Fucosylation of chitooligosaccharides by human α1,6-fucosyltransferase requires a nonreducing terminal chitotriose unit as a minimal structure

FUT8, a eukaryotic alpha 1,6-fucosyltransferase, catalyzes the transfer of a fucosyl residue from guanine nucleotide diphosphate-beta-l-fucose to the innermost GlcNAc of an asparagine-linked oligosaccharide (N-glycan). The catalytic domain of FUT8 is structurally similar to that of NodZ, a bacterial alpha 1,6-fucosyltransferase, which acts on a chitooligosaccharide in the synthesis of Nod factor. While the substrate specificities for the nucleotide sugar and the N-glycan have been determined, it is not known whether FUT8 is able to fucosylate other sugar chains such as chitooligosaccharides. The present study was conducted to investigate the action of FUT8 on chitooligosaccharides that are not generally thought to be a substrate in mammals, and the results indicate that FUT8 is able to fucosylate such structures in a manner comparable to NodZ. Surprisingly, structural analyses of the fucosylated products by high performance liquid chromatography, mass spectrometry and nuclear magnetic resonance indicated that FUT8 does not utilize the reducing terminal GlcNAc for fucose transfer but shows a preference for the third GlcNAc residue from the nonreducing terminus of the acceptor. These findings suggest that FUT8 catalyzes the fucosylation of chitooligosaccharide analogous to NodZ, but that a nonreducing terminal chitotriose structure is required for the reaction. The substrate recognition by which FUT8 selects the position to fucosylate might be distinct from that for NodZ and could be due to structural factor requirements which are inherent in FUT8.