The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) [1,2] 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) (see <PDOC00318>). 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), [3] 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) (see <PDOC00528>), carries the first permease-specific phosphorylation site, an histidine which is phosphorylated by phospho-HPr. The second domain (IIB) (see <PDOC00795>) is phosphorylated by phospho-IIA on a cysteinyl or histidyl residue, depending on the sugar transported. Finally, the phosphoryl group is transferred from the IIB domain to the sugar substrate concomitantly with the sugar uptake processed by the IIC domain. The IIC (see <PDOC51103>) domain forms the translocation channel and the specific substrate-binding site. An additional transmembrane domain IID, homologous to IIC, can be found in some PTSs, e.g. for mannose [1,3,4,5,6].

We have developed a profile for this domain, which cover the entire PTS EIID domain.