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A bifunctional epimerase‐reductase acts downstream of the MUR1 gene product and completes the de novo synthesis of GDP‐L‐fucose in Arabidopsis
Author(s) -
Bonin Christopher P.,
Reiter WolfDieter
Publication year - 2000
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2000.00698.x
Subject(s) - biochemistry , mannose , arabidopsis thaliana , arabidopsis , fucose , biology , nucleotide sugar , gene , gene product , biosynthesis , galactose , gene expression , mutant
Summary 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.