The DsbI (223 aas and 4 TMSs in a 3 + 1 arrangement)/DsbL (222 aas and 1 N-terminal TMS) disulfide bond oxidoreductase/thio:disulfide interchange protein together form a dithiol oxidase system, acting on the periplasmic enzyme arylsulfate sulfotransferase, AssT (598 aas, 1 N-terminal TMS, Q8FDI4) which requires a disulfide bond for activity. The 3-d structure of DsbL at 1.55 Å resolution has been determined. DsbL is one of the most reactive oxidizing thioredoxin-like protein known (Grimshaw et al. 2008).  These three enzymes are encoded within a tricistronic operon.