Phosphotransferase system, EIIB component, type 2 (PTS_EIIB_2)
Type: Domain

The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) is a major carbohydrate transport system in bacteria. The PTS catalyses the phosphorylation of incoming sugar substrates and coupled with translocation across the cell membrane, makes the PTS a link between the uptake and metabolism of sugars.

The general mechanism of the PTS is the following: a phosphoryl group from phosphoenolpyruvate (PEP) is transferred via a signal transduction pathway, to enzyme I (EI) which in turn transfers it to a phosphoryl carrier, the histidine protein (HPr). Phospho-HPr then transfers the phosphoryl group to a sugar-specific permease, a membrane-bound complex known as enzyme 2 (EII), which transports the sugar to the cell. EII consists of at least three structurally distinct domains IIA, IIB and IIC . These 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).

According to structural and sequence analyses, the PTS EIIB domain (

) can be divided in five groups :

The PTS EIIB type 1 domain, which is found in the Glucose class of PTS, has an average length of about 80 amino acids. It forms a split α/β sandwich composed of an antiparallel sheet (beta 1 to beta 4) and three α helices superimposed onto one side of the sheet. The phosphorylation site (Cys) is located at the end of the first β strand on a protrusion formed by the edge of β1 and the reverse turn between β1 and β2 .

The PTS EIIB type 2 domain, which is found in the Mannitol and Fructose class of PTS, has an average length of about 100 amino acids. It consists of a four stranded parallel β sheet flanked by two α helices (α1 and 3) on one face and helix α2 on the opposite face, with a characteristic Rossmann fold comprising two right-handed β-α-β motifs. The phosphorylation site (Cys) is located at the N terminus of the domain, in the first β strand.

The PTS EIIB type 3 domain, which is found in the Lactose class of PTS, has an average length of about 100 amino acids. It is composed of a central four-stranded parallel open twisted β sheet, which is flanked by three α helices on the concave side and two on the convex side of the β sheet. The phosphorylation site (Cys) is located in the C-terminal end of the first β strand .

The PTS EIIB type 4 domain, which is found in the Mannose class of PTS, has an average length of about 160 amino acids. It has a central core of seven parallel β strands surrounded by a total of six α-helices. Three helices cover the front face, one the back face with the remaining two capping the central β sheet at the top and bottom. The phosphorylation site (His) is located at the surface exposed loop between strand 1 and helix 1 .

The PTS EIIB type 5 domain, which is found in the Sorbitol class of PTS, has an average length of about 190 amino acids. The phosphorylation site (Cys) is located in the N terminus of the domain.

An EIIB-like type 2 domain can be found in bacterial transcriptional regulatory proteins . In these cases, the EIIB-like domain is found in association with other domains like the DeoR-type HTH domain or the PTS regulatory domain (a transcriptional antiterminator). It may possess a regulatory function through its phosphorylation activity, or act as a simple phosphoryl donor.

This entry represents the EIIB type 2 domain.