Label-Free Quantitative Comparison of N-Glycoproteomics between Camel and Cow Milk

To understand the differential N-glycoprotein characteristics of camel versus cow milk, we employed label-free quantitative N-glycoproteomics to compare the N-glycoprotein composition and the number of N-glycosylation sites between the two milks and utilized bioinformatics tools to predict potential biological functions of their N-glycoproteins. A total of 137 N-glycoproteins harboring 224 N-glycosylation sites were identified in camel milk, and 116 N-glycoproteins with 183 N-glycosylation sites in cow milk. Compared with cow milk, camel milk exhibited greater diversity in both N-glycoprotein types and N-glycosylation site number. Most identified N-glycoproteins contained only one N-glycosylation site, with only a minority displaying hyperglycosylation. Gene Ontology (GO) enrichment analysis revealed that differentially expressed N-glycoproteins were predominantly localized in the extracellular region and extracellular space and played an important role in immune response involving enzymatic activity, extracellular matrix organization, molecular binding, and signal transduction. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that these proteins were mainly enriched in metabolic processes such as complement and coagulation cascades and lysosomal pathways. Collectively, these findings provide molecular-level insights into the differences in N-glycoprotein composition and glycosylation between cow and camel milk.