A bifunctional epimerase-reductase acts downstream of the MUR1 gene product and completes the de novo synthesis of GDP-L-fucose in Arabidopsis.
L-Fucose is a monosaccharide found as a component of glycoproteins and cell wall polysaccharides in higher plants. The MUR1 gene of Arabidopsis thaliana encodes a GDP-D-mannose 4,6-dehydratase catalyzing the first step in the de novo synthesis of GDP-L-fucose from GDP-D-mannose (Bonin et al. 1997, Proc. Natl Acad. Sci. USA, 94, 2085-2090). Plant genes encoding the subsequent steps in L-fucose synthesis (3,5-epimerization and 4-reduction) have not been described previously. Based on sequence similarities to a bacterial gene involved in capsule synthesis we have cloned a gene from Arabidopsis, now designated GER1, which encodes a bifunctional 3, 5-epimerase-4-reductase in L-fucose synthesis. The combined action of the MUR1 and GER1 gene products converts GDP-D-mannose to GDP-L-fucose in vitro demonstrating that this entire nucleotide-sugar interconversion pathway could be reconstituted using plant genes expressed in Escherichia coli. In vitro assays indicated that the GER1 protein does not act as a GDP-D-mannose 3, 5-epimerase, an enzymatic activity involved in the de novo synthesis of GDP-L-galactose and L-ascorbic acid. Similarly, L-ascorbate levels in GER1 antisense plants were unchanged indicating that GDP-D-mannose 3,5-epimerase is encoded by a separate gene.
Bonin
C P
CP
University of Connecticut, Department of Molecular and Cell Biology, Storrs, CT 06269, USA.
Reiter
W D
WD
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism; D029681:Arabidopsis Proteins; D001483:Base Sequence; D002238:Carbohydrate Epimerases / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D017343:Genes, Plant; D006154:Guanosine Diphosphate Fucose / Q000096:biosynthesis*; D006801:Humans; D007438:Introns; D007658:Ketone Oxidoreductases; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes; D016376:Oligonucleotides, Antisense / Q000235:genetics; D010088:Oxidoreductases / Q000378:metabolism*; D030821:Plants, Genetically Modified; D017386:Sequence Homology, Amino Acid; D013401:Sugar Alcohol Dehydrogenases / Q000378:metabolism*
D029681:Arabidopsis Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D016376:Oligonucleotides, Antisense; C110682:wcaG protein, E coli; D006154:Guanosine Diphosphate Fucose; D010088:Oxidoreductases; D013401:Sugar Alcohol Dehydrogenases; D007658:Ketone Oxidoreductases; D002238:Carbohydrate Epimerases; C407922:GER1 protein, Arabidopsis