Renaturation of lysozyme--temperature dependence of renaturation rate, renaturation yield, and aggregation: identification of hydrophobic folding intermediates.

Renaturation of denatured-reduced hen egg white lysozyme was analyzed at temperatures between 4 and 70 degrees C using the reduced/oxidized glutathione renaturation system. With an increase in temperature to 50 degrees C both renaturation rate constant and renaturation yield increased while formation of aggregates decreased. Denatured-reduced lysozyme and early folding intermediates were less stable against heat than native lysozyme at temperatures above 60 degrees C. Renaturation at 70 degrees C resulted in no reconstitution of lysozyme activity but the highest level of aggregation. Renaturation of denatured-reduced hen egg white lysozyme was further analyzed in the presence of the hydrophobicity-indicating fluorescence dye 1-anilinonaphalene-8-sulfonate at temperatures between 10 and 40 degrees C. The change in fluorescence intensity, the generation of enzyme activity, renaturation yield, and the formation of aggregates were studied. The results showed that early folding intermediates possess a strong hydrophobic nature. With an increase in temperature both the renaturation rate and the decay rate of hydrophobicity-mediated fluorescence increased. Consequently, with increasing temperature, accumulation of hydrophobic folding intermediates and formation of insoluble aggregates decreased, leading to an increase in the renaturation yield.