The succinyl transferase, MdoC, OpgC or YmdD (formerly DUF418), is of 385 aas and 10 TMSs. Osmoregulated periplasmic glucans (OPGs) of E. coli are anionic oligosaccharides that accumulate in the periplasmic space in response to low osmolarity of the medium. Their anionic character is provided by the substitution of the glucosidic backbone by phosphoglycerol originating from  membrane phospholipids and by succinyl residues from an unknown origin. The mdoC gene is within the mdoGH operon necessary for the synthesis of the OPG backbone (Lacroix et al. 1999). The same is true for Rhodobacter spheroides in which in correspondng operon is the opgGIHC operon (Cogez et al. 2002).