8.A.7 The Phosphotransferase System Enzyme I (EI) Family
Enzymes I (EC# 2.A.7.9.3) of the phosphotransferase system (PTS) serve as energy coupling proteins for PTS porters. Phosphoenolpyruvate (PEP) is the energy source and phosphoryl donor. PEP phosphorylates a histidyl residue in EI; this is then passed to a histidyl residue in a heat stable phopho-carrier protein called HPr, and the phosphoryl group is then transferred to a histidyl residue in the IIA domain/protein of a PTS porter (TC #4.A.1-4.A.7) (Brackenbury and Isom, 2011).
Enzymes I are homologous to PEP synthases (EC# 18.104.22.168) and pyruvate:orthophosphate dikinases (EC 22.214.171.124). Five Enzyme I paralogues are encoded within the genome of E. coli. The functions of several of these proteins are not known, but they probably function in PTS-related transport, phosophorylation or regulatory capacities.
Enzyme I of the PTS (Araki et al., 2011)
Enzyme I of Rhodococcus jostii (Q0S1M9)
Phosphoenolpyruvate: protein phosphotransferase, PTS Enzyme I (based on homology)
Enzyme I of Haloterrigena turkmenica (D2RXA5)
Enzyme I, PtsI (functions with 4.A.2.1.15; Pickl et al., 2012)
Enzyme I of Haloferax volcanii (D4GYE2)
Enzyme I of 591 aas. Enzyme I transfers the phosphoryl group from phosphoenolpyruvate (PEP) to the phosphoryl carrier protein (HPr). This protein is encoded in the same operon with an HPr (TC# 8.A.8.1.5) and the IIC and IID genes of a mannose-type PTS system (TC# 4.A.6.1.20).
Enzyme I of Caldithrix abyssi
Enzyme I of an archaeal mannose (Man)-type PTS; 566 aas.
Enzyme I of Thermofilum pendens