PROSITE documentation PDOC51103

PTS EIIC domain profiles

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 domain forms the translocation channel and the specific substrate-binding site. An additional transmembrane domain IID (see <PDOC51108>), homologous to IIC, can be found in some PTSs, e.g. for mannose [1,3,4,5,6].

According to sequence analyses [1,4,5,6], the PTS EIIC domain can be divided in five groups.

• The PTS EIIC type 1 domain is found in the Glucose class of PTS and has an average length of about 80 amino acids.
• The PTS EIIC type 2 domain is found in the Mannitol class of PTS and has an average length of about 90 amino acids.
• The PTS EIIC type 3 domain is found in the Lactose class of PTS and has an average length of about 100 amino acids.
• The PTS EIIC type 4 domain is found in the Mannose class of PTS and has an average length of about 160 amino acids.
• The PTS EIIC type 5 domain is found in the Sorbitol class of PTS and has an average length of about 190 amino acids.

We have developed five profiles that cover the entire PTS EIIC domains. These profiles are directed respectively against the Glucose class of PTS, the Mannitol class of PTS, the Lactose class of PTS, the Mannose class of PTS, and the Sorbitol class of PTS.