Phosphocarrier HPr protein, a small cytoplasmic protein, is a component of the phosphoenolpyruvate-dependent sugar phosphotransferase
system (PTS) major carbohydrate transport system in bacteria [8246840, 2197982]. The phosphoryl group from phosphoenolpyruvate (PEP) is transferred to HPr, the phosphoryl carrier protein, by enzyme I. Phospho-HPr then transfers it to the permease. In some bacteria HPr is a domain in a larger protein that includes a EIII(Fru)
(IIA) domain and in some cases also a EI domain.
The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS)
is a major carbohydrate transport system in bacteria. The PTS catalyses
the phosphorylation of sugar substrates during their translocation across
the cell membrane. The mechanism involves the transfer of a phosphoryl
group from phosphoenolpyruvate (PEP) via enzyme I (EI) to enzyme II (EII)
of the PTS system, which in turn transfers it to a phosphocarrier protein
(HPr) [7853396, 7704530].
There is a conserved histidine in the N-terminus of HPr, which serves as an acceptor for
the phosphoryl group of EI. In the central part of HPr there is a conserved serine which, in Gram-positive bacteria only, is phosphorylated by an
ATP-dependent protein kinase, a process which probably plays a regulatory role in sugar