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

UDP-sugars serve as substrates in the synthesis of cell wall polysaccharides and are themselves generated through sequential interconversion reactions from UDP-Glc (UDP-glucose) as the starting substrate in the cytosol and the Golgi apparatus. For the present study, a soluble enzyme with UDP-Xyl (UDP-xylose) 4-epimerase activity was purified approx. 300-fold from pea (Pisum sativum L.) sprouts by conventional chromatography. The N-terminal amino acid sequence of the enzyme revealed that it is encoded by a predicted UDP-Glc 4-epimerase gene, PsUGE1, and is distinct from the UDP-Xyl 4-epimerase localized in the Golgi apparatus. rPsUGE1 (recombinant P. sativum UGE1) expressed in Escherichia coli exhibited both UDP-Xyl 4-epimerase and UDP-Glc 4-epimerase activities with apparent Km values of 0.31, 0.29, 0.16 and 0.15 mM for UDP-Glc, UDP-Gal (UDP-galactose), UDP-Ara (UDP-L-arabinose) and UDP-Xyl respectively. The apparent equilibrium constant for UDP-Ara formation from UDP-Xyl was 0.89, whereas that for UDP-Gal formation from UDP-Glc was 0.24. Phylogenetic analysis revealed that PsUGE1 forms a group with Arabidopsis UDP-Glc 4-epimerases, AtUGE1 and AtUGE3, apart from a group including AtUGE2, AtUGE4 and AtUGE5. Similar to rPsUGE1, recombinant AtUGE1 and AtUGE3 expressed in E. coli showed high UDP-Xyl 4-epimerase activity in addition to their UDP-Glc 4-epimerase activity. Our results suggest that PsUGE1 and its close homologues catalyse the interconversion between UDP-Xyl and UDP-Ara as the last step in the cytosolic de novo pathway for UDP-Ara generation. Alternatively, the net flux of metabolites may be from UDP-Ara to UDP-Xyl as part of the salvage pathway for Ara.

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A series of carbosilane dendrimers uniformly functionalized with hemagglutinin (HA) binding peptide (sialic acid-mimic peptide, Ala-Arg-Leu-Pro-Arg) was systematically synthesized, and their anti-influenza virus activity was evaluated. The carbosilane-based peptide dendrimers, unlike sialylated dendrimers, cannot be digested by virus neuraminidases. The peptide dendrimers exhibited intriguing biological activities depending on the form of their core frame, with a dumbbell-type peptide dendrimer showing particularly strong inhibitory activities against two human influenza viruses, A/PR/8/34 (H1N1) and A/Aichi/2/68 (H3N2). The IC50 values of the dumbbell-type peptide dendrimer for both strains were 0.60 μM, the highest activity among the HA-binding peptide derivatives. The results suggest that a dumbbell-shaped carbosilane dendrimer is the most suitable core scaffold for HA-binding peptide dendrimers.