A Bifunctional Enzyme with L-Fucokinase and GDP-L-fucose Pyrophosphorylase Activities Salvages Free L-Fucose in Arabidopsis

Abstract

Monomeric sugars generated during the metabolism of polysaccharides, glycoproteins, and glycolipids are imported to the cytoplasm and converted to respective nucleotide sugars via monosaccharide 1-phosphates, to be reutilized as activated sugars. Because L-fucose (L-Fuc) is activated mainly in the form of GDP derivatives in seed plants, the salvage reactions for L-Fuc are expected to be independent from those for Glc, Gal, L-arabinose, and glucuronic acid, which are activated as UDP-sugars. For this study we have identified, in the genomic data base of Arabidopsis, the gene ( The monosaccharide L-fucose (L-Fuc) is found as a constituent of cell wall polysaccharides and sugar moieties of glycoproteins and has important physiological functions in seed plants.L-Fucosyl residues, for example, occur as nonreducing terminal residues attached through ␣-(132)-linkages to penultimate sugar residues in xyloglucan and arabinogalactan protein (1, 2). The L-fucosylated trisaccharide side chains of xyloglucan modulate the interaction of xyloglucan with cellulose microfibrils, thereby affecting the mechanical properties of plant cell walls (3, 4), whereas some N-glycans of plant glycoproteins have L-fucosyl residues attached through ␣-(133)-linkages to the proximal GlcNAc residues (sugars mentioned in this paper belong to the D-series unless otherwise noted.), which are characteristic of plants but are not found in mammals and are responsible for the immunogenicity of plant glycoproteins in mammals (5). L-Fucosyl residues are also attached through ␣-(134)-linkages to L-rhamnosyl residues in pectic rhamnogalacturonan II (RG-II) 2 in seed plants (6). These L-fucosyl residues are transferred onto the glycoconjugates by actions of respective L-fucosyltransferases, which use GDP-L-Fuc as the L-fucosyl donor. Recent studies have identified a xyloglucan-specific L-fucosyltransferase, AtFUT1 (7), and the related L-fucosyltransferase genes (AtFUT2-10) have also been found in the genome of Arabidopsis (8).GDP-L-Fuc, the activated form of L-Fuc, is generated through both de novo and salvage pathways (9, 10). Recently, the importance of levels of GDP-L-Fuc for the architecture of L-Fuc-containing cell wall polysaccharides was demonstrated through the study of the L-Fuc-deficient mutant of Arabidopsis, mur1. The mur1 mutant has reduced L-Fuc content in RG-II because of a defect in GDP-Man 4,6-dehydratase (EC 4.2.1.47) that catalyzes the first step of conversion of GDP-Man to GDP-L-Fuc in the de novo pathway (11,12). The loss of L-fucosyl residues indispensable for the boron-mediated dimer formation of pectic RG-II reduces the growth of rosette leaves in the mutant. The dwarf phenotype of mur1, however, can be rescued by exogenously applied monomeric L-Fuc, possibly because a compensating supply of GDP-L-Fuc is generated from L-Fuc via L-Fuc 1-phosphate (L-Fuc-1-P) in the salvage pathway (11). It is

Metabolic click-labeling with a fucose analog reveals pectin delivery, architecture, and dynamics in Arabidopsis cell walls

“…GDP-L-fucose is the substrate for fucosyltransferases in plants and animals and can be synthesized de novo from GDP-Dmannose (23) or generated from free fucose via a salvage pathway (24), suggesting that exogenous fucose might compete with FucAl for incorporation. To test this hypothesis, we assessed the ability of various monosaccharides to inhibit FucAl incorporation.…”

KONJAC1 and 2 Are Key Factors for GDP-Mannose Generation and Affect l-Ascorbic Acid and Glucomannan Biosynthesis in Arabidopsis

“…This raised two possibilities: rKJCs stimulated the activity of rVTC1 or rKJCs gained GMPP activity by interacting with rVTC1. To examine these possibilities, rKJCs and rVTC1 with a point mutation in the highly conserved nucleotide sugar pyrophosphorylase consensus motif, rVTC1 K23A, rKJC1 K33A, and rKJC2 K30A, were prepared (Supplemental Figure 11B) (Kotake et al, 2008). While rVTC1 K23A did not show any activity even in the presence of rKJCs, high activity was observed for mixtures of normal rVTC1 and rKJC1 K33A, and normal rVTC1 and rKJC2 K30A ( Figure 7B).…”

Generation of nucleotide sugars for biomass formation in plants

“…For example, GDP-L-Fuc is generated from fructose 6-phosphate via four intermediate compounds, Man 6-phosphate, Man 1-phosphate (Man 1-P), GDP-Man, and GDP-4-keto-6-deoxy-Man involving five different enzymes in the de novo pathway (Figure 1; Reiter 2008). On the other hand, GDP-L-Fuc can be synthesized from L-Fuc through just two reactions in the salvage pathway ( Figure 1; Kotake et al 2008). The salvage reactions for free monosaccharides are generally composed of two reactions, phosphorylation of the monosaccharides catalyzed by monosaccharide kinases and formation of nucleotide sugars from monosaccharide 1-phosphates (monosaccharide 1-Ps) and the corresponding nucleoside triphosphates by nucleotide sugar pyrophosphorylases.…”

“…Higher plants have a bifunctional L-fucokinase/GDP-L-Fuc pyrophosphorylase, FKGP, which has low but significant sequence similarity to a bacterial bifunctional enzyme, Fkp (Coyne et al 2005). FKGP catalyzes the phosphorylation of L-Fuc in the presence of ATP and the conversion of L-Fuc 1-P to GDP-L-Fuc in the presence of GTP, as does Fkp (Figure 1; Kotake et al 2008). FKGP has a pyrophosphorylase-consensus motif conserved for nucleotide sugar pyrophosphorylases in the N-terminal region and an ATP-binding motif required for the activity of monosaccharide kinases in the C-terminal region.…”