PDI AND GLUTATHIONE-MEDIATED REDUCTION OF THE GLUTATHIONYLATED VARIANT OF HUMAN LYSOZYME

A mutant human lysozyme, designated as C77A-a, in which glutathione is bound to Cys95, has been shown to mimic an intermediate in the format ion of a disulfide bond during folding of human (h)-lysozyme. Protein disulfide isomerase (PDI), which is believed to catalyze disulfide bon d formation and associated protein folding in the endoplasmic reticulu m, attacked the glutathionylated h-lysozyme C77A-a to dissociate the g lutathione molecule. Structural analyses showed that the protein is fo lded and that the structure around the disulfide bond, buried in a hyd rophobic core, between the protein and the bound glutathione is fairly rigid. Thioredoxin, which has higher reducing activity of protein dis ulfides than PDI, catalyzed the reduction with lower efficiency. These results strongly suggest that PDI can catalyze the disulfide formatio n in intermediates with compact structure like the native states in th e later step of in vivo protein folding.