N-Glycoprofiling of immunoglobulin G and lactoperoxidase from sheep milk using LC-MS/MS

The N-glycan diversity of sheep milk glycoproteins is not well characterised. Immunoglobulin G (IgG) and lactoperoxidase (LPO) were purified from sheep milk whey and probed for N-glycan heterogeneity using RP-UHPLC-MS/MS. Glycan diversity of IgG revealed only biantennary complex types (LacNAc) at its lone glycosylation site (NST). Relative abundance indicated differential core fucosylation at 50%, bisecting GlcNAc (22%) and sialylation with mainly Neu5Gc at 7%. The N-glycan repertoire of LPO at five sites indicated the range of glycans such as high-mannose, complex and hybrid types with varying abundances. High-mannose glycans were specifically observed at N222LS and N258TT sites. Mainly complex glycans composed of LacdiNAc moieties with prominent core fucosylation and sialylation (Neu5Gc) were found at N6VT. Complex glycans having LacdiNAc/LacNAc residues with prominent core fucosylation and sialylation were present at N349NS. Site N112RS revealed differential glycosylation with only 25% occupancy of high-mannose, neutral and sialylated complex/hybrid glycans without core fucosylation (LacdiNAc/LacNAc).