LEWIS-X-BIOSYNTHESIS IN HELICOBACTER-PYLORI - MOLECULAR-CLONING OF ANALPHA(1,3)-FUCOSYL-TRANSFERASE GENE

The lipopolysaccharide of certain strains of Helicobacter pylori was r ecently shown to contain the Lewis X (Le(x)) trisaccharide (Gal beta-1 ,4-(Fuc alpha(1,3))-GlcNAc). Le(x) is an oncofetal antigen which appea rs on human gastric epithelium, and its mimicry by carbohydrate struct ures on the surface of H. pylori may play an important part in the int eraction of this pathogen with its host, Potential roles for bacterial Le(x) in mucosal adhesion, immune evasion, and autoantibody induction have been proposed (Moran, A, P., Prendergast, M. M., and Appelmelk, B. J. (1996) FEMS Immunol, Med, Microbiol, 16, 105-115). In mammals, t he final step of Le(x) biosynthesis is the alpha(1,3)-fucosylation of GlcNAc in a terminal Gal beta(1-->4)-GlcNAc unit, and a corresponding GDP-fucose:N-acetylglucosaminyl alpha(1,3) fucosyltransferase (alpha(1 ,3)-Fuc-T) activity was recently discovered in H. pylori extracts, We used part of a human alpha(1,3)-Fuc-T amino acid sequence to search an H. pylori genomic data base for related sequences, Using a probe base d upon weakly matching data base sequences, we retrieved clones from a plasmid library of H. pylori DNA, DNA sequence analysis of the librar y clones revealed a gene which we have named fucT, encoding a protein with localized homology to the human alpha(1,3)-Fuc-Ts. We have demons trated that fucT encodes an active Fuc-T enzyme by expressing the gene in Escherichia coil, The recombinant enzyme shows a strong preference for type 2 (e.g. LacNAc) over type 1 (e.g. lacto-N-biose) accepters i n vitro. Certain residues in a short segment of the H. pylori protein are completely conserved throughout the alpha(1,3)-Fuc-T family, defin ing an alpha(1,3)-Fuc-T motif which may be of use in identifying new f ucosyltransferase genes.