Effects of structure-forming solutes on chicken egg white lysozyme after reductive cleavage of disulfide bonds

As an approach to learning more about structure-forming processes in chicken egg white lysozyme, the reduced protein was studied in the presence of methanol, 2-chloroethanol, trifluoroethanol, and sodium dodecyl sulfate, at various concentrations in aqueous solution. The mixtures were subjected to gel filtration chromatography, with circular dichroism (CD) examination of the resulting polymers and monomers. Changes in CD behavior, indicating development of ordered structure, were seen to be associated only with polymer formation. Contributing to these changes were increases in beta structure as well as alpha-helix. Since the solutes studied are known as helix formers, it is suggested that studies on many proteins, carried out in the presence of these and other structure-modifying solutes, may have been complicated by formation of beta structure as well as by polymerization. The reduced monomer formed no structure in the hydrophobic environment afforded by these solutes, but only randomized further. Thus, hydrophobic interactions may be of no significance to lysozyme chain folding in its early stages. As an alternative, the long range interactions stabilized by native tertiary cross links may be critical for the transition to native secondary structure.