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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1nsj

E.C. namephosphoribosylanthranilate isomerase
SpeciesThermotoga maritima (Bacteria)
E.C. Number (IntEnz) 5.3.1.24
CSA Homologues of 1nsj1dl3,1lbm,1pii,1v5x,
CSA Entries With UniProtID Q56320
CSA Entries With EC Number 5.3.1.24
PDBe Entry 1nsj
PDBSum Entry 1nsj
MACiE Entry M0328

Literature Report

IntroductionPhosphoribosyl anthranilate isomerase is a key enzyme in the biosynthesis of tryptophan, catalysing the interconversion of the aminoaldose phosphoribosyl anthranilate (PRA) and the aminoketose 1-[(2-carboxyphen-yl) amino]-1-deoxyribulose 5-phosphate (CdRP). It shares significant structural and sequence homology to other aldose-ketose isomerases, notably the analogous enzyme in the Histidine biosynthesis pathway, HisA which catalyses a similar reaction. The two are assumed to follow the same mechanism, namely Amadori rearrangement with acid base catalysis.
MechansimThe general mechanism for this reaction is an Amadori rearrangement. Protonation of the ribosyl ring oxygen by Cys 7 results in ring opening and formation of an imine intermediate. This intermediate is electrophilic due to the positive charge on the nitrogen, so deprotonation of C2 by Asp 126 can occur, leading to the formation of the enol tautomer of the product, which rapidly tautomerises to the keto form, the product CdRP.
Reaction

Catalytic Sites for 1nsj

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AspA126126macie:sideChainActs as general base to deprotonate C2 of the ribosyl moiety leading to the formation of the enol of CdRP.
CysA77macie:sideChainActs as general acid to protonate the ribosyl ring oxygen, precipitating ring opening and the formation of the electrophilic imino intermediate.

Literature References

Notes:
Henn-Sax M
Two (betaalpha)(8)-barrel enzymes of histidine and tryptophan biosynthesis have similar reaction mechanisms and common strategies for protecting their labile substrates.
Biochemistry 2002 41 12032-12042
PubMed: 12356303
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