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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1e7q

E.C. nameGDP-L-fucose synthase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 1.1.1.271
CSA Homologues of 1e7q1bsv,1bws,1e6u,1e7r,1e7s,1fxs,1gfs,
CSA Entries With UniProtID P32055
CSA Entries With EC Number 1.1.1.271
PDBe Entry 1e7q
PDBSum Entry 1e7q
MACiE Entry M0227

Literature Report

IntroductionGDP-4-keto-6-deoxy-D-mannose epimerase/reductase (GMER) is a bifunctional enzyme, catalysing the last 2 steps, epimerisation and reduction, in the biosynthesis of GDP-L-fucose, the substrate of fucosyl transferases.
In bacteria, fucose is a component of the capsular polysaccharides and lipopolysaccharides which function as antigenic determinants. In human, fucose is a Lewis system antigen. It is a ligand to selectin and is involved in leukocytes and tumour cell adhesion to the endothelium. Human deficient in the biosynthesis of GDP fucose suffer from immune disorder adhesion deficiency type II, which cna lead to serious symptoms, for instance, immunodeficiency and psychomotor retardation
MechansimEpimerisation of GDP-4-keto-6-deoxy-D-mannose occurs at C3 and C5 of the sugar. The mechanism involves the formation of a enolate intermediate from the keto substrate. Tyr136 acts as a general acid/base catalyst. With its pKa lowered by Lys140, it transiently protonates C4-keto group of the sugar to promote the formation of the enolate intermediate and also stabilise it. C3 or C5 of the enolate intermediate is then deprotonate by a base and reprotonate again from the opposite face of the sugar ring. Based on crystal structure and site-directed mutagenesis studies, both Cys109 and His179 can play the role of this base in abstracting a proton from C3 or C5 of the sugar ring.
Reaction

Catalytic Sites for 1e7q

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
CysA109109macie:sideChainIt deprotonates C3 or C5 of the enolate intermediate and reprotonates it again from the opposite face of the sugar ring.
HisA179179macie:sideChainIt deprotonates C3 or C5 of the enolate intermediate and reprotonates it again from the opposite face of the sugar ring.
TyrA136136macie:sideChainIt transiently protonates the C4-keto group of the sugar to promote the formation of the enolate intermediate and also stabilise it.
LysA140140macie:sideChainIt lowers the pKa of Tyr 136 by electrostatic effects.

Annotated By Reference To The Literature - Site 2 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
TyrA136136macie:sideChainIt acts as a general acid to protonate the C4 oxygen in concomitant to hydride transfer to C4 from NADPH.
AlaA107107macie:sideChainIt acts as a proton shuttle between the sugar and the phenolic side chain of Tyr 136.
LysA140140macie:sideChainIt lowers the pKa of Tyr 136 by electrostatic effects.

Literature References

Notes:The reductase activity is described in another csa entry under 1e7q.
Somers WS
GDP-fucose synthetase from Escherichia coli: structure of a unique member of the short-chain dehydrogenase/reductase family that catalyzes two distinct reactions at the same active site.
Structure 1998 6 1601-1612
PubMed: 9862812
Rosano C
Probing the catalytic mechanism of GDP-4-keto-6-deoxy-d-mannose Epimerase/Reductase by kinetic and crystallographic characterization of site-specific mutants.
J Mol Biol 2000 303 77-91
PubMed: 11021971
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