Fucose, biosynthesis structure

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. 

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. 

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).

Suzuki, N. (1995). Structure, function, and biosynthesis of sperm-activating peptides and fucose sulfate glycoconjugate in the extracellular coat of sea urchin eggs. Zool. Sci. 12, 13-27. 

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