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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 fucosyltransferases (FucTs) in cercariae of the avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1--4]GlcNAcbeta-R alpha1--3-FucT and a novel GDP-Fuc:Fucalpha-R alpha1--2-FucT. Triton X-100 extracts of cercariae were assayed for FucT activity using a variety of acceptor substrates. Type 1 chain (Galbeta1--3GlcNAc) based compounds were poor acceptors, whereas those based on a type 2 chain (Galbeta1--4GlcNAc), whether alpha2'-fucosylated, alpha3'-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 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 the activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly inhibitory. Large scale incubations were carried out with Galbeta1--4GlcNAc, GalNAcbeta1--4GlcNAcbeta-O -(CH2)8COOCH3 and Fucalpha1--3GlcNAcbeta1--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 ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1--4[Fucalpha1--2Fucalpha1--3]GlcNAc, GalNAcbeta1--4[Fucalpha1--2Fucalpha1--3]GlcNAcbe ta-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 structural element that have been described on schistosomal glycoconjugates. |
