InterPro: IPR013546 PII-uridylyltransferase/Glutamine-synthetase adenylyltransferase

This entry represents a region found in a family of nucleotide transferases that includes bifunctional uridylyl-removing enzymes/uridylyltransferases (UR/UTases, GlnD; EC:2.7.7.59) and glutamine-synthetase adenylyltransferases (GlnE; EC:2.7.7.42). The region described in this family is found in many of its members to be C-terminal to a nucleotidyltransferase domain, and N-terminal to an HD domain and two ACT domains [1].

Bifunctional uridylyl-removing enzymes/uridylyltransferases are responsible for the modification of the regulatory protein PII, or GlnB, thereby acting as the sensory component of the nitrogen regulation (ntr) system [2]. The ntr system modulates nitrogen metabolism in response to the prevailing nitrogen source and the requirements of the cell. During nitrogen fixation, ammonia and 2-oxoglutarate can be used to produce glutamate. In response to nitrogen limitation, these transferases catalyse the uridylylation of the PII protein, which in turn stimulates deadenylylation of glutamine synthetase (GlnA), leading to the activation of glutamate synthetase and to the stimulation of NtrC-dependent promoters [3]. Uridylylated PII can act together with NtrB and NtrC to increase transcription of genes in the sigma54 regulon, which include glnA and other nitrogen-level controlled genes [4]. Under high concentrations of fixed nitrogen, PII is de-uridylylated leading to the inactivation of the glutamate synthetase pathway and switching off NtrC-dependent promoters [5]. It has also been suggested that the product of the glnD gene is involved in other physiological functions such as control of iron metabolism in certain species [4].

Glutamine-synthetase adenylyltransferase is an adenylyl transferase comprised of an adenylylating domain and a deadenylylating domain which modulate glutamine synthetase (GS) activity, where GS plays an important role in nitrogen assimilation [6].