Cloning and characterization of the alpha(1,3/4) fucosyltransferase of Helicobacter pylori

The gastric pathogen Helicobacter pylori can express the histo blood group antigens, which are on the surface of many human cells. Most H. pylori stra ins express the type II carbohydrates, Lewis X and Y, whereas a small popul ation express the type I carbohydrates, Lewis A and B. The expression of Le wis A and Lewis X, as in the case of H. pylori strain UA948, requires the a ddition of fucose in alpha 1,4 and alpha 1,3 linkages to type I or type II carbohydrate backbones, respectively. This work describes the cloning and c haracterization of a single H. pylori fucosyltransferase (FucT) enzyme, whi ch has the ability to transfer fucose to both of the aforementioned linkage s in a manner similar to the human fucosyltransferase V (Fuc-TV). Two homol ogous copies of the fucT gene have been identified in each of the genomes s equenced. The characteristic adenosine and cytosine tracts in the amino ter minus and repeated regions in the carboxyl terminus are present in the DNA encoding the two UA948fucT genes, but these genes also contain differences when compared with previously identified H. pylori fucTs. The UA948fucTa ge ne encodes an approximately 52-kDa protein containing 475 amino acids, wher eas UA948fucTb does not encode a full-length FucT protein. In vitro, UA948F ucTa appears to add fucose with a greater than B-fold preference for type I I chains but still retains significant activity using type I accepters. The addition of the fucose to the type II carbohydrate accepters, by UA948FucT a, does not appear to be affected by fucosylation at other sites on the car bohydrate acceptor, but the rate of fucose transfer is affected by terminal fucosylation of type I accepters. Through mutational analysis we demonstra te that only FucTa is active in this H. pylori isolate and that inactivatio n of this enzyme eliminates expression of all Lewis antigens.