Thermally induced fibrillar aggregation of hen egg white lysozyme

We study the effect of pH and temperature on fibril formation from hen egg white lysozyme. Fibril formation is promoted by low pH and temperatures close to the midpoint temperature for protein unfolding ( detected using far-ultraviolet circular dichroism). At the optimal conditions for fibril formation (pH 2.0, T = 57 degreesC), on-line static light-scattering shows the formation of fibrils after a concentration-independent lag time of similar to48 h. Nucleation presumably involves a change in the conformation of individual lysozyme molecules. Indeed, long-term circular dichroism measurements at pH 2.0, T = 57 degreesC show a marked change of the secondary structure of lysozyme molecules after similar to 48 h of heating. From atomic force microscopy we find that most of the fibrils have a thickness of similar to4 nm. These fibrils have a coiled structure with a periodicity of similar to30 nm and show characteristic defects after every four or five turns.