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
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.
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