Histidine-containing phosphocarrier protein (HPr) is a small cytoplasmic protein that is a component of the phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS). The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) is a major carbohydrate transport system in bacteria. The PTS catalyses the

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

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). In some bacteria HPr is a domain in a larger protein that includes an EIII(Fru) (IIA) domain and in some cases also an EI domain. There is a conserved histidine in the

N-terminus The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...

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 most Gram-positive bacteria and certain Gram-negative bacteria, is phosphorylated by an ATP-dependent protein kinase, a process which probably plays a regulatory role in sugar transport.

References

{{InterPro content, IPR000032 Protein families