Amyloid Self-Assembly of Lysozyme in Self-Crowded Conditions: The Formation of a Protein Oligomer Hydrogel

A method is designed to quickly form protein hydrogels, based on the self-assembly of highly concentrated lysozyme solutions in acidic conditions. Their properties can be easily modulated by selecting the curing temperature. Molecular insights on the gelation pathway, derived by in situ FTIR spectroscopy, are related to calorimetric and rheological results, providing a consistent picture on structure–property correlations. In these self-crowded samples, the thermal unfolding induces the rapid formation of amyloid aggregates, leading to temperature-dependent quasi-stationary levels of antiparallel cross β-sheet links, attributed to kinetically trapped oligomers. Upon subsequent cooling, thermoreversible hydrogels develop by the formation of interoligomer contacts. Through heating/cooling cycles, the starting solutions can be largely recovered back, due to oligomer-to-monomer dissociation and refolding. Overall, transparent protein hydrogels can be easily formed in self-crowding conditions and their properties explained, considering the formation of interconnected amyloid oligomers. This type of biomaterial might be relevant in different fields, along with analogous systems of a fibrillar nature more commonly considered.

Gels of Amyloid Fibers

Protein self-assembly and formation of amyloid fibers is an early event of numerous human diseases. Continuous aggregation of amyloid fibers in vitro produces biogels, which led us to suspect that amyloid plaques and neurofibrillary tangles in Alzheimer’s disease are of biogels in nature. We applied atomic force microscopy, size exclusion chromatography, and differential scanning calorimetry to elucidate the gel’s structure, kinetics of gel formation, and melting point. We found that (1) lysozyme gelation occurs when the protein concentration is above 5 mg/mL; (2) nonfibrous protein concentration decreases and plateaus after three days of gel synthesis reaction; (3) colloidal lysozyme aggregates are detectable by both atomic force microscopy (AFM) and fast protein liquid chromatography (FPLC); (4) the gels are a three-dimensional (3D) network crosslinked by fibers coiling around each other; (5) the gels have a high melting point at around around 110 °C, which is weakly dependent on protein concentration; (6) the gels are conductive under an electric field, and (7) they form faster in the presence than in the absence of salt in the reaction buffer. The potential role of the gels formed by amyloid fibers in amyloidosis, particularly in Alzheimer’s disease was thoroughly discussed, as gels with increased viscosity, are known to restrict bulk flow and then circulation of ions and molecules.

Unfolding Pathways of Hen Egg-White Lysozyme in Ethanol

The aggregation of amyloid fibrils can lead to various diseases including Alzheimer's, Parkinson's disease, and transmissible spongiform encephalopathy. Amyloid fibrils can develop from a variety of proteins in the body as they misfold into a primarily β-sheet structure and aggregate. Human lysozyme has been shown to have far reaching effects in the human health-a homologous enzyme, hen egg-white lysozyme, has been shown to denature to a primarily β-sheet structure at low pH and high alcohol content solution. We have studied these systems in atomic-level detail with a combination of constant pH and microsecond long molecular dynamics simulation in explicit solvent, which cumulatively total over 10 μs of simulation time. These studies have allowed us to determine two potential unfolding pathways depending on the protonation state of a key glutamic acid residue as well as the effect of solution dynamics and pH on the unfolding process.

Direct matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis of lysozyme contained in hen egg white

As a natural antibacterial peptide, lysozyme (LZ) is widely used in medicine and the food industry. Despite many years of research on this compound, its new antibacterial properties are still to be determined. The primary aim of this work is to demonstrate the application of the matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometric analysis of LZ directly in hen egg white samples without extraction thereof. The egg white samples were kept over 10 weeks at room temperature and measured every week. The resulting positive and negative ion mass spectra were then compared to determine the intensity of the LZ mass peak. Storage of the egg white for over 10 weeks did not influence the LZ mass peak intensity (both positive and negative). It can be concluded that the LZ concentration in the egg white samples did not vary with time. The effect of the matrix/sample ratio on LZ detection was also examined, and it was found to be different in the case of positive and negative ionization. The mass peaks of LZ oligomeric forms were observed in all mass spectra, so the MALDI method could be used in subsequent studies.