Differential Acceptance Specificity of Human Fucosyltransferases toward GDP-Azidofucose and GDP-Alkynylfucose as Glycosylation Probes

Fucosylated glycans on glycoproteins and glycolipids play critical roles in functional regulation, significantly impacting human health and disease. Fucosylated glycans in humans are categorized into three types: core fucose, terminal fucose, and O-linked fucose, with each type contributing uniquely to physiological and pathological processes. Fucosylation is associated with various conditions, including cancer, autoimmune diseases, and developmental disorders, and it can also affect the efficacy of therapeutic antibodies. To investigate aberrant fucosylation in disease progression, azido- and alkynylfucose analogs have been utilized as orthogonal clickable probes, though mostly in nonhuman species. However, it remains unclear whether all human fucosyltransferases (FUTs) can accept these probes. In this study, we evaluated the utilization of GDP-fucose analogs, including GDP-6-azidofucose (GDP-6-Az-Fuc), GDP-6-alkynylfucose (GDP-6-Alk-Fuc), and GDP-7-alkynylfucose (GDP-7-Alk-Fuc), as donor substrates and natural N-glycans as acceptors, and compared their specificity with GDP-fucose for nine human FUTs (FUT1-9) that are involved in the biosynthesis of glycoproteins. We determined key kinetic parameters and catalytic efficiencies of individual FUTs for their fucosylation of specific biantennary N-glycan acceptors to assess their incorporation of these analogs into glycoprotein N-glycans. Compared to GDP-fucose, all analogs were much weaker substrates for FUTs except FUT4, which exhibited better tolerance toward the analogs, especially GDP-7-Alk-Fuc. Notably, GDP-7-Alk-Fuc was accepted better than GDP-6-Alk-Fuc and GDP-6-Az-Fuc as a substrate for these nine human FUTs. These findings reveal the variability in the acceptance specificity and catalytic efficiency of the human FUT family toward the probes and emphasize the potential bias in identifying fucosylated glycans as therapeutic targets.