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Search The CSA
PDB ID
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Catalytic Site Atlas

CSA LITERATURE entry for 1ecf

E.C. nameamidophosphoribosyltransferase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 2.4.2.14
CSA Homologues of 1ecfThere are 14 Homologs
CSA Entries With UniProtID P0AG16
CSA Entries With EC Number 2.4.2.14
PDBe Entry 1ecf
PDBSum Entry 1ecf
MACiE Entry M0214

Literature Report

IntroductionGlutamine phosphoribosylpyrophosphate amido transferase (GPATase) catalyses the transfer of the glutamine amide nitrogen to phosphoribosylpyrophosphate to generate phosphoribosylamine, pyrophosphate and glutamate. The enzyme is a member of a family of proteins which utilise the amide nitrogen of glutamate for the biosynthesis of amino acids, nucleotides, amino sugars and coenzymes.
MechansimThe enzyme is described as complex; its reaction is catyalysed as two half reactions, each occurring at separate catalytic sites along a single polypeptide chain. The two sites are highly coupled, facilitating the transfer of NH3 between them. The N terminal domain is a member of the Ntn hydrolase family and catalyses the hydrolysis of glutamine to glutamate and ammonia, while the C terminal domain, the ammonia acceptor domain, a member of the phophoribosyltransferase (PRTase) family is responsible for the coupling of ammonia to phosphoribosyl pyrophosphate (PRPP). The PRTase active site is described as non classical, since no catalytic residues have been identified. However, it has been suggested by analogy with a homologue mechanism that the main function of the enzyme is not to promote catalysis, but rather to bring the reactants together appropriately and preventing unwanted side reactions.
Reaction

Catalytic Sites for 1ecf

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
CysA12macie:sideChainThe side chain sulphur acts as a nucleophile towards the glutamine substrate, forming a thioester intermediate and a proton donor towards the leaving group, forming ammonia. A binding pocket recognises glutamine specifically and orientates the substrate so that the amide group binds with carbonyl group located in the oxyanion hole, its carbon atom aligned for attack from the sulphur and the departing NH2 group close enough to the residue to receive a proton and depart as NH3.
AsnA101102macie:sideChainThe residue forms an oxyanion hole in the active site pocket, stabilising the anionic thioester intermediate.
GlyA102103macie:mainChainAmideThe residue forms an oxyanion hole in the active site pocket, stabilising the anionic thioester intermediate.

Literature References

Notes:
Muchmore CR
Crystal structure of glutamine phosphoribosylpyrophosphate amidotransferase from Escherichia coli.
Protein Sci 1998 7 39-51
PubMed: 9514258
Smith JL.
Glutamine PRPP amidotransferase: snapshots of an enzyme in action.
Curr Opin Struct Biol 1998 8 686-694
PubMed: 9914248
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