Glycoproteomic analysis of regulatory effects of bisecting N-glycans on N-glycan biosynthesis and protein expressions in human HK-2 cells.

Bisecting N-glycan is known to be a metastasis suppressor and plays a regulatory role in the biosynthesis of N-glycans. Previous studies have shown that bisecting N-glycans are capable of modulating both the branching and terminal modifications of glycans. However, these effects have been investigated mainly by glycomic approaches and it remains unclear how they alter when glycans are attached to different glycosites of proteins. Here, we systematically investigated the regulatory roles of bisecting N-glycans in human HK-2 cells using StrucGP, a strategy we developed for structural interpretation of site-specific N-glycans on glycoproteins. The glycoproteomics analysis showed that most of bisecting N-glycans are complex type and often occur in company with core fucosylation. With the overexpression and knockdown of MGAT3, the only enzyme responsible for bisecting N-glycan synthesis, we found that bisecting N-glycans can impact the biosynthesis of N-glycans from multiple aspects, including glycan types, branching, sialylation, fucosylation (different effects for core and terminal fucosylation) as well as the presence of terminal N-acetylglucosamine. Furthermore, gene ontology analysis suggested that most proteins with bisecting N-glycans located in the extracellular region or membrane, where they function mostly in cell adhesion, extracellular matrix regulation and cell signaling. Finally, we showed that overexpression of bisecting N-glycans had a broad impact on the protein expressions of HK-2 cells, involving multiple biological processes. Taken together, our work systematically demonstrated the expression profiles of bisecting N-glycans, and their regulatory effects on the biosynthesis of N-glycans and protein expressions, which provide valuable information for the functional elucidation of bisecting N-glycans.