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Catalytic Site Atlas

CSA LITERATURE entry for 1f6d

E.C. nameUDP-N-acetylglucosamine 2-epimerase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 5.1.3.14
CSA Homologues of 1f6d1o6c,1v4v,1vgv,3beo,3dzc,
CSA Entries With UniProtID P27828
CSA Entries With EC Number 5.1.3.14
PDBe Entry 1f6d
PDBSum Entry 1f6d
MACiE Entry 1f6d

Literature Report

IntroductionThe non-hydrolysing bacterial UDP-N-acetylglucosamine 2-epimerase catalyses the conversion of UDP-N-acetylglucosamine to UDP-N-acetylmannosamine, an intermediate in the biosynthesis of several cell surface polysaccarides. The enzyme is allosterically regulated by its substrate, UDP-N-acetylglucosamine, a reaction feature specific to the bacterial form of the enzyme. The structure of the enzyme shows homology with the glycosyl transferases.
MechansimThe binding of UDP-N-acetylglucosamine to one subunit induces a conformationa change across the dimer interface that converts the dimer partner to the catalytically active form. It has been suggested that the anit-elimination occurs by an E2 character E1 mechanism, with the transition state showing significant oxocarbenium ion character. His 213 is a good candidate for acting as a general acid to the departing UDP, generating an intermediate 2-acetamidoglucal.. The subsequent syn re-addition of UDP gives the UDP-N-acetylmannosamine product.
Reaction

Catalytic Sites for 1f6d

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA213213macie:sideChainThe residue is positioned correctly to act as a general acid to the departing UDP, forming the transient oxocarbenium-character intermediate 2-acetamidoglucal.
ArgA215215macie:sideChainThe residue is hydrogen bonded to the UDP-N-acetylglucosamine hydroxyl that interacts with UDP and to one beta phosphate group UDP, and has the role of stabilising the two beta phosphate oxygen atoms of UDP. The lower Hill coefficient associated with the R215A mutant suggests the residue is important in the allosteric regulation of the enzyme.
The residue is brought into position by the large realignment of loop between His213-Glu219 on binding of the allosteric regulating UDP-N-acetylglucosamine.
Interestingly, Arg215 is only conserved in bacterial UDP-N-acetylglucosamine 2-epimerases. The crucial role of Arg215 in catalysis and conformation is unique to the bacterial non-hydrolysing UDP-N-acetylglucosamine 2-epimerases.
AspA9595macie:sideChainThe residue is thought to participate in catalysis by either acting as a general acid/base towards the substrate C2 position, leading to the formation of the oxocarbenium character intermediate or by stabilising the positive charge of this intermediate through hydrogen bonding.
GluA117117macie:sideChainThe residue is thought to participate in catalysis by either acting as a general acid/base towards the substrate C2 position, leading to the formation of the oxocarbenium character intermediate or by stabilising the positive charge of this intermediate through hydrogen bonding.
GluA131131macie:sideChainThe residue is thought to participate in catalysis by either acting as a general acid/base towards the substrate C2 position, leading to the formation of the oxocarbenium character intermediate or by stabilising the positive charge of this intermediate through hydrogen bonding. The residue has also been implicated in the allosteric activation of the catalytic site.
HisA246246macie:sideChainThe residue is thought to play a key role in allosteric activation and to stabilise the UDP intermediate.

Literature References

Notes:
Livingston VG
Rupture of the tendo achillis.
J Am Podiatry Assoc 1975 65 19-33
PubMed: 1110647
Velloso LM
A structural basis for the allosteric regulation of non-hydrolysing UDP-GlcNAc 2-epimerases.
EMBO Rep 2008 9 199-205
PubMed: 18188181
Murkin AS
Identification and mechanism of a bacterial hydrolyzing UDP-N-acetylglucosamine 2-epimerase.
Biochemistry 2004 43 14290-14298
PubMed: 15518580
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