Disulfide bond oxidoreductase-D, DsbD. of 565 aas and 9 TMSs.  DsbD provides reducing equivalents to a large array of periplasmic redox proteins. These proteins use the reducing power received from DsbD to correct non-native disulfides, mature c-type cytochromes, protect cysteines on secreted proteins from irreversible oxidation, reduce methionine sulfoxides, and scavenge reactive oxygen species such as hydrogen peroxide (Cho and Collet 2013). DsbD x-ray structures are known, revealing its unusual redox properties and extreme rigidity (Stirnimann et al. 2006). DsbD contains two periplasmically oriented domains at the N- and C-termini (nDsbD and cDsbD) that are connected by a central transmembrane (TM) domain. Each domain contains a pair of cysteines that are essential for catalysis. Cys109 and Cys461 form a transient interdomain disulfide bond between nDsbD and cDsbD in the reaction cycle. The crystal structure of this catalytic intermediate at 2.85 Å resolution revealed large relative domain movements in DsbD as a consequence of a strong overlap between the surface areas of nDsbD that interact with DsbC and cDsbD (Rozhkova et al. 2004).