A Mutant Truncated Protein Disulfide Isomerase with No Chaperone Activity

A mutant human protein disulfide isomerase with the COOH-terminal 51 amino acid residues deleted (abb'a') has been expressed in Escherichia coli. Its secondary structures are very similar to those of the native bovine enzyme. The mutant enzyme shows neither peptide binding ability nor chaperone activity in assisting the refolding of denatured D-glyceraldehyde-3-phosphate dehydrogenase but keeps most of the catalytic activities for reduction of insulin and isomerization of scrambled ribonuclease. It assists the reactivation of denatured and reduced proteins containing disulfide bonds, acid phospholipase A2, and lysozyme to different levels, which are significantly lower than those by the native bovine enzyme.