deglycosylation

Deglycosylation is the enzymatic or chemical removal of glycan (carbohydrate) units from glycoproteins, glycolipids, or proteoglycans. It can affect protein folding, stability, trafficking, recognition by lectins and receptors, and the turnover of glycosylated biomolecules. In cells, deglycosylation occurs as part of normal processing, quality control, and degradation pathways, and it can influence immune recognition and pathogen interactions.

Enzymatic deglycosylation is carried out by glycosidases. PNGase F cleaves the bond between the innermost GlcNAc of an N-linked glycan and the asparagine residue, converting Asn to Asp by deamidation. PNGase A differs in substrate tolerance and pH dependence. Endo H cleaves within the chitobiose core of high-mannose and some hybrid N-glycans, leaving a single GlcNAc attached to the Asn. For O-linked glycans, specialized O-glycosidases remove certain core structures; many O-glycans require sequential enzymatic treatment or chemical deglycosylation. Chemical methods such as hydrazinolysis can remove glycans but are non-specific and can damage the peptide backbone.

Biological significance: In eukaryotic cells, deglycosylation participates in quality control and turnover. During ER-associated degradation, N-glycans are removed by PNGases as the substrate is retrotranslocated to the cytosol for proteasomal destruction. Deglycosylation can influence protein folding, stability, trafficking, and interactions with lectins or receptors, and can modulate immune recognition, antigen presentation, and pathogen–host interactions.

Applications and considerations: In research and diagnostic settings, deglycosylation is used to analyze glycoprotein glycosylation patterns, map glycosylation sites, and prepare samples for mass spectrometry. PNGase F is a standard reagent for releasing N-glycans; Endo H helps classify glycan types. O-glycosidases enable selective O-glycan analysis, though complete desialylation may require multiple steps. Deglycosylation changes molecular mass and can affect conformation and function, so experimental design should account for potential structural effects.