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GDP-L-fucose biosynthesis I (from GDP-D-mannose)

General Background L-fucose is an important monosaccharide found in a diverse array of organisms. It is a carbohydrate component of bacterial lipopolysaccharides, mammalian and plant glycoproteins and various plant cell wall polysaccharides. Fucosylation is performed by fucosyltransferases which require the activated form GDP-L-fucose as the donor substrate. The formation of GDP-L-fucose occurs via two routes, a de novo synthesis route from GDP-alpha-D-mannose (this pathway), and a eukaryotic salvage pathway leading to the formation of UDP-fucose from free L-fucose (see :PWY-6). The de novo synthesis of GDP-L-fucose from GDP-D-mannose comprises three catalytic steps: a 4,6-dehydration, a 3,5-epimerization, and a 4-reduction. The first reaction step is catalyzed by : GDPMANDEHYDRA-CPLX, which involves the formation of the intermediate GDP-4-dehydro-6-deoxy-D-mannose. This compound is also a common intermediate in the synthesis of other bacterial deoxyhexoses derived from GDP-D-mannose (see MetaCyc pathways : PWY-5738 : PWY-5739 : GDPRHAMSYN-PWY and : PWY-5740). In bacteria (including E. coli), fungi, plants and humans, the second and third reactions have been shown to be catalyzed by a single bifunctional polypeptide, GDP-fucose synthase . In the Enterobacteriaceae colanic acid (M antigen) is a polyanionic extracellular heteropolysaccharide containing a repeat unit with D-glucose, L-fucose, D-galactose, and D-glucuronate sugars that are nonstoichiometrically decorated with O-acetyl and pyruvate side chains . The sugars must be activated in the form of nucleotide sugars (such as : GUANOSINE_DIPHOSPHATE_FUCOSE) before their assembly (see pathway COLANSYN-PWY). Colanic acid biosynthesis has been linked to a cluster of 19 wca genes that includes wcaG (fcl) encoding GDP-fucose synthase . About This Pathway L-fucose is biosynthesized as the sugar nucleotide GDP-L-fucose. Its biosynthesis from GDP-D-mannose begins with dehydration of this compound to GDP-4-dehydro-6-deoxy-D-mannose by the product of gene gmd. Then the bifunctional GDP-fucose synthase catalyzes the two-step (epimerase/reductase) synthesis of GDP-fucose from GDP-4-dehydro-6-deoxy-D-mannose via a GDP-4-dehydro-6-L-deoxygalactose intermediate . The overall reaction is defined by EC and is carried out at a single active site on the enzyme . This pathway requires NADPH as a reducing cofactor. Overexpression of endogenous NADPH-regenerating enzymes in recombinant E. coli increased GDP-L-fucose production under optimized conditions . In another study, overexpression of : CPLX0-322 encoded by gene gsk led to a significant improvement of GDP-L-fucose production. This was attributed to the increased level of intracellular GMP as a source of GTP which is required for this pathway (as shown in the pathway link to : PWY-5659) .

from BIOCYC source record: ECO_PWY-66
Type: pathway
Taxonomic scope
organism-specific biosystem
Escherichia coli

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