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NanE, GlcNAc-6P epimerase, and the uridylylated PII protein allosterically activate NagB by direct protein-protein interactions, overview. Uridylylated PII (but not underivatized PII) activates NagB about 10fold at low concentrations of substrate, whereas NanE increases NagB activity about 2fold. NanE activates NagB in the absence or presence of GlcNAc-6P, but histidine-phosphorylatable phosphocarrier protein (HPr) and U-PII activation requires the presence of GlcNAc-6P. NanE-dependent activation of NagB is not dependent on 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. The uridylylated PII protein (U-PII) is generated by posttranslational modification under nitrogen-limiting conditions involving the glutamine/2-oxoglutarate ratio-sensing uridylyltransferase/uridylyl-removing enzyme GlnD. PII (GlnB)-dependent activation of NagB depends on the uridylylation state of GlnB, kinetics for NagB in the presence of PII at different stages of PII modification involving uridylylation by GlnD, overview. The effect is greater at pH 7.5 than at pH 8 due to the allosteric behavior of the Ser-1 mutant NagB, resulting from an increased Hill coefficient, also noticed for the wild-type NagB. Modeling of HPr/U-PII and of HPr/NanE binding to NagB. The PII protein is known to be a regulator of both the activity and the synthesis of glutamine synthetase (GlnA) in enteric bacteria, and of nitrogen metabolism in many other bacteria, archaea, and eukaryotes, in response to the availability of nitrogen sources |
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