GlnA

glnA is the gene that encodes glutamine synthetase (GS), an essential enzyme in nitrogen metabolism. GS catalyzes the ATP-dependent amination of glutamate with ammonium to form glutamine, a pivotal step in nitrogen assimilation and the provision of amino groups for biosynthetic reactions. GlnA sequences are associated with the glutamine synthetase type I family in many bacteria, though GS enzymes also occur in type II and type III forms in other organisms.

In bacteria, the organismal regulation of glnA activity is tightly controlled. The enzyme often exists as a multimeric complex and its catalytic activity is modulated by reversible adenylylation of subunits by the adenylyltransferase GlnE in response to nitrogen availability. Nitrogen sensing systems, including PII signaling proteins and the GlnD uridylyltransferase, feed into transcriptional and post-translational control, coordinating glnA expression with cellular nitrogen status.

GlnA homologs are distributed broadly across life, occurring in bacteria, archaea, and eukaryotes. In bacteria, glnA typically encodes the nitrogen-assimilating GS I enzyme. In plants, algae, and some other eukaryotes, glutamine synthetase exists as multiple isoforms (often designated GS1 and GS2 in plants) that are targeted to different cellular compartments, reflecting diversified regulation and roles in nitrogen metabolism. GS functions in the GS–GOGAT cycle, supplying amino groups for the biosynthesis of glutamate and other amino acids.

In research and biotechnology, glnA is a classic model for nitrogen regulation. Inhibitors of glutamine synthetase, such as methionine sulfoximine, are used to study enzyme function and nitrogen metabolism, though practical use depends on organismal context and enzyme form.