DsbC activation by the N-terminal domain of DsbD

The correct formation of disulfide bonds in the periplasm of Escherichia coli involves Dsb proteins, including two related periplasmic disulfide-bond isomerases, DsbC and DsbG. DsbD is a membrane protein required to maintain the functional oxidation state of DsbC and DsbG. In this work, purified proteins were used to investigate the interaction between DsbD and DsbC. A 131-residue N-terminal fragment of DsbD (DsbD alpha) was expressed and purified and shown to form a functional folded domain. Gel filtration results indicate that DsbD alpha is monomeric. DsbD alpha was shown to interact directly with and to reduce the DsbC dimer, thus increasing the isomerase activity of DsbC. The DsbC-DsbD alpha complex was characterized, and formation of the complex was shown to require the N-terminal dimerization domain of DsbC. These results demonstrate that DsbD interacts directly with full-length DsbC and imply that no other periplasmic components are required to maintain DsbC in the functional reduced state.