Fucose, biosynthesis

Another Arabidopsis mutant, murl, which lacks the ability to synthesize 1-fucose, possesses a defective gene encoding GDP-d-Man-4,6-dehydratase, a key enzyme in 1-fucose biosynthesis. Further analysis revealed that 1-Fuc is replaced by 1-Gal, a structurally similar monosaccharide, in the cell walls of this mutant with no adverse effects on plant physiology or metabolism (Rayon et al, 1999). Transgenic plants containing this mutation can also be used for foreign protein production. 

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). 

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. 

GDP-Fuc regeneration cycle was constructed by incorporating two more enzymes GDP-mannose-4,6-dehydratase (GMD) and GDP-fucose synthase (GFS) into the same biosynthetic pathway of GDP-Man from Fm-6-P (Schem 5). Both GMD and GFS were cloned from Helicobacter pylori. With the bifuctional gene PMI/GMP adjacent to them, GMD, GFS and PMI/GMP array in sequence to form the GDP-fucose biosynthesis gene cluster in the chromosome genome of Helicobacter pylori (22). 

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-... 

In the biochemistry of D-fucose and its derivatives, there are larger lacunae in our knowledge. The biosynthesis of D-fucose has not been examined, so that it is not yet known how this sugar is produced in the organisms that contain it (mainly plants and some micro-organisms). In plants, it occurs especially in the form of steroid glycosides, whereas, in micro-organisms, it has been particularly located in antibiotic substances. It has not been identified in animals. 

Figure 1. The structure presented is based on the earlier composite structure (37, 38) for the A, B, H, Lea, and Leb substances and shows the relationships of the type 1 and type 2 determinants upon which these antigens are built. It is subject to all of the limitations considered earlier. As in the earlier studies, incomplete chains are present and can result from incomplete biosynthesis or by degradation in the cyst cavity. The bracketed substitution on carbon-4 of the 3, 4, 6-linked galactose could be galactose whatever the residue, it must be a sequence capable of giving galactitol on peeling. From the analytical composition one to two additional fucoses are present which have not been located (27).

Melancon CE IB, Liu HW (2007) Engineered biosynthesis of macrolide derivatives bearing the non-natural deoxysugars 4-epi-D-mycaminose and 3-N-methylamino-3-deoxy-D-fucose. J Am Chem Soc 129 4896 1899... 

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. 

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