ACCEPTOR SPECIFICITY OF THE HUMAN-LEUKOCYTE ALPHA-3 FUCOSYL-TRANSFERASE - ROLE OF FUCT-VII IN THE GENERATION OF SELECTIN LIGANDS

The alpha 3 fucosyltransferase, FucT-VII, is one of the key glycosyltr ansferases 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 t he primary interaction between circulating leukocytes and activated en dothelium. In order to characterize the enzymatic properties of the le ukocyte alpha 3 fucosyltransferase FucT-VII, the enzyme has been expre ssed in Trichoplusia ni insect cells, The enzyme is capable of synthes izing both sLe(x) and sialyl-dimeric-le(x) structures in vitro, from 3 '-sialyl-lacNAc and VIM-2 structures, respectively, with only low leve ls of fucose transfer observed to neutral or 3'-sulfated accepters, St udies using fucosylated NeuAc alpha(2-3)-(Gal beta(1-4)GlcNAc)(3)-Me a ccepters demonstrate that FucT-VII is able to synthesize both di-fucos ylated and tri-fucosylated structures from mono-fucosylated precursors , but preferentially fucosylates the distal GlcNAc within a polylactos amine chain, Furthermore, the rate of fucosylation of the internal Glc NAc residues is reduced once fucose has been added to the distal GlcNA c, These results indicate that FucT-VII is capable of generating compl ex selectin ligands, in vitro, however the order of fucose addition to the lactosamine chain affects the rate of selectin ligand synthesis.