8.A.8 The Phosphotransferase System HPr (HPr) Family
The HPr family consists of bacterial and archaeal proteins, all of which function as phosphoryl transfer proteins. They are energy-coupling constituents of the phosphotransferase system (PTS) (TC #4.A.1-4.A.7) which catalyzes sugar uptake via a group translocation mechanism. HPr proteins are not known to be homologous to any non-PTS proteins. The E. coli genome encodes five HPr paralogues. The functions of several of these proteins are known. They function in PTS-related regulatory capacities.
Ruminiclostridium cellulolyticum has incomplete PTS components (Xu et al. 2023). Inactivation of the HPr homolog reduced rather than increased carbohydrate utilization. In addition to regulating transcriptional profiles, PTS associated CcpA (Catabolite Control Protein A) homologs diverged from previously described CcpA with varied metabolic relevance and distinct DNA binding motifs. The DNA binding of CcpA homologs is independent of HPr homologs, which are determined by structural changes at the interfaces of CcpA homologs. Thus, results support functional and structural diversification of PTS components in metabolic regulation and bring novel understanding of regulatory mechanisms of incomplete PTSs in cellulose-degrading clostridia (Xu et al. 2023).