Thermally induced fibrilar aggregation of hen egg white lysozyme

We study the effect of pH and temperature on fibril formation from hen egg white lysozyme (HEWL). Fibril formation is promoted by low pH and temperatures close to the midpoint emperature for protein unfolding (detected using far-UV circular dichroism (CD)). At the optimal conditions for fibril formation (pH 2.0, T = 57°C), on-line static light scattering shows the ormation of fibrils after a concentration independent lag time of around 48 h. Nucleation resumably involves a change in the conformation of individual lysozyme molecules. Indeed, long term CD measurements at pH 2.0, T = 57°C show a marked change of the secondary structure of lysozyme molecules after about 48 h of heating. From atomic force microscopy we find that most of the fibrils have a thickness of about 4 nm. These fibrils have a coiled structure with a periodicity of about 30 nm and show characteristic defects after every 4 or 5 turns.