FUNCTIONAL-PROPERTIES OF THE INDIVIDUAL THIOREDOXIN-LIKE DOMAINS OF PROTEIN DISULFIDE-ISOMERASE

The two thioredoxin-like domains of human protein disulfide isomerase (PDI) have been produced in bacteria as individual soluble, folded pro tein molecules, and their functional properties have been compared to those of intact PDI. The two individual domains were very similar in t heir functional properties, and there were no indications of synergy b etween them, so it is unlikely that they have intrinsically different functions in PDI. Both domains efficiently introduced disulfide bonds into unfolded model proteins and peptides but were less efficient than PDI with folded substrate protein molecules. Relative to PDI, neither domain had substantial activity in catalyzing disulfide bond isomeriz ation. This pattern of activities is very similar to that of the bacte rial catalyst DsbA and probably reflects similarities in the catalytic mechanisms of these proteins. The differences in activity between PDI and its thioredoxin-like domains suggest that other features of the P DI molecule are also required for its complete range of thiol-disulfid e exchange activities.