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),  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
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