The Nitrogen Regulatory PII Protein (GlnB) andN-Acetylglucosamine 6-Phosphate Epimerase (NanE) Allosterically Activate Glucosamine 6-Phosphate Deaminase (NagB) inEscherichia coli

ABSTRACTAmino sugars are good sources of both ammonia and fructose-6-phosphate, produced by the glucosamine 6-phosphate deaminase, NagB. NagB is known to be allosterically regulated byN-acetylglucosamine 6-phosphate (GlcNAc-6P) and the phosphocarrier protein of the bacterial phosphotransferase system, HPr, inEscherichia coli. We provide evidence that NanE, GlcNAc-6P epimerase, and the uridylylated PII protein (U-PII) also allosterically activate NagB by direct protein-protein interactions. NanE is essential for neuraminic acid (NANA) andN-acetylmannosamine (ManNAc) utilization, and PII is known to be a central metabolic nitrogen regulator. We demonstrate that uridylylated PII (but not underivatized PII) activates NagB >10-fold at low concentrations of substrate, whereas NanE increases NagB activity >2-fold. NanE activates NagB in the absence or presence of GlcNAc-6P, but HPr and U-PII activation requires the presence of GlcNAc-6P. Activation of NagB by HPr and uridylylated PII, as well as by NanE and HPr (but not by NanE and U-PII), is synergistic, and the modeling, which suggests specific residues involved in complex formation, provides possible explanations. Specific physiological functions for the regulation of NagB by its three protein activators are proposed. Each regulatory agent is suggested to mediate signal transduction in response to a different stimulus.IMPORTANCEThe regulation of amino sugar utilization is important for the survival of bacteria in a competitive environment. NagB, a glucosamine 6-phosphate deaminase inEscherichia coli, is essential for amino sugar utilization and is known to be allosterically regulated byN-acetylglucosamine 6-phosphate (GlcNAc-6P) and the histidine-phosphorylatable phosphocarrier protein, HPr. We provide evidence here that NanE, GlcNAc-6P epimerase, and the uridylylated PII protein allosterically activate NagB by direct protein-protein interactions. NanE is essential forN-acetylneuraminic acid (NANA) andN-acetylmannosamine (ManNAc) utilization, and the PII protein is known to be a central metabolic nitrogen regulator. Regulatory links between carbon and nitrogen metabolism are important for adaptation of metabolism to different growth conditions.

The Bacterial Phosphotransferase System: New Frontiers 50 Years after Its Discovery

In 1964, Kundig, Ghosh and Roseman reported the discovery of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), which they subsequently proposed might catalyze sugar transport as well as sugar phosphorylation. What we have learned in the 50 years since its discovery is that, in addition to these primary functions, the PTS serves as a complex protein kinase system that regulates a wide variety of transport, metabolic and mutagenic processes as well as the expression of numerous genes. Recent operon- and genome-sequencing projects have revealed novel PTS protein-encoding genes, many of which have yet to be functionally defined. The current picture of the PTS is that of a complex system with ramifications in all aspects of cellular physiology. Moreover, its mosaic evolutionary history is unusual and intriguing. The PTS can be considered to serve many prokaryotes in capacities of communication and coordination, as do the nervous systems of animals.