Reprogramming the enzymatic assembly line for site-specific fucosylation

Fucosylated carbohydrate determinants are common components of cell surface glycoconjugates and secreted unconjugated glycans, which play pivotal roles in many physiological and pathological processes. The biosynthesis of Lewis antigens involves multiple fucosyltransferases that catalyse the fucosylation of the poly-N-acetyllactosamine carbohydrate backbone in a non-site-specific manner and thus generate heterogeneous and incompletely fucosylated Lewis antigen regioisomers. In this study, an alpha 2,6-sialylation module was used to introduce alpha 2,6-linked sialic acid to specific sites as the protecting group against fucosylation, thus precisely controlling enzymatic fucosylation of poly-N-acetyllactosamine glycans in a site-specific manner. The sialic acid protecting group can be easily removed by sialidase after fucosylation to provide a variety of fucosylated poly-N-acetyllactosamine glycans with defined fucosylation patterns. The general applicability and robustness of this reprogrammed enzymatic assembly line was exemplified in the synthesis of 22 complex Lewis antigens and chimeric histo-blood group antigens with a total of 10 enzyme modules for the construction of 10 different glycosidic linkages.