Glycosylation is an important post-translational modification of proteins. Based on the different linkage modes between the glycan and peptide chains, protein glycosylation can be divided into N-glycosylation and O-glycosylation. N-glycosylation involves the linkage between the reducing end of N-acetylglucosamine (GlcNAc) and the nitrogen atoms on certain asparagine (Asn) side chain amides in the peptide chain.