Glycosylation builds branched sugar chains onto proteins one enzymatic step at a time as they pass through the Golgi, and the final glycan structure changes how that protein folds, signals and is recognized.
chain_i(t+1) = chain_i(t) + 1 if donor bound & elongation event
glycan complete after N residues
- Sugar donors — activated nucleotide-sugars (UDP-GlcNAc, GDP-fucose) supplying the monosaccharide unit.
- Glycosyltransferase sites — Golgi enzyme active sites that catalyze addition of one specific sugar to the growing chain.
- Donor affinity — how tightly a given donor sugar binds its transferase before the transfer reaction fires.
- Chain elongation rate — how quickly a bound sugar is added and the enzyme frees up for the next donor.
Glycan structures on antibodies (like the core-fucose on IgG) directly control immune effector function, which is why biopharma companies engineer CHO cell glycosylation pathways to tune therapeutic antibody potency.