PROSITE documentation PDOC00162
Glutamine synthetase signatures


Glutamine synthetase (EC (GS) [1] plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine.

There seem to be three different classes of GS [2,3,4]:

  • Class I enzymes (GSI) are specific to prokaryotes, and are oligomers of 12 identical subunits. The activity of GSI-type enzyme is controlled by the adenylation of a tyrosine residue. The adenylated enzyme is inactive.
  • Class II enzymes (GSII) are found in eukaryotes and in bacteria belonging to the Rhizobiaceae, Frankiaceae, and Streptomycetaceae families (these bacteria have also a class-I GS). GSII are octamer of identical subunits. Plants have two or more isozymes of GSII, one of the isozymes is translocated into the chloroplast.
  • Class III enzymes (GSIII) has, currently, only been found in Bacteroides fragilis and in butyrivibrio fibrisolvens. It is a hexamer of identical chains. It is much larger (about 700 amino acids) than the GSI (450 to 470 amino acids) or GSII (350 to 420 amino acids) enzymes.

While the three classes of GS's are clearly structurally related, the sequence similarities are not so extensive. As signature patterns we selected three conserved regions. The first pattern is based on a conserved tetrapeptide in the N-terminal section of the enzyme, the second one is based on a glycine-rich region which is thought to be involved in ATP-binding. The third pattern is specific to class I glutamine synthetases and includes the tyrosine residue which is reversibly adenylated.

Expert(s) to contact by email:

Tateno Y.

Last update:

December 2004 / Pattern and text revised.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

GLNA_1, PS00180; Glutamine synthetase signature 1  (PATTERN)

GLNA_ADENYLATION, PS00182; Glutamine synthetase class-I adenylation site  (PATTERN)

GLNA_ATP, PS00181; Glutamine synthetase putative ATP-binding region signature  (PATTERN)


1AuthorsEisenberg D. Almassy R.J. Janson C.A. Chapman M.S. Suh S.W. Cascio D. Smith W.W.
TitleSome evolutionary relationships of the primary biological catalysts glutamine synthetase and RuBisCO.
SourceCold Spring Harb. Symp. Quant. Biol. 52:483-490(1987).
PubMed ID2900091

2AuthorsKumada Y. Benson D.R. Hillemann D. Hosted T.J. Rochefort D.A. Thompson C.J. Wohlleben W. Tateno Y.
TitleEvolution of the glutamine synthetase gene, one of the oldest existing and functioning genes.
SourceProc. Natl. Acad. Sci. U.S.A. 90:3009-3013(1993).
PubMed ID8096645

3AuthorsShatters R.G. Kahn M.L.
TitleGlutamine synthetase II in Rhizobium: reexamination of the proposed horizontal transfer of DNA from eukaryotes to prokaryotes.
SourceJ. Mol. Evol. 29:422-428(1989).
PubMed ID2575672

4AuthorsBrown J.R. Masuchi Y. Robb F.T. Doolittle W.F.
TitleEvolutionary relationships of bacterial and archaeal glutamine synthetase genes.
SourceJ. Mol. Evol. 38:566-576(1994).
PubMed ID7916055

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