CHAPERONE-LIKE ACTIVITY OF PROTEIN DISULFIDE-ISOMERASE IN THE REFOLDING OF A PROTEIN WITH NO DISULFIDE BONDS

D-Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a protein contai ning no disulfide bonds; the guanidine HCl-denatured enzyme shows only a limited extent of refolding and reactivation upon dilution, and the enzyme is particularly prone to aggregation during the dilution proce ss. With increasing GAPDH concentration, reactivation decreases and ag gregation increases, The presence of protein disulfide isomerase in th e dilution mixture markedly increases reactivation of GAPDH and at the same time prevents the aggregation of GAPDH as shown by light-scatter ing measurements. It is suggested that upon dilution, denatured GAPDH is faced with two competing processes of correct folding and assembly to yield the native enzyme and non-productive association of the parti ally refolded species to form aggregates. Independent of the isomerase activity as no disulfide bond is present in GAPDH, protein disulfide isomerase assists the refolding of GAPDH to its active state by suppre ssing aggregation in a way closely similar to the action of chaperones .