This model recognizes a distinct clade of phophoenolpyruvate (PEP)-dependent enzymes. Most members are known or deduced to function as the phosphoenolpyruvate-protein phosphotransferase (or enzyme I) of PTS sugar transport systems. However, some species with both a member of this family and a homolog of the phosphocarrier protein HPr lack a IIC component able to serve as a permease. An HPr homolog designated NPr has been implicated in the regulation of nitrogen assimilation, which demonstrates that not all phosphotransferase system components are associated directly with PTS transport.
Jiyao W et al.(2023). "The conserved domain database in 2023.",