Glycosylation is one of the most important protein post-translational modifications and plays a crucial role for living organisms. Glycosylation is present in more than 50% of proteins and is involved in many biological processes such as cellular immunity, protein translation regulation, and protein degradation.
Glycans are saccharide polymers that attach to amino acid side chains to form glycoproteins. The most common components of glycans are hexoses, including glucose, galactose, mannose, and some of their simple modifications, such as substituting the α-hydroxyl group of glucose by an acylated amino group to produce N-acetylglucosamine. Protein glycosylation can be classified into the following four categories according to different protein modifications:
O-linked glycosylation
O-linked glycosylation occurs when the glycan is linked to oxygen on serine or threonine residues adjacent to proline.
N-linked glycosylation
In N-linked glycosylation, glycans modify proteins by linking amide nitrogen with asparagine side chains. In animal cells, the sugar attached to asparagine is almost always N-acetylglucosamine (GlcNAc), and the linkage is always in the β-configuration.
N-glycosylation can be divided into high-mannose, complex, and heterotrimeric depending on their terminal fine structure. Asn-Xaa-Ser/Thr (Xaa is any amino acid other than Pro) is considered a prerequisite for N-glycosylation, although in a few cases the Asn-Xaa-Cys sequence can also be glycosylated.
C-linked glycosylation
In C-linked glycosylation, a protein is modified by attaching a molecule of mannose group to position C of the tryptophan indole ring 2 through a C-C bond. This modification mostly occurs at the first tryptophan residue of the W-X-X-W W-X-X-C or W-XX-F sequence. It is not uncommon in living organisms.
Glycosylphosphatidylinositol (GPI)-anchored ligation
Containing the sugar core, GPI anchors attach proteins to the cell membrane by binding to the C-terminus of the protein. The polysaccharide composition in the structure of different GPI anchors is different. Such glycosylation is present in many proteins, including some hydrolases, adhesion proteins, immunoproteins, complement regulatory proteins, etc.
Glycosylation has become a research hot topic in the field of protein post-translational modification because of its important role in living organisms.
The methods and techniques of protein glycosylation studies based on biological mass spectrometry have gradually matured. In mass spectrometry, the glycoprotein backbone including glycan backbone and protein backbone will have certain breakage patterns. Using the map obtained by mass spectrometry, we can analyze glycosylation site, protein sequence, glycan structure, and so on.
Creative Proteomics uses a comprehensive and mature mass spectrometry platform to provide glycomics-related analysis services. Please contact us for any service requests.