The disulfide bond isomerase DsbC is activated by an immunoglobulin-fold thiol oxidoreductase: Crystal structure of the DsbC-DsbDα complex

Abstract

The Escherichia coli disulfide bond isomerase DsbC rearranges incorrect disulfide bonds during oxidative protein folding. It is specifically activated by the periplasmic N-terminal domain (DsbDα) of the transmembrane electron transporter DsbD. An intermediate of the electron transport reaction was trapped, yielding a covalent DsbC-DsbDα complex. The 2.3 A crystal structure of the complex shows for the first time the specific interactions between two thiol oxidoreductases. DsbDα is a novel thiol oxidoreductase with the active site cysteines embedded in an immunoglobulin fold. It binds into the central cleft of the V-shaped DsbC dimer, which assumes a closed conformation on complex formation. Comparison of the complex with oxidized DsbDα reveals major conformational changes in a cap structure that regulates the accessibility of the DsbDα active site. Our results explain how DsbC is selectively activated by DsbD using electrons derived from the cytoplasm.