Gelation of a model globular protein

Hen egg white lysozyme (HEWL) was exposed to various physical and chemical denaturing environments to encourage protein denaturation and consequent gelation. its phase behavior was examined as a function of pH, temperature and also in the presence of the reductant dithiothreitol (DTT). Transparent viscoelastic gels form at low pH values while opaque gels form under alkaline conditions. No increase in viscosity was observed for systems in pure water unless 20 mM of DTT was added, which is known to break the disulfide bridges present in HEWL. The microstructure of the gel was studied using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). Gels formed at low pH contain fibrils similar to 10 nm in diameter with various lengths while at high pH the gels are dominated by particulate aggregates. Thinner fibrils that are 4-6 nm in diameter are observed in the gels formed in the presence of DTT. in this case the distinct feature of the gels is they are thermoreversible and can be melted and reformed easily by varying the temperature.