A-l,3-Fucosylation

Similar results were recently obtained with a human monoclonal antibody, with KDEL sequences fused to the C-termini of both heavy chains, expressed in tobacco [33]. As observed for the invertase-HDEL fusion, about 90% of the N-linked glycans on this antibody were of the high-mannose type, with 6-9 mannose residues, while a fraction contained the immunogenic P(l,2)-xylose glyco-epitope (Fig. 15.6). However, this antibody was not a(l,3)-fucosylated, a glycan modification occurring in the trans Golgi [34]. 

M. M. A. Olsthoorn, I. M. Lopez-Lara, B. O. Petersen, K. Bock, J. Haverkamp, H. P. Spaink, and J. E. Thomas-Oates, Novel branched nod factor structure results from a-(l->3) fucosyl transferase activity The major lipo-chitin oligosaccharides from Mesorhizobium loti strain NZP2213 bear an a-(l->3) fucosyl substituent on a nonterminal backbone residue, Biochemistry, 37 (1998) 9024-9032. 

The in situ generation of GDP-Fuc from P-fucose-1-phosphate coupled with the transfer of the fucose moiety on to A -acetyllactosamine has also been probed on an analytical scale [96]. In the presence of GTP P-fucose-1-phosphate is converted to GDP-Fuc by GDP-fucose pyrophosphorylase. GDP-Fuc is then used by an a(l-3)fucosyl transferase to transfer the fucose moiety on to A -acetyllactosamine. The released GDP is recycled and phosphorylated to give GTP by a phosphokinase with phosphoenol pyruvate as phosphate source. The pyrophosphate produced in the complete cycle is decomposed by pyrophosphatase (see Scheme 16). 

Scheme 16. 1) GDP-fucose pyrophosphorylase 2) a(l-3)fucosyl transferase 3) phosphokinase 4) pyrophosphatase.

For the spectral interpretation, 52 is conceived of as an extension of 42 with a Fuc group a-(l— 3)-linked to GlcNAc-5. The spectral parameters of the structural-reporter groups of the fucosylated core pentasaccharide of 42 are found unaltered in 52 the same holds for those of the sialylated, upper branch. It may be mentioned that the apparent heterogeneity of the peptide moiety of 52 (and 42) clearly affects the... 

Table 4. Substrate specificity of deoxygenated acceptors for a-(l->3/4)fucosyltransferase fucosylation...

Here again, it is as probes that carba-oligosaccharides find their best applications. Compounds 7 and 8 were both submitted to the action of a-(l-3/4)-fucosyltransferase in the presence of GDP-fucose. Only 7 was accepted and fucosylated to give the Lewis analog 9 showing that this enzyme has a different mode of action regarding the synthesis of Lewis s (Scheme 8.3) [16]. 

XylMan3GlcNAc2) also non-xylosylated and a-l,6-fucosylated core structures occur. It has to be mentioned that in plant glycoproteins the frequently found xylosylated trimannosyl-A,A -diacetylchitobiosyl core structure can occur with a 1,3-linked in stead of a 1,6-linked oFuc residue, attached at the asparagine-bound GlcNAc unit (for a review, see ref [38]). 

Carbohydrates of human serotransferrin are not fucosylated, while those of human lactotransferrin have an a-l,6-fucose bound to the N-acetylglucosamine residue linked to the peptide chain, and an a-l,3-fucose bound to the N-acetyllactosamine residues. 

A tetramer of a-L-Fuc-(1 2)-6-0-Bn-a-D-Gal-(l- 3)-a-D-GlcNAc-(l- 3)-L-Fuc joined by a-(l- 3) linkages between the fucosyl units gave a linear 24 unit product which was purified by reverse phase chromatography by use of a lipophilic ester derivative. ... 

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