The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) [8246840, 2197982] is a major carbohydrate transport system in bacteria. The PTS catalyzes the phosphorylation of incoming sugar substrates concomitant with their translocation across the cell membrane. The general mechanism of the PTS is the following: a phosphoryl group from phosphoenolpyruvate (PEP) is transferred to enzyme-I (EI) of PTS which in turn transfers it to a phosphoryl carrier protein (HPr). Phospho-HPr then transfers the phosphoryl group to a sugar-specific permease which consists of at least three structurally distinct domains (IIA, IIB, and IIC)  which can either be fused together in a single polypeptide chain or exist as two or three interactive chains, formerly called enzymes II (EII) and III (EIII).
The first domain (IIA) carries the first permease-specific phoshorylation site, a histidine, which is phosphorylated by phospho-HPr. The second domain (IIB) is phosphorylated by phospho-IIA on a cysteinyl or histidyl residue, depending on the permease. Finally, the phosphoryl group is transferred from the IIB domain to the sugar substrate in a process catalyzed by the IIC domain; this process is coupled to the transmembrane transport of the sugar.