Glycosylation is a post-translational modification of proteins, involving the addition of sugar chains (oligosaccharides) to proteins. This modification typically occurs on specific amino acid residues of proteins, such as asparagine (N-glycosylation) or serine/threonine (O-glycosylation) residues. Glycosylation leads to an increase in the molecular weight of proteins for the following reasons:
Increased sugar molecule mass:
Sugar chains are composed of multiple monosaccharide units, each with a specific molecular mass. When these sugar chains are added to proteins, they increase the overall molecular mass of the protein.
Diversity and complexity of sugar chains:
Sugar chains can be composed of different monosaccharides, such as glucose, galactose, mannose, fucose, etc., each with a different molecular mass.
The length and branching of sugar chains can also vary, which affects their molecular mass.
Modifications of sugar chains:
After formation, sugar chains may undergo further modifications, such as sulfation or acetylation, which also increase the molecular mass of the sugar chain.
Heterogeneity of sugar chains:
Even the same protein may have different glycosylation patterns, a phenomenon known as glycosylation heterogeneity. This heterogeneity results in multiple glycosylated forms of the protein, each with a slightly different molecular mass.
Impact of sugar chains on protein structure:
Glycosylation not only increases the molecular mass of the protein but can also affect its three-dimensional structure and conformation, thereby influencing its function.
Dynamic changes of sugar chains:
Sugar chains can be dynamically added and removed within cells, and this dynamic change can also affect the protein’s molecular mass.
Due to the increase in molecular mass caused by glycosylation, the migration speed and detection signal of glycosylated proteins in protein analysis, such as SDS-PAGE electrophoresis or mass spectrometry, may differ from those of non-glycosylated proteins. Moreover, glycosylated proteins may also exhibit differences in stability, solubility, and immunogenicity within the organism.
