Nitrogen regulatory protein P-II
SMART accession number:SM00938
Description: P-II modulates the activity of glutamine synthetase.
Interpro abstract (IPR002187):

In Gram-negative bacteria, the activity and concentration of glutamine synthetase (GS) is regulated in response to nitrogen source availability. PII, a tetrameric protein encoded by the glnB gene, is a component of the adenylation cascade involved in the regulation of GS activity [(PUBMED:1702507)]. In nitrogen-limiting conditions, when the ratio of glutamine to 2-ketoglutarate decreases, P-II is uridylylated on a tyrosine residue to form P-II-UMP. P-II-UMP allows the deadenylation of GS, thus activating the enzyme. Conversely, in nitrogen excess, P-II-UMP is deuridylated and then promotes the adenylation of GS. P-II also indirectly controls the transcription of the GS gene (glnA) by preventing NR-II (ntrB) to phosphorylate NR-I (ntrC) which is the transcriptional activator of glnA. Once P-II is uridylylated, these events are reversed.

P-II is a protein of about 110 amino acid residues extremely well conserved. The tyrosine which is uridylated is located in the central part of the protein. In cyanobacteria, P-II seems to be phosphorylated on a serine residue rather than being uridylated. In methanogenic archaebacteria, the nitrogenase iron protein gene (nifH) is followed by two open reading frames highly similar to the eubacterial P-II protein [(PUBMED:2068380)]. These proteins could be involved in the regulation of nitrogen fixation. In the red alga, Porphyra purpurea, there is a glnB homologue encoded in the chloroplast genome.

Other proteins highly similar to glnB are:

GO process:regulation of nitrogen utilization (GO:0006808)
GO function:enzyme regulator activity (GO:0030234)
Family alignment:
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There are 1785 P-II domains in 1779 proteins in SMART's nrdb database.

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