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Catalytic Site Atlas

CSA LITERATURE entry for 1gpm

E.C. nameGMP synthase (glutamine-hydrolysing)
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 6.3.5.2
CSA Homologues of 1gpm2vxo,2ywb,2ywc,
CSA Entries With UniProtID P04079
CSA Entries With EC Number 6.3.5.2
PDBe Entry 1gpm
PDBSum Entry 1gpm
MACiE Entry M0234

Literature Report

IntroductionThe Class I glutamine amidotransferase an example of a single enzymatic reaction being catalysed by two modules, each responsible for a distinct component of the reaction. It catalyses the amination of the nucleotide precursor xanthosine 5'-monophosphate to form GMP in the de novo purine biosynthesis pathway. The amidotransferase domain is found in related enzymes of the purine, pyrimidine, tryptophan, arginine, histidine and folic acid pathways. This domain includes a conserved Cys-His-Glu triad, responsible for the abstraction of the amide nitrogen from glutamine. Unlike other enzymes with a catalytic triad, the Class I amidotransferase domain does not function alone, requires XMP and ATP, as hydrolysis of glutamine is tightly coupled with product formation. The synthetase domain catalyses the addition of ammonia to an acceptor substrate. They are designed to work in concert to ensure efficient coupling of catalytic functions, it is suggested that a flexible hinge exists to bring the two sites together for concerted ammonia transfer.
MechansimThe beta-phosphate deprotonates the XMP substrate, which then initiates a nucleophilic attack on the alpha-phosphate of ATP, eliminating pyrophosphate aided by Asp239 and Lys381. His181 deprotonates Cys86, activating it for a nucleophilic attack upon L-glutamine, forming an enzyme-substrate covalent bond. The negative charge is stabilised, by an oxyanion hole involving Tyr87 and Gly59. The tetrahedral intermediate collapses, liberating ammonia, which deprotonates His181 and then passes to the other catalytic domain. Ammonia is deprotonated by the phosphate of the intermediate, activating it for a nucleophilic attack on the intermediate, which liberates AMP and the GMP product. In the glutamine site His181 deprotonates a water molecule, which initiates a nucleophilic attack on the Cys-bound intermediate. The tetrahedral intermediate collapses, liberating Cys86, which deprotonates His181, and the glutamate product.
Reaction

Catalytic Sites for 1gpm

Literature References

Notes:
Massière F
The mechanism of glutamine-dependent amidotransferases.
Cell Mol Life Sci 1998 54 205-222
PubMed: 9575335
Tesmer JJ
The crystal structure of GMP synthetase reveals a novel catalytic triad and is a structural paradigm for two enzyme families.
Nat Struct Biol 1996 3 74-86
PubMed: 8548458
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