Core a l,3 -Fucose

As mentioned earlier, glycosyl groups that are unique to plants, such as P(l,2)-xylose and core a(l,3)-fucose, are also responsible for increased allergenicity of plant-derived proteins. A number of approaches have been employed to circumvent this problem, and a few are mentioned here. 

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 2004, Strasser et al. generated a xylT knockout mutant that no longer produced [3(1,2)-linked xylosyltransferase, and nfucTA andfucTB double knockout mutant that was unable to produce a(l,3)-fucosyltransferase, in 

Another way that P(l,2)-linked xylose can be removed from plant proteins involves the use of P(l,2)-xylosidase. This is a degradative enzyme that is easily prepared from potatoes. If the 3-position of this maimose is not occupied, P(l,2)-xylosidase releases xylose residues that are P(l,2)-linked to the heta-mannose of an A-glycan core. This techiuque can also be applied to plant-derived therapeutic glycoproteins to remove potential immunogenic epitopes (Lerouge et al., 1998). 

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). 

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C5-1 antibody was produced in alfalfa, the glycan component consisted predominantly of a mature oligosaccharide comprising a core a(l,3)-fucose residue, a bisecting P(l,2)-xylose residue and two terminal GlcNAc residues (Fig. 15.4) [6],... 

Bardor, M., Faveeuw, C., Fitchettew, A.-C., Gilbert, D., Galas, L Trottein, F., Faye, L., and Lerouge, P. (2003). Immunoreactivity in mammals of two typical plant glyco-epitopes, core a(l, 3)-fucose and core p(l, 2)-xylose. 

Fig. 15.3 Plant and mammalian N-glycans have different structures. As illustrated here, a core structure (in gray) is common to plant and mammalian biantennary complex N-glycans. However, differences in the glycan processing machineries in plants and in mammals result in the absence of sialic acids in the terminal position of the antennae and the presence of a bisecting p (1,2) -xylose and of an a(l,3)-fucose residue in PMPs instead of the a(l,6)-fucose linked to the proximal N-acetylglucos-amine of native mammalian N-glycans.

D). However, PNGase F will not remove oligosaccharides containing a(l,3)-linked core fucose commonly found on plant glycoproteins PNGase A can be used for this purpose. 

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