Sialyl Lewis modifications

In granulocytes, no branching of poly-Al-acetyllactosamines is observed, a 1-3-Fucosyltrans-ferase-catalyzed modification of the linear chains leads to the Lewis x antigen. If a2-3-sia-lyltransferase acts before fucosylation, sialyl Lewis x is formed. These carbohydrate stmc-tures are involved in a number of cell-cell interactions during the inflammatory response and... 

A number of non-natural fucosyl donors have also been probed with this enzyme [89]. As can be seen from Fig. 12, the C-6-atom of fucose is open for modifications. L-Gal and o-Ara are good substrates, whereas replacement of the 2-OH group of the fucose donor apparently is not tolerated by FucT VI. Indeed, Hindsgaul and coworkers succeeded in attaching the blood group A trisaccharide to the 6-position of the fucose donor and proved the biocatalytic transfer of this strange sugar [90]. The combination of non-natural donors with non-natural acceptors by enzymatic fucosyltransfer has also been probed which proved to be instrumental in the assembly of a library of sialyl-Lewis tetrasaccharides (Fig. 12) [91]. 

Several fucosyltransferases have been isolated and used for in vitro synthesis. The Lewis A al,4-fucosyltransferase transfers unnatural fucose derivatives in from their GDP esters [23]. The enzyme al,3-fiicosyltransferase has been used to L-fucosylate the 3-position of the GlcNAc of A-acetyllactosamine and of sialyl a2,3-N-acetyllactosamine [24]. Several acceptor substrates with modifications in the GlcNAc residue could also be... 

Another specific modification of polylactosaminoglycan chains is the introduction of a3-Fuc residues to non-terminal GlcNAcs along the chain to yield a (sialyl-) oligomeric-Lewis structure. In leukocytes the formation of this structure, which is a ligand for E- and P-selectin, is catalyzed by two different a3-FucTs, the myeloid FucT (FucT IV) and the leukocyte FucT (FucT VII) [92, 93] (Figure 10) (see also Section 23.20, o314-Fucosyltransferase Family below). 

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