Temperature dependent aggregation mechanism and pathway of lysozyme: By all atom and coarse grained molecular dynamics simulation

Lysozyme impacts gel properties of egg white protein via electrostatic interactions, polarity differences, local pH regulation, or as a filler

The effects of lysozyme on egg white gel properties and their underlying causes were investigated under comparison between lysozyme removed with ion exchange resin and three levels of commercial lysozyme powder (1/2, 2/2, 3/2 the natural concentration in egg white) re-added in the lysozyme-removed system. Results showed that a lysozyme-removed gel obtained the best water holding capacity (61.61 %), lowest cooking loss (11.85 %), and enhanced textural properties (hardness, 638.04 g; resilience, 0.57; and gumminess), which was attributed to lysozyme promoting protein aggregation and weakening electrostatic repulsion by charge neutralization and competition for water, and this could be eliminated by removing lysozyme. Besides, the stronger intermolecular interactions (enhanced ionic bonds, hydrogen bonds and inhibited hydrophobic interactions), the shorter transverse relaxation time (T₂₁ and T₂₂), as well as more uniform microstructure formed in the lysozyme-removed gel, allowing the gels to bind more water molecules. With return of lysozyme, the gel properties were weakened to varying degrees, which was also ascribed to the filling of lysozyme in gel matrix narrowed interspace for binding and storage of water. In sum, adjustment on the content of lysozyme can regulate the gel properties of egg white, so as to obtain gels with regulable gel quality and processing characteristics.

Aggregation of Lysozyme in the Presence of a Mixed Bilayer of POPC and POPG

Understanding the molecular mechanisms by which amyloidogenic proteins interact with membranes is a challenging task. Amyloid accumulates from many human diseases have been observed to contain membrane lipids. In this work, coarse-grained molecular dynamics simulations have been used to inspect hen egg white lysozyme (HEWL) aggregation and membrane association in the presence of a pure POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) bilayer and a POPC and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol) mixed bilayer. It was observed that, in both cases, two HEWLs formed aggregates. In the presence of a mixed bilayer, after aggregation, the aggregated system started to interact with the membrane. It has been found that one of the lysozymes which came closer to the mixed bilayer unfolded more. The process of the initial insertion of an aggregated system in the mixed bilayer has been analyzed. The structural rearrangements of the protein and lipids were analyzed as well along the course of the simulation. Although with a pure POPC bilayer, aggregation was observed, the aggregated system moved away from the membrane. We believe that our study will provide considerable insights into lysozyme aggregation in the presence of a membrane environment.