The ruminant parasite Haemonchus contortus expresses an α1,3-fucosyltransferase capable of synthesizing the Lewis x and sialyl Lewis x antigens

Glycoproteins from the ruminant helminthic parasite Haemonchus contortus react with Lotus tetragonolobus agglutinin and Wisteria floribunda agglutinin, which are plant lectins that recognize alpha 1,3-fucosylated GlcNAc and terminal beta-GalNAc residues, respectively. However, parasite glycoconjugates are not reactive with Ricinus communis agglutinin, which binds to terminal beta-Gal, and the glycoconjugates lack the Lewis x (Le(x)) antigen or other related fucose-containing antigens, such as sialylated Le(x), Le(a), Le(b) Le(y), or H-type 1. Direct assays of parasite extracts demonstrate the presence of an alpha 1,3-fucosyltransferase (alpha 1,3FT) and beta 1,4-N-acetylgalactosaminyltransferase (beta 1,4GalNAcT), but not beta 1,4-galactosyltransferase. The H. contortus alpha 1,3FT can fucosylate GlcNAc residues in both lacto-N-neotetraose (LNnT) Gal alpha 1 --> 4GlcNAc beta 1 --> 3Gal beta 1 --> 4Glc to form lacto-N-fucopentaose III Gal beta 1 --> 4[Fuc alpha 1 --> 3]GlcNAc beta 1 --> 3Gal beta 1 --> 4Glc, which contains the Le(x) antigen, and the acceptor lacdiNAc (LDN) GalNAc beta 1 --> 4GlcNAc to form GalNAc beta 1 --> 4[Fuc alpha 1 --> 3]GlcNAc. The alpha 1,3FT activity towards LNnT is dependent on time, protein, and GDP-Fuc concentration with a K-m 50 mu M and a V-max of 10.8 nmol-mg(-1) h(-1). The enzyme is unusually resistant to inhibition by the sulfhydryl-modifying reagent N-ethylmaleimide. The alpha 1,3FT acts best with type-2 glycan accepters (Gal beta 1 --> 4GlcNAc beta 1-R) and can use both sialylated and non-sialylated accepters. Thus, although in vitro the H. contortus alpha 1,3FT can synthesize the Le(x) antigen, in vivo the enzyme may instead participate in synthesis of fucosylated LDN or related structures, as found in other helminths.