N-glycans of bovine submaxillary mucin contain core-fucosylated and sulfated glycans but not sialylated glycans.

Bovine submaxillary mucin (BSM) is a heavily-glycosylated macromolecular (approximately 4 MDa) protein and is used in various biomaterial applications in light of its high viscosity and biocompatibility, in addition to use as a biochemical substrate or inhibitor as a result of its abundant O-glycans. Although it has been reported that N-glycosylation provides stability of human mucins, most BSM research has been focused on its O-glycans, while N-glycans have not been reported to date. In this study, a common N-glycan core component was detected by monosaccharide analysis of BSM, and the structures of the N-glycans and their relative quantities were determined by liquid chromatography-tandem mass spectrometry. Seventeen N-glycans comprising ten complex-type [FucoseHexoseN-acetylhexosamineSulfate; 61.1% (the sum of the relative quantities of each N-glycan out of the total N-glycans)], two high-mannose-type (HexoseN-acetylhexosamine; 12.0%), and five paucimannose type (FucoseHexoseN-acetylhexosamine; 26.9%) were identified, but no hybrid-type or sialylated N-glycans were found. Additionally, these are less-branched structures compared to human mucins. Of these, ten glycans (77.2%), including two sulfated glycans (8.0%), were core fucosylated, which confer unique biological functions to glycoproteins. The N-glycosylation sites were identified from the analysis of glycopeptides from BSM. This study is the first confirmation of N-glycan attachment to BSM.