-sheet-rich protofibrils. The self-assembly is promoted at high concentrations, elevated temperatures, and pH values close to the peptide isoelectric point, and presumably mediated by hydrogen bond, hydrophobic and electrostatic interactions, and π-π interactions (from the F residue). At 15 mg/mL and pH 3.5, the peptide self-assembled and formed a self-supporting hydrogel exhibiting viscoelastic behaviour with G' (1 Hz) ~2300 Pa as determined by oscillatory rheology measurements. The study describes a straightforward method to monitor the self-assembly of plant protein derived peptides; further studies are needed to demonstrate the potential application of the formed hydrogels in food and biomedicine.

Spectroscopic Characterization of the Binding and Release of Hydrophilic, Hydrophobic and Amphiphilic Molecules from Ovalbumin Supramolecular Hydrogels

Protein-based hydrogels have attracted growing attention for pharmaceutical and biomedical applications. Ovalbumin (OVA), the hen egg white albumin, possessing good foaming and gelling properties and being widely used in the food industry, has recently been indicated as a potential pharmaceutical vehicle. In this study, the binding and release properties of pure OVA hydrogels were investigated by electron paramagnetic resonance (EPR) spin labeling. The comparative analysis between OVA and serum albumin (SA) hydrogels revealed the same release kinetics of hydrophilic 3-carbamoyl-proxyl and 3-carboxy-proxyl, suggesting the diffusion-dominated release of small probes from both hydrogel types. The results obtained with the amphiphilic 16-doxylstearate (16-DS) indicate that OVA, unlike SAs, does not possess a specific fatty acid binding site. However, the OVA hydrogels were able to accommodate a two-fold excess of 16-DS, resulting from protein thermally induced conformational changes, as confirmed by Raman spectroscopy. Similarly, the hydrophobic modified paullone ligand HL, which was initially free in the OVA solution, was bound in the hydrogel. The hydrogels were found to retain a significant amount of 16-DS and HL after 7-day dialysis in physiological saline. The observed facilitated binding of amphiphilic/hydrophobic molecules in OVA hydrogels compared to the solution, and their sustained release, demonstrate the applicability of OVA hydrogels in pharmaceutics.