Conformational changes of lysozymes with different numbers of disulfide bridges in sodium dodecyl sulfate solutions

Four disulfide bridges of hen egg-white lysozyme were selectively reduced to obtain its derivatives with three, two, and zero disulfide bridges (designated as 3SS, 2SS, and 0SS lysozymes, respectively). The 3SS lysozyme maintained the native conformation at pH 7.0 and 3.0. Even upon the reduction of two disulfide bridges, the protein conformation still remained unchanged at pH 7.0. Upon the reduction of all four disulfide bridges, the helicity, θ]₂₇₀, and tryptophan fluorescence changed at pH 3.0 as well as at pH 7.0. The helicity of each derivative increased in a solution of sodium dodecyl sulfate (SDS). The SDS-induced helicity of the 0SS lysozyme was lower at pH 7.0 and higher at pH 3.0 than that of the intact lysozyme with four disulfide bridges. The helix formation appears to occur in originally nonhelical parts in each derivative at pH 7.0. In the cases of the 2SS and 0SS lysozymes at pH 3.0, however, some of the helices appear to be reformed also at moieties where the original helices are disrupted upon the cleavage of disulfide bridges. Received: 17 September 2000/Accepted: 24 March 2000