Identification of an alpha3-fucosyltransferase and a novel alpha2- fucosyltransferase activity in cercariae of the schistosome Trichobilharzia ocellata: biosynthesis of the Fucalpha1-->2Fucalpha1-- >3[Gal(NAc)beta1-->4]GlcNAc sequence

Fucose is a major constituent of the protein- and lipid-linked glycans ofthe various life-cycle stages of schistosomes. These fucosylated glycansare highly antigenic and seem to play a role in the pathology ofschistosomiasis. In this article we describe the identification andcharacterization of two fucosyltransferases (FucTs) in cercariae of theavian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1-->4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-Ralpha1-- >2-FucT. Triton X-100 extracts of cercariae were assayed forFucT activity using a variety of acceptor substrates. Type 1 chain(Galbeta1- ->3GlcNAc) based compounds were poor acceptors, whereas thosebased on a type 2 chain (Galbeta1-->4GlcNAc), whetheralpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whetherpresent as oligosaccharide or contained in a glycopeptide or glycoprotein,all served as acceptor substrates. In this respect the schistosomal alpha3-FucT resembles human FucT V and VI rather than other known FucTs. N-ethylmaleimide, an inhibitor of several human FucTs, had no effect on theactivity of the schistosomal alpha3-FucT, whereas GDP-beta-S was stronglyinhibitory. Large scale incubations were carried out withGalbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 andFucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and theproducts of the incubations were isolated using a sequence ofchromatographic techniques. By methylation analysis and 2D-TOCSY andROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1-->4[Fucalpha1-->2Fucalpha1-->3]GlcNAc,GalNAcbeta1-->4[Fucalpha1-- >2Fucalpha1-->3]GlcNAcbeta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1-->3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric)Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structuralelement that have been described on schistosomal glycoconjugates.