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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1a95

E.C. namexanthine phosphoribosyltransferase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 2.4.2.22
CSA Homologues of 1a95There are 47 Homologs
CSA Entries With UniProtID P0A9M5
CSA Entries With EC Number 2.4.2.22
PDBe Entry 1a95
PDBSum Entry 1a95
MACiE Entry 1a95

Literature Report

IntroductionXanthine-guanine phosphoribosyltransferase catalyses the conversion of guanine, xanthine and, to a lesser extent, hypoxanthine to GMP, XMP and IMP, respectively. E. coli has three PRTases, which are components of the purine salvage pathway.
MechansimAsp92 deprotonates the guanine which initiates a nucleophilic attack upon the C2 of the ribose ring of alpha-D-5-phosphoribosyl 1-pyrophosphate in a substitution reaction, eliminating diphosphate.
Reaction

Catalytic Sites for 1a95

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AspA8888macie:sideChainStabilises positive charge on oxocarbonium ion.
AspA8989macie:sideChainStabilises positive charge on oxocarbonium ion.
AspA9292macie:sideChainDeprotonates the guanine at N7, allowing it to initiate a nucleophilic attack on the ribose ring.

Literature References

Notes:11258886 suggests that a general base is not required, but a strong hydrogen bond with the N7 of the purine substrate provides sufficient transition-state stabilisation to permit relatively efficient catalysis. However this doesn't prove that the mechanism *isn't* acid/base, just that it doesn't *have* to be.
Vos S
Structures of free and complexed forms of Escherichia coli xanthine-guanine phosphoribosyltransferase.
J Mol Biol 1998 282 875-889
PubMed: 9743633
Shi W
The 2.0 A structure of human hypoxanthine-guanine phosphoribosyltransferase in complex with a transition-state analog inhibitor.
Nat Struct Biol 1999 6 588-593
PubMed: 10360366
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