N-Glycosylation
N-glycosylation is the enzymatic attachment of complex carbohydrate chains to asparagine (Asn) residues at the sequon Asn-X-Ser/Thr. Unlike Glycation (non-enzymatic, glucose adduct), N-glycosylation is a controlled, structure-specific modification added in the ER and Golgi.
Distinction from Glycation (Glycation)
| Feature | Glycation | N-Glycosylation |
|---|---|---|
| Mechanism | Non-enzymatic (Maillard reaction) | Enzymatic (glycosyltransferases) |
| Residue | Lys, N-terminus | Asn (Asn-X-Ser/Thr sequon) |
| Product | Simple hexose adduct (+162 Da per sugar) | Complex oligosaccharide chains |
| Reversibility | Partly (Schiff base) | Irreversible during protein lifetime |
| Clinical example | HSA glycation in diabetes | Transferrin N-glycosylation in liver disease / CDG |
Relevance to this research
- Transferrin: N-glycosylation changes (carbohydrate-deficient transferrin, CDT) are a clinical marker of chronic alcohol use and liver disease
- HSA: HSA is NOT N-glycosylated under physiological conditions (no Asn-X-Ser/Thr sequon in the exposed sequence); all glycation on HSA is non-enzymatic
- PTM-CQFD project: N-glycosylation of other plasma proteins will be profiled in the multi-protein TDP platform