Pathways & interactions
Phosphotransferase system, glucitol/sorbitol-specific IIA component (IPR004716)
Short name: PTS_IIA_glucitol/sorbitol-sp
Overlapping homologous superfamilies
- Phosphotransferase system, glucitol/sorbitol-specific IIA component (IPR004716)
The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) [PMID: 8246840, PMID: 2197982] 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 [PMID: 1537788]. 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).
The first domain (IIA or EIIA) carries the first permease-specific phosphorylation site, a histidine which is phosphorylated by phospho-HPr. The second domain (IIB or EIIB) 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. This third domain (IIC or EIIC) 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 [PMID: 8246840, PMID: 1537788, PMID: 7815935, PMID: 11361063].
The Man family is unique in several respects among PTS permease families:
- It is the only PTS family in which members possess a IID protein.
- It is the only PTS family in which the IIB constituent is phosphorylated on a histidyl rather than a cysteyl residue.
- Its permease members exhibit broad specificity for a range of sugars, rather than being specific for just one or a few sugars.
This family consists only of glucitol-specific transporters, and occur both in Gram-negative and Gram-positive bacteria. The system in Escherichia coli consists of a IIA protein, and a IIBC protein. This family is specific for the IIA component.