N- and O-glycans in Unfertilized Chum Salmon (Oncorhynchus keta) Eggs Using Glycomic Techniques

Genomic analysis of various fish has advanced in recent years; however, predicting glycan information from the genomic data alone remains challenging. Glycomic techniques have therefore attracted considerable attention. In this study, we analyzed N- and O-glycans in unfertilized Oncorhynchus keta eggs using glycomic techniques, such as a glycoblotting procedure, a sialic acid linkage-specific alkylamidation, and an evaporative β-elimination with pyrazolone. N-Glycomic analysis revealed that biantennary N-glycans were predominant, and that sialylation occurred via an α2,3 linkage. In addition, numerous sulfated N-glycans were observed, some of which had not been reported previously. Tandem mass spectrometry analyses indicated that most of the sulfate groups were attached to GlcNAc linked to mannose within the core structure. The sulfation sites of the unknown sulfated glycans were the same; however, a GlcNAc residue was lost from the core structure. In O-glycomics, oligo-sialylated O-glycans, which contain between one to seven sialic acid residues, were observed in the unfertilized eggs. Most of the sialic acids in the O-glycans were Neu5Gc, and there was no α2,3 linkage.