DsbC activation by the N-terminal domain of DsbD

The correct formation of disulfide bonds in the periplasm of Escherichia co il 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 pro teins were used to investigate the interaction between DsbD and DsbC. A 131 -residue N-terminal fragment of DsbD (DsbD alpha) was expressed and purifie d and shown to form a functional folded domain. Gel filtration results indi cate that DsbD alpha is monomeric. DsbD alpha was shown to interact directl y with and to reduce the DsbC dimer, thus increasing the isomerase activity of DsbC. The DsbC-DsbD alpha complex was characterized, and formation of t he complex was shown to require the N-terminal dimerization domain of DsbC. These results demonstrate that DsbD interacts directly with full-length Ds bC and imply that no other periplasmic components are required to maintain DsbC in the functional reduced state.