L-Fucose biosynthesis

It is believed that the apiofiiranose (Api residue of side chain A, but not that of side-chain B, is involved in RG-II dimerization. Recently mutant Arabidopsis murl strains, which are defective in L-fucose biosynthesis, have been shown to result in small changes in chain A of RG-II the L-fucose residue is replaced by L-galactose. This seemingly minor modification in a complex oligosaccharide structure results in a significant reduction in RG-II dimer formation and has a dramatic impact of plant morphology(/P). It is not yet clear which structural features of RG-II are key to borate ester formation and stability. 

In summary, the transgenic plant studies described have indicated that it is possible to knock out genes related to P(l,2)-linked xylose and a(l,3)-linked fucose biosynthesis to produce more mammalian-like glycoproteins (Von Schorwen et al., 1993 Rayon et al., 1999). 

Little research has as yet been published on the biochemistry of incorporation of L-fucose into bacterial glycans. Most of the studies have been made on the genetics of the biosynthesis of colanic acid in Gram-... 

By analogy to results obtained in studies on the biosynthesis of dTDP-L-rhamnose,18 dTDP-6-deoxy-L-talose,17 and GDP-L-fucose,41 it seems very likely that dTDP-6-deoxy-L-/yxo-hexos-4-ulose (21), formed by the 3,5-epimerase reaction, remains enzyme-bound. 

Human a-l,3-fucosyltransferases are found in milk,51 53 saliva,54 and other specific cell lines.55-57 Through cloning studies, a role for an a-1,3-fucosyltransferase in cell adhesion was identified for the biosynthesis of sialyl Lewisxon neutrophils.58-59 As these studies link a-l,3-fucosyltransferase to cell adhesion and since the activated fucose species used by this enzyme is GDP-L-fucose, Luengo, et al.,eo prepared the C-glycoside analog of GDP-fucose shown in Figure 1.4.4. 

Thus, in the first group of bacteria, GDP-D-mannose inhibits its own synthesis by a simple feed-back inhibition. A similar mechanism is also operative in the second group, where GDP-L-fucose inhibits both GDP-D-mannose pyrophosphorylase and GDP-D-mannose oxi-doreductase. In the third group, where both sugar nucleotides are needed for polysaccharide synthesis, their biosynthesis is individually controlled, so that imbalance in the supply of these two sugars will not occur. 

Hormonal effects on the biosynthesis of sulphated glycoprotein in the endometrium of rabbit uterus have been shown to be confined to the microsomal level. Oestrogen increases the incorporation of L-fucose and 2-acetamido-2-deoxy-D-glucose from their respective nucleotides into a microsomal fraction, while progesterone suppresses the incorporation of the two sugars. 

Two different glycolipid L-fucosyltransferases, involved in the biosynthesis of blood-group related glycosphingolipids, were detected in a membrane preparation isolated from a human neuroblastoma-derived clonal cell line. One catalysed the transfer of L-fucose to neolactotetraosyl- or pentaosyl-ceramide to form H-1 and B-1 glycolipids respectively. The second catalysed the transfer of L-fucose to lactotriaosylceramide to form a tetraosylceramide which was an intermediate in the synthesis of the Le -type glycolipid. 

Figure 10.7. Biosynthesis of 6-deoxyhexoses dTDP-L-rhamnose, GDP-D-rhamnose, and GDP-L-fucose.

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