STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF DSBC, A PROTEIN INVOLVED IN DISULFIDE BOND FORMATION IN ESCHERICHIA-COLI

DsbC is a soluble protein of the bacterial periplasm that was identifi ed genetically as being involved in protein disulfide formation. The g ene sequence was corrected to include an additional proline residue an d was then consistent with the molecular weight of the purified protei n. Gel filtration and subunit hybridization indicate that DsbC is a st able dimer of identical subunits. Each subunit has a -Cys-Gly-Tyr-Cys- segment that forms an unstable and reactive disulfide bond; only the first cysteine residue is accessible, similar to thioredoxin and DsbA. The other two cysteine residues of DsbC form a buried, structural dis ulfide bond. The reactivities and stabilities of the active site disul fide bond of DsbC have been characterized and compared to that of DsbA . Both are very unstable and can be transferred rapidly to reduced pro teins and peptides, although they differ somewhat in their kinetic rea ctivities. The two active sites of the DsbC dimer appear to function i ndependently. DsbC is much more active than DsbA in catalyzing protein disulfide rearrangements, and this may be its main function in vivo.