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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1i7q

E.C. nameanthranilate synthase
SpeciesSerratia marcescens (Bacteria)
E.C. Number (IntEnz) 4.1.3.27
CSA Homologues of 1i7qThere are 56 Homologs
CSA Entries With UniProtID P00897
CSA Entries With EC Number 4.1.3.27
PDBe Entry 1i7q
PDBSum Entry 1i7q
MACiE Entry 1i7q

Literature Report

IntroductionAnthranilate synthase catalyses the initial reaction in tryptophan biosynthesis in microorganisms and plants. This enzyme is one of a family of glutamine amidotransferases, enzymes that utilise the amide of glutamine in the biosynthesis of amino acids, nucleotides, coenzymes, and an amino sugar. Glutamine amidotransferases thus exert major role in utilisation of assimilated nitrogen. Anthranilate synthase is the most thoroughly characterised glutamine amidotransferase. The enzyme from Serratia marcescens is a heterotetramer of anthranilate synthase (TrpE) and glutamine amidotransferase (TrpG) subunits.
MechansimIn the TrpG subunit ADIC synthase produces ADIC from chorismate via transfer of an amino group, using a catalytic triad of with well-known mechanism consisting of Cys85 His172 and Glu174. In the second AIDC lyase part of the reaction a standard second-order elimination can be invoked to yield the double bond between C2 and C3 with His398 as the base abstracting the C2 proton and pyruvate as the leaving group. Mg2+ and water provide an assisting acid group.
Reaction

Catalytic Sites for 1i7q

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA398397macie:sideChainActs as a general base to deprotonate C2 in formation of final anthanilate product.
CysB8584macie:sideChainActs to form a tetrahedral intermediate by attack on Gln carbonyl group, subsequent break down of this releases ammonia which aminates chorismate to form ADIC.
HisB172170macie:sideChainncreases nucleophilicity of Cys85 via deprotonation of thiol side chain. Subsequently protonates leaving ammonia group.
GluB174172macie:sideChainActs to stabilise histidine via hydrogen bonding.

Literature References

Notes:
Spraggon G
The structures of anthranilate synthase of Serratia marcescens crystallized in the presence of (i) its substrates, chorismate and glutamine, and a product, glutamate, and (ii) its end-product inhibitor, L-tryptophan.
Proc Natl Acad Sci U S A 2001 98 6021-6026
PubMed: 11371633
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