E Structural view of UBE2S C118 interacting with I44 of Ub in the "closed" conformation of UBE2S~Ub. UBE2S (PDB: 1ZDN) was aligned to a "closed" form of UBE2D~Ub (PDB: 4AUQ) (Dou et al., 2012; Sheng et al., 2012). 