GLN2

GLN2 is a gene designation used in several organisms to encode an isoform of glutamine synthetase, commonly referred to as glutamine synthetase type II (GS II). It is part of the glutamine synthetase family and is contrasted with type I enzymes, often encoded by GLN A or glnA in bacteria and GLN1 in some plants.

GS II catalyzes the ATP-dependent condensation of ammonium with glutamate to form glutamine, a central step in nitrogen assimilation and distribution to biosynthetic pathways. Glutamine serves as a key amino-group donor for nucleotide, amino acid, and amino-sugar biosynthesis, linking inorganic nitrogen to cellular growth and metabolism.

In plants and algae, GLN2 typically designates plastid-localized GS2; in other taxa, GS II isoforms may be cytosolic or organellar depending on lineage. Subcellular localization reflects the specialized roles of nitrogen metabolism in different cellular compartments.

GLN2 expression is commonly responsive to nitrogen availability, development, and environmental factors including carbon status and light in plants. In microorganisms, GS II can be regulated at the transcriptional level and by post-translational modification (for example adenylylation in some bacteria), adjusting enzyme activity to nitrogen supply and cellular needs.

GLN2 genes are part of a broader glutamine synthetase gene family that includes GS I (glnA/GLN1) and GS III in some lineages. Gene duplication and divergence have yielded GS1/GS2 isoforms with different subcellular localization and regulatory properties. Orthologs of GLN2 are found across bacteria, archaea, and eukaryotes, reflecting the conserved role of glutamine synthetase in nitrogen metabolism.

See also glutamine synthetase; GS I; GS II; GLN1; glnN.