Glutamine synthetase
| glutamate—ammonia ligase | |||||||||
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Active site between two monomers of glutamine synthetase from Salmonella typhimurium. Cation binding sites are yellow and orange; ADP is pink; phosphinothricin is blue.
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| Identifiers | |||||||||
| EC number | 6.3.1.2 | ||||||||
| CAS number | 9023-70-5 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / EGO | ||||||||
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| Search | |
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| PMC | articles |
| PubMed | articles |
| NCBI | proteins |
| Glutamine synthetase, beta-Grasp domain |
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| Identifiers | |||||||||
| Symbol | Gln-synt_N | ||||||||
| Pfam | PF03951 | ||||||||
| InterPro | IPR008147 | ||||||||
| PROSITE | PDOC00162 | ||||||||
| SCOP | 2gls | ||||||||
| SUPERFAMILY | 2gls | ||||||||
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| Available protein structures: | |
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| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
| Glutamine synthetase, catalytic domain |
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12-subunit enzyme glutamine synthetase from Salmonella typhimurium.
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| Identifiers | |||||||||
| Symbol | Gln-synt_C | ||||||||
| Pfam | PF00120 | ||||||||
| Pfam clan | CL0286 | ||||||||
| InterPro | IPR008146 | ||||||||
| PROSITE | PDOC00162 | ||||||||
| SCOP | 2gls | ||||||||
| SUPERFAMILY | 2gls | ||||||||
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| Available protein structures: | |
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| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
| glutamate-ammonia ligase (glutamine synthetase) | |
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| Identifiers | |
| Symbol | GLUL |
| Alt. symbols | GLNS |
| Entrez | 2752 |
| HUGO | 4341 |
| OMIM | 138290 |
| PDB | 2qc8 |
| RefSeq | NM_002065 |
| UniProt | P15104 |
| Other data | |
| EC number | 6.3.1.2 |
| Locus | Chr. 1 q31 |
Glutamine synthetase (GS) (EC 6.3.1.2) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:
Glutamate + ATP + NH3 → Glutamine + ADP + phosphate
Glutamine Synthetase uses ammonia produced by nitrate reduction, amino acid degradation, and photorespiration. The amide group of glutamate is a nitrogen source for the synthesis of glutamine pathway metabolites.
Other reactions may take place via GS. Competition between ammonium ion and water, their binding affinities, and the concentration of ammonium ion, influences glutamine synthesis and glutamine hydrolysis. Glutamine is formed if an ammonium ion attacks the acyl-phosphate intermediate, while glutamate is remade if water attacks the intermediate. Ammonium ion binds more strongly than water to GS due to electrostatic forces between a cation and a negatively charged pocket. Another possible reaction is upon NH2OH binding to GS, rather than NH4+, yields γ-glutamylhydroxamate.
Glutamine Synthetase can be composed of 8, 10, or 12 identical subunits separated into two face-to-face rings. Bacterial GS are dodecamers with 12 active sites between each monomer. Each active site creates a ‘tunnel’ which is the site of three distinct substrate binding sites: nucleotide, ammonium ion, and amino acid. ATP binds to the top of the bifunnel that opens to the external surface of GS. Glutamate binds at the bottom of the active site. The middle of the bifunnel contains two sites in which divalent cations bind (Mn+2 or Mg+2). One cation binding site is involved in phosphoryl transfer of ATP to glutamate, while the second stabilizes active GS and helps with the binding of glutamate.
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