Acceptor specificity of the human leukocyte α3 fucosyltransferase:: role of FucT-VII in the generation of selectin ligands

The alpha 3 fucosyltransferase, FucT-VII, is one of the key glycosyltransferases involved in the biosynthesis of the sialyl Lee is X (sLe(x)) antigen on human leukocytes, The sialyl Lewis X antigen (NeuAc alpha(2-3)Gal beta(1-4)[Fuc alpha(1-3)]GlcNAc-R) is an essential component of the recruitment of leukocytes to sites of inflammation, mediating the primary interaction between circulating leukocytes and activated endothelium. In order to characterize the enzymatic properties of the leukocyte alpha 3 fucosyltransferase FucT-VII, the enzyme has been expressed in Trichoplusia ni insect cells, The enzyme is capable of synthesizing both sLe(x) and sialyl-dimeric-le(x) structures in vitro, from 3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels of fucose transfer observed to neutral or 3'-sulfated accepters, Studies using fucosylated NeuAc alpha(2-3)-(Gal beta(1-4)GlcNAc)(3)-Me accepters demonstrate that FucT-VII is able to synthesize both di-fucosylated and tri-fucosylated structures from mono-fucosylated precursors, but preferentially fucosylates the distal GlcNAc within a polylactosamine chain, Furthermore, the rate of fucosylation of the internal GlcNAc residues is reduced once fucose has been added to the distal GlcNAc, These results indicate that FucT-VII is capable of generating complex selectin ligands, in vitro, however the order of fucose addition to the lactosamine chain affects the rate of selectin ligand synthesis.