The O-linked fucose glycosylation pathway. Identification and characterization of a uridine diphosphoglucose: Fucose-β1,3-glucosyltransferase activity from Chinese hamster ovary cells

O-Linked fucose is an unusual carbohydrate modification in which fucose is linked directly to the hydroxyl groups of serines or threonines. It has been found on the epidermal growth factor-like modules of several secreted proteins involved in blood coagulation and fibrinolysis. We have recently reported the existence of an elongated form of O-linked fucose in Chinese hamster ovary cells consisting of a glucose linked to the 3'-hydroxyl of fucose (Glcβ1,3Fuc-O-Ser/Thr). This structure is highly unusual for two reasons. First, in mammalian systems fucose is usually a terminal modification of N- and O-linked oligosaccharides. Here the fucose is internal. Secondly, terminal β-linked glucose is extremely rare on mammalian glycoconjugates. Thus, the Glcβ1,3Fuc structure is a very unique mammalian carbohydrate structure. Here we report the identification and initial characterization of a novel enzyme activity capable of forming this unique linkage: UDP-glucose: O-linked fucose β1,3 glucosyltransferase. The enzyme utilizes UDP-glucose as the high energy donor and transfers glucose to α-linked fucose residues. The activity is linearly dependent on time, enzyme, and substrate concentrations and is enhanced in the presence of manganese ions. Activity is present in extracts of cultured cells from a variety of species (hamster, human, mouse, rat, chicken) and is enriched in brain and spleen of a normal adult rat. Thus, while this glycosyltransferase appears to be widespread in biology, it forms a very unique linkage, and it represents the first mammalian enzyme identified capable of elongating fucose.