Chaperone activity of DsbC

DsbC, a periplasmic disulfide isomerase of Gram-negative bacteria, displays about 30% of the activities of eukaryotic protein disulfide isomerase (PDI ) as isomerase and as thiol-protein oxidoreductase. However, DsbC shows mor e pronounced chaperone activity than does PDI in promoting the in vitro rea ctivation and suppressing aggregation of denatured D-glyceraldehyde-3-phosp hate dehydrogenase (GAPDH) during refolding, Carboxymethylation of DsbC at Cys(98) decreases its intrinsic fluorescence, deprives of its enzyme activi ties, but lowers only partly its chaperone activity in assisting GAPDH reac tivation, Simultaneous presence of DsbC and PDI in the refolding buffer sho ws an additive effect on the reactivation of GAPDH. The assisted reactivati on of GAPDH and the protein disulfide oxidoreductase activity of DsbC can b oth be inhibited by scrambled and S-carboxymethylated RNases, but not by sh orter peptides, including synthetic 10- and 14-mer peptides and S-carboxyme thylated insulin A chain. In contrast, all the three peptides and the two n onnative RNases inhibit PDI-assisted GAPDH reactivation and the reductase a ctivity of PDI. DsbC assists refolding of denatured and reduced lysozyme to a higher level than does PDI in phosphate buffer and does not show anti-ch aperone activity in HEPES buffer. Like PDI, DsbC is also a disulfide isomer ase with chaperone activity but may recognize different folding intermediat es as does PDI.