Identification of an α3-fucosyltransferase and a novel α2-fucosyltransferase activity in cercariae of the schistosome Trichobilharzia ocellata:: biosynthesis of the Fucα1→2Fucα1→3[Gal(NAc)β1→4]GlcNAc sequence

Fucose is a major constituent of the protein-and lipid-linked glycans of the various life-cycle stages of schistosomes, These fucosylated glycans are highly antigenic and seem to play a role in the pathology of schistosomiasis, In this article we describe the identification and characterization of two fucosyl-transferases (FucTs) in cercariae of the avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Gal beta 1-4]GlcNAc beta-R alpha 1-->3-FucT and a novel GDP-Fuc:Fuc alpha-R alpha 1-->2-FucT. Triton X-100 extracts of cercariae were assayed for FucT activity using a variety of acceptor substrates, Type 1 chain (Gal beta 1-->3GlcNAc) based compounds were poor accepters, whereas those based on a type 2 chain (Gal beta 1-->4GlcNAc), whether alpha 2'-fucosylated, alpha 3'-sialylated, or unsubstituted, and whether present as oligosaccharide or contained in a glycopeptide or glycoprotein, all served as acceptor substrates, In this respect the schistosomal alpha 3-FucT resembles human FucT V and VI rather than other known FucTs, RT-ethylmaleimide, an inhibitor of several human FucTs, had no effect on the activity of the schistosomal alpha 3-FucT, whereas GDP-beta-S was strongly inhibitory, Large scale incubations were carried out with Gal beta 1-->4GlcNAc, GalNAc beta 1-->4GlcNAc beta-O-(CH2)(8)COOCH3 and Fuc alpha 1-->3GlcNAc beta 1-->2Man as acceptor substrates and the products of the incubations were isolated using a sequence of chromatographic techniques, By methylation analysis and 2D-TOCSY and ROESY H-1-NMR spectroscopy the products formed were shown to be Gal beta 1-->4[Fuc alpha 1-->2Fuc alpha 1-->3]GlcNAc, GalNAc beta 1-->4[Fuc alpha 1-->2Fuc alpha 1-->3]GlcNAc beta-O-(CH2)(8)COOCH3, and Fuc alpha 1-->2Fuc alpha 1-->3GlcNAc beta 1-->2Man, respectively. It is concluded that the alpha 2-FucT and alpha 3-FucT are involved in the biosynthesis of the (oligomeric) Lewis(x) sequences and the Fuc alpha 1-->2Fuc alpha 1-->3GlcNAc structural element that have been described on schistosomal glycoconjugates.