AN IN-VIVO PATHWAY FOR DISULFIDE BOND ISOMERIZATION IN ESCHERICHIA-COLI

Biochemical studies have shown that the periplasmic protein disulfide oxidoreductase DsbC can isomerize aberrant disulfide bonds, Here we pr esent the first evidence for an in vivo role of DsbC in disulfide bond isomerization, Furthermore, our data suggest that the enzymes DsbA an d DsbC play distinct roles in the cell in disulfide bond formation and isomerization, respectively. We have shown that mutants in dsbC displ ay a defect in disulfide bond formation specific for proteins with mul tiple disulfide bonds. The defect can be complemented by the addition of reduced dithiothreitol to the medium, suggesting that absence of Ds bC results in accumulation of misoxidized proteins, Mutations in the d ipZ and trxA genes have similar phenotypes, We propose that DipZ, a cy toplasmic membrane protein with a thioredoxin-like domain, and thiored oxin, the product of the trxA gene, are components of a pathway for ma intaining DsbC active as a protein disulfide bond isomerase.